Lightweight refractory materials, as the main materials for the inner lining and insulation layer of high-temperature kilns and high-temperature equipment, compared with dense refractory materials, have the characteristics of low bulk density, low thermal conductivity and compressive strength, and high apparent porosity. They can effectively prevent heat flow from passing through the enclosure structure and outward, reducing the heat loss of kilns and other high-temperature equipment. Common lightweight refractory materials include: lightweight clay bricks, lightweight high alumina bricks, high alumina polycarbide bricks, mullite polycarbide bricks, lightweight silica bricks, and alumina polycarbide ball bricks. So, what are the characteristics of lightweight insulating firebricks? Please see below:

1. Low bulk density

Bulk density refers to the ratio of the dry weight of the product to its total volume. The bulk density of lightweight refractory materials is very small, generally between 0.6 and 1.2 g/cm³; while the bulk density of semi-lightweight materials is generally between 1.2 and 1.8 g/cm³. As one of the main factors for measuring lightweight materials, in the production of lightweight refractory materials, the bulk density of the material is generally reduced as much as possible while meeting the usage strength of the kiln or high-temperature equipment.

2. Low thermal conductivity

Thermal conductivity is one of the main factors for evaluating the insulation effect of refractory materials. Under the condition of ensuring the material's service strength, a lower thermal conductivity is beneficial for maintaining the heat flow in kilns or high-temperature equipment and reducing heat loss. Lightweight refractory materials have a significant heating effect and low thermal conductivity due to the presence of a large number of pores and the excellent insulation effect of the gas in the pores. Whether the pores inside the product are fine and uniform directly determines the thermal conductivity and service strength of the material. Generally, the smaller the pore diameter, the better the thermal insulation effect of the product. The thermal conductivity of lightweight refractory materials is relatively small, mostly less than 1.0 W/(k·m) (600℃×3h), while that of semi-lightweight refractory materials is generally less than 1.26 W/(k·m) (600℃×3h).

3. Low compressive strength

Due to the high apparent porosity and low bulk density of lightweight refractory materials, the crystals within their internal structure do not form effective and dense connections. Therefore, compared with dense refractory materials, their compressive strength is relatively low, and their wear resistance and erosion resistance are also poorer. In daily use, they are generally not used as the working layer but placed behind the working layer as an insulating layer. Therefore, on the basis of ensuring the required strength (for load-bearing purposes), the bulk density and thermal conductivity are usually reduced as much as possible.

4. High Apparent Porosity

The most intuitive indicator of lightweight insulating refractory materials is porosity. For lightweight insulating refractory materials, porosity mainly comes from added pore-forming agents, which form through foaming, burning off, or reacting. Generally, it can be divided into three types: (1) open pores; (2) closed pores; (3) connected pores. Among them, connected pores are the most harmful to the material, while closed pores have better insulating effects. For lightweight insulating refractory materials, apparent porosity refers to the ratio of the volume of all pores in the lightweight insulating refractory material to its total volume. Generally speaking, the apparent porosity of lightweight insulating refractory materials is greater than 45%, and when preparing lightweight materials with a volume density of about 0.5 g/cm³, the apparent porosity can even reach 80%.

5. Wide Application

Lightweight refractory materials are generally used as inner linings or insulation layers of industrial kilns and furnaces. Due to their low thermal conductivity, they can reduce the heat loss of brickwork in kilns and other equipment, save energy, and effectively improve production efficiency. However, due to their high apparent porosity, loose structure, low strength, and poor resistance to various erosions and wear resistance, they can only be used in inner linings, insulation layers, and other parts of high-temperature thermal equipment such as kilns, and are generally not suitable for working linings and areas with heavy loads.