The ratio of the pore volume in the material to the total volume of the material is divided into true porosity, closed porosity and apparent porosity. Usually in the refractory industry in my country, porosity refers to apparent porosity. The pores in refractory materials can be roughly divided into three categories: closed pores, open pores, and through pores. Generally, the above-mentioned three types of pores are combined into two categories, namely open pores (including through pores) and closed pores. Apparent porosity refers to the bulk density of all open pores in the material, which is the ratio of the dry mass of the refractory to its total volume (the sum of the volume of solids, open pores and closed pores), that is, the mass per unit volume of the material, expressed in g/cm³ or It is expressed in kg/m³.
The bulk density of dense shaped refractory products shall be determined according to the national standard GB/T2997-2000. The bulk density of shaped heat-insulating refractory products should be in accordance with national standards
GB/T2998-2001 for determination. The bulk density of dense refractory castables shall be determined according to YB/T5200-1993.
Porosity is the basic technical index of most refractory materials, which affects almost all properties of refractory products, especially strength, thermal conductivity, erosion resistance, thermal shock resistance, etc. In general, porosity increases, strength decreases, thermal conductivity decreases, and erosion resistance decreases.
The porosity of refractory materials is affected by various factors such as all raw materials and process conditions. Generally speaking, selecting dense raw materials, adopting reasonable particle gradation according to the principle of the tightest packing, selecting appropriate binders, fully mixing the materials, high-pressure molding, increasing the firing temperature and prolonging the holding time are all conducive to reducing the porosity.
