Some Physical Properties of High‐Density Thorium Dioxide

The values for a number of physical properties are reported for a very high density form of thorium dioxide. When specimens of a mixture of 99½% ThO 2 and ½% CaO, by weight, were hydrostatically pressed at 30,000 lb. per sq. in. and heat‐treated for 1 hour at 1800°C., they attained 99.0% of theoretical density. All the test specimens were extremely brittle. Physical‐property values determined at room tempera‐ ture were the following: lattice constant; bulk and theoretical (X‐ray) densities; compressive and impact strengths; Knoop hardness; modulus of rupture and Young's modulus, determined by a static method; Young's modulus and the shear modulus, determined by a dynamic method; Poisson's ratio and the bulk modulus, calculated from the dynamic‐test data; and the velocity of sound through the material. The properties determined at elevated temperatures were the following : linear thermal expansion modulus of rupture and Young's modulus, determined by a static method; Young's modulus and the shear modulus, determined by a dynamic method; and Poisson's ratio, calculated from the elevated‐temperature dynamic‐test data. “Martin's diameter” grain counts were taken for the material both before and after heat‐treatment.