Development of mullite and spinel coatings on graphite for improved.pdf

Available online at Ceramics International 36 (2010) 1837–1844 /locate/ceramint Development of mullite and spinel coatings on graphite for improved water-wettability and oxidation resistance Sk.A. Ansar a, S. Bhattacharya b, S. Dutta a, S.S. Ghosh a, S. Mukhopadhyay a,* a Department of Chemical Technology, Calcutta University, 92 APC Road, Kolkata 9, India b Calcutta Institute of Engg. and Management, 24/1A C. G. Road, Kolkata 40, India Received 15 June 2009; received in revised form 24 February 2010; accepted 17 March 2010 Available online 29 April 2010 Abstract Mullite and spinel forming sols were prepared from hybrid precursors having both organic and inorganic origins. Refractory grade graphite flakes were coated by these sols and their performances were compared in terms of oxidation resistance and water-wettability. Particle size distribution, structural evolution and related characteristics of both mullite and spinel gels have been investigated by dynamic light scattering (DLS), differential thermal analysis (DTA), X-ray diffraction (XRD) and infrared spectra (IR) studies. Coated graphites have also been studied by IR and XRD tests along with scanning electron microscopy (SEM) with energy dispersive spectral (EDS) analysis. The better performance of spinel coated graphite was confirmed. The mechanism of spinel formation on graphite was suggested to take place via intermediate gamma alumina phase formation from boehmite sol. It was clarified by DLS, XRD and microstructural analysis of dried and ca