The corrosion resistance and wear life of carbon-bonded magnesia refractories make them attractive for use in the highly oxidizing atmospheres of steelmaking. It is known that aluminum added in small amounts inhibits oxidation of the carbon, and that impurities in the individual constituents of magnesia-graphite-aluminum composite bricks may significantly alter the reaction temperatures in the system. Past studies have dealt with the effects of impurities upon mechanical properties, corrosion resistance and wear life of the refractory. The objective of this study is to develop a fundamental understanding of the level and type of impurity upon the basic pyrochemical reaction sequences and resultant phase stability in the mgo-c-al system. It has been shown that because of the large aggregate size of the magnesia grain, the matrix is the component of the brick that undergoes significant pyrochemical reaction. This study assumes that approximately 75 pct of the magnesia present in the system (i.e., the fraction that is considered large-grain) does not react with the other constituents. The experimental matrix used in these studies is 44.45 Wt pct magnesia, 44.45 Wt pct graphite, and 11.1 Wt pct aluminum. A systematic variation in range of impurity levels was obtained by using four magnesia sinters that were 96, 97, 98, and 99 wt pct magnesia. Impurities present in the magnesia sinters are al2o3, b2o3, cao, fe2o3, and sio2. Impurities in the graphite are sio2, al2o3, and fe2o3.