Development of Ceramic Coatings Using Redmud - A Solid Waste of Alumina Plants

Abstract

Plasma Spraying is a surface modification technique that combines particle melting, rapid solidification and consolidation in a single process. But as high cost of spray grade powders limits the adoption of this technique, exploring newer and cheaper materials suitable for plasma spray coating has drawn a lot of attention. This work reports an attempt to spray coat red mud (the waste generated in alumina producing plants) on different metal substrates. Plasma sprayed coatings of red mud have been developed at different operating power levels of the plasma gun on aluminium and copper substrates. Coating adhesion strength and deposition efficiency were studied at various operating conditions. Characterization of the coatings includes micro hardness measurement and scanning electron microscopy (SEM). It was observed that the operating power appreciably influences the coating adhesion strength and coating thickness. Coatings deposited at very low and very high power levels show poor adhesion. Maximum interface adhesion strength of ~8MPa was recorded at operating power of 12 kW. This work establishes ‘red mud’ as a potential coating material, which may be suitable for wear resistant applications. It also suggests a value added utilization of this industrial waste.