PURPOSE: To ensure good controllability of chemical compsn. and particle size and to improve heat resistance by subjecting reaction products of acidic aluminum phosphates with amines and, optionally, boric acid to a heat shock after drying.

CONSTITUTION: An aq. soln. of acidic aluminum phosphates is prepd. by reacting 1 mol aluminum hydroxide with 2-3 mol phosphoric acid in the presence of water and 2-6 base equiv. amines and, optionally, boric acid are added to the aq. soln. and reacted at 20-120°C to prepare an aq. soln. contg. 40-96 wt.% reaction products. This aq. soln. is dried at ≤250°C under atmospheric pressure to form granules having 0.01-1 cm average diameter and the granules are subjected to a heat shock of ≥200°C to obtain the objective heat resistant hollow beads having 10-500 g/l bulk density.