High-Temperature Properties of Unburned MgO-C Bricks Containing Al and Si Powders

• Published in: Journal of the American Ceramic Society Vol. 81; no. 11; pp. 2910 - 2916
• Main Authors: Uchida, Shigeki, Ichikawa, Kenji, Niihara, Koichi
• Format: Journal Article
• Language: English
• Published: Westerville, Ohio American Ceramics Society 01.11.1998; Blackwell; Wiley Subscription Services, Inc
• Subjects: Applied sciences; Building materials. Ceramics. Glasses; Chemical industry and chemicals; Exact sciences and technology; Refractory products; Special refractories; Fire brick; Elastic modulus; Mechanical properties; Magnesite carbon refractory; Aluminium; High temperature; Experimental study; Thermal properties; Bending strength; Thermal expansion; Additive; Unfired refractory; Silicon; Porosity; Microstructure
• ISSN: 0002-7820; 1551-2916
• DOI: 10.1111/j.1151-2916.1998.tb02713.x

Changes in the mechanical and thermal properties, as well as in the microstructure, of unburned MgO‐C bricks containing Al and Si powders were investigated at selected temperatures. Specimens with heat treatments at 500°C shrank and exhibited higher apparent porosity than untreated specimens. The bending strength and elastic modulus at 500°C were much lower than those of untreated specimens, and the apparent porosity increased and the mechanical properties at 500°C decreased with each repeating heat treatment. It was predicted that when the volatile matter was no longer generated, microstructure shrinkage would stop and the mechanical properties become constant. The bending strength and static elastic modulus at 800°, 1000°, and 1300°C were higher than those at 500°C because of the binding effect of the reaction products (i.e., Al4C3, SiC, and MgAl2O4), although the apparent porosity was higher than at 500°C. Repeated heat treatment from room temperature (RT) to the respective temperature, however, degraded the properties to nearly the same level as at 500°C because of the increased apparent porosity and the cracks generated in magnesia particles by the reaction products. Plastic deformation appeared to occur at 1300°C just before bricks were fractured. In addition, the thermal expansion ratio decreased through repeated heating and cooling from RT to 500°, 1000°, or 1300°C, and finally decreased to a constant value, as predicted.