Carbide and Nitride Overlayers on Early Transition Metal Surfaces: Preparation, Characterization, and Reactivities

摘要

Interstitial carbides and nitrides of early transition metals (groups IVB—VIB) are produced by dissolving carbon and nitrogen atoms into the metal lattices. These carbide and nitride materials have unique physical and chemical properties, which combine the characteristic properties of three different classes of materials: covalent solids, ionic crystals, and transition metals. They demonstrate the extreme hardness and brittleness of covalent solids; they possess the high melting temperature and simple crystal structures typical of ionic crystals; and they have electronic and magnetic properties similar to transition metals. For example, carbides and nitrides are characterized by melting temperatures ≥ 3300 K and by values of hardness ≥ 2000 kg mm~(-2) and tensile strength ≥ 300 GPa, which are in the range of ceramic materials. At the same time, values of their electric conductivity, magnetic susceptibility and heat capacity are in the metallic range. The refractory and the conducting nature of carbides and nitrides makes them good candidates for various applications in material science.