Title of Invention

"A PROCESS FOR THE PREPARATION OF STRONTIUM TITNATE POWDERS"

Abstract

This invention relates to a process for the preparation of strontium titanate (SrTiO3) comprising preparing strontium salt solutions and preparing a titanium salt solution such as described herein, mixing the strontium salt solution and titanium salt solution in the ratio of 1:2.5 to 3 respectively, adding 1ON sodium hydroxide solution to the solution formed in step c in the ratio of 1: 2 to 3 at a temperature of 85° to 90°C under continuous stirring to get a stable solution having pH in the range of 8-13 so as to get the precipitate of strontium titanate, filtering the said precipitate and subjecting the same to the steps of washing, the precipitate is first washed with 0.1 N hydrochloric acid and then with the distilled water till precipitate is alkali free, and drying at a temperature preferably 110°C for three hours to obtain said chemically pure strontium titanate.

Full Text

This invention relates to a process for the preparation of Strontium titanate (SrTiO3 ). Strontium titanate of the electroceramic grade is prepared by solution derived procedures in the known art. There are disadvantages associated with the prior art. One of the main disadvantages is that the strontium titanate obtained by the conventional process is not pure. Therefore the main object of the present invention is to propose a process for the preparation of SrTiO3 at low temperatures. Yet another object of the present invention is to propose a process for the preparation of SrTiO3 wherein there is phase purity of the end product obtained by the avoiding premature precipitation of constituent cations. Another object of the present invention is to propose a process for the preparation of SrTiO3 wherein good control of the particle size of the ceramic powder is achieved. According to this invention there is provided a process for the preparation of the strontium titanate (SrTiO3) comprising: a) preparing strontium salt solutions such as described herein. b) preparing a titanium salt solution such as described herein. c) mixing the strontium salt solution and titanium salt solution in the ratio of 1:2.5 to 3 respectively. d) adding 1ON sodium hydroxide solution to the solution formed in step c in the ratio of 1: 2 to 3 at a temperature of 85° to 90°C under continuous stirring to get a stable solution having pH in the range of 8-13 so as to get the precipitate of strontium titanate. e) filtering the said precipitate and subjecting the same to the steps of washing, the precipitate is first washed with 0.1 N hydrochloric acid and then with the distilled water till precipitate is alkali free, and drying at a temperature preferably 110°C for three hours to obtain said chemically pure strontium titanate. In accordance with this invention the process for preparing strontium titanate (SrTio3) comprises in preparing a strontium precursor/salt solution and titanium precursor/salt solution separately. The strontium precursor/salt solution and titanium precursor/salt solution so obtained are mixed in the ratio of 1:2.5-3 respectively. The stabilizing agents, modifiers (for example 1ON sodium hydroxide solution) then added to said mixed solution in a controlled manner to obtain a stable solution. The pH of the stable solution is adjusted to 8 to 13 using alkali and alkaline earth metal basic salt at a temperature of 85° to 90°C and under continuous stirring so as to obtain the direct precipitation of strontium titanate (SrTio3). The precipitated SrTio3 is filtered from the solution and subsequently subject to the steps of washing with dilute Hydrochloric acid and then with distilled water until the precipitate is alkali free. A process for the preparation of strontium titanate according to a preferred embodiment is herein described and illustrated in the accompanying example. According to the process of the invention, strontium salt solution first prepared by dissolving commercial grade strontium chloride into distilled water in the ratio of one part strontium chloride and 4 to 5 part distilled water, filter it and store. Similarly titanium salt solution is prepared by adding titanium tetrachloride into distilled water under constant stirring in the ratio of one part titanium tetrachloride and 2 to 3 part distilled water and the bottle is kept in a cold bath of ice-common salt mixture. After complete addition, stirring is continued for half an hour and then volume is made up to 20 litres with distilled water. The weight of the titanium content in the solution is preferably 0.14g/ml. The next step of the process is that titanium tetra chloride solution is mixed the strontium chloride solution at room temperature in the ratio of 1:2.5 to 3 respectively. This mixed solution of titanium and strontium constituents is then added slowly to the stabilizing agent, modifiers for example 1ON Sodium Hydroxide solution in the ratio of 2 to 3:1 respectively under continuous stirring at a temperature of 85° to 90°C. The pH of the solution was adjusting using alkali and alkaline earth metal basic salt. The Sodium Hydroxide solution is prepared by dissolving 200g Sodium Hydroxide in 500ml of distilled water. the step of addition of mixed solution to the sodium hydroxide solution, white precipitate of strontium titanate is formed. After the addition is complete stirring and heating is continued for another two hours and then the precipitated solution is allowed to be cooled. The precipitate then filtered and washed first with hydrochloric acid (0.1N) and then with distilled water until the washings are alkali free. Washed precipitate is then dried at 110°C for three hours and is ground to fine powder of strontium titanate. 90 grams of strontium chloride was dissolved in 750 ml distilled water to prepare strontium salt solution which was subsequently filtered and stored. 200 ml titanium tetra chloride was slowly added to 500 ml distilled water in bottle and which was kept in a cold bath ice-common salt mixture. After the complete addition, stirring was continued for half an hour and then the volume was made upto 2 litres with distilled water. The weight of titanium content was 0.14 g/ml in the titanium salt solution. 200 ml titanium salt solution was mixed with 750 ml strontium chloride solution at room temperature. The mixture so obtained was added slowly to 500ml of 10N sodium hydroxide solution under continuous spray at a temperature of 9dP C so as to get a white precipitate of strontium titanate. After the addition is complete stirring and heating was continued for another two hours and then the precipitate solution was allowed to be cooled. After cooling, the precipitate was filtered, washed three times with 100 ml portions of dilute hydrochloric acid (0.1N) and then four or five times with 100ml portions of distilled water until the washing are alkali free. The precipitate was subsequently ground to get the fine powders of strontium titanate. The strontium titanate powder so obtained was subjected to chemical analysis are given here under table one. TABLE L Ti (Wt. 7.) - 27.19 Sr (Wt 7.) - 48.9 Mole ratio C8r/Ti3 - 1.01 WE CLAIM; 1. A process for the preparation of strontium titanate (SrTiO3) comprising: a) preparing strontium salt solutions such as described herein. b) preparing a titanium salt solution such as described herein. c) mixing the strontium salt solution and titanium salt solution in the ratio of 1:2.5 to 3 respectively. d) adding 1ON sodium hydroxide solution to the solution formed in step c in the ratio of 1: 2 to 3 at a temperature of 85° to 90°C under continuous stirring to get a stable solution having pH in the range of 8-13 so as to get the precipitate of strontium titanate. e) filtering the said precipitate and subjecting the same to the steps of washing, the precipitate is first washed with 0.1 N hydrochloric acid and then with the distilled water till precipitate is alkali free, and drying at a temperature preferably 110°C for three hours to obtain said chemically pure strontium titanate. 2. A process as claimed in claim 1 wherein said Strontium salt solution is prepared by dissolving strontium chloride in the distilled water, such as one part strontium chloride in 4 to 5 parts distilled water. 3. 4. A process as claimed in claim 1 wherein said titanium salt solution is prepared by adding titanium tetrachloride solution to the distilled water in the ratio of one part titanium salt solution in 2 to 2:5 part of distilled water under continuous stirring, and keeping the content in a cold bath of ice-common salt mixture. 5. A process for the preparation of Strontium Titanate SrTio3 substantially as herein described and illustrated.

Documents:

3847-del-1998-abstract.pdf

3847-del-1998-claims.pdf

3847-del-1998-correspondence-others.pdf

3847-del-1998-correspondence-po.pdf

3847-del-1998-description (complete).pdf

3847-del-1998-form-1.pdf

3847-del-1998-form-19.pdf

3847-del-1998-form-2.pdf

3847-del-1998-form-3.pdf

3847-del-1998-form-4.pdf

3847-del-1998-form-5.pdf

3847-del-1998-gpa.pdf