Tungsten carbide coating on diamond particles in molten mixture of Na2CO3 and NaCl

• Diamond particles were coated with WC in molten salts containing Na2CO3 at 630–680 °C.
• Energy saving is evaluated based on heat quantity to raise temperature of feedstock.
• Compared with a NaCl bath process at 900 °C, the heat quantity was reduced by 50%.
• The WC coated diamond had lower specific resistance (220 Ω·cm) than non-Na2CO3 method.
• Na2CO3 addition to molten salts increased the efficiency of the WC coating.

Diamond compacts are prepared by bonding diamond particles with substrates. In the bonding process using a metal binder by electro-deposition, it is better to use diamond particles coated with tungsten carbide (WC) because of higher bonding efficiency between WC and the substrates caused by higher electric conductivity of WC. In this study, diamond particles were coated with WC in molten salts containing Na2CO3. Thermodynamically, sodium tungstate and WC were predicted to be generated by the reaction between metallic tungsten and Na2CO3, and the WC generation was confirmed experimentally. When the diamond powder and metallic tungsten powder were heated in a molten mixture of Na2CO3 and NaCl at 630–680 °C, the diamond was coated with the WC generated by the reaction as mentioned above. Such treatment temperatures are lower than those in the previously proposed methods (800–1500 °C). This reduces use of the heat quantity to raise the temperature of the feedstock by 50% compared with a NaCl bath process at 900 °C. The specific resistance of the diamond particles decreased with increasing of the WC coating thickness, because of the WC layer with higher electric conductivity than diamond. The specific resistance of the diamond particles treated in a molten mixture of Na2CO3–NaCl was 220 Ω·cm, whereas that of the diamond treated in a molten mixture of NaCl and KCl exceeded the upper detection limit in the used measurement system (> 1948 Ω·cm). Therefore, in a Na2CO3 containing molten mixture, the WC coating on the diamond particles proceeds effectively.