96/05940 Characterization of fly ash from cement and concrete

Abstract

This study is focused on the effect of the porosity and chemical reactivity with silicon of the carbon preforms on the properties of SiC pieces produced by reactive infiltration. Petroleum residues were selected as carbon precursor because of their unique combination of properties. On the one hand, semicoke powders with optimum self-sinterability can be obtained from them to develop a wide range of porous carbon preforms without addition of binder to carry out the porosity study. On the other hand, reactivity of the carbon material with silicon can be modified by employing semicokes with different mesophase microstructure obtained from petroleum residues with different chemical composition. SiC yield was strongly affected by the degree of anisotropy of the carbon material, the most ordered carbon being more reactive. SiC pieces made from the optimum carbon preforms (made up by combining the most graphitic carbon and 40% of open porosity) achieved bending strength values of around 260 MPa. Chemical reactivity of carbon substrates was also modified by graphitization treatment. An improvement in the mechanical properties of SiC pieces up to 66% was achieved due to the structural modification caused by graphitization of the carbon preforms. Bending strengths twice the value of commercially available ones were achieved.