Influence of Chemical Reactions in Magnesia‐Graphite Refractories: I, Effects on Texture and High‐Temperature Mechanical Properties

Four formulations of magnesia‐graphite‐aluminum metal (antioxidant) bricks were prepared from the same raw materials, using the standard commercial practices. Chemical analysis and determination of room‐temperature modulus of rupture and Young's modulus, as well as a complete microstructural characterization of the as‐received materials, were performed. For high‐temperature modulus‐of‐rupture and Young's modulus data, test samples of the four brick compositions were heated to 1000°, 1200°, and 1450°C in flowing argon (<1000 ppm oxygen at 1000°C) and then loaded mechanically in flexure. Modulus‐of‐elasticity values ranged from 3.7 to 16.2 GPa and reflected strong effects of aluminum‐metal concentration and treatment temperature. Young's modulus evolution with temperature was determined by the evolution of the microstructure in the bulk of the specimens. Modulus‐of‐rupture values ranged from 6 to 21 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 lessthan equal to 1200°C) and by phase assemblages in the surface regions of the specimens‐essentially by the presence of the dense MgO zone‐at 1450°C.