The Effect of Porosity on the Creep Rate of Refractory Materials

When a refractory material is subjected to a certain stress under its ultimate strength, especially at high temperature, it will have plastic deformation. Its deformation increases with the increasing of the load time. This can damage the material. This phenomenon is called creep. 

When the material has a high content of liquid phase, especially when glass phase works as the bonding phase, the creep is determined by the glass phase. When there is too much glass phase and its viscosity is low, viscous activities can happen even under a low stress, so, the creep can be severe at high temperature. When refractories contain a high content of impurities that can constitute the liquid at high temperature, liquid phase increases and its viscosity decreases with the drop of temperature, so creep is severe. 

 

The creep rate of a refractory material is the function of temperature, stress, time and material composition. The high the temperature is, the bigger the stress is, the longer the time is, and the bigger the creep rate is. When the material is entirely composed of crystals, the creep is affected by the vacancy dispersion, dislocation movement, grain boundary sliding and the bonding between the grains in addition to the strength of the bonds. When the defects of crystals and the grain boundaries are less and the bonding of the crystals are stronger, the creep is less likely to happen. 

 

The pores or cracks in the grains can directly cause the sliding of the grain boundaries. In addition, at high temperature, the liquid phase can penetrate into the pores of the solid phase, especially the small pores less than 25μm. So, pores can also affect the creep. 

 

Therefore, the pores of refractory materials have great impact on the creep rate.