The impurity is refers in refractory material different from the main component content rarely, and resistance to high temperature properties of the refractory material often brings about chemical composition harm.
Some impurities of refractories is fusible fabrics, some itself has very high melting point, but coexist with principal components, but can produce the fusible fabrics. Therefore, the presence of impurities often helps the melt of the strong role of the principal component. Fluxing action is sometimes helpful for material liquid phase sintering, but the serious harm of the material resistance to high temperature. Fluxing effect is strong, which is due to the presence of impurities, the system began to form in the low temperature liquid phase is the formation of liquid phase, or more, or with the increase of temperature of liquid phase of growth faster, better and more low wettability and the formation of liquid viscosity, the more serious the harm. Visible, if Na2O and SiO2 coexist, since the start of the liquid phase formation temperature is very low, refractory material so as to SiO2 as a main component, if it contains a small amount of Na2O, can bring the serious harm to the high temperature property. If SiO2, Al2O3 and TiO2 respectively containing refractory material as a main component, although SiO2 - Al2O3 and SiO2 - TiO2 two system co melting temperature close, respectively is 1595 degrees and 1550 degrees, but generated every 1% oxide impurity in the eutectic temperature within the system of quantity of liquid phase is the difference of the former is about the latter 1.9 times. Moreover, with the increase of temperature, the greater the difference, such as under 1600 degrees, about 2.3 times as much as. Therefore, the impurity Al2O3 is TiO2 flux effect on SiO2 strong. The high temperature properties of alumina to silica refractory material of great harm. In addition, when the impurity and principal component coexist, if the generated liquid with low viscosity, and the viscosity decreases with increasing temperature and faster and better wettability, is more serious harm to the refractory material.
Therefore, in order to improve the resistance to high temperature performance of refractory materials, must strictly control the content of impurities.
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