Some Properties of Hafnium Oxide, Hafnium Silicate, Calcium Hafnate, and Hafnium Carbide

Abstract

The behavior of hafnium oxide was studied particularly in the temperature range 1500° to 18OO°C. Properties of HfO 2 at these temperatures and its reactions with ZrO 2 , SiO 2 , and CaO are given in terms of lattice and other physical measurements, many of which are new. Mono‐clinic hafnium oxide is stable to 1700°C., which is 600° higher than the corresponding inversion temperature of zirconia. Otherwise HfO 2 closely resembles ZrO 2 (a) in its lattice dimensions and sintering behavior, (b) in forming a high‐temperature tetragonal phase closely resembling tetragonal ZrO 2 , (c) in forming a continuous series of solid solutions with ZrOz, (d) in forming with silica a single compound (HfO 2 .SiO 2 ) similar to zircon, (e) in forming a carbide, (f) in uniting with up to 40% CaO to form cubic solid solutions; thereafter a compound CaO.Hf O 2 appears which is very similar to the corresponding zirconia compound.