Abstract
The thermal expansion ratio of baked MgO-C bricks under an applied load (TEAL) of 4MPa decreased in the temperature range of 400-700°C and became negative at room temperature (RT) after heating and cooling, due to volatile matter in the resin binder. The thermal expansion ratio under free load (TEFL) was almost constant in the temperature range of 400-700°C and became positive at RT after heating and cooling. The TEAL could not be correlated with the TEFL and both exhibited nonelastic characteristics. For MgO-C bricks after heat treated twice at 1000°C, the effect of the volatile matter in the resin could not be confirmed, and the TEFL at 1000°C was lower than that at the same temperature for the baked samples. The TEAL remained unchanged at temperatures ranging from RT to 400°C and became negative at RT after heating and cooling, due to the irreversible effect of thermal expansion absorption caused by the free carbon in the resin. The TEAL could be correlated with the TEFL by assuming an elastic-like modulus for the free carbon. When the effect of the free carbon ended, the TEAL changed linearly and was close to the estimated thermal expansion ratio based on those of the raw materials. For MgO-C bricks containing 3% Al, the elastic modulus at temperatures above 700°C was higher than that of the samples without Al because of the formation of metal reaction products. Furthermore, the TEAL in the former case was higher than that in the latter case, when the effects of volatile matter in the resin and the free carbon could be neglected.
