Effect of Extended Milling of Scheelite Ore with Activated Charcoal on Direct Synthesis of Nanotungsten Carbide

Abstract

Nanosized tungsten carbide is mostly synthesized from pure precursor(s) like W, WO₃, W(CO)₆, WCl₄, and WCl₆ which makes its production costly. These pure precursor(s) are obtained after lengthy, multistage processing of the ores, mainly scheelite (CaWO₄) and Wolframite (FeWO₄). This paper investigates the effect of extended milling of 150 h of scheelite ore with activated charcoal for direct synthesis of nanosized tungsten carbide. The reaction mechanism was studied with the help of thermodynamic analysis. The investigations revealed that reaction of CaWO₄ with carbon at 1032°C will lead to the formation of WC phase without creation of any undesired phases like WO_2.72, WO₂, W₂C, or W. To remove impurities and unwanted reaction products, the calcined powders were leached by dilute acid (1:1 HCl) followed by base (0.25 M NaOH) treatment. The final leached powders contained 5 to 30 nm size WC particles and little amount of unreacted scheelite particles.

Keywords:

• ceramics
• electron microscope
• nanoparticles
• particle size distribution
• scheelite
• Tungsten carbide

Acknowledgment

Harjinder Singh is thankful to Ms Samita Thakur for helping in Rietveld analysis.