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 qualit ies, were fabricated, using standard commercial practices. Chemical analysi s 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 te mperature (1000 degrees, 1200 degrees, and 1450 degrees C) was done in term s of Young's modulus and MOR in an argon atmosphere (<1000 ppm oxygen at 10 00 degrees C). Modulus-of-elasticity values ranged from 4 to 16 Cpa, and th eir evolution with temperature was determined by the evolution of the micro structure in the bulk of the specimens. A strong effect of aluminum-metal c oncentration on Young's modulus overrode other microstructural differences among the materials. MOR values ranged from 6 to 20 MPa, and their evolutio n with temperature was determined by the evolution of the microstructure in the bulk of the specimens at the lower testing temperatures (T less than o r 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 1 450 degrees C, The thickness of the dense MgO zone in the aluminum-containi ng materials was determined by the amount of aluminum and the MgO aggregate size.