The research on thermal insulation materials is one of the key issues in the development of energy-saving technology. The research on its new material system, new preparation technology and performance improvement has become a research hotspot and frontier topic in the field of energy conservation and environmental protection. Insulating refractory materials refer to materials used in the thermal insulation layer of iron and steel metallurgy and other thermal furnaces. They have the characteristics of low thermal conductivity, high apparent porosity, and low bulk density, so they are also called lightweight refractory materials. The use of heat-insulating refractory materials in the insulation layer on the outside of the working lining can effectively reduce the heat loss of thermal kilns and make an important contribution to the goal of energy saving and emission reduction in industrial production. There are many types of thermal insulation refractory materials, which are mainly classified according to their chemical composition, service temperature, existing form and microstructure.
According to the different use temperature, heat insulation refractory materials can be divided into three categories:
(1) Low-temperature heat-insulating refractory materials, the service temperature is less than 600°C;
(2) Medium-temperature heat-insulating refractory materials, the service temperature is 600-1200°C;
(3) High-temperature heat-insulating refractory materials, the service temperature is greater than 1200°C.
According to the composition of chemical minerals, there are high-alumina heat-insulating refractory materials, silicon-based heat-insulating refractory materials, and mullite heat-insulating refractory materials.
According to the shape of the product, it is divided into powdery, shaped, fibrous heat-insulating refractory materials and composite heat-insulating refractory materials.
According to the different structural characteristics, it can be divided into three types:
(1) Gas phase continuous structure type or open pore structure type;
(2) Solid phase continuous structure type or closed pore structure type;
(3) The mixed structure type in which both the solid phase and the gas phase are continuous phases.
The main purpose of preparing lightweight heat-insulating refractories is to increase the porosity and try to form small-diameter closed pores inside the material, which reduces the quality of the material and also achieves the effect of heat insulation. How to introduce pores into materials is the key technology for preparing thermal insulation materials. Common methods for preparing thermal insulation materials include foaming method, chemical reaction method, burn-off addition method and porous material method.
(1) Foaming method: Add foam enhancer and stabilizer to the mixed raw materials to prepare heat-insulating refractory materials with high porosity. This method is suitable for pouring heat-insulating refractory materials. The preparation method is simple and low cost. Low, the disadvantage is that the pore distribution and size of the preparation are difficult to control.
(2) Chemical reaction method: The reaction between the components in the raw material is used to generate bubbles. The gas can exist stably and form pores in the product to achieve the purpose of creating pores. This method is only suitable for materials with good slurry fluidity and specific reactions.
(3) Burnout method: Add combustible substances into the formula, and burn out the combustible substances during sintering to leave pores. This method is currently the main method for preparing heat-insulating refractory materials. The main advantage is that the preparation process is simple and controllable, and the pore-forming agent is economical and affordable, such as polyethylene balls or sawdust. The pores left are not uniform, causing structural defects.
(4) Porous material method: The natural or artificial porous aggregate is used as a raw material and directly introduced into the pores. The raw material cost of this method is high, and it is often used to prepare high-grade heat-insulating refractory materials such as zirconia and alumina.