Introduction

THE REFRACTORY METALS--tungsten, molybdenum, niobium, tantalum, and rhenium--are distinguished by several common characteristics, including high density, high melting point, and superior resistance to wear and acid corrosion. Tungsten, for example, has a density over twice that of iron and a melting point of 3410 °C (6170 °F), the highest of any element. These metals have body-centered cubic crystal structures (with the exception of rhenium, whose crystal form is hexagonal). All are subject, however, to severe oxidation above 500 °C (930 °F) and must be protected for service by coatings or nonoxidizing atmospheres.

The refractory metals are extracted from ore concentrates, processed into intermediate chemicals, and then reduced to metal, which can be in the form of powder. The pure or alloyed powders are pressed, sintered, and subsequently worked. This article discusses the raw materials, processing steps, powder properties, and finishing techniques (blending, handling, inspection and packaging) involved in the production of refractory metal and carbide powders. For information on applications of these materials, see the article "Refractory Metals" in this Volume.

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