Patented Dec. 4, 1951 is ..." 2,577,627 UNITED STATES PATENT OFFICE 2,577,627 COMPOSITION AND METHOD OF MAKNG SAME Alexis G. Pincus, Southbridge, Mass., assignor to American Optical Company, Southbridge, Mass., a voluntary association of Massachusetts No Drawing. Application May 1, 1947, Serial No. 745,239 10. Claims. (CI, 106-4)

- - - - - This invention relates to fluoride resistant characteristics have been encountered which and has particular reference to a glass have rendered most of these prior art glasses which is highly resistant to attack by hydro commercially impracticable. There are several fluoric , anhydrous fluoride and characteristics which are required in glasses of fluorides in general, and to improved composi this nature: tions and methods of making the same. (1) That the glass first has a high resistance One of the principal objects of the .invention to attack by hydrofluoric acid, anhydrous hydro is to provide glasses of the above character, in gen fluoride and fluorides in general; proved compositions therefor and methods of (2) That the compositions be such that they making the same, which can be fabricated in O may be readily fabricated by known commercial large scale commercial production by known means; commercial methods and within the usual tem (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. . . . . 5 homogeneity; . A further object is to provide a glass composi (4) That they possess high resistance to attack tion of the above nature consisting essentially of by ; 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 P2O5 and method 20 efficient and resistance to breakage from thermal of making the same whereby, during melting, a Shock. minimum loss of P2O5 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 form, large commercial batches of Such glasses, ous characteristics. Some difficulties as to the fabrication of the Another object is to provide a aluminum glasses occurred even though smaller size melts phosphate type of glass containing a controlled could be successfully fabricated. amount of boric . The present invention, therefore, is directed to A further object of the invention is to provide the obtaining of a glass possessing all of the a glass substantially free from attack by fluoride 30 above enumerated desirable characteristics and vapors, hydrofluoric acid, which glass consists which may be made in large commercial melts essentially of pentoxide, an ingredi and by known commercial processes or methods. ent or ingredients selected from the con In Patent No. 2,381,925 issued 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 hydrofluoric acid formed by combination of consisting of one or more df the bivalent : P2O5, Al2O3 and ZnO. BeO and PbO were men oxide, oxide and , tioned in said patent as equivalents of ZnO. and with or without the addition of minor in Small additions of alkali oxide or fluoride were gredients such as fluorine, alkali oxides and cal mentioned therein also as assisting the melting cium oxide. . 40 and Working of such glasses. In said patent it Other objects and advantages of the invention was mentioned that definite attempts were made | will become apparent from the following de to eliminate as far as possible any trace of sili Scription and it will be apparent that many con dioxide (SiO2) or boric oxide (B2O3) for, as changes may be made in the specific formulas, a result of research at that time and with the compositions and methods described herein with proportions of P2O5 and Al2O3 given, such in out departing from the spirit of the invention gredients proved detrimental to the fluoride re as expressed in the accompanying claims. I, sistance of the resultant glass. therefore, do not wish to be limited to the exact It has been found, however, by research and formulas, compositions and methods given herein experimentation that by increasing the P2O5 con as the preferred examples only have been set 50 tent to the upper limits set forth in said patent forth by way of illustration. - and by decreasing the Al2O3 content it now be Fluoride resisting glasses are not new in the comes practical to introduce B2O3 either as a art. Several different attempts have been made substitute for the Al2O3 or for use in combina to provide glasses possessing this characteristic tion therewith, and thereby obtain compositions but, in most instances, one or more undesirable 55 at this high P2O5 level which have better work 2,577,627 3 4. ing characteristics as to large batch fabrication P2O5 content of melt No. 2. The glasses of the and making possible the obtaining of maximum above melts were Subjected to a hydrofluoric acid durability against fluorides. test Such as Will be described in more detail here It has not only been found that, B2O3 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. 1 (0.15 as naterial 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 Al2O3 or B2O3 set Example B above, the desired composition may forth herein, the functions of Zno may be exert be derived from a batch consisting of: cised by the use of MgO, BeO and CaO either O Parts by weight separately or jointly, although it is still preferred Aluminum metaphosphate ------40 to use ZnO as the major bivalent oxide constitu Zinc metaphosphate------14 ent. Magnesium metaphosphate ------23 The present invention relates to glass compos Boric acid crystals------9 sitions as follows, in which are stated the range 5 and parts by Weight by which the various in nitrate------2 gredients may be varied and also certain specific Phosphoric anhydride ------8 examples of actual formulas Within this range It will be noted, that, as far as possible, meta Which have produced desirable results: phosphates are used as the raw materials be 20 cause it has been found that this yields a dry, Parts by Weight Specific easily weighed, and easily mixed batch with a Range of Examples Ingredient Parts by minimum tendency to volatilize the P2O5 during weight melting. The Said batch can be melted in any A. B C ordinary , through preferably 25 one of the high aluminum type, at a temperature (POs) 72-85 77 77 75 AiLiminuin Oxide (Al2O3).----- 5- 9 8 8 7 of about 2500 F. The melting should be rapid Boric Oxide (BO3).------. 1-8 5 5 5 and the furnace should not be held at this maxi Bivalent Oxides (RO).------1-12 | 10 mum temperature any longer than absolutely OO necessary for complete melting. ortho such as: 30 phosphate is available as a source of B2O3 and Zinc Oxide (ZnO) ------5 2 P2O5, and its use makes possible omission of (MgO) 5 3. Beryllium. Oxide (BeO). O O phosphoric anhydride from the batch. . Oxide. (CaO). O 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 ------O 3, 2 Alkali Oxides------0- Na30 or between 1900 and 2200 E. The Said melt has Li2O O. 0.5 Satisfactory working characteristics and the re Sultant glass can be lamp-Worked Without de 00. 99.5 vitrification of the parent gaSS or Surface grey It will be noted by reference to the above that ing during prolonged heating in a gas fiane. the P2O5 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 P2O5 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 s ing. Such as griniding 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 nients are present in approximately the meta within the usual ranges and cooled slowly from phosphate ratios. In order to maintain a high approximately 1100'. F. by conventional anneal F2O5 content, it has been found best to use, as 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 drofluoric acid at room temperature (usually 26 for the shortest possible time to minimize loss 5 to 27° C., approximately 78° F.) for one hour of P2O5 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 (ngs. per sq. cm. per ings according to Example 'C' indicated the hour). By this test ordinary silicate glasses following end results: 60 Would be. So rapidly corroded that they would be USeleSS in less than one hour, while the glasses Melti1 Melt i2 of the present invention show almost no visible

attack after one hour, retain their transparency 72.85 7.14 and exhibit weight losses of the order of mg. 2.58 65 per SC. Cn. per hour. 3.90 5. 41 Specimens of glass such as set forth in Ex 5.88 0.43 amples “B” and “C” have been used as containers 0. for 4.8% hydrofluoric acid at relatively high room 0.58 0. temperatures, and at the end of 592 hours had 98.96 98.94 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 The major difference between the two is the lower 5 the test the glass has remained transparent, and 2,377,627 5 6 a slight film formed by fumes of HF above the culties, their use-in formulas of this type is not liquid line can be readily-rinsed off...... Ordinarily desirable. However; where it is de - The above is true for glasses made on a large Sired to include fluorine in the formula as dis commercial scale and, while possessing these de cuSSed below, fluorspar (calcium fluoride) 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 fluorine. As much as 5% of tioned above, characteristics which afford much calcium fluoride 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 and in appreciable pro set forth in said issued patent. 10 portions are undesirable in any formulas of high While the glasses mentioned herein are highly P2O5 content of 72% or more because they in resistant to hydrofluoric acid, they are also of crease the tendency to devitrification. 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 of 1.8% by a stand 5 fer sharply from the other bivalent oxides, pro ard laboratory test by which ordinary moting better workability and excellent hydro has a solubility of 4%. This low solubility in fluoric acid resistance at the 72 to 85% P2O5 water is controlled primarily by the relative pro level. A particularly useful formula, is: portions of P2O5 and Al2O3, secondarily by the amount of B2O3, and only to a minor extent by 20 Parts by Weight the nature and, amounts of the... additional con Phosphorus pentoxide (P2O5).------85 stituents, It has been found that, as P2O5 in Aluminum oxide (Al2O3).------5 creased to the high levels of the present teach Boric oxide (B2O3).------ings, the minimum amount of Al2O3 required to Zinc oxide (ZnO).------1. maintain Water Solubility, at low levels becomes 25 (BeO).------8 lower than previously thought necessary. For example, a glass consisting of 75% P2O5 plus 5% 100 Al2O3 plus 20% ZnO has a water solubility of 18%, whereas a glass consisting of 80% Paos This formula melted and worked fairly well plus 5% Al2O3 plus 15% ZnO has a Water solu 30 and had excellent durability against hydrofluoric bility of only 5%. Keeping Al2O3 constant at acid (0.04 mg. per Sq. cm. per hour), against 10%, the effect on water solubility of lowering water (1.3%), and SOdium. P2O5 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 Per Cent Water HF Resist various polyvalent oxides such as the oxides of POs ZnO Solubility ance boron, , and . The bene ficial effects of the introduction of boric oxides have already been described but it has been 40 found that silica and the oxides of arsenic and antimony may also be added at the high P2O5 level of 72 to 85% without affecting the hydro fluoric 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 46 fortunate that its presence is not harmful be taining the P2O5 at a high level of approximately cause some silica, is almost certain to be present 72% or more, Al2O3 at least at 5%, and includ in commercial glasses from attack on the re ing some B2O3, 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 P2O5 glasses but they should be kept low because 50 effects on workability and durability. of their unfavorable effects on thermal expan Other polyvalent oxides which it has been Sion. (Na2O) or oxide found can be included in the formula include (K2O) can be as high as 1%, oxide (Li2O) those of , , , , as high as 4%. These alkali additions accelerate , , , , , melting, lower critical temperatures and usually 5 and ... . These have not been decrease devitrification tendency. Lithia (Li2O) found as practical as the preferred polyvalent has the most favorable reactions in this high ingredients set forth above because of less favor P2O5 range of 72 to 85%, presumably because it able effects on hydrofluoric acid resistance and has the lowest atomic weight of these three alkali workability, coloring effects in some cases, or Oxides. Among the possible bivalent oxide constituents, because of the high cost compared to the pre oxide, lead oxide, and ferred ingredients. If it is desired, however, in oxide are not essential, as far as hydro some particular instance to include any of these fluoric acid resistance is concerned, but their ingredients, they may be added in amounts of inclusion in Small quantities in the glass formula a fraction of 1% to approximately 12% depend may serve some useful purpose as, for example, ing upon the relative proportions of the other they have been found to improve resistance essential constituents. against the ordinary and alkalis. Because the specific effects of Substitutions particularly favors low Water vary with the base composition to which they solubility even at low aluminum oxide, content are added, it is recommended that, before in but, because the effects of these constituents on cluding any of these possible variants in the resistance to attack by hydrofluoric 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 P2O5 which can be main study. Generally, these variants should be in tained Without excessive devitrification difi 75 troduced in place of or partly in place of the 2,577,627 7 8 bivalent oxide constituent of the general formula, by weight, boric oxide (B2O3) 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 metalic elements Such as fluorine, , Sull oxide (CaO) and mixtures thereof comprising phul and Seleinium. These may contribute Spe from 1 to 12 parts by Weight, fluorine ranging cific desirable resultS Such as accelerating melt from near 0 to 5 parts by weight and an alkali ing, improving refining, lessening rearn aid inodi oxide Selected from the group consisting of SOdin. fying color. They would be added in relatively Oxide, , potaSSiun OXide and miX Small amounts, usually less than 1%. O 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 net Sane completely in the neighborhood. Of desired, Suitable coloring agentS Such as , 2500 F. and rapidly cooling the net to a temper , nanganese, or iron may be included ature in the neighborhood of 1830 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 gaSS composition to roor temperature. fect upon the hydrofitoric 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 20 fluoric acid, the fluoride and fluoride Vapors that simple, efficient and economical neans and comprising mixing phosphorus pentoxide (P2O5) ninethod have been provided for accomplishing all ranging from approximately 72 to 85 partS by the objectS and advantages of the invention, Weight, aluminum oxide (Al2O3) ranging fron ap aWig described lay invention, I claii: proximately 5 to 9 parts by Weight, boric oxide 1. A glass resulting from the fusing together of: 25 (B2O3) ranging from approximately 1 to 8 parts Range of parts icy Weight by Weight, and metal OXide Selected fron the Phosphorus pentoxide group consisting of Zinc oxide, calciuin oxide, (F2O5) ------Approximately i3 beryllium oxide, magnesium oxide and mixtures Aluminum oxide (A32O3).---- Approximately 7 thereof approximately 1 to 12 parts by Weight, and 3oric Oxide (B2C3) ------Approxiiately 5 30 controlling the silica, content to be, at nost, only Zinc oxide (ZnO).------w Siiraately 2 of a regligible amount, heating the inixture to Magnesium oxide (MgO). Agproxiiiately. 3 neit the same completely in the neighborhood of Calcius, OXide (CaO) ------AcroXiately 3. 2500 E. and readily cooling the melt to a tern Fluorine ------Approximately 3.2 perature in the neighborhood of 800 to 2200 i. Sodium oxide (Na2O)------Approximately 0.5 35 to allow working thereof, further permitting the glass to cool slowly to relieve mechanical strains. 2. A glass reSuiting from the fusing together of: 7. A glass resulting from the fusing together of: - Range of parts by Waight Range of parts by weight Phosphorus pentoxide Phosphorus pentoxide (F2C5 ------Approximately 77 40 (P2O5) ------Approximately 77 Alufinuin oxide (Al2O3).---- Approximately 3 Aluminum oxide (Al2O3) --- Approxiinately 8 Boric Oxide (B2O3).------Approximately 5 Boric oxide (B2O3) ------Approxiinately 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 (i2O) ------Appi'OXiately 0. (21C), magnesium oxide (MgO), beryllium oxide 8. A Substantially Water-insoluble glass having (BeO), (CaO) and mixtures there high resistance to attack by the fluorine ion an: Cf, itS Silica, content, at nost, being only of a consisting essentially of the following ingredients negligible anouint. and percentages therefor by weight: 3. A glass resulting fron the fusing together of: Phosphorous pentoxide------2 to 85 Range of parts by weight Aluminum oxide------5 to 9 Phosphoi's pentoxide Boric oxide------to 8 (F2C5is 3 ------Approximately 77 Metal oxide from the group consisting Aluminum oxide (Al2O3).---- Approximately 8 of zinc oxide, magnesium oxide, bery. Boric OXide (B2O3) ------Approximately 5 lituin oxide, calcium oxide and mix Magnesium oxide (MgO) -- Approximately 5 tures thereof.------1 to 12 Zinc oxide (ZnO) ------Approximately 5 Sodiuin Oxide (Na2O)------Approximately 0.i. and the Silica, content, at most, being only of a 60 inegligible 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 fusorine in ar. Phosphorus pentoxide consisting essentially of the following ingredients; (P2O5) ------Approximately 85 and percentages therefor by Weight: Aiuininuin oxide (Al2O3).----- Approximately 5 hosphorous pentoxide------72 to 3 Bolic Oxide (B2O3).------Approximately Aluminum oxide------5 to 9 Zinc CXide (ZnO) ------Approximately 1. Boric oxide------i to 8 Beryllium oxide (BeO)--- Approxiiately 8 Metal oxide from the group consisting 5. The process of making a glass composition 70 of Zinc oxide, inagnesium oxide, beryl Which is highly resistant to attack by hydro?iuolic lium oxide, calcium oxide and mix acid, the fluoride ion and fluoride vapors con tures thereof.------to 2 prising the Steps of mixing phosphorus penioxide Said glass containing an alkali oxide selected from (P2O5) iranging from 72 to 85 parts by weight, the group consisting of lithium oxide,y sodiumski aluminuin oxide (Al2O3) ranging from 5 to 9 parts 75 Oxide, and mixtures thereof, in 2,577,627 9 O proportion of less than one per cent, and with the group consisting of fluorine and chlorine, with its silica content, at most, being only of a negli the proportion thereof being less than five per gible amount. cent, and its silica, content, at nost, being only of 10. A substantially water-insoluble glass having a negligible amount. high resistance to attack by the fluorine ion and ALEXIS G. PNCUS. consisting essentially of the following ingredients and percentages therefor by Weight: REFERENCES CTED Phosphorous pentoxide------72 to 85 The following references are of record in the Aluminum oxide------5 to 9 file of this patent: Boric oxide------1 to 8 UNITED STATES PATENTS Metal oxide from the group consisting Number Nanne Date of zinc oxide, magnesium oxide, beryl 1961,603 Berger ------June 5, 193-4 lium oxide, calcium oxide and mix 2,077,481 Huppert et al. ------Apr. 20, 1937 tures thereof.------1 to 12 s 2,294,844 Gelstharp ------Sept. 1, 1942 said glass containing a halogen Selected from 2,423,128 Tillyer ------July 1, 1947