Effect of Particle Size on Bulk Density and Strength Properties of Uranium Dioxide Specimens

Fused uranium dioxide was separated into fractions of varying particle size by air separation. Specimens of the nominal size of 1 / 8 by 1 / 4 by 1½ in. were formed by hydrostatic pressing, firing, and lapping. Specimens prepared from the 0 to 5 μ fraction were the strongest and most dense. The room‐temperature density was about 92% of theoretical and the room‐temperature flexural strength was about 12,000 1b. per sq. in. When tested at 1000°C., the strength was about 18,000 1b. per sq. in. The flexural strength of specimens decreased and their density decreased as the starting particle size was increased. The crystallization of the urania fragments which had occurred during the firing treatment was observed.