Comparison Of Sintered Corundum And Fused Corundum

The sintered codundum has a high Al2O3 content, up to 99.5%-99.6%, and a low content of impurities. The organizational structure of sintered corundum is a dense polycrystalline sintered body and there is no glass phase, while fused corundum is composed of flat plate-like single crystals. Sintered corundum is composed of irregular polygonal crystals in microns, while fused corundum is composed of flaky and rod-like micron large crystals. 

Sintered corundum has better sintering behavior than fused corundum, because it is sintered at 1800 degree. The crystal size ranges from microns to larger.  A dense sintering between crystals is achieved. The most obvious difference between sintered corundum and fused corundum is the crystal size and pores. Most pores of fused codundum are large and open and the shape is not fixed. The porosity of sintered corundum is similar to that of fused corundum, but most pores are closed and distributed in the particles in spherical shapes or concentrated at the grain boundaries. During calcinating, sintering corundum has larger shrinkage than fused corundum. Since the shrinkage during calcinating is large, the shrinkage during firing is small, which ensures the accurate dimensions of products. Fused corundum products almost have no change after firing. They are difficult to sintere and difficult to generate the strength of the molded body. 

 

Sintered corundum has larger strength than fused corundum, since there is stiny unevenness on the surface of crystal particles. It is easy to conbine the binding agent as a whole. Since the crystals have no excessively growth and retain appropriate active, they are easy to combine densely various binding agents with high strength. The crystals of fused corundum grow from hundreds of microns to thousands of microns and have smooth surface and lack active, so they are difficult to form a strong combination with the binding agent. The mechanical strength of the sintered corundum is not only related to the crystalline size, but also the porosity. Since the sintered corundum has a large density and small pores, the strength is high. 

 

Based on the above reasons, the sintered corundum has high chemical stability, high melting and softening temperature, high thermal conductivity, excellent resistance to thermal shock resistance, strong corrosion resistance to molten metal and slag, excellent high temperature and low-temperature electrical insulation, stability under oxidizing and reducing atmosphere, high hardness and high wear resistance.