The possibility of obtaining niobium carbide in the form of powder and coatings by deposition from a vapor mixture in the temperature range 1500-1900·C has been investigated.
The principal properties characteristic of niobium carbide are a high melting point and microhardness, a high resistance to the action of molten metals and metal vapors, reasonable strength at elevated temperatures, low vapor pressure, high electrical conductivity, and good emissivity. These properties determine the field of application of NbC, namely for the manufacture of heating elements for high -temperature furnaces and of evaporating plants for aluminum, for protective coatings, for coating thermionic emission elements, and for use in heat-resistant alloys.
In general, NbC can be produced by the following basic methods: synthesis from the elements, reduction of the metal oxides by carbon, electrolysis of molten salts, and deposition from the vapor phase.
However, it is impossible to obtain NbC having a high degree of purity and a strictly stoichiometric composition by using these methods. Methods of producing porosity-free specimens of refractory compounds are practically nonexistent. In consequence, the properties of NbC have been studied on porous specimens affected by the following factors: impurities, pores, complex contact phenomena, and cracks. These investigations have shown it to be essential to prepare the compounds (and in particular NbC) in a state similar to the cast state or as high-purity single crystals. Almost the only way of obtaining NbC in this state is by deposition from a vapor mixture. The method is based on the reaction between the components of a vapor mixture consisting of a halide compound of the metal, a carbon-containing gas, and hydrogen, followed by the deposition of the reaction products in the form of a finely dispersed powder on a heated surface.
For more information, please visit http://www.samaterials.com/niobium-compounds/63-niobium-carbide-powder.html