CA1250600A

CA1250600A - Hydrogen-containing glass microfoams and gas-ceramics

Info

Publication number: CA1250600A
Application number: CA000525550A
Authority: CA
Inventors: John F. Macdowell; George H. Beall
Original assignee: Corning Glass Works
Current assignee: Corning Glass Works
Priority date: 1986-08-18
Filing date: 1986-12-17
Publication date: 1989-02-28

Abstract

Abstract of the Disclosure The present invention is concerned with the preparation of glass microfoams and gas-ceramics having compositions selected from the systems of SiO2-Al2O3-B2O3-RO-R2O, SiO2-Al2O3(B2O3)-P2O5-Li2O-[ZrO2(TiO2)], and SiO2-P2O5-B2O3-[RO], wherein RO is selected from the group of MgO, CaO, SrO, BaO, and ZnO, and R2O is selected from the group of alkali metal oxides. The foams comprise hydrogen-containing cells produced through the inclusion in the batch of a hydrogen-generating agent selected from the group of ammonium salts and/or a combination of amines and/or carbohydrates and/or hydrocarbons with phosphates.

Description

~ Beall-MacDowell 47~19A

~YDROGEN-CO~TAINING G~AS5 MICROFOAMS AND GAS~CERAMICS

Back round of the Inve~tion Gas evolution from glasses has been studied both from the ~tandpoints c>f refir~ing of glass and the creation of gla~s foams. As an examp}e of ~ glass fozm, a comrnercial material marketed ~ander the tradeInark FO~MGI~S by Pitt~burgh-Corning, :Pittsburgh, Pennsylvania is pxoduced iD lars~e s~olume by mel ing a typical soda-lime glass under highly oxidizing condi~ions (utilizirlg Na2S04 ~n the batch), r:~mminuting the gl~ss ~o a fine parti~le size, and firing the glass particles in combination with powdered carbon. A
I coarse ~oamed glass of low density (<0.2 g/cm ~ is fo~ned containing carbon dioxide bubbles of 6everal millimeters' diameter. The glass is gray or black in color wi~h a pvrous and dull surfac~.
Porous glasse~, glass-ceramics, and sintered _ ceramics have fre~uently been described in the paten~
literatureO Examples of su~h diæclosures incl~de:
UOS. Pate~t No. lrl08,007 i~ dir~c~ed to the melting o~ ba~alt in graphite cru~ibles. The molten ~asalt reacts with the graphite and bubbles o~ a gas ~not identif ied) are entrained in the melt ., Upon cooling, the melt crystallizes to A porous body.

~Z ~O~

U.S. Patent No. 2,978,340 is concerned with the preparation of hollow glass spheres from discrete, solid particles consisting of an alkali metal silicate, e.g., sodium silicate, a metal oxide which forms an insoluble glass when melted with the silicate, e.g./
B203, and a bloating agent. An extensive list of gasifying agents is furnished, none of which is singled out as exhibiting any unusual behavior.
U.S. Patent No~ 3~189,512 is drawn to foamable ceramic cements wherein a combination of SiC and S03 comprised the foaming agent. The cements were composed of PbO, a metal fluoride, SiC, S03, and a lithium aluminosilicate material ~conveniently petalite).
V.SO Patent No. 3,261,696 reports a method for forming insulating foamed materials comprising the ; steps of: (a) combining ZrO2, A1203, and powder~d aluminum; (b) adding H3P04 to the mixture to cause a reaction to occur which liberates water vapor and hydrogen to foam the mass; and (c) curing the mass at 15oo-8oooF.
U.S. Patent No. 3,634,111 discusses foamable ceramic cements. The cements consisted of a glass having a composition within the Li20-A1203-SiO2-TiO2 system containing SiC as the cellulating ag~nt, and being essentially free from PbO, S03, and fluoride.
U.S. Patent No. 3,811,852 discloses the preparation of porous glass-ceramic masses comprising the steps of frothing the initial glass melt witn gas liberated through fuel combustion in the melt, forming glass ribbon from the melt, and thereaft~r heat treating the glass ribbon in a two-step process to convert the glass into a glass-ceramic.

U.S. Patent No. 4,011,093 describes a foamable ceramic cement consisting essentially of a glass frit having a composition within the Li20-A1203-CeO2-SiO2 system with, opti.onally, ZnO into which SiC is incorporated as a foaming agent.
U.S. Patent No. 4~084,980 is drawn to the production of a foamed body comprising the steps of:
(a~ mixing the following four components, viz., an aqueous solution of an acid or a water soluble acidic phosphate, a cement material or an anhydrous alkali metal silicate, a metal blowing agent, and a foaming stabilizer, to obtain a pasty mass; (b) shaping the pasty mass into a desired geometry; and (c) allowing the shaped mass to stand to eff~ct foaming.
U.S. Patent No. 4,116,703 is directed to the preparation of a foamable cement which comprises mixing together crystalline hydraulic cement, a hydraulic cement in the form of a silicate glass powder, and quaternary ammonium silicate, and then allowing the mixture to react and set at a temperature below 150C.
: U.S. Patent No. 4,133,691 is concerned with the development of an inorganic foam which comprises the steps of: (a) mixing particulate aluminum with an aqueous solution of an alkali metal base to cause the formation of hydrogen gas; (b) folding that mixture into an aqueous alkali metal silicate solution in a manner to xetain concentrated areas of the mixture in the silicate solution; and ~c) thoroughly mixing the ma~erials to form a solid foam.
U.S. Patent No. 4,404,291 reports a method for forming a molded sintered porous body comprising the following steps: (a~ mixing a powdered organic combustible material with powdered glassJ devitrifying solder glass, or glass-ceramic; (b~ heatiny the mi~ture to a temperature sufficient to burn off the organic material ~o form open pores in the resul~ant mass; and then (c) heating the mass to a temper,~ture sufficient to sinter the powders together into an integral body.
As can be observed from the above, various mechanisms have been employed to prepare foamed glass and glass-ceramic bodies. Nevertheless, the production of foamed glasses and glass-ceramics exhibiting the highly desirable combination of fine bubble size, low density, and a non-porous surface has not been satisfactorily achieved. Hence, the primary objective of the present invention is to provide such products.

Summary of the Invention The basis of the instant invention is the finding that foamed, closed-pore glass and glass-ceramic articles, ~herein ~ery fine bubbles composed predominantly of hydrogen are present, can be formed over a range of compositions in the following fundamental systems; viz., SiO2-A1203-B203 RO-R20, P205-SiO~-B203-~RO], and SiO2-A1203(B203)-P205-Li20-[ZrO2~TiO2j], wherein RO is selected from the group of MgO, CaO, SrO, BaO, and ZnO, and R20 is selected from the group of alkali metal oxides, conveniently Li20, Na20, and/or K20. Ammonium salts constitute the preferred source of hydrogen, although similar effects can be obtained in certain compositions through a combination of carbohydrates, hydrocarbons, and amines with phosphates.
As used herein, the term gas-ceramic indicates a body formed by a process wherein foaming concurrently ~5--accompanies crystalli~ation; glass microfoam designates a body formed by a process wherein foaming is generated without crystallization. Gas-ceramics can be produced either through foaming by controlled nucleation of bubbles upon heat treatment of a precursor glass body or by spontaneous nucleation upon coo:ling of a molten glass to a solid body.
In a general composition survey of the three operable systems, three limitations appear to be unqualifiedly mandatory; viz., at least 8% by weight SiO2, at least 30% by weight B203~A1203+P205, and at least 10% by weight B203+P205. Although both B203 and P~05 are desirable in combination in all composition systems, neither alone is absolutely necessary.
Furthermore, all the compositions appear to be "acid";

2 2 3 123~P2s RO+R20, and B203+Al O +
P205>RO+R20. Fluorides appear to be undesirable, as are most easily reducible metal oxides, although sometimes minor amounts of TiO2 and rather considerable levels of ZnO can be tolerated.
The most effective batch ingredients for the introduction of hydrogen-forming species include 4 2 4' 4)2 4~ NH4Cl, NH4B407, and starch and/or suyar with Al(P03)3. Concentrations of those materials ranging from 0.5 to over 50% of the total batch have been found effective, depending upon the base glass composition.
Foaming of the samples was accomplished by heating at about 700-1000C, ~epending upon the base composi~ions thereof, for times ranging from about 10 minutes to several hours.
The hydrogen~containing cells or bubbles are believed to be the result of either the breakdown of 6~g~

ammonium species in the glass, followed by dissolution of hydrogen molecules in the glass at high temperatures and subse~uent release at low tempera1:ures, or by the reduction of stable OH ions in the glass network S through reaction with a reduced phosphorus species such as P 3 or P in the glass.

Si2-Al~~-B 03-RO-R 0 System Operable compositions in this system, expressed in terms of weight percent on the oxide basis, consist essentially of 25-65% Si02, 15-35~ A1~03, 12-35~ B203, and 1.5-20% RO+R20, consisting of 0-15% RO (alkaline earth oxides and/or Zn0) and 0-20% R20 (alkali metal oxides). The level of A1203 in terms of mole percent is maintained higher than the sum of RO+R20. The inclusion of 0.5-10% P205 is desirable but not mandatory.
A heat treatment in the vicinity of 800C i5 generally effective in developing gaseous hydrogen in this system, although temperatures over the range of 700-950C can be operable. Mullite (3A1203.2Si02) and sometimes anorthite solid solution l(Ca,Sr).A1203.2Si02] and AlP04 have been identified through x-ray diffraction analysis. The preferred alkaline earth oxide is CaO, since its presence favors the generation of small bubbles. Ca0-containing, aluminosilicate glasses have been recognized as exhibiting high resistance to gas permeation and low ionic mobility, this latter phenomenon resulting in glasses Qf high electrical resistivity. Because it has been postulated that the rate of hydrogen diffusion controls the rate of bubble growth and the size of the bubbles, glasses demonstrating low permeability to gases have been deemed to be preferred.
The products of this composition system combine a dense glassy skin of good chemical durability with densities typically in the range of about 0~9-2.0 g/cm . The dimensions of the bubbles generally vary from about 50 microns to 1 mm. With the inclusion of low concentrations of Pd, however, which acts as a nucleating agent in amounts of 0.001~0.01% by weight, bubbles having diameters down to 20 microns have been observed.

SiO~-Al~O~(B O~)-P O,-Li~O-[ZrO (TiO~)¦ System The compositions of this system normally crystallize to a substantial degree, the major crystal phase being identified as a ~-quartz solid solution having the general formula nsio2-xLiAlo2 yAlpo4 wherein n~x+y. Although the inclusion of B203 appears to increase ~he proportion of glassy phase after crystallization, it has been conjectured that some BPO~
enters into the quart~ structure in place of silica.
The principal components of the system comprise 25 SiG2, A123t 2 5' 2 ' 2 recorded below, expressed in terms of weight percent on the oxide basis, with TiO2 being capable of replacing at least part of the ZrO2 as a nucleating agent. Total replacement of ZrO2 with TiO2, however, appears to yield products containing coarse blisters.

Si02 ~0-50 Zr2 0-10 P205 10=25 2 Li20 1-7 Ammonium acid phosphate or aluminum metaphosphate combined with starch comprises the preferred hydrogen-generating batch materials. The principal advan~ages of the gas-ceramics derived from this composition system are two; viz~, the potential fox materials exhibiting very low coefficients of thermal expansion arising from the presence of the ~-quartz solid solution phase, and substantial mechanical strength due to the high crystallinity of the bodies.
Heat treatments between about 775-1000C are generally satisfactory to secure the desired high crystallinity.
The bubble sizes typically vary over the range oE about 0.5-5 mm.

Si0 -B~0~-P
This pseudobinary system, in which Si02 and BP04 are the major ylass forming constituents, yields the most uniform glass microfoams with bubbles of the smallest dimensions. Very smooth and uniform solid glass skins encase the foamed articles, the thickness of such skins being variable according to the body composition. Hence, cell diameters range about 1-100 microns, with preferred foams having 5-20 micron cells.
The den~ities of the products average about 1.0 g/cm .
Operable compositions, expressed in terms of weight percent on the oxide basis, consist essentially 2' 5 20% B203, and 15-60~ P 0 narrower composition area being defined in terms of 6~

40 60~ SiO 7-20% g203~ and 20 35~ 2 5 insure the production of uniform foams with glassy skins, an alkaline earth oxide and/or ZnO (RO) may desirably be added. Thus, the lowest density foams have contair~ed about 0-20% MgO, 0-20% CaO, and 0-15~
ZnO. It has been hypothesized that those additions prevent restriction of cell expansion resulting from the crystallization of BP04, and enable the generation of a very fine uniform cell size and the formation of a smooth, glassy, monolithic skin on the foam bodies.
Ammonium acid phosphate is the preferred batch ingre~ient for both hydrogen generation and as the source of P205. It has been observed that compositions containing >13% MgO and/or ZnO tend to foam spontaneously upon cooling, either as poured into a glass body or after the glass body has been placed into an annealer. It has also been observed, however, that MgO and CaO additions greater than about 5~ and 2nO
additions greater than about 10% may result in the body exhibiting a measure of hygroscopic behavior or poor chemical durability~ Therefore, from a practical point of view, the total of MgO+CaO~ZnO will be limited to 0.5-10%, consisting of 0-5~ MgO, 0-5% CaO, and 0-10%
ZnO.
The preferred compositions in this system crystallize only partially (custom~rily <50~ by volume) during foaming, thereby permitting foam cell expansion.
Where crystallization does occur ~750-950C), the principal phases are BP04, exhibiting a ~-cristobalite structure, and/or magnesium pyrophosphate, Mg2P207.
The chemical durability of BP04-containing glass systems is typically quite poor, but can be improved dramatically by: (a) increasing SiO2 above 40~ by weight; (b) reducing B203 below 104 by weight; ~c~
reducing modifier additions to less than 5~ by weight;
and/or (d) adding A1203 up to 10~ ~y weight.

S~ruc~ure and Properties f the Inventive Products .

Several analyses ~f ~he bubbles occurring in the three composition sy,t~ms ~ere cc,rcucted utilizing mass spectrometry. Hydrogen always constituted the pxedominant species. Nitrogen was usually present to some extent, occasionally appearing as air csntamination twith the normal ratio of argon), but sften as primary nitrogen, i.e., without argon, presumably resulting ~rom NH3 breakdown.
The effects of varying the thermal treatment on the generation of hydrogen bubbles are generally dissimilar to those observed in conventional glass-ceramics. For example, whereas it is normally beneficial to optimize nucleation at high viscosities and low crystal growth rates with a "nucleation hold", the rate of bubble nucleation at high viscosities does not appear optimum. Thus, better nucleation is often achieved at higher temperatures where the glass readily deforms; viz., at least 200C above the glass transition temperature~
F~xthermore, there seems to be no clear relationship between the crystallization e-~ent and the formation of hydrogen bubbles. To illustrate, in the mu~lite syste~ ~Si2-Al23-B2G3 RO R2 ) to accompany crystallization in most compositions, but generally precedes crystallization in the other two systems. Even in the high alumina compositions, bubble nucleation appears geometrically unrelated to that of mullite crystallization, with bubble nuclei occurring widely separated by about 100 microns and mullite crystals separated by less than 0.1 micron. In fact, palladium has a far greater effect upon hydrogen nucleation rates than does mullite. Hence, less than 0.01% by weight Pd can increase hydrogen nucleation rates by over an order of magnitude in the high alumina glasses.
The hydrogen bubbles are generally spherical in shape and produce a closed pore foam. As the volume percent of gas increases, the bubbles begin to impinge, thereby producing flat glassy regions separating bubbles. Customarily, the volyme percent of gas does not exceed about 75%. Smaller bubbles are frequently nucleated in the glassy region between large bubbles, thereby indicating that nucleation continues during bubble growth.
The size of the bubbles is dependent upon the rate of nucleation, that rate appearing to be most rapid in the alkaline earth borosilicophosphate system and slowest in the ~-quartz gas-ceramic system. The average bubble diameter in low density foams ranges from about 10 microns in Mg-Zn borosilicophosphates to several millimeters in the ~-quartz system. Bubbles of smaller size (~1 micron) can be observed during the early stage of bubble generation, but the volume percent of gas in the bodies is quite small at that time.
A unique and useful characteristic of the inventive foams is the glossy dense skin which is maintained during bubble generation. It appears that the bubbles do not nucleate or grow within the surface of the bodies~ This phenomenon is believed to be due to hydrogen diffusing out from the surface which causes a depleted layer where bubbles cannot form. The thickness of this hydrogen-depleted layer is variable and can range up to 1 mm.
This dense skin imparts several advantages to these foams. First, it provides relatively higher strength to the body because no bubbles pene~rate the surface to ~reate large fla~s. Second, it permits the surface to be cleaned easily and creates a barrier to penetration by foreign particles. Third, the aesthetic appearance of the inventive materials is far superior to those of standard commercial foam glasses. Fourth, increased strength through thermal tempering may be imparted.
It will be appreciated that the extent of bubble development is affected by ambient pressure. For example, when a material that would normally generate a gas-ceramic containing very small cells and exhibiting a density greater than 1 g/cm upon heating under one atmosphere pressure was heated in a vacuum furnace, a coarse foam of very low density, i.e., less than 0.5 cm was produced. Conversely, when a small glass slab was heated between glass-ceramic plates with excess pressure being applied by stacking refractory bricks upon the upper glass-ceramic plate, the resulting foam had a higher than normal density and the bubbles were elongated parallel to the plates~ i.e., in the minimum stress direction. Furthermore, the specimen, itself, was substantially elongated in the same direction and the surface thereof took on the characteristics of the surfaces of the plates. Quite unexpectedly, no adhesion persisted between the foam body and the plates after cooling. The above activity clearly demonstrates that the inventive gas~ceramics and glass microfoams may be reshaped, reformed, and embossed during thermal treatment without loss of the dense surface layer.
The phenomenon of photosensitive behavior was observed in foams of the borophosphosilicate composition system. After hydrogen generativn, the foam bodies typically exhibit a white coloration, but, after being exposed to the radiation from laboratory fluorescent lamps for a few hours, the surfaces of the bodies take on a distinct pink, orange, or brownish hue. Exposure to direct sunlight produces a more ne~tral gray coloration in the surface. The glass bodies before hydrogen generation manifest no photos~nsiti~e effects.
The development of the pink-orange hue has also been observed when the glasses are undertreated, i.e., heated at temperatures below those at which the best foaming occurs. Also, it has been observed that the color can be bleached out of the surface by heating the bodies above about 500C for a few minutes.
The color of the original glasses in the three composition systems ranges from colorless through gray or brown to black. In the mullite system the color depends upon the presence of P205 and ammonium salts.
Where NH4Cl constitutes the sole a~monium salt in the glass batch, the original glasses are commonly light brown or salmon colored. When ammonium phosphate is present, the glasses are dark brown or black~ Upon generation of hydrogen bubbles, those glasses generally become white and opaque. The opacity is deemed to be due to light scattering by the bubbles, but the change in color from dark to white is not fully understood but -14~

is believed to represent the oxidati.on of reduced phosphorus ions as hydrogen is generated.
In the Li20-containing, higher phosphate, ~-quartz gas-ceramics, the original glasses are yellow to ~rown, orl if TiO2 is present, dark blue to black. The foamed bodies are commonly gray-white or blue, again with a general lightening of color.
In contrast, the borophosphosilicate original ylasses are clear or pale blue or violet, but can darken to a brown or pink-orange color upon hy~rogen generation. When fully foamed at the upper end of the heat treating temperatures, however, the foamed bodies typically tend to become white, as previously described.
Because of the glassy and non-porous skin characteristic of hydrogen glass microfoams, the inventive products are much stronger than the s-tandard commercial foam glasses. For example, abraded modulus of rupture values have been measured on typical mullite gas-ceramics with a density of about 1.3 g/cm averaginy about 4500 psi. Borophosphosilicate glass microfoams of the smallest cell size ~lO micron cell diameter and about l g/cm density), exhibit moduli of rupture averaging about 2500 psi.
A wide variety of thermal expansion characteristics can be found in the inventive gas-ceramic systems. To illustrate, gas ceramics containing mullite and AlPO4 generally exhibit coefficients of thermal expansion (0-300C) between about 40-9OxlO /C; ~ quart~ solid solution yas-ceramics can demonstrate coeffi.cients as low as lOxlO /C; and the smallest bubble foams in the alkaline earth borophosphosilicate system display coeffic~ents over the 40-50xlO /C interval, a good match for silicon metal.
Because of the inclusion of P205 and/or B203 in a number of the compositions, the refractoriness thereof is not very high. Thus, the top use temperature of the products with no thermal distortion will range about 450-900C.
Exceptional dielectric properties have been measured on the inventive products prepared from non-alkali metal compositions in both the SiO2-A1~03-2 3 2 5 Si2-B23-Mg systems Very dielectric constants, low loss tangents, and high electrical resistivities are quite prevalent. For example, a dielectric constant of 2.6 at 25~C and 100 KHz with a corresponding loss tangent of 0.01 was measured on a mullite gas-ceramic, and a dielectric constant ranging from 2.21-2.27 and a loss tangent ranging from 0.000-0.002 over an interval of ; tempera$ures (25-2G0C) and frequencies (100-10 H~) were measured on a borophosphosilicate glass microfoam.
Inasmuch as those products exhibit thermal expansions closely tracking alumina and silicon, their potential for electronic packaging is clear.
In like manner to the circumstances present in many conventional glass and glass-ceramics containing substantial quantities of B203 and/or P205, the silicophosphate foams containing B203 demonstrate poor chemical durability. However, additions of A1203 or an increase in SiO~ appear to bignificantly improve the resistance to chemical attack, as does the crystallization of BP04 and/or Mg2P207 therein which leaves a siliceous continuous glassy phase.

~2~

In the mullite~containing gas-ceramics with little or no P205, and Al203 present in amounts greater than 20~ by weight, the chemical durability is quite good.
The resistance to chemical attack exhibited by the S ~-quartz solid solution-containing materials can also be ~uite good.

Related Application 10 U.S. Application Serial No. 737,204, filed concurrently with the predecessor of the instant application, now Patent No. 4,576,9~0, discloses the preparation of conventional glass-ceramic bodies having compositions within the system B203-P205-Si02.
Description of Preferred Embodiments Table I records a number of batched glass compositions, expressed in terms of parts by weight on the oxide basis, illustrating the compositional parameters of the inventive products encompassed within the i 2 2 3 2 3 2 Y
the individual constituents totals or closely approximates 100, for all practical purposes the figure tabulated for each component can be considered to indicate percent by weight. Other than the hydrogen-forming ingredients, which are tabulated in excess of the base composition, the actual batch constituents may comprise any materi~ls, either oxides or other compounds, which, when melted together, will be converted into the desired oxides in the proper proportions. It will be appreciated that volatile species ]ike NH3 do not fully remain in the glass.

6~

The batches were compounded, ballmilled to aid in securing a homogeneous melt, and charged into silica crucibles. The crucibles were covered, introduced into a furnace operating at about 1400-1600C, and the batches melted for about 2-4 hours. The melts were cast into glass slabs having dimensions of about 8"X4"X0O375", and those slabs were annealed overnight at about 500~-700C.
Table I

SiO 60.0 58.3 35.0 3~.0 37.0 40.0 35.0 40.0 2~3 20.0 20.1 25.0 25.0 25.025.0 25.0 30.0 B203 17.5 19.1 25.0 25.0 25.030.0 25.0 30.0 Li 0 - - ~ ~ ~ 5.0 - 5.0 Na20 2.5 2.5 - - - - -K20 - - 15.0 13.013.0 15.0 NH4Cl 1.0 1.0 2.5 - 0.5 0.50.5 0.5 (NH4)2HP04 - - - 1.01.0 1.01.0 1.0 Cr203 0.05 _ _ _ _ _ 20 F - 1.0 - - - - - -Pd ~ 0.0006 0.0006 _ 10 11 12 13 14 15 16_ SiO2 37.5 ~0.0 38.037.0 31.0 39.0 37.5 40.0 A123 25.0 25.0 26.027.0 26.0 27.0 27.0 25.0 B203 30.0 28.0 28~028.0 30.0 28.0 28.0 15.0 Li20 2~0 2.0 - - - 1.0 - -Na20 - - 2~0 2.0 - 1.5 - -CaO 5.5 5.0 5.0 5.0 5.0 3.5 7.5 10~0 NH4C1 0.5 0.5 0.5 0.5 0.7 0-5 O.S 0.5 (NH4)2HP041.0 1.0 - - _ _ _ 4 2 4 2.0 4.01.5 10.0 8.0 Pd .0006 .0006 .0006 .0006 .0006 .0006 .0006 .0006 BaO - - - - 8.0 2 5 ~ - 10.0 __ _ SiO2 40.0 38.0 ~0.0 40.0 35.0 38.0 40.0 33.0 A123 25.0 25.0 25.0 25.0 20.0 25.0 25.0 24.0 2 3 15.0 17.0 15.0 20.0 2000 17.0 15.0 16.0 20CaO 10.0 10.0 - - - - 10.0 10.0 BaO - - - - - - - 12.0 P O 10.0 10.0 10.0 10.0 10.0 10.0 10.0 5.0 Starch 1.0 NH3 - 1~4 1.5 0.7 1.5 1.5 0.5 1.0 25C1 - 0.33 0.33 0.33 0.33 0-33 ~ 0 5 Pd ~ 0.01 0.003 0.001 0.001 0.001 - 0.0006 Specimens of suitable geometry for use in conducting tests for various physical and chemical properties were cut from the slabs and those specimens placed inside an electrically-heated furnace. Although more rapid or slower heating rates can be employed, as a matter of convenience the temperature wi~hin the 6~

furnace was raised as a rate of about 5C/minute to the foaming temperature recited in Table II, and that temperature maintained for the period of time listed in Table II. Likewise, whereas faster or slower rates of 5 cooling the foamed bodies to room temperature can be operable, as a matter of convenience the electric power to the furnace was merely cut off and the furnace permitted to cool with the bodies retained therewithin.
This cooling practice has been termPd "cooling at furnace rate" ~nd averages about 2-3~C/minute.
Table II also records a visual description of the original glass, a visual description of the gas ceramic, various properties exhibited by the gas-ceramicsr and crystal phases identified therein.
Table II
Heat Glass Treatment Gas-Ceramics Appearance, Example Appearance C-hrs. Properties, and Crystals l Transparent, 750-2 Transparent, turquoise some seeds, 800-4 color, grown seeds, turquoise mullite color 2 Clear, some 750-2 Scattered bubbles, seeds and 800-4 mullite stones

3 Clear, brown 750 2 <l mm bubbles, ~10%
streaks, few 800-4 by volume bubbles, seeds some distortion

4 Clear, brown 750-2 Clear surface layer, streaks, few 800-4 ~10% by volume fine seeds bubbles Dark brown- 750-2 Clear surface layer, to~black, 800-4 ~10% by volume fine streaky bubhles : 6 Dark brown- 750-2 ~20~ by volume fine to~black, 800-4 bubbles streaky 7 Gray, 700-12 Glassy skin, ~15 swollen by volume fine buhble area, bubbles patchy bottom nucleation 8 Black with 850-4 Blue-gray, bubbles, some area of ~50% by volume body brown translucent expansion 9 Clear, pale 800-4 Fine gas-ceramic, ;: gray streaky, ~30-40%
by volume body expansion, 50-100 micron bubbles, mullite Gray with 800-4 25% linear, 20%
fine bubbles vertical, and 40 on bottom by volume body expansion, glossy, mullite ll Black 800 4 45~ hydrogen bubbles, streaks whitel fine-grained 12 Black 800-4 50~ hydrogen bubbles, streaks white, fine-grained, density 1.28 g/cm , 4400 psi MOR

13 ~lack- 800-4 30% by volume body clear, expansion, medium-cordy grained 14 Bulged, 800-4 Fine-grained gas-fine glass- ceramic ceramic in middle Largely 800-4 120% by volume body ~ black with expansion, 60~
~ 20 light brown hydrogen fine bubbles, ~: cord mullite 16 Clear, 800-4 130% by volume body pale brown expansion, floats on water, white, ~ine bubbles, AlPO4 17 Clear with 950-4 Clear with many dark cord blisters 18 Brown, 850-4 Gray, fine-grain ; : black fracture, floats on water 19 Black with 850-4 Gray, medium bubbles, areas of floats on water brown translucence Clear with 850-4 Medium-coarse bubbles, brown streaks blue-white, density 0.7 g/cm 21 Gray, light 850-4 Glossy skin, medium brown areas bubbles, density 1.1 g/cm of transparency 22 Seedy 850-4 Blisters and bubbles, floats on water 23 Clear, dark 950-4 Clear with medium streaks bubbles, ~10~ by volume bubbles 24 Black, 850-4 White, fine bubbles, bands of density 1.2 g/cm , translucency 30% expansion thickness Table III lists several batched glass compositions, expressed in terms of parts by weight on the oxide basis, illustrative of compositions included within the 2 2 3~23~ P2os-Li2o-[zro2(Tio2)~
system. Inasmuch as the sum of the individual constituents of the base glass totals or closely approximates 100, for all practical purposes the value recited for each component may be deemed to reflect weight percent. Other than the hydrogen-forming ingredients, which are tabulated is~ excess of the base composition, the actual batch constituents may comprise any materials, either oxides or other compounds, which, when melted together, will be converted into the desired oxides in the proper proporti3ns. Again, the volatile compounds NH3 and starch are vaporized off to a great extent during glass form~tion.
The batches were compounded, ballmilled to assist in obtaining a homogeneous melt, and charged into silica crucibles. The crucibles were covered, introduced into a furnace operating at about 1500C, and the batches melted for about 4 hours. The melts were cast into glass slabs having dimensions of abou~
8"x4"x0.375", and those slabs were annealed overnight at about 500C.
Table III

SiO2 42.1 42.0 47.048.5 A123 29.3 25.0 20.0 2 3 10.0 10.031.0 Li20 2.0 4.0 4.0 6.0 P205 21.6 20.0 20.014.5 MgO 5.0 - - _ 2 _ 5.0 2 - 5.0 - 3 0 NH3 ~ 5.3 4.9 4~9 3.5 Starch - 1.0 - -Samples of proper configuration for use in conducting tests for various physical and chemical properties were cut from the slabs and those samples, along with the remairsder of the slabs, were inserted into an electrically-heated furnace. In like manner to the glasses of Table I, the samples were heated at a ' ,t -~4-rate of about 5C/minute to the foc~ing temperature recorded in Table IV, maintained at that temperature for the period of time listed in Table IV, and thereafter cooled at furnace rate.
Table IV also presents a visual description of the original glass, a visual description of the gas-ceramic, ~arious properties exhibited by the gas-ceramics, and crystal phases identified therein.
Table IV
Heat Glass Treatment Gas-Ceramic Appeaxance, Example Appearance C-hrs. Properties & Crystals Clear/ seedy 775 2 Gray/ ~15% by 990-4 volume bubbles, fine grained, ~-quartz solid solution 26 Black with 750-4 Blue, ~75% by 23 raised volume bubbles, blisters coarse-grained, floats on water 27 Dark blue 850-4 ~50% by volume coarse bubbles, ~ blisters 28 Seedy, 850-4 Clear~ cherty colorless fracture, ~50% by volume bubbles, : blisters, ~~quartz solid solution ~25~

Table V records a variety of batched glass compositions, expressed in terms of parts by weight on the oxide basis, indicating compositions encompased within the P205-Si02-B203-[RO] system. Si~ce the to~al of the individual constituents of the base glass equals or closely approaches 100, for all practical purposes the concentration listed for each component may be considered to comprise weight percent. Other than the hydrogen-forming ingredients, which are tabulated in excess of the base composition, the actual batch constituents may be any material, either the oxide or other compound, which, when melted together, will be converted into the desired oxide in the proper proportions. Yet again, most of the NH3 is volatilized off during glass formation.
The batches were compounded, ballmilled to aid in achieving a homogeneous melt, and charged into silica crucibles. The crucibles were covered, intxoduced into a furnace operating at about 1600C, and the batches melted for about 2 hours. The melts were cast into glass slabs having dimensions of about 8"x4"x0.25", and those slabs were annealed overnight at about 600C.
Table V
29 _ 31 32 33 34_ Si02 30.0 23.733.3 10.0 15.0 25.0 B203 11.2 11.419.0 14.4 13.6 12.0 MgO 13.0 - - 16.7 15.8 13.9 Ca0 ~ 18.3 4.1 - - -205 45.8 46.643.7 59.0 55.6 49.1 NH3 11.2 11.410.7 14.4 13.6 12~0 6~
--~6-_ 36 37 38 3940_ SiO235.621.7 34~1 34.8 33.8 33.8 B20325.812.6 19.8 15.2 14.7 14.7 MgO - 14.5 5.7 8.8 8.5

5 ZnO ~ 5 2 3 2.9 P2~538.651.2 40.4 41.2 ~0.0 40.0 NH39.4 12.5 9.~ 10.1 9~8 9.8 SiO240.039.0 41.1 40.~ 37.3 50.5 B20313.913.5 14.3 9.5 17.3 11.0 MgO2.7 ZnO5.4 10.6 5.6 11.1 10.1 8.6 P20537~3 36.9 38.9 38.6 35.3 29.9 NH3 9.3 9.0 9.5 9.4 8.6 7.3 SiO252.8 53.4 56.1 58.0 59.~
P20531.3 31.4 26.5 27.4 23.4 2 311.5 15~4 9.8 6.7 17.2 ZnO - - 7.6 7.9 MgO 4.4 NH3 7.7 7.7 6.5 6.7 5.7 ~ Specimens of the proper shape for use in determining various physical and chemical properties were cut from the slabs and those specimens, along with the remainder of the slabs, except ~or Examples 32-34, were inserted into an electrically-heated fuxnace.
Examples 29-31 and 35-42 were heated at a rate of about 5C/minute to the foaming temperatures recorded in Table VI, held at that temperature for the period of ~ ~'3 time reported in Tabl~ VI, and then cooled at furnace rate~ Examples 43~46 were heated at a rate of about 50C/hour to the foaming temperature xeported in Table VI, held thereat for the times specified in Table VI, and thereafter cooled ~t furnace rate Examples 47-51 were heated at a rate of about 5C/minute to about 800C and thereafter the samples were raised at about 50C/hour to the foaming temperatures listed in Table VI, maintained at that temperature for the times recorded, and then cooled at furnace rate. Examples 32-34 spontaneously developed into gas-ceramics as the melts cooled to slabs.
Table VI also includes a visual description of the original glass, a visual description of the heat treated product, various properties exhibited by the heat treated product, and crystal phases identified therein. Several specimens were immersed into boiling ; water for 1-3 hours and their appearance examined thereafter. A rating of 1-5 was assigned; l indicating very little or no change and 5 reflecting severe attack.
Table VI
Heat Heat Treated Glass Treatment Product Appearance, 25 Example Appearance C-hrs. Properties, & Crystals 29 White, 775-4 White, deformed, density translucent 0.6 g/cm , fine-medium bubbles White 775-4 White, deformed, fine opal, waxy bubbles, density 0.7 fracture g/cm 31 Clear, 775-4 Medium-to-coarse bubbles, seedy orange skin, density 0.8 g/cm , floats on water 32 Spontaneous Glassy skin, 300~
gas-ceramic by volume body expansion 33 Spontaneous Glassy skin, 250~ by gas-ceramic volume body expansion 34 Spontaneous Glassy skin, 400% by gas-ceramic volume body expansion Clear 900-2 Fine-grained, light orange, glossy skin, few large blisters, 36 Clear B00-2 Medium cells, uneven matte skin, 400% by volume body expansion, Mg2P207 37 Clear 900-2 Fine cells, glossy skin, 350% by volume body expansion, amorphous 38 Clear 900-2 Very fine bubbles, light pink, glossy skin, 300~
by volume body expansion, amorphous, H20 test 5 o~
~29-39 Translucent 900-2 Coarse cells, white, White matte skin; 400% by volume body expansion, H20 test 3 Clear 900-2 Very fine cells, pink, glossy skin, 300% by volume body expansion, hygroscopic, amorphous 41 Clear 900-2 Very fine cells, ivory-white, glass skin, 300%
by volume body expansion, amorphous, H~0 test 2 42 Clear 900-2 Very fine cell.s, ivory-white, glass skin, 300%
~: by volume body expansion, amorphous, H20 test 2 ~; 20 43 Clear 900-2 Extremely fine cells, orange, glass skin, 200% by volume body expansion, H20 test 1 44 Clear 900-2 Extremely fine cells, orange, glass skin, : 200% by volume body ~ expansion, H20 test l-t .: ..

!

~2~ Q

Clear 900-2 Very fine cells~ ivory, glass skin, 300~ by volume body expansion, amorp]hous, H20 test 5 46 Clear 900-2 Very fine cells, ivory, ; glass skin, few glassy cords, 150% by volume body expansion, H20 test 1~

47 Clear 950-2 Very fine-celled, ivory-white with smooth, glassy skin, 300~ by volume body expansion, H20 test 2 48 Clear 1000-1 Fine-celled, salmon pink foam with glassy skin, very few small blisters, 150% by volume body expansion, H20 test 1 49 Clear 950-2 Very fine-celled light orange foam with smooth glassy skin, 300~ by volume body expansion, H20 test l 50 Clear 950-2 Very fine-celled light orange foam with smooth glassy skin, 200~ by volume body expansion, H20 test 1 51 Clear 1000-1 Very fine-celled white foam with white opal glass ~kin, 203% by volume body expansion, H20 test 1 Table VII illustrates that ~he density of the inventive products decreases with heat treatment, corresponding to an increase in cell volume and cell diameter.
Table VII
Example No. 42 Heat Treatment Density (~!cm ) Cell Diameter (microns~
None 2.40 5C/min. to 850C-hold 2 hrs. 1.64 5 20 5C/min. to 900C-hold 2 hrs. 1.10 20 5C/min. to 25 g50C-hold 2 hr's. 1.04 50 Table VIII records ~he results of mass spectrometry bubble analyses on several foam compositions in terms of mole percent.
3~

~ '~

~32-_ble VIII
ExamE~ e ~ Nitr~
-3 98 ~ 7~3%
1;~! 95~9%4~1.%
17 9E~%
26 98 ~ 7%lo 3~6 33 99 . 39~0 0 7%

:~ 20

Claims

WE CLAIM:

1. Hydrogen-containing glass microfoams and gas-ceramics having compositions selected from the systems of SiO2-A1203-B203-RO-R20, Si02-Al203(B203)-P205-Li20-LZrO2(Tio2)], and SiO2 -P2O5 -B2O3 -[RO], wherein RO is selected from the group of MgO, CaO, SrO, BaO, and ZnO, and R20 is selected from the group of alkali metal oxides.

2. Hydrogen-containing glass microfoams and gas-ceramics according to claim 1 containing, expressed in weight percent on the oxide basis, at least 8% SiO2, at least 30% B203+A1203+P205, and at least 10%
B2O3+P2O5 , wherein SiO2+B203+Al203+P205>>R0+R20 and B203+A1203+P205>R0+R20.

3. Hydrogen-containing glass microfoams and gas-ceramics according to claim 1 having glassy skins selected from the system SiO2 -Al2O3-B2O3-RO-R2O
consisting essentially, expressed in weight percent on the oxide basis, of:
SiO2 25-65 RO 0-15 B203 12-35 RO+R20 1.5-20

4. Hydrogen-containing glass microfoams and gas-ceramics according to claim 1 selected from the system SiO2-A1203(B203)-P205 Li20-[Zr02(Ti02)]
consisting essentially, expressed in weight percent on the oxide basis, of:
SiO2 40-50 Zr02 0-10 P205 10-25 Ti02 0-5 Li20 1-7

5. Hydrogen-containing glass microfoams and gas-ceramics according to claim 1 having glassy skins selected from the system SiO2-B203-P205-[RO] consisting essentially, expressed in weight percent on the oxide basis, of 10-65% SiO2, 5-25% B203, and 15-60% P205.

6. Hydrogen-containing glass microfoams and gas-ceramics according to claim 5 also containing 0.5-10% MgO+CaO+ZnO consisting of 0-5% MgO, 0-5% CaO, and 0-10% ZnO.

7. Hydrogen-containing glass microfoams and gas-ceramics according to claim 5 consisting essentially, expressed in terms of weight percent on the oxide basis, of 40-60% SiO2, 7-20% B203, and 20-35%
P205.

8. Hydrogen-containing glass microfoams and gas-ceramics according to claim 7 also containing 0.5-10% MgO+CaO+ZnO consisting of 0-5% MgO, 0-5% CaO, and 0-10% ZnO.

9. A method for making hydrogen-containing glass microfoams comprising the steps of:
(a) melting a batch for a glass having a composition selected from the systems of Si02-Al203-B203-RO-R20, Si02-Al203(B203)-p205 -Li20-[ZrO2(TiO2)] and SiO2-P205-B203-[R0], wherein RO is selected from the group of MgO, CaO, SrO, BaO, and ZnO
and R20 is selected from the group of alkali metal oxides, and containing a hydrogen-generating agent selected from the group of ammonium salts and/or a combination of amines and/or carbohydrates and/or hydrocarbons with phosphates;
(b) cooling the melt and simultaneously forming a glass shape of a desired configuration therefrom; and thereafter (c) heat treating said shape at about 700°-1000°C
for a sufficient length of time to cause the generation of hydrogen containing cells therein.

10. A method according to claim 9 wherein said glass microfoams contain, expressed in weight percent on the oxide basis, of at least 8% SiO2, at least 30%
B203+A1203+P205, and at least 10% B203+P205, wherein Si02+B203+Al203+P203 >> RO+R20 and B203+A1203+P2O5>RO+
R20 .

11. A method according to claim 9 wherein said glass microfoams are selected from the system SiO2-A1203-B203 -RO-R20, have glassy skins, and consist essentially, expressed in weight percent on the oxide basis, of:
SiO2 25-65 RO 0-15 Al203 15-35 R20 0-20 B203 12-35 RO+R20 1.5-20

12. A method according to claim 9 wherein said glass microfoams are selected from the system SiO2-A1203 (B203)-P205-Li20-[ZrO2(TiO2)], have glassy skins, and consist essentially, expressed in weight percent on the oxide basis, of:
SiO2 40-50 Zr02 0-10 Al203 15-35 B203 0-15 P205 10-25 Ti02 0-5 Li20 1-7

13. A method according to claim 9 wherein said glass microfoams are selected from the system Si2-B203-P205-[RO], have glassy skins, and consist essentially, expressed in weight percent on the oxide basis, of 10-65% SiO2, 5-25% B203, and 15-60% P205.

14. A method according to claim 13 also containing 0.5-10% MgO+CaO+ZnO consisting of 0-5% MgO, 0-5% CaO, and 0-10% ZnO.

15. A method according to claim 13 wherein said glass microfoams consist essentially, expressed in terms of weight percent on the oxide basis, of 40-60% SiO2, 7-20% B203, and 20-35% P205.

16. A method according to claim 15 also containing 0.5-10% MgO+CaO+ZnO consisting of 0-5% MgO, 0-5% CaO, and 0-10% ZnO.

17. A method according to claim 9 wherein said hydrogen-generating agent is selected from the group of NH4H2P04, (NH4)2HP04, NH4Cl, NH4B407, and starch and/or sugar with Al(P03)3.

18. A method for making hydrogen-containing gas-ceramics comprising the steps of:
(a) melting a batch for a glass having a composition selected from the systems of SiO2-A1203-B203-R0-R20, Si02-Al203(B203)-P205-Li2o-[zro2 (TiO2 )], and SiO2-P205-B203-[RO], wherein RO is selected from the group of MgO, CaO, SrO, BaO, and ZnO, and R20 is selected from the group of alkali metal oxides, and containing a hydrogen-generating agent selected from the group of ammonium salts and/or a combination of amines and/or carbohydrates and/or hydrocarbons with phosphates;
(b) cooling the melt and simultaneously forming a glass shape of a desired configuration therefrom; and thereafter (c) heat treating said shape at about 700°-1000°C
for a sufficient length of time to cause the generation of hydrogen-containing cells and the growth of crystals therein.

19. A method according to claim 18 wherein said gas ceramics contain, expressed in weight percent on the oxide basis, at least 8% SiO2, at least 30%
B203+A1203+P205, and at least 10% B203+P205, wherein Si02+B0203+Al203+P205>>R0+R20 and B203+A1203+P205>RO+R20.

20. A method according to claim 18 wherein said gas-ceramics have glassy skins, are selected from the system SiO2-A1203-B203-RO-R20, contain mullite as the predominant crystal phase, and consist essentially, expressed in weight percent on the oxide basis, of Si02 25-65 R0 0-15 B203 12-35 RO+R20 1.5-20

21. A method according to claim 18 wherein said gas-ceramics are selected from the system Si02-Al203(B203)-P205-Li20-[Zro2(TiO2)], have glassy skins, contain .beta.-quartz solid solution as the predominant crystal phase, and consist essentially, expressed in weight percent on the oxide basis, of:
SiO2 40-50 Zr02 0-10 A1203 15-35 B203 0-l5 P205 10-25 Ti02 0-5 Li20 1-7

22. A method according to claim 18 wherein said gas-ceramics are selected from the system SiO2-B203-P205-[R0], have glassy skins, contain BPO4 and/or Mg2P207 as the predominant crystal phase, and consist essentially, expressed in weight percent on the oxide basis, of 10-65% SiO2, 5-25% B203, and 15-60%
P205.

23. A method according to claim 18 also containing 0.5-10% MgO+CaO+ZnO consisting of 0-5% MgO, 0-5% CaO, and 0-10% ZnO.

24. A method according to claim 22 wherein said gas-ceramics consist essentially, expressed in terms of weight percent on the oxide basis of 40-60% SiO2, 7-20%
B203, and 20-35% P205.

25. A method according to claim 24 also containing 0.5-10% MgO+CaO+ZnO consisting of 0-5% MgO, 0-5% CaO, and 0-10% Zn0.

26. A method according to claim 18 wherein said hydrogen-generating agent is selected from the group of NH4H2P04, (NH4) 2HP04, NH4Cl, NH4B407, and starch and/or sugar with Al(P03)3.

27. A method for making spontaneous hydrogen-containing gas-ceramics containing BP04 and/or Mg2P207 as the predominant crystal phase comprising the steps of:
(a) melting a batch for a glass consisting essentially, expressed in weight percent on the oxide basis, of SiO2 10-65 MgO 0-20 B203 5-20 ZnO 0-15 P205 15-60 MgO+ZnO >13-20 and containing a hydxogen-generating agent selected from the group of ammonium salts and/or a combination of amines and/or carbohydrates and/or hydrocarbons with phosphates; and, thereafter, (b) cooling the molten glass to a solid body.

28. A method according to claim 27 wherein said hydrogen-generating agent is selected from the group of NH4H2P04, (NH4)2HP04, NH4Cl, NH4B407, and starch and/or sugar with Al(PO3)3.