Carbothermic Reduction of the Waste Chromium Oxide Rods from Thermal Spray Processes

Abstract

The waste chromium-oxide rods from thermal spray processes contained the valuable components of high chromium. The carbothermic reduction with graphite powders can be used to recover the chromium from the chromium-oxide rod. The waste rods were prepared into small pieces with a half-dimensions of 6.3 mm diameter and 5 mm length, and heated under the reducing atmosphere at 1150 – 1350 °C. Besides, the effect of different types and sizes of reducing agent on the reduction was observed. During the heating and cooling period, argon gas was fed into the atmosphere. Chromium carbide formation was promoted when the temperature and time were increased. Cr-O and Cr-O-Al-Si were observed in the microstructures before and after the reduction. The outermost part of the waste rod can be reduced to chromium because of the interphase zone. Consequently, the carbothermic reduction is one possible recycling method for utilizing ceramic rod wastes from the thermal spray process.