Refractory Metals Refractory metals Refractory metals are characterised by their high melting points, exceeding an arbitary value of 200 C, and low vapor pressures, two properties exploited by the electronics industry. Only for refractory metals, molybdenum, niobium, tantalum and tungstun, are available in quantities of industrial significance. Molybdenum, niobium, tantalum and tungstun have been produced commercially for many years, mainly as additives to steels, nickels and cobalt alloys and for certain electrical applications. In addition to high temperature strength, the relatively low thermal expansions and high thermal conductivities of the refractory metals suggest good resistance to thermal shock. There are however two characteristics, ready oxidation at high temperatures and, in the case of molybdenum and tungston, brittleness at low temperatures, which limit their applications.
Tantalum is a white lustrous metal resembling platinum.
It is highly acid resistant and is classed as a noble metal. Tantalum will hold a fine cutting edge on tools. By adding silicon to tantalum, its hardness can be made close to dimond. Anode film has better dielectric properties than Al. Very low ductile-brittle transition temperature.