The chemical composition of mullite sand has a significant influence on its refractoriness, which is mainly reflected in the following aspects:

I. Alumina (Al₂O₃) content

Alumina is one of the main components of mullite sand, and its content has an important influence on refractoriness. Generally speaking, the higher the alumina content, the higher the refractoriness of mullite sand. For example:

When the alumina content reaches more than 65%, the refractoriness of mullite sand can reach 1790℃.

When the alumina content is above 75%, the fire resistance can even exceed 1800℃.

II. Content of silicon dioxide (SiO₂)

Silica is another main component of mullite sand, and its content will also affect the fire resistance. The chemical composition of mullite sand is usually 3Al₂O₃·2SiO₂, that is, the ratio of alumina to silica has a direct influence on the refractoriness. Generally speaking, when the content of silica is between 45% and 55%, the refractoriness of mullite sand is higher.

III. Impurity content

Impurities such as iron oxide (Fe₂O₃), titanium oxide (TiO₂) and alkali metal oxides (such as Na₂O and ko) will reduce the refractoriness of mullite sand. For example:

When the content of iron oxide is between 1.0% and 1.2%, the refractoriness of mullite sand can reach 1770℃.

When the iron oxide content increases to 2.0% to 3.0%, the fire resistance will decrease to about 1700℃.

Increasing the content of alkali metal oxides (such as Na₂O and KO) will also significantly reduce the fire resistance.

IV. Influence of main crystal phase

The main crystal phase of mullite sand is mullite (3Al₂O₃·2SiO₂), which has a stable crystal structure and can provide high refractoriness. In addition, mullite sand may also contain a small amount of corundum (α-ALO), and the presence of corundum can further improve the fire resistance.

V. Influence of sintering process

Sintering temperature and sintering process also have significant effects on the refractoriness of mullite sand. High temperature sintering can improve the crystallinity of mullite sand, thus improving its fire resistance.

VI. Summary

The refractoriness of mullite sand is mainly determined by its chemical composition, especially the content of alumina and silica. High alumina content and low impurity content can significantly improve the refractoriness of mullite sand. In addition, the optimization of sintering process can further improve its fire resistance.