The three most important indexes in choosing crucibles

1.Refracotriness Under Load

It means the highest possible temperature that the refractory material can hold before it deforms under load. This is an index that reflects both the material’s temperature resistance and its capability to bear the load, hence a very useful factor in choosing the refractory materials. The material’s mineral composition and microstructure will influence its refractories under load. Silicon crucible, which is comprised of crystal of quartzite and phosphorus quartz, has better performance on this parameter with an entertwined web structure and high viscosity, while magnesium crucible, which is mainly composed of magesite crystal, has flexible refractoriness, depending on adhesive substance.

2.Thermal Shock Resistance

It means the refractory material’s ability to withstand instant hot and cold. This is an index that will be influenced by a lot of factors including the material’s mechanical strength, thermal conductivity, density, coefficient of thermal expansion, modulus of elasticity, the size and thickness of the material, etc. The lower the coefficient of thermal expansion, the larger the thermal conductivity, the better the mechanical strength, the higher the modulus of elasticity, the better the material’s thermal shock resistance. Usually, adding spinel, graphite and zirconia to crucible materials will boost its thermal shock resistance.

3.Apparent Porosity

It means the porosity in the refractory material that can be filled with fluids. It is an index showing the percentage of porosity volume against the entire volume. For refractory material, the index can vary from 0% up to 80% but the average is 10% to 28%. To lower down the apparent porosity, it is very important to improve the density of the products. High-density clay crucible and graphite crucible have very good performance on this index.