Synthesis of Graphite/SiC Micro-composites and their influence on MgO-C Refractories

Abstract

The magnesia carbon (MgO-C) refractory is a classical choice for the working lining of steel making furnaces because of slag corrosion and thermal shock resistance. However, the poor oxidation resistance of carbon beyond 900oC eventually damage the brick, and subsequent necessities of reinstallation enhance the cost of steel. Hence, minimization of carbon content without compromising of existence properties of MgO-C brick is one of the prime research areas. The present investigation aims to replace a part of the carbon (mostly graphite flakes) with graphite-SiC microcomposite (C/SiC). The latter non-oxide SiC is known to have excellent high temperature strength, better oxidation resistance, high abrasion resistance and moderate thermal conductivity. The basic objective of this dissertation is to carry out systematic laboratory and pilot industrial scale preparation of composites and understand the effect of microcomposites on MgO-C refractory properties. The micro-composite has been synthesised by a simple carbothermal reduction of microfine silica (SiO2) in presence of graphite flakes in the temperature range of 1600 - 1650oC under a reducing atmosphere created by packing the reactants within petroleum coke in raising hearth furnace (RHF)/ tunnel kiln (TK) or either controlled atmospheric furnace (CAF). It has been observed that two different morphologies of the SiC phase namely fibre/rod and ribbon developed based on the specific condition of synthesis. A different grade of MgO-C bricks has been prepared through the addition of a different percentage of synthesized graphite-SiC composites at an optimum processing condition and evaluated their physical, thermo-mechanical, oxidation and slag corrosion behaviour. An optimum content of SiC present in the synthesized graphite – SiC microcomposite exhibits better oxidation resistance, hot modulus of rupture and slag corrosion properties compared to the only graphite content brick or addition of equivalent amount of free commercial grade - SiC containing MgO-C brick.