What Does the Porosity in Refractory Brick Indicators Refer To?

Porosity is an important indicator of refractory bricks. It is one of the reference indicators for thermal shock resistance, mechanical strength, volume stability, thermal conductivity, etc. Therefore, when choosing refractory bricks, we need to pay special attention to porosity.

1. What is Porosity?

Terminologically, porosity is also called "apparent porosity," which is the ratio of the volume of open pores in a refractory material to its total volume.

Lightweight Insulating Bricks of High Porosity

2. The Impact of Porosity on Refractory Materials

Porosity is inversely proportional to thermal shock resistance, mechanical strength, and volume stability. Higher porosity reduces strength, but increased porosity also reduces the thermal conductivity of refractory bricks, making them more suitable for insulation in high-temperature kilns.

Regarding thermal shock resistance, higher porosity in refractory bricks can lead to uneven internal thermal expansion at high temperatures, resulting in stress concentration and a tendency to crack or spall. Therefore, higher porosity makes refractory bricks less suitable for direct flame exposure.

Regarding mechanical strength, higher porosity in refractory bricks reduces their overall density, which directly affects their strength. Higher porosity reduces both the compressive and flexural strengths of refractory bricks.

Regarding corrosion resistance, higher porosity results in lower density. Porosity within the material easily allows slag, molten metal, and corrosive gases to penetrate the refractory bricks, which can significantly shorten the lifespan of the refractory bricks.

In terms of volume stability, excessive porosity can cause refractory bricks to expand or contract abnormally in high-temperature environments, affecting their structural stability.

In terms of thermal conductivity, while excessive porosity is detrimental to refractory bricks, it actually improves their insulation performance. Increased porosity reduces thermal conductivity, making them more suitable for insulation.

Dense Refractory Brick of Low Porosity

3. Application of Porosity in Refractory Bricks

Controlling porosity is crucial in refractory bricks. For refractory bricks used in critical areas and exposed to direct flames, such as high-alumina bricks, high-chrome bricks, silicon carbide bricks, and magnesia bricks, the lower the porosity, the better. This ensures the refractory bricks possess excellent corrosion resistance, strength, and dimensional stability, enabling them to withstand high temperatures, erosion, and thermal shock. However, for refractory bricks requiring thermal insulation, such as lightweight mullite bricks, lightweight clay bricks, and lightweight silica bricks, these bricks are generally not exposed to direct flames. They are typically used as the outermost layer of high-temperature kilns to provide insulation. This requires an increased porosity in the refractory bricks.

Porosity significantly impacts refractory bricks. In practical applications, the porosity and other performance parameters of the refractory bricks must be optimized, taking into account operating conditions such as operating temperature and the chemical properties of the medium, to fully realize their performance advantages and achieve optimal results.