1. Industrial Research and Consultancy Centre, Ministry of Industry and Trade, PO Box 268, Khartoum, Sudan.
2. Dept. of Science and Technology, Campus Norrköping, Linköping Univ., SE-601 74 Norrköping, Sweden.
3. Materials and Nanotechnology Research Centre, Faculty of Engineering, Univ. of Khartoum, PO Box 11115, Khartoum, Sudan (corresponding author). ORCID: .