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Physical and chemical properties of sillimanite brick and andalusite brick for glass kiln
Jan 02, 2019

The so-called sillimanite products are made by adding a certain proportion of sillimanite, andalusite or kyanite and other trace elements to the ingredients of high-aluminum bricks, so that the thermal shock resistance of the products is improved, especially for the products. The high temperature creep rate is reduced. Some people call this brick a low creep high alumina brick.

The sillimanite, andalusite and kyanite have the same heating phase transition behavior, and both decompose to form mullite and SiO2 phase, and the latter can form cristobalite or form a glass phase. The difference is that the volume expansion of sillimanite and andalusite into mullite is small; while kyanite is extremely large, the reaction is carried out as follows:

Since sillimanite and andalusite have only a small volume effect in the heated mullite process, they can be directly used for brick making. It can be burned or not. The Al2O3 content of sillimanite bricks is generally 50%~60%, and its significant advantages are high temperature volume stability, load softening point and thermal shock resistance are better than high alumina bricks. In modern large-scale melting furnaces, sillimanite bricks must be used to ensure the stability of the furnace structure.

Silica stones are typically fired below the temperature at which the sillimanite decomposes. In use, if the use temperature is slightly lower than the decomposition temperature of sillimanite, the volume stability of the brick is very good, there is no obvious volume effect; if it is higher than the decomposition temperature, the sillimanite is decomposed into mullite and liquid phase. A small volume expansion can offset the shrinkage caused by the liquid phase and maintain a relatively stable volume.

It is fired at a high temperature, that is, it is fired at a temperature higher than the decomposition temperature of sillimanite and andalusite, and a Moly petrochemical product can be obtained, and the volume expansion of the brick in the firing can be controlled, and a product having superior performance can be obtained. The results show that the sillimanite and andalusite are not pre-fired with mature materials, and the resulting brick has a better microstructure. This can be explained as: the calcined clinker, the formed mullite crystal network will be destroyed when pulverized, and it is impossible to form a mullite bonding network when further firing, which will reduce the compactness and high temperature of the product. performance.

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