Influence of chemical reactions in magnesia-graphite refractories:: II, effects of aluminum and graphite contents in generic products

A group of magnesia-graphite and magnesia-graphite-aluminum materials, the compositions of which represent a wide range of graphite contents (similar to 10-16.4 wt%), aluminum contents (0-5.2 wt%), and MgO and graphite qualities, were fabricated, using standard commercial practices. Chemical analysis and determination of room-temperature modulus of rupture (MOR) and Young's modulus, as well as a complete microstructural characterization of the as-received materials, were performed, Mechanical characterization at high temperature (1000 degrees, 1200 degrees, and 1450 degrees C) was done in terms of Young's modulus and MOR in an argon atmosphere (<1000 ppm oxygen at 1000 degrees C). Modulus-of-elasticity values ranged from 4 to 16 Cpa, and their evolution with temperature was determined by the evolution of the microstructure in the bulk of the specimens. A strong effect of aluminum-metal concentration on Young's modulus overrode other microstructural differences among the materials. MOR values ranged from 6 to 20 MPa, and their evolution with temperature was determined by the evolution of the microstructure in the bulk of the specimens at the lower testing temperatures (T less than or equal to 1200 degrees C) and by phase assemblages in the surface regions of the specimens - essentially by the presence of the dense MgO zone - at 1450 degrees C, The thickness of the dense MgO zone in the aluminum-containing materials was determined by the amount of aluminum and the MgO aggregate size.