BigPatents India

A thermal plasma process has been developed to prepare hard diamond like carban coating on SiC grains/powder within 15-30 minutes. By exposing SiC to a thermal plasma produced by non-transferred arc using graphite electrodes and inert gas/nitrogen/inert gas +nitrogen mixture as plasmagen gas, the carbide compound got dissociated above 2800°C to produce carbon coated SiC grains whose surface microhardness was found to be more than 3500 VHN 0.1. The following arc conditions were maintained in a 35 kW dc plasma reactor/furnace to carry out the diamond like coating deposition: Voltage 30-50 V, Current 250-400 A, Are length 1-2.5 cm. The plasmagen gas was passed at the rate of 0.5-1.5 lit.per min. The grains/powder were exposed to plasma flame for 15-30 minutes and then were furnace cooled up to room temperature for 2-3 hours. Growth of the carbon layer/coating on SiC lattice was found to take place in situ. Surface topography of the carbon layer studied under SEM showed a cuboid type grain growth which is typical in diamond like lattice. Recovery of plasma treated powder/grains after furnace cooling was found to be 80-90% by weight.