Aluminosilicate refractories can be classified according to the alumina content. While the principal mineralogical phases are mullite and corundum, a minor amount of glass phase in the grain boundary plays an important role in determining the refractory properties at elevated temperatures. The temperature withstanding properties of the aluminosilicate refractories largely depend on the alumina content of the system and accordingly the application areas are decided.

Hi Rajorshi,

In the SiO2-Al2O3 system there is a eutectic at approx. 8 wt% Al2O3 with a melting temperature of 1587°C. From this point towards 100% Al2O3 in the phase diagram the melting temperature rises. This means that from 8% Al2O3 every further increase in the Al2O3 content drives the melting point of the mixture up. In this sense, for a refractory, 25% Al2O3 (melting temperature approx. 1750°C) is better than 20% Al2O3 (melting temperature approx. 1720°C).

Hi dear Rajorshi,

actually the 25 wt% Al2O3 is better than 20 wt% one.

If you look at the phase diagram , you can see that 25% wt of composition has higher melting point. This fact says, the links of this ceramic structure is stronger than 20% wt . when a material has a strong structure , we can predict that the refraction of it can be higher. if you test this material in the mechanical properties lab with rebound method you can see this fact.

With Regard