CA1058877A - Method for hydrating silicate glasses - Google Patents

Abstract

METHOD FOR HYDRATING SILICATE GLASSES

Abstract of the Disclosure The present invention is concerned with a single-step process for hydrating alkali metal-containing silicate glasses starting with such fine-dimensioned forms as powders, granules, flakes, fibers, and thin sheets. The process permits the precise control of the quantity of water taken into the glass structure and, where the water content in the glass is held within about 1-25%
by weight, the hydrated product of the above-cited powders, gran-ules, etc., can be thermoplastically formed into sound bulk articles. A layer of the anhydrous powders can be applied to a substrate and then hydrated in situ to form glassy paints and coatings.

Description

The hydration of alkali metal-containing silicate glass bodies utilizing treatment in steam at elevated temperatures and pres-sures has been described in the prior art. For example, United States Patent No. 3,498,802 discusses the hydration of alkali silicate glass powders to yield thermoplastic materials and hydraulic cements. The glass powders consisted essentially in mole percent on the oxide basis, of 80-94% SiO2 and 6-20% Na2O
and/or K2O, the total of those constituents comprising at least 90 mole percent of the total composition. Various compatible metal oxides such as PbO, BaO, MgO, B2O3, A12O3, and ZnO could, optionally, be included but CaO and Li2O were desirably avoided.
The hydration process involved contacting the glass powders with a gaseous environment of at least 50~ by weight water at a pressure of at least one atmosphere and a temperature commonly within the range of about 100-200C. This treatment in the H2O-containing environment was continued for a period of -1- . ~ ' time sufficient to produce at least a surface layer on the powders containing up to 30~ by weight of H20. Temperatures of 80-120C. were observed as causing the hydrated powders to become adhesive and cohesive thereby enabling forming thereof through such conventional methods as pressing, rolling, extrusion, and injection molding.
In United States Application Serial No. 445,453, now United States Patent No. 3,912,481, filed concurrently herewith in the names of R. F. Bartholomew, H. F. Dates, S. D. Stookey, and W. H. Tarcza, the production of alkali silicate materials is disclosed which will exhibit forming characteristics and physical behavior approaching those demonstrated by high polymer organic plastics. The products discussed therein are described as displaying thermoplastic properties, by which is meant the ability of the material to flow sufficiently to allow shaping thereof utilizing methods well-recognized in the plastics art at temperatures below those at which conventional glasses commonly flow. Thus, as defined, thermoplastic materials can be formed at temperatures ranging from above the freezing point of water to about 500C. The invention disclosed contemplates subjecting alkali silicate glass bodies of specified composition to a two-step process involving, first, a hydration treatment, and, second, a dehydration treatment.
In brief, the glass compositions described therein comprise, in mole percent, 3-25% Na20 and/or K20 and 50-95% SiO2, the sum of those components constituting at least 55 mole percent of the total composition. Various compatible metal oxides such as A1203, BaO, B203, CaO, MgO, PbO, CdO, and ZnO can be advantageously added to improve melting and forming of the glass or to modify the chemical and physical properties of the shaped glass. PbO, CaO, ZnO, and B203 can be useful in amounts up to 25%, MgO can be included in amounts up to about 35%, BaO

lOS8877 and A12O3 are operable at values up to 20%, but individual addi-tions of the other optional oxides are preferably maintaine`d below 10%. CaO frequently yields an opaque body which, obviously, would render it useless in applications where transparency is re-quired. Li2O was found to inhibit hydration so was a less desir-able addition, but could be tolerated in amounts up to about 5%.
The method of that invention comprises first contacting the glass at a temperature of at least 100C. with a gaseous H2O-containing environment wherein the H2O pressure is sufficiently high to achieve an essentially saturated atmosphere. This con-tact is maintained for a sufficient period of time to develop at least a surface portion in the glass which is saturated with water. The amount of water diffused within the glass is depend-ent upon the composition thereof. For example, those glasses containing relatively small amounts of Na2O and/or K2O will normally absorb no more ~han about 10% by weight of water and, in some instances, less than 5% by weight, whereas glasses con-taining substantial amounts of Na2O and/or K2O will generally absorb water in amounts exceeding 15% by weight and can range up to 35%. Following this hydration step, the water content introduced into the glass thereby is reduced through exposure to a gaseous environment of lower relative humidity. The de-hydration step improves the chemical durability of the glass, increases the mechanical strength thereof, and inhibits the spontaneous dehydration phenomenon frequently observed in glasses containing high water contents. Although the glass body can be dehydrated to an essentially anhydrous state, such practice effectively eliminates the capability for displaying thermoplastic behavior. Therefore, the water content is custom-arily reduced to between about 1-12% by weight, depending upon the composition of the glass, the higher values reflecting those lOS8877 compositions ahsorbing more water during the initial hydration step.
In general, the hydration step described therein is con-ducted in an atmosphere of 100% relative humidity to expedite the diffusion of water within the glass and the dehydration is conducted at low relative humidities to promote the rapid xe-moval of water. The two-step process enables glass articles of substantial mass having controlled very low water contents to be secured in relatively short periods of time.
However, a serious problem encountered in carrying out the two-step practice of that invention was the incidence of crack-ing, foaming, spalling, and/or deformation of bulk bodies during the dehydration step. Thus, extreme control of temperature, pressure, and relative humidity was required to achieve sound bodies.
Therefore, the primary objective of the instant invention is to provide a method for hydrating such fine-dimensioned bod-ies as beads, granules, powders, ribbon, etc., of alkali metal-containing silicate glasses wherein the water content absorbed therein can be carefully controlled and the amount of such water will be effective to impart thermoplastic properties thereto.
We have discovered that this objective can be achieved in a single-step hydration procedure applied to glass compositions generally found suitable in the above-described two-step, hydration-dehydration process. The glass compositions operable in this process include, in mole percent on the oxide basis, 3-25% Na2O and/or X2O and 50-95% SiO2, the sum of those constituents comprising at least 55 mole percent of the total composition. Additions advantageously included to improve melting and forming of the glass and/or to modify the chemical and physical properties thereof include such metal q:

lOS8877 oxides as A12O3, B~O~ CdO, B2O3~ CaO~ M~O~ PbO~ ZrO2~ WO3, MoO3, TiO2, SrO, and ZnO. With the eXception of pbO~ CaO, ZnO, and B2O3 which can demonstrate utility up to about 25%, MgO which is operable up to about 35%, and BaO and Al2O3 which can advantage-ously be present in amounts up to about 15%, individual additions of other optional metal oxides will preferably be held below about 10%. The presence of CaO will frequently result in an opa~ue body which, obviously, would limit its utility to those applications where transparency is not required. Li2O appears to inhibit hydration so ought not to be included, if at all, in amounts greater than 5%. The well-recognized glass colorants such as CdS-Se, Co2O3, Cr2O3, CuO, Fe2O3, and Nio may be incor-porated into the glass composition in the customary amounts up to a few percent. It should be recognized that these latter ingredients can be tolerated in amounts up to about 10% where their function is not limited to their effect as a colorant.
Finally, where necessary, conventional fining agents can be included in customary amounts.
The procedure of the instant invention contemplates in certain aspects various embodiments depending upon the glass com-positions treated. One embodiment, demonstrating utility regard-less of composition, involves exposing fine-dimensioned glass bodies at a temperature of at least 100C. to a gaseous H2O-containing environment having a relative humidity less than 75%
and, preferably, less than 50%. Another embodiment is operable with glass compositions containing relatively low quantities of Na2O and/or K2O, viz., less than about 10 mole percent, or up to about 17 mole percent thereof but containing more than 15 mole percent total of metal oxides (MxOy), wherein the metal has a valence of at least 2, the sum of those components consti-tuting at least 70% of the total composition, and comprises contacting fine-dimensioned bodies of such compositions at tem-peratures in excess of 225 C. with a H2O-containing gaseous en-vironment having a relative humidity greater than about 50%.
Examples of such metal oxides are sao, PbO, CaO, CdO, MgO, A12O3, SrO, TiO2, ZrO2, MoO3, WO3, and ZnO-United States Patents Nos. 3,498,802 and 3,498,803, supra,specifically note the use of environments of high water contents at temperatures ranging up to 200C. with the comment that the quality of the rubbery product developed at temperatures above 200C. was not significantly better than that obtained at lower temperatures and, furthermore, that in certain instances the product was not sound. In contrast thereto, we have discovered that, with the low alkali metal-containing compositions or those glasses containing more than 15% MxOy, i.e., metal oxides wherein the metal has a valence of at least 2, it is highly advantageous to employ temperatures considerably in excess of 200C. to pro-mote the hydration. And, whereas a low humidity environment can be successfully employed with such glasses at very elevated tem-peratures and for very extended treatment times, atmospheres approaching and including saturation are to be preferred.
Hence, in essence, the low alkali metal-containing glasses can be considered a special embodiment of the present invention wherein a high humidity environment is preferred. We have learned that the maximum H2O content of low alkali metal-containing glas-ses can be controlled by the glass composition even in the pre-sence of saturated atmospheres and pressures. Hence, by choice of composition, the maximum amount of water which will be absorbed by the glass during hydration even at 100% relative humidity can be determined. It will, of course, be recognized that such con-trol will likewise be readily achieved employing lower humidityenvironments but the exposure times, for the same temperature, will be much longer.

~ -6-Thus the present invention provides a method for making a glass body exhibiting thermoplastic properties which comprises subjecting a fine-dimensioned anhydrous glass body comprising, in mole percent on the oxide basis, about 3-25% Na2O and/or K2O and 50-95% SiO2, the sum of those com-ponents constituting at least 55~ of the total composition, the remainder being substantially materials chosen from the group A12O3, BaO, CdO, B2O3, CaO, MgO, PbO, ZrO2, W03, MoO3, TiO2, SrO, and ZnO, and up to 5% of Li20; to a H20-containing gaseous environment having a relative humidity of at least 5% but' less than 50% at a temperature in excess of 225C. for a period of time sufficient to develop at least a surface portion having an amount of water absorbed therein effective to impart thermoplastic properties thereto. The amount of water absorbed will normally range between about 1 to 25% by weight.
In another embodiment the present invention provides such a method adapted for forming shapes from fine-dimensioned hydrated glass bodies exhibiting thermoplastic properties, which comprises the steps of forming a mass of fine-dimensioned hydrated glass bodies to a shape of a des~red con-figuration under pressure and at a temperature ranging from about room temperature. Preferably said mass of fine-dimensioned hydrated glass bodies is formed at temperatures between about 100-400C.
In another aspect this invention provides a method for forming a hard, durable, glassy coating on a substrate material comprising the steps of:
(a) preparing a powder of a glass comprising, in mole percent on the oxide basis, about 3-25% Na20 and/or K20 and 50-95% SiO2, the sum of those components constituting at least 55% of the total composition, and the remainder being substantially materials chosen from the group A12O3, BaO, CdO, B2O3, CaO, MgO, PbO, ZrO2, WO3, MoO3, TiO2, SrO, and ZnO, and up to 5% of Li2O;
(b) applying said powder on a substrate; and, thereafter, (c) exposing to a H2O-containing gaseous environment having a relative humidity of at least 5% but less than 50~ at a temperature in excess of 100C. for a sufficient period of time to cause the powder to flow and thereby coat the substrate.
- 6(a) -The instant invention, therefore, enables the hydration of fine-dimensioned glass bodies to be undertaken in a manner to obtain levels of absorbed water which can be carefully control-led. Furthermore, the method permits water contents up to about ; 25% by weight to be obtained within the glass that are adequate to impart thermoplastic properties thereto but which do not give rise to the foaming and cracking phenomena frequently encountered during the dehydration step of the two-step practice described above in United States Patent Application Serial No.
445,453. Also, the amount of water absorbed can be readily ; controlled and maintainea at a sufficiently low value to assure good chemical durability in the hydrated body in those composi-tions where the anhydrous glass exhibits inherent good durability.
It can be recognized that the expression relative humidity is limited ln its description of a water-containing atmosphere at very high temperatures. This situation is founded in the fact that the definition of relative humidity necessarily con-templates a level of saturated vapor pressure. Thus, there is a maximum temperature at which any gas can be liquified, this temperature being defined as the critical temperature. Concomi-tantly, there is a critical pressure, i.e., the pressure demanded to liquefy a gas at the critical temperature. For water, the critical temperature is about 374C. and the critical pressure is about 3200 psi. Above the critical temperature H20 has been defined as a fluid which is not considered to be either a liquid or a gas.
This situation is exemplified in FIGURE 1 taken from page 180 of "Hydrothermal Crystal Growth", R. A. Laudise and J. W.
Nielsen, Solid St Physics, 12, pp. 149-222, Academic Press, New York, 1961, which sets forth pressure-temperature curves for H20 at constant volume. The straight lines in the drawing depict various filling factors, i.e., the percentage of the vol-ume of the autoclave or other pressure vessel which is filled with liquid H2O at ambient temperature. The minimum filling factor, i.e., the minimum amount of liquid H2O which will produce a saturated steam atmosphere (100% relative humidity) can be cal-culated from standard steam tables. As is pointed out in FIGURE
1, this critical filling factor for 374C. is about 30%. FIGURE
1 also illustrates that with filling factors greater than about 30%, the liquid H2O expands to such an extent that the vessel is filled therewith at temperatures below the critical point, viz., 374C., such that the vessel is subjected to hydrostatic pressure. This phenomenon is demonstrated in FIGURE 2 taken from page 181 of the above-noted literature citation. The curves therein were drawn from the density data of H2O liquid and gas phases up to the critical temperature and reflect the height of the meniscus in a pressure vessel as a function of temperature at representative fills.
A study of FIGURE 1 points out the fact that the pressure-temperature curves at constant fill are substantially linear beyond the coexistence curve (the temperature and pressure limits at which liquid and gaseous H2O can exist together) and can probably be safely extrapolated. And, inasmuch as the in-stant invention contemplates treating glass bodies in a gaseous H2O environment, it is believed apparent that a person of ordin-ary skill in the art, with FIGURE 1 and the standard steam tables before him, could readily determine the necessary filling factor to achieve a desired saturated or less than saturated steam atmosphere at temperatures below 374C. and, at temperatures above 374C., could choose a filling factor to achieve any de-sired pressure at a particular temperature. Since the pressure-temperature curves at constant fill are virtually linear beyond 105887~

the coexistence curve, one can essentially extrapolate the behavior of the environment from that of an environment of a certain rela-tive humidity below the critical temperature.
Further treatment of critical temperature, filling factor, etc. can be found in such texts as Steam Tables--Thermodynamic Properties of Water Including Vapor, Liquid, and Solid Phases (English Units), J. H. Keenan, F. G. Keyes, P. G. Hill, and J. G. Moore, John Wiley & Sons, New York, 1969 and Thermodynamic Properties of Steam, Includin~ Data for the Liquid and Solid Phases, J. H. Keenan and F. G. Keyes. Reference is made to those studie for further explanation of these phenomena.
Table I reports a group of glass compositions, expressed in mole percent on the oxide basis, which are operable in the instant invention. The batches therefor can be compounded from any materials, either the oxides or other compounds, which, when fused together, will be converted to the desired oxide composition in the proper proportions. The batch components were carefully mixed together, normally in a ball mill to aid in obtaining a homogeneous melt, and then melted in open plati-num or silica crucibles for about 16 hours at 1450-1600aC.
Larger melts, of course, can be made in pots or continuous melt-ing tanks in accordance with conventional commercial glassmaking practice. Subsequently, the melts were cooled and shaped into glass bodies. Frequently, small particles of glass were made by passing a stream of molten glass through a hot flame, through an air blast, or into water. Where desired, thin ribbon can be drawn which can be hydrated in that form or broken into flakes.
In general, a thickness dimension of 15 mm. has been deemed a ; practical maximum with less than 5 mm. being preferred for speed in securing complete hydration.

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~OS88~7 The hydration step has been carried out in an autoclave since control of steam pressure, relative humidity, and temperature can readily be had in such an apparatus. The thin glass sheet ribbon was point supported above the base plate of the autoclave on re-fractory or TEFLONR or other non-adhering and non-reactive mater-ial horizontally supported above the floor of the autoclave. The autoclave is sealed and heated to generate steam at a desired pressure. In general, steady state operation of the autoclave was reached in about one-half hour, although at the highest tem-peratures employed a somewhat longer period of time was frequentlyrequired.
The length of time needed to achieve hydration throughout the glass or to a desired depth therein is directly related to the composition of the glass and the H2O pressure and tempera-ture utilized in the hydration process. Thus, it is generally true that glasses wherein the alkali metal contents are greater will hydrate more rapidly and to higher water concentrations so long as the ratios of the remaining glass constituents do not change. Such glasses will, in the main, be less chemically durable. Higher treatment temperatures and H2O pressures will also normally result in more rapid hydration. Also, of course, the time for complete reaction is inversely proportional to the smallest cross section of the anhydrous glass body employed.
Finally, whereas the preferred embodiment of the invention in-volves hydrating the glass completely through, it can be appre-ciated that a utility can be had in achieving a surface layer only which is hydrated.
In the following description, a commercially-available autoclave was employed having a chamber of one cubic foot.
Steam pressure was generated by heating distilled water placed in the bottom of the vessel. The pressure was regulated by controlling the temperature. The desired humidity therein was achieved by predetermining the amount of water needed for that humidity at a particular temperature. Hence, the autoclave can be calibrated at any temperature as to the quantity of water required to yield a specific humidity. To insure reproducibil-ity of results, the autoclave was completely dried before using.
With small amounts of glass, the water taken up thereby during hydration is not sufficient to cause a loss in pressure. In the following illustrative examples, filling factors of about 10%
and less were generally employed.
For ease in subsequent forming operations utilizing appar-atus conventional in shaping organic plastic bodies and/or to achieve substantial hydration in not unreasonably long times, particles varying in size from a No. 4 United States Standard Sieve (4.76 mm.) to a No. 400 United States Standard Sieve (37 microns) have been commonly used. Obviously, for the very fine particles, only a relatively short treatment time, e.g., 2-4 hours, in the autoclave will be required at any particular tem-perature, whereas longer exposure times, e.g., 24-72 hours or longer, will be demanded with the larger particles. After a treatment, the autoclave is normally permitted to cool to at least below 100C. at its own rate before the samples are re-moved. However, removal at elevated temperatures is feasible after water has been drained out of the autoclave. The water content taken up by the glass is determined by comparing the weight of the glass before and after the hydration step.
Where the particles are to be formed into a bulk body, it is generally to be preferred that hydration has proceeded com-pletely therethrough. Frequently, the glass particles will flow during the hydration process to form a solid body.

. 1058877 Table II reports a comparison of the water contents in weight percent absorbed by several of the glasses of Table I
utilizing particles passing a No. 18 United States Standard Sieve (1 mm.) wherein an autoclave operati~g for 16 hours at - a temperature of 300C. and at various relative humidities up to 100% was employed.

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105t3877 Table III sets forth a comparison of the water contents absorbed by glasses of Table I after hydrating particles pass-ing a No. 18 United States Standard Sieve in an autoclave operating for 16 hours at a temperature of 350C. at various relative humidities. .

~ABLE III
Relative Humidities and Steam Pressures Example 17.5% 20.6% 25.9% 30.9% 37.1%
~o. (420 psi)(495 psi)(622 psi)(740 psi)(ugo psi)

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13 2.7 2.8 3.6 _ 4.4 - 2.2 - - 6.9 1~ 3.2 7.0 - _ _ Table IV records a comparison of the water content absorbed by glasses of Table I after treatin& particles passing a No. 18 United States Standard Sieve in an autoclave operating for 16 hours at a temperature of about 374C. at various relative hunidities.

TABLE IV
Relative Humidities and Ste~m Pressures Example 16.6% 19.7% 24.1% 27.5%
No. (530 ~si) (630 ~si) (770 PSi) (880 ~si) 3 _ 5.9 9 2.2 3.4 4.o ~.5 - 0.8 - 1.3 11 - 1.4 2.3 2.7 12 1.0 1.4 1.4 2.8 13 2.1 2.4 2.8 3~5 - - 9,0 17 2.4 - ~.3 5.0 Table V illustrates the effect of low alkali metal con-tent upon the water that will be absorbed upon hydration.
Hence, Examples 18-25 contain less than 10 mole percent of ~a20 and/or K20 and Table V reports the amount of water absorbed `oy powders of those glasses passing a No. 200 United States Stand~rd Sieve~'(74 microns) after expGsure in an &uto-clave for 16 hours to a 100% relative humidity atmosphere at 20 250C.

TABLE V

SiO2 80 80 72 87 81 71 ~5 93 Na20 7 7 7 3 3 3 3 5 PbO 5 13 21 4 10 20 2 3 . ~ ~ - - 2 % H20 ~.8 g.2 9,0 ~.,0 9-6 5.3 9.4 8.1 This latter type of glass, viz., compositions containing 10 le percent or less Na20 and/or K20, illustrates the second embodiment of the present invention. Thus, such glasses are preferably hydrated within a practical length of time at high temperature and essentially saturated steam at spheres. Hydra-tion at low relative humidities, while feasible, is not economi-cally attractive due to the time required therefor. Furthermore, as can be seen, the maximum absorbed water content will not exceed about 15~ by weight and is, in general, controlled by the glass composition. This water content is sufficient to impart ther plastic properties to the glass bodies but, concomitantly, yields a hydrated product with good chemical durability.
The effect of the amount of water absorbed in the glass upon the chemical durability thereof is clearly exhibited in Table VI
below. Where the absorbed water content exceeds about 15% by weight, the durability o~ the body is seriously impaired. As a general statement, the lower the absorbed water content, the better the chemical durability. Conversely, as a general pre-mise, the lower the absorbed water content, the less ther -plasticity exhibited by the body. Nevertheless, certain compo-sitions, e.g., those glasses containing a large amount of PbO
such as Examples 9-1~ supra, will de nstrate sufficient thermo-plasticity to be shaped utilizing low temperature forming tech-ni~ues conventional in the plastics art where they contain as little as about 1% absorbed water. In view of these factors, therefore, the preferred bodies will contain about 1-12% by weight water.
Table VI reports the results observed and measured after the exposure of discs pressed Yrom hydrated glass powders of glasses of Table I to distilled water at a temperature of 70C. for 20 hours. A weight loss of less than about 100 micrograms/cm2 has been deemed indicative of satisfactory chemical durability for the ma~ority of general applications.
; ~,; --1 9--i ~-In pressing the discs, the hydrated glQsses were sized according to the particles recorded in Table VI, United States Standard Sieve sizes being emp}oyed. The particles were placed into a 1 1/4" diameter mold, the mold heated to soften the glass, and then a plunger applied at Q load of Qbout 5000-8000 p8i to shape the particles into discs about 1j8"-1/4" thick.

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A practical minimum operable relative humidity with the treating environment has been determined to range about 5%.
However, as has been observed above, the greater the H2O pres-sure and the higher the temperature within the treating environ-ment the more rapid the process of hydration. Hence, with environments exhibiting very low relative humidities, e.g., 5-10%, very high temperatures will commonly be required to promote hydration at a reasonably practical rate. In light of this factor, temperatures in excess of 300C. and, preferably, in excess of 350C. will generally be required where the H2O
pressure employed is very low.
A hydration temperature of at least 100C. and, preferably, higher than 150C., has been demanded to complete the hydration within a reasonable length of time for those glasses of high Na2O and/or K2O content. Such temperatures, however, are not truly practical with the low alkali glasses. Advantageously, a temperature of at least 225C. and, more preferably, higher than 250C. will be utilized for such compositions.
The maximum hydrating temperature is, in actuality, governed by the capability of the equipment employed, assuming that soften-ing andjor melting of the fine-dimensioned material is not deleterious to the purpose envisioned therefor. Hence, tempera-tures of 500-600C. are mechanically feasible. However, hydra-tion will normally, but not necessarily, be undertaken at a temperature below the softening point of the anhydrous glass.
Bulk shapes can be produced from the hydrated particles employing forming methods conventional in the organic plastics art. Thus, the thermoplastic behavior of the materials permits them to be dry pressed, injection molded, or extruded in like manner to organic polymers. Each forming operation commonly contemplates the mass being shaped under pressure and, although 1058t~77 it is sometimes possible for shapes to be formed at about room temperature, elevated temperatures, e.g., about 100-400C., are utilized where better flow in the hydrated material can be obtained. A practical maximum temperature of about 500C. has been determined for the glass compositions of this invention.
Since some volatilization of the absorbed water can take place at the forming temperatures utilized, shaping of the arti-cles within an autoclave or other pressurized system may be warranted. Various atmospheres may also be employed at suit-able pressures to inhibit excessive volatilization of water.
Table VII contrasts the products resulting from bodies of hi~gh and 10N water contents. Particles passing a ~o. 140 United States Standard Sieve (105 microns) of anhydrous glass of each example of glasses of Table I were ffl drated for four hours at 270C. The hydration re~ulted in the softening and coalescing together of the particles into a patty. The patty was broken into variously-sized pieces and these pieces placed into a 1 1/4" diameter mold which preferably had been preheated and a slight pressure (10-50 psi) applied. The unit was there-after heated and at about 270-300C. the glass began to soften.
Thereupon, a load of between about 5000-8000 psi was applied to the mold. After about three minutes, the heat was removed and the mold allowed to cool below 60C. The load was then released and a disc (1/8"-1/4" in thickness) taken from the mold.

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-24_ -T~e haze appearing in examples 3, 6, and 9, utilizing the 38%
relative humidity treatment, and the translucency in example 9, employing the 100% relative humidity treatment, could be elimina-ted through a more carefully controlled hydration procedure.
A180, the cracking phenomenon is frequently observed in bodies containing high water contents unless care is taken in drying the body after the forming step.
We have found these materials to be very useful as paints or coatings on varicus substrates which do not react with the mater-I0 ials in a deleterious manner. Very hard, durable coverings canbe secured by comminuting the glass to a fi~e powder, e.&., pass-ing through a No. 400 United States Standard Sieve, and, option-ally, mixing the powder with a liquid vehicle such as water or methanol to produce a thick slurry. m e dry powder or slurry is applied to a desired substrate, such, for example, as a steel or aluminum plate, a glass s1ide, or a cera~ic article, and the coated ob~ect treated in an autoclave. I~e hydration practice employed will be the same as that recited above for the glass bodies, themselves, and will be dependent upon the alkali metal oxide content of the covering material.
Ex.amples 18 and 20, after treatment at 100% relative humid-ity for two hours at 250C., flowed into hard, clear, glassy coatings.
Examples 1, 3, and 13, after treatment at ~9% relative humidity for 16 hours at 250C., flowed into clear, hard, well-adhered, glassy coatings.
Although in the above working examples air comprised that part of the atmosphere other than steam, it will be appreciated that various inert gases such as heli-lm, argon, and nitrogen can be introduced.

-~5

Claims (9)

The embodiments of the present invention in which an exclusive property or privilege is claimed are defined as follows:

1. A method for making a glass body exhibiting thermoplastic properties which comprises subjecting a fine-dimensioned anhydrous glass body comprising, in mole percent on the oxide basis, about 3-25% Na20 and/or K20 and 50-95% SiO2, the sum of those components constituting at least 55% of the total composition, and the remainder being substantially materials chosen from the group A12O3, BaO, CdO, B203, CaO, MgO, PbO, ZrO2, W03, MoO3, TiO2, SrO, and ZnO, and up to 5% Li20; to a H2O-containing gaseous environment having a relative humidity of at least 5% but less than 50%
at a temperature in excess of 225°C. for a period of time sufficient to develop at least a surface portion having an amount of water absorbed therein effective to impart thermoplastic properties thereto.

2. A method according to claim 1 wherein said temperature ranges up to about the softening point of the anhydrous glass.

3. A method according to claim 1 wherein said temperature ranges up to about 600°C.

4. A method according to claim 1 wherein said fine-dimensioned glass body has a thickness dimension no greater than about 15 mm.

5. A method according to claim 1 wherein said period of time ranges between about 2-72 hours.

6. A method according to claim 1 wherein the amount of water absorbed ranges between about 1-25% by weight.

7. A method for forming a hard, durable, glassy coating on a substrate material comprising the steps of:
(a) preparing a powder of a glass comprising, in mole percent on the oxide basis, about 3-25% Na20 and/or K20 and 50-95% SiO2, the sum of those components constituting at least 55% of the total composition, and the remainder being substantially materials chosen from the group A12O3, BaO, CdO, B2O3, CaO, MgO, PbO, ZrO2, WO3, MoO3, TiO2, SrO, and ZnO, and up to 5% of Li2O;
(b) applying said powder on a substrate and, thereafter, (c) exposing to a H2O-containing gaseous environment having a relative humidity of at least 5% but less than 50% at a temperature in excess of 100°C. for a sufficient period of time to cause the powder to flow and thereby coat the substrate.

8. A method for forming shapes from fine-dimensioned hydrated glass bodies exhibiting thermoplastic properties made in accordance with the method of claim 1 which comprises the steps of:
(a) forming a mass of said fine-dimensioned hydrated glass bodies to a shape of a desired configuration under pressure and at a temperature ranging from about room temperature to about 500°C.;
and, thereafter, (b) bringing said shape to room temperature.

9. A method according to claim 8 wherein said mass of fine-dimensioned hydrated glass bodies is formed at temperatures between about 100°-400°C.