Method for making high purity metal oxide particles and materials made thereof
View Patent ↗The present invention is directed to a method of making metal oxide and mixed metal oxide particles. The method includes treating a mixture formed from a metal source, such as metal alkoxide, a surfactant, and a first alcohol in an aqueous media at a very high metal oxide yield. The mixture is reacted using a catalyst to form metal oxide particles having a desired particle size in said mixture. The method is particularly suitable for forming silica particles. The metal oxide particles can then be heat treated to form synthetic fused metal oxides such as, for example, synthetic fused silica.
1. A method for making high purity synthetic silica comprising:
forming a first phase comprising a mixture of water, a silica source, a first catalyst, a first surfactant, and a first alcohol;
adding the first phase to a second phase comprising water, a second alcohol, and a second surfactant to form a blend;
treating the blend with a measured amount of a phase enhancer;
treating the blend with a second catalyst to form silica particles; and
heat treating the silica particles to form fused synthetic silica.
2. The method of claim 1 , wherein the silica particles comprise total cationic impurities of less than 100 ppb.
3. The method of claim 2 , wherein the silica particles comprise cationic impurities of less than 10 ppb.
4. The method of claim 1 , wherein the molar ratio of water to silica source in the first phase is from about 0.5 to about 4.0.
5. The method of claim 1 , wherein the silica source comprises a siloxane oligomer derived from alkoxysilane, and the molar ratio of water to siloxane oligomer derived from alkoxysilane provides at least a siloxane heptamer, a cyclic siloxane, or mixtures thereof.
6. The method of claim 1 , wherein the silica source comprises at least one of a tetra-alkyl orthosilicate, a vinyl orthosilicate, an aryl orthosilicate, or a combination of two or more thereof.
7. The method of claim 1 where primary particles agglomerate to sizes from about 5 microns to about 1000 microns.
8. The method of claim 1 , wherein the silica particles have a primary particle size of about 0.5 microns to about 100 microns.
9. The method of claim 7 , wherein at least 80% of the silica particles have a size of about 70 to about 350 microns.
10. The method of claim 1 where the first catalyst comprises a base catalyst chosen from ammonium hydroxide, quaternary ammonium hydroxides, hydroxylamines, derivatives of hydroxylamines, amino pyridines, or combinations of two or more thereof.
11. The method of claim 1 , wherein the base catalyst is a composition comprising about 0.01% to about 10% by weight of a base catalyst material.
12. The method of claim 1 , wherein the phase enhancer comprises a slightly polar alcohol.
13. The method of claim 1 , wherein the pH of the mixture prior to treating the blend with the second catalyst is no greater than about 3.5, and the pH of said mixture during said treating step is no greater than about 6.
14. The method of claim 1 , wherein the first surfactant is a co-surfactant system comprising a non-polar compound and a slightly polar compound chosen from an alcohol.
15. The method of claim 1 , wherein the second surfactant is a nonionic surfactant.
16. The method of claim 15 , wherein the nonionic surfactant is chosen from a polyethoxylate, a polypropoxylate, a phenolate, or a polyol having a molecular weight of about 400 to about 100,000, or a combination of two or more thereof
17. The method of claim 1 , wherein the temperature of the first phase is about 30° to about 80° C.
18. The method of claim 1 , wherein the temperature of the second phase is about 30° C. to about 100° C.
19. The method in claim 1 , where the blend is mixed with an agitator at a tip speed of about 0.2 to about 0.8 feet per second.
20. The method of claim 1 , wherein the silica source comprises an alkoxysilane.
21. The method of claim 1 , wherein the silica source comprises tetramethylorthosilicate, tetraethylorthosilicate, tetrapropylorthosilicate, tetrabutoxy silane, methyl trimethoxy silane, methyl triethoxy silane, phenyl trimethoxy silane, isobutyl trimethoxy silane, or a combination of two or more thereof.