Heat-induced gelation of hydroxy-aluminosilicate synthesized by instantaneous mixing of sodium silicate and aluminum chloride

Imogolite is expected to be used as various industrial materials, but its mass production is needed before application. Imogolite is synthesized by heating solutions containing hydroxy-aluminosilicate (HAS) ions. It is possible to prepare fairly concentrated solutions of HAS ions. But heating the concentrated solution does not lead to the successful formation of imogolie. We prepared HAS solution containing 0.1 mol L^-1 Al and heated it in erlenmeyer flasks with and without cover. Heating without cover induced heterogeneous cooling of the solution from the surface by the droplets of condensed water. Under this condition, HAS spontaneously coagulated to form transparent brittle gel, whereas the solution heated with cover became turbid uniformly. X-ray diffraction and infrared spectroscopy showed that the structure of the products were basically similar to that of allophane and imogolite. There was little structural difference between the products from different heating condition. The products were morphologically different from allophane and imogolite. Extremely small specific surface area of the products, 0.8 to 1.4m² g^-1, suggested that the products were aggregates of HAS with strong inter particle bonding.