In a program on possible new compounds for nuclear fuels, the refractory uranium compounds UC, UC2, UN, UB2, and UBe13 were investigated. Methods of preparing these compounds and techniques for sintering them to densities of 90 per cent or greater are described.
The carbides were prepared by arc-melting stoichiometric mixtures of uranium metal and high-purity carbon. The mononitride was prepared by first forming U2N3 by reaction of powdered uranium metal and nitrogen; the sesquinitride was subsequently converted to the mononitride by heating at a reduced pressure. The diboride was formed by the solid-solid reaction of UH3 and boron powder at 1300 to 1400 C. The beryllide was prepared by heating a mixture of UH3 and beryllium metal (with beryllium in excess) in an argon atmosphere at 1550 C.
Dense specimens for property measurements were fabricated by hydrostatic pressing of fine powders, obtained by crushing and grinding the compounds, and sintering the compacts in vacuum or in argon at temperatures ranging from 1550 C for UBe13 to 1850 for UN.
Thermal expansion was measured for the beryllide and the monocarbide. The mean linear coefficient from 20 to 1000 C was 14.2 × 10-6 per deg Cent for UC and 16.7 × 10 6 per deg Cent for UBe13. The thermal conductivity of the beryllide was found to be appreciably higher than that of uranium dioxide and to approach that of uranium metal.
The rate of reactions of several of the compounds with water vapor, oxygen, and nitrogen at temperatures up to 500 C was investigated. In general, the compounds were most resistant to nitrogen and reacted most rapidly with oxygen. The beryllide was generally the least reactive of the compounds and reacted less rapidly than uranium metal with the three gases. The diboride reacted with oxygen more rapidly than did uranium metal but was more resistant than uranium to water vapor and nitrogen. The dicarbide reacted most rapidly, and its rate of reaction was greater than that of uranium metal with the three gases.