Patented Dec. 4, 1951 ~ 2,577,627

UNITED STATES PATENT OFFICE

GLASS COMPOSITION AND METHOD OF MAKING SAME Alexis G. Pincus,‘ Southbridge, Mass., assignor to American Optical Company, Southbridge, Mass., a voluntary association of Massachusetts No Drawing. Application'May '1, 1947,v , _ _ Serial No. 745,239 10 Claims. (Cl. 106-47)

This invention relates to ?uoride ‘resistant characteristics have been encountered which glasses and has particular referencerto ‘a glass have rendered most of these prior art glasses which is highly resistant to attack by hydro commercially impracticable. There are several ?uoric acid, anhydroushydrogen ?uoride ‘and characteristics which are required in glasses of ?uorides in general, and’ to improved composi this nature: ’ tions and methodsof making the same. ' (1) That the glass ?rst has a high resistance One of the principal-objects of the-invention to attack by hydro?uoric acid, anhydrous hydro is to provide'glasses of' the above character, im gen ?uoride and ?uorides in general; proved vcompositions therefor and methods 01’ (2) That the compositions be such that they making the same, which can be fabricated’ in 10 may be readily fabricated by known commercial large scale commercial production by known means ;' H a commercial methods and‘within the usual :tem~v (3) That they possess’ characteristics which perature ranges, and which possess characteris will enable refabrication by heat or mechanical tics enabling refabrication while retaining a means without loss of desired transparency and transparent homogenous vitreous nature. 1, ~ homogeneity; ' VA furtherobject is to provide a glass composi " (4) That they possess high resistance to attack tion of the above nature consisting essentially of vby water; the metaphosphates of metallic elements of. low (5)] And that they possess desirable and prac atomic weight so that the resulting glass has a tical characteristics as to thermal expansion co relatively high percentage of P205 and method 20 efficient and resistance to breakage from thermal of making the same whereby, during melting, a shock. ' r ' , minimum loss of P205 by volatilization will occur Some more recent glasses possessed most of the and which melt can be cooled and fabricated above desirable characteristics but it has been without harmful tendency to form crystals, ream found that, when attempts have been made to or other loss of homogeneous, transparent, vitre 25 formllarge commercial batches of such glasses, ous characteristics. ' some'di?iculties as to the fabrication of the Another object is to provide a zinc aluminum glasses occurred even though smaller size melts phosphate type of glass containing a controlled could be successfully fabricated. i amount of boric oxide. - a The present invention, therefore, is directed to ' A further object of the inventionis to provide the obtaining of a glass possessing all of the a glass substantially free from attack by ?uoride 30 above enumerated‘desirable characteristics and vapors, hydro?uoric acid, which glass consists which may be made in large commercial melts essentially of phosphorus pentoxide, an ingredi and by known commercial processes or methods. ent or ingredients selected’ from the group con In‘ Patent No. 2,381,925issued August 14, 1945 sisting of aluminum oxide and boric oxide and an to applicant, there are disclosed glasses resistant ingredient or ingredients selected. from the group 35 to hydro?uoric acid formed by combination of consisting of one or more of the bivalent oxides: PzOs,,AlzO3 and ZnO. BeO and PhD were men beryllium oxide, magnesium oxide and zinc oxide, tioned in said patent as equivalents of ZnO. and with or without the addition of minoruin small'additions of alkali oxide or ?uoride were gredients such as ?uorine, alkali oxidesand cal mentioned therein also as assisting the melting cium, oxide; , ' " Q 1' ' and working of such glasses. In said patent it ' [Other objects and ‘advantages of theinvention was mentioned that de?nite attempts were made will become apparent from the ' following de to eliminate as far as possible any trace of sill scription and it ‘will be vapparent that many jean dioxide (S102) or boric oxide (B203) for,’ as changes may be ma'dein the specific'formulas, h, aw result of research at that time and with the compositions and ‘methods described herein with proportions of P205 and A120: given, suchvin out departing, from the‘spiritgof the-invention gredients proved detrimental ‘to the ?uoride re as expressed in,_ the accompanying ‘claims. , I, sistance‘ of the resultant glass. therefore; do not wish tobe limited to the'exact , ‘It has been foundghowever, by research‘ and formulas, compositions and methods givenherein experimentation that by increasingrthePzOs con as the preferred‘. examplesonglyrhave been set ‘terit to the upper limits set forth in said patent forthlby way of ‘illustration. " " ' ‘ ' and by decreasing the A1203 content it now be Fluoride resisting gl 's'ses are notfnew inv the comes practical to introduce B203 either as a ‘art. Several different attempts‘haveb'een made substitute for the A1203 or for use in' combina to" provide glasses possessing this ‘characteristic tiontherewith', and thereby ‘obtain compositions but,‘in most instances, oneor more undesirable 55 at this highiP'zOs level'which have better “work' 2,577,627 3 4 ing characteristics as to large batch fabrication P205 content of melt No. 2. The glasses of the and ‘making possible the obtaining of maximum above melts were subjected to a hydro?uoric acid durability against fluorides. test such as will be described in more detail here It has not only been found that B203 may now inafter, and melt No. 2 was attacked at an ap be added without detriment to the glass but that preciably higher rate than melt No. l (0.15 as material amounts may be added with decidedly compared with 0.10). advantageous results. It has also been found In the forming of a glass melt such as given in that, with the proportions of A1203 or B203 set Example B ‘above, the desired composition may forth herein, the functions of Zno may be exer= be derived from a batch consisting of: cised by the use of MgO, BeO and CaO either 10 Parts by weight separately or jointly, although it is still preferred Aluminum metaphosph-ate ______40 to use ZnO as the major bivalent oxide constitu ent. ‘Zinc metaphosphate ______-_ 14 The present invention relates to glass compo= Magnesium metaphosphate ______23 some acid crystals ______9 sitions as follows, in which are stated the range 15 and parts by weight by which the various in Sodium nitrate ______0.2 gredients may be varied and also certain speci?c Phosphoric anhydride ______18 examples of actual formulas within this range It will be noted, that, as far as possible, meta which have produced desirable results: phosphatés are used as the raw materials be 20 cause it has been found that this yields a dry, Parts by Weight Speci?c easily weighed. and easily mixed batch with a Range of Examples Ingredient Parts by minimum tendency to volatilize the P205 during Weight melt-ing. The said batch can be melted in any A B C ordinary ceramic refractory, through preferably 25 one of the highaluminum type, at a temperature Phosphorus Pentoxide (P105) 72-85 77 77 75 of about 25Q0° F. The melting should be rapid Aluminum Oxide (Al2O3)_____ 5—' 9 8 8 7 Boris Oxide (B203) ______.. 1~ 8 5 5 5 and the furnace should not be held at this maxi Bivalent Oxides (R0) ...... _ 1-12 ’ I 10 mum temperature any longer than absolutely 100 necessary for complete melting. Boron ortho such as: 30 phosphate‘ is available as a source of B203 and Zinc Oxide (ZnO) ______-. ___ 5 2 P205,- and its use makes possible omission of Magnesium Oxide (MgO)__ 5 3 Beryllium Oxide (BeO)__ 0 0 phosphoric anhydride from the batch.‘ _ Calcium Oxide (02.0)"..- 0 3 8 The melt can then be dropped to about 2000“ Optional Ingredients F. for further homogenization and for working. 35 The best working range has been found to lie Fluorine ______0- 5 ______V__ 0 3.2 Alkali Oxides ______. 0- 1 NayO or between 1900“ and 2200° F. The said melt has no 0. l O. 5 satisfactory working characteristics and the re 100. 1 99. 5 sultant glass can be lamp-worked without de vitri?cation of ' thev parent glass or surface grey ing during prolonged heating in a gas ?ame. ‘It will be noted by reference to the above that l the P205 content is relatively high and, according That is; the glass will retain its initial inherent to the present teachings, the higher the amount transparency‘ throughout the melting, working of P205 present, the more resistant the resultant and after working. The" glass also lends itself glass will be to hydrofluoric acid attack. well to the usual mechanical methods of shap In forming the glass batches for producing ing such as grinding with loose abrasives, polish~ such glasses, it is desirable to so select the pro ing with rouge, cutting, edging and drilling. portions of the ingredients that the positive ele Glasses of this nature may also be annealed ments are present in approximately the meta ' within the usual ranges and cooled slowly from phosphate ratios, In order to maintain a high approximately 11000 F. by conventional anneal B205 content, it has been found best to use, as 5' ing methods. the metallic oxide constituents, elements of low It has been found that the glasses disclosed atomic weight such as beryllium, aluminum, herein are resistant to a chemical test as follows: boron and magnesium. During the melting it is A weighed test piece is immersed in 48% hy~ desirable to melt at a minimum temperature and dro?uoric acid at room temperature (usually 26 for _, the shortest possible time to minimize loss to 27° 0., approximately 78° F.) for one hour of P205 by volatilization. without agitation. Then the piece is re-weighed For example, actual chemical analyses of and the results expressed as loss in weight per glasses obtained by semi-production scale melt, unit area per unit time (mgs. per sq. cm. per ings according to Example “C” indicated the hour). _ By this test ordinary silicate glasses following end results: would be so rapidly corroded that they would be useless in less than one hour, While the glasses Melt #1 . Melt #2 of the present invention show almost no visible attack after one hour, retain their transparency and exhibit weight losses of the order of 1% mg. per sq. cm. per hour. Specimens of glass such as set forth in Ex amples"‘B” and “C” have been used as containers won-eminence for 48% hydro?uoric acid at relatively high room m?omeoomcno 70 temperatures, and at the end of>592 hours had lost only 37.4 mg. per sq. cm. or 0.06 mg. per sq. cm. per hour. At the end of 4550 hours the loss Melt No. 2 differed from melt No. 1 only in in weight was about 224 mg. per sq. cm, or a rate being held in the furnace about 12 hours longer. of 0.05 mg. per sq. cm. per hour. Throughout ,Themajor difference between the two is the lower 7.5 the test the glass has remained transparent, and amass? 5, a slight ?lm formed by fumes of 'HF above the culties, their-use- in formulasv of this ftypeais not liquid line can be readily rinsed off . » . _. ordinarily desirable. Howevenawhere it is de 'I’he'above is true for glasses made ona large sired to include ?uorine in the formula as dis commercial scaleand, while possessing these de cussed below, ?uorspar (calcium ?uoride) has sired characteristics, further possess, as dis been, found to be an economical and desirable tinguished from applicant’s issued patent men means of adding ?uorine. As much as 5%‘ of tioned above, characteristics which afford much calcium ?uoride has been added in certain for greater 'ease of fabrication in large scale pro mulas without detrimental effect. The bivalent duction and is therefore preferable to the glasses oxides of cadmium and lead in appreciable pro set forth in said issued patent. ' I - 10 portions are undesirable in any formulas of high -While the glasses mentioned herein are highly P205 content 1of 72% or more because they in resistant to hydro?uoric acid, theyare also of crease the tendency to devitri?cation. excellent resistance to attack by water. For ex ‘The bivalent oxides of the elements of lowest ample,'-the particular glass batch “B” mentioned atomic weight-‘-beryllium and magnesium-dif above has a water solubility of 1.8% by arstand 15 fer sharply from the other bivalent oxides, pro ard laboratory test by which ordinary crown glass moting better workability and excellent hydro has a solubility of 4%.’ This low solubility in ?uoric acid resistance at the 72 to 85% P205 water is controlled primarily by the relative pro level. A particularly useful formula is: portions of-P2O5 and A1203, secondarily by.-ithe amount of B203, and only to .a minor extent by 20 : Parts by weight the nature andamounts of themadditional-cone Phosphorus pentoxide (P205) ______85 stituents. P It has been found that, as P205 in Aluminum oxide (A1203) ______v5 creased to the high levels of the present teach Boric oxide (B203) ______1 ings, the minimum amount of A1202‘ required to Zinc oxide (ZnO) ______1 maintain water solubility. atlow'lev'els becomes 25 Beryllium oxide (BeO) ______8 lower than previously thought necessary. For example, a glass consisting of 75% P205 plus 5%' 100 A1202 plus 20% iZnO has a water solubility of 18%, whereas a glass consisting of 80% P205 This formula melted and worked fairly well plus 5% A1203 plus 15% ZnO has a water solu 30 and had excellent durability against hydro?uoric bility of only 5%. Keeping A1203 constant at acid (0.04 mg. per sq. cm. per hour)‘, against 10%, .the effect on water solubility of lowering water. (1.3%), hydrochloric acid and sodium P205 by replacing it with ZnO was found to be: hydroxide. . . In addition to the alkali oxides and bivalent 35 oxides, it is also possible to include in the formula Per Cent Per Cent P $235131‘: HF Resist various polyvalent oxides such as the oxides of P205 ZnO Solubility anee boron, silicon, arsenic and antimony. The bene ?cial effects of the introduction of boric oxides 80 1O 1. 7 0. 1 have already been described but it has been 75 15 1. 3 0. 2 , 70 20 2. 6 0. 9 40 found that Silica and the oxides of arsenic and 65 25 . 11.0 8. 5 antimony may also be added at the high P205 level of 72 to 85% without affecting the hydro ?uoric acid resistance too unfavorably. The According to the present invention, a wide introduction of silica does not contribute any variety of substitutions are possible provided the highly favorable effects to the glass but it is fundamental teachings. are followed of main-' 45 fortunate that its presence is not harmful be taining the P205 at a high level of approximately cause some silica is almost certain to be present 72% or more, A1203 at least at 5%, and includ in commercial glasses from attack on the re ing some B203, preferably about 5%. For ex fractories. Antimony and arsenic, particularly ample, alkalis may be introduced into such high the latter, have been found to have favorable ‘P205 glasses but they should be kept low because 60 effects on workability and durability. of their unfavorable effects on thermal expan Other polyvalent oxides which it has been sion. Sodium oxide (NazO) or potassium oxide found can be included in the formula include (K20) can be as high as 1%, lithium oxide (Li20) those of titanium, tantalum, thorium, zirconium, as high as 1/2%.- These alkali additions accelerate lanthanum, tin, cerium, tungsten, vanadium, melting, lower critical temperatures and usually manganese and iron. These have not been decrease devitri?cation tendency. Lithia (LizO) found as practical as the preferred'polyvalent has the most favorable reactions in this high ingredients set forth above because of less favor P205 range of 72 to 85%, presumably because it able effects on hydro?uoric acid resistance and has the lowest atomic weight of these three alkali workability, coloring effects in some cases, or oxides. ' ' because of thehigh cost compared to the pre Among the possible bivalent oxide constituents, ferred ingredients. If it is desired, however, in barium oxide, lead oxide, cadmium oxide and some particular instance to include any ‘of these strontium oxide are not essential, as far as‘hydro ingredients, they may be added in amounts of ?uoric acid resistance is concerned, but their a fraction of 1% to approximately 12% depend inclusion in small quantities in the glass formula ing upon the relative proportions of theother may serve some useful purpose as, for example, they have been found 'to improve resistance essential constituents. against the ordinary mineral acids and alkalis. ' Because the speci?c effects of substitutions Barium oxide particularly favors low water vary with the base composition to which they solubility even at low aluminum oxidecontent are added, it is recommended that, before in but, because the effects of these constituentson cluding any of these possible variants in the resistance to attack by hydro?uoric acid are gen formula, their utility should be appraised when erally in the wrong direction and because ‘they they are added to the particular base glass under lower the maximum P205 which can be main study. Generally, these variants should be in tained without excessive devitri?cation diffi troduced in place of or partly in place of the 2,677,627 7 8. bivalent oxide constituent of the general formula by weight, boric oxide (B203) ranging from 1 to 8 “A” quoted above. " parts by weight and metal oxide selected from the It has also been found possible and. in some group consisting of zinc oxide (ZnO), magnesium cases desirable to include in the formula. non oxide (MgO), beryllium oxide (BeO), calcium metallic elements such as ?uorine, chlorine, sul oxide (CaO) and mixtures thereof comprising phur and selenium. These may contribute spe from 1 to 12 parts by Weight, ?uorine ranging cific desirable results such as accelerating melt from near 0 to 5 parts by weight and an alkali ing, improving re?ning, lessening ream and modi~ oxide selected from the group consisting of sodium fying color. They would be added in relatively oxide, lithium oxide, potassium oxide and mix small amounts, usually less than 1 %. 10 tures thereof ranging from near 0 to 1 part by In general, it is preferable that the glass be of a weight, and controlling the silica content to be at clear, colorless, transparent nature, but it is most of a negligible amount, heating the mixture pointed out, however, that if a colored glass is to melt same completely in the neighborhood of desired, suitable coloring agents such as cobalt, 25000 F. and rapidly cooling the melt to a temper nickel, manganese, copper or iron may be included 15 ature in the neighborhood of 18500 to 2200° F. to in the batch. These coloring ingredients or allow Working thereof, and thereafter slowly cool agents may be used without any appreciable ef ing the glass composition to room temperature. fect upon the hydrofluoric acid resistance of the 6. The process of making a glass composition glass. which is highly resistant to contact by hydro From the foregoing description, it will be seen fiuoric acid, the fluoride ion and ?uoride vapors that simple, e?icient and economical means and comprising mixing phosphorus pentoxide (P205) fnethod have been provided for accomplishing all ranging from approximately 72 to 85 parts by the objects and advantages of the invention. weight, aluminum oxide (A1203) ranging from ap ' Having described my invention, I claim: proximately 5 to 9 parts by Weight,‘ boric oxide 1. A glass resulting from the fusing together of : 26 (B203) ranging from approximately 1 to 8 parts Range of parts by Weight by weight, and metal oxide selected from the Phosphorus pentoxide group consisting of zinc oxide, calcium oxide, beryllium oxide, magnesium oxide and mixtures (P205) ____l ____ u‘ ______Approximately ‘F5 Aluminum oxide (Al2'O3)____ Approximately '? thereof approximately 1 to 12 parts by weight, and Boric oxide (B203) ______Approximately 5 controlling the silica content to be, at most, only Zinc oxide (ZnO) ______. rozi'nately 2 of a negligible amount, heating the mixture to melt the same completely in the neighborhood of 2500° F. and readily cooling the melt to a tem FluorineMagnesiumCalciumSodium oxideoxide______oxide (NazO)(CaO) (MgO)______1. Approximately 0.5 perature in the neighborhood of 1800 to 2200° F. 35 to allow working thereof, further permitting the glass to cool slowly to relieve mechanical strains. 2. A glass resulting from the fusing together of : 7. A glass resulting from the fusing together of : 3 Range of parts by Weight 7 Range of parts by weight Phosphorus pentoxide Phosphorus pentoxide 40 (P205) ___»______- ______Approximately 7'3’ (P205) ______Approximately 7'? Aluminum oxide (AlzOz)i_~___ Approximately 8‘ Aluminum oxide (AlzO3)___ Approximately 8 Boric oxide (B203) ______- Approximately 5 Boric oxide (B203) ______Approximately 5 and a Magnesium oxide (MgO)___ Approximately 5 Metal oxide ______Approximately 10 Zinc oxide (ZnO) ______Approximately 5 selected from the group consisting of zinc oxide ' Lithium oxide (LizO) ______Approximately 0.1 (Z110), magnesium oxide (MgO), beryllium oxide 8. A substantially Water-insoluble glass having (BeO), calcium oxide (0%)) and mixtures there~ high resistance to attack by the ?uorine ion and its silica content, at most, being only of a consisting essentially of the following ingredients negligible amount. and percentages therefor by weight: 3. A glass resulting from the fusing together of: Phosphorous pentoxide ______'72 to 85 7 Range of parts by weight Aluminum oxide____- ______5 to 9 Phorphorus pentoxide Boric‘ oxide ______1 to 3 (P205 ______Approximately 77 Metal oxide’ from the group consisting Aluminum oxide (A1203) ____ Approximately 8 of Zinc oxide, magnesium oxide, beryl~ Eoric oxide (B203) ______Approximately 5 lium oxide, calcium oxide and mix~ Magnesium oxide (MgO)___ Approximately 5 tures thereof ______'____ 1 to 12 Zinc oxide (ZnOV) ______i Approximately 5 Sodium oxide (NazO) ______Approximately 0.1 and the silica content, at most, being only of a 60 negligible amount. ‘ 4. A glass composition substantially as follows: - 9. A substantially water-insoluble glass having Range of parts by Weight high resistance to attack by the fluorine ion and Phosphorus pentoxide consisting essentially of the following ingredients; and percentages therefor by weight: (P205) ______Y_____ Approximately 85 Aluminum oxide (A1203)_____ Approximately 5 Phosphorous pentoxide ______'72 to "55 Boric oxide (B262) ______'__ Approximately 1 Aluminum oxide ______5 to 9 Zinc oxide (Z110) ______W Approximately 1 Boric oxide ______1 to 8 Beryllium oxide (BeO) ______Approximately 8 Metal oxide from the group consisting 5. The process of making a glass composition of zinc oxide, magnesium oxide, beryl which is highly resistant to attack by hydro?uoric lium oxide, calcium oxide and mix acid, the ?uoride ion and ?uoride vapors com tures thereof ______1 to 12 prising the steps of mixing phosphorus pentoxide said glass containing an alkali oxide selected from (P205) ranging from 72 to 85 parts by Weight, the group consisting of lithium oxide, sodium aluminum. oxide (A1293) ranging from 5 to 9 parts 75 oxide, potassium‘oxide and mixtures thereof, in 27,577,627 9 . 10 proportion of less than one per cent, and with the group consisting of ?uorine and chlorine, with its silica content, at most, being only of a negli the proportion thereof being less than ?ve per gible amount. cent, and its silica content, at most, being only of 10. A substantially water-insoluble glass having a negligible amount. high resistance to attack by the ?uorine ion and 5 ALEXIS G. PINCUS. consisting essentially of the following ingredients ~ and percentages therefor by weight: REFERENCES CITED Phosphgygus pentoxide ______72 to 35 The following references are of record in the Aluminum oxide ______5 to 9 m ?le of this patentr Borticl 0Xi€1ie-'-f--,---€1;----~' ------t--_ 1 to 8 UNITED STATES PATENTS Me a oxi e rom e group consis ing ’ _ of zinc oxide, magnesium oxide, beryl- Numbel Najme Bat‘? hum. oxide,. calcium. oxide. and mix. 1,961,603 Bergei ______June 5, 193+ tures thereof 1 to 12 2,077,481 I-Iuppert et a1 ______Apr. 20, 1937 """""""""""" '“ 15 2,294,844 Gelstharp -______Sept. 1, 1942 said glass containing a halogen selected from 2,423,128 Tillyer ______"July 1, 1947