Thorium Carbides

The volume comprises an updated and critical description of the binary and ternary thorium carbides. These compounds are of technological interest because of their possible use as fertile materials in advanced nuclear power reactors. The fuel for the Thermal Breeder consists of a ThC-UC solid solution and that for the Thorium High Temperature Reactor of coated ThC2-UC2 particles. The binary Th-C system and ternary carbides were intensively investigated worldwide for nearly 20 years. Because of general discussions on the use of nuclear technology, interest in advanced nuclear reactors declined in recent years. Nevertheless, the research activity in the solid state science of binary and ternary thorium carbides increased and the Th-C system became one of the best known binary systems. At high temperatures there exists a series of solid solutions ranging from Th metal to the hypostoichiometric cubic ThC1.96' including the monocarbide ThC. A body-centered cubic Th2C3 of the Pu2C3 structure type only exists at pressures above 30 kbar. The Th carbides are refractory compounds with high melting points, e.g., 2500° C for the composition ThC0.97. Ternary carbides are either stoichiometric compounds, like ThAl4C4, ThAlC2, and Th4Al2C5 in the Th-Al-C system, or they form solid solutions with more or less broad ranges of composition. On the other hand, ThC is immiscible with group IV and V transition metal carbides because of its large unit cell. The normally metastable Th2C3 can be stabilized by forming solid solutions like (Th, La)2C3 with other sesquicarbides. Some ternary phases are superconductors with transition temperatures as high as 17 K.