The stability of refractories at high temperature mainly depends on their unique physical and chemical characteristics, which enable them to maintain structural integrity and function in extreme high temperature environment. The following are the key factors to maintain the stability of refractories at high temperatures:

I. High melting point and high fire resistance

A basic characteristic of refractories is their high melting point. Melting point refers to the temperature at which a material changes from solid to liquid. Refractory materials are usually composed of inorganic compounds with high melting point, such as alumina (Al₂O₃, melting point about 2072℃), magnesia (MgO, melting point about 2800℃) and silica (SiO₂, melting point about 1713℃). These components endow refractories with the property of being solid at extremely high temperatures.

Refractory refers to the temperature at which materials do not soften or melt at high temperature. The fire resistance of refractory materials is usually higher than its actual use temperature to ensure that the structure will not collapse or deform in high temperature environment. For example, the refractoriness of high alumina brick can reach above 1750℃, and it can be used stably in iron and steel smelting furnace (working temperature is about 1500℃) for a long time.

II. Low thermal conductivity

The low thermal conductivity of refractories is another important factor to maintain their high temperature stability. Low thermal conductivity means that the material can effectively block the transfer of heat and reduce the diffusion of heat from high temperature area to low temperature area. Insulating brick is designed with this characteristic, and it usually contains a large number of pores or fiber structures, which can hinder the heat conduction.

For example, ceramic fiber products (such as ceramic fiber carpets and ceramic fiber board) have extremely low thermal conductivity (about 0.04-0.08 W/m k), which can effectively insulate heat in high temperature environment. This low thermal conductivity not only protects the structure of the equipment, but also reduces the waste of energy and improves the energy utilization efficiency.

III. Good chemical stability

In high temperature environment, refractories will come into contact with various chemicals, such as slag, molten metal, corrosive gas and so on. Therefore, refractories need to have good chemical stability to resist the corrosion of these chemicals.

Corrosion resistance: the chemical composition and microstructure of refractories determine their corrosion resistance. For example, high-alumina bricks contain a high proportion of alumina, which can resist the erosion of acidic and alkaline slag; Magnesium brick is mainly used in alkaline slag environment because it has good chemical stability to alkaline substances.

Oxidation resistance: In high temperature oxidation environment, refractories need to have oxidation resistance to prevent structural damage caused by surface oxidation of materials. For example, silicon carbide (SiC) refractories have excellent oxidation resistance and can be used stably in high temperature oxidation environment for a long time.

IV. High strength and thermal shock resistance

Refractory materials not only need to withstand high temperature in high temperature environment, but also may be affected by mechanical stress and thermal stress. Therefore, refractories need to have high strength and good thermal shock resistance.

High strength: the strength of refractory refers to its ability to resist external damage at high temperature. For example, refractory bricks need to have sufficient compressive strength and flexural strength to withstand the gravity of the furnace body and the pressure of slag. The compressive strength of high alumina brick can reach 100-200 MPa, which can meet the requirements of high temperature equipment such as iron and steel smelting furnace.

Thermal shock resistance: thermal shock resistance refers to the ability of materials to resist cracking when the temperature changes rapidly. Refractory materials may experience frequent temperature changes during use, such as furnace opening, furnace stopping or local temperature fluctuation. Good thermal shock resistance can prevent the material from cracking or peeling due to temperature change. For example, nano-composite refractories can significantly improve the thermal shock resistance of materials by introducing nano-particles into the microstructure.

V. Microstructure design

The microstructure of refractories plays an important role in its high temperature stability. By optimizing the microstructure of the material, its high temperature resistance can be significantly improved.

Dense structure: Dense microstructure can improve the corrosion resistance and strength of materials. For example, sintered corundum (α-ALO) has a highly dense crystal structure, and its refractoriness and corrosion resistance are excellent.

Porous structure: For thermal insulation refractory, porous structure can effectively reduce thermal conductivity. For example, insulating brick contains a large number of tiny air holes, which can hinder the heat conduction, reduce the weight of materials and facilitate construction and installation.

Composite structure: Composite refractories combine the advantages of various materials by combining different types of materials. For example, silicon carbide-alumina composites combine the high thermal conductivity of silicon carbide and the high fire resistance of alumina, and can show excellent performance in high temperature environment.

VI. Stability guarantee measures in practical application

In practical application, in addition to the characteristics of refractories, some measures need to be taken to further ensure their high temperature stability.

Reasonable construction technology: the construction quality of refractory directly affects its use effect. For example, the water-cement ratio and vibrating compactness of refractory castable need to be strictly controlled during construction to ensure the strength and uniformity of the material. After the construction is completed, proper curing and baking are needed to avoid thermal stress damage caused by moisture residue.

Protective coating: in some special circumstances, the corrosion resistance of refractory can be improved by coating protective coating on its surface. For example, in a iron and steel smelting furnace, the surface of the furnace lining can be coated with a slag resistant coating to prevent the slag from eroding the refractory.

Regular maintenance and inspection: During the operation of high-temperature equipment, it is essential to inspect and maintain the refractories regularly. By detecting the surface condition, thickness change and cracks of materials, potential problems can be found in time and repaired, which can prolong the service life of refractories and ensure the safe operation of equipment.

VII. Summary

The stability of refractories at high temperature is achieved through the joint action of many factors. High melting point and high fire resistance make it able to withstand extreme high temperature; Low thermal conductivity effectively blocks heat transfer; Good chemical stability enables it to resist chemical erosion; High strength and thermal shock resistance ensure its structural integrity under mechanical and thermal stress; The microstructure design further optimized the properties of the materials. In addition, reasonable construction technology, protective coating and regular maintenance also provide important guarantee for the high temperature stability of refractories. These characteristics enable refractories to play an important role in high-temperature industry and provide a solid foundation for the efficient operation of modern industry.