Comparison of solid state and sol–gel derived calcium aluminate coated graphite and characterization of prepared refractory composite

Abstract

This paper entails an extended investigation on sol–gel thin film of calcium aluminate (CaAl2O4) over graphite flakes that improved their oxidation resistance and water wettability. The commercial preparation of calcium aluminate has been compared with the sol–gel synthesis by differential thermal analysis (DTA) and X-ray diffraction (XRD) to assess the feasibility of the latter for coating preparation. Poorly crystalline nanostructured Ca-doped γ-Al2O3 is considered to be an important intermediate for this preparation. Scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) of the calcined gel have been carried out to ascertain its composition. Quantitative chemical analysis of sol gel derived calcium aluminate was also estimated. Atomic force microscopy (AFM) has been conducted to ensure the evolution of hydrophilic nanosized cementitious phases on graphite. Zeta potential values of coated and uncoated graphites with increasing pH have also been determined to distinguish between their compatibility in a refractory castable matrix. Improved physical properties of that high alumina castable containing coated graphite, e.g. apparent porosity (AP), bulk density (BD), cold crushing strength (CCS) have been measured to evaluate the refractory quality. The reasons for its better performance are explored by taking further insight on the microstructural analyses of the fired castable (1500°C) soaked for an extended period.