What key factors influence and limit the thermal conductivity of insulation bricks?
Release Time : 2025-12-15
The thermal conductivity of insulation bricks is a core indicator for evaluating their insulation performance, directly determining building energy consumption and the stability of the indoor thermal environment. Thermal conductivity is influenced by multiple factors, including material composition, microstructure, density, pore size, ambient temperature and humidity, and heat flow direction. These factors significantly affect the insulation effect of insulation bricks by altering the heat conduction path or the properties of the medium.
Material composition and microstructure are the intrinsic determinants of thermal conductivity. Insulation bricks made of different materials exhibit drastically different thermal conductivity due to differences in molecular vibration and electron transfer characteristics. For example, inorganic insulation bricks, such as aluminosilicate fiber bricks, rely on their amorphous structure to restrict molecular thermal motion, resulting in typically low thermal conductivity; while organic insulation bricks, such as polystyrene foam bricks, hinder heat conduction through their long molecular chain structure. In terms of microstructure, closed-cell insulation bricks, because the internal gas is trapped in independent micropores, effectively suppress convective heat transfer, resulting in a significantly lower thermal conductivity than open-cell materials. Furthermore, the fiber alignment also affects thermal conductivity; the thermal conductivity perpendicular to the fiber direction is generally lower than that parallel to it.
The influence of density and porosity characteristics on thermal conductivity follows a U-shaped curve. When the density of insulation bricks is too low, the solid-phase skeleton is discontinuous, and the large pores lead to enhanced convective heat transfer. As the density increases, solid-phase conduction paths gradually form, while the pores become smaller, reducing the influence of gas on heat conduction. However, when the density is too high, solid-phase conduction becomes dominant, and the thermal conductivity actually increases. Porosity is another key parameter; theoretically, higher porosity results in lower thermal conductivity, but in practical applications, pore size and distribution must be considered. If the pore diameter is too large, internal air convection may occur, increasing heat transfer. High-quality insulation bricks typically have pore diameters controlled within a certain range and uniformly distributed to maximize insulation performance.
Changes in ambient temperature significantly alter the thermal conductivity of insulation bricks. As temperature increases, the thermal motion of molecules within the material intensifies, increasing the proportion of radiative heat transfer and leading to an increase in thermal conductivity. Most insulation bricks experience a proportional increase in thermal conductivity with each increase in temperature. In high-temperature environments, some organic insulation bricks may soften or decompose, further deteriorating their insulation performance. Therefore, when used in high- or low-temperature environments, insulation brick materials with stronger temperature resistance should be selected.
Humidity has a more direct and significant impact on thermal conductivity. When insulation bricks absorb moisture, the water replaces the air in the pores. Since water has a much higher thermal conductivity than air, this causes a sharp increase in thermal conductivity. Studies show that for every increase in the moisture content of insulation bricks, the thermal conductivity can increase by several percentage points. In low-temperature environments, the moisture in the pores freezes, further increasing the thermal conductivity and causing even more severe performance degradation. Therefore, keeping insulation bricks dry is crucial for maintaining their insulation performance.
The direction of heat flow also significantly affects the thermal conductivity of insulation bricks. When the heat flow is parallel to the fiber direction, the insulation performance weakens; while when the heat flow is perpendicular to the fiber direction, the thermal insulation performance of the insulation material is optimal. This characteristic requires special attention during the laying and installation of insulation bricks. Optimizing the laying direction can further improve the overall thermal insulation effect of the insulation system.
Material aging and construction techniques also have a long-term impact on the thermal conductivity of insulation bricks. Physical aging, such as shrinkage, cracking, and settlement, alters the pore structure, while chemical aging, such as oxidation and decomposition, directly damages the molecular structure, leading to a gradual decrease in thermal conductivity. Construction quality is equally crucial. Defects such as loose joints, uneven insulation layer thickness, and thermal bridging in anchors can cause localized increases in thermal conductivity, significantly reducing overall thermal insulation performance. Therefore, in the application of insulation bricks, both material selection and construction quality control must be considered to achieve the best thermal insulation effect.