Tungsten Carbide Production Volumes and Use Pattern

Tungsten carbide is manufactured by direct carburization of tungsten with carbon (Roempp, 2003). Mixtures of metal and carbon black or graphite are heated at a temperature of 1400 . 2000 °C in vacuum or under hydrogen (Tulhoff, 2000):
W + C-> WC.

When heating a mixture of tungsten and carbon in a carbon tube or high-frequency furnace to ca. 2800 °C, cast tungsten carbide is obtained (Gmelin, 1993). However, most tungsten carbide is sold as powders with distinct ranges of grain sizes (Tulhoff,2000).
Purity and grain size determine the physical properties and the technical applicability of tungsten carbide. Since milling changes the chemical composition and the shape of the grains, coarse powders of tungsten carbide can not be milled to obtain fine-grained powders. Instead, to obtain the desired industrial product, the particle size of the raw materials is carefully selected. The grain size of the product is also influenced by namufacturing parameters like temperature, reaction time, presence of humidity and Typical production lines start from tungsten ore (W, Nb, Fe-oxides), tungsten scrap, scheelite (CaWO4), tungsten acid (H2WO4), and ammonium paratungstate ((NH4)10W12O41 x 5 H2O), Typical intermediates are yellow (WO3) blue (approximately W4O11) and brown tungsten oxide (WO2). There are severaJ methods for the manufacturing of the technical tungsten carbide powders (Tulhoff, 2000): Tungstic acid powder is reduced to tungsten by hydrog at 750°C.The metal particles are carburized at 1400°C.This method is applied for fine powder with an average grain size of 1 ｕm.