METHOD OF MANUFACTURING POROUS SINTERED PYREX®-TYPE GLASS AND METHODS OF SYNTHESIZING COMPOSITES AND POWDERS OF ALKALINE EARTH SILICATES

Abstract

The invention provides a process for preparing a porous glass, comprising mixing borosilicate glass powder with calcium carbonate particles to form a mixture, sintering the mixture at a temperature in the range from 750 to 850 C. to obtain a sintered body, cooling the sintered body and leaching calcium carbonate from the cooled sintered body with the aid of an acid. The invention also provides a process for the preparation of one or more alkaline earth metal silicates by reacting a vitreous material and an alkaline earth carbonate, optionally in the presence of a transition metal or post-transition metal oxide, at a temperature lower than 1200 C., to form a composite consisting of one or more alkaline earth metal silicates and a residual glass, and optionally recovering the one or more silicates.

Claims

1. A process for preparing a porous glass, comprising mixing borosilicate glass powder with calcium carbonate particles to form a mixture, sintering the mixture at a temperature in the range from 750 to 850 C. to obtain a sintered body, cooling the sintered body and leaching calcium carbonate from the cooled sintered body with the aid of an acid.

2. A process for preparing a porous glass according to claim 1, further comprising processing the mixture into aa desired geometrical shape under the application of pressure and optionally in the presence of a binder, sintering at a temperature in the range from 750 to 850 C. to obtain a sintered body, wherein the cool down of the sintered body includes a step quenching of the sintered body at a temperature high enough to suppress calcium hydroxide formation; and leaching calcium carbonate from the quenched sintered body with the aid of a mineral acid.

3. A process according to claim 2, wherein the sintered body is quenched to a temperature in the range of 350 C. to 450 C.

4. A process for the preparation of one or more alkaline earth metal silicates by reacting a vitreous material and an alkaline earth carbonate, optionally in the presence of a transition metal or post-transition metal oxide, at aa temperature lower than 1200 C., to form a composite consisting of one or more alkaline earth metal silicates and aa residual glass, and optionally recovering the one or more silicates.

5. A process according to claim 4, wherein a vitreous material in a powder form, alkaline carbonate powder, and optionally one or more transition metal or post-transition metal oxide powders are mixed, and the mixture is subjected to at least one cycle of particle size reduction, to form a finely ground mixture.

6. A process according to claim 4, wherein the vitreous material is in the form of borosilicate glass powder.

7. A process according to claim 6, wherein the reaction occurs at a temperature in the range of 850 C. to 950 C.

8. A process according to claim 4, wherein the alkaline earth metal silicate has the formula M.sub.aM.sub.b.sup.IM.sub.c.sup.IISi.sub.dO.sub.e in which: M is an alkaline earth metal Ca, Sr or Ba, and a is 1 or 2; M.sup.I is a transition metal, and b is from 0 to 1, inclusive; M.sup.II is a post transition metal, and c is from 0 to 1, inclusive; such that the sum of b and c equals 0 or 1; d is an integer in the range from 1 to 5, inclusive; and e is an integer in the range from 3 to 10, inclusive.

9. A process according to claim 8, wherein b and c both equal zero.

10. A process according to claim 9, comprising mixing borosilicate glass powder and barium carbonate powder to form a composite consisting of BaSi.sub.2O.sub.5 and residual glass.

11. A process according to claim 8, wherein M.sup.I is Cu or Ti, M.sup.II is Sn, 0.1<b1 and 0c<0.9.

12. A process according to claim 11, comprising mixing borosilicate powder, alkaline earth carbonate powder and one or more powders selected from CuO, TiO.sub.2 and SnO.sub.2, wherein the composite prepared comprises an alkaline earth metal silicate selected from the group consisting of: BaCuSi.sub.2O.sub.6, BaCuSi.sub.4O.sub.10.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0034] FIG. 1 shows XRD patterns of 20 wt. % CaCO.sub.3 mixture with ball milled Pyrex-type powder before sintering (sample code JH-052-117A), after sintering at 750 C. (sample code JH-052-117B) and after leaching the sintered sample in HCl solution (sample code JH-052-117C).

[0035] FIG. 2 shows an XRD pattern of 20 wt. % CaCO.sub.3 in ball-milled soda lime container glass after sintering at 700 C. and leaching in HCl solution (sample code JH-053-86A1).

[0036] FIG. 3 shows XRD patterns of 30 wt. % CaCO.sub.3 in ball-milled soda lime container glass after pressing (sample code JH-053-78), after sintering at 700 C. (sample code JH-053-78B) and after leaching the sintered pellet in HCl solution (sample code JH-053-78C1).

[0037] FIG. 4 shows an XRD pattern of an unbroken pellet made of 30 wt. % CaCO.sub.3 and ball milled Pyrex-type glass, after sintering at 850 C. (sample code JH-054-7B2).

[0038] FIG. 5 shows an XRD pattern of broken pellet made of 30 wt. % CaCO.sub.3 and ball milled Pyrex-type glass, after sintering at 775 C. (sample code JH-054-7B11).

[0039] FIGS. 6A-6D and 7A-7D present SEM images (1000 and 5000 magnifications, respectively) of four pellets of Table 7 which were prepared with 20 wt. % (Example 73; JH-054-8A16), 30 wt. % (Example 76; JH-054-8B16), 40 wt. % (Example 79; JH-054-8C16) and 50 wt. % (Example 82; JH-054-8D21) CaCO.sub.3.

[0040] FIG. 8 shows an XRD pattern of the pellet of Example 85, made of 50 wt. % BaCO.sub.3 and 50 wt. % Pyrex-type glass after sintering at 850 C. (sample code JH-054-13D-8).

[0041] FIG. 9 shows an XRD pattern of the pellet of Example 86, made of 50 wt. % SrCO.sub.3 and 50 wt. % Pyrex-type glass after sintering at 850 C. (sample code JH-054-22D-5).

[0042] FIG. 10 shows an XRD pattern of Example 87, the reaction product of ball milled Pyrex-type glass powder and BaCO.sub.3 at 850 C. (sample code JH-052-127).

[0043] FIG. 11 shows an XRD pattern of Example 88, the reaction product of amorphous silica and BaCO.sub.3 at 850 C. (sample code JH-052-129A).

[0044] FIG. 12 shows an XRD pattern of Example 89, the reaction product of quartz and BaCO.sub.3 at 850 C. (sample code JH-052-129B).

[0045] FIG. 13 shows an XRD pattern of Example 90 (sample code JH-054-48), indicating BaCuSi.sub.2O.sub.6 formation.

[0046] FIG. 14 shows an XRD pattern of Example 91 (sample code JH-054-49), indicating BaCuSi.sub.4O.sub.10 formation.

[0047] FIG. 15 shows an XRD pattern of Example 92 (sample code JH-054-50), indicating CaCuSi.sub.4O.sub.10 formation.

[0048] FIG. 16 shows an XRD pattern of Example 93 (sample code JH-054-73), indicating SrCuSi.sub.4O.sub.10 formation.

[0049] FIG. 17 shows an XRD pattern of Example 94 (sample code JH-056-9B1), indicating BaTi.sub.0.25Sn.sub.0.75Si.sub.3O.sub.9 formation.

[0050] FIG. 18 shows an XRD pattern of Example 95 (sample code JH-056-11), indicating Ba.sub.2TiSi.sub.2O.sub.8 formation.

[0051] FIG. 19 shows an XRD pattern of a bar made of ball milled Pyrex-type glass and BaCO.sub.3 powder sintered at 900 C. for 1 hour, Example 96 (sample code JH-054-38).

[0052] FIG. 20 shows a dilatogram of the bar sintered at 900 C. for 1 hour, Example 96 (sample code JH-054-38).

[0053] FIG. 21 shows an XRD pattern of a bar made of Pyrex-type glass sintered at 900 C. for 1 hour, Example 97 (sample code JH-054-66).

[0054] FIG. 22 shows an XRD pattern of a bar prepared by modified procedure and sintered at 900 C., Example 98 (sample code JH-054-87).

[0055] FIG. 23 shows an XRD spectrum of bar prepared by a modified procedure and sintered at 950 C., Example 99 (sample code JH-054-88).

[0056] FIG. 24 shows an XRD pattern of a bar prepared by a modified procedure and sintered at 850 C., Example 100 (sample code JH-054-90).

[0057] FIG. 25 shows a dilatogram of the 3.sup.rd run of a bar prepared by a modified procedure and sintered at 900 C., Example 98B (sample code JH-054-87B).

[0058] FIG. 26 shows a dilatogram of the 3.sup.rd run of a bar prepared by a modified procedure and sintered at 850 C., Example 100B (sample code JH-054-90B).

[0059] FIG. 27 shows a dilatogram of the 3.sup.rd run of a bar prepared by a modified procedure and sintered at 950 C., Example 99B (sample code JH-054-92B).

EXAMPLES

[0060] Materials and Methods

[0061] Ethanol (96%), Isopropanol (abs.), Poly Vinyl Alcohol (99%), Hydrochloric acid (37%), CaCO.sub.3 (99%), and SrCO.sub.3 (98%) were purchased from Sigma-Aldrich, BaCO.sub.3 (minimum assay 99.5%) from BDH Chemicals LTD. (AnalaR, Lot #: 6546190), amorphous SiO.sub.2 was purchased from Alfa Aeasar (Lot #: C09Q03) and quartz silica from Cerac (Lot #: X0029011). All of the chemicals were used without further purification.

[0062] The present invention was demonstrated using waste pieces of Pyrex-type or soda lime container (bottle) glasses.

[0063] Pressing of the powder was performed using precision press tool model 8, die diameter 8 mm of P. O. Weber GmbH, and manual Carver press. The pressure used was 3000-3500 psi.

[0064] Calculation Methods

[0065] 1) Density

[0066] The accuracy of the digital micrometer is 0.01 mm and the weight accuracy is 0.0001 g therefore the error in the density measurement (=m/v=m/(IIr.sup.2h), where m is pellet mass, r radius of pellet and h is thickness of pellet) /=m/m+2r/r+h/h is estimated 1-2% for typical pellet's weight and dimensions, m=0.2 g; r=3.5 mm and h=2 mm.

[0067] 2) Total Porosity (TP)

[0068] The total porosity (TP) was calculated from the apparent density (.sub.app, measured from weight and dimensions of the pellet) and the density of Pyrex-type glass 2.24 g/cm.sup.3 or the density of soda lime container glass 2.42 g/cm.sup.3:

TP(%)=(1.sub.app/.sub.pyrex)100

[0069] Analytical Methods:

[0070] 1) X-Ray Diffraction (XRD)

[0071] Phase formation due to reaction with pore forming materials (MCO.sub.3 where M=Ca, Sr, Ba) and heat treatment were measured by XRD Powder Diffractometer Empyrean (Panalytical B. V., Almelo, the Netherlands) equipped with position sensitive detector XCelerator. Data were collected in the /2 geometry using Cu K.sub.a radiation (=1.54178 ) at 40 kV and 30 mA. Scans were run for 15 min in a 2 range of 10-60 with a step equal to 0.03.

[0072] 2) Surface Area

[0073] The surface area was measured by the BET method using Quantachrome Nova Touch LX3. The surface area of ball milled Pyrex-type glass powder was 2.12 m.sup.2/g and the surface area of CaCO.sub.3 was 2.87 m.sup.2/g.

[0074] 3) Porous Structure

[0075] The porous structure was investigated by a Scanning electron Microscope (SEM). Model: Quanta 200 FEI Company with Backscattered Electrons SEM imaging, Secondary Electrons SEM imaging, and Energy dispersive X-ray spectroscopy (EDS).

[0076] 4) Dilatometry

[0077] Dilatometry testing for linear coefficient of expansion was performed on Orton dilatometer 1000D.

Preparations 1 to 4

Preparations of Glass Powders

[0078] 1) 60 Mesh Pyrex-Type Glass

[0079] Pieces of Pyrex-type glasses were washed with water, rinsed with ethanol, and crushed into powder with a stainless steel pestle and mortar. The powder was sieved through a 60 mesh screen (250 microns).

[0080] 2) 60 Mesh Soda Lime Container Glass

[0081] Pieces of soda lime container (bottle) glasses were washed with water, rinsed with ethanol, and crushed into powder on a stainless steel pestle and mortar. The powder was sieved through a 60 mesh screen (250 microns).

[0082] 3) Ball Milled Pyrex-Type Glass

[0083] 60 mesh powder of Pyrex-type glasses was ball milled with isopropanol for 24 hours and the glass slip was sieved through a 325 mesh screen. After evaporation of isopropanol, the powder was dried in an oven at 100 C.

[0084] 4) Ball Milled Soda Lime Container Glass

[0085] 60 mesh powder of soda lime container glass was ball milled with isopropanol for 24 hours and the glass slip was sieved through a 325 mesh screen. After evaporation of isopropanol, the powder was dried in an oven at 100 C.

Examples 1-18 (Reference)

Sintering of Glass Powder (without CaCO.SUB.3.)

[0086] The glass powders of preparations 1-4 were sintered without the pore forming material (i.e., CaCO.sub.3). Table 1 collects data (processing temperature, average apparent density and estimated total porosity) for all four types of glass powders.

TABLE-US-00001 TABLE 1 Sintering and total porosity data for 4 types of glass powder at 625 C.-775 C. temperature range Powder Processing .sub.app average, T.P. Example preparation Temp., C. g/cm.sup.3 average, % 1 1 700 1.58 28.3 2 1 725 1.70 22.9 3 1 750 1.82 17.7 4 1 775 1.92 12.7 5 2 625 * * 6 2 650 1.79 29.1 7 2 675 1.86 26.1 8 2 700 2.15 14.7 9 3 625 1.32 40.8 10 3 650 1.33 40.4 11 3 675 1.34 39.9 12 3 700 1.60 28.5 13 3 725 1.77 20.6 14 3 750 2.05 8.1 15 3 775 2.07 7.2 16 4 650 1.51 40.1 17 4 675 1.92 23.6 18 4 700 2.41 4.4 * disks were broken during the measurement; this is an indication of poor sintering.

[0087] As seen from Table 1, ball milled Pyrex-type powder practically does not sinter in the 625 C.-675 C. temperature range, almost no change in apparent density and estimated total porosity.

[0088] Sintering increases above 675 C. and at 750 C.-775 C. range, sintering is enhanced with small total porosity. Useful porosity range is limited to 675 C.<T<750 C. temperature range and total porosity is <300. As expected, the sintering of 60 mesh Pyrex-type glass is shifted to higher temperatures relative to ball milled Pyrex-type glass because of its smaller surface area. Similar behavior is shown by the soda lime container glass, ball milled glass powder sinters at lower temperatures in comparison to 60 mesh powder. The examples devoid of the use of pore forming material were done to obtain information for the processing of powders with pore forming materials.

Preparations 5 and 6 (Reference) and 7 to 10 (Invention) Pelletizing Mixtures of Glass Powders and CaCO.SUB.3

[0089] 5) Pellets of Ball Milled Soda Lime Container Glass+20% CaCO.sub.3

[0090] Ball milled soda lime container glass powder (preparation 4) was mixed with fine (1-10 m) CaCO.sub.3 powder (percentage of 20% by weight) and ground together with isopropanol in an agate mortar and pestle to homogenize the mixture. After evaporation of isopropanol, 3% PVA solution in water (as a binder) was added to the dry mixture and the mixture was ground again in agate pestle and mortar to obtain uniform distribution of PVA in the powder. After PVA addition the powder (about 0.2 g) was pressed by precision press tool and manually by Carver press to obtain three pellets.

[0091] 6) Pellets of Ball Milled Soda Lime Container Glass+30% CaCO.sub.3

[0092] Ball milled soda lime container glass powder (preparation 4) was mixed with fine (1-10 m) CaCO.sub.3 powder (percentage of 30% by weight) and ground together with isopropanol in an agate mortar and pestle to homogenize the mixture. After evaporation of isopropanol, 3% PVA solution in water (as a binder) was added to the dry mixture and the mixture was ground again in agate pestle and mortar to obtain uniform distribution of PVA in the powder. After PVA addition the powder (about 0.2 g) was pressed by precision press tool and manually by Carver press to obtain three pellets.

[0093] 7-10) Pellets of ball milled Pyrex-type glass with CaCO.sub.3

[0094] Ball milled Pyrex-type glass powder (of preparation 3) was mixed with fine (1-10 m CaCO.sub.3 powder (20 wt. %-preparation 7; 30 wt. % preparation 8; 40 wt. %-preparation 9; 50 wt. %-preparation 10) and ground together with isopropanol in an agate mortar and pestle to homogenize the mixture. After evaporation of isopropanol, 3% PVA solution in water (as a binder) was added to the dry mixture and the mixture was ground again in agate pestle and mortar to obtain uniform distribution of PVA in the powder. After PVA addition the powder (about 0.2 g) was pressed by precision press tool and manually by Carver press to obtain three pellets for each of preparations 7 to 10.

Examples 19-24 (Reference)

Sintering of Pellets Consisting of Ball Milled Soda Lime Container Glass and CaCO.SUB.3

[0095] Based on data of Examples 1-18, ball milled soda lime container glass with pore forming CaCO.sub.3 was sintered at temperatures above 675 C.

[0096] The pellets of preparations 5 and 6 (3 pellets of every preparation) were placed on platinum foil and heated in a furnace according to the next scheme: gradient of 20 C./min for ramp to maximum temperature (sintering temperature), dwell of 24 minutes at maximum temperature and cool down with gradient 20 C./min.

[0097] After cool down, the pellets were weighted (analytical balance) and measured (with digital micrometer) and the weight and dimensions were recorded. For some compositions, pellets were immersed in 1:1 HCl solution at 80 C. for 4 hours.

[0098] After leaching in the acid, the pellets were washed with deionized water, dried in an oven and their weight and dimensions were recorded.

[0099] The densities and total porosities of pellets consisting of CaCO.sub.3 and ball milled container glass after sintering and leaching in HCl solution are shown in Table 2.

TABLE-US-00002 TABLE 2 Average Average .sub.app T.P. after Proc. Average after HCL HCl Example and Pellet Temp., .sub.app, leaching, leaching, sample code prep. C. g/cm.sup.3 g/cm.sup.3 % 19, JH-053-75G-I 5 675 1.73 no treatment 20, JH-053-75D-F 5 685 1.89 1.68 33.30 21, JH-053-75A-C 5 700 2.11 1.98 21.43 22, JH-053-78G-I 6 675 1.74 1.31 48.22 23, JH-053-78D-F 6 685 1.86 1.36 46.23 24, JH-053-78A-C 6 700 1.95 1.43 43.26

[0100] According to data from Table 2, well sintered pellets were obtained. Apparent densities were recorded after sintering and in some temperatures (685 and 700 C. for 20 wt. % of CaCO.sub.3) also after leaching in HCl solution. All the pellets with 30 wt. % CaCO.sub.3 were treated with HCl solution. Total porosity increases with the decrease in sintering temperature. 20 wt. % of CaCO.sub.3 pellets sintered at 675 C. were not treated with HCl solution and were kept as a control for assessment of the pellet's stability. After 15 months the dimensions and weights of these pellets were recorded and compared with initial values, no change in dimensions and weights (within experimental error) were found. Pellets with 30 wt. % of CaCO.sub.3 have higher porosities after HCl leaching and the trend of porosity increase with a decrease in sintering temperature discussed above for the 20 wt. % of CaCO.sub.3, is maintained with a moderate increase. FIG. 2 shows the XRD pattern of a pellet containing 20 wt. % CaCO.sub.3 and ball milled soda lime container glass after sintering at 700 C. and after leaching in HCL solution, indicating that a portion of CaCO.sub.3 did not dissolve. XRD patterns of samples with 30 wt. % CaCO.sub.3, i.e., the pellet of Preparation 6 (JH-053-78), the sintered pellet of Example 24 (JH-053-78B) and the post-leaching pellet (JH-053-78C1) are shown in FIG. 3. FIGS. 2 and 3 show that pellets with 20 wt. % of CaCO.sub.3 behave differently than pellets with 30 wt. % of CaCO.sub.3.

Examples 25-72 (Comparative)

Sintering of Pellets Consisting of Ball Milled Pyrex-Type Glass and CaCO.SUB.3

[0101] The pellets of preparations 7 to 10 (three pellets of each preparation) were placed on platinum foil and heated in a furnace according to the following scheme: gradient of 20 C./min for ramp to maximum temperature (sintering temperature), dwell of 24 minutes at maximum temperature and cool down with gradient 20 C./min.

[0102] In view of the data shown in Table 1, four sintering temperatures were chosen for the study (775 C., 800 C., 825 C., and 850 C., and twelve pellets were heat-treated at each run, i.e., at each sintering temperature (three for preparation 7-20% of CaCO.sub.3; three for preparation 8-30% of CaCO.sub.3; three for preparation 9-40% of CaCO.sub.3 and three for preparation 10-50% of CaCO.sub.3). Hence, a total number of forty-eight pellets were sintered.

[0103] After cool down, the pellets were weighted (analytical balance) and measured (with digital micrometer) and the weight and dimensions were recorded. The data for pellets made of ball milled Pyrex-type glass with 20 wt. % of CaCO.sub.3 (Preparation 7) are in Table 3, for 30 wt. % of CaCO.sub.3 (Preparation 8) are in Table 4, for 40 wt. % of CaCO.sub.3 (Preparation 9) are in Table 5 and for 50 wt. % of CaCO.sub.3 (Preparation 10) are in Table 6.

TABLE-US-00003 TABLE 3 Ball milled Pyrex-type glass with 20 wt. % of CaCO.sub.3 Sintering Temp., Example C. d, mm h, mm m, g .sub.app, g/cm.sup.3 25 850 6.747 2.464 0.1695 1.924 26 850 6.681 2.174 0.1523 1.991 27 850 6.740 2.632 0.1757 1.871 28 825 6.877 2.629 0.1796 1.839 29 825 6.939 2.616 0.1792 1.812 30 825 6.859 2.521 0.1731 1.858 31 800 7.330 2.704 0.1760 1.543 32 800 7.289 2.749 0.1788 1.559 33 800 broken broken broken broken 34 775 broken broken broken broken 35 775 broken broken broken broken 36 775 broken broken broken broken

TABLE-US-00004 TABLE 4 Ball milled Pyrex-type glass with 30 wt. % of CaCO.sub.3 Sintering Example and Temp., .sub.app, sample code C. d, mm h, mm m, g g/cm.sup.3 37 850 6.752 1.746 0.1209 1.933 38 JH-054-7B2 850 6.868 2.707 0.1924 1.918 39 850 6.845 2.335 0.1573 1.831 40 825 broken broken broken broken 41 825 7.175 2.491 0.1643 1.631 42 825 7.135 2.440 0.1663 1.705 43 800 broken broken broken broken 44 800 broken broken broken broken 45 800 7.533 2.728 0.1670 1.374 46 775 broken broken broken broken 47 JH-054-7B11 775 broken broken broken broken 48 775 broken broken broken broken

TABLE-US-00005 TABLE 5 Ball milled Pyrex-type glass with 40 wt. % of CaCO.sub.3 Sintering Temp., Example C. d, mm h, mm m, g .sub.app, g/cm.sup.3 49 850 6.922 2.118 0.142 1.782 50 850 6.881 1.944 0.1406 1.945 51 850 6.841 1.907 0.1335 1.905 52 825 7.370 2.177 0.1480 1.593 53 825 7.515 2.155 0.1454 1.521 54 825 7.349 2.086 0.1444 1.632 55 800 broken broken broken broken 56 800 broken broken broken broken 57 800 broken broken broken broken 58 775 broken broken broken broken 59 775 broken broken broken broken 60 775 broken broken broken broken

TABLE-US-00006 TABLE 6 Ball milled Pyrex-type glass with 50 wt. % of CaCO.sub.3 Sintering Temp., Example C d, mm h, mm m, g .sub.app, g/cm.sup.3 61 850 7.149 1.927 0.1355 1.751 62 850 7.205 1.940 0.1361 1.721 63 850 7.224 1.662 0.1166 1.712 64 825 broken broken broken broken 65 825 broken broken broken broken 66 825 broken broken broken broken 67 800 broken broken broken broken 68 800 broken broken broken broken 69 800 broken broken broken broken 70 775 broken broken broken broken 71 775 broken broken broken broken 72 775 broken broken broken broken

[0104] At a temperature of 850 C. mechanically strong pellets were obtained. However, the presence of a reaction product between the glass and calcium carbonate, namely CaSiO.sub.3, was detected by XRD analysis in the samples. FIG. 4 shows an XRD pattern of a sample consisting of an unbroken pellet of Example 38 (JH-054-7B2), in which a characteristic peak at position 30 2, assigned to CaSiO.sub.3, was observed. Thus, a temperature of 850 C. was too high to suppress the reaction of calcium carbonate with the glass under the test conditions.

[0105] Unfortunately, sintering the pellets at a lower temperature, i.e., at a temperature equal to, or lower than, 825 C., to prevent the reaction between the glass and calcium carbonate, afforded mechanically weak pellets. When the pellets were taken out of the furnace, they were cylindrical in shape and strong, and their weights and dimensions could be recorded. When left in closed glass vials for several days some of them turned into powder. The results tabulated in Tables 3 to 6 indicate that the number of broken pellets increases with an increase in the concentration of CaCO.sub.3 in the pellets and with a decrease in sintering temperature. XRD analysis of a sample consisting of a broken pellet of Example 47 (JH-054-7B11), which was sintered at 775 C., revealed new peaks located at positions 18 and 34 2, assigned to Ca(OH).sub.2 (FIG. 5). Ca(OH).sub.2 phase was not detected in the XRD patterns of the mechanically strong pellets sintered at 850 C., suggesting that the presence of Ca(OH).sub.2 accounts for the breakage of the pellets produced in the 600-800 C. temperature range. Across this temperature range, calcium carbonate decomposes to give calcium oxide and carbon dioxide:

CaCO.sub.3.fwdarw.CaO+CO.sub.2

[0106] Without wishing to be bound by theoretical explanation, it is suspected that calcium oxide, owing to its high reactivity, can pick up water molecules from the atmosphere at a temperature lower than 300 C., to form Ca(OH).sub.2, which has a smaller density (2.343 g/cm.sup.3) than CaO (3.346 g/cm.sup.3). Formation of Ca(OH).sub.2 from CaO causes expansion (volume increase of about 43%) and generates high stress which can lead to the breakage of sintered pellet.

Examples 73-84 (of the Invention)

Sintering of Pellets Consisting of Ball Milled Pyrex-Type Glass and CaCO.SUB.3 .at 800 C., Quenching at 400 C. Followed by Immediate Leaching

[0107] The pellets of preparations 7 to 10 (three pellets of each preparation) were placed on platinum foil and heated in a furnace according to the next scheme: gradient of 20 C./min for ramp to 800 C. sintering temperature, dwell of 24 minutes at maximum temperature and cool down with gradient 20 C./min to 400 C. and quenching (the pellets were taken out of the furnace at 400 C.) and immediately immersed in the 1:1 HCl solution at 80 C. for 4 hours. This procedure does not allow sufficient time for Ca(OH).sub.2 formation, thus all CaO and traces of Ca(OH).sub.2, if formed, are dissolved.

[0108] After cool down, the pellets were weighted (analytical balance) and measured (with digital micrometer) and the weight and dimensions were recorded.

[0109] The data (dimensions, weights, apparent densities, and total porosity) for pellets consisting of ball milled Pyrex-type glass powder and CaCO.sub.3 (Preparations 7-10) sintered at 800 C., quenched at 400 C. and leached with HCl solution is shown in Table 7.

TABLE-US-00007 TABLE 7 Example and CaCO.sub.3, .sub.app, T.P., sample code wt. % d, mm h, mm m, g g/cm.sup.3 % 73 JH-054-8A16 20 7.129 2.544 0.1442 1.42 36.3 74 20 7.138 2.584 0.1468 1.42 36.3 75 20 7.100 2.599 0.1467 1.43 36.1 76 JH-054-8B16 30 7.381 2.563 0.1313 1.20 46.3 77 30 7.267 2.607 0.1320 1.22 45.3 78 30 7.216 2.572 0.1316 1.25 43.9 79 JH-054-8C16 40 7.529 2.196 0.0994 1.02 54.4 80 40 7.534 2.247 0.1026 1.02 54.4 81 40 7.540 2.248 0.1045 1.04 53.3 82 JH-054-8D21 50 7.590 2.248 0.0878 0.86 61.3 83 50 7.654 2.319 0.0898 0.84 62.3 84 50 7.488 2.036 0.0792 0.88 60.4

[0110] It is seen that no pellets breakdown occurred, across the 20-50 wt. % CaCO.sub.3 concentration levels. The porosities of the pellets after leaching in an acid solution are high (36 to 62% calculated porosities).

[0111] FIGS. 6A-6D and 7A-7D present SEM images (1000 and 5000 magnifications, respectively) of four pellets of Table 7 which were prepared with 20 wt. % (Example 73; JH-054-8A16), 30 wt. % (Example 76; JH-054-8B16), 40 wt. % (Example 79; JH-054-8C16) and 50 wt. % (Example 82; JH-054-8D21) CaCO.sub.3. The SEM images show that porosity increases with increasing concentration of CaCO.sub.3. Sintering extent also increases in the order 20>30>40>50 wt. CaCO.sub.3.

Preparations 11 to 12 (Comparative)

Preparations of BaCO.SUB.3 .and SrCO.SUB.3.-Containing Pellets

[0112] 11) Pellets of Ball Milled Pyrex-Type Glass with 50 wt %. BaCO.sub.3

[0113] Ball milled Pyrex-type glass powder (preparation 3) was mixed with fine 50 wt. % BaCO.sub.3 and ground together with isopropanol in an agate mortar and pestle to homogenize the mixture. After evaporation of isopropanol, 3% PVA solution in water (as a binder) was added to the dry mixture and the mixture was ground again in agate pestle and mortar to obtain uniform distribution of PVA in the powder. After PVA addition the powder (about 0.2 g) was pressed by precision press tool and manually by Carver press to obtain three pellets of composition for preparation 11.

[0114] 12) Pellets of Ball Milled Pyrex-Type Glass with 50 wt %. SrCO.sub.3

[0115] Ball milled Pyrex-type glass powder (preparation 3) was mixed with fine 50 wt. % SrCO.sub.3 and ground together with isopropanol in an agate mortar and pestle to homogenize the mixture. After evaporation of isopropanol, 3% PVA solution in water (as a binder) was added to the dry mixture and the mixture was ground again in agate pestle and mortar to obtain uniform distribution of PVA in the powder. After PVA addition the powder (about 0.2 g) was pressed by precision press tool and manually by Carver press to obtain three pellets of composition for preparation 12.

Example 85 (Comparative)

Sintering of Pellets Consisting of Ball Milled Pyrex-Type Glass and BaCO.SUB.3

[0116] The three pellets of preparation 11 were placed on platinum foil and heated in a furnace according to the next scheme: gradient of 20 C./min for ramp to 850 C. sintering temperature, dwell of 24 minutes at maximum temperature and cool down with gradient of 20 C./min.

[0117] The XRD pattern of the sintered pellet is shown in FIG. 8. The XRD pattern shows that BaSi.sub.2O.sub.5 (Sanbornite) was the main crystalline phase formed, with some cristobalite. No BaCO.sub.3 was left and the hump of the glass at about 25 2 disappeared, suggesting that the reaction between BaCO.sub.3 and the glass occurred and went to completion. Residual glass, if present, is probably not a Pyrex glass; it may not be vitreous but still amorphous.

Example 86 (Comparative)

Sintering of Pellets Consisting of Ball Milled Pyrex-Type Glass and SrCO.SUB.3

[0118] The three pellets of preparation 12 were placed on platinum foil and heated in a furnace according to the next scheme: gradient of 20 C./min for ramp to 850 C. sintering temperature, dwell of 24 minutes at maximum temperature and cool down with gradient of 20 C./min.

[0119] The XRD pattern of sintered pellet is shown in FIG. 9. The XRD pattern shows the formation of two Sr silicates, SrSiO.sub.3 and Sr.sub.2SiO.sub.4, some cristobalite, unreacted SrCO.sub.3, whereas the hump of the glass at about 25 2 does not appear clearly. The reaction, in this case, is not complete and there are unidentified diffraction lines that may belong to other strontium silicates. Thus, SrCO.sub.3 also reacts with Pyrex-type glass at low temperatures, akin to BaCO.sub.3, but at a slower rate.

Example 87 (of the Invention)

The Reaction of Ball Milled Pyrex-Type Glass Powder with BaCO.SUB.3

[0120] Ball milled Pyrex-type glass powder of preparation 3 (2.00 g) and BaCO.sub.3 (3.202 g, 16.2258 mmol) were ground together with isopropanol in an agate mortar, dried, and heated in Pt crucible at 850 C. for 4 hours. The net weight of the reaction product after heating was 4.438 g (weight loss is 5.202 g-4.438 g=0.764 g). The theoretical weight loss for the complete reaction of BaCO.sub.3 with glass is 0.714 g (16.2258 mmol of BaCO.sub.3 release 0.714 g of CO.sub.2) and it is very close to the experimental (0.764 g). Therefore, the reaction of BaCO.sub.3 with the glass powder almost reached completion after four hours at 850 C. FIG. 10 presents the XRD of Example 87 (sample code JH-052-127) after the heat treatment. The XRD shows the formation of two barium silicates, BaSi.sub.2O.sub.5 as a major phase, Ba.sub.5Si.sub.8O.sub.21 as a secondary phase as well as some cristobalite.

Examples 88 (Invention) and 89 (Comparative)

Comparison of Reactions of Vitreous and Crystalline Phase Silica with BaCO.SUB.3 .at 850 C.

[0121] Commercial amorphous silica (2.00 g) and BaCO.sub.3 (3.284 g, 16.643 mmol) were ground together with isopropanol in an agate mortar, dried, and heated in Pt crucible at 850 C. for 4 hours (Example 88, sample code JH-052-129A).

[0122] Commercial quartz (2.00 g) and BaCO.sub.3 (3.284 g, 16.643 mmol) were ground together with isopropanol in an agate mortar, dried, and heated in Pt crucible at 850 C. for 4 hours together with Example 88 (Example 89, sample code JH-052-129B).

[0123] The theoretical weight loss in both examples for the complete reaction of BaCO.sub.3 with glass is 0.732 g (16.643 mmol of BaCO.sub.3 release 0.732 g of CO.sub.2). The net weight of the reaction product after heating for Example 88 was 4.528 g (weight loss is 5.284 g-4.528 g=0.756 g), indicating the completion of the reaction. The net weight of the reaction product after heating for Example 89 was 5.118 g (weight loss is 5.284 g-5.118 g=0.166 g).

[0124] The results show that amorphous phase silica (Example 88, sample code JH-052-129A) reacted completely with BaCO.sub.3 while crystalline phase silica (quartz, Example 89, JH-052-129B) reacts at a much slower rate. FIG. 11 shows the XRD pattern of Example 88 (sample code JH-052-129A), indicating that no BaCO.sub.3 was left. FIG. 12 shows the XRD pattern of Example 89 (sample code JH-052-129B), indicating incomplete reaction with peaks of unreacted BaCO.sub.3, quartz, and only a small quantity of Ba.sub.2SiO.sub.4 formed.

Examples 90-95 (of the Invention)

[0125] The preparations of six silicates composites The preparations of six silicates composites are given in Table 8 (the same procedure of Example 87). The table details the ingredients and their weights in grams, the conditions of the heat treatment, and references to the corresponding XRD and major crystalline phases identified.

TABLE-US-00008 TABLE 8 Example Ingredients, g Heat and code Pyrex BaCO.sub.3 CuO TiO.sub.2 SnO.sub.2 CaCO.sub.3 SrCO.sub.3 treatment XRPD 90 JH-054-48 3.00 3.99 1.6084 900 C., 1 hr FIG. 13 BaCuSi.sub.2O.sub.6 91 JH-054-49 6.00 3.99 1.6084 900 C., 1 hr FIG. 14 BaCuSi.sub.4O.sub.10 92 JH-054-50 6.00 1.6084 2.0219 900 C., 1 hr FIG. 15 CaCuSi.sub.4O.sub.10 93 JH-054-73 6.00 1.6084 2.9849 900 C., 1 hr FIG. 16 SrCuSi.sub.4O.sub.10 94 JH-056-9B1 3.00 2.660 0.2693 1.5236 950 C., 1 hr FIG. 17 1100 C., 8 hr BaTi.sub.0.25Sn.sub.0.75Si.sub.3O.sub.9 95 JH-056-11 3.00 7.981 1.6157 950 C., 1 hr FIG. 18 Ba.sub.2TiSi.sub.2O.sub.8

Example 96

Thermal Expansion of a Composite Made from Ball Milled Pyrex-Type Glass Powder and BaCO.SUB.3

[0126] Ball milled Pyrex-type glass powder of Preparation 3 (3.0 g, 81% SiO.sub.2, 40.4 mmol of SiO.sub.2) and BaCO.sub.3 powder (3.99 g, 20.2 mmol of BaO, the molar ratio of BaO/SiO.sub.2 is ) were ground together with 45 drops of 3% PVA solution and shaped into a bar. The bar was dried on a hot plate to remove water, placed on Pt foil, and heated with 20 C./min gradient to 900 C. sintering temperature. After keeping the bar at 900 C. for 1 hour, it was cooled down to room temperature.

[0127] The XRD of the sintered bar (the sample code is JH-054-38) is presented in FIG. 19. It shows that the main phase formed is BaSi.sub.2O.sub.5 (Sanbornite). It is not clear about the presence of cristobalite, because all BaCO.sub.3 reacted completely and there are no other phases of barium silicate in the XRD, and the dilatometer run is linear around 200 C. (FIG. 20). So, we conclude that after 1 hour at 900 C. the composite contains BaSi.sub.2O.sub.5 (Sanbornite) as a major phase and residual glass which contains the other ingredients of Pyrex (B.sub.2O.sub.3, Na.sub.2O, K.sub.2O, Al.sub.2O.sub.3 and traces of Fe.sub.2O.sub.3, MgO and CaO) and perhaps some dissolved BaSi.sub.2O.sub.5. If all SiO.sub.2 in the Pyrex-type glass reacted with all BaCO.sub.3 to form BaSi.sub.2O.sub.5, there are 5.53 g of BaSi.sub.2O.sub.5 and 0.57 g of residual glass. The wt. % of residual glass is estimated as 9.34.

[0128] The sintered bar was measured in a dilatometer. The dilatogram is presented in FIG. 20 (sample code JH-054-38). The data shows that the linear coefficient of expansion in the 200-400 C. range is 12.66 ppm/c.

[0129] FIG. 20 shows that percent linear change (PLC) is linear from room temperature to almost 500 C. (as also indicated by the constant value of the derivative of coefficient expansion (DCE). Linear PLC around 200 C. is an indication that cristobalite is not present in the glass composite. The average linear coefficient of expansion in the 100-400 C. range is 12.610.sup.6C.sup.1. The dilatometer software selects the Tg (542 C.) and the dilatometer softening point Ts (821 C.) of the composite. These values, especially Ts, seem high for the residual glass (sodium aluminoborate glass); based on the published composition of Pyrex glass, the composition in wt. % of residual glass is 65.7 B.sub.2O.sub.3; 21.9 Na.sub.2O; 11.5 Al.sub.2O.sub.3; 0.5 CaO; 0.26 MgO; 0.21 Fe.sub.2O.sub.3.

Example 97 (Reference)

Thermal Expansion of a Composite Made from Ball Milled Pyrex-Type Glass Powder

[0130] Ball milled Pyrex-type glass powder from Preparation 3 without BaCO.sub.3 was subjected to the same heat treatment used for Example 96, in order to account for the SiO.sub.2 phase in FIG. 19. The XRD of the heat-treated Pyrex-type powder (1 hour at 900 C.) is given in FIG. 21 (sample code JH-054-66) and it shows that Pyrex crystallizes after the heat treatment. It seems that the bar preparation procedure of Example 96 (sample code JH-054-38) did not form a homogeneous mixture, i.e., probably some large agglomerates of the Pyrex glass still existed in the mixture and they crystallized during sintering.

Example 98-100

A Modified Procedure for Making a Composite Bar from Ball Milled Pyrex-Type Glass Powder and BaCO.SUB.3

[0131] Ball milled Pyrex-type glass powder from Preparation 3 (3.0 g) and BaCO.sub.3 powder (3.99 g) were ground together with isopropanol in an agate mortar, dried, and then ground together with 45 drops of 3% PVA solution and shaped into a bar. The bar was dried on a hot plate to remove water and then sintered. The procedure includes the extra grinding step in agate mortar compared to Example 96.

[0132] Three bars with the same weight and materials used as in Example 96 were prepared using the modified procedure. The bars were placed on Pt foil and heated with a 20 C./min gradient to sintering temperature. After keeping the bar at the sintering temperature for 1 hour, it was cooled down to room temperature.

[0133] The bars were sintered for 1 hour at 900 C. (Example 98-sample code JH-054-87), 950 C. (Example 99-sample code JH-054-88), and 850 C. (Example 100-sample code JH-054-90). The bar from Example 99 (sample code JH-054-88) sintered at 950 C., broke before dilatometer measurements and the broken bar was used for XRD measurement. New bar identical to the bar from Example 99 was prepared (assigned new code JH-054-92). The XRD's of Example 98 (sample code JH-054-87), Example 99 (sample code JH-054-88), and Example 100 (sample code JH-054-90) are presented in FIGS. 22, 23 and 24.

[0134] The dilatometer measurements were performed three times for each of the bars. After the first run, the sample was left in the dilatometer and run again (to examples numbers and sample codes were added letter A), and after the second run, the sample was left in the dilatometer and run again for the third time (code changed from A to B).

[0135] The dilatograms of 3.sup.rd run for the Examples 98, 99 and 100 are presented on FIGS. 25, 26 and 27 respectively (Example 98B-JH-054-87B-900 C.; Example 99B-JH-054-90B-850 C.; and Example 100B-JH-054-92B-950 C.) and are identical to the dilatogram of the bar from Example 96 (sample code JH-054-38).

[0136] The dilatometer data of the samples are in Table 9 (three runs for each bar). There are presented also data for the first run of Example 96 (sample code JH-054-38). Run No. 1 was discarded (in the first run the bar may slightly move and can affect the measured TCE, in the second and third runs the bar is locked in the dilatometer and cannot shift), as only data for runs 2 and 3 were used to compare samples. The average TCE (200-400 C.) of Example 98 (sample code JH-054-87) (runs 2 and 3) is 12.310.sup.6/ C., the corresponding values for Examples 99 (sample code JH-054-90) and Example 100 (sample code JH-054-92) are 11.9510.sup.6/ C. and 12.410.sup.6/ C. respectively. The TCE of Example 98 (sample code JH-054-87, 900 C. sintering) and Example 100 (sample code JH-054-92, 950 C. sintering) are the same within experimental error. The corresponding TCE for Example 99 (sample code JH-04-90, 850 C. sintering) is slightly lower 11.9510.sup.6/ C.

TABLE-US-00009 TABLE 9 Example and CTE (200-400 C.) Heat Run code 10{circumflex over ()}6 Treatment number 96 JH-054-38 12.7 900 C., 1 hour 1 98 JH-054-87 10.6 900 C., 1 hour 1 98A JH-054-87A 12.4 900 C., 1 hour 2 98B JH-054-87B 12.2 900 C., 1 hour 3 99 JH-054-90 10.8 850 C., 1 hour 1 99A JH-054-90A 11.8 850 C., 1 hour 2 99B JH-054-90B 12.1 850 C., 1 hour 3 100 JH-054-92 12.7 950 C., 1 hour 1 100A JH-054-92A 12.4 950 C., 1 hour 2 100B JH-054-92B 12.4 950 C., 1 hour 3