What changes will occur in the performance of insulation bricks when used in high temperature environments?
Release Time : 2025-09-25
The performance changes of insulation bricks in high-temperature environments involve multiple aspects, including physical structure, thermodynamic properties, and chemical stability. Key manifestations include thermal conductivity fluctuations, thermal shock resistance tests, high-temperature structural strength degradation, changes in volume stability, chemical stability challenges, and pore structure evolution. These interactions determine the applicability and lifespan of insulation bricks in high-temperature environments.
Thermal conductivity is a key metric for measuring the insulation performance of insulation bricks. In high-temperature environments, the thermal conductivity of insulation bricks can exhibit different trends depending on the material composition and microstructure. For example, insulation bricks containing crystalline phases may experience increased thermal conductivity due to enhanced lattice vibrations at high temperatures, while insulation bricks containing pores may experience reduced insulation effectiveness due to enhanced gas convection. However, closed and evenly distributed pores can suppress gas convection and maintain a low thermal conductivity.
Thermal shock resistance is directly related to the insulation bricks' resistance to cracking during sudden temperature changes. When insulation bricks cool rapidly from high temperatures, the different shrinkage rates between the surface and interior can easily lead to stress concentration. If a material's thermal expansion coefficient is too high or its tensile strength is insufficient, it can cause microcracks to propagate or even cause overall spalling. For example, hollow alumina sphere insulation bricks, through their hollow structure, can effectively buffer thermal stresses and improve thermal shock resistance.
High-temperature structural strength degradation is a core challenge facing insulation bricks exposed to long-term high temperatures. As temperature rises, atomic vibrations within the material intensify, weakening the bonding strength between grain boundaries and leading to a decrease in mechanical properties such as compressive and flexural strength. For example, clay lightweight bricks may lose their supportive properties at high temperatures due to softening of the glass phase. However, high-alumina poly lightweight bricks, due to their high aluminum content, maintain good high-temperature structural strength and are suitable for insulation layers in reducing atmosphere furnaces.
Volume stability changes manifest as the shrinkage or expansion of insulation bricks at high temperatures. This property is closely related to the firing temperature of the material. If the firing temperature is insufficient, unreacted raw materials may remain within the brick, causing further phase transformation at high temperatures and resulting in volume changes. If the firing temperature is too high, excessive liquid phase formation may cause excessive shrinkage. For example, mullite insulation bricks achieve a balance between volume change and strength gain within a specific firing temperature range.
Chemical stability challenges primarily arise from the interaction between the material and the surrounding medium at high temperatures. In acidic or alkaline atmospheres, components such as calcium and magnesium in insulation bricks may react chemically, leading to structural porosity or corrosion. For example, magnesia insulation bricks easily form magnesium sulfate in sulfur-containing environments, reducing their strength. Zirconia insulation bricks, on the other hand, are more suitable for alkaline corrosion due to their greater chemical inertness.
The evolution of pore structure has a dual impact on the performance of insulation bricks. On the one hand, well-distributed closed pores can reduce thermal conductivity; on the other hand, open pores can serve as infiltration channels for moisture or corrosive media, accelerating material degradation. For example, aerated concrete blocks, due to their high open porosity, require waterproofing before use in humid environments.
The performance changes of insulation bricks at high temperatures are the result of the combined effects of multiple factors. In practical applications, it is necessary to select insulation bricks with suitable thermal conductivity, good thermal shock resistance, stable high-temperature structural strength, excellent volume stability, strong chemical stability and reasonable pore structure according to specific working conditions, and achieve a balance between high-temperature performance and economy by optimizing the firing process and structural design.