Abstract: A process for producing a spherical silica gel, which comprises supplying a liquid mixture of an alkali silicate solution and an acid solution to a spraying apparatus, spraying the liquid mixture to obtain droplets, bringing the droplets into contact with a liquid for recovering a silica gel, and recovering the formed spherical silica gel together with the liquid for recovering a silica gel, as a slurry.

Abstract: An acid component-removing agent which comprises sodium hydrogencarbonate having a volume-based mean particle diameter of from 1 to 9 &mgr;m as measured by a laser diffraction and scattering method.

Abstract: A hollow glass microsphere having an average particle size of at most 15 &mgr;m based on volume, a maximum particle size of at most 30 &mgr;m and an average particle density of from 0.1 to 1.5 g/cm3, which has a glass composition consisting essentially of the following components by mass %: 1 SiO2 50.0-90.0%,   Al2O3 10.0-50.0%,   B2O3 0-12.0%, Na2O + K2O + Li2O 0-1.0%,  CaO 0-10.0%, MgO 0-10.0%, BaO + SrO 0-30.0%.

Abstract: Hollow aluminosilicate glass microspheres which are hollow glass microspheres having an average particle size of from 1 to 20 &mgr;m based on volume, an average particle density of from 0.20 to 1.50 g/cm3, a sphericity within a range of 1≦(long axial length/short axial length)<1.2 and a composition comprising from 30 to 85 mass % of SiO2, from 6 to 45 mass % of Al2O3, from 0 to 30 mass % of an alkali metal oxide, from 0 to 30 mass % of an alkaline earth metal oxide and from 0 to 1 mass % of B2O3, and which have a strength at 10 volume % collapse of at least 10% of the theoretical strength given by the formula 16.7×E×(t/2a)2.5, where E is the Young's modulus (unit: GPa) of the glass constituting the hollow glass microspheres, t is the thickness (unit: mm) of the shell of the hollow glass microspheres, and a is the hollow radius (unit: mm) of the hollow glass microspheres.

Abstract: It is an object of the present invention to obtain solid spherical silica particles having no depression or crack on the surface. The present invention provides a process for producing spherical silica particles, which comprises dispersing silica gel particles having an average particle size of from 0.05 to 3.0 &mgr;m in a mixed solution of an alkali silicate and an acid, spraying the dispersion to obtain droplets, and heating the droplets in a gas and gelating the mixed solution portion of an alkali silicate and an acid in the droplets.