Plasma spray coating of fly ash pre-mixed with aluminium powder deposited on metal substrates

Plasma spray technology has the advantage of being able to process low-grade-ore minerals to produce value-added products, and also to deposit ceramics, metals and a combination of these, generating homogenous coatings with the desired microstructure on a range of substrate. The present work deals with the development of a ceramic composite coating on metal substrates using fly ash (the thermal power plant waste) pre-mixed with Al powder. Mixtures of fly ash with 5 and 15 wt.% Al powder were plasma sprayed onto copper and stainless steel substrates at various plasma torch power levels ranging from 10 to 20 kW DC. The coatings produced were characterised by X-ray diffraction, optical and electron microscopic studies and measurement of interface adherence strength. A maximum strength of 52 MN m(-2) was recorded with a copper substrate. It is found that the coating quality and properties are improved with higher aluminium content in the feed material and are affected by the operating power level of the plasma. (C) 2000 Elsevier Science S.A. All rights reserved.