Title of Invention

A PROCESS OF MAKING ULTRA LOW EXPANSION GLASS CERAMICS

Abstract

The present invention relates to a process of making ultra low expansion glass ceramics. The glass ceramic material finds use in electronic devices, heat engine components, spark plug or as hot plate tops, domestic cooking ware and other such applications where zero to a moderate thermal expansion coefficients and higher mechanical strength are required. The novelty of the present invention lies in making ultra low expansion glass ceramics with low glass melting temperature, broader working range. Moreover the expansion coefficients obtained was very low of the order of 3-12 X 10-70 C between the temperature range room temperature to 500°C.This has been achieved by forming a glass batch using a combination of ground blast furnace slag and china clay and a moderator in the form of boric acid.

Full Text

The present invention relates to a process of making ultra low expansion glass ceramics. The glass ceramic material finds use in electronic devices, heat engine components, spark plug or as hot plate tops, domestic cooking ware, high quality telescope mirror blanks and such other applications where zero to a moderate thermal expansion coefficients and higher mechanical strength are required. The present day method of making glass ceramic material with low thermal expansion coefficient consists of using SiO2, AI2O3, Li2O, TiO2, ZrO2 etc. in their carbonate or oxide form, melting to form glasses, drawing for fabrication of shape, annealing, nucleation and crystallisation, references for which may be made to L. F. OLDFIELD, D. J. HARWOOD, B. LEWIS in Journal of Material Science.1 (1966) 29-40,142-153, THAKUR, R. L and THIAGARAJAN, S in Tenth International Congress on Glass, pp 14.83-14.87 (1974). Tokyo, Ceramic Society of Japan, 1974, V. A. Ulazovski. Belorus. Politekh. Inst. Im. V. I. Stalina, Sbornik Nauch. Trudov 1960, No. 86, 61-4, cf. CA 53, 6561 c. It is also made by using various other raw materials as a source of SiO2, AI2O3, Li2O, TiO2, ZrO2 etc. like blast furnace slag or china clay and different aluminosilicate raw materials references for which may be made to Wafa I . Abdel - Fattah & R. Abdellah in Ceram International, 23 (6) 463-469 (1997), K. Nakagawa & T. Izumitani in Journal of Non Crystalline Solids, 7 168-180 (1972), M. C. Wang & M. H. Hon in Nippon Seramikkusu Kyokai Gakujutsu Ronbunshi, 98 (7) 625-29, 1990 and in Journal of Material Science, 32 (91) 83-89, January, 1997, Jounal of Non Crystalline Solids, 210 (1) 87-94, Feb 1997. The main drawbacks of the above mentioned processes are 1. Glass melting temperature is high (1550°-1650°C) 2. Working range is very short which creates problem during fabrication of shapes 3. Selection of working composition of base glass is very difficult 4. Precision control of nucleation and crystallization temperature is required The main object of the present invention is to provide a process for making ultra low expansion glass ceramic which obviates the drawbacks as detailed above. Another object of the present invention is to lower down glass melting temperature. Still another object of the present invention is to use industrial wastes as raw materials. Yet another object of the present invention is to broaden the nucleation temperature range. Still another object of the present invention is to broaden the crystallization temperature range. Accordingly, the present invention provides a process of making ultra low expansion glass ceramics which comprises; a process of making ultra low expansion glass ceramics which comprises; mixing 125-520 gms. of ground blast furnace slag, 140 to 500 gms. of ground china clay, 90 to 300 gms. of ground silica, 50 to 165 gms. of ground alumina, 20 to 50 gms. of ground titania, 100 to 150 gms. of ground lithium compound, 50 to 70 gms. of ground boric acid, mixing the ingredients by known methods to obtain glass batch, melting the glass batch at a temperature in the range of 1400 - 1450°C, maintaining the temperature of the melt till complete refining, shaping the melt so obtained by known methods, annealing the shapes at a temperature in the range of 415°-520°C fora period of 0.5 hour to 4.0 hours, nucleating by heat treating the annealed specimen at a temperature in the range of 530 - 590°C for a period in the range of 0.5 to 4 hours, crystal sing the nucleated specimens by heat treating at a temperature in the range of 750 - 825°C for a period in the range of 2 to 12 hours to obtain the product. In an embodiment of the present invention the ground blast furnace slag used may be such as obtained directly from the blast furnace or remelted blast furnace slag of any source. In another embodiment of the present invention the china clay used may be of composition silica (40-50%), alumina (30-40%) with minor impurities in the range of 2-3%. In yet another embodiment of the present invention lithium compound used may be derived from lithium carbonate, lithium nitrate. In still another embodiment of the present invention alumina used may be derived from sources such as LR grade hydrated alumina, aluminium ore, pure aluminium oxide. The details of the present invention are given below. 1.125 - 520 gm of ground blast furnace slag, 140 - 500 gm of ground china clay, 90 - 300 gm of ground quartz, 50-165 gm of alumina, 20 - 50 gm of ground titania, 100-150 gm of ground lithium compound, 50 - 70 gm of ground boric acid, mixing the ingredients by known mixing methods for the preparation of glass batch. 2. The glass batch was melted in a refractory crucible at a temperature in the range of 1400° - 1450bC for a period in the range of 4-6 hours in an oil fired horse shoe furnace to ensure complete refining. 3. Test specimens were made by known methods. 4. The tost specimens woro annoalod at a tomporaturo in the range of 415°-520°C for a period in the range of 0. 5 hrs. to 4 hrs. 5. The annealed specimens were heat treated for nucleation at a temperature in the range of 530° -590°C for a period in the range of 0. 5 hrs. to 4 hours. 6. Nucleated specimens were heat treated for crystallisation at a temperature in the range of 750-825°C for a period in the range of 2 to 12 hours. The novelty of the present invention lies in making ultra low expansion glass ceramics with low glass melting temperature, broader working range. Moreover the expansion coefficients obtained was very low of the order of 3-12 X 10-7/°C between the temperature range room temperature to 500°C. The inventive steps are forming a glass batch using a combination of ground blast furnace slag and china clay and a moderator in the form of boric acid. The following examples are given by way of illustration and therefore should not be construed to limit the scope of the present invention. Example 1 520 gm of ground blast furnace slag, 208 gm of ground china clay, 94 gm of ground quartz, 21 gm of ground titania, 103 gm of ground lithium compound, 56 gm of ground boric acid were mixed by known methods. The mixed materials were melted at 1425°C for 4 hours. Rods were drawn by known methods. The rods were then annealed at 520°C for 30 minutes. The annealed specimens were nucleated at 530°C for 30 minutes and then crystallised at 750°C for 1 hour. Example 2 499 gm of ground blast furnace slag, 220 gm of ground china clay, 100 gm of ground quartz, 30gm of ground titania, 99 gm of ground lithium compound, 53 gm of ground boric acid were mixed by known methods. The mixed materials were melted at 1425°C for 4 hours. Rods were drawn by known methods. The rods were then annealed at 510°C for 45 minutes. The annealed specimens were nucleated at 530°C for 1 hour and then crystallised at 750°C for 2 hours. Example 3 186 gm of ground blast furnace slag, 465 gm of ground china clay, 107 gm of ground quartz, 37gm of ground titania, 138 gm of ground lithium compound, 66 gm of ground boric acid were mixed by known methods. The mixed materials were melted at 1440°C for 5 hours. Rods were drawn by known methods. The rods were then annealed at 500°C for 1 hour. The annealed specimens were nucleated at 540°C for 2 hours and then crystallised at 762°C for 4 hours. Example 4 169 gm of ground blast furnace slag, 139 gm of ground china clay, 296 gm of ground quartz, 161 gm of ground alumina, 37 gm of ground titania, 146 gm of ground lithium compound, 53 gm of ground boric acid were mixed by known methods. The mixed materials were melted at 1440°C for 5 hours. Rods were drawn by known methods. The rods were then annealed at 480°C for 2 hours. The annealed specimens were nucleated at 580°C for 2 hours and then crystallised at 762°C for 6 hours. Example 5 134 gm of ground blast furnace slag, 164 gm of ground china clay, 283 gm of ground quartz, 162 gm of ground alumina, 45 grn of ground titania, 147 gm of ground lithium compound, 66 gm of ground boric acid were mixed by known methods. The mixed materials were melted at 1440°C for 5.5 hours. Rods were drawn by known methods. The rods were then annealed at 460°C for 2.5 hours. The annealed specimens were nucleated at 585°C for 2 hours and then crystallised at 800°C for 6 hours. Example 6 127 gm of ground blast furnace slag, 381 gm of ground china clay, 191 gm of ground quartz, 54 gm of ground alumina, 38 gm of ground titania, 141 gm of ground lithium carbonate, 68 gm of ground boric acid were mixed by known methods. The mixed materials were melted at 1450°C for 6 hours. Rods were drawn by known methods. The rods were then annealed at 440°C for 2.5 hours. The annealed specimens were nucleated at 590°C for 2 hours and then first crystallised at 762°C for 6 hours and at 800°C for 10 hours. Example 7 205 gm of ground blast furnace slag, 246 gm of ground china clay, 242 gm of ground quartz, 126 gm of ground alumina, 29 gm of ground titania, 101 gm of ground lithium compound, 51 gm of ground boric acid were mixed by known methods. The mixed materials were melted at 1450°C for 6 hours. Rods were drawn by known methods. The rods were then annealed at 425°C for 4 hours. The annealed specimens were nucleated at 590°C for 3 hours and first crystallised at 762°C for 8 hours and at 800°C for 12 hours. xample 8 169 gm of ground blast furnace slag, 139 gm of ground china clay, 296 gm of ground quartz, 161 gm of ground alumina, 37 gm of ground titania, 146 gm of ground lithium compound, 53 gm of ground boric acid were mixed by known methods. The mixed materials were melted at 1450°C for 6 hours. Rods were drawn by known methods. The rods were then annealed at 480°C for 2 hours. The annealed specimens were nucleated at 540°C for 1 hour and then crystallised at 762°C for 8 hours. The results obtained by the process of present invention are given in table 1 by way of illustration. Table -1 : Values of Co-efficient of linear thermal expansion (a X 10-7/°C) of different heat treated specimens. Specimen no. > (Table Removed) The main advantages of the present invention are : 1. Melting temperature of the base glass was comparatively low. 2. Very good working range of the base glass may be obtained. 3. Nucleation temperature was in broad range of temperature. 4. Crystallisation temperature was also in broad range of temperature. Claim: 1. A process of making ultra low expansion glass ceramics which comprises; mixing 125-520 gms. of ground blast furnace slag, 140 to 500 gms. of ground china clay, 90 to 300 gms. of ground silica, 50 to 165 gms. of ground alumina, 20 to 50 gms. of ground titania, 100 to 150 gms. of ground lithium compound, 50 to 70 gms. of ground boric acid, mixing the ingredients by known methods to obtain glass batch, melting the glass batch at a temperature in the range of 1400 - 1450°C, maintaining the temperature of the melt till complete refining, shaping the melt so obtained by known methods, annealing the shapes at a temperature in the range of 415° - 520°C for a period of 0.5 hour to 4.0 hours, nucleating by heat treating the annealed specimen at a temperature in the range of 530 - 590°C for a period in the range of 0.5 to 4 hours, crystalising the nucleated specimens by heat treating at a temperature in the range of 750 - 825°C for a period in the range of 2 to 12 hours to obtain the product. 2. A process as claimed in claim 1 wherein ground blast furnace slag used is obtained directly from the blast furnace or remelted blast furnace slag of any source. 3. A process as claimed in claims 1-2 wherein the china clay used is of composition silica 40-50%, alumina 30-40% with minor impurities in the range of 2-3%. 4. A process as claimed in claims 1-3 wherein the lithium compound used is derived from lithium carbonate, lithium nitrate. 5. A process as claimed in claims 1-4 wherein the alumina used is derived from sources such as LR grade hydrated alumina, aluminium ore, pure aluminum oxide. 6. A process of making ultra low expansion glass ceramic substantially as herein described with reference to the examples.

Documents:

190-del-2000-abstract.pdf

190-del-2000-claims.pdf

190-del-2000-correspondence-others.pdf

190-del-2000-correspondence-po.pdf

190-del-2000-description (complete).pdf

190-del-2000-form-1.pdf

190-del-2000-form-19.pdf

190-del-2000-form-2.pdf