CHANGE OF PHYSICAL-PROPERTIES OF UNBURNED MGO-C BRICKS UNDER VARIOUS HEATING CONDITIONS

The thermal expansion ratio of baked MgO-C bricks under an applied loa d (TEAL) of 5 MPa decreased in the temperature range of 400-700 degree s C and became negative at room temperature (RT) after heating and coo ling, due to volatile matter in the resin binder. The thermal expansio n ratio under free load (TEFL) was almost constant in the temperature range of 400-700 degrees C and became positive at RT after heating and cooling, The TEAL could not be correlated with the TEFL and both exhi bited nonelastic characteristics. For MgO-C bricks after heat treated twice at 1000 degrees C, the effect of the volatile matter in the resi n could not be confirmed, and the TEFL at 1000 degrees C was lower tha n that at the same temperature for the baked samples, The TEAL remaine d unchanged at temperatures ranging from RT to 400 degrees C and becam e negative at RT after heating and cooling, due to the irreversible ef fect of thermal expansion absorption caused by the free carbon in the resin, The TEAL could be correlated with the TEFL by assuming an elast ic-like modulus for the free carbon. When the effect of the free carbo n ended, the TEAL changed linearly and was close to the estimated ther mal expansion ratio based on those of the raw materials, For MgO-C bri cks containing 3 % Al, the elastic modulus at temperatures above 700 d egrees C was higher than that of the samples without Al because of the formation of metal reaction products, Furthermore, the TEAL in the fo rmer 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.