Abstract

The refractoriness of a basic brick is primarily defined by its secondary interstitial phases. What matters in this respect is not only the absolute quantity of interstitial phases, but also particularly which type of phases they form. The most common by-elements in magnesia and magnesia products respectively are Ca, Si, Fe, as well as Al and Cr. Depending on the bulk chemical composition these elements form different types of interstitial phases. In general the temperature of formation of melting phases decreases with increasing number of elements. The effect of the different interstitial phases on the refractoriness of magnesia products is sufficiently described in literature. The target of the study described in the present paper was the improvement of the properties of magnesia products rich in alumina and iron oxide, especially at elevated temperature. In the course of a laboratory trial iron-rich magnesia bricks were produced and fired at different temperatures. With increasing firing temperature increasing values in refractoriness under load could be detected. The same effect was observed with iron-rich magnesia-spinel bricks. On the other hand these bricks showed an increasing firing shrinkage with increasing temperature, which can cause big problems in the production of refractory bricks. The target of the trials was to counteract this firing shrinkage whilst maintaining the high refractoriness of the bricks by incorporation of certain elements into the interstitial phases of the brick. The addition of phosphate has proven successful for a controlled modification of the interstitial phases in order to be able to produce iron-rich and alumina-rich bricks with improved refractoriness.