A NEW OXIDATION PROCESS OF POTASSIUM TITANIUM-DIOXIDE BRONZE WITH THE HOLLANDITE STRUCTURE

Potassium titanium dioxide bronze (KxTi8O16) was synthesized by heating a mixture of K2CO3 and TiO2 at about 1000°C under a mixed gas flow of H2 and CO2. The dioxide bronze was obtained as dark blue powder having the hollandite structure and underwent isomorphous oxidation up to about 680°C by heating in the air to change to a nonstoichiometric titanate. Raw bronze products elute potassium into HCl aqueous solution, which is rapid in the very early stages and slows successively. Oxygen uptakes with the isomorphous oxidation indicate that the content of Ti3+ in raw bronze is considerably smaller than that expected from reaction mixtures and almost constant. The elution behavior shows that the nonstoichiometric parameter "x" is near 1.1 and not very dependent on valves expected from the starting mixtures. It is suggested from the new oxidation process that the migration of oxygen atoms and holes from the surface to the inside of the bronze grains is preferred, in air, to that of K+ ions and electrons in the opposite direction. © 1991.