The importance of porosity to refractory castables

 The ratio of the volume of pores in a material to the total volume of the material can be divided into true porosity, closed porosity and apparent porosity. It is usually called apparent porosity in the refractory industry in my country. The pores in refractory materials can be roughly divided into three categories: closed pores, open pores, and through pores. Generally, the above three types of pores are combined into two types, namely, open pores (including through pores) and closed pores. The apparent porosity refers to the volume density of all open pores in the material, which is the ratio of the dry mass of the refractory material to its total volume (the sum of the volume of solid, open pores and closed pores), that is, the mass per unit volume of the material use g/cm3 or kg/m3 said.

The bulk density of dense shaped refractory products should be determined according to the national standard GB/T2997-2000. The bulk density of shaped heat-insulating refractory products shall be determined according to the national standard GB/T2998-2001. The bulk density of dense refractory castables should be measured according to YB/T5200-1993.

Porosity is the basic technical index of most refractory materials. It almost affects all properties of refractory products, especially strength, thermal conductivity, corrosion resistance, and thermal shock resistance. Generally speaking, the porosity increases, the strength decreases, the thermal conductivity decreases, and the corrosion resistance decreases. Refractory castable is an unshaped refractory made of granular and powdered refractory materials according to a certain composition, plus a certain amount of binder and water, and formed by stirring and vibration casting. It is widely used in metallurgy, glass, cement, petrochemical, High-temperature industries such as energy.

Refractory castables will inevitably produce pores in the dehydration and sintering stages of the molding and heat treatment process. According to statistics, in the dense refractory castable, the matrix accounts for 25% of the total volume of the castable, and the pores account for about 10% of the total volume of the matrix. It can be seen that the pores are an important part of the matrix microstructure. The pore structure parameters include a very rich content, such as porosity, pore shape and distribution, pore size and pore size distribution, pore volume, etc. They all determine the mechanical and thermal properties of refractory castables to a large extent.

Article Source：The importance of porosity to refractory castables
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