Shaped gel articles and sintered articles prepared therefrom

A method of making a sintered article, the method comprising:

• a) providing a mold having a mold cavity;
• b) positioning a casting sol within the mold cavity, the casting sol comprising:
• 1) 2 to 65 weight percent surface modified silica particles based on a total weight of the casting sol, wherein the surface modified silica particles comprise a reaction product of silica particles having an average particle size no greater than 100 nanometers and a surface modification agent composition comprising a silane modification agent having a radically polymerizable group and wherein the surface modified silica particles are 50 to 99 weight percent silica and wherein the casting sol contains no more than 50 weight percent silica;
• 2) 0 to 40 weight percent of a polymerizable material based on the total weight of the casting sol, wherein the polymerizable material does not contain a silyl group;
• 3) 0.01 to 5 weight percent radical initiator based on the total weight of the casting sol;
• and
• 4) 30 to 90 weight percent organic solvent medium based on the total weight of the casting sol, wherein the surface modification agent composition, the polymerizable material, and the radical initiator are soluble in the organic solvent medium;
• c) polymerizing the casting sol to form a shaped gel article that is in contact with the mold cavity;
• (d) forming a dried shaped gel article by removing the organic solvent medium;
• (e) removing either the shaped gel article or the dried shaped gel article from the mold cavity;
• and
• (f) heating the dried shaped gel article to form a sintered article, wherein the sintered article has a shape identical to the mold cavity (except in regions where the mold cavity was overfilled) and to the shaped gel article but reduced in size proportional to an amount of isotropic shrinkage.