Intermetallic Compounds

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TERNARY COM POUNDS

RE F ER ENC ES INDE" CHAPTER I .

I NTR D I N O UCT O .

THE fact that metals are capable o f forming chemical combinations among themselves has only gradually received recognition . Alloys

o f co m were generally regarded as mixtures , and their variability position was cited during the controversy between Proust and Berthollet as to the d e ﬁ nite ne ss o f proportions in chemical co m bination . The earliest suggestions that compounds might be o n present in certain alloys were based thermal observations . In the course o f a series of careful determinations o f the freezing l R udbe r points Of some fusible alloys , g Observed that the ther

o m e te r m generally showed two arrests during cooling, the ﬁrst

o n o f depending the composition of the alloy, whilst the position

o ne c o n the second was constant throughout any series . . Such a

- - stant lower freezing point was Observed in the series lead tin ,

- - - - lead bismuth , bismuth tin , bi smuth zinc , and zinc tin , and was attributed to the formation o f a compound or chemical alloy

a Formul e were assigned to several Of these supposed compounds ,

V which are now known to be eutectic mixtures . This iew long

r o f Lev o l 2 su vived , and received much support from the work , who observed that liquation occurred in all alloys of silver and copper,

o f with the exception that containing per cent Of silver,

’ d eﬁ n i te c o m o und which he therefore assumed to be a p , with the

A Cu . formula g 3 2 (using the modern atomic weights) At a much G o f O b later date, uthrie, in the course a study Of salt solutions , served the occurrence o f a constant minimum freezing- point in many series , and this he regarded as due to the chemical com ” o f bination salt and water to form a cryohydrate, stable only 3 V at low temperatures . This erroneous iew unfortunately pre o f O vailed , although the true nature the minimum , as the point f th e intersection Of the ice curve and salt solubility curve, had f been Shown earlier by Rii d o rff Guthrie afterwards conducted extensive researches into the freezing Of salt solution s and v t “ g a s 1 s o 9f

V alloys, and , correcting his former iew, introduced the word eutectic to denote the mixtures o f constant m inimum fre e z 5 - ing point . The assigning O f a chemical formula to a eu tecti c alloy is to be found even in some recent work , where freezing- point curves have been determined experimentally

o f without a proper comprehension their meaning . This false assumption o f chemical compounds is not to be confused with the quite legitimate attempt to discover deﬁnite atomic or mo le c o f ular ratios in eutectic mixtures , the heterogeneous nature the 6 eutectic equilibrium being fully re cognized .

ff O A more promising approach was made in a di erent way . S 7 fa r 1 8 K o f co lo un o f back as 39 , arsten Observed the change

alloys of copper and zinc with the composition , and found that the action O f acids o n those alloys exhibited a discontinuity at the point at which copper and zinc were present in equal propor

tions . He therefore suggested the presence o f a compound in

the series . Attempts were next made to isolate deﬁnite compounds from alloys by a process Of partial fusion and of mechanical separation O f the solid and liquid phases . The ﬁrst extensive experiments 8 o f ro o ke wit this kind are due to C , who examined in this way

many amalgams , and also alloys Of copper with tin , lead , zinc ,

etc . This plan was adopted by many other investigators , most o f l o w whom employed amalgams, on account of their melting o f point and the consequent facility of handling . The validity

this method is discussed below (p . 9 Calvert and Johnson attempted in the same way to isolate the chemical compounds which they assumed to be present in

O o r alloys , accompanied by an excess f one the other component, 10 but their later work opened up a more fruitful ﬁeld o f investiga

O f tion . By determining the values certain physical constants,

such as the thermal and electrical conductivity, hardness , and

O f O b speciﬁc gravity Of a number alloys in a given series, and serving the manner in which the property selected varied with

the composition Of the alloys, they established the fact that dis

continuities occur, which were rightly attributed to the presence w Of intermetallic compounds . The same course was follo ed, with

Matthi e se n i mportant results , by s and his collaborators, whose very extensive and accurate determinations O f many o f the physi 11 Th cal properties of alloys placed the subject on a new basis . e I N TROD UCTI ON 3 general conclusions to be drawn from these investigations were summed up by Matthie sse n in his Report o n the Chemical ” 2 Nature of Alloys 3 Alloys were here fo r the first time regarded o r m as solidified solutions , in which definite compounds might ight

o f e not be present, and good use was made the electrical condu f tiv ity in distinguishing between the two conditions . Such c o n u sion as is to be found in the interpretation of the curves arises

o f from the presence in many alloys of solid solutions , the nature which was not at that time understood . The V iew that the law o f deﬁnite proportions was no t invariable 1 3 was d iﬁi c ul advanced by Cooke, as a means of escape from the ties presented by the alloys of zinc and antimony, but such an

was evasion was seen to be unnecessary , and not adopted by others , although it has been quite recently revived in order to explain f “ certain anomalies in the alloys o bismuth and thallium . This

i s C point discussed below (p . It is lear that only over whelming evidence would justify any departure from the funda

O f mental principles the atomic theory , and it will not be generally admitted that Obscurities in the behaviour o f a few alloys pro vide a suffi cient reason fo r a reversion t o the abandoned view o f o f Berthollet that compounds indefinite composition may exist . The modern systematic study o f intermetallic compounds begins with the accurate determination o f freezing - point curves presenting maxima and discontinuities . The first determinations o f this kind were very inaccurate, but they were soon followed by 15 o f He co ck the extremely accurate investigations y and Neville , who succeeded in establishing the true form Of the freezing- point

o f . curve for a number binary metallic systems The same authors , 16 o f in their examination of the alloys aluminium and gold , cor related the thermal and microscopical Observations in such a way

o f o f as to establish the existence a number compounds, whilst 17 their classical investigation o f the alloys o f copper and tin f inaugurated the much more di ﬁcult and complex study , by o f o f thermal and mic roscopical methods , that part the equilibrium

- diagram which lies below the freezing point curve . It is unnecessary to enter in detail into the history o f metallo o f graphy . The principal additions to the list intermetallic a Tammann compounds h ve been made by and his pupils , in a f 1 0 long list O memoirs from 9 3 onwards . For reasons which the m me author has discussed elsewhere , the experi ental thods adopted I 4 INTERMETALLIC COM P O UN D S

c as have been Open to riticism , and there is much uncertainty to

many O f the proposed formul a . A gradual revision O f the most no w w important systems is in progress in various laboratories , ith the result that, whilst a few systems have been Shown to be more uh simple than had been supposed, others have proved to be expectedly complex . The unsatisfactory nature Of the available data presents a serious obstacle to any general treatment O f the f intermetallic compounds, and this di ﬁculty has been felt through out the preparation of the present monograph . Moreover , the existing material has proved peculiarly intractable to theoretical

o f treatment, and the attempts to form a theory the constitution o f intermetallic compounds, which are brieﬂy discussed in a later

c section , have been omparatively unsuccessful . The subject offers

o f c a promising ﬁeld resear h , and the results are likely to have an important bearing on the further development of atomic and molecular theory.

O f The number intermetallic compounds is very large . A 18 list published in 1 9 00 inc luded the formul a of thirty - seven such 19 1 0 1 0 compounds . In 9 9 this had grown to 9 , whilst a list

2 6 a published in the present year includes 3 formul , and the presence of many more compounds has been recognized, although the investigations have not been sufficiently complete for any definite formul a to be assigned to them . Further research is c ertain to increase this number very largely. In the following sections the occurrence O f intermetallic com pounds as indicated O n the equilibrium diagram and determined by the method O f thermal analysis is first discussed . This is followed by a short note o n the microscopical control o f the thermal indications . An account is then given Of the methods which have been adopted with the Object Of isolating intermetallic compounds in a pure condition , and of their assumed occurrence

l S O as native minera s . little success has been met with in this

o f direction , however, that our knowledge of the properties such compounds is mainly derived from a study of the alloys in which they occur . The succeeding sections are therefore devoted to a consideration o f the inﬂuence which the presence of intermetallic compounds exerts on some of the most important physical pro

t pe ties of alloys . It is also shown that the systematic investiga

o f tion certain properties , especially of the electrical conductivity

- and the thermo electric power , affords the most delicate means in I N TROD UCTI ON 5 a large number of cases o f determining whether chemical co m

n t c bination takes place in a given series or o . An ac ount is then given o f the scanty data which we possess as to the crystal lo ra hi c o f g p characters Of intermetallic compounds, and the evidence for the existence Of compounds in liquid alloys , and the " concluding section reviews the theoretical aspect o f the subject .

" Th e practi cal m eth o ds empl o y e d i n i nve s tiga t io ns Of th i s ki nd are de scribe d ’ “ ” - i n th e a uth o r s Me tall o ra h Te t o o ks O f h s cal Ch em tr ed . S i r . g p y ( x B P y i is y , W Ram a . 2 nd e dn . Lo n o n s y d , CHAPTER I I .

T RMAL ANAL I S HE YS .

MOST of the intermetallic compounds added to the literature by recent investigators have been detected in the ﬁrst instance by m the ethod of thermal analysis . This method depends on the fact that a change from one phase to another, such as the sol idi ﬁcatio n o f of a liquid, or the polymorphic transformation a solid , is almost always accompanied by the development or absorption o f heat . The exceptional cases in which a change of phase occurs without any appreciable change O f thermal energy may be neg l e cte d fo r the moment . Restricting ourselves to the study of binary metallic systems , the method is applied by determining ,

f o f for a su ﬁcient number alloys in the series , the temperatures at

o r n which such thermal changes take place during heating cooli g . o f I n this way a number curves are Obtained , exhibiting the tem p e ra t u re at which each change takes place as a function o f the o f o f composition the alloys , and these curves form the basis the

o f equilibrium diagram , the construction Of which is the ﬁrst task the metallographer who undertakes the complete investigation o f

o f any system alloys .

The ﬁrst curve, and that which is in general most readily

- o r determined , is the freezing point curve liquidus , representing

- the variation o f the initial freezing point with the composition .

o f r I n the early days thermal analysis , this was the only cu ve 20 determined , and it was not immediately recognized that its uncontrolled indications might lead to fallacious conclusions .

It will , however, be convenient to consider this curve before proceeding to the other parts o f the equilibrium diagram . The liquidus curve of a system Of two mutually indifferent e metals is usually composed o f either o n or two branches . If the metals are completely isomorphous , the curve has only a single

- o f branch , which may lie entirely between the freezing points the

o r o r two components, may pass through a maximum a mini 6 THERMAL ANAL YS I S 7

o f mum . If there is a gap in the miscibility the two metals in the solid state, the curve consists of two branches, which may intersect either at a eutectic point o r at a point at which a c hange 21 Of direction occurs without actual reversal . Each branch then represents the separation from the liquid Of crystals of a single

t e s ‘ be i n type , the two y p g in this case either the pure metals , or n solid solutions of the o e metal in the other. The presence Of any additional branch Of the liquidus indicates that a new type o f — — crystals a ne w solid phase makes its appearance within a cer

O f tain range composition . Such a new branch may be due to a

o ne o f o r polymorphic modiﬁcation Of the component metals, to an intermetallic compound . It is not always easy to distinguish

o f o f the two cases , and the aid other methods investigation must

o f be frequently invoked , but the study this curve is generally the preliminary to the determination o f the formul a o f th e inter

i h o f metallic compounds any series alloys . The examination Of the liquidus was practised as a means o f detecting intermetallic compounds before the principles of thermal analysis were correctly

a understood, and many erroneous formul have in this way found an entrance into the literature . The view was very commonly held that a break in the curve indicated the presence o f a com

O f pound , the composition which could be determined by dropping a perpendicular on to the axis Of abscissa . The demonstration 22 of the true nature o f eutectics led to a modiﬁcation o f this V iew as far as eutectic points were concerned , but the recognition Of the fact that a discontinuity does not necessarily occur at the O composition corresponding with a compound , has only been f slow growth . as The ﬁrst case which falls to be considered , exhibiting most O clearly the conditions f the problem , is that in which the inter mediate branch O f the liquidus passes through a maximum tem

e ra ure p t . It may occasionally happen that the maximum lies far

- o f f above the freezing point either o the component metals . The o f interpretation the curve in such a case is unambiguous . An

- intermetallic compound must be present, the high freezing point o f which indicates that it is formed from its components with the o f liberation a large amount Of energy. A familiar example

o f occurs in the amalgams the alkali metals , which are, within a

o f certain range composition , relatively very infusible . In every such case it is found that the maximum corresponds with a 8 I N TERM E TA LLI C COM P O UN D S

deﬁnite intermetallic compound Of great stability. A list Of

- compounds of this class is given below , the freezing points Of the component metals being added for comparison

° ° ° A uMg I I 5O Au 1 06 2 Mg 6 50 ° ° M 60 6 2 s g 3 9 Sb 9 ° ° 2 2 S nMg2 783 Sn 3 ° ° Bi 2 0 zMg 3 7I 5 Bi 7 ° ° N aCd 8 2 1 2 3 4 Na Cd 3 H ° g 2N a 360 Hg ° ° H K 2 0 K 2 g 2 7 6 ° ° 2 2 Hg 2Cs 08 C s 6 S imilar conspicuous maxima are presented by the tellurides o f many metals , compounds which may be considered to form a connecting link between the intermetallic compounds and the sulphides ° ° ° ZnTe 1 2 38 Zn 4 1 9 Te 4 51 ° ° CdTe 1 0 50 Cd 3 2 1 ° ° P bTe 9 1 5 Pb 3 2 7 ° HgTe 6 10 Hg ° ° BiTe 573 Bi 2 70

o ne o f When the components is a relatively infusible metal , the maximum due to an intermetallic compound , although very

- strongly marked , may fail to reach the freezing poi nt Of the less

O f fusible component . The following compounds are examples this class

° ° P tS n 1 2 80 Pt 1 755 ° P tS b 1 2 0 2 3 ° A g Mg 8 2 0 ° A uZn 744 0 Ma 2 59 5 ° ° Mgs 551 Pb 3 2 7 ° ° ° A u S n 4 1 8 Au I O6 2 Sn 2 3 2

o f whilst relative maxima, somewhat less conspicuous , are very frequent occurrence .

When the liquidus comprises several intermediate branches ,

o r o f it is quite possible for two more these to present maxima .

This is the case, for example, with the alloys of gold with

o f magnesium , each the following compounds being represented 1 by a distinct maximum o n the curve (ﬁg . ) A uM A u M A u M g , gg , g 3 ,

I O I N TERM E TA LLI C COMP O UN D S

the position of the maximum . Should the curve be greatly f flattened , it may be di ficult to determine this position exactly, and the difficulty is increased if the apparent atomic ratio is high

c Bi Tl or omplex . For example , the compound ﬁ 3 is described as presenting a maximum at but it is evident that further experiments are necessary before such a formula can be accepted , whilst a maximum described as corresponding with the co m d 26 pound C n K is still more open to doubt . a o f a Actu lly, the establishment such formul by thermal analysis does not depend solely o n the determination O f the to position Of the maximum . A great extension was given the 27 method by Tammann when he proposed a quantitative inter

re tati o n o p of the cooling curves f individual alloys . In addition to the arrests which are employed in the construction o f the

o f liquidus, representing the ﬁrst separation the solid phase from the molten alloys , the cooling curves may present other b e arrests , due to the solidiﬁcation of eutectics, to reactions tween the liquid and solid phases , or to transformations within

o f co m the solid alloys . Any such arrest is limited to a range position within which the phases actually concerned are present it is absent from all alloys having a composition which lies outside

ro that range. Further, the duration of the arrest, which is p portional to the thermal c hange in question (all the cooling curves being assumed to be determined under comparable co n d iti o ns) must be a maximum in that alloy in which the substance

F o r undergoing the change occurs in a pure form . example , a development of heat due to the polymorphic change Of a com pound must be a maximum for the pure compound , whilst a development of heat due to the solidiﬁcation o f a eutectic must vanish at the composition at which one o f the phases composing the eutectic disappears . In a series from which solid solutions are absent, and composed of the two metals A and B , forming a

A - single compound B with maximum freezing point, there are two eutectics , the constituents of which are A and AB, and AB and B

c respectively. I n the ﬁrst half of the series, the eutecti arrest 0 o f b e vanishes at the composition AB (5 atomic per cent B), cause alloys containing a larger proportion o f B do not contain A as a solid phase, and the same reasoning applies to the second half of the system . On the other hand, if the compound AB o undergoes a polymorphic transformati n , the arrest due to that THERMAL A NAL YS I S I I

f trans ormation is a maximum at 50 atomic per cent . Hence the “ ” plotting o f the arrest - times against the composition gives a valuable means of determining the composition Of compounds , — always assuming and this is in practice an important qua liﬁca tion—that the conditions Of cooling are such that equilibrium is attained .

Many intermetallic compounds , appearing as maxima on the

- r o f freezing point cu ves, are capable forming solid solutions with o ne o r o f fo r both their components . The capacity doing so varies within wide limits, being almost absent in such cases as those of the compounds Of magnesium with tin , lead or bismuth , whilst it is very strongly marked in the compounds Of mag ’ ne si um Ta mmann s with gold . method is then applicable with no t certain restrictions . The arrests due to eutectics do vanish

o f at the composition the compounds, but at an earlier point , namely, at the composition of the saturated solid solution con taining the compound . Limits are thus determined, within which

o f the composition the compound must lie , but it is not ﬁxed more precisely. On the other hand , a polymorphic transforma n tio , if such occurs , is still Of great value in ﬁxing the point

fre required . Further, as the temperature Of transformation is quently lowered by the presence of a metal in solid solution , the form o f the transformation curve may be employed in the same manner as that of the liquidus . All such points as these are best understood after the study o f a few actual equili b rium diagrams . A maximum may occur, when solid solutions are formed ,

o f without the presence of a compound . Series solid solutions

- o f with a maximum freezing point, without distinct evidence chemical combination , are occasionally met with in organic

r - w o f chem ist y, the best kno n examples being the mixtures the 28 2 : 6 2 t ribro mo to lue ne s d isomeric 4 and 3 5 , and of and 29 l car o x ime s v . An instance o f a possibly erroneous interpretation o f a maxi

i n - - c mum occurs the series lead thallium . The freezing point urve ° o f these alloys has a very ﬂat maximum at 380 between 30 and 3 0 0 o f Le wko n a 4 atomic per cent lead , and this was regarded by j P l O as indicating a compound g , capable f forming solid solu

K ur nako ff tions with both components . On the other hand , and 3 1 Pushin concluded that such a compound was absent , although I 2 INTERMETALLIC COM P O UN D S

the presence of the maximum was also recognized by them . The

: o f grounds for this conclusion were the flatness the maximum , indicating that the compound , if present at all , must be highly dissociated , and the fact that its position was displaced by the n addition of tin , the maximum of the curve in the ter ary system separating the field O f crystallization of tin from that of the solid I 2 solution occurring at the ratio Pb Tl I instead of : . This plan o f Observing the influence O f a third metal o n the position o f th e ~ m ax i mum is o ne o f great value in de c iding whether

o r a given solid solution contains a compound not , but it has been

c resorted to very rarely. The method of electri al conductivity

o f lends itself particularly to the solution such doubtful cases , and in this instance the evidence from the conductivity is opposed to the hypothesis of a compound, as neither the conductivity nor the 3 2 - co effi cie nt temperature exhibits any discontinuity . A more difficult case of the occurrence o f a maximum O f doubtful significance presents itself in the alloys of bismuth and

- . v thallium The freezing point cur e is of peculiar form , having 25 2 8 . three m axima , at 37 , 9 , and 9 9 atomic per cent of thallium

no t The two latter do correspond with any simple atomic ratio ,

s uﬂi ci e ntl whilst the ﬁrst is y close to 375 per cent, the propor 1 Bi T . tion required for a compound s 3 It appears , however, that micrographic examination and determ inations of the electrical

- co e ffi c ie nt conductivity , temperature of resistance, and hardness all agree in fixing the composition o f the compound at 36 atomic “ per cent Tl , which does not correspond with any simple ratio . K urnak o ff and his colleagues therefore conclude that the solid “ ” to phase in question belongs the class of indefinite compounds, the existence Of which was maintained by Berthollet as against Proust in the early controversy as to the law O f definite propor tions . o ne The system is, however, a very complex . Reactions in the solid state point to the formation at low temperatures o f

BiTl o f d ifﬁ another compound , possibly g . In view the great culty of Obtaining equilibrium in such alloys (the lowest eutectic point being at whilst the reaction in the solid state occurs below it is reasonable to assume that the period of anneal f ing was insu ﬁcient to ensure equilibrium , and that the alloys employed fo r the physical determinations contained metastable

o f phases , which would readily lead to errors i n the position the compound . THERMAL ANAL YS I S 1 3

An intermediate branch of the liquidus which does not present a maximum corresponds with the formation Of a new solid phase

o f but not necessarily a compound . The new phase may be a polymorphic modiﬁcation of the solid phase separating along the

o f o r next higher branch the curve , it may contain a new com

two pound . The cases are not always readily distinguishable, but an application of the method o f plotting arrest- times is Often suc c es ful F o r s in deciding between them . example , the liquidus

2 T curve in Fig . exhibits discontinuities at and p in addition to the eutectic point, l that is , the iquidus has two intermediate

c W e bran hes. may suppose that the heat change taking place at the temperature of the line p g is found to be a maximum at the com A B w position 2, as sho n by the inverted dotted curve . It may then be attributed t o the for mation o f a phase hav

F I G . 2 . ing that composition

o f o r from crystals solid B and the liquid phase during cooling, to

o n t i the corresponding decomposition hea ng , represented by the equation . A f B o . Z 2 B (liquid solution A in B) 2 The second break in the liquidus of Fig . is exactly similar in aspect to the ﬁrst . An application of the method of arrest tim es to the alloys between T and 5 shows that the maximum heat - change occurring along the line 75 i s found at the same co m n E A . positio , Q , as shown by the second dotted curve The arrest must therefore be due to a polymorphic transformation of that

c compound . Had it been due to a further rea tion between the solid phase and the liquid, the maximum would not have been A B found at the composition 2, but at so me point further to the A B left, such as AB or 2 3 . If the c ompound is capable o f entering into solid solution

o ne . 2 with of its components , such a diagram as that in Fig is I 4 INTERMETALLIC COM P O UN D S

° mo diﬁe d a s r s no t w , the lines pg and are continuous as sho n

o f in the diagram . The principle thermal analysis , however , re ma ms - the same, and the maximum heat change occurs at the o f n composition corresponding with that the compou d, if the

o f conditions are such as to favour the attainment equilibrium .

o f I n actual practice , the slowness a reaction between two solid to phases and a liquid , such as that on the line p g , tends prevent c o f the omplete attainment equilibrium , and the maximum heat

o r change appears to be more less displaced . This error may be avoided o r corrected by means which are described in the text 27 o f o r o f Ta mmann books metallography , in the original papers . Microscopical examination furnishes a means O f determining the o f extent of the deviation from equilibrium , and computing the

o f o f true composition the compound , whilst the examination fully annealed specimens furnishes the most satisfactory means o f o f delimiting the regions stability of the respective phases . The application o f these principles may be best illustrated by o f a concrete example. The alloys mag nesium and silver have been subjected to thermal analysis with great care, and apparently 3 3 with satisfactory experimental precautions . The equilibrium diagram constructed from the thermal Observations is given in the upper part of Fig. 3 . The liquidus presents a single maximum ,

O f and also a discontinuity the kind just described . The alloys were not perfectly homogeneous after annealing , and it is possible that under conditions more nearly approaching equi librium , the distance between the liquidus and solidus curves on the right - hand portion o f the diagram would be still further o f reduced , whilst the vertical lines bounding the regions solid solutions I and I I would be slightly displaced . Solid solutions are no t formed to any considerable extent in alloys containing 2 less than 5 atomic per cent Of silver. The discontinuity in the liquidu s curve does not occur at the c A M h o f omposition of the compound g g a, but somew at to the left 2 it , namely, at 3 atomic per cent Ag. The position of the vertical line at 2 5 per cent ind icates that the thermal effect o f the reaction

solid solution I liquid Ag Mg 3

' a t th at s should be a maximum composition , and al o that the thermal effect due to the solidiﬁcation O f the eutectic Should s vanish at that point . The conclusions from the thermal result o f have been fully , conﬁrmed by the study the mechanical and

o f see e . electrical p roperties the alloys ( b low , p THERMAL ANAL y s zs

I G F . 3 . I 6 INTERMETALLIC COM P O UN D S

A compound which is capable o f entering into solid solution in all proportions with both o f its components may give rise to

o f o f a peculiar modiﬁcation the form the liquidus curve , an example of which is seen in the alloys o f magnesium and cad M mium (Fig . The compound n forms a continuous series o f o solid solutions with b th magnesium and cadmium . There i s thus a point o f i nﬂe x io n in the liquidus curve at 50 atomic per cent , and the solidus , which at this point coincides with

co n the liquidus , diverges from it in both directions , only verging again towards the pure metals at the limits o f the

o f diagram . I t is probable that at the composition the com pound both liquidus and solidus have a horizontal tangent, but the curves have not yet been determined experimentally with

f the su ﬁcient accuracy to decide this point . Further evidence of presence o f the compound is afforded by a decomposition which takes place at a lower temperature . The crystals , which are homogeneous throughout the series at temperatures immediately below the solidus , undergo resolution on further cooling, and the curve representing the change passes through a maximum tem

e rat ure o f M p at the composition the compound n . Repeated reference is made in the sequel to this remarkable system . Different views have been held by investigators as to the

o f o f interpretation intermediate branches the liquidus . In ex ce pti o na l cases such a branch may be clearly attributed to the

o ne o f existence of a polymorphic modiﬁcation of the components , but in some other cases the interpretation is less Obvious in the

- o . o ne absence f a maximum freezing point On the hand , Ta mmann and his school have assumed that an intermediate

o f type crystal must contain an intermetallic compound , and an attempt has been made to assign a formula in every such case .

On the other hand , Bancroft and his school have inclined to reject the assumption o f a compound unless clearly indicated by a

o r V a maximum in some other way . On this iew , two metals m y

o f form , not merely two series solid solutions separated by a gap ,

o n as shown theoretical grounds by Roozeboom , but any number f o . such series, separated by a corresponding number of gaps

For example , in a study of the alloys of copper and zinc , 34 Shepherd has shown that these metals form no less than s ix

a « 8 e 7 t e different solid phases , B, y, , , and 7, each of which is

a o f p resented by distinct branch the liquidus, and he does not

1 8 I NTERME TALLI C COM P O UN D S

in a pure state, that is, without forming solid solutions to an

to appreciable extent, and the solid components then unite form a compound at a temperature below the eutectic point . As the

e o f reacting phases are the two metals, the temp rature combina tion remains constant throughout the series, and the reaction

mA ”B A mBn is represented o n the equilibrium diagram by a horizontal line

(Fig . Such a case is stated to occur in the alloys of lead and antimony. The eutectic point is at and an arrest has been observed on the cooling curves only slightly below this, at

3 7 - . The magnitude of the heat change at this point is small , and appears to attain a maximum in the neighbourhood of60 atomic o f o f o per cent antimony, pointing to the formation such a comp und 3 8 b G ue rtler S . as s 3 This explanation is provisionally adopted by , f o f but demands further veriﬁcation . The di ﬁculty obtaining equilibrium in such alloys is particularly great, as the supposed reaction is o ne be t w e e n t w o s o l i d phases at a tempera ture so low that the molecular mobility is

extremely small . The evidence is entirely derived from the ther

mal measurements , as it has not been found possible to recognize the formation of a o 10 20 3 0 4 0 50 70 so 90 mo new m i c r o g r a p h i c 0 Ato mﬁ constituent in the F I G . 4 .

annealed alloys . Pre c i sely similar conditions have been suspected in the alloys o f lead ° o f 1 at and tin , a development heat at 55 during cooling being m o f tributed to the for ation a compound , :The evidence ff here is even less satisfactory, and the thermal e ect Observed has “0 d been attributed to polymorphism , and to the un ercooling of solid The same remarks apply to the alloys o f tin and

o f ti n bismuth , in which the development heat occurs at and z inc tin and cadmium and tin and mercury — 38 THERMAL ANAL YS I S 1 9

c On the whole, the hypothesis of the formation of a ompound

o ne o f in these alloys must be regarded as an improbable , in view the facts that microscopical evidence is lacking, that the chemical relations o f the metals concerned are not such as to suggest the

o f o r probability combination , and that polymorphism undercool f ing is quite capable of giving rise to the ef ects observed . The difﬁc ulty o f obtaining satisfactory evidence from a micro sco p ic a l examination in such a case is obvious from Fig . 4 . The t wo metals A and B are assumed to crystallize in the pure state. I mmediately below the eutectic temperature , therefore,

o f the solid alloys consist the two solid phases A and B , inter

i n o f mixed the form a eutectic, in which are embedded crystals

o f o ne o r c n . the other metal , a cordi g to the composition At a lower temperature, a new solid phase is formed by the reaction 2 B A B A 2 this reaction proceeding at constant temperature . The reacting substances , however , are solid and in a dispersed form , and all alloys except that which contains 33 3 atomic per cent of A have an excess o f o ne or other constituent above that proportion which

fo r c is required the rea tion . These conditions tend to hinder the att a inme nt o f equilibrium, and in the case o f metals o f lo w melt

- s o ing point , the molecular mobility is small that annealing for many weeks may be necessary in order that the formation o f

o f the new phase may proceed to an appreciable extent . None the systems mentioned above have yet been studied from this

o f s uﬂi c i e t c point view with n accura y .

c A omplex case, which is , however, better supported by

1‘ 2 o f microscopical evidence, is that of the alloys nickel and tin , i S n in which a compound, N 3 , stable above reacts with another solid phase to form a new compound, which is either i o r i S n S n . N 4 N 6 At a somewhat lower temperature alloys o f containing a larger proportion tin undergo decomposition , the same compound being formed by dissociation o f the compound i n N 3 S . Ni S n N i S n N i S n 5 3 3 4 3 2 Ni N i S n N i n n S . or 3 3 S 6 S Q

Even this statement must be regarded as hypothetical , although o f the formation a new solid phase is certain . It is possible fo r the range of stable existence o f a compound to be limited in temperature both upwards and downwards . An 9k 2 2 0 INTERMETALLIC COM P O UN D S

i n o f example presents itself the alloys gold and magnesium , 23 43 r which were independently investigated by U az o ff and Vogel . Certain differences between these two authors were subsequently “ reconciled in a joint paper . The probable equilibrium diagram

. 1 . A u M is shown in Fig The compound z g 5 has no deﬁnite ° - 6 o f melting point, but decomposes at 79 into crystals the com n A u M pou d g 3 and a liquid alloy . On the other hand , the solid

c compound, which does not form solid solutions with its o m

o n e nts o n p , decomposes cooling past according to the equation A u M A uM A u M g g 5Z g2 g 3 , the thermal and microscopi c al evidence combining to conﬁrm this conclusion .

o f The case a compound which , whilst stable at high tempera f tures , undergoes decomposition with alling temperature , presents certain features of interest . A possible example , in which the

o f reaction takes place without the formation solid solutions,

i n m N S . c has been entioned above ( 3 , p but the ase is more frequent in systems which include solid solutions . It has recently been shown 45 that a great similarity exists

- - c between the three systems , copper zinc , silver zin , and silver

n 0 6 0 cadmium , especially as regards alloys containi g from to

c atomi per cent of the more fusible metal . The three partial dia

o f grams are reproduced in Fig . 5. The form the liquidus curves w bet een these limits indicates that two series of solid solutions,

a n . designated and Brespectively , crystallize from the molte alloys

« The third solid phase, y, is in each case a deﬁnite compound,

d - 2 A 2 n o r A C . a Cu 2 n3 , g 2 3 , g 2 3 The solution has a considerable

o f 0 0 and 0 range composition , extending from to between 3 4 — atomic per cent at the ordinary temperature. The Bsolution is in each case remarkable in that its range o f composition narrows o n both sides with falling temperature, ultimately vanishing at

n a eutectoid point . There is no co clusive evidence that a com

CuZn A A - pound , , a , or n is actually present in the Bsolu o f tion , but the position of this branch the liquidus in the diagram

o f is strongly suggestive its presence, and the electrical evidence ,

n . discussed below, points to a similar co clusion The formation of a compound during the c ooling o f an alloy

o f may , in the absence of nuclei that compound , be suppressed by

c undercooling . This is most likely to occur when the ompound THERMAL ANAL VS I S 2 I

is formed by a reaction between a solid and a liquid phase, or between two solid phases . It has, however, been observed also

o f . in the solidiﬁcation liquid alloys Thus, in the system cad 46 mium - antimony the freezing- point curve has a maximum at 4 5 c orresponding with the solidiﬁcation o f the stable compound

Cd b w - o f S . Bet een this point and the freezing point antimony there i s a eutectic point at I n alloys containing more ° c 1 0 cadmium , a reaction takes pla e at 4 Cd S b Cd S b liquid 3 2.

Freezing only takes place in this way, however, if the alloy is

c d b n C S . i o ulated with the solid compound Failing inoculation , nuc lei of this compound do not appear as the temperature

a n d f - falls, a dif erent (metastable) freezing point curve is obtained ,

‘ /0 20 3 0 4 0 50 60 10 20 3 0 10 50 60 10 20 3 0 4 0 5 0 60 3 ’ Ato Z A A Z r A . C % n, to m L to % m, m a

F I G . 5. having a maximum at corresponding with the compound

Cd S b t wo 3 2, and a eutectic point at at which the solid d b phases C 3 S 2 and Sb are in metastable equilibrium . I f alloys containing from 40 to 50 atomic per cent Sb are cooled in

wa this y a rearrangement takes place in the solid state, and the passage to the stable condition , in accordance with the equation Cd 5b Cd S b 3 2 Sb 3 o r takes place more less completely , with the development of a

o f considerable amount heat . 2 2 INTERMETALLIC C OM P O UN D S

The alloys of zinc and antimony behave in a similar manner, but in this case the maximum on the curve of the stable system

4‘7

n S b . represents the compound Z a 2 It is the compound Zn S b whi ch i s formed under stable conditions by a reaction between Z m 2 and antimony , and does not make its appearance in the s . Zn S b absence of inoculation A meta table equilibrium between 3 2 ° 2 and antimony is thus obtained , and a eutectic point , 3 below its the normal eutectic point , makes appearance .

The two systems just described are closely analogous, and it is interesting to observe that very similar conditions have recently been fou n d to present themselves in the related system cadmium 48 o n - arsenic . There are two maxima the freezing point curve, at ° 2 1 d A s 7 and corresponding with the compounds C ,, 2 and

dA 3 o f C 2 respectively . In the absence inoculation with crystals of the latter compound , its formation from the liquid is suppressed

o f re re by undercooling, and the descending branch the curve p ° n o f d A 5 2 senti g the freezing C 3 2 may be prolonged 9 into the n Cd A s metastable region , endi g in a eutectic point g 2 As . At this point the reaction Cd A s CdA S 3 2 4As 3 2 w o f f takes place ith development heat, the system dif ering in this respect from the two systems described above, in which reversion to the stable condition does not take place until after complete solidiﬁcation . This liability to undercooling may persist in the presence o f a

o f third metal . Thus , in the examination of the ternary alloys 9 , " cadmium copper, and antimony it was Observed that the forma Cd S b tion of the compound depended on inoculation , failing which a metastable equilibrium was obtained , in which the solid ' C b Cd S b Cu S b S b phases , instead of being q and , were 2 , , and d w C S b . 3 2 Then , at a temperature much belo the solidus , a sudden development of heat was observed, due to the com bination between two solid phases and reversion to the stable system . CHAPTER I II .

MI C S I C R C R RO COP S T U TU E .

I N o f o f any complete investigation a series alloys, the micro sco pical examination should go hand in hand with the thermal

o f study . The examination metals under the microscope at temperatures other than atmospheric has proved impracticable , and etching at high temperatures has found only a very limited

- application . The metallographer is therefore restricted in practice

‘ o f o f to the examination alloys , the structure which has been developed by suitable means at the ordinary temperature . I t follows that a comparison o f the microscopic structures o f a series of slowly cooled alloys reveals the solid phases which are

o ne in equilibrium with another at about I n other words , it determines the intercepts of the vertical and inclined lines o f the equilibrium diagram on a horizontal line drawn across the diagram at It is possible , however , to obtain much more f information than this with the aid o the microscope . By the device o f rapidly quenching selected alloys from known tem

e ra ture s d o f p , and eveloping the structure the quenched specimen

13 by etching, it possible to determine the phases which were

o f assu present in the alloy at the temperature quenching , the mp tion being made that the rate o f cooling was sufﬁ cient to suppress r completely all changes taking place at a lower tempe ature . It n ofte happens that this condition is not strictly fulﬁlled , but the appearance o f the micrO S CO pic structure usually reveals to the

o f practised observer the nature the change that has taken place, . t o fo r and it is possible allow it , more or less accurately , in drawing conclusions from the examination . The simplest example is that o f a binary metallic system in which a single compound occurs , and solid solutions are not formed to an appreciable extent . Starting from the pure metal o f A , the addition of small quantities B leads to the appearance s of a eutectic in the alloys , which increases with increa ing pro

f o f W e portions o B until it composes the whole the alloy. h n 2 3 2 4 I N TE RM E TA L LTC COM P O UN D S

o f B is increased beyond the eutectic proportion , crystallites the A B compound m n make their appearance in increasing quantity.

e c A B Wh n the exa t composition m n is reached, the alloy is homogeneous . When the proportion of B is increased still further , a similar series of changes in structure is passed through

the o f in reverse order, the quantity of crystallites the compound d iminishing until the second eutectic alloy is reached . The determination o f the composition of the compound is a very

o f accurate one, as the presence a very small quantity of the

o f ﬁrst or second eutectic by means the microscope is easy. When the compound is o ne which has been directly deposited from the liquid alloy at a maximum freezing- point during v cooling , the application of the above method is comparati ely

o n simple . It is liable to greater error if, the other hand , the compound has been formed by a reaction between a solid and

c o f ff a liquid phase . On ac ount the slowness of di usion in solids , the reaction is very apt to remain incomplete under

o f o f ordinary conditions cooling , and the solid phase later

o f formation coats the crystallites the earlier phase , and hinders further reaction with the surrounding material . Hence such alloys are frequently seen when cold to consist o f three solid phases . As such a condition is incompatible with equilibrium in a binary system (except at a triple point) , warning is at once given by such a structure that the alloy is in an unstable condition . Equilibrium is most readily attained by cooling

fi ne - rapidly in the first instance to ensure a grained structure , and then again heating the alloy and maintaining it for a s ufli c i e nt f time in the neighbourhood o the temperature of reaction . f Di fusion is thus facilitated . This treatment is often desirable, as the case just discussed is of very frequent occurrence . The conditions are again altered by the formation of solid

o f o ne o f solutions the compound with or both its components .

o f Reverting to the case ﬁrst discussed, the structure the alloys A B becomes homogeneous before the composition m n is reached , o r n o f o r remains so until a further qua tity B is present , the homogeneous region may extend in both directions . It is now only possible to conclude as to the composition o f the intermetallic compound that it lies somewhere within the limits of homogeneous no t structure , and examination by means of the microscope does yield further information .

C HAPTER IV .

THE I S LATI N OF I N T RM TALL I C C M UN DS O O E E O PO .

I N o f C other branches inorganic as well as of organic hemistry , the isolation o f a compound in a pure condition is usually a necessary preliminary to its study and description . Mixtures containing the compound are subjected to the physical processes o f f c . o a co m crystallization , distillation , etc , by means which the

c o f panying substances are in turn removed , until the onstancy properties o f the resulting product under further treatment in di cate s that a deﬁnite compound has been obtained . Such physical processes are supplemented , or even entirely replaced ,

w s o h by treatment with chemical reagents , hich are c osen as to convert the accompanying impurities into easily removable s ub stances , whilst leaving the desired product unattacked . It is natural that similar methods should be applied to metal o n lic alloys, and the number of investigations conducted this

l a n ' i p s in fact very large . F o r reasons which will no w be examined , the results have been unsatisfactory and frequently misleading , and chemical literature has been burdened with an extremely large number o f formul a and descriptions o f supposed Be o f . compounds , the majority which are probably erroneous

o f i m fore the doctrine phases had been applied to alloys , the probability that intermetallic compounds could be isolated by such

wa s no t m means apparent, but it is unfortunate that many me oirs continue to be published, especially in French journals , in which

o f the defective methods are employed , in spite their now fully demonstrated unﬁt ne s s fo r the purpose .

o f c r sta lli za Amongst physical methods , those fractional y tion and fractional distillation alone suggest any probability of success when applied to the I solation o f intermetallic compounds a ff i n from lloys . Crystallization from an indi erent solvent is applicable, the only available solvents being other metals , which form alloys with the material under examination . The method 2 6 THE I S OLA TI ON OF INTERME TALLIC COM P O UN DS 2 7 o f fractional c rystallization is attended by certain experimental d iﬂi cultie s o f t e , of which the most serious is the impossibility m — oving the adhering mother liquor completely from the crystals , washing being impracti cable o n account o f the immiscibility o f molten metals with other liquids . Nevertheless , the method has been frequently employed , some attempt being generally made to reduce the adherence o f the mother- liquor to a mini mum o r to allow fo r its presence by means of some special device . Its application offers the greatest simplicity in the case o f amalgams, owing to the fact that mercury is liquid at the

o f ordinary temperature, and the validity the method is most

o f conveniently examined in this case . A careful study amal f gams , with the object o determining whether deﬁnite chemical 5° 51 K e r compounds were formed , is due to p , whose results served a s the basis for the formula adopted in textbooks until very recently , when they were corrected by the more trustworthy o f method thermal analysis . Some early analyses o f the c rystals obtained by separating the solid and liquid portions of sodium and potassium amalgams

a N a H K H w gave the formul g 6 and gm, ith comparatively little o f o f variation composition . Apparently deﬁnite products this kind had been previously obtained by other workers . The more detailed investigations o f K e rp showed that over the range of ° ° temperature from 0 to 1 00 the solid phase in equilibrium with

was o f liquid sodium amalgam constant composition , containing 2 1 a H s 3 per cent of sodium , whilst the formula N g 5 require o per cent . The crystals were separated by draining n a Gooch

o f crucible, kept at the temperature the experi ment, using a

m . vacuu pump In a similar manner , crystals corresponding with the following deﬁnite formul a were obtained L K H Ba H R . g l z, g m, n 5, n m ’ K e rp s later experiments also led to the conclusion that a second

N a H sodium amalgam , g G, was the stable solid phase at tempera tures below whilst several other potassium amalgams were recognized . The following compounds were also described

M H S Ba H Cd H . g sa n m, g 13 . 2 g 7 A comparison with the results of thermal analysis renders it evident that the crystals were not completely free from mother

o f i s liquor , and that the proportion mercury consequently in all cases too high . 2 8 I N TE RM E TA LLI C COM P O UN D S

The manner in whic h mercury adhere s to the crystals in su c h

c experiments as these is very remarkable . Crystals whi h have been drained by means o f the ﬁlte r - pump and pressed down by a pestle until mercury ceases to es c ape may appear to be entirely

w o f free from adhering liquid , hilst the application considerable

w C i s pressure, as by rapping in hamois leather and squeezing,

o f followed by the expulsion of a further quantity liquid . 52 Such observations even led to the assumption that the com

o f position the solid phase is altered by pressure , but it is obvious that the very moderate pressures employed could have no su ch

f c e fect, and that the liquid is only held me hanically by the solid .

' K e rp observed that so me o f the solid amalgams formed loose o f masses crystals , traversed by capillary cavities, and that such

c o r m a mass, when immersed in mer ury liquid a algam , soaked it up like a sponge, the liquid thus absorbed being again expelled fﬁ on the application of su cient pressure.

n w h as The followi g method , hich been applied to compounds f of the alkali metals , of ers a closer analogy with the method of precipitation s o c ommonly employed in other departments of 53 chem istry. The alkali metal and the other metal with which f combination is required are melted separately under liquid para ﬁn , and mixed at a temperature below the melting- point of the co m pound . A crystalline precipitate is obtained , and in some cases , such as that o f sodium bism uthide,this prec ipitate is insoluble in f an excess o sodium . By employing the theoretical quantities of the two metals , the compound is obtained in an apparently pure c w ondition . The crystals are then merely cooled and ashed with

to f o f benzene or light petroleum remove para ﬁn , but if an excess alkali metal has been employed , this must be removed by means of liquid ammonia . The compounds , which are frequently highly reactive , are then dried in an atmosphere of nitrogen .

V o urna so s obtained by these means the following compounds, the existence of which has been independently established by thermal analysis m 6° Na Bi . . 3 , small leaﬂets p 77 ° K Bi 6 1 3 , minute crystals 7 ° N a 0 s , 4 5 ° a S n N 2 , 477

I f the second metal , for example bismuth or tin , be present the in excess, an alloy is formed , from which compound is only THE I S OLA TI ON OF INTERMETALLIC COM P O UN D S 2 9

f isolated with great di ﬁculty. Considerable heat is evolved during

o f bi s muthid e s c the formation the , but the ompounds are never t h e l e s s highly reactive , being spontaneously inﬂammable in dry

1 a r . Liquid ammonia had been previously employed for removing

e o f an xcess an alkali metal from alloys, and the following com 54 pounds had been isolated by its means .

A s N a b N i n a S a B a S . N 3 , 3 , s , and N 4 Lithium and antimony were even found to react at a low tem p e ra t ure when brought into contact below the surface of liquid Li b 55 S . ammonia, forming the compound 3 The practical difﬁculties of isolation are considerably increased if the temperature at which solid and liquid phases have to be separated be above the atmospheric temperature , as is the case with all but a very few alloys . The liquid may be expelled by 56 c i m means of a centrifugal ma hine, but its removal is always perfect . A n ingenious device has been employed by several 57 58 investigators , consisting in the addition to the system of a small known quantity o f a foreign substance which dissolves in t h e o f liquid , but does not enter into the composition the solid phase . When the crystals are subsequently analysed , a deter mination o f the proportion o f added material enables the quantity

- c h of the adhering mother liquor to be cal ulated . This met od has n o f not often been employed . An insta ce its use is found in a 5° o f o f c study the tin amalgams . Deﬁnite quantities admium were added to the amalgams , and the crystals and the liquid were analysed after separation . On the assumption that the whole

o f of the cadmium remained dissolved in the liquid , the quantity

- mother liquor adhering to the crystals could be calculated, and

o f the composition the solid phase was thus determined . In

o f another case, a smal l quantity silver was added to alloys of tin

n o f and a timony, in order to determine the quantity mother 57 liquor retained by the solid phase .

In the absence of any such special device, there are no means o f determining how much of the mother- liquor has been me ch a ni

re tai néd o f cally , and the clear and glistening surface the crystals f o f c is no su ﬁcient guarantee their chemi al homogeneity . A few concrete examples may illustrate this point . When copper and aluminiu m are melted together in about equal proportions by

- o f weight , and the mother liquor is poured off after a portion the 30 INTERMETALLIC COM P O UN D S

- w alloy has solidiﬁed, large, glistening, silver hite crystals , several 6 0 centimetres in length , may be obtained . An analysis of these crystals gives ﬁg ure s which correspond very closely with the formula

u A 1 f C C . o 4 9 The thermal analysis of the alloys opper and alu c minium has, however , made it clear that no su h compound is

o f c w formed , and that an alloy su h a composition ould be made

8— 8- up of crystals and eutectic . The constituent is, in all prob Cu A l ability, a deﬁnite compound, 2, and the higher proportion of aluminium found in the experiments just quoted is due to the

n presence of a co siderable quantity of liquid eutectic , relatively richer in aluminium than the crystals , adhering to their surface at

- c the moment of removing the mother liquor by de antation . The experiment was repeated by Carpenter and Edwards, who also found it impossible to separate the 8- crystals completely from 61 the eutectic .

The general remarks made above (p . 7) in connexion with the principles of thermal analysis will sufﬁce to make it clear that no relian ce can be placed on formul a Obtained by such a method

as that j ust described . Admitting , even , that it is possible so far to overcome the experimental difﬁculties as to obtain a correct

analysis of the crystals, the values Obtained merely determine the composition of the s o lid phase in equili brium with the liquid at

o f the temperature experiment . Such a phase may be a deﬁnite

c w ompound , but it may also , ith somewhat greater probability ,

‘ be a solid solution , which may or may not contain a compound . The validity o f the formula calculated from the results of analysis

f o f is there ore dependent on the absence solid solutions , a condi tion which can only be determined by thermal analysis o r by an

c ele trical method, either of which yields the required result with

o ut O f the necessity isolating the solid phase . The process o f distillation has been applied in cases I n which o ne o f the component metals of the alloy is volatile at a moderate

n temperature . It is rendered more ge erally applicable by the f o f employment o reduced pressure . The isolation a compound A q by the distillation o f an excess o f cadmium from alloys of cadmium and gold 62 is discussed in connexion with the existence o f compounds in the liquid state (p . The compounds

' A uZn Cu S b o f and 3 , the existence which is proved by other e vidence, have similarly been obtained in a condition approach ing to purity by removal of an excess of zinc and antimony THE I S OLA TI ON OF I N TE RME TA L LI C COM P O UN D S 3 1

° 63 respectively by distillation at 1 1 00 under a pressure o f 1 mm . The crystalline compounds Cdt and Mgt were also obtained “ by removing the excess o f volatile metal by distillation . The treatment o f alloys with chemical reagents for the pur

o f o ne pose removing an excess of component , leaving a residue of the intermetallic compound , has been adopted very frequently, and has obtained an undeserved conﬁdence, which is only grad ually disappearing before criticisms grounded o n the doctrine

o ne of phases . A reagent being added which dissolves of the o n component metals without acting the other , the reaction frequently comes to a standstill when a part only o f the soluble metal has been removed, the assumption being made that the undissolved portion is in a state o f chemical combination with

o r the second metal . I n order to avoid the objection that two more solid phases may be intimately entangled , the alloy may be powdered before being submitted to the action of the reagent , and whenever possible the action o f two or more distinct re

t wo agents is examined . When chemically dissimilar reagents

a c o m attack the alloys, leaving residue of the same constant

o h position , the inference that a deﬁnite compound has been taine d is considerably strengthened . The validity o f the method is dependent o n the compound sought fo r having a greater resistance towards the reagent em ployed than the component present in excess in the alloy taken fo r the experiment .

f o f o f The practical di ﬁculties the examination residues , and

o f the errors interpretation to which they may easily give rise,

o f are well illustrated by the example the copper silicides . 55 Earlier experiments had led to the conclusion that a single Cu S i stable compound, 4 , existed in this series . I n a detailed 66 i t investigation , Philips found impossible to obtain a deﬁnite o f silicide from alloys containing an excess copper, as all reagents capable of dissolv ing the free copper attacked the sili

o r cide to a greater less extent , whilst a concentrated solution Of

potassium cyanide even dissolved the alloy completely. On the

o f other hand, alloys containing an excess silicon , if attacked by

means of potassium hydroxide, left a residue which appeared

Ga S i . to be of a deﬁnite character, having the formula 7 2 The same residue was obtained when the reagent used was potassium

carbonate . An examination by the thermal method, assisted by 3 2 INTERMETALLIC COM P O UN D S

microscopical examination , had previously indicated the presence

U I c of C 3 S , fairly distin tly marked as a maximum on the freezing 67 c point curve . The only other sili ide recognized in this thermal Cu S i a study was considered to have the composition g 4, formula f in itself improbable, and supported by such insu ﬁcient evidence

c that it may be unhesitatingly rejected . A second sili ide prob ably exists , but it is impossible to deduce its formula from these o f c observations . On the silicon side the ﬁrst eutecti point ,

- however, the freezing point curve has been more satisfactorily

n o f c determi ed , and there is no indication whatever the presen e f i o Cu S . a compound 7 2 It thus appears that the method of the analysis of residues tends to indicate too low a proportion of silicon in the solid phase. The nature o f the error involved has been discussed by 68 G ue rtle r , who bases his conclusions on previous observations in

o f o f the study metallic silicides . An alloy consisting a silicide together with free silicon is attacked by alkali hydroxides, the silicon being removed as silicate , but the action is never confined o f to that part the silicon which is present in the free state . The silicide is also attacked superficially , although less rapidly, with w the result that its particles become coated ith a layer of metal , which hinders further solution and produces a fictitiou s appear

o f . ance equilibrium On analysis , the apparently unattacked residue is found to contain a proportion of silicon which is appreciably less than that which was actually present in combina tion before the attack . This behaviour has been observed in the 6° 70 alloys of iron and of nickel with silicon , and accounts fully for the anomalous results obtained by Philips . f o f An ef ect this kind is by no means conﬁned to silicides, but may present itself in the analysis of metallic residues from other alloys , the undissolved portion becoming coated with an imper v io us o f layer the insoluble component , the proportion of which is

consequently found o n analysis to be too high .

Moreover , the fundamental assumption which underlies the

o f o f method the examination residues , namely , that an inter metallic compound is less readily attacked by reagents than the G ue r l n . t e r more reactive of its compo ents, is not always justiﬁed mentions the following instances o f intermetallic compounds which are more reactive than their components

o f M P b M n Compounds magnesium , including g 2 , n , and

CHA PTER V.

TI I NT RM TAL LI C C M NDS N A VE E E O PO U .

COMP ARATI VELY few o f the metals are found in the earth in the native state, such occurrences being almost conﬁned to the iron group (iron , cobalt , and nickel), the metals, mercury, copper, o f silver, and gold , the group the platinum metals , and the semi metals arsenic, antimony, bismuth , and tellurium . It is therefore not surprising that few intermetallic compounds are known to

o f occur as minerals , and that the majority those which are known

- are compounds with the semi metals , and therefore approach in chemical character the sulphides and other typical mineral compounds . o f o r That a mineral , composed two more metals , has a deﬁnite crystalline form and an approximately uniform composition, does not prove it to be a deﬁnite compound . In many cases a micro s co ical p examination is lacking, and we are ignorant whether the

o f o ne mineral is actually composed homogeneous crystals Of kind , f o r o . is an intergrowth two or more crystalline phases Moreover, as has become clear in the discussion of artiﬁcial crystals , a homo

e ne o us o f g crystalline mass may consist merely a solid solution, the composition of which bears no necessary relation to that o f any compound which may be formed by the component metals .

no t Nevertheless, chemical individuality is to be denied to a mineral because no compound o f similar composition i s found by thermal analysis . Compounds occurring as minerals may have been produced in the wet way , by deposition from

o r complex mixtures , under great pressures , otherwise under such conditions as to yield a compound which has no range o f stability within the limits o f an ordinary investigation by o f s o f means thermal analysi , that is , by fusion binary mixtures

F r . o under atmospheric pressure example , the thermal analysis o f the alloys o f metals o f high melting- point with arsenic is u sually limited to alloys containing 50 pe r cent o f arsenic or 34 NATIVE I N TE RMETA L LI C COM P O UN D S 3 5

o n o f o f less , account the volatility arsenic under atmospheric pressure , but metallic arsenides containing much larger proportions o f n arsenic are know to occur as minerals, and their chemical individuality is hardly doubtful , especially when their close analogy with the sulphides is taken into account . It must therefore be assumed that such minerals must have been p ro d uce d under an increased pressure , or possibly by reactions

o f occurring at a low temperature . Some these native arsenides

o f are stable when melted in a closed tube , but lose their excess arsenic if heated under atmospheric pressure .

- Of the metals enumerated above , those of high melting point o f have a great tendency to form solid solutions, and such their

F o r alloys as occur in nature are generally o f that class . ex

o f ample , the meteoric irons are composed solid solutions of iron

o f and nickel , whilst terrestrial alloys those two metals are also G known under the names of Awaruite and Josephinite . old occurs in the form of solid solutions with palladium , rhodium , and silver, the last alloy being known as electrum . I ridosmine contains iridium and osmium . Silver amalgams are occasionally fo r found, but their composition does not correspond with the

o f mula any deﬁnite compound . A native alloy of gold and h as A u Bi im bismuth been described as a compound , z , but it is probable that any such compound exists, and the mineral may be a mere mixture .

The following arsenides and antimonides , which have been

a recorded as minerals , have formul corresponding with com pounds already recognized by the method o f thermal analysis A S b Dyscrasite , g 3 Gu A s Domeykite, 3 i cco lit e iA s N , N Bre ithau h ite Ni S b p , LOlli n ite g , A 3 . Fe 2 A rse no fe rr1te ,

w a The follo ing minerals have received formul , but are prob ably solid solutions , more or less unsaturated

S hA s Allemontite, 3 A S b (Variety of) Dyscrasite , g ﬁ Cu A s Whitneyite, g Cu A s Algodonite, ﬁ r CU S b Ho sfordite , G 3 i f 36 I N TERM E TA LLI C COM P O UN D S

A rse na r en tite A A s w g , represented as g 3 , and Chilenite , to hich the f Bi A . ormula g 6 has been given , may be mixtures The fo llo wmg minerals contain more arsenic than any c o m pound of the corresponding series which has been studied by b ut thermal analysis , they probably represent deﬁnite com pounds

Smaltite,

S afﬂo rite ,

Chloanthite, I N AS° Rammelsbergite , S kutte ro dite Co A s , 3 P tA 5 Sperrylite , 2 m Co A s Bi Bismutos altite, ( , )a F e A s m F eA s Leucopyrite, 3 4, is possibly a ixture of and

F e A sg . The following well - d e ﬁne d tellurides occur in nature

A e H essite, n A u Te Petzite , (Ag, )2 m Bi Te Tetrady ite, 2 3 H Te Coloradoite, g

P bTe Altaite , S tii t zite A Te o f Of other tellurides , , g 4 , may be a mixture A e Ni Te the compound n with silver , and Melonite, z s, more ' NiTe e probably contains the known compound . Jos ite is a variable bismuth telluride . A Te A u Te K Sylvanite , g , , Calaverite, z, and rennerite (Ag , A u Te d ) 2, are recognized as deﬁnite minerals, but compoun s corresponding with them have not been obtained by fusion , the only tellurides recognized in these series by thermal analysis

A e A Te A Te u T . being g g , g , and z s K al o o rlite H A u A Te G o ld sch The complex minerals g , g z g 6 6 ; midtite A A u Te - , g 2 6 ; and Wehrlite, a silver bismuth telluride, may i s also be mentioned . No reference here made to the very numerous minerals in which arsenic and tellurium are partly o r

- wholly replaced by sulphur and selenium , distinctly non metallic ale elements . I t will be observed that all the compounds enumerated above

o f co m are a heteropolar character . Homopolar intermetallic

pounds have not been observed to occur in nature .

’ Th e names and assume d fo rmul a o f th e ab o v e minerals are tak en fro m Dana s t ner l o Sy s em of Mi a gy . C HAPTER VI .

I CA R TI PHYS L P OPER ES .

THE principal physical properties of alloys , including the density, hardness , conductivity for heat and electricity , thermoelectric power, magnetic susceptibility , etc . , are profoundly modiﬁed by

o f o f the formation intermetallic compounds . In the absence

c compounds , ea h such property is in general a continuous function of the composition in any given series of alloys . It may be an approximately linear function , as the speciﬁc volume o f o r conglomerates and solid solutions , it may pass through a

o r c o nd uc maximum minimum , as the hardness and electrical tivity o f solid solution" Discontinuities may occur in cases o f

c limited mis ibility in the solid state, the curve which represents the variation of the property with composition then exhibiting an abrupt change of direction at the point at which a new phase n makes its appearance . Failure to recognize this conditio is responsible fo r the attribution o f deﬁnite chemical formul a to a

o f o f o f large number alloys , each which is merely the limit

o f n saturation a solid solutio . It is necessary to examine the relation o f each individual property to the composition sepa rate l o f y , and to determine in which cases the discontinuity the

n o n c o f function depe ds the appearan e a new phase , and in which it presents itself at the concentration of the compound . "

This is done in the following sections . A new ﬁeld o f metallography has been opened up by the

o f o f detailed study , in a large number concrete examples , the dependence o f the physical properties o f alloys o n their composi tion . The thermal and microscopical methods determine the nature of the heterogeneous equilibrium in metallic systems, that is, the limits of temperature and composition within which each

s . phase is table These methods do not , however, give direct

no t information as to homogeneous equilibria, that is , they do indicate directly the nature o f the molecules which compose any 37 38 INTERMETALLIC COMP O UN D S

single phase . This is , in fact, a question to which the doctrine o f o f phases is incapable furnishing an answer . I t is true that certain inferences may be drawn from the thermal observations . It has been assumed in the discussion in

- Chap . I that a maximum on the freezing point curve is due to f o f the ormation an intermetallic compound , the formula of which is given by the composition at which the maximu m occurs . In the absence o f any extended series o f solid solutions there can hardly be any doubt as to the truth Of such a conclusion , but ambiguity is possible when the branch o f the curve o n which the

o f s maximum occurs represents the freezing solid solutions , a in

o f I I the case the alloys of lead and thalliu m , mentioned on p . .

In such a case the thermal investigations leave the question open , except in so far as i ndications are afforded by an examination o f ternary systems . The microscope does not furnish any decisive evidence on such a point . A microscopically homogeneous alloy may contain chemically d ifferent molecules without any obvious difference of structure .

o Investigations , however, most of which have been carried ut

a in recent years , h ve now proved that the determination Of certain o f physical properties is capable throwing light, not only on hetero

e ne o us o n . g , but also homogeneous equilibria Such properties

fo r as the electrical conductivity and thermoelectric power, ex

n o t ample, are only dependent on the number and relative propor

o f o f tion the constituent phases, but also on the concentration

o ne some kind of molecule within a homogeneous phase . I n such a case the property reaches a maximum or minimum for that composition of the phase at which the c once t ratio n o f the molecules in question is a maximum. Whilst , therefore , the density and some other properties vary continuously within

e the limits of miscibility in the solid state, the electrical condu ti vity and thermoelectric power only do so if the molecules composing the solutions increase o r decrease continuously in number from the one limit to the other. Should the series include a deﬁnite compound, entering into solid solution with both its components , the property curve exhibits a marked o f discontinuity at the composition the compound, that is , at the point at which the concentration o f the compound is a maximum . The discontinuity is often such as to produce a o n sharp cusp the curve . P H YS I CA L P ROP ERTI ES 39

o f Further , it is often possible , by an examination the form of to the curve , draw some conclusions as to the degree of dissocia

o f c tion the ompound within the phase , whether the latter be

o r o f liquid solid . This branch the study has not yet received much attention . The relationships dealt with in this section are very clearly

o f exhibited by the remarkable alloys magnesium and cadmium , to which resort has been had to establish several o f the general principles involved . These two metals form a single com d M C . pound , g (p which enters into solid solution with both components and in all proportions . Its physical properties have therefore been studied in some detail (pp . 4 3 , At lower temperatures , the homogeneous solid solutions undergo resolution into two constituents , and it is therefore possible to observe, in 1 o f a single ser es alloys , the gradual change from a simple to a complex system .

CI I C Vo L ME SPE F U .

An alloy which consists o f a simple conglomerate o f its component metals has a speciﬁc volume which bears a nearly linear relation to its composition , and may therefore be calculated from the speciﬁc volumes o f the pure metals and their relative

o n proportions . The linear relation does not hold exactly , account of deviations from the condition o f closest packi ng which

o f occur in an intimate mixture two solid phases , such as a eutectic alloy . These deviations are, however, small , and the

o f rule has been veriﬁed in a large number instances , the slight variation from a straight line , where noticeable , being of the order expected . The simple linear relation also subsists in the case o f a c o n

s e o f tinuo u s ries homogeneous solid solutions . On the other

e - hand , the sp ciﬁc volume concentration curve deviates, some times to a very considerable extent , from the straight line when a new solid phase , containing an intermetallic compound , makes its appearance in the series . It most frequently happens that a compound has a smaller speciﬁc volume than its components , but the reverse condition is also observed . When only a

c single ompound occurs in a series , and solid solutions are no t - c o nc en formed to any large extent, the speciﬁc volume t rat io n o f curve is made up two straight lines , intersecting 40 I N TE RM E TA LLI C COM P O UN D S

o f at the composition the compound , and thus enabling its formula to be inferred directly. Where there is a limited mutual solubility in the solid state , a discontinuity , often very slight, and

f o f di ﬁcult to Observe , occurs at the limit of saturation each solid solution . Thus , if an intermetallic compound forms solid solutions

o f to a limited extent with each its components , a condition ofvery

o f frequent occurrence, the speciﬁc volume curve is made up three

o f straight lines . The two points intersection merely mark the compositions at which the new intermediate phase makes its a p

e arance c p , and it is not possible to infer from them the omposition o f i nte rsec the compound . It was formerly supposed that every tion indicated the presence of a compound of that composition , and it has been a frequent practice to describe as deﬁnite compounds mixtures corresponding with breaks in a density or speciﬁc volume curve .

Where only a single intermetallic compound is present , and the curve is made up , as described above , of three intersecting o f straight lines, it is sometimes possible to obtain an indication the probable formula of the supposed compo und by produci ng the ﬁrst and last of these lines , and observing the composition at which they then intersect . I f several compounds are formed,

o n they may be separately indicated the curve , or it may happen that only o ne of them deviates sufﬁciently from the mean to be

n recognizable , the others bei g formed from their components

o f with comparatively little change volume. 71 Mae The principal data on this question are due to y , who determined the speciﬁc volume of a number of series, and also recalculated the observations of others , who had mostly plotted

o f c the values the density against the omposition , a method which f fails to represent the relations with su ﬁcient simplicity. The

s e best of these older determinations are due to Mat thi e s n . I n the following cases the compound is formed with contrae

c tion , and the curve is omposed of two straight lines

P er Ce nt

S t em C m un Co ntract o n . o o . y s . p d i A b Ag Sb g aS 5

Ag Sn A g 3 S n 5 F e S b 1 6 Fe Sb s 2

In the following series, the contraction due to the compound

4 2 I N TERM E TA L LI C COM P O UN D S

o f atomic volumes) consists three straight lines , intersecting at

c Cd A 5 compositions corresponding with the two ompounds . 3 2

o n CdA 5 appears as a maximum the curve , 2 only as an abrupt o f change direction . The constitution of the alloys has been deﬁnitely established by thermal and microscopical analysis . It is worthy of remark that the compounds which have been proved to be formed from their component metals with increase o f l m o r vo u e are either antimonides arsenides . As an example o f the somewhat hazardous attempts to i nv e s tig ate the constitution of complex series by the method o f speciﬁc

o f o f volumes, mention may b e made a study metallic silicides, in which the discontinuities observed were more numerous than 75 e would be xpected from the thermal data .

A RDN SS H E .

The hardness in a series o f conglomerates is approximately proportional to the composition , the Slight deviations usually observed being due to the fact that the constituents o f a ﬁ ne grained eutectic support one another, so that the hardness as determined by most ordinary methods is slightly increased . On the other hand , the hardness in a series of solid solutions is much

o f and greater than that calculated by the rule mixtures , the

n - hard ess composition c urve commonly passes through a maximum .

o f The hardness an alloy containing equal parts of silver and gold ,

o f o f for example , is nearly twice that either the component t 76 me als . An intermetallic compound is usually harder than its com

o ne nts . p , although this cannot be stated as an invariable rule f The dif erence is often very great , the extreme hardness of such a

Cu S n r . compound as g , for example, being ve y remarkable

The methods adopted for the determination of hardness , f although dif ering widely in character and theoretical signiﬁcance, have comparatively little inﬂuence on the form o f the curve connecting hardness and composition , provided that all the alloys are examined in the crystalline condition without being strained

' li io n by the app ca t o f mechanical work . Four such methods are

o f in general use in the investigation this property, namely, the

o n o f sclerometric method, depending the production of a scratch

th e measurable breadth the indentation method , in which extent P H YS I CA L P ROP ERTIES 43 o f the y ielding under the pressure o f a loaded ball o r cone is w f measured ; the elastic reaction method, in hich the coe ficient of restitution is determined when a hard object falls on to the specimen from a height ; and the plastic flow method, in which the material is forced through an orifice under the application o f U o f very high pressures . nlike as these four methods testing appear to be, they yield remarkably concordant results when applied to normal crystalline alloys . The third is the least valuable for this purpose, whilst the first and second are very generally applicable, and the fourth , which is impracticable except o f o f in the case relatively soft materials, has proved value in f the theoretical comparison o hardness with other properti e s .

A series of alloys containing a single compound , and free

o f ha s from solid solutions appreciable concentration , a hardness curve composed o f two straight lines intersecting at the com o f position the compound . A compound which forms solid solution s in all proportion s with both components has its hardness increased by the addition of either metal , and the

o f curve thus has two maxima , the composition the compound being indicated by a cusp directed downwards (Fig . This case presents itself in the alloys of magnesium and cadmium at

- temperatures above their transformation point (Fig . H ow i n s ever, the conditions this series are somewhat les simple, as m Cd M 8 ro the co pound g , which in its , state is miscible in all p portions with cadmium and magnesium , has only a limited

- so miscibility in the a condition , that determinations of the hardness o f the slowly cooled alloys yield a rather more complex

o f curve, with minor discontinuities at the limits of saturation the 77 d o wnwafd s un solid solutions . The cusp directed indicates o f mistakably the position the compound, in a case in which the

o f thermal analysis leaves the existence a compound unproven , mic ro sc 0 i c although probable, whilst the p structure of the entire

fro m ' t rans fo rmat i o ns series is , apart at a lower temperature, completely homogeneous . A more complex series is seen in the alloys of magnesium and silver (Fig . The equilibrium diagram in the upper part 3 3 o f a re o f the ﬁgure shows that two compounds formed, which

A M - the ﬁrst , g g s, decomposes below its melting point and does n o t enter into solid solution to any appreciable extent, whilst the

A M m o n - second, g g , appears as a maximu the freezing point curve , 44 I N TE RM E TA LLI C COM P O UN D S

and forms solid solutions with both silver and mag

n e s i u m n . T h e h a r d e s s

curve, shown immediately

b e l o w , i n d i c a t e s t h a t A g Mg 3 has a hardness , ’ measured by Bri ne ll s ball method , more than six times as great as that of either

magnesium o r silver . Silver i s hardened in a very marked

— F I G . 6 . ar ne cur e H d ss v . degree by the entry o f mag n e s ium into solid solution with it, thus causing the second maximum in the curve . T h e c o m p o u n d , A M g g , appearing as it does in the midst o f a series o f 8 solid solutions , is indicated 55 by a cusp directed down

wards . I t is nevertheless nearly three times as hard 78 as its components . 0 I0 20 3 0 40 50 60 70 These two curves are

F I G typical o f those obtainable . 7. from alloys containing intermetallic compounds, and P H YS I CA L P ROP ER TI ES 4 5

a i m necess ry to cite further examples in detail . The technically

o f o n portant alloys copper with zinc , tin , and aluminium , account o f their highly complex constitution , yield less satisfactory curves ,

v but a few conclusions may ne ertheless be drawn from them . The alloys o f copper and zinc have a maximum hardness at the o f Cu l n composition the compound z s , which is ten times as hard as copper, using either the Brinell ball test or the elastic reaction 79 c u S n . C method The ompound g is determined by the sclero 8 0 S ic CO e r COp method to be twelve times as hard as pp . The

Cu A l c compound 3 is also mu h harder than its components, 61 CO e r being about seven times as hard as p p .

E E TRI N D TI I T L C CAL CO UC V Y.

The general laws connecting the electrical conductivity with the constitu tion o f alloys have been well established by the 1 Ma tthi e s se n labours of a number of investigators , beginning with . Alloys which consist of simple conglomerates of the component metals have a conductivity which bears an almost linear relation

fre to the composition by volume, the Small deviations which are quently observed being o f the order of perturbations due to the

C n mechanical arrangement Of the constituent phases . When a o t i nuo u s series Of solid solutions is formed, the conductivity curve

' passes through a minimum , the fall being extremely steep in the

o f o f neighbourhood the pure metals . When the concentration

C o f the solid solutions is limited , an abrupt hange direction is f observed at the limits o saturation . The presence o f intermetallic compounds profoundly modiﬁes the form of the conductivity curve . The principal relations 81 G u e rtle r K urnak o ff S che mt have been stated by , and by and 76 sch n ch u y . Whilst the composition by volume is undoubtedly the proper basis o f a quantitative comparison of the conductivity o f c o n

o r use glomerates of solid solutions , it is preferable to the atomic percentages when the Object is to determine whether intermetallic

o r compounds are present not in a given series of alloys . For the

o f systematic study a series , it is desirable to construct a diagram

a in the ﬁrst instance having atomic percentages as absciss , and

o f o f then , in the case any Singularities pointing to the presence s intermetallic compounds being ob erved , to divide the system into 46 I N TE RM E TA L LI C C OM P O UN D S

c as many binary systems as are thus indicated, and to constru t a

a w corresponding number of partial diagr ms , in hich percentages

a by volume are employed as absciss .

w c The further question , hether the speciﬁc resistan e or spec iﬁc conductivity should be adopted for the ordinates of the diagram , can only be answered by saying that both may be employed . As a rule, any discontinuities are more clearly marked on the curve

u c of cond ctivity than on that of resistance, but the contrary ase sometimes presents itself when the compound occurs near to a

c mini mum in the onductivity.

An intermetallic compound , if well deﬁned , may be regarded

v con eniently as a separate component, forming alloys with the pure metals or with other compounds in the same series . The condu c tivity of a c ompound is always less than that of the better c onducti ng o f the two metals of which it is com

posed . As the condu ctivity o f a pu re metal is al ways l owered by alloying with a second metal with wh ich it

forms solid solutions , the same may be expected to hold good of an intermetallic com

pound . Should the com pound be capable of enteri n g - I G 8 C n uct t curve . F . . o d vi y i into solid solution with both o f its components in all proportions, the conductivity curve should 8 have the form shown in Fig. , the compound being indicated by a cusp, since its conductivity is necessarily lowered by an excess o f either component . This case is met with in the alloys of mag n e s i um and cadmium at temperatures above their transformation point (Fig . The curve showing the conductivity of the alloys ° f - at 300 refers to the homogeneou s series o Bsolid solutions . The M o f e compound n occurs in the middle this series . Its condu t ivity is not muc h more than half . that o f magnesium at the same e temperature , and is depress d by alloying with either of the com ° e nt 00 s two p o n s. The conductivity diagram at 3 thus consist of

U - a pproximately shaped curves , meeting in a sharp cusp directed 77 u M . pwards, at the composition n P H YS I CA L P ROP ER TI ES 47

— o f At a lower temperature, such as the Bsolid solutions medium concentration have undergone conversion into the a - modi

ﬁ cati o n , which is restricted within certain limits of concentration .

o f — There are now two ranges stable Bsolutions , adjoining the

10 20 3 0 4 0 50 60 70 00 9 0 100 0 Ato m /5 5 0

F I G . 9 .

o f m magnesium and cadmium ends the series respectively , a iddle

o f a - o range stable alloys , and two intermediate regi ns in which a no w and Bare present in equilibrium with o n e another . It is possible to predict the form o f the conductivity- composition curve 48 I N TERM E TA L L I C C OM P O UN D S

for The a - region corresponds with two U - shaped curves

- w a. uniting in a cusp directed up ards , the two Bregions with 8 c straight lines, whilst the terminal , solid solutions are indi ated by conductivity curves falling steeply from the values for the

' Ato m % 7e

F I G . I O .

f . o pure metals This is the . actual form the curve determined ° 2 experimentally . At temperatures intermediate between 5 and

- the a region diminishes in extent with rising temperature. The form o f the transformation curves has in fact been determined m ore accurately by electrical than by thermal means .

50 I N TE RM E TA L LI C COM P O UN D S

bi s muth and that of , the two M —M Bi series g g 3 2

M Bi - Ri S im and g 3 2 are

ple conglomerates . On

the other hand, the conductivity cu rves o f the series magnesium

- lead , magnesium tin ,

- and magnesium zinc , all indicate the forma tion Of solid solutions to an appreciable ex tent at the magnesium 82 o f end the series . O ther systems are

represented in Figs .

1 0 1 1 . 9 , , and The A S b c o m p o u n d s g 3

b . Te and S 2 3 are clearly indicated by c usps di

re cte d upwards . On

the other hand , the c u s p corresponding

Bi Te c with z 3 is dire t

ed downwards . The reason for the maxi mum o n the tellurium

side is not evident, but it appears to point to imperfect e quilib ri um in the alloys used

fo r the measurements . It is remarkable that the curve of thermo

electric power, shown i n the lower part o f

the diagram , does not 0 10 20 3 0 40 5 0 60 70 80 00 /00 exhibit any irregular A t0m % 0d .

ity at this point, but F I G 1 2 . . has an exceptionally P H YS I CA L P ROP ER TI ES 51

U - co m sharp cusp, with a smooth shaped curve between the pound and the tellurium end o f the series . 1 2 The al loys Of antimony and cadmium (Fig . ) have been plotted with the resistance instead of the conductivity, as the compound S d is more clearly marked in this way . An exactly similar curve is given by the alloys o f antimony and zinc , with the cusp at the composition of the compound 83 bZn S . The only rule which has been enunciated with respect to the relative conductivities of intermetallic compounds is , that the

- o ne o f conductivity is lower , the less electro positive the com

o ne nts o f p the compound is . Thus antimonides and arsenides

- have a low conductivity , and in fact approach non metallic sub stances in their electrical properties . The temperature - co e ﬂi cie nt o f the resistance o r o f the con d uct iv ity is as characteristic a function of the constitution o f an alloy as the conductivity itself. Like the conductivity, it varies

o f and in a linear manner in a series conglomerates, along a curve

o f passing through a minimum in a series solid solutions . Alloys h av m f h g a temperature coe ﬁcient near to zero, suc as are used

o f for the construction resistance coils , are always solid solutions , near to such a minimum .

The temperature- co efﬁ ci e nt of the resi stance is approximately the same for all pure metals , being always positive , and usually

0 0 0 - 0 0 0 co from 3 4 at about atmospheric temperatures . The ffi e cient is not a constant , but decreases with rising temperature . A complex formula is necessary to express the relation o f resist ance to temperature over any extended range . Homopolar intermetallic compounds are found to have temperature coeffi cients which are approximately the same as o f those pure metals . They are thus clearly distinguished from those alloys which consist merely o f solid solutions o f their f components . This is su ficiently indicated by the following o f table , in which an alloy consisting a solid solution is selected

c - from each series for omparison , being placed in the right hand 82 part o f the table ' 52 I N TERMETA LLI C COM P O UN DS

“ “ e es Ref r S as. e ence

Mgs

M g CuQ

M 6 Z n 3 5 g . 5 0 A 0 M 7 g , 3 g A M g . 77 5 g

’ The very low values fo r the co e ﬂI ci e nt o f the resistance in the case o f solid solutions are in striking contrast with the uniformly high values fo r intermetallic compounds .

o f The curves for a complex system , the alloys copper and zinc, are given in Fig. The resistance curve has two cusps , Cu Zn at compositions corresponding with the compounds z 3 and f CuZn . o , The maximum in the ﬁrst part the curve is that due

- o a . t wo o ne t the solid solution The conductivity curve has cusps, CuZn o f which is placed exactly at the composition , whilst the uZn C . other is more nearly at 5 A third discontinuity perhaps

- co e ﬂﬁci e nt represents Cua . On the temperature curve the four CuZn CuZn CuZ n Cu upward cusps correspond with , , , G, and a f CuZn respectively . Pushin there ore regards the compounds ,

CuZ n CuZn Cu . , , and ,, as certain, and a as possible This fe ectio n o f Cu Zn fo r involves the j Z s , a compound which there is n much other evide ce, but which Pushin regards merely as the

r - o f CuZn . limiting concentration the y phase , containing , There CuZn does not seem to be any good reason for this . The point 2 is not marked on the conductivity curve, although it appears so

- o e ﬂi c ie nt lo w conspicuously o n the temperature c curve . The

o f u Zn fo r coefﬁ cient C 2 3 may be accounted by supposing it to approach the antimonides and other heteropolar compo unds more o f s re closely than the other members the eries, a view which ce iv e s support from other facts . P H YS I CA L P ROP ER TI ES 53

An interesting feature of the curves is the prominence of the

CuZ n o f - compound , the central constituent the Bphase, the existence of which has been sometimes questioned . The electrical behaviour o f alloys at low temperatures is best

Ato m . %Zn

F I G 1 . 3 . examined by considering the resistance instead o f the con sg °° d uctiv it r y . Much recent work goes to conﬁrm the view that the electrical resistance o f pure metals becomes zero at o r so mewhat above the absolute zero o f temperature . Solid 54 I N TE RM E TA LLI C COM P O UN D S

o n solutions , the other hand , exhibit a resistance which indeed diminishes with falling temperature, but reaches a ﬁnite constant

o f value instead vanishing at very low temperatures . The “ ” o r c alcu solution resistance, additional resistance above that

o f lated by the rule of mixtures , due to the formation a solid solution is in fact independent of the temperature .

’ - - me talli c o x id e s Semi conductors (non metals , and sulphides , ff etc . ) behave somewhat di erently. Their resistance passes through a minimum at a deﬁnite temperature, below which the

- co e fﬁ c i e nt o f i w temperature the resistance is negat ve, hilst above

F e 0 it it is positive . Thus magnetite , 3 4 , has an inversion tem pe ra tu re o f It is likely that the more heteropolar inter metallic compounds have similar properties . Should this be ' conﬁrmed when a s uﬂi c ie nt number o f such compounds have been examined over a wide range of temperature, it would be an interesting addition to the evidence in favour of the view that

no n - such compounds approach the metals in their properties .

H RM N D TI I T E AL CO UC V TY .

The thermal conductivity o f alloys follows similar laws to the electrical conductivity , but is much less conveniently measured . The thermal conductivity of a few intermetallic compo unds has 91 - co n been determined . I n the antimony cadmium series the ducting power o f the compound S d for heat is little more

o f o ne - ﬁfth fo r than that window glass, and about of that quartz

- co eﬂi ci e nt o f or felspar. Moreover , the temperature the thermal k ° -190 o f conductivity has a value for metals , whilst for A 0 0

S d 2 8 n o n - it has the value , being about 3 for conducting crystals . The ratio of thermal to electrical conductivity is also an 2° important quantity. The ratio has almost the same value for 16

1ncre ase s pure metals at a given temperature, and proportionately A 92 A rat I O to the absolute tempe rature . The o ° has (91 (90 a value for pure metals approaching

is regularly higher for solid solutions than for pure metals, [C P H YS I CA L P ROP ER TI ES 55

co m and may be much higher for intermetallic compounds . The

S d 1 2 - pound (Fig. ) which approaches the non metals in its pro A 0 0 ' 6 t 1 0 = I 8 pe ties, has 5 , a value comparable with that for x o o carbon ,

THE RM - E E TRI R O L C C POWE .

Although many determinations of the thermo e lectric power o f allo ys have been made since the original observations o f Seebeck 1 82 6 o f in , and although some the results obtained have played a prominent part in discussions relative to the conduction of electricity in metallic solid solutions , little attention has been

f o f devoted to the ef ect intermetallic compounds on this property . “ A communication by Haken , however , contains results which show that the singularity in a curve due to the presence o f a compound is sometimes exceptionally well marked in the case

f - o the thermo electric power . The curves here reproduced are ’ ’le re su lt s taken from Haken s .

- o f o f In general , the thermo electromotive force a series binary alloys varies with the composition in the same manner as the electrical conductivity. The variation is linear in conglomerates

o f of the pure metals , exhibits sudden changes direction if solid

a U solutions are formed to limited extent , and has the typical shape if the two metals form a n unbroken series o f solid solu 95 tions . These rules have been veriﬁed in a number of instances . ’ Haken s investigation relates mainly to series in which o ne o r

o f more intermetallic compounds are present , and the form the curves indicates that this property is even more sensitive than the electrical condu c tivity in detecting miscibility of one or other component with the solid binary compound . As an example ,

- 1 1 the system bismuth tellurium (Fig . ) may be considered . The w thermal diagram , sho n in the upper part of the ﬁgure , had been 96'97 o f obtained independently by two investigators , neither whom o f Observed the formation solid solutions , although their measure ments were n o t sufﬁ ciently exact to prove the complete absence

f - o such a condition . The maximum on the freezing point curve

o f Bi Te points decisively to the existence a stable compound, g a. The same compound is indicated in a most striking manner on

" Th e cur e s h a e een re - l o tte u n ato m c erce nta e a s a sc ss i v v b p d , si g i p g s b i a n l c e o f e rc enta e s b we h t p a p g y ig . 56 I N TE RM E TA LLI C COM P O UN D S

i f ﬁ ure the curve shown in the lowest compartment of the g . The

interpretation of such a diagram is not difﬁcult . The steep rise o f the curve at the bismuth end o f the series shows that solid

solutions in bismuth exist to a small limiting concentration . The

r sharp cusp at the composition of the compound , the two b anches o f the curve then falling away with remarkable steepness , indicates

c Bi Te o f n that the ompound z 3 is capable retaini g a small excess o f o r bismuth tellurium in solid solution . From the limiting con ' centration of this solution o n e ach s id e the thermo - electromotive m force varies in an almost linear anner with the composition , although the errors of experiment are somewhat too great to allow of the determination of the exact points of intersection o f the respective branches .

It appears that the electrical conductivity in this instance, as o f represented in the middle compartment the ﬁgure, although

o f showing quite clearly the position the compound , is less sensi tive as an indication of the formation of solid solutions .

o f o f The next example , that the alloys antimony and tellurium (Fig. is , of interest as conﬁrming a somewhat unusual form of equilibrium diagram arrived at as the result o f 9 8 - h as thermal analysis . The freezing point curve a maximum S b Te wh i ls t o n corresponding with the compound g 3 , the antimony side the curve is continuous , passing through a minimum , showing that antimony and its telluride are completely isomorphous . On the tellurium side the freezing- point curve has the form usual in

i fe ro us o f a e ute ct series . The electrical properties the alloys are in complete accordance with these conclusions . The curve o f thermo - electromotive force has a sharp cusp at the composition

- Te U . s s , and a smooth shaped branch between that compound o n and antimony, whilst the short descending branch the tel l uri um side indicates that solid solutions with that element are t only formed to a very limited exten . The extreme sharpness 0 i of the cusp is noticeable , a fall of 4 per cent in the proport on f M no E . F . 8 to o f tellurium causing a diminutio the . from 3 50. o f o f In the third example selected , that the alloys silver and ff antimony (Fig . 9) the conditions are so far di erent that the only S A S b compound present in the eries , g 3 , is broken up below its

" Th e m etal u se fo r co m ar o n thro u h o ut th e s e e er m en ts was Co er d p is g xp i pp . ° M nct o n was ma nt a n e a t 1 and th e o ther at Th e E . F . i s cal ula t O ne j u i i i d 9 . c ed ° ff nce o f t m erature fo r 1 di ere e p .

58 I N TERM E TA LLI C COMP O UN D S

of determination are partly theoretical and partly experimental . The theory of the equilibrium between an alloy and an electro lyte has only been established for the simplest cases , those

o f of solid solutions and simple conglomerates , whilst the manner in which an intermetallic compound , or a solid solution containing such a compound, dissolves (in other words, the nature of the ion s which it sends o ut into the solution) remains f almost entirely unknown . The experimental di ficulties consist w in finding an electrolyte ith which the alloy can be in equilibrium , and in overcoming the disturbing effect o f supe rficial changes in the composition of the alloy . Certain conclusions as to the conditions of equilibrium have 105 o f o f been reached by Reinders , by means an application the ’ a o f phase rule . Reinders formul have been verified in the case

w o f two o f the cadmium amalgams , hich consist series solid solutions , separated by a gap . Determination s of electrolytic potential have , in fact , been employed with success to ﬁx the 106 o f limits of the gap at different temperatures . The limits saturation o f the two solid solutions are clearly marked by discon tinuiti e s o f in the curve electrolytic potential . o f In the case a compound , the assumption made by Reinders , fo r purposes of calculation , is that the ions sent out preserve the

f a ssum same ratio o the two metals as in the compound . This p tion is almost certainly untrue for many alloys, the compound being resolved into its components at the surface of contact with

s o o ne . v the electrolyte , that only metal passes into solution E en w f ith this assumption , it is di ﬁcult to determine the composition

c of an ele trolyte which shall be in true equilibrium with the alloy, and in most actual investigations a more or less arbitrary com

o f position the electrolyte has been adopted . The earliest investigations having any claim to exactness are

those of Laurie , who neglected one important factor , the con

centration of the electrolyte, but adopted precautions to reduce

f - o . the effect polarization to a minimum Thus , the copper tin

alloys were studied by constructing a cell with a porous partition , the alloy being immersed in a solution of stannous Chloride in o ne i m compartment , whilst the other electrode was a rod of copper

me rse d o f C in a solution opper sulphate . I n this way a discontinuous

E M F - . . . curve was Obtained, with a well marked break at the 107 u S n C . composition ,, In a similar manner, the alloys of gold P H YS I CA L P ROP ER TI E S 59 and tin were found to exhibit a discontinuity at the composition 108 A u S n . 109 e rs hko wi tsch The later work of H c is more extensive . In this investigation , the electrolyte was in each case a normal solu

o f tion the more positive metal , whilst the electrode for comparison

o f n was a rod the less positive metal , an arra gement which is i n open to objection , and the results Obtained were some cases ambiguou s . 110 o f Pushin adopted .the plan employing as an electrolyte, wherever possible, an acid or alkali which forms a sparingly soluble

o f salt with the more positive metal , the ionic concentration which i n the solution is thus kept as low as possible . The simplest case is that in whi c h the two metals unite to form a single compound , which does not enter into solid solution with either of its components . The potential of the alloys is

o f o f then that the more positive metal , as long as any the latter is present as a distinct phase . The disappearance of this phase w coincides ith the composition of the compound , and at this point the potential falls abruptly to a lower value. If two or more

o f compounds are formed , a corresponding number of abrupt falls

. O n potential may be Observed the other hand , if solid solutions

o f are formed, the potential varies continuously within the limits w any solid solution , and only varies abruptly at the point at hich

c a phase disappears . It may be impossible in su h a case to infer

o f the composition the compound with certainty.

A simple example is presented by the thallium amalgams , 1 shown in the upper part of Fig. 4 . The potential in this w example is compared ith that of a mercury electrode, and the M F . E . of the combination rises gradually from zero to 33 3

o f c atomic per cent thallium , beyond whi h it remains constant , indicating that the compound n Te forms simple conglomerates with thallium , but enters into solid solution with mercury . ’ A few o f P ush i n s curves are redrawn in the lower part o f 1 Fig . 4 , from which it will be seen that certain discontinuities are very distinctly marked . The points are not always su f ﬁc i e ntly close together t o allow o f the determination o f the true form of the curve , and in some instances changes have probably been represented as abrupt which on a more careful examination

o f would prove to be gradual . As a means detecting inter a l met llic compounds, the method may give resu ts which err in 6 0 I N TERM E TA L LI C COM P O UN D S

o f either of two directions . On the one hand, the occurrence solid solutions may give rise to discontinuities indicating more c o n ompounds than actually exist ; the other , a compound may have an electrolytic potential which differs so little from that of o ne o f the components that the change in direction o f the curve is imperceptible . The former case is exempliﬁed in the list below by the alloys of silver and zinc, and the latter by those of silver and tellurium .

Awmw%

F I G . 1 4. w The follo ing compounds , the existence of which has f o n su ﬁciently established by other methods, are indicated ’ P ushi n s curves of electrolytic potential , although in some cases the curves have been wrongly interpreted . A correction has now been made by comparison with the thermal diagram

— m s I O b . co o t I n A gsS Slightly indicated The distinct break at the p b o f o f A g 2S merely marks the limit saturation the solid

solution . — f A S n . o . g s Very distinct Limit solution also indicated — f S O Te . o A g2 Very distinct The potential this compound is

near to that of tellurium that the second compound ,

A Te . g , is not indicated n — A A g22 3 Wrongly interpreted as a g . P H YS I CA L P ROP ERTI ES 6 1

A Zn — o n g Z 5 Probably indicated the curve . The remaining breaks o f only mark the limits solid solutions . — - A l Cu system A single break occurs near 50 atomic per cent , A lCu attributed to a compound , but really marking the o f A 1 u limit 2C . A n— ss Observed only in contact with acid electrolyte .

A s n — zS 3 Observed in acid and alkaline electrolytes . A u n— S Very distinct . A uS n —A A u S n f small but distinct break . The compound , is

not indicated .

uZ — A n Very great change in potential . Zn — A uZn o r A u . 2 Indistinctly marked A further compound , 6 A u n f Z . S , is aintly indicated Cd Cu — Cd Cu n B z Erroneously given as 2 , this being ear the limit o f o f d Cu saturation solid solution . The compound C 2 is o n entirely without inﬂuence the curve.

u n— C sS Very distinct . The only other compound found is

C n . q , and this is almost certainly erroneous — Te u Te . Cu C z Very distinct A compound is also inferred , but o n finds no justification the curve . — CUgZfl g This compound is probably the cause o f the very distinct

u n break attributed to C Z , . The other compounds inferred o f mark the limits so lid solutions . d— no t s P The other existing compounds are indicated . — P bgP t Distinct . — o f P t Distinct . The potential this compound is close to

o f no t that platinum , and the third compound is indicated . — bT . P e . Distinct A simple case , with one break — S bNi D istinct . i — b i N S N . s 5 Recorded as 3 Equilibrium in these alloys is not

readily attained . b n— S S Distinct . b — S 2S n Only slightly marked . —3 S bZn Very distinct . b n — S 2 . 2 3 Distinctly indicated e— S nT Very distinct . A clear and simple example .

HEAT OF RMATI N FO O .

The direct calorimetric determination o f the heat o f formation f o f intermetallic compounds has rarely been attempted . A e w 6 2 I N TERME TA LL I C CO MP O UN D S

112 calorimetric measurements were made by Person , but none of “ 3 the series examined by hi m contained compounds . Berthelot showed that the heat - change o n dissolving silver in mercury did no t indicate the production o f a compound having any appreciable

o f heat formation .

Indirect methods have been frequently applied . Thus , 114 o f Berthelot prepared amalgams sodium and potassium , and measured the heat evolved when they were decomposed by f o . w means a dilute acid Plotting his Observations , and allo ing ff for the di erent atomic weights employed by him , it is found that a maximum heat o f formation occurs at the compositions

a H K H w N ﬁ g and I Z g respectively . This is not in accordance ith the results of subsequent thermal analysis , and the determina tions have not been repeated with modern precautions . The heat o f formation may be determined indirectly by measuring the heat developed when alloys containing the c o m i n pound question are dissolved in some suitable reagent, and comparing it with that whic h would be obtained by dissolving

the component metals separately under the same conditions .

o f C This method was applied to the alloys zinc and opper, dilute 115 was nitric acid being used as the solvent . This procedure 116 shown to be illegitimate , as the chemical reactions Obtained vary w ff ith the composition of the alloy , di erent nitrous gases being

r obtained as the propo tion of zinc varies . The same and other 109 He rschk o wit sch alloys were also examined by , who used a

o f solution bromine in potassium bromide as solvent , thus avoid

o f ing the difficulty just mentioned , but the number his observa n tions is insuffi cient to establish any definite co clusions . The same solvent was employed in a study of the alloys o f Copper 117 and aluminium , the inference being drawn that the maximum

o f c Cu A l fo r heat formation orresponded with a compound g , which there is no other evidence . The experimental results are, however, quite consistent with the assumption that the principal f o f Cu A l heat o formation is that the known stable compound 3 . Very irregular results were obtained by dissolving alloys ‘ o f aluminium and zinc in dilute hydrochloric acid . The best calorimetric determinations o f this kind refer to the 118 n alloys o f Copper and zi c . The solvents used were solutions of ferric ammonium chloride and cupric ammonium chloride , the two series o f experiments giving closely concordant results . The P H YS I CA L P ROP ER TI E S 6 3

Cu Zn u Z n heat of formation of alloys between the limits and C 2 is considerable 6 uZn . C 4 cal per gramme.

Cu22 n3 46

zh Gu 2

I I AT SPEC F C H E .

The additive character o f speciﬁc heat as a property is pre

i o f served n the intermetallic compounds . The early work Regnault “ 9 showed that the speciﬁc heat of fusible metals followed the mixture rule at temperatures sufﬁciently far below

- - their melting point , but that as the melting point was approached the speciﬁc heat was always greater than that calculate d . The examination of a large number of alloys containing intermetal lic ’ o f Tamma nn s compounds , prepared in the course researches , showed that the deviations from the mixture rule were less than ) ” 121 4 per cent I t was observed that the speciﬁc heat o f

o f magnesium compound s was always smaller, and that antimony compounds greater, than that calculated by the mixture rule .

c c f The spe iﬁc heat increases with the temperature, the oe ﬁcient

o f decreasing with rise temperature .

o f Some the results are collected in the table , the deviations from the values calculated by the mixture rule having been added in the last column

TI CAL R RTI S OP P OPE E .

A few observations o f the optical properties o f alloys have a been made , but only a single investigation de ls with the relation 64 I N TERME TA LL] C COM P O UN D S

122 between these properties and the composition, the latter being expressed as percentages by volume . The alloys were examined in a polished condition, and the following results were o h tai ne d

There is no indication whatever o f a compound in the alloys o r o f of iron and nickel , nickel and silicon , although the occur o f rence chemical combination is possible in the former, and certain in the latter instance. The indices of refraction and of absorption both bear a simple linear relation to the composition o f C by volume . I n the alloys opper and aluminium a minimum in the absorptive index and a maximum in the refractive index l correspond rather with the formula CuA than with either Cu3A l l CuA . or z This is a series, the electrical constants Of which

t e - o f o f require determination . In the case the alloys copper

no t a with nickel and with iron , which do cont in compounds , the variation of the optical constants with the composition by volume

o f is not linear , but is similar to that the electrical conductivity.

P T - L CTRI C R RTI S HO O E E P OPE E .

The photo - electric prope rties of a number of metals and a o f few alloys have been examined . One method is that con d e n sin o n g metallic vapours a quartz plate in a high vacuum , 123 good mirrors being thus Obtained without polishing . In another investigation the metallic surfaces were smoothed by a “ o f steel scrubber working in a high vacuum . The rate photo electric fatigue increases with the electro - positive character o f the O metal . The alloys f antimony and cadmium , which have been selected by many investigators o n account of the very strongly marked discontinuities in the electrical properties due to the Cd S b compound , have been examined in this way , and are found to exhibit a linear relation between photo - electric fatigue and 125 o f composition . The behaviour alkali amalgams , and of the o f alloys sodium and potassium , has also been examined with 126 - co n respect to their photo electric sensitiveness . The curves n ecting the photo - electric sensitiveness with the wave length o f the incident light are found t o present maxima in the case o f o f s o tas sodium and potassium . The liquid alloy odium and p o f sium also has a maximum , which is not a mere summation the effects fo r the component metals . An examination of solid and liquid potassium amalgams showed that the selective photo

66 I N TERM E TA L LI C COM P O UN D S

° temperature o f iron lies at 750 and that o f nickel at At the atmospheric temperature the stable modiﬁcatio ns are a - iron

- o f w he a . t and nickel , both hich are ferromagnetic From fact that the cooling of alloys o f iron and nickel under ordinary conditions yields alloys of apparently homogeneous structure, it has been generally assumed that the two a - mo diﬁcati o ns o f also form a continuous series solid solutions . Such an f assumption , however, causes great di ﬁculties in the interpretation o f the remarkable magnetic transformations undergone by these alloys . The tra nsformation curve falls from iron with increasing i quantities of n ckel , appears to reach a eutectoid point , and then

‘ ° 600 6 rises , passing through a maximum at about and 7 atomic

o f per cent nickel , and then again falls to the value for pure nickel . This last part of the curve , including the maximum ,

f o f does not present any special di ﬁculties interpretation . The transformation temperatures Obtained during heating and during ff cooling di er only slightly , and the curve may be fully accepted as

o f representing an actual phase change . The occurrence the maximum at a composition corresponding very closely with the

1 F e : 2 F e N i atomic ratio Ni suggests that a compound , is concerned in the change, but there is nothing to indicate whether it is present in the high temperature or the lo w tem

e rature p system . The principal difﬁculty in the interpretation o f the magnetic phenomena exhibited by these alloys presents itself in connexion

with the alloys containing less than 33 atomic per cent of nickel . The temperature at which the alloys become magnetic o n cooling lies much below that at which they lose their magnetic properties

o n ff two i ncre a s heating , the di erence between the temperatures

o f r ing with increasing percentage nickel . The alloys are the e “ ” “ ” fore divided into irreversible and reversible alloys , the 0 former containing less , and the latter more , than about 3 atomic 128 per cent of nickel . The great temperature lag in the irreversible alloys renders the determination o f this part of the diagram very

f c di ﬁcult . I ts interpretation has been reached by a omparison of

. the artiﬁcial alloys with . meteoric irons

As already stated , artiﬁcially prepared alloys of iron and

o f and i s nickel consist homogeneous solid solutions , this the case th whether the specimens are cooled slowly or rapidly. On e me s o f n co ntrary, teorites compo ed iron and nickel alone contai P H YS I CA L P ROP ER TI ES 67

o f three micrographic constituents , which two , kamacite and 6 2 taenite, are solid solutions containing about per cent and 7 per

le ss ite cent of nickel respectively, whilst the third , p , is evidently 130 a eutectic or eutectoid mixture of kamacite and taenite . If we assume that the homogeneous Bry- solid solutions are resolved le ssite into separate constituents at a lower temperature , p must be regarded as a eutectoid . The eutectoid point has usually been placed at about the transformation curves obtained during f cooling being taken to determine the orm of the diagram .

Cartaud 1 0 Osmond and , however, suggested in 9 4 that these curves might owe their position to undercooling , and that the curves obtained on heating might approach more closely to the

o f position equilibrium , thus placing the eutectoid point some what below The fact that meteoric irons are converted by annealing into homogeneous solid solutions co mpletely resembling the artiﬁcial 131 - le ss ite - alloys , led to the hypothesis that the kamacite p taenite

no t structure is an unstable one , reproducible in the laboratory , and owing its origin perhaps to extremely prolonged diffusion below This somewhat improbable hypothesis has now been o f no w rendered unnecessary. The structure meteoric iron has 1 32 been reproduced by preparing an alloy with 1 2 per cent o f

fo r nickel by the aluminothermic process , and providing very slow cooling below P le s site is reproduced in this way f without di ﬁculty, the contrary results obtained previously being due to the annealing temperature adopted having been above The structure is far less coarse than that o f the natural w meteorite , o ing to the slowness with which segregation can take place in a solid at so low a temperature as It thus appears that kamacite and taenite are two limited

a - a - solid solutions containing iron and nickel , and there is no

o f o f F e Ni conclusive evidence the existence a compound g , although the occurrence o f the maximum in the transformation curve almost exactly at that composition is at least a remarkable coincidence. The abnormalities of magnetic behaviour are no doubt accounted fo r by the difﬁ culty o f Obtaining equilibrium in

F o r n . o f the alloys of this series the same reason , determinatio s the electrical conductivity have hitherto given only irregular and inconclusive results . The transformation cu rves in the analogous system iron -co balt 5 9K 6 8 I N TERM E TA L LI C C OM P O UN D S

no t have been determined over the whole range of composition .

- The freezing point curve is almost ﬂat , without indication of a f i n compound, and the magnetic trans ormation exhibits wide fe rva l s between the temperatures obtained o n heating and on 13 3 cooling .

Intermetallic compounds, one component of which is a ferro

- c magnetic metal , are almost invariably non magneti , whilst solid solutions which do not contain a compound may be magnetizable

The in a high degree if the solvent metal be itself ferromagnetic . 1 3 ° e n following table is modiﬁed from o n given by Ta mman . The list of compounds has been revised , only those being now included which have been determined to exist by evidence of a satisfactory kind . It should be said that the test applied is in most cases the rough o ne of Observing whether a magnetic needle is deﬂected by the alloy at the ordinary temperature . The possibility is not excluded that some o f these alloys may become appreciably magnetic at lower temperatures .

F e A s F e As F eA s Co As C0 As Co As z , 3 2, , z , 3 2, F A s e 2

e P F e P F 3 , z F e s b F e S b a z, 2

F eZ n F eZ n s, 7

Of the compounds enumerated in the above table , only

i M e S b N z g and F 3 2 exhibit appreciably magnetic properties, and o ne it therefore appears that intermetallic compounds , component o f - which is a ferromagnetic metal , are most frequently non mag

o f . netic . This is also true other than intermetallic compounds Thus the majority o f the oxides o f the ferromagnetic metals are only very feebly magnetic , magnetic properties among the oxides

of iron , for example, being almost entirely conﬁned to the single

F e o w compound 3 4 , hich is properly regarded as ferrous ferrite ,

F e O F e 0 o ne o f o f , 2 3 , a series magnetic ferrites in which the

P e 0 e o n e m c o f oxide z 3 behaves as an acid oxid , and to odiﬁ ation 1 3 5 F e 0 . ferri c o x ide 2 3 P H YS I CA L P R OP ER TI ES 69

o f m The borides the etals of this group are magnetic, but not 1 3 6 s o strongly . The contrast between compounds and solid solutions in such

a cases s those mentioned above is very great . Solid solutions in which a ferromagnetic metal is the solvent, that is , in which it is present in by far the larger proportion , are themselves ferro

c . magneti , but their intermetallic compounds are only paramagnetic This probably accounts for the difference between the amalgam 1 37 o f of nickel which is very feebly magnetic, and those iron and 1 3 8 cobalt which are strongly magnetic .

o f A few series magnetic measurements exist , from which some more quantitative conclusions may be drawn respecting 139 these relationships . Thu s, according to Honda, the magnetic susceptibility o f the alloys of nickel and tin lies between the

o f susceptibilities the two component metals , the curve being

o f o f composed of a number straight lines , each pair which intersect at a point corresponding with the appearance o f a

o f Ni S n new phase . The composition the compound s 2 is very no t distinctly marked in this way , but the measurements would ,

c o f in the absen e of data from other sources, allow any conclusion

o f o f as to the existence such a compound , as the limit saturation o f the solid solutions rich in nickel is equally well marked by a

o f similar intersection . It is, in fact, the appearance a new phase , and not the nature o f that phase (compound or solid solution) which determines the appearance of a discontinuity. The alloys of nickel and aluminium exhibit the condition

o f somewhat more clearly . The susceptibility the compound

iA l s usce ti N is about the same as that Of aluminium , whilst the p bilit iA l iA l y of the compounds N 3 and N 2 is very much smaller, so that th e system o f i ntersecting straight lines passes through a minimum . This would not be likely to occur if the intermediate phases were solid solutions , not containing compounds . Whilst the facts cited above Show that the magnetic properties o f a ferromagnetic element disappear wholly o r partly when that element enters into combination with another metal , the more

a remarkable reverse case, of the formation of a ferrom gnetic compound by the combination of paramagnetic o r even dia w magnetic elements, is also kno n to occur, and the discovery has opened up an entirely n e w ﬁeld of inquiry in regard t o the magnetism of alloys . 70 I N TE RM E TA L LI C COM P O UN D S

The ﬁrst instance observed of the formation o f a magnetic compound from non - magnetic elements is that of chromium oxide . Chromium is faintly paramagnetic ; oxygen is para

O r magnetic diamagnetic in its compounds , although strongly

Cr O paramagnetic in the free condition . The compound 4 9 14° Cr O 2 CrO fa r 1 8 ( g g , 3) was observed as back as 59 to be strongly ff magnetic , whil st the same has been stated of an oxide of di erent 141 Cr O 2 r 0 r C C O . composition , 5 9 ( 2 3 , 3) Other magnetic com ” 2 o f pounds chromium probably exist. 143 1 8 2 The observation was made in 9 that, whilst commercial

- - - C ferro manganese and ferro aluminium are non magnetic, ertain ternary alloys prepared by mixing them , containing only o f a small proportion iron , are very strongly magnetic . This was followed by the further discovery that the entirely non magnetic alloys o f copper and manganese are rendered magneti c by alloying with a suitable proportion of certain third

wa The ﬁrst metal used s tin , but aluminium was soon found to f produce a still greater ef ect . The number of investigations dealing with the Heusler alloys , as they have been called , is extremely large, and the conditions have proved to be highly complex . The principal results will be summarized here, but the complexity of the systems involved is very great, and as n o f metastable co ditions are frequent occurrence , the properties o f any Heusler alloy of given compo sition depend o n its previous thermal and mechanical treatment . Metallographic considerations to o have received far little attention in this department , and a great mass of observations has therefore accumulated , referring f n to alloys O unknown o r doubtful internal constitutio . The subject has also been encumbered with much polemical matter, dealing with questions of priority . m One fact has been established with certainty, na ely , that the appearance o f magnetic properties in the alloys is associated w o n o f co m ith , and dependent , the formation intermetallic pounds . The system which has been most fully investigated is o f that copper, aluminium , and manganese . Heusler originally 4° made the tentative suggestion 1 that a compound Mn A l might w o f be concerned , in vie of the fact that the maximum magnetic properties was found in a ternary alloy containing manganese and aluminium in approximately atomic proportions, alloyed

C o n with an excess of opper. Little stress was , however, laid P H YS I CA L P R OP ER TI ES 71

this suggestion, and the objections to it were recognized and admitted . An explanatio n which at ﬁrst appeared plausible was a d 147 va nce d G by uillaume. This was to the effect that manganese was a ferromagnetic metal with a very low temperature o f trans ff formation , and that the e ect of alloying with the m etals in question was merely to raise the transformation point above the atmospheric temperature. This hypothesis is untenable . Man ganese does not become ferromagnetic when cooled in liquid “ 8 air, and many other magnetic compounds have since been discovered to which such an explanation is inapplicable . The rel ation o f intermetallic compounds to magnetism he came much more clear when the data accumulated by Heusler o and his colleagues, with reference to the alloys of c pper, alu

o n minium , and manganese, were plotted a triangular diagram , o f i o f the type generally employed n the study ternary alloys . The alloys o f maximum magnetic properties lie o n a line m Cu A l Mn A l . co joining the compounds 3 and g These two

so l utio n S e wi th o ne pounds form solid another. Heusler and —149 Ri ch arz therefore proposed the following hy p o the sI S The alloys corresponding with the maximum o f m ag neti sa tion may perhaps be regarded as chemical compounds of A l M the general type x M , where M represents partly Mn, partly

C u atoms in vary ing proportions . Heusler and his collaborators have made constant use of this hypothesis . It is badly stated by them, in a form implying the

o f F o r m . existence ternary co pounds example, the maximum o n the line shown in their triangular diagram occurs at the com

2 Cu A l Mn Al . position 3 , s , and this is regarded by the authors as a c A a Cu A l Mn ompound z, a member of the series , ( , no o f o f There is evidence the existence such a compound . At ’ He usle r s t o the same time meaning is clear from the analogy ,

n o f which he draws attentio , with the double carbides iron and C Mn manganese, , ( , These are more properly regarded as F e C Mn C isomorphous mixtures of the carbides a and s , and in Similar manner we may consider the magnetic alloys to be isomorphous mixtures (solid solutions) o f the two deﬁnite c o m Cu A l Mn A l pounds 3 and s . The distinction is less important than o f may appear at ﬁrst sight . In a solid solution progressively

n c o f o ne cha ging composition , mole ules the kind are successively 72 I N TERM E TA L LI C C OM P O UN D S

c replaced by molecules of the other, whilst in an atomi complex

c o f of the type assumed above, the repla ement is one atoms of one

o f kind by atoms of another. In our present state of knowledge n n the inter al co stitution of solid solutions containing compounds , it would be difﬁcult to distinguish effectively between the two conditions .

The form of the hypothesis suggested independently , in a 1 50 G . slightly later paper, by Ross and ray is preferable These v Cu A l authors had obser ed that the compound 3 , although only so faintly magnetic, was more strongly than any other alloy o f - w Mn A l the copper aluminium series , hilst the compound 3 is known to be the most strongly magnetic member o f the man 151 - n ganese alumi ium series . I t was therefore suggested that the

n t wo mag etic Heusler alloys were solid solutions , containing these compounds in varying proportions . It is characteristic of the H eusler alloys that the ir magnetic pro

erti e s c p are not fully exhibited by freshly cast spe imens , but that it is necessary to subject them to an annealing pro cess of a special

c kind in order that the maximum magneti quality may appear . The most detailed experiments in this connexion are due to 1 52 wh o w tre atm e nt r Take, ﬁnds that the relations bet een thermal .

c and magnetic properties are extremely compli ated . The greatest susceptibility is obtained by quenching the alloys rapidly from a “ ” red heat and then ageing them at as lo w a temperature as

. ° ° 1 0 0 1 80 possible ( H eating to for several hours , followed by slow cooling, is the most suitable thermal treatment for the 1 53 alloys generally employed . The complicated nature o f the magnetic transformations is due to th e fact that both chemical and physical changes are w involved , the nature of hich is still imperfectly understood .

The metallographic study of the copper- alumi n ium - manganese series has not yet been completed , but a detailed study of a part 1 54 w c o n of the system has sho n the close resemblance, over a s id e rabl e range of composition , between these ternary alloys and

o f C e the binary alloys opper and aluminium . It may therefor be expected that the He us le r ' a ll o y s will c rystallize as homogeneous solid solutions or as two - phase systems according to the conditions “ ” c of cooling . The ageing process may therefore be a omplex

a d e c o m one, involving ( ) the formation , and perhaps also the

O f c 0 o f position , intermetalli compounds ; ( ) the equalization

74 I N TE RME TA L LI C COM P O UN D S

13 9 o ne - o f ganese boride is about half that steel . Honda has studied the dependence o f permanent magnetic quality on con stituti o n - in the case of the manganese tin alloys , and has found that the permanent magnetization attains a maximum value in Mn S n the pure compound 4 , and is rapidly lowered by small

O f additions either manganese or tin .

C With the exception of hromium boride, compounds of this class not containing manganese have not hitherto been observed to be magnetic . Vanadium forms magnetic oxides and sul

h id e s n p , but its alloys have not yet been studied from this poi t of view. The paramagnetism of alloys is greatly inferior in interest to the exceptional cases of ferromagnetism , but even here the n i ﬂuence of intermetallic compounds is to be traced . The para

- m agnetism O f a series o f alloys is directly proportional to their composition when they consist of a conglomerate o f two solid phases, but a discontinuity occurs at any composition at which a new solid phase makes its appearance , as in the cases of i n i n l i N S N S Ni A A l . s z, 3 , s, and N z, mentioned above (p The alloys o f bismuth with tellurium and with thallium are all

o f diamagnetic . The su sceptibility curve the former series is 158 o f given as continuous , but the number alloys examined was

a d o n too small to make this quite certain , n it is possible that examination o f a larger number o f alloys o f intermediate com p osition a small cusp might. be found at the composition of

Bi e - T . the compound 2 3 The bismuth thallium susceptibility curve, Bi 1 T . however, has a distinct cusp at the composition 5 3

ALL A N D ER S T H N N EFFECTS .

f o r h The Hall ef ect, the transverse electromotive force w ich is produced by the displacement of equipotential lines in a plate w of metal through which a current is ﬂowing longitudinally, hen ﬁ a magnetic eld is applied , has been determ ined for a few series o f f h a s alloys . The ef ect been observed to bear a relation to the

- thermo electric power, and a close similarity between the relations o f the two properties to the composition has been found in the two cases examined in which compounds are present . These are 83 o f . the alloys antimony with cadmium , and of antimony with zinc

1 2 . The curves for the former series are shown in Fig . The com P H YS I CA L I P R OP E R TI E S 75

S d n c o m pound is most conspicuously indicated , but the seco d o n pound S b n 3 is apparently without inﬂuence the form of the o f curve, although it must be admitted that the number alloys ex a mine d was not sufﬁciently large to prove conclusively that there

- is no small discontinuity. The antimony zinc alloys give a curve o f o f f precisely the same form , with an enormous rise the ef ect

to S bZn o f near the compound , and no apparent indication the b second compound S 22n3 .

The value plotted as ordinates is the Hall constant , which is , however, subject to a correction which would change its absolute

o f value , but without altering the form the curve . f o f The Nernst e fect, or the developed when a plate metal through which heat is ﬂowing is brought into a magneti c

ﬁeld, so that the lines of magnetic force are perpendicular to the

o f plane the plate, has been determined for the same alloys in the Of ff course the same investigation . This e ect also is a maximum bZn for the compounds S d and S in their respective series .

1 2 fo r Comparing together the curves in Fig . the antimony

o f cadmium alloys, and the precisely similar group curves obtained

o f for the alloys antimony and zinc, it is clear that a close relation exists between the various electrical properties o f an intermetallic compound, a fact which is of high importance in connexion with

o f the electronic theory metallic conduction .

R S TA LLI N RM C Y E FO .

re Most of the metals crystallize in the cubic system , the ma ind e r w o f , ith the exception tin , being hexagonal . It has 19° been shown by Barlow and Pope that the axial ratios o f the hexagonal elements approximate more o r less closely to those o f - o f the closest packed assemblage equal spheres , namely , to a 0 I 1 6 0 1 I ’ I 2 33 or 4 4 . Binary compounds composed of two elements of equal valency have been Shown by the same o r authors to crystallize also in the cubic hexagonal system , but usually in a class which does not possess the highest symmetry o f o f the system . Very few the intermetallic com pounds have been subjected to crystallographic measurement . This is very fﬁ f largely due to the di culty o obtaining perfect crystals . When an alloy o f the exact composition of an intermetallic compound is

i rre u prepared, it usually forms a compact mass which breaks g 76 I N TE RME TA LLI C COM P O UN D S l rl a . y , without yielding deﬁnite crystals On the other hand , crystals isolated from an alloy containing an excess of one o r

c n o ff other ompone t by pouring a fusible eutectic , or by treat

o r ment with chemical reagents , are most commonly striated deformed to such an extent that satisfactory goniometric

as measurements are impossible . The data to crystalline form are consequently very scanty , and complete reliance cannot

c always be pla ed in the axial ratios . Moreover, it appears that some intermetallic compounds have a tendency to assume the

o f appearance a higher symmetry than they actually possess .

F o r r o f S bS n example , the c ystals which are a conspicuous constituent of many bea ring metals have the appearance of cubes, and have been described as such , but they are really

o f o n crystals lower symmetry, as the apparent cube angles prove measurement to differ from The following intermetallic compounds (incl uding some native arsenides) have been examined crystallographically and described

I T M CUB C SYS E .

o f Combinations octahedron and rhombic dodecahedron .

Octahedra .

Hessite . Many observed forms . A ltaite . Mostly massive, but with cubic cleavage . Smaltite Chloanthite i Pyr tohedra . Skutterudite Sperrylite

TETRAGON AL S T M SY E .

a z c I

RT R M I C S T M O HO HO B SY E .

Cd S b 0 1 3 2 0 7 59 I F e S b 2 0 A S b g 3 Dyscrasite . Pseudohexagonal combinations a 0 C 0 5775 I

ce t wh ere o th er re fe re nc e s are e n the at a fo r art ﬁ c al cr s tal s are Ex p giv , d i i y m ’ - taken fro G ro th s Ch emis ch e K ry sta l l og r aphi e an d th o se fo r mi n eral s fro m ’ Dana s Mi ner a l ogy P H YS I CA L P ROP E R TI E S 77

a : 0: e 0 7 6n 1 Lollingite d : 0: c = 0 6 6 89 : I Rammelsbergite Axial ratios not determined S afﬂo rite

a z 0 =

E" T M H AGON AL SYS E .

CUS n N 0 data given

’ " Resembles corundum a z e = I : I 2 760 N i cco lite Bre ithaupite

- Artiﬁcial a ze = 2 940

Rh o mbo h e Tetradymite . dral a : c = Melonite

N LI N I T M MO OC C SYS E .

a : 0: e = 1

’

ro m mea ur ement b Mr. A S co tt i n th e auth o r s l a o rato r . F s s y . b y CHAPTER VII .

THE E"I S TEN CE OF I NTERMETALL I C COMPOUNDS I N THE LI QUI D S TAT E .

THE question o f the possible existence o f intermetallic compounds in liquid alloys is very closely related to that o f the existence o f hydrates in aqueous solutions , although the former problem presents certain special experimental difﬁculties of its o wn . A consideration o f the facts as a whole suggests the great probability o f such a continued existence o f compounds in the liquid state .

o f In accordance with the principle mass action , a compound which may at certain temperatures dissociate into its components must, under conditions of equilibrium , be accompanied by its products of dissociation , even if in minute quantity . The con

i io n s o f d t electrical conductivity in solid solutions (p . 4 5) point to the probability that solid intermetallic compounds are more o r less dissociated, and the degree of dissociation must increase with increasing temperature . There is , however, no reason to assume

- that the dissociation becomes complete at the melting point , and there is in fact much experimental evidence to show that undis s o ci ate d molecules are present, although in diminished numbers ,

’ even at much higher temperatures . There is at any given

o f temperature, an equilibrium the form A B mA E B m n 2 and this holds good of the liquid as well as of the solid state .

In the ﬁrst place , certain conclusions may be drawn from the form of the freezing - point curve in binary series when the curve n exhibits a maximum . Were a compound to melt e tirely without

o f o f dissociation, the addition one the components to the molten compound should (assum i ng that solid solutions are not formed) ’ - depress the freezing point in accordance with Raoult s law, and the descending branch of the freezing - point curve should approximate to a straight line . As this reasoning applies to the addition of either of the constituents A and B to the compound A mB it follows that the ideal form o f the maximum in th e case o f an 78 I N TERM E TA L L I C COM P O UN D S I N THE LI Q UI D S TA TE 79 entirely undissociated compound would be an acute intersection o f b two straight lines . Whether such a maximum is possi le in 1 59 o ne reality has been disputed . On the hand it has been argued

- that a freezing point curve must, whenever the solid and liquid phases are identical in composition, have a horizontal tangent , which excludes the possibility of a sharp angle at the maximum .

On the other hand , the latter condition has been claimed to exist 160 o f o f in binary mixtures methyl iodide and pyridine, and I Cl 161 iodine and chlorine at the composition , whilst the theoretical

o n f possibility has also been maintained , apparently insu ﬁcient 1 62 e x e ri grounds . It is impracticable to decide the question p

O f mentally, as the unavoidable errors the thermal method leave it uncertain whether the ascending and descending branches o f the curve intersect o r pass into o ne another continuously within a o f very short range composition . All metallic alloys hitherto examined depart in an unmistakable manner from this ideal f o e e . case, the rounding the maximum b ing very p rceptible The extent o f the rounding i s a measure o f the degree of dissociation 163 - of the compound at its melting point . It may be made quanti t ati v e o f - by determining the normal depression freezing point, and comparing it with the observed curve . This is most simply done by adding to a liquid mixture having the composition o f the

o ne o f co mpound an inert substance , that is, known molecular weight, which dissolves in it and crystallizes from it without

n o r formi g either a compound a solid solution . This method has been applied with some success to a n umber o f systems composed of organic substances, the results indicating, for example, that the additive compound o f aniline and phenol is dissociated to the

o f 2 0 - C o f extent per cent at its melting point, and the ompound “ phenol and picric acid to 2 7 per cent? The normal depression o f may also be calculated from the heat fusion when this is known , ’ ’ ff h as hith e rto bee n using van t Ho s formula . This method not applied to metallic alloys , although its application should be possible in many instances if the assumption o f the validity o f ’ Raoult s law in such cases should prove to be justified . The influence o f the dissociation of the compound in the liquid phase o n the solidification o f the system has been exhaustively discussed from the theoretical point o f view by 165 Roozeboom . The possible cases are, however, mostly such

no t as do present themselves in the study of alloys , and the 80 I N TERM E TA L LI C COM P O UN D S

graphical methods used in the discussion , although of consider

w o f able interest , do not allo of the solution of any the problems mentioned above with the data now available .

Amongst alloys , the sharpest maxima observed are due to m M S b compounds of agnesium , especially g 3 2, and it must there fore be assumed that these compounds dissoc iate to an ex c e ti o n a ll o n w p y small extent melting , a conclusion hich is in accordance with their behaviour in the solid state . The fact that these and other intermetalli c compounds are capable o f existing in the liquid phase in a largely undissociated condition at the melting - point renders it certain that undis s o c i ate d molecules must also exist, although in smal ler number , w at higher temperatures , the degree of dissociation increasing ith

v the temperature . There is also direct e idence to the same

o f c o m effect . In the alloys aluminium with antimony the pound A l melts above but is only formed very slowly

e x e ri from its components in the liquid state, so that in one p ment only three - fourths o f the quantity of compound theoretic ally obtainable was found in the solid alloy, after the component metals had been heated together for thirty minutes at It is possible that this sluggishness may have been partly due to

o f imperfect mixture the two metals , the experimental method used being open to Objection , whilst aluminium frequently forms

o f c globules, covered with a thin pellicle oxide, whi h obstinately

s . resi t union with other metals , forming an emulsion Making allowance for this fact , however, it appears probable that the reaction between aluminium a nd antimony in the liquid state A l is a slow one, molecules of the compound being formed

c gradually, and persisting in the liquid ondition .

c The measurement of electrolytic onductivity, which has been so constantly employed in the study o f aqueous and other solu

c tions , is not applicable to liquid alloys , in which ele trolytic conduction has never been observed to occur . Experiments to determine the point Showed a complete absence o f electrolytic 1 67 n conduction , eve at high temperatures . Moreover, there is no evidence o f any gradual transition from metallic to electrolytic c d ucﬁ o n o n .

On the other hand , molten alloys conduct metallically, and some very remarkable results . have been obtained by de te rmi ni ng the variation of conductivity with concentration at

82 I N TE RME TA L LI C COMP O UN D S

o n - c a distinct peak the conductivity omposition curve (Fig . ° ° The two curves shown represent determinations at 3 50 and 4 50

o n respectively, and the position of the peak each curve clearly

o f H N a points to the existence the compound g 2 in an undis s o ciate d c condition at the two temperatures onsidered . The remaining compounds of sodium and merc ury which are known to exist in the solid state are insufﬁ ciently stable at higher tem

e rat u re s to f c p produce any marked ef ect on the condu tivity.

n - 1 The correspondi g compound in the potassium mercury ser es , K n , appears to be less stable than its sodium analogue, in

- accordance with its lower melting point, and it is in consequence o n less distinctly marked the conductivity curve , the peak being considerably ﬂattened . An unstable compound , dissociating

- below its melting point , naturally has no inﬂuence on the liquid

o f conductivity , and there is thus no break in the curve the

- a K potassium sodium alloys at the composition N z .

With liquid as with solid alloys, the manner in which the conductivity varies with the temperature is intimately connected

o f co with the constitution the alloys , and the temperature eﬂi ci e nt curve may be employed in place o f th e c onductivity curve fo r the purpose of determining the presence Or absenc e of

compounds . As in the case o f solid so l

ut io ns d i sco nt i n , the u iti e s due to this cause may be even more strongly marked I n the temperature co efﬁcient than in the ‘

conductivity itsel f. 1 6 Fig . represents the conditions in liquid alloys o f cop

per and antimony .

o e ﬂi' c i e n t 0 70 20 3 0 40 so 60 70 00 90 700 The c plotted i s that of

F I G . 1 6 . c the spe iﬁc resistance , 3 1 0 multiplied by . The very sharp change in direction of the curve occurs at a composition in close agreement with the

u co m formula C n . A minimum occurs at about the same I N TE RME TA L LI C COM P O UN D S I N THE LI Q UI D S TA TE 8 3

position in the conductivity curve , but there is no abrupt dis continuity, and it would not be possible from that curve alone to determine whether the compound was present in an und i s so ci I n ated condition , as minima have also been observed alloys

o which do n t contain a compound . 1 6 One remarkable feature in the curve shown in Fig . de f serves attention . The temperature coe ﬁcient is negative through o ut a considerable range o f composition in the neighbourhood

fﬁ re o f Cu S b . the compound s A negative coe cient of the si stance , that is, a diminution of the resistance with increasing

o f co nd ucto rs whil st temperature, is characteristic electrolytic , the

f o f coe ﬁcient metallic conductors is normally positive . There

o is , however, n reason to assume electrolytic conduction in this

ff c f i fo r case . The e e t is su ﬁc ently accounted by the progressive thermal dissociation o f the solid compound Cun with rise o f

C temperature . Dissociation into opper and either free antimony o r C b , more probably, the second compound q , undoubtedly

o f takes place . Alloys in the immediate neighbourhood the

u b l o C S . w compound 3 exhibit the following peculiarity At tem

e rat ure s w f p , o ing to dissociation of the compound , the coe ﬁcient

o f is negative, but at higher temperatures the concentration the dissolved undissociated compound i s too small to neutralize the f normal positive coe ﬁcient which characterizes alloys in general .

o f o f Alloys this series , lying within a certain range temperature,

o f c thus possess a temperature inversion , above which the o e fﬁ ci e nt is positive, whilst it is negative below that point . The temperature o f inversion is found by experiment to lie at for an alloy containing 66 atomic per cent of Copper (that ° 8 m o l e c Cu sb 1 1 00 fo r 8 . r per cent s ) and at an alloy c

r m o le c 0 o 0 . Cu S b taining 9 atomic per cent Cu , 4 per cent 3 . is probable that the negative temperature coefﬁcient of the s i stance o f molten cuprous sulphide is to be explained similar manner by simple thermal dissociation rather th '

electrolytic dissociation . Other physical properties o f liquid alloys furnish s i n

less precise, indications . The diffusivity of various Ir 170 f a n d f mercu ry has been measured, when the atomic di

o f e plotted as a function the atomic weight, the valu

to o n cadmium , tin , and lead are found lie a smooth o f metals the alkalies and alkaline earths, together 6 air 84 I N TERM E TA LLI C COM P O UN D S

o n f also yield points which lie a smooth curve , but the dif usivity is throughout lower than in the former case. The characteristic ff di erence between the two groups is that the former, from

- the evidence of the freezing point curves, do not combine w chemically with mercury , hilst the alkali metals and their o r companions form one more compounds with mercury. The lower rate o f diffusivity is thus to be accounted for by the

o f presence of compounds in solution , so that each atom the dissolved metal bears attached to it o ne o r more atoms o f mercury. A very similar effect is observed in the surface tension of 171 f amalgams . The sur ace tension of mercury is reduced by the addition of sodium , potassium , rubidium , and caesium , raised by ff that of lithium , calcium , and barium , and scarcely a ected by that of zinc, cadmium , thallium , gold , tin , or lead . With the o f exception of thallium and possibly gold , the grouping is the fu same as in the case of the dif sivity. The active metals are those which form compounds , whilst the inactive metals are

ff o f chemically indi erent . Both series experiments conﬁrm the presence of undissociated molecules of intermetallic compounds in the liquid amalgams .

I T M THE VAPOUR PHAS E OF META LL C SYS E S .

Determ inations o f the vapour density of alloys are com

le te l o f p y lacking, and only a single instance a deﬁnite inter metallic compound having an apparent existence in the gaseous n o f condition is recorded . This is the compou d magnesium and ' nc M o f , a 2, the existence which has been proved by the l erm a and microscopical methods . When mixtures of these

0 o f metals, containing an excess zinc, are heated together in a d o f M vacuum , crystals the compound m are condensed on 172 o o l e r parts o f the glass vessel employed . The temperature no t e e experiment is given, but the J na glass tube used to o ne n the materials showed signs of collapse in case, and ri p e rature may therefore be assumed to have been about fact that crystals o f the compound are obtained by 1 g the vapour does not prove the presence o f undis t aseo us molecules o f the compound . It is possible hat ,

a ne sium i s g less volatile than zinc, the two metals

re - co m a mixture, the compound being formed by I N TERM E TA LLI C COM P O UN D S I N THE LI Q UI D S TA TE 8 5

o f bination the vapours when the temperature falls , the liquid alloy thus Obtained subsequently crystallizing . This point might be tested by performing a series o f distillations at different tem

e rat ure s o f p and pressures , and determining whether a distillate

i s constant composition obtained.

Studies o f the vapour- pressure relations o f alloys have only been carried s o far as to yield practical methods for the separa

o f o r o f tion metals the isolation intermetallic compounds , and the data are not available for the construction o f a complete concentration - temperature pressure diagram in even a single f . o case In the absence solid solutions , the vapour pressure of a binary series at a given temperature may be expected to fall suddenly when the concentration o f the more volatile component falls to that corresponding with a compound which is stable at that temperature . The case is then completely analogous with that of hydrated salts . That this condition actually presents

w o f itself is sho n by the success , in a number of instances, the method of removing an excess o f a volatile metal by distillation at constant temperature, leaving a residue composed of a deﬁnite

e o f compound (se p . The isolation of a compound gold and cadmium by distilling O ff an excess o f cadmiu m h a s been o f mentioned as an example this process . CHAPTER VI I I .

THE R LATI N S O F I NT RM TA LL I C C M UN DS To CA R I D S E O E E O PO B E , D ET S I L I CI S C . E ,

CERTA I N non - metallic elements are capable of forming compounds o f distinctly metallic character with metals, and these elements f may there ore enter into the composition of alloys . The transition from the compounds in question t o those considered in the

o ne previous sections is a perfectly gradual , and it is impossible to make any sharp distinction between intermetallic compounds and the binary compounds o f metals with elements o f p ro no unce d - w electronegative character . The non metals hich have the greatest tendency to form compounds havi ng metallic pro

e rt ie s l c p with the meta s are boron , arbon , silicon, titanium , phosphorus, arsenic , selenium , and tellurium . O f these, silicon ,

o f arsenic , and tellurium habitually form compounds such distinctly metallic character that they may be grouped fo r the present

n purpose with the metals . N itroge , oxygen , sulphur , and possibly hydrogen may be regarded as alloy - forming elements under certain special conditions .

o f In general , the metallic properties compounds of this kind are most pronounced when the metallic element is present in a w large proportion . With phosphorus , for example, hen a metal

o f forms a series pho sphides, their metallic properties diminish as the atomic proportion o f phosphorus increases . The binary

o f Cu P mixtures, for example, copper with the ﬁrst phosphide, s , are true alloys , but with increasing phosphorus the metallic o f properties the mixtures diminish .

The alloy- forming properties o f oxygen and sulphur are w o f extremely limited . The lo er oxides copper and nickel , however, form true alloys with the respective metals , and the i binary systems Cu CugO and Ni N O are strictly comparable e ut ec t i fe r with metallic o us systems . The eutectic structures are remarkably well developed in these two cases . As the proportion 86 THE REL A TI ON S OF I N TERM E TA L LI C COM P O UN D S 87 o f oxide in the alloys increases , the brittleness increases and the conductivity falls , until the pure oxides are unmistakably non o r metallic . Other oxides are usually either insoluble soluble to a very limited extent in the molten metals , but other cases of miscibility may possibly be found to exist .

Copper , lead, and silver alloy with their sulphides , retaining their metallic character when the proportion o f sulphide is not

e P bS e A e . C too large Similarly, the selenides q , , and n form w alloys ith the corresponding metals . Arsenides and tellurides are included in the tabular summaries in the next section . o f The nitrides are rarely metallic , only. the compounds the heavy metals of groups VI , VII , and VI I I having that character .

Their alloys have not been examined , but iron appears to form

F e N an alloy with nitrogen , in which the compound 5 2 is doubtless present . Titanium , chromium , and manganese also absorb nitro gen to form solid solutions . The nitrides described as possessing

c Mn N Mn N Mn N CrN MO N metalli properties are 3 2, 5 2, 7 2, , 3 2, C0 N F e N F e N F e Ni o f 2 , 5 2, z , The nitrides manganese are re ferromagnetic . Compounds derived from ammonia by the placement o f hydrogen by the lighter metals are entirely no n

: N metallic , whilst compounds containing the group 3 , and derived from hydrazoic acid , behave as true salts . Excluding these

c compounds , the only metallic nitrides whi h are stable at the ordinary temperature are those formed by metals o f the A sub

O f s ub - groups the periodic system , the metals of the B groups yielding nitrides which are only stable in liquid air, and explode 173 below the atmospheric temperature . The nitrides of mangan “ e se are stable above a red heat .

o f o f The electrical conductivity the nitrides magnesium , cal c i u m o f , and aluminium is very small , whilst the conductivity the nitrides o f chromium and manganese is o f the same order 1 75 as that of the pure metals . The borides exhibit a considerable resemblance to the nitrides , but are much more stable. I t is mainly the metals of the last three groups in the periodic system which form stable metallic borides, but even in the earlier groups some stable w borides, hich conduct electricity, have been prepared, including M B aB C A IB . g 3 2, 6 and Z m a o f n o t l The metallic borides , the for ul which are yet we l a r established, e ' 8 8 I N TERM E TA L LI C COM P O UN D S

CrB MO B WB MnB MuB F e B F e B F e B C0 B CO B , 3 4, 2, , Z, z , , , , 2 , ,

GO E i B NiB N i B ; 2, N z , , and , The carbides o f the alkali and alkali earth metals and those o f aluminium and the rare earth metals are readily dec omposed

by water, yielding various hydrocarbons . On the other hand,

the carbides of some of the heavier metals are extremely stable ,

and form true alloys with the metals . These stable carbides include V C Cr c P Cr C Mo C MO C W C U C ; 4 ( ) , 3 2 ; z , ; 2 , WC ; 2 M F F i n C e C e C N C. 3 ; 3 , z ; s i s c o f o f It possible that several other arbides iron exist , capable

alloying with iron .

H M AL I M N DS T E C HE I CAL NATURE OF I N TERMET L C CO POU .

From the point of view of structural inorganic chemistry , the intermetallic compounds constitute at present a somewhat obscure

group . Their classiﬁcation and systematic treatment present

fﬁ o f special di culties , from the want of consistency the observed f composition with the current conceptions o valency. The

principle of a constant valency, ﬁxed and invariable for each

element , has long been abandoned by inorganic chemists, but

o f a s such variations valency occur in oxides, halides , and metallic

salts follow certain fairly simple rules , and conspicuous anomalies

. o ne are rare When metals combine with another, however ,

much greater irregularities are observed . There is no reason to suppose that the law o f deﬁnite proportions loses its validity in o f this class compounds . It is generally possible to assign to an intermetallic compound a formula which only involves small

o f a numbers atoms, the few formul of a high order (such as N a H m g l a) which are recorded in recent memoirs being in all proba

bili t . y erroneous N evertheless , although only relatively simple c o f atomic ratios oc ur, those ratios are, in perhaps the majority u cases, irreconcilable with the valencies sually assigned to the

metals . Abandoning, therefore , any attempt to determine the

o f structure intermetallic compounds , at least until certain pre

liminary problems have been solved, it will be well to consider

what regularities of composition are to be observed , and the direction in which an explanation of the anomalous position of these compounds is to be sought .

f o f o ur e m The imper ection exp ri ental data , to which repeated

90 I N TERM E TA L LI C COM P O UN D S

1 - . Neighbouring elements in a natural group (a sub group of the periodic system) do not form compounds with one

another . 2 . An element either forms compounds with all the members

o f o r a natural group, with none of them . The members of the ﬁrst two Short periods in the periodic s o classiﬁcation were provisionally excluded from these rules, that each natural group was regarded as consisting ordinarily 182 of three members . I n a later paper, the same author sup

c ported these con lusions by a quantity of further evidence .

As regards the ﬁrst rule, its scope is actually wider than is

o f sub - stated above . The elements a natural group, whether

o r o ne neighbouring not , do not form compounds with another, the only recorded exception being the compound o f iodine with bromine . The rule at once breaks down if it is extended

o f F o r to include the elements the ﬁrst two short periods .

instance, magnesium forms compounds with zinc , cadmium ,

and mercury , whilst sodium combines with potassium and prob

o f i ts ably also with the succeeding elements group .

The second rule is subject to numerous exceptions . The

o f i extent its applicability s discussed below . ’ Me nd e l e e ff s According to conception of the periodic system , the sum of the valencies o f any element towards oxygen 8 and towards hydrogen is equal to . It was suggested by 1 83 K urna ko ff that the types o f combination observed in the l alkali ama gams might be accounted for in this way . The

o f 1 valency the alkali metals towards oxygen is only , and a maximum valency o f 7 towards elements differing widely

from oxygen , such as other metals , might therefore be ex d o f p e cte . The results of a thermal investigation amalgams

were regarded as conﬁrming this view, but the rule has not

o f been found use in practice . The relations between electro - a fﬁ n i ty and valency have been 1 84 ff f considered by Abegg . The e ective valency o an element depends o n the nature of the element (or group) with which it is , f in combination , and is the more variable the greater the dif erence

f c between the elements concerned . This dif eren e is expressed

- afﬁ ni t i e s c by the electro , or , in the periodic classiﬁ ation , by the

horizontal distance between the two elements in the table. Com p ounds built up o f two widely separated elements are hetero THE REL A TI ON S OF I N TERM E TA L LI C C OM P O UN D S 9 1

polar, and those of closely neighbouring elements homopolar.

o ne d i s The class passes continuously into the other, but the tinction is clear when it is seen that potassium chloride is a typically heteropolar compound, whilst iodine chloride is an

Th e extreme instance of homopolar combination . intermetallic compounds are obviously of the latter type, and the application o f this conception to the data collected by Tamman n has been 185 made by Abegg . This author distinguishes between normal

- o f and contra valencies , the maximum number which is shown in the table below

G ro up .

N o rm al val en cie s 1 2 3 Co ntra- val en ci es 7) 6) 5)

- a fﬁ n it Negative electro y is in general much weaker than positive ,

- and this is particularly evident in the contra valencies , hence the

no t numbers in brackets are maximum values , often actually attained . Two elements o f the same natural group will only combine

' together if the change o f electro - aﬂi n ity with atomic weight o f is considerable . This is mainly the case with the elements f w low atomic weight (members o the t o short series) . Hence aluminium combines with boron and silicon with carbon , but not '

th e h i h e r sub - with g m embers of the respective groups .

o f The more strongly heteropolar any pair elements may be, the more probable is it that they will combine with o ne another in accordance with their maximum normal valencies , whilst homo

t o polar pairs are more likely combine in varying proportions , f dif ering widely from the normal valencies . The intermetallic

o f compounds are typical representatives the latter class . The transition from o ne class to the other may be illustrated f by the example o the phosphides . Phosphorus forms com pounds o f distinctly heteropolar character with strongly positive

v metals , such as potassium and calcium , these phosphides ha ing the properties of weak salts , hydrolysed by water to a metallic hydroxide and hydrogen phosphide . In contrast with these , the C m weakly positive metals such as iron , nickel , and opper, for 9 2 I N TE RM E TA L LI C COM P O UN D S

phosphides of distinctly metallic character, which may be fairly classed among alloys . ’ Ta mma nn s first rule finds its justification in the absence of any marked difference o f electro - affi nity between members of the

- o f - afﬁ nit same sub group . The change electro y in the two short

i s series , however, considerable , and it is therefore natural to expect that the elements belonging to these series will combine with the elements o f higher atomic weight belonging to the same

o f group . This conclusion may now be examined in the light the more complete data which have accumulated since the publi

o f cation the papers to which reference has been made . It is not necessary to assume that the combining power o f the metals with o ne another ﬁnds its full expression in the results o f thermal analysis . A compound is only recognized by this

o f method when it is capable existing as a distinct phase , in

o ut equilibrium with other phases . Abegg has pointed , however , that such an independent existence presupposes that the com pound in question reaches s o high a concentration in the solution f (liquid or solid) that saturation occurs . When the a ﬁnity between i two homopolar elements s small , combination may indeed take n place, but the concentration of the compou d thus formed may " o f so not reach the limit saturation , that a distinct phase does

o f not make its appearance . Improvements in the methods de t e rmi ning the electrical conductivity and thermo - electric p ro e rti e s o n o f p , by throwing light the constitution homogeneous

o f phases , may make the detec tion combination possible even in these cases . — Gr o up L Systems o f two alkali metals have been little

- examined . Lithium , in its alloy forming properties , resembles magnesium rather than sodium, and its behaviour is in some respects anomalous . Molten lithium is hardly miscible with 186 o r sodium potassium . Sodium forms a single compound ,

Na K 2 , with potassium , but this compound dissociates below its 187 - melting point . It is probable that both lithium and sodium

o n would prove, investigation , to form compounds with rubidium

the o f s ub- and caesium , but that metals the potassium group would not combine with one another.

- In the second sub group , copper, silver, and gold alloy to

o r gether, forming solid solutions either completely to a limited m N aA u extent . Sodium for s a single compound with gold, z,

94 I N TERME TA LLI C COM P O UN D S

191 o f a complete o r almost complete series solid solutions . I t

o n does not appear that arsenic combines with bismuth fusion , and there are even indications that only limited miscibility occurs 192 in the liquid state .

Gro u VL—A p lloys of chromium , molybdenum , tungsten, and

o n no t uranium with e another have been investigated . The

o ne group sulphur, selenium , tellurium is a natural , with a progressive increase of metallic properties with increasing atomic

o f weight . The oxides , sulphides , selenides, and tellurides the

elements o f the sixth group are entirely non - metallic in char

n o t to acter, and are be classed amongst alloys . — Gr o up VI Z Manganese is the only known metallic element ’ Ta mmann s in this group . An exception to ﬁrst rule occurs

th e no n - amongst metallic members of the group, iodine forming

a compound with its neighbour bromine . In accordance with

- afﬁ nit t wo the rapid change of electro y in the short series, ﬂuorine

a nd chlorine combine readily with the succeeding members .

Gro u I I I — - V . p This group includes three sub groups, each

o f o f composed three closely allied elements . The members each sub - group form a continuous series o f solid solutions with o ne another. In the iron group the relations are somewhat

o f complex , as there is some evidence chemical combination

occurring between iron and nickel , and between iron and cobalt , although the conditions o f existence o f the compounds have not f been deﬁnitely determined . The isom orphism o the two sub

o f groups platinum metals respectively appears to be perfect .

As regards the relations o f the three sub - groups to o ne n w another , iro and platinum form alloys hich undergo some 193 i n what complex changes the solid state . C obalt and nickel

form solid solutions with platinum and palladium , but the limits o f concentration are quite unknown .

COMPOUN DS OF META LS OF G ROUP I WI TH THE METALS OF OTHE R G R U S O P .

o f G IA The alkali metals roup , have been mainly investigated ,

fo r o f obvious reasons, in their relations to metals comparatively

- low melting point, and their combinations with the less fusible

metals are little known . Taking the second group ﬁrst, neither

no r sodium potassium forms a compound with magnesium , whilst

each combines with zinc to form a compound , provisionally THE RELA TI ON S OF I N TERME TA LLI C COM P O UN D S 9 5

N aZn o r K o f represented as 11 a although the actual number zinc atoms is uncertain . The compounds with cadmium include

LiCd LiCd a Cd N aCd , z, N z, 6 , and potassium compounds of doubtful composition . The alkali amalgams are remarkable for the number

o f fo r and variety the compounds they contain , and the high melt ing- point of the principal compound in each series

Li H N a H K H R S g 3 g g n 6 L i H P N a K H Z g n 2 g2 L Na K H n n 2 g 3 L Na H K H P n 2 g z g g L Na H P K H P n 3 7 g 8 g l o a H N g 2

N a H g 4 R H o ne . the compound g 2 being the most stable in each case

Sodium and potassium do not combine with aluminium , and the only compounds of alkali metals with metals of G roup I I I are

N a T1 ? a Tl NaTl K Tl ? K Tl P . those with thallium , 5 2 , N 2 , ; 2 , and

Tin and lead combine with the alkali metals , and the following c ompounds are describ ed

Li S n a S n K S n ? K P 4 N 4 2 s Li S n a S n K S n ? K ? 3 2 N z s Li S n Na S n K S n K b 2 5 4 3 2 P 4 N a S n K S n , a S n N 2 o f In the ﬁfth group , the nitrides, phosphides , and arsenides the alkali metals are in no respect metallic . They contain almo st invariably three atoms o f the alkali metal united with one atom o f the element of the higher valency, although combination may

o f also take place in other proportions , as in the case the com HN pounds derived from hydrazoic acid , which , however, have

o f all the properties true salts . An approach to the character o f intermetallic compounds is seen in the antimonides and bi s muth id e s : Li S b a S b 3 N s N a S b 96 I N TERM E TA LLI C COM P O UN D S

In the sixth group , the sulphides, selenides, and even tellurides , are not to be regarded as forming alloys, although the equilibrium diagrams closely resemble those of binary metallic mixtures . In most instances several compounds are formed .

- G I B o f The sub roup , consisting the metals copper, silver , and

s ub - gold , differs so widely from the alkali group that close

c analogies are not to be expected . The following ompounds with metals of the second group are well established

CuzMg A g Mg A u Mg CuM A M A u M g 2 g g 3 g2 A u M z g 5

A iI Mg 3

A n A Cd g 2 3

A n 3 P o f The nature the compounds with mercury is still unknown . m o f G Of compounds with etals roup I II , only those with aluminium are known

Cu4A l P A u4A l P

Cu A l A u A l s 5 2 l l CuA A ugA CuA l A uA l 2 A uA l 2

C o r Thallium does not combine with opper, silver, gold .

A few regularities in the above series may be observed . Compounds in which o ne atom o f the univalent metal is united o f o f with two atoms the bivalent metal are frequent occurrence , and generally exhibit the greatest stability o f the series

LiCd L Na Cd Na K C CuM , , n z ; 2, n ; n ; n , ; g2, Cu P A uM h a a ; g2. A silver compound of this type s not been

8 T R ME T LLI C C MP 9 I N E I A O O UN D S d A Mn . G compound gz As regar s roup VII I , there is a well

marked tendency to form solid solutions with the copper group ,

o f o f and there is no proof the existence any compound .

COMPOUN DS OF THE METALS OF GROUP I I WI TH METALS OF O THER GROUPS .

Magnesium is remarkable for its power of forming intermetallic o f compounds great thermal stability, which dissociate very little

o n . o n fusion Calcium has been little investigated , and , account o f a fﬁ experiment l di culties, little reliance is to be placed in the a o f published formul most of its compounds with metals . With Group I I I are formed A l Mg4 s

M T1 P g 8 3 M CaTl gn 3 M Tl Ca g 3 2 n 4 CaTl M i f A deﬁnite metallic silicide, n , exists , and the ollowing compounds with tin and lead have been described n Ca S n ? Mn s Ca Ca M gs Ca 3 G M Bi I n roup V , the compounds and g 3 2 are wel l

M A s l S . established, and g 3 2 highly probable Nothing is known o f o f o r alloys magnesium with chromium manganese . In the eighth group , magnesium combines with nickel , forming the M Ni M Ni compounds g g and g z, and probably with the platinum metals , but quantitative data are lacking . The alloys of the metals of the sub - Group I I B have been o f no w the object much investigation , but the data are even very incomplete, especially in regard to the amalgams .

Z s . inc combine with aluminium , forming a compound which Zn A 1 probably has the composition 3 2, but cadmium and aluminium

o f . do not alloy, and the nature aluminiu m amalgam is unknown n o r f m Thallium does not co mbine with zi c cadmium, but or s a H Tl compound g 2 with mercury . No compounds o f metals o f Group I I B with those o f G roup I B G V exist . The compounds with roup V are as follows THE RELA TI ON S OF I N TERM E TA LLI C COM P O UN D S 99

Hgn P

Cd A 5 3 2 s CdA 2

Zn S b Cd S b ,, 2 3 2 ZnS b Cd S b Bismuth does not combine with any o f the metals o f the sub group . The sulphides and selenides o f the zinc metals have the simple

a Zn S . . formul , etc , but are hardly at all metallic The tellurides ZnTe CdTe H Te , , and g are well deﬁned , and combination does not take place in other proportions . Chromium and manganese undoubtedly combine with the metals of the zinc group , but the formul a o f their compounds are unknown . o f In the eighth group complex series of compounds occur, which the following have been established with more o r less certainty Zu F e 7 a F e

Zn Ni a ZnNi

P Zn 4Co

The platinum metals form numerous compounds with zinc , m f a cadmiu , and mercury , but their ormul have not been de i n ﬁnitely established a single case .

COMPOUNDS O F T HE META LS OF GROUP II I WI TH METALS OF O THER G R U S O P .

m o r Aluminium does not co bine with silicon , tin , lead , and

o f indium forms a complete series solid solutions with lead .

A l Ce A l Ce A lCe A lCe Aluminium forms the compounds 4 , z , , , , 194 l e and A C 3 with cerium . Thallium does not combine with o f silicon or tin , and the doubtful possibility a compound with lead has been previously discussed (p. s A l Aluminium form the compound , but does not combine TI S b with bismuth . Thallium appears to form the compound S , m in which its rese blance to the alkali metals is apparent , and

Tl Bi Tl Bi P co m also the co mpounds s and s s Further, the 1 00 I N TERME TA LLI C COM P O UN D S

A lCr A l Mn P A a pounds 3 , s and 3 have been recorded . Alu minium certainly combines with the less fusible metals of G roup

o f VI , but the statements as to the nature the com pounds formed are uncertain and conﬂicting . The following compounds have been recorded in G roup VI I I A l F e P A l Ni Co ? s s Al 4 A 1 N i A 1 C0 P 2 5 2 A lNi A lCo

o f Thallium does not combine with any metals the iron group . Of compounds of aluminium and thallium with the platinum A 1 P t metals, the only representatives deﬁnitely known are 3 and TlP t .

COMPOUNDS O F THE META LS O F G ROUP IV WI TH METALS F THER R U S O O G O P .

F o r the present purpose, silicon mu st be included amongst the metals so far as its compounds with the less fusible metals are concerned . The following compounds of tin and lead with the G elements of roups V, VI , and VI I may be tabulated S n A s P b A s P ,, 2 s 4 S nA s

S HA S ? Q

S n 5b 3 2 S n S b W Neither tin nor lead combines ith bismuth . S nS e P bS e

S n 2S e P

S nTe P bTe

r Chromium does not combine with tin o lead . Manganese does o f not unite with lead , but forms a series compounds with silicon and tin S nMn

S n Mn2 n Mn S 4 The conditions VI I I are fairly complex S iF e [S n- F e compo und o f unknown co m S i F e 2 position]

f I N TERME TA LLI C C OM P O UN D S

COMPO UN DS O F THE META LS O F G RO UP VI WI TH THOS E OF G R U S A N D O P VI I VI I I .

fe w o f Very the tellurides have been studied , the only formula

P tTe established with any certainty being 2. Tellurium combines with iron , nickel , and cobalt , and probably also with the other

o f un platinum metals , but the composition the compounds is known .

Chromium enters into solid solution with manganese , iron ,

o f h as cobalt, and nickel , and the formation com pounds been suspected , but not yet proved . Its alloys with the platinum metals have received little attention . The relations of molybdenum and tungsten to the metals o f the eighth group appear to be very complex , but little reliance can be placed in the formula hitherto published for such co m o f pounds , based as they are mainly on the chemical analysis o f n residues . Thus , an extraordinarily complex series compou ds 19 5 o f molybdenum with manganese and iron have been described , but with little justification . o f G Manganese is the solitary metallic member roup VI I , f o f and , whilst it readily orms solid solutions with the members G roup VI I I , there are no definite indications of the formation of compounds . The data summarized in this section may n o w be briefly reviewed from the theoretical standpoint , as far as their imperfect character permits .

’ Ta mm a n n s h o f In the ﬁrst place , second rule, t at an element THE RELA TI ON S OF I N TERME TA LLI C COM P O UN D S 1 03 o ne sub- group forms compounds with all the elements o f another s ub - o r its group with none of them , may be tested in application to intermetallic compounds . One conspicuous exception was n noticed by Ta mm a n himsel f. Lead does not combine with copper, and does not even form a homo geneous liquid with it

- at the melting point . I t alloys readily with silver, but again without chemical combination . On the other hand, lead and f gold combine together, orming two deﬁnite intermetallic com pounds . o f Further examples the same kind may be noted . Whilst f nearly all the metals orm antimonides, a much smaller number combines chemically with bismuth . Aluminium combines with m zinc , but not with cadmium , whilst thallium does not co bine with

o r so . either zinc cadmium , but does with mercury Manganese and also copper combine with tin , but apparently not with lead .

The exceptions all tend in the same direction , the readiness to form compounds increasing with the heteropolarity of the two elements concerned . A o f begg remarks , however , that the data the thermal method , being obtained at relatively high temperatures , ﬁx only a lower o f o f limit to the combining power the metals, as the stability to labile homopolar compounds, which class most intermetallic

to i ncre as compounds belong, may be expected diminish with ing temperature . The more exact thermal methods which ’ have been devised since the publication o f Abegg s paper have made possible also the detection o f compounds which are formed in the solid state at comparatively low temperatures, but the best results are to be expected from physical determinations , performed o n alloys which have been brought to a condition o f equilibriu m by very prolonged a nnealing below the temperature at which combination is suspected to take place . Such compounds with a low temperature range o f stability may prove very important in ﬁlling the gaps and explaining the anomalies of the periodic arrangement . In view o f the uncertainty that prevails as to the composition o f the majority of intermetallic compounds , it would be futile to

e o Re attempt any structural r presentati n of their constitution .

m a o r o ference ust , however, be m de to one two suggesti ns which

e have been put forward in this connexion . The int rmetallic compounds found in certain amalgams, and containing a number 104 I N TE RM E TA LLI C COM P O UN D S

of mercury atoms associated with a single atom o f a metal 5‘ K e r usually regarded as of low valency, were considered by p o f to contain mercury crystallization, and to be comparable with a H hydrated salts . Thus , N g 5 was regarded as being either H o r H H Na H a . g , 4 g , N z g , 9 g There is here an obvious attempt a to obtain formul consistent with the ordinary valencies , sodium

being univalent, whilst mercury is represented as univalent in

a V so the ﬁrst and biv lent in the second formula . This iew is far justiﬁed that there is an undoubted resemblance in the

equilibrium diagrams of many alloys and hydrated salts . A liquidus curve with several maxima is obtained in such systems

f - o f a as erric chloride water, whilst the decomposition n inter metallic compound o n heating into a new solid phase and a

- mother liquor , such as

° 460

“ T A q o f A u , Sb (liquid alloy and Sb) is completely comparable with the decomposition o f many hy d rate s o n heating , for example

° 3 9

Zn O H 0 Zn S O 6 H O S . 4, 7 2 2 4, 2 (saturated solution) r The constitution of hydrated salts is, howeve , still so obscure

that the analogy is not directly very helpful , although it points

to the probable ad vantage of considering the c o - ordination

numbers of the metals , to which reference is made below . The next view is that which regards metals as uniting with co nt rav ale nc ie s one another by means of their or latent valencies.

This is the view adopted by Abegg . It does not appear to be

applicable in a quantitative sense . Thus , whilst silver and mag

ne si um , according to their positions in the periodic system , have

I 2 co nt rava le ncies the normal valencies and , and the 7 6 and respectively, this fact does not enable us to understand why the only two compounds which are formed under the con d itio ns o f thermal analysis should have the formul a A g Mg and

A a M . C g g 3 It also fails to account for such compounds as a C o ne and n 10, in which the number of atoms of the metal associated with a single atom of the other exceeds the maximum

number o f co nt ravale nc i e s . It is probable that light may be thrown on the constitution o f the intermetallic compounds by a careful study O f their crystal 1 96 line form . The important hypothesis of Barlow and Pope

1 06 I N TERM E TA LLI C COM P O UN D S

” o n stannide, etc . , based an analogy with silicide, arsenide , “ ” . C m he x ame rcurid e and antimonide Thus n s is caesiu ,

M 5 n i s . m s g 2 magnesium stannide, etc This exa ple, which suggest o f no t the possibility a systematic nomenclature, has been ’l° f l e d f generally o lo w . The introduction o mineralogical names for the separate micrographic constituents o f non- ferrous alloys “ ” “ ” . o f be derived from the austenite, sorbite , etc , steels , is to o f deprecated, as leading to an accumulation trivial names , and o f standing in the way a scientiﬁc nomenclature .

" This plan h as n o w b ee n ado pted i n th e large L e xico n der ano rga nisch e n ” e n n n i n s f ubl t n un er th to r h f M. K o ffmann V rbi d u ge co ur e o p ica io d e edi s ip o . H Le ( ipzig) . A I " C H PTER .

T NAR ER Y CO MPO UN DS .

THE number o f ternary intermetallic compounds hitherto recorded i s is very small , although it possible that others may be discovered when more ternary systems have been investigated with sufﬁcient

to attention . I n general , however, it appears be possible to predict the character o f a ternary system from a co nSid e ra tio n o f m its component binary syste s , and new phases, peculiar to the no t ternary system , do in such cases make their appearance . Ternary compounds should be looked for in systems containing strongly heteropolar elements .

Two such compounds have been recorded from amalgams . A maximum i s found o n the freezing- point surface o f the cadmium sodium amalgams at corresponding with a compound

a a Cn N . This m y perhaps be regarded as derived from f o ne f N a Hg 2 by the rep lacement o atom o mercury by the closely NaCd N a H . allied cadmium , or as a double compound , z, g2

- Similarly, in the sodium potassium amalgams a maximum has

K Na been Observed at corresponding with a compound n . This is most conveniently regarded as a double compound o f a H K H two members of the corresponding binary series , N g and g . Both of these compounds have been described o n the evidence o f cooling curves taken in the i mmediate neighbourhood o f the

- maxima in question, and in each case the initial freezing point o f was found to be lowered by the addition the components . The no t complete liquidus surfaces have yet been described . The third compound o f this class occurs in the system a - - luminium magnesium zinc, and has a more complex composi 201 s - tion . A plane ection through the space model , having as A l M M base a line joining the two compounds 3 g 4 and a 2, is f 1 . o shown in Fig. 7 The thermal analysis alloys falling within o f o f this range composition indicates the formation a compound , melting with decomposition at and forming solid solutions 1 07 1 08 I N TE RM E TA LLI C COM P O UN D S

- with the aluminium magnesium compound . The maximum heat o f reaction compound 2 liquid and solid solution ° at 50 5 occurs at the composition A l M M o r A l Z n M 3 g 4 , 3 a 2, 3 6 g 7.

IO 20 4 0 5 0 6 0

F G 1 I . 7. The maximum brittleness is also found to coincide with

composition . The micrographic examination fails in this

c o f of the system , on a count the brittleness of the alloys and of the very slight differences in electrolytic character between con

s it s t ue n t present in the same section . A closer study of similar systems will probably reveal the i o f existence of other ternary compounds , but any d scussion

their constitution would be premature .

I I O I N TERME TA L LI C COM P O UN D S

41 D M . z tt te a h M eta l l o r e 1 1 1 2 a z o o I n rn t . Z ei tsc . a h 1 8 . , g p i , 9 , , 9 42 . o s s Z ei tsch . a no r . Ch em. 1 0 8 . G V , g , 9 , 57, 3 4 43 R. o el i . 1 0 6 1 6 . V g , bid , 9 9 , 3, 9 4 4 . . Ura z o ff a nd R. o el . 1 1 0 6 2 . G G V g , ibid , 9 , 7, 44 45 . t M t l l a h 1 1 2 0 C . . Car ent e r I nterna t . Z ei sch . e a o r e 1 . H H p , g p i , 9 , 3 , 7 46 N . S . K urn ako ff and N . S . K o nstanti no ff Z ei tsch . a no r . Chem . 1 08 , g 9 , 58 4 7 S . . S ch emtsch usch n . 1 06 8 . F y , ibid , 9 , 49, 3 4 48 S . . n e na t Z i t h Meta l a S ch e mtsch uschn I t r . e sc . l o r h i e 1 1 2 28 . F y , g p , 9 3 , 4, 49 A . S ch l e ch e r i . 1 1 1 02 . i , ib d , 9 3 , 3 , 5° . K er Z ei h a n C em 1 8 8 2 8 tsc . o r . h . 1 . W p , g , 9 , 7, 4 51 B n r nd I n a . K er . Ott er . te a . e 0 . 1 00 2 1 . W p , W g , H Wi , H gg , i id , 9 , 5, 52 A . un t and F é ré e Co m t . r en . 1 00 1 1 1 82 . G z , p d , 9 , 3 , 53 A Be 1 1 6 . . C . Vo urna so s r . 1 2 6 , , 9 , 44, 3 54 L . e ea u Co m t . r en . 1 00 1 0 02 . P b , p d , 9 , 3 , 5 5 5 I . 1 02 1 2 8 . bid , 9 , 34, 4 56 C . v an k c K A ka . Wetensch . Ams ter a m 02 E r o . . 1 1 0 8 . y , P d d , 9 , , 59 57 A v n Bi l r t ei t h s a l C e 1 8 1 a e Z sc . h i k . h m . j , p y . , 9 , 8, 3 43 . 58 . D . ancro ft . h si ca l Ch em. 1 02 6 1 8 . W B , 7 P y , 9 , , 7 59 . . van e teren Z eztsch . a no r . Ch em. 1 0 2 1 2 . W J H , g , 9 4 , 4 , 9 50 0 . Br n k B 0 1 2 u c er . 1 . , , 9 , 34, 73 3 51 . t M h . C . Car nt r a n C . A . wa r s ro c I ns . ec . e e d . E n . 1 0 H H p Ed d , P g , 9 7, 57. 52 T He c k n N l l T ns Ch e S c 1 8 C . . o c a d . . e e ra . m . o . 2 6 1 1 . y F H vi , , 9 , , 9 4 63 C . R. ro es and T . Turn e r d . 1 1 2 1 01 8 . G v , ibi , 9 , , 5 5 5 4 r D . R. . o k nso n R. a n and A . . . e sbo ro u h Ch em. N ews W E H dg i , W i g, P H g , , 1 8 5. 65 . L e e au Co m t . r en . 1 06 1 2 1 . P b , p d , 9 , 4 , 54 66 M l l 0 8 6 1 . M. h l s e ta u r e 1 P i ip , gi , 9 7, 4, 5 7, 3 67 l ﬁ ei ts n Ch em . 1 0 2 1 6 . . Rudo Z ch . a o r . E , g , 9 7, 53 , 6 8 G t M a l i 8 1 8 6 2 1 . u er l er et l u r e 1 0 . W , g , 9 , 5, 4 , 6 9 a h 1 r m i t c n r . C 0 m nn Z e s h . o e . . G ue tl er a nd . Ta a m 1 6 W G , g , 9 5, 47, 3 . 7° 1 0i d 1 06 . . , 9 , 49, 93 71 M 1 1 1 1 . ae Z ei tsch . h si ka l . Chem 8 2 0 1 8 2 8 2 2 1 0 E y , p y , 99 , 9, 9 ; 9 , 3 , 9 , 9 ; 9 4,

72 M 1 A . at thi es se n h l . Tra ns . 1 860 1 0 . , P i , , 5 , 77 73 . van A u el Co m t . ren . 1 0 1 1 2 1 2 66 . E b , p d , 9 , 3 , 74 t e t M l h S . . S ch e mtsch us ch n I n ter na . Z i s ch . e ta l o r a e 1 1 F y , g p i , 9 3 , 4. 75 R F ril l e Rev . d e Méta l l ur i e 1 1 1 . . y , g , 9 , 8, 457 76 h N . S . K urna ko ff a nd S . . S ch e mtsch usch n Z ei tsc . a no r . Ch F , em. , 1 08 y g 9 ,

77 . Ura z o ff 0 . 1 1 1 1 . G . G , i id , 9 , 73 , 3 78 . . S m rno ff and N . S . K urn a ko ff i 0i d . 1 1 1 2 1 . W J i , , 9 , 7 , 3 79 M Mu ra I n t. M e ta l s 1 0 8 . T. Turner a n d . T. r s y , , 9 9 , 2 , 9 8 0 h - A t 1 8 0 2 6 A t M t K t c n . uchs m . . Mar e ns t . . e Ve s . r 8 , i , 9 , , 3 31 a h m 1 06 . G uertl e r Z ei ts ch . no r . C e . 1 . W , g , 9 , 5 , 397 82 N . . S te ano ff . 1 1 2 8 I . J p , ibid , 9 , 7 , 8 3 m th h . R e 1 1 1 1 8 . A . . S s v . 2 W i , P y , 9 , 3 , 7 84 a Z ei Meta l l o h N K n i n m rn o ff nte n t t ch . a W A . S I r . s r S o sta nt o ff a nd . e . . i , g p i ,

8 5 N A ush n a n d A . Ba sko ff Russ . h s . Ch em . S o c . 1 1 6 . . P i . V , P y 9 3 , 45, 74 . 8 5 N . A . ush n and . R a sch sk Z ei tsch . a no r . Ch em. 1 1 82 0 . P i W j y , g , 9 3 , , 5 87 N . A . ush n and . . Di sch l er i i . 1 1 80 6 . P i E G , b d , 9 3 , , 5 8 8 B ni ki Ch h 1 1 2 . . ro ews A nn . m. s . 2 W , i P y , 9 , [viii] , 5, 5 8 9 D h l 1 8 8 . w nd l m n . Ma . 2 26 1 2 1 . e ar a . A . e 6 J J F i g, P i g , 9 , [v] , 34, 3 ; 93 , [v] , 3 , 7 9 ° . rnst K r f n n m nn S tz . k. A ka d . W ss . er l n W N e . o e a d . A . L e a , F , W i d , i i B i ,

1 1 1 6 2 . 9 0, 5, 47 RE FE REN CE S I I I

91 A . uck n e and G . G ehlho ff Be d t r . en . h si ka l . G e 1 1 s . 2 1 1 6 . E , p y , 9 , 4, 9 92 . e emann d a n R. r an o . A nn . 1 8 G Wi d F z , P gg , 53 , [ii] , 89, 49 7. 93 . ae e r - a nd . Diesselho rst A bk h te h n . s . c . Rei chsa ns t . 1 00 2 6 . W J g H , p y , 9 , 3 , 9 9 4 . a ke n A nn . h si k , . 1 1 0 2 2 1 . W H P y , 9 , [iv] , 3 , 9 9 5 . Rud o l ﬁ Z ei ts h c . a no r . Ch em. 1 1 0 6 E , g , 9 , 67, 5 . ”6 K M . Onk m e e e r 0 . 1 0 6 1 . y , i id , 9 5, 4 , 4 5 9 7 . P élabo n C m o t. r end . 1 08 1 6 1 H , p , 9 , 4 , 39 7 9 3 F . a and . A h y . s le A mer . Ch em . A 1 0 2 2 H H E y , 3 , 9 , 7, 95. 99 . I . e trenko Z ei tsch . a no r . Ch em. 1 06 1 G P , g , 9 , 50, 33 100 R. o el i 0i d 1 V g , . , 45. 101 . lt a nd M kl . ec en ur . 1 0 2 25 W Bi z W b g , ibid , 9 9 , 64 , 103 M . Ko a a h i . 1 1 0 6 I . b y s i , bid , 9 , 9 , 1 03 K . Hitttn er an d . Ta mmann i 0i d 1 0 1 1 G , . , 9 5, 441 3 : 104 . F a a nd C . . lls n A mer h e . 1 y o . C m 2 02 2 8 1 . H B Gi , 3 , 9 , 7, 105 . Re n r i h e s Z e ts c . h i ka l Chem 1 s . . 0 2 2 2 . W i d , p y , 9 3 , 4 , 5 105 . C . l i 0 d i . 1 0 2 2 6 1 . H Bij , , 9 , 4 , 4 1 07 A . . La T ur e r a ns . Ch em S o c. 1 888 1 0 P i , . , , 53 , 4 . 1 08 A . . La ur e h l M a 1 . 8 2 P i , P i g . , 9 , [v] , 33 , 94 . 1 09 M. He rschko wi t h t s c Z ei sch . h si ka l . C h em. 1 8 8 1 2 , p y , 9 , 27, 3 . 1 1° N . A . ush i n Z e tsch . a no r . Ch em . 1 0 I . P i , g , 9 7, 56, 111 A . S uch e ni Z l t c h . E t e s l ek ro ch e m. 1 06 2 6 , , 9 , 1 2 , 7 . “ 3 erso n A n n h . C i m. h s . 1 8 8 2 1 2 P , P y , 4 , [iii] . 4, 9 113 M . . r . e th el o t i 0i d . 1 0 1 Vii 22 1 . P E B , , 9 , [ ] , , 3 7 “ f l bi d 1 8 V a 79 . [ ] , 18. 433 11 5 A . a lt P r o c . Ro . S o c. E n . 1 8 8 22 1 G , y di , 9 , , 37 116 . . la s t n l Ma 1 00 2 1 o e h . . V 0 J H G d , P i g , 9 , [ ] . 5 . 3 11 7 . . L u i i n n a nd A . S ch u kare ff A r ch . S ci . h s na t . I W F g , p y , 3 , 5 I

1 0 W 1 . 9 3 . [ ] . 5. 49 11 8 T . . a ke r hi l . Tra ns . 1 0 1 1 6 A J B , P , 9 , 9 , “ 9 . R n l h s 8 1 1 2 . e a u t A n n . Chi m . . 1 I H V g , P y , 4 , , 9 1 20 . S h im ff c Z ei tsch . h si ka l . Chem. 1 1 0 1 2 . H p , p y , 9 , 7 , 57 1 21 A . S . a o sh n iko ff R u ss . h s . Chem. S o c. 1 0 1 1 08. V p , P y , 9 9 , 4 , 7

T. L ttl to n R e 1 1 e h s . v . 1 i , P y . 9 . 33 , 453 1 3 3 R. o hl a n d n d h zka l 8 1 1 0 . P ri sh e im Ber . en t . s . G 8 2 I 6 6 P P g , p y " 9 . 4: 5 . 54 124 K r m a n n . e r i d . H , bi , 557. l 25 10i d . , 573 . 126 R . o h l a nd P ri n sh e im i 1 1 0 1 2 2 1 6 1 0 : P P . g , bid . , 9 , , 5, 349 , 9 7, 39 127 R. Ruer nd z Meta l l ur i e 1 1 0 1 a . S ch ii E , g , 9 » 7, 4 5 1 3 3 k n c 8 . o so n r o Ro S o c . 1 0 J H p i , P . y . , 9 , 47: 129 Re h e h 1 2 0 c n ac o . A nn . 1 86 1 1 i b , P g g , , 4, 99 , 5 13 0 Méta l l ur i e 1 0 1 6 . . smo n a nd . Ca rt aud Rev d e F O d G , . g , 9 4, , 9 131 i tsch . a no r . Chem. 1 08 1 6 . . rae nkel a nd . Tamm ann Z e 60 W F G , g , 9 , , 4 13 2 C . en ks d Méta l l u r e 1 1 1 8 . e c Re v . e 8 B di , gi , 9 , , 5 13 3 h 0 . G u r mmann Z ei tsch . a no r . C em. 1 2 0 . e tl er a nd . Ta W G , g , 9 5, 45, 5 134 Tamm n n e t si a l Ch em 1 08 ° . a Z i sch . h k . 6 G , p y " 9 , 5, 73 13 5 S . l ert Ber . 1 0 2 2 2 8 Hi p , , 9 9 , 4 , 4 13 5 Mo s 1 1 8 6 2 . s a n Co m t . r en . 1 8 1 20 122 H i , p d , 95, , 73 ; 9 , » 4 4 13 7 i v - 1 1 5° . W ri ns ch e A nn . h s k . 1 0 2 H , P y i , 9 , l l . 7. 13 8 i 6 N a ao ka . 1 8 6 iii - 6 ° H . g , ib d , 9 . [ l , 59 . 1 3 9 K . o n a A nn . h si k . 1 1 0 2 1 00 ° H d , P y , 9 , [iv] , 3 : 3 “ 0 W Ohl e r A n n a l en 1 8 1 1 F . , , 59 , 1 1 1 , 7 1 41 I . I . S h uko ff Co m t . r en 1 08 1 6 I 6 , p d . , 9 . 4 , 3 9 142 P . as ca l . 1 0 1 8 1 6 ~ , P , ibid , 9 9 , 4 , 4 3 “ 3 T . . o Ch em . N ews 1 8 2 66 . 1 0 W H gg, , 9 . 4 I 1 2 I N TERME TA LLI C COM P O UN D S

1 44 l r Verk . en t h . eu e i ka l . G s 1 . s e . 0 2 1 . F H s , d p y , 9 3 , 5, 9 1 45 . S tar k and . au t 2 2 2 . W E H p , ibid . , 1 46 . eu ler Z ei tseh . a n ew . Chem. 1 0 1 260. F H s , g , 9 4 , 7, 147 C ll me A c . . u au tes . S o c . h el v . S ci na t 1 0 . 88 . E G i , . . 9 7, i “ 3 . reu er D sser ta t Mar ur 1 8 o n 0 . W P ss , i i , b g , 9 1 49 . eusl er and . Ri ch arz Z ei tsch . a no r . Chem. 1 0 6 1 2 6 . F H F , g , 9 9 , , 5 1 50 d A . D . Ro s an R. C . ra ro c. Ro . S o c . E n . 1 0 2 2 . s G y , P y di , 9 9 , 9, 74 151 . Hindri ch s Z ei tsch . a no r Ch em 1 08 1 G , g . . , 9 , 59, 4 4 . 1 52 . Take A bh . k G es . i s G t i 1 W s ii t n en 1 1 N . . . . 8 o 2 E , g , 9 , [ii] , , 1 53 A . D. Ro ss Tr a ns . F a ra a S o c . 1 1 2 8 1 8 . , d y , 9 , , 5 1 54 . Ro senh a n a nd C A s rr c t Mech . En . 1 1 0 . . . . Lant be ro . I ns . W i F H y , P g , 9 ,

1 1 9 .

1 2 . 40, 59 1 56 ' T D Hil e 1 t and . eckma n . 1 8 1 S n 1 1 2 . . p i , ibid , 9 , 44, 3 1 57 T D m nn - a 1 S . l ert . eck a and . Co l er G laue rt Tra ns . F ra a S o c . 1 2 Hi p , i , E v , d y , 9 ,

8, 207. 1 58 Men e n h al l and 0 C . . . . L e nt h s . Rev . 1 1 1 2 6 . E d W F , P y , 9 , 3 , 4 1 9 5 r Z ei tsch h s ka l h e R Rue . i . C m . 1 0 1 1 08 . . , p y , 9 7, 59 , ; 9 , 64, 357 1 50 A . . . Aten ro c . K . A ka . Wetensch . A ms ter a m 1 0 68 . H W , P d d , 9 4 , 7, 4 1 51 . S to rt enb e cker Z ei tsch . h si ka l . Ch em . 1 88 1 1 . W , p y , 9 , 3 , ’ 1 6 2 h ns a l R. Kremann A re S mm un 1 0 1 e ft 6 2 . , g , 9 9 , 4, H , 3 1 63 h 8 t nbe cker Z ei t . i 8 2 1 . W S to r e sc h s ka l . Ch em. 1 . , p y , 9 , 1 0, 3 1 64 M sh 1 1 1 R. K remann o na t . 0 2 2 . , , 9 4, 5, 5 1 65 . Ro o ebo o m Z ei tsch . h si ka l . Ch em . 1 0 8 . S ee a l s o W . H . B z , p y , 9 5, 53, 44

n l n M k T n Ch m . c . 1 0 0 . A a a d c m an ra s . e S o 1 . Fi d y E . . Hi s , , 9 7, 9 , 9 5 1 65 mmann Z i seh a o Che 1 0 Ta e t . n r . m. . G . , g , 9 5, 48, 53

K nsk Z ei tsch . E l ektr o chem. 1 08 06 i y , , 9 , 4, 4 . 1 63 rn nn n M l l Me ta l l ur e 1 1 0 6 . K o ema a d . u er . B P , gi , 9 , 7, 39 1 69 K . o rneman n and . vo n Rausch en l at . 1 1 2 . B G p , ibid , 9 , 9, 473 1 70 i M P h a l S m th Z ei t eh a no r . Chem. 1 08 8 1 . . c s . 8 G i , g , 9 , 5 , 3 1 71 . S chm t A nn . h s k. 1 1 2 1 1 08 . F id , P y i , 9 , [iv] , 39 , 172 A . . err r o c. R o . S o c . 1 1 1 86 A 67. J B y , P y , 9 , , 173 sch er a nd S chré t er Ber . 1 1 0 1 6 . F . Fi F . , , 9 , 43 , 4 5 174 . e ek n and T e t . 1 08 1 6 . E W d i d . V i , ibid , 9 , 4 , 3 7 9 1 75 I S h uk ff h o c 1 1 0 . I . o Russ . P s Chem. S . 0 . , y . , 9 , 42 , 4 1 75 d u i x h h 1 0 1 . A net asso n e A nn . C m. s . 1 . Bi J , i P y , 9 9 7, 45 177 M ss n o 8 A . o a C m t. r en . 1 8 1 1 1 . i , p d , 94, 9 , 5 1 78 1 . 1 8 6 1 22 2 1 6 . bid , 9 , , 74 , 4 3 179 rt r M et l a hi rl n i n urse o f u l i cati o n . . G ue l e a l o r e e co W , g p (B i , p b ) 18° ’ K rn emann D bi nci r Meta l l e i er n n en al l e i n co ur e o f ubl i ca ti o n . o i e en B , g g (H , s p ) 1 81 Tammann Z ei tsch a no r . Ch em . 1 06 1 1 . G . , . g , 9 , 49, 3 182 6 . 1 i d 1 0 2 8 . , 9 7, 55, 9 183 N . S . K urn ako ff . 1 00 2 . , ibid , 9 , 3, 439 1 84 R b 0 0 A e . 1 . gg , ibid , 9 4, 39 , 33 . 1 85 I . 1 06 0 0 . bid , 9 , 5 , 3 9 186 8 Ma s n and a ann . 1 1 0 6 1 . . G . T mm G i g , ibid , 9 , 7, 3 187 M d k n Bl i sw k i . 1 1 2 1 2 . . L . C . van Ro sen Ho o en v a e G . s g y y , bid , 9 , 74, 5 1 3 8 M Meta l o r a h e 1 1 1 1 1 . ath I t t t h . 0. . ewso n n erna . Z ei sc l H , g p i , 9 , , 5 1M N . aar Z ei tsch . a no r . Ch em . 1 1 1 0 2 . B , g , 9 , 7 , 35 I 9 " Me ll o ra h e 1 1 2 0 N . at t a ano and de Ces ari s I n tern . Z ei tsch . ta 2 P v P . , g p i , 9 , , 7 1 91 8 N . P arravano and . an A tti . R . A cca . L nce 1 1 0 1 . E Vivi i , d i i , 9 , [v] , 9, i , 35 1 92 K r M ta l l r i e 1 08 1 8 . . r e ch a nd ,A . L ero u e u F i d i x , g , 9 , 5, 5 1 93 I saac and Ta mmann Z ei tseh . a no r . Chem. 1 0 6 . E . G . , g , 9 7, 55, 3 1 94 R o e l . 1 1 2 1 . . V g , ibid , 9 , 75, 4

" I NDE .

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- man a ne e n all s 1 0 . ERR O MA E T allo s 6 c o C . g s zi y , 7 F GN I y , 5

n ckel allo s 6 ract o nal c r s tal l sat o n 26 . i y , 9 . F i y i i , ’ mal m r - A a s d ﬂ usivi t o f 8 . re e n o n t cur e 6 . g , y , 3 F zi g p i v , 3 , - h o to el ectr c ro ert e s o f 6 . sco n t nu t e s i n . p i p p i , 4 di i i i , 7

se arat o n o f cr st al s fro m 2 . nterme ate ranch e s o f 8 p i y , 7 i di b , , f - ur ace t en s o n o f 8 1 6 . s i , 4 . Amm l t o n a u as a re a e n 2 . ma ma o n 8 8 i , iq id , g , 9 xi , 3 , 7 . A nt mo n -ca m um allo s 2 1 1 i y d i y , , 5 , 54 , 6 - m n s OLD a e um allo 2 0 . 4 , 74. G g si y , 9 , c o e r all o 8 pp y s , 3 . l e a allo s 1 8 . A L L e ffect . d y , H , 74

s lver al lo s 0 6 ar ne ss 2 . i y , 5 , 5 . H d , 4 t ell r m ll 0 6 at f f rm t o n 6 1 u u a o s . e o o a . i y , 5 , 5 H i ,

t i n all o s 1 8 e t ero o l ar co m o un s 6 1 . y , . H p p d , 3 , 9

nc all o 2 2 1 . e usl er all o s 0 . zi y s , , 5 , 74 H y , 7 - Arre t t me 1 0 . o mo eneo us e u l r a 1 6 . s i s , H g q i ib i , - A rsen c ca m um al l o s 2 2 o mo o l ar co m o un 6 1 1 . i d i y , . H p p ds , 3 , 5 , 9

Br mu r ns r f I MP E F T l r um 1 0 s m s arat o n 2 8 R E e u 2 . e o . C 2 , p p i , q i ib i , 4 . , 4 - mu m m all s I n eﬁ n te o m un s 1 . th a n es u o . c o Bis g i y , 49 d i p d , , 3 - t el lur um al lo 0 . I ro n n ckel al lo s 6 . i y s , 5 , 55 i y , 5

thal l um a llo 1 2 I so l at o n o f co m o un s 2 2 6 . i y s , . i p d , ,

o ri e 8 . I so mo r h sm 1 0 . B d s , 73 , 7 p i , 5

- CA nmru M ma n e um all o s 1 6 L E AD ~ th alli um all o s 1 1 . g si y , , 39 , y ,

6 t in allo s 1 8 . 4 . y ,

- mercur o um all o s 1 0 . L u us 6 . y s di y , 7 iq id , l er all o 2 0 si v y s , . - Carb e s 88 MA E S UM l er a l l o s 1 . id , . GN I si v y , 4, 43

Ch m l l 1 M net ro e rt e s 6 . e ca al o s . a c i y , g i p p i , 5

Co e rc ve fo rce Man ane se m a ne t c co m o un s o f . i , 73 . g , g i p d , 73

- - Co lo ur 2 Mercur o t ass um so um al l o s 1 0 . , 5. y p i di y , 7

Co n uct t e l ectr cal . th all u m al l o s . d ivi y , i , 45 i y , 59

o f l u a ll o s 80 . ti n all o s 2 . iq id y , y , 9

th erm al Mete r c ro n s 66 . , 54. o i i , C nt r - n o a val e c e s 1 . i , 9

Co er s l c es 1 NAT V E m neral s . pp i i id , 3 . I i , 34

nc al l o s 1 2 62 atural ro u s 0 . zi y , 7, 5 , . g p , 9

Cr o h ra tes 1 . ern t e ffect . y y d , s , 74 - Cr l l n m N cke l tin all o s 1 6 . ta e fo r . y s i , 75 i y , 9 , 9

N t r e s 8 . i id , 7 D E S TY . N o m en c l ature 1 0 . N I , 39 , 5

D ama net c all o s N um er o f nt e rm et al l c co m o un s . i g i y , 74. b i i p d , 4 ' Di ﬂ usivi t 8 y , 3 .

D s o at o n 8 ARA A E C al l o s . c . M T i s i i , 7 P GN I y , 74

D s t l l at o n 0 8 . e r o c s stem 0 ° i i i , 3 , 5 P i di y , 9 1 1 5 1 1 6 I N TERME TA LLI C COM P O UN D S

h o s h e s 1 . S o l state reac t o ns i n 1 1 2 1 . P p id , 9 id , i , 7, 9 , - h o t o el ectr c ro ert e s 6 . S ec ﬁ c h e at 6 . P i p p i , 4 p i , 3 m h s cal ro ert e s . o l u e . P y i p p i , 37 v , 39 t m ll f S ul e s 8 o as u a o o 6 . h . P si , ys , 5 p id , 7 S us t l t ma n t c 6 ce e . p ibi i y , g i , 9

REA CT I V T Y o f co m o un s 2 . I p d , 3 Rea e nt s act o n o f o n allo s 1 TE L L U R U M-ti n all o s g , i , y , 3 . I y , 57. R s n r l T rn r m un s 1 e sta ce ele ct ca 6 . e a co o 0 . i , i , 4 y p d , 7 - m r r i n f 1 82 . Th erm l n l 6 t e e atu e co e fﬁc e t o a a a s s 1 0 . p , 5 , — y i , , Th ermo el ect r c o wer . i p , 55 S E M -co n ucto r I d s , 54.

S l c e 86 1 00 . U DERCO OL 2 1 . i i id s , , N ING ,

anal s s o f 2 . y i , 3

- S l er nc all o 2 0. A L E CY 88 1 0 . i v zi y s, V N , , 4 - S o um mercur allo 8 1 . a o ur at o n o f all o s 8 . di y y s , V p iz i y , 4

- S o l h ases s e arat o n o f 2 2 . o l ume co m o s t o n id p , p i , 7, 9 V p i i , 45. so l ut o ns 1 1 i , .

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