US Patent 7569614 Process for producing acidic aqueous alumina sol

A process for producing a stable acidic aqueous alumina sol containing columnar secondary particles having a length of 50 to 400 nm which are formed by face-to-face coagulation of rectangular plate-like primary particles having a length of one side of 10 to 40 nm and a thickness of 2.5 to 10 nm when observed through an electron microscope, by use of an aqueous alkali aluminate solution and liquid or gaseous carbon dioxide as starting materials. The obtained acidic aqueous alumina sol has a low viscosity and is stable for salts. The dried gel obtained from the sol is characterized in that the gel structure thereof is rigid even though it is porous.