|
|Section2= |Section4= |Section8= }} Tantalum carbides form a family of binary chemical compounds of tantalum and carbon with the empirical formula TaCx, where x usually varies between 0.4 and 1. They are extremely hard, brittle, refractory ceramic materials with metallic electrical conductivity. They appear as brown-gray powders which are usually processed by sintering. Being important cermet materials, tantalum carbides are commercially used in tool bits for cutting applications and are sometimes added to tungsten carbide alloys. The melting points of tantalum carbides peak at about 3880 °C depending on the purity and measurement conditions; this value is among the highest for binary compounds.〔The claim of melting point of 4000 °C in TaC0.89 is based not on actual measurement but on an extrapolation of the phase diagram, using an analogy with NbC, see Emeléus〕 Only tantalum hafnium carbide may have a slightly higher melting point of about 3942 °C, whereas the melting point of hafnium carbide is comparable to that of TaC. ==Preparation== TaCx powders of desired composition are prepared by heating a mixture of tantalum and graphite powders in vacuum or inert gas atmosphere (argon). The heating is performed at temperature of about 2000 °C using a furnace or an arc-melting setup.〔〔 An alternative technique is reduction of tantalum pentoxide by carbon in vacuum or hydrogen gas atmosphere at a temperature of 1500–1700 °C. This method was used to obtain tantalum carbide back in 1876, but it lacks control over the stoichiometry of the product.〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Tantalum carbide」の詳細全文を読む スポンサード リンク
|