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GIELISSE, Peter Jacob M., 1934- INVESTIGATION OF PHASE EQUILIBRIA IN THE SYSTEM ALUMINA-BORON OXIDE-SILICA.

The Ohio State University, Ph.D., 1961 M ineralogy

University Microfilms, Inc., Ann Arbor, Michigan INVESTIGATION OP PHASE EQUILIBRIA IN THE SYSTEM ALUMINA-BORON OXIDE-SILICA

DISSERTATION

Presented in Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy in the Graduate School of the Ohio State University

By

Peter Jacob M. Gielisse, M. S.

The Ohio State University 1961

Approved by

Adviser Department of Mineralogy ACKNOWLEDGMENTS

The writer wishes to extend his sincere thanks to the many people without whose help the preparation of this dissertation would have been impossible. He is indebted in particular to his adviser, Dr. Wilfrid R. Foster, for his invaluable aid, advice and many kindnesses; to the other members of the faculty of the Department of Mineral ogy, Drs. Ernest G. Ehlers, Henry E. Wenden, and Rodney T Tettenhorst; and to his friend and colleague, Thomas J. Rockett. Acknowledgment is also made for financial support re­ ceived under contract No. AF 33(616)-3189, sponsored by Aeronautical Research Laboratories, Air Force Research Division, Wright Patterson Air Force Base, Ohio; as well as for aid received through a Mershon National Graduate Fellowship awarded to the writer by the Mershon Committee on Education in National Security for 1960-‘61'. It goes without saying that he is also most grate­ ful to his wife, Anna, for her excellent help and encour­ agement over the years. TABLE OF CONTENTS

Page INTRODUCTION ...... 1 PRESENTATION OF THE PROBLEM...... 3 LITERATURE S U R V E Y ...... 3 The Binary S y s t e m s ...... 3 The Ternary S y s t e m ...... 9 METHOD OF INVESTIGATION ...... 11 General Remarks ...... 11 Raw Materials...... 11 Preparation of Samples ...... 14 Heat Treatment of Samples...... 16 Phase Identification ...... 20 PRESENTATION OF EXPERIMENTAL D A T A ...... 22 The Binary System AI2O3-B2O3 ...... 22 The Ternary System Al2 0 3-B2 0>$-Si0 2 ...... 23 DISCUSSION OF RESULTS ...... 40 The Binary System AI2O3-B2O3 ...... 40 Compound stability ...... 40 Attempted synthesis of jeremejevite ...... 49 Liquidus d a t a ...... 36 Tentative phase diagram ...... 37 The Ternary System Al2 0 3-B2 0 3~Si02 ...... 62 Compound formation . 62 Attempted synthesis of sillimanite with boron oxide f l u x ...... 63 Phase compatibilities...... 7^ Liquidus data and primary fields ...... 77 Tentative Phase diagram ...... 80 SUMMARY ...... 84 BIBLIOGRAPHY ...... 86 AUTOBIOGRAPHY . 90

iii LIST OF TABLES

Table Fage 1. Compilation of important optical and x-ray d a t a ...... 25 2. Thermal data for firings in the system Na2 0—AI2O3—B2O3 ...... 26 3. Selected thermal data for AI2O3-B2OZ mix­ tures ...... 27 4-. X-ray results of selected firings on the stability of 2AI2OV.B2O3 in sealed platinum capsules ...... 29 5. Summary of firing data of selected tour­ malines ...... 30 6. Experimental data on attempted sillimanite s y n t h e s i s ...... 31 7. Compositional and thermal data for solid • state reactions in the system AI0O3-B2O2- S i 0 2 ...... • • • 33 8 . Experimental data for the determination of liquidus temperatures in the system alumina-boron oxide-silica ...... 36

iv LIST OF ILLUSTRATIONS

Figure Page 1 . Diagrammatic presentation of the experiment­ al work carried out in the system alumina- boron oxide ...... 42 2. X-ray diffractometer patterns: (A) the com­ pound 9AI2O3.2B2O3; (B) the compound 2AI2O3. B203 . 48 3. X-ray diffractometer patterns of magnesium tourmalines...... 55 4. X-ray diffractometer patterns of alkali tourmalines...... 5 5 5. Tentative phase diagram for the system alumina-boron oxide ...... 5 9 6. X-ray diffractometer patterns: (A) mullite; (B) sillimanite; (C) sillimanite synthesis. . 69 7» X-ray diffractometer patterns: (A) mullite; (B) decomposed alkali tourmaline; (C) sil­ limanite synthesis; (D) 9AI2O3.2B2O3. . . . 72 8 . Preliminary phase diagram for the system alumina-boron oxide-silica ...... 82

v INTRODUCTION

This investigation is concerned with the high tem­ perature equilibrium phase relations between the oxides of aluminum, boron and silicon at atmospheric pressure.

The elements silicon and aluminum list second and third respectively in abundance of all elements in crust- al rocks, and form, in coordination with oxygen, the ba­ sic building blocks of many minerals. Their oxides are well known for their natural occurrence as quartz and corundum. Not so abundant is the lesser known element boron, which in nature occurs chiefly in such minerals as axinite, tourmaline, dumortierite, kernite and borax.

Technologically the properties of the highly re­ fractory AI20^ and SiOg are well known. They become ex­ tremely important when combined into the compounds

3Al2 0^.2Si02 (mullite) and the various polymorphs of A^Oj.SiC^. They are of great value in the ceramic in­ dustry and are used in porcelahs and ceramic ware be­ cause they are highly refractory, have relatively low thermal expansion and good resistance to heat shock (Poster I960). Lastly, boron oxide has long been used as a flux and mineralizer in both ceramic technology

1 2 and experimental mineralogy, and boroaluminate has been suggested as a refractory.

Because of its great importance in silicate tech­ nology, the system A^O^-SiO^, has, ever since its first presentation by Bowen and Greig (1924), attracted large numbers of investigators and has consequently been changed and rechanged. However, the lack of available information on the phase relations between these oxides and both binary and ternary, stands in sharp con­ trast with the wealth of data accumulated over the years for the system AlgO^-SiOg*

An investigation of the system A^O^-B^O^-SiOg > therefore, is of importance - mineralogically and tech­ nologically - from both the theoretical and the prac­ tical point of view. PRESENTATION OP THE PROBLEM

The thermal relations of with many other ox­ ides, both refractory and non-refractory, are well known. Reliable phase diagrams depicting the equilib­ rium relations of boron oxide with these oxides are readily available (Levin et al, 1956). There are, how­ ever a few exceptions. The binary system for example, does not appear to have been thoroughly investigated heretofore, while the only work in the ternary system has been confined to liquidus determinations in the high silica portion of the diagram by Dietzel and Scholze (1954)* High vis­ cosity of the melts, especially in the high SiC^ reg­ ions, and high volatility of boron oxide, especially at the elevated temperatures necessitated by the re­ fractory nature of two of the oxides, is believed to account for the absence of systematic studies of phase equilibria in these systems to date.

It is in view of these considerations that the main purpose of this investigation, to develop a suit­ able phase diagram for the systems AlgOj-BgO^ and

5 within limits of the experimental equipment at hand, seems warranted.

Furthermore, a most vexing problem in petrology, that of the precise relationship between the polymorphs of AlgO^.SiC^, is bound to receive additional attention in any thermochemical investigation among the oxides in question. Subsequently experiments were carried out to synthesize the mineral sillimanite at atmospheric pres­ sure. They have, however, led to results which cast doubt on the synthesis reported in the literature. Fur­ thermore, a correlation was made between the product of this synthesis and that of the decomposition product of alkali tourmalines, which is believed to be a boron-con­ taining mullite. LITERATURE SURVEY

The Binary Systems

Of all three binary systems involved, only one, the system Al20 ^-Si0 2 , bas been systematically investigated and presented as a phase diagram. Knowledge of the other two binary systems is limited to direct knowledge from studies made of the thermal behavior of compositions of the oxides or compounds, or deduction from other, chief­ ly ternary systems. As already pointed out, the system AlgO^-BgOj will be described in the present study, while investigations in the system SiO^-B^O^ are currently be­ ing finished and prepared for publication by my colleague Thomas J. Rockett in the mineralogical laboratories of the Ohio State University.

The first reliable diagram for the system Alo0 -Si0o d $ £ was prepared as early as 1924 in a classic study by Bowen and Greig. It showed that mullite (3A120^.2Si02), as the only stable compound at high temperatures, melted incon- gruently to corundum and liquid at 1810°C. A eutectic be­ tween Si02 and mullite occurred at a composition contain­ ing approximately 5% A120^ at 15^5°C. Since the appear­ ance of this diagram, numerous investigators have published

5 6 revisions which resulted mainly from a difference in opinion over the exact composition, solid solution re­ lationships, and melting behavior of the compound mul­ lite. The diagram by Aramaki and Roy (1959)* which re­ sulted from a two-year examination of the system, is currently accepted as best depicting the true equilib­ rium relations and will be used in this presentation. It shows mullite, of variable composition, to melt con- gruently at 1850°C with the eutectic between mullite and at 1840°C. The composition of the mullite- silica eutectic appears unchanged, and its temperature is given as 1595°C.

The first attempt at formulation of a phase diagram

for the system S±02~^2^^ was 11181(16 indirectly by Morey and Ingerson (1937)• It was derived from data obtained

in a study of the system Ga0 -B2 0^-Si0 2 « It shows a li­ quidus dipping sharply from the melting point of SiO^ at 1713°C to 1000°C at 10% ^2^3 content, then remains

flat to a composition containing 55% ^2^3’ a^ 6r which it gradually slopes off to the melting point of at 470°C. In its essentials it is thus shows monotectic behavior at the B^O^ side and the possibility for an ex tensive two-liquid area. A possible liquidus point at 1200°C, deduced from solubility data by Foex (3.9 moles of Si(>2 per 100 moles of anhydrous B20^) would lie far above such a tentative liquidus. The experimentally de­ termined liquidus (Rockett and Foster, 1961) shows in outline remarkable conformity to the liquidus proposed by Uorey and Ingerson. The possible two-liquid area at 1080°C, however, appears greatly reduced. Experimental evidence for such a two-liquid area is almost unobtain­ able by conventional optical methods because of the great uniformity of the indices of refraction of the SiC^-BgO^ glasses. A two-liquid area is, however, greatly supported

by recent studies of the system Li20-B20j-Si02 by Sastry and Hummel (1959)• They found an extensive two-liquid area, coming as close as to within 1% of the Bo0 -Si0o d $ d side line. Conclusive evidence for the suggested possible existence of one or more B20j-Si0 2 compounds has not been obtained. Indeed, Dietxel's rules (194-2 and 1953) for compound formation would eliminate such possibility. One might argue, however, that, in as much as the Si ion is known often to act geochemically in the same way as the A1 ion, compound formation between Si02 and B20^ analog­

ous to that between A120 ^ and B20^ is not impossible, but is less likely.

Although numerous studies have been made of the ther­ mal behavior of alumina-boron oxide mixtures, no serious attempts appear yet to have been made to prepare a phase 8 diagram for the system. Boroaluminate compounds have long been recognized, and have been investigated as possible refractory materials. Aa? long ago as 1887 Mal­ lard identified the compound in some products prepared by Ebelman thirty-six years earlier. Benner and Baumann (1938) secured a patent on similar material which, as later work by Baumann and Moore (194-2) and by Scholze (1938) indicated, had the formula 9Alo0 .2Bo0_, rather 23 23 than 3AI2O2 .B2OJ. Scholze (1958) reported an additional compound A third boroaluminate is recognized as the rare pegmatite mineral jeremejevite, k l ^ p ^ B r p y A few single crystals of this mineral were first found associated with orthoclase and quartz on Mt. Soktuy in the Nertschinsk district of Eastern Siberia. Damour and

Websky as early as 1883 reported beautiful crystals from the Urals which, according to them, had the chemical form­ ula A^O^.I^O^. Ivlichel-Levy (194-9) has recorded the syn­ thesis of this mineral in the course of the attempted syn­ theses of tourmaline, and Kurylenko (1951) has reported the possible formation of jeremejevite in the thermal de­ composition of natual tourmaline. Structural work on single crystals of jeremejevite by Golovastikov et al (1955) indicates that jeremejevite may be a hydrated boroaluminate.

Foex (1 9 3 8) has provided a possible point on the liqudus 9 curve of the alumina-boric oxide system. He reported that the solubility of A ^ O ^ in at 1200 °G amounts to 1 ,0 5 per cent by weight (Figure 1, point F), Baumann and Moore (194-2) presented a pouring temperature curve for the alum­ ina-rich compositions, and a cone-fusion curve for the boron-oxide-rich compositions (Figure 1, short-dash curves). Baumann and Moore (194-2) and Scholze (1956) sr*e in agree­ ment as to the incongruent melting of But the temperatures assigned in these two studies are 1950°C and 1440°C - 20°C, respectively (Figure 1, points BM and S-l). Scholze (1956) placed the incongruent melting of - 20°C (Figure 1, point S-2). No data are available as to the temperature at which A^O^* ^jeremejevite) melts, except for a possible decom­ position of this mineral at red heat, as described by Damour and Websky (1883)*

The Ternary Systems

A partial investigation of the system Al2 0^-B20j-Si02 was carried out by Dietzel and Scholze (1954-) in the high

Si02 region of the system. Liquidus temperatures were ob­ tained on some fourteen different mixtures of compositions

as high as 30% in ^2^^ A^Oj* No ternary com­ pounds were encountered, but some evidence for a possible 10 solid-solution relationship between '^SiO^ and.

9Al2 0^.2B20j was given. Such a solid solution also seems to be supported by the work of Gelsdorf, et al (1958) and the synthesis of a boron-containing aluminosilicate by Letort (1 9 5 2), which - in composition - lies very close to the mullite-^A^O^^B^O^ join. METHOD OP INVESTIGATION

General Remarks

The study of any system containing ^2^5 as one °** phases is necessarily fraught with many difficulties. Liquid horon oxide vaporizes, predominantly as at all temperatures up to its boiling point(Soulen, 1956). This effect is, of course, especially pronounced at the relatively high temperatures necessary in this investig­ ation and would require chemical analysis of each fired sample if no special steps were taken to combat this prob­

lem. B2 0j-containing alumina-silica glasses are rather viscous, especially in the low Al^O^ region. This would rule out the full application of the standard quenching techniques. Alternatively, an essentially solid state approach was not always entirely satisfactory. The at­ tainment of equilibrium in systems containing highly stable compounds becomes a most vexing problem. The de­ viations from the more standard experimental approach will be treated more fully in following paragraphs.

Raw Materials

Since liquidus determinations were involved, it was of greatest importance that the reagents were of the

11 12 highest purity possible. While in the case of the oxides this prerequisite was rather easily attained by the ex­ clusive use of C. P. grade chemicals, the same cannot be said of certain of the compounds. In the latter case purity was assured by careful microscopic and x-ray dif­ fraction examination. Secondly, the extensive use of solid state sintering reactions required raw material to be ps fine-grained as possible. They were ground finer

than 2 0 microns, but were predominantly 1 0 microns or less.

The source of alumina was pure Linde Type A alpha alumina or Linde Type B gamma alumina, both of 99-9 per cent purity and average particle size of 0.1 micron. The source of silica was Malvern 10 micron grade, designated

No. 1250 Novacite, analyzing 99*5 per cent Si0 2 * which was leached in diluted hydrochloric acid to remove any traces of iron that might have been present. Pure crystal­ line water-free B^O^, prepared during this investigation,

and pure anhydrous fused B2 0 ^ were used as the source of Boron oxide.

Several attempts to prepare crystalline water-free

^2 ^ 3 were made, of which only the following appeared en­ tirely satisfactory: Small quantities of crystalline Bo0, 13 were obtained by experiments patterend after those of previous investigators (Me Colloch, 1937* Kracek, Morey and Merwin, 1938, and Rizzo, Weber and Schwartz, 1957)* These were used as seeds to induce crystallization of molten E^BO^. Complete conversion was attained within twelve hours at about 200°C in most cases. Optical studies showed no appreciable glass, while vacuum dehydration at 4-00°C for seven days yielded the anhydrous crystalline end product.

For the compounds, a supply of 2kX^p^*b^p^ was pre­ pared from the two oxides as outlined by Scholze (1958)» while a generous amount of electric-furnace ^kX^X^,2.b^>^y provided by the Carborundum Company, and some Norton Mul­ lite (composition JA^O^'^SiO^) also served as raw mater­ ials. Their essential purity was established by optical and x-ray methods. No Al^O^.B^O^ (jeremejevite) was avail­ able .

For certain selected experiments a variety of other raw materials was used: sodium borate decahydrate (Na^B^O^. lOH^O) as "Baker Analyzed Reagent" and DuPont Baymal Col­ loidal alumina of technical grade. Further, the following natural tourmalines were used: a blue (indicolite) and green variety from Governador Voladaros, Minas Geraeis, Brazil; a"Brazilian clear" tourmaline (achroite); a pink variety (rubellite) from Pala, California; and a brown tourmaline (dravite) from Gouverneur, New York. Through­ out the rest of this presentation the above two reagents will be referred to as borax and colloidal alumina, re­ spectively, while the tourmaline varieties will be dist­ inguished by their specific mineral names.

Preparation of Samples

The approximately one hundred different compositions prepared in the course of this investigation have been mixed in one of two ways, depending upon whether they contained free ^ 0 ^ or not. In preparing mixtures con­ taining no uncombined and consequently not sub­ ject to severe hydration, the ingredients were carefully ground and weighed (to the nearest tenth of a milligram) and thoroughly mixed by repeated rolling and stirring. Whenever tiny quantities were to be blended with larger amounts, the above method was followed by mixing in a fluid medium (xylene) and subsequent evaporation to dry­ ness .

Samples containing uncombined Bo0 required a special approach. To minimize possible hydration each batch was 15 weighed out in a specially constructed dry-air enclosure, then thoroughly ground and mixed in a mortar under xylene. The resulting slurry was dried at a temperature below the decomposition temperature of the organic fluid. Homogene­ ity of all mixtures was ascertained by careful optical examination. All batches, including some of the starting materials,and all fired samples were stored over desiccators.

Initially,samples large enough to permit x-ray dif­ fractometer investigation, were wrapped in platinum foil. Volatilization losses, especially at higher temperatures, led to the substitution of platinum capsules (about 1/16 inch inside diameter) which, after filling, were careful­ ly fused on both ends with a carbon arc welder. Evaluation of any weight losses due to leakage and subsequent vola­ tilization was made possible by careful weighing of the sample and the sealed capsule before and after firing. In order to minimize the bursting of these capsules, as experienced in the preliminary investigations, all cap­ sules were "crimped" just beyond the charge so as to in­ crease the volume available for gas expansion without rupture.Chemical analysis to assess compositional chan­ ges was thus avoided. This technique, however, required careful weighing of the specimen before and after firing 16 in order to determine whether a perfect seal had been made. Secondly, the phase relationships of the systems were be­ ing investigated at pressures somewhat greater than one atmosphere. These pressures, as determined by calculations from the size of the tube and the reported strength of platinum, could be as high as 20 atmospheres at 1000°C.

To promote reactions in those experiments that were solid state, or essentially solid state, the appropriate mixtures were pressed into disks under a pressure of ap­ proximately 5000 lb. per square inch. Where necessary a few drops of xylene were used as a binder and the pellets were carefully sintered to expel the gaseous constituents and prevent cracking of the sample before firing.

Heat Treatment of Samples

Many of the difficulties mentioned made it necessary to decide upon an experimental technique which, in cer­ tain aspects, differs from more conventional, well estab­ lished methods. Severe volatilization, hydration, high viscosity of melts, and high liquidus temperatures ex­ cluded the use of the otherwise much desired quenching method (Morey 1956). Liquidus temperatures in both the binary and ternary diagrams were obtained by what could 17 be called a modified quenching technique. This method of approach has already proven successful in many applic­ ations by previous investigators in these laboratories (e. g., De Pablo-Galan and Poster, 1959)* Instead of the usual glasses, uniform batches of the appropriate composition, prepared as described in a previous section of this chapter, were fired at selected temperatures. The liquidus temperature was then determined by braket- ing between the temperatures at which growth crystals develop in the melt and those at which a uniform glass is obtained. Deviations from uniformity within the in­ dividual charges - combatted in the standard technique by repeated fusing, crushing and re-fusing - might be expected. However, this tendency has not proven to be a difficulty in this investigation. No unreacted start­ ing materials were observed in any of the firings. In as much as the high temperature equilibria are approached from below, this method in effect eliminates metastable retention of the vitreous phase below the actual liquid­ us temperature, if crystallisation can be induced at all. Initially, all samples were held at temperature for six­ teen to eighteen hours. Later, when it was found that the reactions could be completed in shorter periods, the run time was reduced (see Tables 3 and 8). The high viscosity of the molten compositions rich in boron oxide and silica 18 made rapid quenching in a mercury hath unnecessary. Such practice would have been less desirable in any case, since accurate weight determination of the charge after firing would have been impossible due to the adhering mercury.

The solid-state sintering method was used to deline­ ate the compatibility relations in the ternary system, to determine compound formation and compound stability, especially in the binary system, and to carry out certain selected experiments related to the attempted synthesis of sillimanite and jeremejevite. Further, this method was resorted to in order to obtain data necessary to out­ line the extent of primary fields in that region of the diagram where liquidus temperatures lie outside the cap­ abilities of the available quenching equipment. In cert­ ain of these mixtures, especially those containing a liquid phase developed at all firing temperatures. Such experiments, therefore, cannot be regarded as solid- state sintering in the strictest sense. However, the pres­ ence of a vitreous phase will in most cases facilitate the reaction and consequently the growth of the reaction products. Due to the diversity of these experiments re­ garding starting materials, as well as time and tempera­ ture necessary to obtain complete reaction, no standard time-temperature schedule was adhered to. All details are, however, outlined in the appropriate tables. The pressed pellet technique was used in all solid-state sintering experiments.

An attempt was made to synthesize jeremejevite by hydrothermal means, using a small hot-seal pot bomb.

In general, all charges were fired in one of the fol lowing furnaces, depending upon type of experiment and range of temperature and accuracy required: a "Blue M" furnace, operating up to 1000°C; a GTobar alumina-tube furnace, capable of reaching 1600°C with a uniformity of - 5°C; and a vertical-tube quenching furnace, with an inner winding of platinum-40% rhodium wire and an outer-kanthal winding, usable up to 1650°0. This quen­ ching furnace is capable of a precision of - 2°C within the limits of its hot zone (3/4 inches long). The fur­ nace was precision-controlled for the duration of the run by an automatic "Oelectray" temperature-control unit. All temperature measurements were made with plat- inum-platinum-10% rhodium thermocouples which were fre­ quently calibrated against the melting points of gold (1063°G), diopside (1391.5°C), and palladium(1555°C). 20

(1063°C), diopside (1591.5°u), and palladium (1555°C).

Phase Identification

The polarizing microscope was used to determine the presence or absence of crystalline material and the kind of phase in the heat-treated samples. Fineness of grain size and sometimes almost identical optical properties generally precluded actual identification of the crystal­ line phases by optical means alone. The optical method alone proved insufficient, especially in distinguishing between mullite and the high-temperature boroaluminate 9Al202*2B20j, when crystallized from a melt. First, both compounds have closely similar optical properties. Measure­ ment of indices of refraction is made difficult by the fact that the extremely small crystals are embedded in glass. Further, there are no morphological criteria upon which a reliable differentiation can be based. The solid- solution relationship between mullite and 9A1~0,.2Bo0,, d o d 0 as described by previous authors (Scholze:1955» Gelsdorf: 1958), results in minute and almost imperceptable differen­ ces for crystals which differ little in composition.

For the various reasons outlined above, accurate phase determinations were made or confirmed by x-ray diffraction techniques. Both a high and a low-angle Norelco x-ray diffractometer with Geiger counter, CuK^ radiation and Ni filter, were used. Wherever only tiny amounts of speci­ men were available, glass-smears were used instead of the standard packing mounts otherwise employed. A complete set of standardized x-ray patterns of all those phases concerned made rapid identification and comparison pos­ sible. Selected optical and x-ray data on the various crystalline phases encountered in this study are presented in Table 1. PRESENTATION OP EXPERIMENTAL DATA

The Binary System A^O^-I^O^

The data employed in the preparation of a phase dia­ gram for the system AI2OJ-B2O2 were obtained from approx­ imately 135 distinct runs. Figure 1 shows the compositions and temperatures of the various runs. Preliminary runs in platinum-foil envelopes are denoted by squares, where­ as runs made in sealed platinum capsules are represented by circles. Solid circles indicate runs yielding crystals, or crystals and glass, while open circles are used for runs that yielded glass only. Figure 1 also contains a pouring-point curve (dashed), a cone-fusion curve (dash- dot), and a cone-blistering horizontal curve (dotted hori­ zontal), all determined by Baumann and Moore (1942). Also included are the melting points for .2B2O^, as re­ ported by Baumann and Moore (1942) and Scholze (1996), and the melting point of by Scholze (1956), desig­ nated BK, S—1, and S-2, respectively. Point F indicates a possible point on the liquidus, as determined in solubi­ lity experiments by Foex (1958), while C indicates the composition of the cone that blistered most in the ex­ periments conducted by Baumann and Moore (1942). Figure 5 shows the tentative phase diagram for the system as 23 described in this study, with, only the compositions and temperatures of the runs pertinent to the determination of the liquidus curve shown as small crosses. All per­ tinent supporting evidence has been tabulated in Tables 3 and 4, while the x-ray diffractometer charts of the two intermediate compounds encountered in this system are brought together in Figure 2. Further, x-ray diffrac­ tometer charts of variously treated alkali and magnesium tourmalines are compared in Figure 4 and Figure 3, respec­ tively, while their thermal treatment is separately ta­ bulated in Table 3- 'The x-ray patterns are of special im­ portance in evaluation of an alleged synthesis of Jere- mejevite by decomposition of tourmalines, and of an al­ leged synthesis of sillimanite.

The Ternary System Al^O^-B^O^-SiC^

The presentation of the data for the ternary system is similar to tnat of the binary system above. Figure 8 shows the various compositions investigated both in liquidus experiments (solid circles) and solid state sintering (open circles). Crosses indicate liquidus de­ terminations carried out previously by Dietzel and Schol­ ze (1954-) - Point G. depicts the composition of a possible limiting solid solution between mullite and 9AiPo ,2B 0 as described by Gelsdorf et al (1958). Figure 8 shows the compatibility joins, indicated by light solid lines, and the proposed (heavy solid lines) and deduced (dashed) boundary curves. Selected isotherms are indicated in degrees centigrade, superimposed. All data are tabulated in Tables 7 and 8. Results of an attempted sillimanite synthesis are given separately in Table 6. X-ray dif­ fraction results from these experiments are compared with those of the pertinent compounds in Figures 6 and 7* 25

TABLE 1 COMPILATION OF IMPORTANT OPTICAL AND X-RAY DATA*

Formula a 2b AS A9B2 A3S2 System Orthorh. Orthorh. Orthorh. Orthorh. Density 2.94 2.95 3.25-3*25 3.156 1.602 1.605 1.655-1*661 1.642-1.648 Indices 1.610 1.610 1.658-1.670 1.644- - 1.627 1.645 1.677-1.684 1.654-1.679 Optic angle 69° 57° 30°-25° 45°-50° Elongation pos. pos. pos. pos. Space group Cmc2i Cmm2 Pbnm Pmmm-Pba C2cm Cm2m Cmcm C222 Cmmm Unit cell a 7*68 14.8 7.43 7.49 A b 14.98 15*1 7-58 7-63 c 5*65 5*6 5.74 2.87

a 9b 2 - 9Ai205*2B203 A3S2 = 3Al205.2Si02 AS Al20^.Si02 A0Bcl = 2A10 d. B2^5

♦Sources: Winchel, A.N. Elements of optical mineralogy. John Wiley and Sons . New York. 1951. Scholze, H. Ueber Aluminiumborate. Zeitschr Anorg. Allg. Chernie 284, 272-277* 1956* 26

TABLE 2 THERMAL DATA FOR FIRING IN THE SYSTEM N a ^ - A l ^ - B ^

Composition Time Products (mole %) (hrs) (x-ray)

Boric oxide (B) - Sodium aluminate (Na) Compositions B Na

50 50 2# 960 sodium aluminate 50 50 2 885 sodium aluminate 43 57 2)6 960 sodium aluminate 43 57 2 885 sodium aluminate 37 63 2yk 960 sodium aluminate 37 63 2 885 sodium aluminate 30 70 2)6 960 sodium aluminate 30 70 2 885 sodium aluminate

Alumina (A) - Borax (Bx) Compositions A Bx

60 40 2 960 9A1205.2B205 60 40 1 900 alumina 40 60 1 900 glass TABLE 3 SELECTED THERMAL DATA FOR AlgO^-BgO MIXTURES

Composition* Time Temp. Products (wt.#) (hrs) C°cO

A a 9b2 A^B B

90 — — 10 18 1400 AqBp f A

90 - - 10 18 900

90 — - 10 16 600 A , A

80 - - 20 18 1400 AqB2* A

- - 18 1100 80 20 A9B2 80 - - 20 18 1000 a qb 2> a 2b 80 - - 20 17 800 A2B

70 - - 30 18 1400 AqB2 i A 70 - - 30 18 900 a 2b 40 - - 60 18 900 a 2b - 30 - 70 18 1400 A9B2 -- 80 18 1300 20 A9B2 20 - - 80 18 900 a 2b 10 - - 90 18 1200 A^B^i glass 10 - - 90 18 1100 A^B2, glass 10 - - 90 18 800 A2B , glass - - 1650 100 6 A9B2 - 100 - - 1A 1600 A^B2, a - - - 100 1 1600 A9B2 - - 60 40 8 1438 A^B2, glass

- - 60 40 12 1075 A^B2, glass

- - 90 50 8 1438 A^B2 , glass

- - 40 60 24 825 A2B , glass

- - 40 60 3 1650 A^B2» glass

- - 40 60 24 825 A^B2, glass 28

TABLE 5 — continued

Composition* Time Temp. Products (wt.%) (krs) c°c5 A a 9b 2 a 2b B

— — 35 65 3 1 6 5 0 A^B2 1 glass - — 30 70 3 1 6 5 0 A9B2, glass - — 30 70 8 1330 A9B2, glass

- — 30 70 24 825 A2B , glass —— 25 75 3 1650 A 9B2 ’ Slass — - 2 0 80 8 154-5 A9B2 ’ glass — — 2 0 80 8 14-80 A9B2’ elass — — 2 0 80 8 14-18 A9B2, glass —— 2 0 80 8 1337 AgB2, glass

- - 2 0 80 16 1175 A9B2, glass — — 2 0 80 16 1075 A9B2, glass - — 2 0 80 24 825 A2B , glass - — 10 90 8 1480 glass — - 1 0 90 9 1400 glass — — 1 0 90 8 1337 A 9B2 * 6lass — — 1 0 90 1 0 1 3 0 0 a 9B2 , glass —— 10 90 1 2 1175 A 9B2 fglass —- 1 0 90 24 825 A2B , glass —— 5 95 1 2 1280 glass — - 5 95 1 2 1218 A 9B2 , glass — — 5 95 24 990 A2B , glass — 5 — 95 22 1425 glass

- 5 - 95 25 1357 glass — 5 — 95 24 1330 glass

* All compositions expressed in terms of starting materials A = A1?0, B =. Bp0, A9B2= 9A*205.2B2O3 A2B = 2Al|O3.B203 TABLE 4

X-RAY RESULTS OF SELECTED FIRINGS ON THE STABILITY OF 2A1205.B205 IN SEALED PLATINUM CAPSULES

Composition* Time Temp. Products (wt.%) (hrs) (°c5 A A2B B

- 100 - 17 1560 A9B2 - 100 - m 1205 A9B2 - 100 - 16 1090 A9B2 — 100 - 12 1075 A9B2 - 100 - 12 1070 A9B2 - 100 - 12 1066 A9B2 - 100 - 120 1050 A9B2 - 100 - 11 1045 A9B2 - — 24 100 1040 A9B2 - - 24 100 1050 A2B - 100 - 24 1020 a 2b

- 100 - 96 1000 a 2b 70 _ 50 8 1070 A9B2 - 8 1050 70 50 A2B 70 - 50 42 1026 a 2b 70 - 50 45 1010 a 2b

70 - 50 188 1000 a 2b

70 - 50 46 980 A2B

70 - 50 70 965 A2b

* All compositions expressed in terms of starting compositions. Last five runs in platinum envelopes. A = A1205 A2B - 2A1205 B = B ^ ^ TABLE 5 SUMMARY OF FIRING DATA OF SELECTED TOURMALINES

Name Locality Time Temp. Products* (days) (°C)

Indicolite Min.Geraeis, 1 1300 mullite Brazil glass Indicolite Min.Geraeis, 4 1050 mullite Brazil glass Green Min.Geraeis, 1 1300 mullite tourmaline Brazi1 glass Green Min.Geraeis, 4 1050 mullite tourmaline Brazil glass Green San Diego, 3 1300 mullite tourmaline California glass Achroite "Brazilian 1 1300 mullite clear" glass Achroite "Brazilian 4 1050 mullite clear glass Dravite Gouverneur,N.Y. 1 1300 glass Dravite Gouverneur,N.Y. 4 1050 cordierit* glass

* Mullite to mean mullite with boron oxide in solid solution. 31

TABLE 6 EXPERIMENTAL DATA ON ATTEMPTED SILLIMANITE SYNTHESIS

Composition* Time Temp. Products ( grams ) (hrs) (°o;

A 4.0776 75 850 a1 20 3’ S 2.4024 mullite (trace) Bx 3.2400 M 0.2592

A 2.0388 96 840 AlpO, Si02 (?) ✓ S 1.2012 Bx 1.6200

A 4.0776 147 850 A12°3 S 2.4024 mullite (trace) Bx 3.2400 M 0.2592

K 3.000 23 860 mullite (?) Bx 1.875 M 0 .1 2 5

K 3.000 147 850 mullite (?) Bx 1.875 M 0.125

66'/2 890 mullite Ac 4.0776 S 2.4024 Bx 3.2400 M 0.2592 52

TABLE 6 — continued

Composition* Time Temp. Products (grams) (hrs) (°C)

Ac A.0776 AO 850 Si02 S 2.A02A

A A.0776 69 900 A1205, Si02 S 2.A02A H^BO^ NW 6.A800 M 0.2592

* A = A1205 M = MgO S = Si02 NW = Na2W04 Bx = borax A, = colloidal Alo0 c $ Mullite = boron-containing mullite 33

TABLE 7 COMPOSITIONAL AND THERMAL DATA FOR SOLID STATE REACTIONS IN THE SYSTEM Al^-BgOj-SiOg

Composition* Time Temp. Products (wt.%) (hrs) c°c5

940 A3SP 95 69 A3S2 B 5

48 1200 a ^s 2 » a 9b2 A3S2 91 B 9

A3S2 80.5 71 940 A3S2 ’ A2B B 19.5

80 1200 a ^s 2 * a 9b2 a 3s2 96 B 20

a ^s 2» A2B A3S2 80 13 900 B 20

40 40 1200 a 3S2✓ A9B2 B 60

A2B 90 69 940 A2B y S S 10

A2B 77 71 940 A2B, s s 23 54

TABLE 7 — continued

Composition* Time Temp* Products (wt.%) (lirs) (°c5

98 A-^ 2 5 1660 A9B2 S 2

96 1660 A9®2 3 A9B2 S 4

94 1660 a 9B2 3 A9B2 S 6

92 1660 A9B2 3 A9B2 S 8

■^9®2 88 3 1660 a9B2 » ■^■3^2 S 12

84 1650 a 9B2 3 A9B2 ’ A3S2 S 16

AqBp 84 164 1200 AqBpi B , C S 16

84 A9B2 60 1030 AqB2i S S 16

A9B2 84 78 970 AqB^y S s 16

84 164 950 a 9B2 A9B2 ’ B s 16 35

TABLE 7 — continued

Composition* Time Temp. Products (wt.%) (hrs) (°c5 a 9B2 74.5 164 1200 a q ®2 * ® ^ S 25.5 a 9b 2 74.5 164 950 A^B2 * s s 25-5

Aq B2 66 164 1200 A9B2 * B ^ s 34

A9B2 66 164 950 A ^ B ^ s 34

A3S2 57.1 3 1650 A9B2 , AjS2 A2B 42.9 a 3s 2 57.1 60 1030 a 2b , a ^s 2» a ^b 2 a 2b 42.9

A3S2 57.1 78 970 A2B, A^Sp, a ^b 2 a 2b 42.9

A9B2 83.2 48 1200 a 9b 2 » a ^s 2 A3^2 16.8 f* A 84.4 48 1200 AqB2 » A^Sp f A B 10.7 s 4.9

AS 50 110 1300 V 2 B 50 * All compositions expressed 'In terms of starting materials S=Si02 A =A1205 A9B2»9A1205.2B205 A2B=2A1205.B205 B=B2C>5 AS=Al205.Si02 A 5S2=*3Al205.2Si02 36

TABLE 8 EXPERIMENTAL DA^A FOR THE DETERMINATION OF THE LIQUIDUS TEMPERATURES IN THE HIGH BORON OXIDE PORTION OF THE SYSTEM ALUMINA-BORON OXIDE-SILICA

Composition Time Temp. Products (wt.%) (hrs) c°c5 AlgO^ BgO Si02

30 60 10 16 1500 crystals, glass

20 70 10 14 1475 glass 20 70 10 5 1450 glass 20 70 10 19 1450 glass 20 70 10 10 1440 crystals, glass 20 70 10 3 1430 crystals, glass 20 70 10 22 1425 crystals, glass 20 70 10 22 1420 crystals, glass 20 70 10 17 1400 crystals, glass

20 63 15 19 1450 glass 20 65 15 10 1440 crystals, glass 20 65 15 3 1430 crystals , glass

20 60 20 23 1455 glass 20 60 20 8 1450 glass 20 60 20 3 14-35 crystals, glass 20 60 20 22 1425 crystals, glass 20 60 20 17 1400 crystals, glass

20 50 30 16 1500 glass 20 50 30 14 14-75 crystals, glass 20 50 30 26 1400 crystals, glass 57

TABLE 8 — continued

Composition Time Temp. Products (wt,%) (hrs) (°c5 A12°3 B2°3 Si02

20 40 40 10 1515 glass 20 40 40 120 1480 crystals, glass 20 40 40 9 1450 crystals, glass

15 75 10 21 1425 glass 15 75 10 9 1415 crystals, glass 15 75 10 18 1400 crystals, glass

15 70 15 19 1430 glass 15 70 15 26 1415 crystals, glass 15 70 15 18 1400 crystals, glass

15 50 55 140 1465 glass 15 50 55 19 1450 crystals, glass 15 50 55 5 1430 crystals, glass

10 80 10 26 1450 glass 10 80 10 9 1400 glass 10 80 10 16 1340 glass 10 80 10 14 1555 crystals, glass 10 80 10 8 1525 crystals, glass 10 80 10 9# 1300 crystals, glass

10 70 20 22}k 1450 glass 10 70 20 15 1360 glass 10 70 20 16 1340 crystals, glass 38

'TABLE 8 — continued

Composition Time Temp, Products (wt.%) (hrs) (°c5 A120^ B20^ Si02

10 60 30 17 1400 glass 10 60 30 12 1390 crystals, glass 10 60 30 7# 1385 crystals, glass 10 60 30 12 1375 crystals, glass 10 60 30 13 1360 crystals, glass

10 40 50 26# 1460 glass 10 40 50 9 1450 glass 10 40 50 18 1440 crystals, glass 10 40 50 3# 1455 crystals, glass 10 40 50 21# 1425 crystals, glass 10 40 50 12 1400 crystals, glass

5 80 15 44 1525 glass 5 80 15 4 1310 crystals, glass 5 80 15 40 1290 crystals, glass 3 80 15 4 1275 crystals, glass 3 80 15 46 1240 crystals, glass

5 63 30 44 1325 glass 5 65 3° 4 1310 crystals, glass 5 65 30 20 1290 crystals, glass 3 65 30 4 1275 crystals, glass 5 65 30 9# 1080 crystals, glass 39

TABLE 8 — continued

Composition Time Products (wt.%) (hrs) A1205 B205 Si02

2.5 90 7.5 19 1200 glass 2.5 90 7.5 22 1190 glass 2.5 90 7.5 2 1150 crystals, glass 2.5 90 7-5 2 1105 crystals, glass 2.5 90 7-5 2 1065 crystals, glass

2.5 6 6 .2 5 31.25 : 46 1240 glass 2.5 6 6 .2 5 31.25 24 1200 crystals, glass 2.5 66.25 31.25 23 1165 crystals, glass 2.5 6 6.25 31.25 37 1100 crystals, glass 2.5 6 6.25 31.25 9/2 1080 crystals, glass DISCUSSION OF RESULTS

The Binary System AI2OJ-B2O2

Compound stability. — The study of the system A^O^-*- ^2^3 was as a reconnaissance of the conditions of compound formation between A ^ O ^ and ^0^. A series of compositions at 10% intervals (by weight) was pre­ pared from H^BOj and gamma alumina, as well as several selected molecular compositions, such as 3Al202*®2^3 and AI2OJ.B2OJ. All of these were dry pressed as thin as one-inch disks and fired at 900°C. The only boro- aluminate encountered proved to be 2Al20^.B20^. Although these results indicated the likelihood of a reasonably fast solid-state reaction in the system, even at low temperatures, they had not successfully produced either of the compounds 9Al20^.2B20^ and A^O^-I^O^* A broader coverage was obtained when eighty-one samples (nine com­ positions at 100° intervals between 600°C and 1400°C) were fired in small platinum envelopes (see Figure 1). For these runs anhydrous fused was substituted

Hj BOj . From x-ray diffraction data on these mixtures, there became apparent three regions in which the be­ havior of samples indicated varying degrees of incom­ plete reaction: - A region of no observed reaction at and below 600°C.

40 Figure 1. Diagrammatic presentation of the experimen­ tal work carried out in the system alumina-boron oxide. 42 — i------1------1------1------1------r s ALL LIQUID AREA 20 0 0 - \ BM O GLASS I SEALED) • CRYSTALS, OR CRYSTALS AND GLASS (SEALED) 1800 ■ CRYSTALS, OR CRYSTALS AND GLASS (UNSEALED)

• • • • 1600

S-l 0 • • 1400 ■ ■ ■ ■ • mo ° H • AREA OF OBSERVED O • • o

FORMATION OF 9AI 2 ° 3 * 2 0 2°3 I 200 't!

TEMP. °C S -2 1000 II i AREA OF OBSERVED

FORMATION OF 2AI 2 ° 3 B2 ° 3 8 0 0

6 0 0 AREA OF NO OBSERVED RE CTION

4 0 0 200 t ± i. 80 Al 2 03 10 20 30 40 50 60 70 90 B2°3 WEIGHT PERCENT I \ \ I A AdB2 A2B B 4 $

Only patterns for corundum were obtained here. The time required Tor solid-state reaction at these low temperatures must he far in excess of the eighteen hours utilized in these experiments. - A region of observed formation between 600°C and an upper temperature of about 1000°C. - A third region in which was found as the only crystalline compound for all compositions at tem­ peratures higher than 1000°C. This behavior is in line with the incongruent melting of These firings, subject to volatilization, and therefore only of an exploratory nature for the formulation of a phase diagram, nevertheless, did result in the synthesis of two of the three alleged compounds. They also clarified some of the melting characteristics of the intermediate compounds, but failed to produce the compound Alo0 .Bo0 . Neither did they answer the question why the compound forms only at temperatures above 1000°C.

A new approach, intended to resolve these points, in­ volved the study of selected mixtures in the system ^ £ 0 - below 1000 °G, thus taking advantage of the fluxing action of soda. Using specially selected A120 j-n&2^ 2B2OJ and Na2 0.Al20^-B20j mixtures, it was hoped to pro­ duce all three reported aluminum borate phases. Selected 44 compositions on the "join" were made up and fired at both 885° and 960°C for two to three days. None of these showed any reaction at all, except for the melting of while x-ray diffraction showed a con­ sistent sodium aluminate pattern. Some additional com­ positions, this time on the "join" and at 960°C gave as the only significant result the form­ ation of 9Al2 0^*2B2 0^ from a mixture of 0 .6 mole % A ^ O ^ and 0.4 mole % borax. The same composition at 900°C, how­ ever, failed to react. Data on runs of the above series are tabulated in Table 2.

The behavior and mutual relationships of the compounds above their temperatures of formation also posed many problems. Baumann and Moore (1942) assigned a melting temperature of 1930°G to the compound , where­ as Scholze (1956) indicated tnat the compound melts in- congruent ly at 1440°C. Tests conducted in this investig­ ation favor the higher melting point, since no fusion was observed in a sealed-capsule sample of 9Alo0_.2Bo0, which had been held at 1650°C for six hours. A similar run in an unsealed platinum envelope resulted in partial decomposition with the formation of corundum. In view of the failure of the sealed-capsule charge to decompose similarily, the corundum formation is attributed to loss 45 of through volatilization, rather than to actual melting. It is possible that such a decomposition was erroneously interpreted by Scholze as the melting phen­ omena. Moreover, charges of high boron oxide content which were fired at 1650°G developed thin, needle-like crystals which corresponded optically to X-ray diffractometry proved the same. Experiments de­ signed to test the stability of 2A1o03.B„0_ have in- 2 5 2 5 dicated an incongruent melting temperature of approx­ imately 1055°C. This is in essential agreement with the value 1050 - 20° given for this compound by Scholze.

A puzzling relationship, and one which has not been explained with entire satisfaction, concerns the respect­ ive temperatures of formation of 9A1o0,.2B_0_ and 2Alo03. 2525 2 5 B20^. The compound 9Al2 0^.2B^0 ^ has not been synthesized from the anhydrous oxide mixtures below 1000 -1 0 5 0°C, whereas the compound SA^O^.BgO^ fcas not been synthesized above this temperature range. The results of x-ray dif­ fraction studies on selected firings of mixtures of

70 Al^O^-JO (weight per cent) at approximately 10 ° intervals between 96>0°C and 1070°C are shown in Table 4. Results of similar firings, but employing pure 2Al20^.

^2®$ as starting material, are also shown in Table 4. Table 4 shows a definite range of temperatures, between 46

1050° and 1045°, in which a mixture of ^k^L20 y 2 B 20^ and could be identified. This relationship was tentatively attributed to a simple case of polymorphism between two crystalline forms of a single compound, rather than a case of two compounds of different com­ position and stability. Similarity in the x-ray patterns of the two phases (see Figure 2) could support such an interpretation. Even the persistence of the "9Alo0_.2B~0 " d o d 0 phase during prolonged holds at temperatures below 1000°C is compatible with this view if one assumes that inversion to the a2kl.^Py'£>rP^n low-temperature phase is extremely sluggish. However, in melting experiments on large grains of in sealed platinum tubes at 1205°C it could be optically observed that a glass phase had "exsolved" as blebs or pellets with a definite crystallographic con­ trol crudely parallel to the long axis of the original grains. An x-ray pattern of the same material showed Identical runs at 1020° and 1050°G show on­ ly the incipient appearance of these blebs. Furthermore,

9Al20^.2B2 0^ has been formed with the aid of a borax flux at temperatures below 1050°C, but never lower than 950°C, and hydrothermally from a mixture of Alo0 and Bo0, at d. 0 d 0 4-4-0 °C. Thirdly, the formula accepted for 9A1 0 .2Bo0 by 2 5 ^ 3 both Baumann and Moore (1942) and by Scholze (1956) could 47

Figure 2. X-ray diffractometer patterns:

(A) The compound 9Al20^.2B20^ (B) The compound JUUI

*• " 40 BO " 7030

03 be advanced as supporting evidence for two separate com­ pounds .

It does not appear that the above results validate a polymorphism hypothesis. In the absence of data sup­ porting such a hypothesis the two phases were accepted as two distinct compounds, as proposed by Scholze (1956) and the experimental results will be accepted as proof for the extreme sluggishness of the highly refractory to form below 1050°C. Apparently the com­ pound 2AI2O2.B2O2 ^orms muck more readily than the re­ latively complex 9A120 ^*2B20^. When ^2®$ is excess the 2:1 proportion, 2Al20^»B20^ forms at temperatures below its melting point and the excess B„0 is volatil- ized. When there is a deficiency of B~0,, 2Alo0 ,B~0, 2 5 2 5 d 5 forms initially, leaving an excess of Alo0,, which will 2 0 not react readily in the solid state to form 9Alo0 .2Bo0 2 5 2 In solid state reactions such behavior is not at all un­ common. It was, for instance, not until recently that the compound mullite was reported to be synthesized by Letort (1952) at a temperature as low as 750°C.

Attempted synthesis of .jereme.jevite.— Attempts to synthesize the compound Al20^.B20^, the mineral jeremeje vite, at one atmosphere by prolonged sintering of Al^.0 2 5 50 and Bo0 in the appropriate proportions, either yielded d 5 2Alo0,.Bn0, or resulted in no observed reaction. In runs d O d. $ up to one month in duration at temperatures between 600 and 900°C no jeremejevite was encountered. It was thus inferred that the compound was probably of limited tem­ perature stability, existing only at temperatures at which the reaction rate between the oxides is too low to be practicable. This would be in line with the find­ ings of Damour (1883) who observed that the mineral, on heating to red heat, lost 33^ of its weight, chiefly boric acid, but afterwards still indicated a strong Bo0 d 3 content. No mention was made of what the fired product consisted of. If jeremejevite has a place in the diagram, the decomposition product might very well have been 2A12^5* B2^3* Unfortunately it was impossible to secure a natural sample of this extremely rare mineral to verify such a hypothesis. Furthermore, efforts to duplicate Llichel- Levy's (19^7) synthesis of the compound by the hydrotherm­ al technique in a high-pressure bomb for several weeks at h5 0°C were not successful.

Yet a third approach patterned after Kurylenko (1951) was tried. Kurylenko found that, contrary to the beliefs of Doelter (1895)1 magnesium tourmaline (dravite) trans­ forms into a mixture of amorphous SiO^, corundum, enstatite 51

(MgSiO^) and probably jeremejevite. His x-ray investig­ ations were believed to confirm these findings in the temperature range from 1030 to 1350°C. In the present study decomposition experiments were conducted on dravite and various alkali tourmalines at both 1030 and 1300°C (see Table 5)* Surprisingly enough, none of the alleged phases were encountered. The magnesium tourmaline at 1030°G gave the crystalline phase Mg^l^Si^O^g (cordier- ite) and all glass at 1300°C (see Figure 3)* From a cryst­ al-chemical standpoint this would indeed be a more likely possibility, in as much as the basic structural unit of tourmaline, the ring, remains unchanged in cor- dierite, but would have to form Si 0, chains in ensta- n 3n tite. In contrast to the behavior of magnesium tourmaline, all the alkali tourmalines gave, at both temperatures, x-ray diffraction patterns which closely resemble, but significantly differ from, the mullite pattern ( see Fig­ ures 6 and 7 )• The phase produced is believed to be a boron-containing mullite. Because of possible relations between these findings and those obtained during experi­ ments on synthetic sillimanite production, these patterns are more fully discussed under the appropriate paragraph of the next chapter.

It is thus by no means certain that jeremejevite can 52

Figure X-ray diffractometer patterns of magnesium tourmalines: (A) Before firing (B) After firing at 1050°C (cordierite) (C) Natural cordierite (Norway) 53

T' m •

i i «

• . * i

* i Figure 4. X-ray diffractometer patterns of alkali tourmalines: (A) Before firing (B) After firing at 1300°C and HF leach (C) After firing at 1050°C (D) After firing at 1300°C. 55

L. 56 form at atmospheric pressure. The only reliable syn­ thesis of jeremejevite, that of Michel-Levy (194-9)» in­ volved a pressure of 4000 kilograms per square centi­ meter. It is interesting to note that Golovastikov et al (1955)i when working out the structure of jeremeje- vite, found definite anomalies in the electron density in certain of their Patterson sections. Their inter­ pretation was that in jeremejevite certain B atoms are replaced by H atoms, resulting in the formula Al^B^O^^(OH)^. In view of the foregoing uncertainties as to the precise stability conditions and chemical constitution of jere- mejevite, the relations of jeremejevite to the system would be entirely hypothetical. Accordingly, no attempt has been made to incorporate a possible com­ pound in the phase diagram of the system (Fig­ ure 5)*

Liquidus data.— The sealed-capsule results permitted the delineation of a continuous liquidus curve as shown in Figures 1 and 5 (solid curves). The wide divergence of this experimental liquidus curve from the pouring- temperature curve by Baumann and i^oore (short-dash curve, Figure 1) is striking. On the other hand, the solubility of alumina in B20^, as determined by Foex at 1200°C (point F, Figure 1), is in good agreement with the determined 57 liquidus. A striking feature of the system is the relative insolubility of Al^O^ in even at elev­ ated temperatures.

Tentative Phase Diagram

The thermal data plotted in Figure 1 and recorded in Tables 3 and 4 permitted the formula cion of a phase diag­ ram. Such a diagram, believed to be correct in its essent­ ial features, appears as Figure 5* Only the compositions and temperatures of the liquidus runs are indicated by small brosses. The diagram follows the two-compound (9Alo0 . £ 5 ^1*2^3 and 2Al2 0^.B20^) proposal by Scholze (1956), rather than the alternative explanation, based upon polymorph­ ism in a single compound, as outlined in an earlier para­ graph. The melting point of at approximately 1950°C is taken from the work by Baumann and ivloore (1942). Their thin sections of boroaluminate heated to 1950°C showed at least a partial melting of the crystals to alumina and high boric oxide glass. Baumann and Moore's (1942) pouring curve (Figure 1) at first glance seems to contradict these findings. It should, however, be remem­ bered that the possiblity of pouring a batch may remain even after the onset of formation of the primary crystals. It will be recalled that in the present study no melting Figure 5. Tentative phase diagram for the syst alumina-boron oxide. i 1--- 1--- 1--- r i r i r 2000 A+LI0U10 1950 LIQUID

1800

1 6 0 0 -

1400

_ A AgB2 + LIQUID + 1200 UA9 B2

TEMP • c 1000 1035

8 0 0 A2 B + LIQUID

6 0 0

4 7 0 4 0 0 >2B + B _L J L _ l L J L At * 0 3 10 20 30 40 50 60 70 80 90 b 203 WEIGHT PERCENT I 1 I A AgBg A 28 B 60 was observed as high as 1650°C. Accordingly, the phase relations in the diagram above 1650°C have been repres­ ented by a dashed curve. The experimental liquidus above 154-5°C has been similarly extrapolated as a smooth con­ tinuous curve to the melting point of alumina at 2020°C. From the rather steep trend of the liquidus it might be conjectured that a two-liquid area of immiscibility might intervene in this extrapolated region. Such a possibility would indeed be extremely likely if Baumann and Moore's (1942) pouring curve proved to be close to the liquidus curve above 1650°C. Even the relative flatness of the extrapolated liquidus curve would not entirely exclude this possitility. However, boron oxide is known to behave towards other oxides in much the same way as does silica towards the same oxides. Silica displays no immiscibility relation towards alumina in the liquid region of the Alo0 ■ Sd02 system, although it does have'an extremely flat li­ quidus near the mulli'ce composition. By analogy, it seems reasonable to conclude that boron oxide also lacks an immiscibility relation towards alumina in the Al^O^-

®2^3 sys'tem*

The possibility of a eutectic horizontal between and 2Al20^.B20^ at about 200°C was suggested by Baumann and Moore (194-2) on the basis of blistering of cones rich in (dotted horizontal, Figure 1). Experiments car­ ried out in this study have given no evidence in support of such a relationship. The proximity of the liquidus to the vertical at 100 % Bo0 ^ would hardly allow any but a monotectic behavior. If a eutectic does exist, it must be very close in composition and melting temperature to that of the pure-end member, E^O^.

Complications were suggested by the possibility of the existence of a polymorphic inversion in the end mem­ ber Kracek, Morey and Merwin (1958) described a possible inversion due to crushing crystalline ^2^3* More suggestive was the fact that there were found to exist three distinctly different x-ray diffraction pat­ terns, presumably all for crystalline boron oxide.(Me Cul loch:19571 Berger:1953» and Senkovits and Hawley). The x-ray diffraction patterns of the crystalline P1*0- posed and used in this investigation have been consistent ly identical with those of Berger (1933)* Through the courtesy of the Champion Spark Plug Company, Detroit, Michigan, x-ray diffractometer charts were obtained on crystalline temperature and at 44-0°C, just 30° below the melting point. The patterns proved identic­ al, except for a small extra peak in the room—temperature pattern, which was found to coincide with the main peak 62 of H j BOj , due to surface hydration during exposure. Un­ less the change is so subtle as to escape x-ray detection, or occurs above 440°G, it is concluded that no inversion exists.

Although it was at first intended to incorporate the compound A^O^.B^O^ in the tentative diagram, such a com­ pound has been omitted from the final version (Figure 5) • It is the feeling of the writer that at present, due to the uncertainty as to the stability and composition of jeremejevite, as discussed in a previous paragraph, such omission is warranted.

The Ternary System Al^O^-J^Oj-SiC^

Compound formation in the ternary system.— The only known basic aluminum borosilicate is the mineral dumor- tierite. Its composition was originally given by both

Dana (1914) and Kintze (1897) as 4 A l . p O 3SiC>2 • Later, when water was regarded as an essential constituent of this pegmatitic mineral, Dana (1954) assigned the formula

8Al2 0^.B2 0^.6Si0 2 *H20 and regarded both boron and water as variable in amount but essential in character. Qual­ itative spectographic analysis of the Ruby-Range dumorti- erite in Montana, as described by Graham and Robertson 63

(1 9 5 1) indicated silicon, aluminum and boron as the es­ sential constituents. Claringbull and Hey (1958) report­ ed approximately the same results for a brown transpar­ ent gem stone from Ceylon and gave a chemical analysis which agreed well with the formula 7(A1, Fe)2®3*®2^3* SSiO^. They found only 0.4% water, which is far less than that required by the minimum number of equivalent (OH) positions in the space group would require. They attribute the water content to either absorption or incipient alteration. It thus appeared possible that dvimortierite could be encountered in the present invest­ igation. Hone of the x-ray diffraction patterns run on the solid-state-sintering samples, however, revealed such a phase; nor has evidence been found during the op­ tical investigation of the liquidus runs. The occurrence of dumortierite as slender prisms, needles, or fibers could possibly have been mistaken for that of mullite or 9Al20^«2B2 0^. However, its pronounced pleochroism, negative optical elongation and relatively low birefring­ ence stands in sharp contrast with the properties ob­ served on the morphologically similar crystals observed in the glass of the liquidus samples. The frequent oc­ currence of tourmaline and sillimanite in association with dumortierite in gneisses and schists, and the oc­ currence of the latter in pegmatite bodies suggests that 64 - pressure or hydrothermal action, or both, may be required for the growth of dumortierite. Both tourmaline and sil- limanite have been synthesized by Miche 1-Levy (194-9 and 1950) under water pressures of 900 and 50 kg/cm^, respect­ ively.

Except for an empirical approach by Dietzel (194-2 and

1 9 5 3)» theoretical calculation s regarding the possibili­ ties of compound formation between certain oxides are as yet not available. Dietzel showed that compound formation between certain oxides in silicate systems could be de­ duced from general crystal-chemical properties of the ca­ tions in question. He introduced the concept of field- strength, z/a^, where z = valence of the cation a = radius of cation + radius of oxygen ion. 2 He then calculated A z/a for various possible oxide com­ binations. Ternary compounds would form if the smallest p difference between the A z/a values was equal to or less than 0.05. In the system this value, using the ionic radii of Goldschmidt, becomes 0.05 or just be­ low this, therefore, would also rule out the likelihood of compound formation. 65

Attempted Synthesis of sillimanite with boron oxide flux.— In as much as the well known controversy over the stability relations of sillimanite and its possible place in a phase diagram involving and SiO^ has not yet been settled, it was thought advisable to extend the investigations of this study in that direction.

i5ver since Bowen and Greig (1924) found mullite OA^O^^SiC^) to be the only stable phase at room temp­ erature in the system A^O^-SiC^, the stability relations of sillimanite have been in doubt. It remained a perplex­ ing problem that sillimanite, so abundant in natui'e, es­ pecially in high-grade metamorphic rocks, could not be as­ signed a place in the appropriate phase diagram. Incontrast mullite, found only in buchites and some porcellanites, is extremely rare in nature, yet it appears in the phase dia­ gram. Support for the stable existence of sillimanite at atmospheric pressure is afforded by thermodynamic calcul­ ations made by Kelley (194-9), Miyashiro (1953), and Thomp­ son (1955), as well as by the so-called geo-experimental phase diagrams by Schuiling (1957) and Hietanen (1956). However, most experimental work appears to contradict these findings: Clark, Robertson, and Birch (1957) de­ termined the kyanite-sillimanite boundary at high pres­ sure and infer that andalusite and mullite are the stable 66 phases at low pressure; Kennedy (1955) claims a complete solid solution between mullite and sillimanite with mere increase of water vapor pressure; while the synthesis by Yoder (1958) and Michel-Levy (1950) also required water pressure.

A second experimental approach, which appears to have received less attention, makes use of mineralizers. The first attempts by this method, made by Bowen and Greig (1924), were without success. The claims by Balconi (1941), and Shears and Archibald (1954), found to be the most promising , were reinvestigated in this study. Since sil- limanite and mullite have nearly identical optical pro­ perties and x-ray diffraction patterns, great care had to be excercised in their experimental distinction. The criteria for differentiation on the basis of powder x-ray methods, given by deKeyser (1952), Scholze (1958), and Neuhaus and Richartz (1958), were applied. The patterns given by these authors were essentially in agreement with the patterns on some natural sillimanite and Horton mul­ lite used for comparison in this study.

In duplicating Balconi*s experiments (1941; for com­ position, see Table 6, #1), only slight reaction was ob­ served. Although the x-ray pattern of the reaction product 67 somewhat resembled that of sillimanite, in no case was it clear enough to warrant indisputable identification. The region from 2 9 - 60° to 28 - 80°, where clear distinction between mullite and sillimanite is possible, gave especi­ ally poor resolution. A new approach was tried when, in the otherwise identical batches, the regular Al^O^ was re­ placed by cooloidal alumina. This time, complete reaction resulted. It was orty after repeated washing in HF solu­ tions that the x-ray diffraction pattern (Figure 6C) was clear enough to be reliably identified. Optical invest­ igation revealed tiny, but well formed, needle-like cryst­ als, about 20 microns long and 4 microns wide. They show parallel extinction and a very pronounced positive elong­ ation. Careful optical work in both white and sodium light showed the indices for the long (V) direction to be be­ tween 1.64 and 1.65* and between 1.60 and 1.61 for the short (ot ) direction. Identical experiments in which Na^WO^, or no flux at all, was used, together with those patterned after Shears and Archibald (1954-), showed very poor react­ ion, or no reaction at all. Details of all firings are tab­ ulated in Table 6.

Figure 6 shows the x-ray diffraction pattern taken on the synthetic material (C), as compared with those of pure mullite (A) and sillimanite (B). At first the pattern was Figure 6. X-ray diffractometer patterns (A) Synthetic Norton mullite (E) Natural sillimanite (C) Product of sillimanite synthesis. i 70 believed to resemble that of sillimanite in which all € / 0 lines were shifted slightly tov/ards higher 2 jangles. This could indicate a sillimanite with the C axis short­ ened due to the replacement of the silicon ion by the much smaller boron ion. However, the detail of the pattern be­ tween 2$ - 60 - 80 never allowed unambiguous identification. Later it was found that there existed great similarity be­ tween the above pattern and that obtained on the decompos­ ition product of alkali tourmalines on the one hand, and mullite on the other hand (Figure 7)* Consequently, the possibility of a mullite with boron in solid solution was entertained. Such an interpretation would receive added support from Dietzel and Scholze (195^) and confirmation by G-elsdorf et al (1958). The former found proof for a partial solid solution between mullite and in which silicon would be replaced by boron. The present findings, pictured in Figure 7» indeed show a definite shift for most of the lines towards higher 2@ angles. This is especially pronounced for reflection with indices in which £ £ 0. Such shifts could be attributable to various factors: first of all, to an error in experimental approach or procedure. For this reason all diffraction patterns were taken on similarly mounted samples under strictly identical machine settings and were run on two diffractometers. Sec­ ondly, thermal treatment of the smaples: the samples yielding 71

Figure 7» X-ray diffractometer patterns: (A) Synthetic Norton mullite (B) Decomposed alkali tourmaline (C) Product of sillimanite synthesis (D) The compound O * .OS os OS 0 4 0 9 OS -v v-%- ' / vr; --jp.'S i * • I 'I 5 ‘ I * ; “ ■ * <' i h i ■i i1

> ■'V

-^V A '-V

r n r*“ry r - | I - 73 the patterns of Figure 7 A, B, and C were synthesized at 1800°, 1300° and 900°C, respectively. This could also ac­ count for the variation in line width of the diffration curves (Scherrer effect), and the noted absence of resol­ ution into , and doublets in the B and C patterns. However, careful examination of the x-ray patterns on the decomposition products of alkaline tourmaline at both 1030 and 1300° did not show the slightest shift in line position. This, therefore, does not appear to support the possibility of temperature dependency. Lastly, the chemical composition of the mullite: it has been established by many investigat­ ors, such as Gelsdorf et al (1936 and 1958)* that mullite can take a great number of elements into solid solution with subsequent observable effects on the lattice. Although no chemical analyses of the various products were made, it is held here that the phase in question, although giving an x-ray diffraction pattern very similar to sillimanite, is essentially a mullite with in solid solution. It is of special interest to note here the findings of Letort

(1952) upon firing a mixture of A ^ O ^ and SiC>2 (mullite proportions) with flux at 930°C: the optical character­ istics and indices of his crystals were identical with those of the crystals obtained in this study in the duplication of the Balconi synthesis. Furthermore, a chemical analysis in­ dicated 12.16 per cent B^O^, while an identical mixture, 74- wit hout the flux, proved to be mullite. The latter fact was proven by infrared absorption measurements.

It must thus be concluded that no evidence for the formation of sillimanite at atmospheric pressure could be found in this study. For the present, the apparent anomaly in nature, alluded to in the beginning of this paragraph, can probably be best explained by the recent findings of Yoder (1955) : the liquidus field of mullite is greatly re­ duced with increase in water pressure.

Phase compatibilities.— Joins and compatibility tri­ angles were determined by the use of solid-state sintering reactions exclusively. The high liquidus temperatures in that portion of the diagram of interest for such an invest­ igation prohibited the use of liquidus data. X-ray diffract­ ion patterns were run on all mixtures after heat treatment to determine the coexisting phases. In most cases, especi­ ally those in which 9Al20^.2B20^ and mullite were involved, x-ray diffraction patterns had to be run on the mixtures before and after firing in order to enable observation of the sometimes very subtle, but, nevertheless, very import­ ant changes. Optical investigation was used as a second check, but did not prove valuable in this particular endeav­ or. In order to obtain as much information as possible from 75 each experiment, all mixtures were made up in compositions falling along possible ,loins or on their crossings. Since no ternary compounds were expected, and indeed none were encountered, the number of possible joins was greatly re­ duced. Simple, gradual elimination would thus yield the equilibrium relations. Such a procedure could not, however, be followed without giving some closer attention to sever­ al problems inherent to this system. For instance, invest­ igation on the joins with 2Al20^.B20^ as one their end members was greatly impaired because is stable only to 1035°C. At this temperature and below it was found that reaction in many ternary mixtures is very slow. Fur­ ther, the x-ray diffraction pattern of a mixture of mullite and 9Al20^*2B20^ can, except for several characteristic lines at about 2 20° and 23° in the 9A1-0 .2Bo0 pat- k 3 2 ^ tern, hardly be distinguished from that of either of the end members. Mien, however, mullite takes some boron into solid solution, the few characteristic mullite lines in the composite pattern appear to shift towards lower 2 6 angles and become increasingly difficult to resolve from the adjacent lines. Furthermore, as in the case of compositions consisting of and SiC^* no re­ action at the particular temperatures used, seems to take place at all. Thus, except for the complimentary evidence of the stability of the starting materials, these 76 these compositions did not directly serve any purpose.

The solid-state sintering data tabulated in Table 7 resulted in the following compatibility triangles: alumina-mullite^A^O^. mullite-9Al205.2B205-2A1205.B205 mullite-2Al20^.B20^-silica silica-2Al«0_.Bo0,-boron oxide. d 0 d o There is good evidence that the mullite-Bo0, assemblage ^ 0 is not an equilibrium state. Various mixtures in this ser­ ies react to give 9A120^.2B20^ or 2A120^.B20^ together with mullite, or 9A120^.2B20j alone, depending upon temperature and composition. Incompleteness of the reaction seems to be definitely shown by the composition at the crossing with the 2A120^.B20^-Si02 series, where some mullite remains in­ stead of converting completely to 2A120^.B20^ and Si02* However, volatilization of B~0, could bring about the same 0 effect, by shifting the composition into the triangle rnul- Iite-2A120^.B20^-Si02. Since no ternary compounds are in­ dicated, the join 2Alo0,. Bo0-,-t>i0_. must be valid. This is ^ 0 d o 2 further confirmed by compositions in this series. Likewise, the validity of the mullite-9Aln0-I.B^O, join has been est- d 0 e- 0 ablished. The possibility of a join between 9Alo0, .2Bo0-, d 0 c. 0 and Si02 arose when no reaction, except for the formation of some cristobalite, was observed in any of the mixtures 77 of these two phases at temperatures up to 1200°C. This view, however, becomes untenable when a mixture made up of these two end members and lying in composition on the crossing with the series mullite-2Al20^.reacts at 1650°C. Difference in x-ray diffraction patterns before and after firing is slight but significant. The sample after firing consists of 9Al20^.2B20^ and boron-contain­ ing mullite. Another sample (again at 1650°) lying in com­ position on the same crossing, but made up initially of the phases mullite and 2Al20^’^2^3’ gave identical results. In this case, however, the 2Al20^.B20^ melted to give whereas the mullite became richer in boron.

Dietzel and Scholze (195^0 and later Gelsdorf et al (1958) have indicated a possible solid-solution relation­ ship between mullite and 9Al20^.2B20^* iSxperiments along this join,in which the compositions were made up from either the compounds or the oxides, gave results which tend to confirm the findings of the authors mentioned above. The join mullite^A^O^• in Figure 8 has ac­ cordingly been cross-hatched to indicate the approximate extent of the solid-solution phenomenon.

Liquidus data and primary fields.— All compositions in the ternary system on which the liquidus temperatures 78 were determined are tabulated, with thermal data, in Table 8. One of the major problems was the optical dist­ inction between mullite, boron-rich mullite, and the primary crystals in the adjacent field of 9A1-0 .2Bo0 . <- *> t 5 Indeed, all primary crystals, in every charge investig­ ated in this study, appeared to have practically identical optical properties: parallel extinction, strong birefring­ ence, very similar indices, and positive elongation. Pos­ sible differences in indices among the phases could not be established, since all crystals were completely en­ closed in glass. Only once, quite by accident, in a charge that had severely leaked, had crystals developed well enough to make more accurate optical determinations pos­ sible. These crystals were lath-shaped, 0.1 mm long and 0.025 mm wide, showed parallel extinction and positive elongation. Their indices for the long direction were Just below 1.65 and, somewhat lower than that, across the laths. A good acute bisectrix interference figure was ob­ tained. These data agree quite well with those for mul- lite. All primary crystals appeared as either very thin, long and needle-like, or as shorter, more stubby, some­ times less well developed crystals. At first, no partic­ ular importance was attached to this subtle difference in morphology. It became, however, very important when all charges with the needle-like crystals were found to 79 fall on the 9Alo0., .2Bo0, side of the latter's boundary d $ d $ with mullite. This boundary had in the mean time been suggested by the course of the various isotherms. The difference in morphology, however slight, does seem to give added support to the location of the above-mentioned boundary curve. Another characteristic of all samples, at temperatures relatively close to the liquidus, is that most crystals appear to grow in groups radiating from a center, while a more dispersed, uniform growth is observed at temperatures well below the liquidus. It should further be emphasized that the use of sealed platinum capsules proved to be of great importance. Identical compositions fired simultaneously and thus at the same temperature, gave completely different results for charges with and without weight losses.

Solid-state sintering attempts to determine the invar­ iant points at which mullite, 9Alo0 .2B.-.0, and 2A1.-P, .B~0-, d y d $ d $ d y on the one hand, and Si02 » and mullite on the other hand, would be in equilibrium proved unsuccessful because of the extreme reluctance for reaction at these low temperatures. More information on the extent of tne corundum field was obtained by firing mixtures of 9Alo0 .

2B20^ and Si02 at 2% intervals between 12% and 2% s i 0 2 at 1650°C. No corundum was observed in any of these charges. 80

It can thus be safely inferred that the 1650° isotherm does not at any point cut the mullite-alumina boundary curve. The invariant point for the fields of mullite, and corundum would thus have to lie at a higher temperature. A suggested location consistent with this requirement is shown in Figure 8.

Tentative phase diagram.— Liquidus data in the high region of the system together with evidence from sintering reactions, have enabled the de­ duction of a tentative phase diagram. Figure 8 shows all relationships as far as they could be deduced from this study. Dashed lines are used for relations which have been postulated, but not experimentally determined here. The extension of the isotherms into the high SiO^ region of the diagram was made possible by liquidus determin­ ations made by Dietzel and Scholze (1954-) • Their data and those obtained in the present study, appear to be in essential agreement.

No evidence for the existence of a possible two-li­ quid region has been found with the petrographic micros­ cope. Since a two-liquid area appears to exist in the system SiC^-I^0^, it seems very probable that such a reg­ ion would extend into the ternary system. Dietzel's rules Figure 8. Preliminary phase diagram for -the system alumina-boron oxide—silica. Si O2 I 713° 83

(194-2), however, would suggest that the extent of such a liquid immiscibility area in the ternary system should be very limited. SUMMARY

penciling tests on alumina-boron oxide mixtures in sealed platinum capsules have enabled the formulation of a phase diagram for the system Such a diagram, believed to be correct in its essential features, is pre­ sented here for the first time. Two incongruently melting compounds have been encountered: 9Al20^ * 2B2<3^ (melting point 1950°C) and (melting point 1035°C). A monotectic relation between 2A1-0., .Bo0_ and Bo0 is sug- <^3 ^ 3 d. 3 gested.

An analogous approach, augmented by sintering experi­ ments, resulted in the determination of the phase relation­ ships in the ternary diagram A^O^-B^O^-SiO^ • A tentative phase diagram for the low-temperature (up to 1630°C) por­ tion of the diagram is given in this study. The present work has not revealed any ternary compounds. Of the var­ ious fields of primary crystallization that of mullite appears to be by far the largest between mullite and 9A1~0-,. ^®2^3* evi(ience for & two-liquid area was encountered. In view of the relations in the binary systems Si02“-B20^ and * no primary field for boron oxide was to be expected.

84 85 and Al20 ^-B20^, no primary field for boron oxide was to be expected.

Attempts to synthesize sillimanite with the help of boron oxide flux resulted in the formation of what is be­ lieved to be a boron-containing mullite. It could further be established that, between 1050 and 1500°C, magnesium tourmaline melts to give cordierite and glass, while al­ kali tourmalines melt to give the above-mentioned boron- containing mullite as the crystalline phase. The results reported in this paragraph cast some doubt on data pre­ viously reported in the literature, relative to the syn­ thesis of sillimanite at atmospheric pressure, as well as to the decomposition of tourmaline. BIBLIOGRAPHY

Aramaki, S., and Roy, R. 1959* Revised equilibrium diagram for the system Al20^-Si0 2» Nature, 184, 631-632. Balconi, M. 1941. Sintesi della sillimanite. Rend. Soc. Min. Ital., 1, 82-86. Baumann, H.N., and Moore, C.H. 1942. Electric furnace boro- aluminate. Journ. Am. Ceram. Soc., 2£, 391-394. Benner, R.C., and Baumann, H.N. 1938* Refractory material. U. 3. Pat. 2, 118, 143, May 24.

Berger, S.V. 1933* The crystal structure of B2O3. Acta Chem. Scand., £, 611-622.

Bowen, N.L., and Greig, J.W. 1924. The system Al20^-Si0 2* Journ. Am. Ceram. Soc., 2» 238-254. Claringbull, G.F., and Hey, M.H. 1958. New data for dumor- tierite. Min. Mag.,^1, 901-907* Clark, S.P., Robertson, E.C., and Birch, F. 1957* Experi­ mental determination of kyanite-sillimanite relations at high temperatures and pressures. Am. J. 8ci., 255, 628-640. Damour, M.A. 1883* Note sur un borate d'alumine crystal- lisee, de la Siberie. Nouvelle espece minerale. Bull. Soc. Min. France., 6, 20-23. Dana, E.3. 1914. The system of mineralogy. 6. edition. John Wiley and Sons. New York. 554— 555* Dana, E.S. 1954. A textbook of mineralogy. 16th printing. John Wiley and Sons. New York. 850p. DeKeyser, W.L. 1951* Contribution to the study of silliman­ ite and mullite by x-rays, Trans. Brit. Ceram. Soc., £0, 349-364. de Pablo-Galan, L., and Foster, W.R. 1959* Investigation of role of betaalumina in the system Na20-Al203-Si0 2* Journ. Am. Ceram. Soc. 42, 491-498.

86 87

Dietzel, A, 1942. Die Kationenfeldstaerken und ihre Be- ziehungen zu Entglasungsvorgaengen, zur Verbindungs- bildung und zu den Schmelzpunkten von Silikaten. Ztschr. Elektrochem., 48, 9-23. Dietzel, A., and Scholze, H. 1955* Untersuchungen im System B203-Al205“Si0 2. Glastecbn. Ber., 28, 47-51* Dietzel, A., and Tober, H. 1955* On zirconia and binary systems with zirconia. Ber. Deut. Kerain. Ges. , 30, 71-82. Doelter. 1895* Reference quoted from: Kurylenko, C. 1951* Foex, M. 1938. Solubilite des oxydes dans 1'anhydride bo- rique fondu a 1200 . Compt. Rend. 206. 34-9-350. Poster, W.R. I960. The sillimanite group - kyanite, anda- lusite, sillimanite, dumortierite, topaz. Industrial Minerals and Rocks, AIME 773-789. Gelsdorf, G. , Mueller-Hesse, H. and Schwiete, H.E. 1958. Einlagerungsversuche an synthetischem Mullit: Arch. Eisenhuettenwes. 2£, 513-519* Golovastikov, N. I., Belova, Y.N., and Belov, N.V. 1955* The crystalline structure of jeremejevite. Dokl. Akad. Nauk. SSSR, 104, 78. Graham, C.E., and Robertson, F. 1951* A new dumortierite locality from Montana. Am. Min. £ 6, 916-917* Hietanen, A. 1956. Kyanite, andalusite and sillimanite in the schist in Boehls Butte Quadrangle, Idaho.AM. Min. 41, 1-27. Hintze, G. 1897* Handbuch der Mineralogie. Verlag von Vat und Comp. Leipzig. Part 2. 362-367. Kelley, K.K. 1949. High temperature heat content, heat capacity and entropy data for inorganic compounds. U. S. Bur. Mines Bull., 476. 241p. Kennedy, G.C. 1955* Pyrophyllete-sillimanite-mullite equi­ librium relations to 20 000 bars and 800 C. Abstact. G.S.A. Bull. 66, 1584. 88

Kracek, P.O., Morey, G.W., and Merwin, H.E. 1938. The system water-boron oxide. Am. J, Sci., 35A, 143-171* Kurylenko, C. 1951* Transformation de la dravite de Dou- brova. Compt. Bend., 2^2, 2109* Letort, Y. 1952. Contribution a 1* etude de la synthese de la mullite. Trans. Intern. Ceram. Cong. Paris. 19-32. Levin, E.M., McMurdie, H.F. and Hall, F.P. 1956. Phase diagrams for ceramists. Am. Ceram. Soc., Columbus, 0. Mallard, E. 1887. Sur diverses substances crystallisees Qu'Ebelman avait preparees et non decrites. Comp. Rend., 10 £, 1260-1267. McCulloch, L. 1937* A crystalline B2O3. Am. Chem Soc. 49, 2651 • Miyashira, A. 1953* Calcium-poor garnet in relation to metamorphism. Geochim.et Cosmochim. Acta, 4, 179-208. Michel-Levy, Mme.M.C. 1949* Synthese de la tourmaline et de la jeremejevite. Comp. Rend. 228, 1814-1816. Michel-Levy, Mme.M.C. 1950. Reproduction artificielle de la sillimanite. Comp. Rend. Acad. Sci. Paris, 230. 2213-2214. Morey, G.W. 1936. Studies in silicate chemistry of Geo­ physical Laboratory of Carnegie Institute of Washing­ ton. J. Soc. Glass Technol. 20, 245-256. Morey, G.W., and Ingerson, E. 1937* The melting of dan- burite: a study of liquid immiscibility in the system CaO-B205~Si02* Am. Min. 22, 37-47* Neuhaus, A., and Richartz, W. 1958. Ueber die Einkristall- zuechtung und Zustandsverhaeltnisse von Mullit. Ber. D. Keram. Gesellsch. 109-116. Rizzo, H.P., Weber, B.C., and Schwartz, M.A. 1957* Behavior of ceramic materials in a corrosive superheated boron oxide-boron environment. WADC Techn. Report. 57-525*

Rockett, T.J., and Foster, W.R. 1961. The system Si02~B203. In preparation. 89

Sastry, B.S.R., and Hummel, F.A. I960. Studies in lithium oxide systems: VII, l^O-B^OA-SiOs. Journ. Am. Ceram. Soc. 4£, 23-33. Scholze, H. 1956. Ueber Aluminiumborate. £. Anorg. Allgem. Chemie. 284, 272-277. Schuiling, R.D. 1957* A geo-experimental phase diagram of Al^SipOc (sillimanite, kyanite, andalusite). Proc. Kon. Hederlandse Akad. van Wetensch., B, 60, 220-226. Senkovits and Hawley. Horth American Aviation,Inc. Downey, Cal. A.S.T.M. file card 6-0297* Shears, E.G., and Archibald, W.A. 1954. Aluminosilicate refractories. Iron and Steel, Jan., 26-30; Feb., 61-66. Soulen, J.R. 1956. Vaporization of BgOj and other group three oxides. Unpublished Ph.D. dissertation. Univ. of Wisconsin. Diss. Abstracts, 16, 885* Thompson, J.B. 1955* The thermodynamic basis for the min­ eral facies concept. Am. J. Sci* 235. 65-103. Yoder, H.S. 1958. Mullite-^O system. Geophys. Lab. Car­ negie Inst. Wash., Yearbook 58. AUTOBIOGRAPHY

I, Peter Jacob M. Gielisse, was born in ' s-Hertogen- bosch, the Netherlands, on March 7» 1934-• I received my secondary-school education at St. John's Lyceum, 's-Her- togenbosch, the Netherlands, and my undergraduate train­ ing at the College of Maritime Engineering, Utrecht, the Netherlands, where I graduated in 1953* From Boston Col­ lege I received the Master of Science Degree in 1959* While in residence there, I was a teaching assistant to Professor James W. Skehan, S. J., in the Departments of Geophysics and Geology, during the years 1957-1959• Ih September 1959 I was appointed research assistant at Ohio State University, where I specialized in the Depart­ ment of Mineralogy under Dr. W. R. Foster. I held this position for two years while completing the requirements for the Doctor of Philosophy Degree. During the academic year 1960-1961 I was awarded a Mershon National Graduate Fellowship.

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