Niobium carbide is a green cubic crystal with metallic luster and belongs to the sodium chloride type cubic crystal system. The relative density is 8.47, the lattice constant a=0.447nm, and the melting point is 2300°C. Microhardness>235Gpa (>2400kg/mm2), harder than corundum. Elastic modulus 338000N/mm2, thermal expansion coefficient 6.65×10-6/K, thermal conductivity 14w/(m.K), heat of formation -140.7kJ/mol, specific heat capacity 36.8J/(mol.K), resistivity 35μΩ.cm. Insoluble in water and in all acids except a mixture of nitric acid and hydrogen fluoride. It is stable at 1000-1100°C, and rapidly oxidizes to niobium pentoxide at temperatures above 1100°C. Niobium carbide is easy to melt in titanium carbide, zirconium carbide, tungsten carbide and other compounds, and together form an isomorphous solid solution mixture.
Lavender gray powder, soluble
in HF-HNO3 mixture. Wear resistant film, coating graphite
in nuclear reactors. Oxidation in
air becomes severe only above
1000°C.
niobium carbide (NbC) is extremely hard refractory materials. TiC, ZrC, VC and NbC are commercially used in tool bits for cutting tools. HfC and NbC can also be used as refractory coatings in nuclear reactors.
