1. Department of Chemical and Metallurgical Engineering, Tshwane University of Technology, P.M.B. X680, Pretoria 0001, South Africa
2. Counil for Scientific and Industrial Research — National Laser Centre, P.O. BOX 395, BLD 46F, Pretoria 0001, South Africa
3. Department of Metallurgical and Materials Engineering, Federal University of Technology, Akure, P.M.B. 704, Akure, Ondo — State, Nigeria