Insultion bricks have many factors affecting their thermal insulation effect due to their complex structure and harsh working environment. And each factor influences each other and is interconnected, so it is difficult to analyze and study precisely. However, among the many influencing factors, the material composition and structure, porosity and characteristics of pores, bulk density, temperature of lightweight thermal insulation bricks are the main factors.
The chemical mineral composition and crystalline structure of the material is the primary factor affecting the thermal conductivity of lightweight thermal insulation bricks. Generally speaking, the more complex the crystalline structure of lightweight thermal insulation brick, the smaller its thermal conductivity. The solid phase of the material can be simply divided into crystalline and glass phases. When the atoms (ions) due to vibration and mutual collision of kinetic energy from the kinetic energy of the higher atoms (ions) to the lower kinetic energy of other atoms (ions), and the glass phase of the atoms (ions) for the disordered arrangement of the movement of the resistance than the orderly arrangement of the crystalline phase is higher. Therefore, the thermal conductivity of the glass phase is lower than that of the crystalline phase. However, when the temperature rises to a certain extent, the viscosity of the glass phase decreases, the resistance of the movement of atoms (ions) decreases, and the thermal conductivity of the glass phase increases. The crystalline phase is the opposite, when the temperature rises, the kinetic energy of the atoms (ions) increases, the vibration increases, resulting in the shortening of the free range, and the coefficient of thermal conductivity decreases. In the internal structure of lightweight insulation brick, the solid phase is separated by many pores of different sizes, the heat can not form a continuous solid-phase transfer, gas-phase heat transfer instead of most of the solid-phase heat transfer, so the thermal conductivity is very low.
The porosity of refractory materials is inversely proportional to the thermal conductivity, which rises linearly as the porosity increases. In this regard, lightweight insulation bricks are particularly outstanding. But for the same porosity, the smaller the size of the pores, the more uniform distribution, the smaller the thermal conductivity. When the pore size is small to a certain extent, the air inside the pore is completely adsorbed by the pore wall, so that the inside of the pore is close to the vacuum state, the thermal conductivity is reduced to low. And when the size of the pore increases to a certain extent, the heat radiation between the inner wall of the pore and the air inside the pore for convective heat transfer increases, the thermal conductivity increases. According to the relevant literature, small pores in the heat radiation is very small, when the pores are very large, especially along the direction of the jet long pores, can increase the effectiveness of heat radiation, and sometimes even with the pores of the products with the thermal conductivity of the products to be larger than the dense products of individual phenomena. The thermal conductivity of closed pores is lower than the thermal conductivity of open pores.
The thermal conductivity of lightweight insulation bricks and bulk density into a linear relationship, that is, the thermal conductivity increases with the increase in bulk density. The size of the bulk density directly reflects the internal porosity of the lightweight insulation brick how small. Bulk density is small, indicating that the products inside the pore space, the contact point between the solid particles is reduced, the solid-phase conductivity of heat is reduced, so that the coefficient of thermal conductivity decreases.
The thermal conductivity of lightweight thermal insulating bricks has a linear relationship with temperature, i.e., the thermal conductivity increases with the increase in temperature. However, compared with dense refractories, the thermal conductivity of lightweight thermal bricks with the increase in temperature is much smaller. This is due to the dense refractory materials are mainly solid-phase heat transfer, the temperature increases the thermal movement of the molecules within the product intensifies, increasing the thermal conductivity. In the lightweight thermal insulating bricks, most of its organizational structure for the gas-phase structure (65 to 78%), the temperature increases in the gas-phase thermal conductivity change is always smaller than the solid phase.
Temperature and humidity are also important factors affecting the performance of lightweight thermal insulation bricks. In a high temperature environment, the heat insulation brick is prone to deformation, cracking and other phenomena; in a low temperature environment, the strength of the heat insulation brick will decrease. Therefore, in the process of use, you need to choose the right type and thickness of heat-insulating bricks according to the actual situation. At the same time, the humidity will also affect the performance of the insulation brick, the humidity is too large will lead to increase the water absorption rate of the insulation brick, the strength of the decline; humidity is too small will lead to cracking of the insulation brick. Therefore, in the process of using, need to control the humidity.
The production process also has a great influence on the performance of lightweight heat-insulating bricks. In the production process, it is necessary to control the mixing ratio of materials, granularity, molding pressure, firing temperature and other parameters. If these parameters are not reasonable, it will lead to a decrease in the performance of the heat-insulating bricks. For example, if the mixing ratio is inappropriate, it will lead to a decrease in the strength of the material; if the molding pressure is insufficient, it will lead to low density and poor strength of the heat-insulating bricks; if the firing temperature is inappropriate, it will lead to the thermal conductivity and strength of the heat-insulating bricks do not meet the requirements.
Load is an important factor affecting the performance of lightweight thermal insulation bricks. In the use of the building process, the heat insulation brick will be subject to a variety of loads, such as gravity, wind, seismic force, etc.. If the load is too large or unevenly distributed, it will lead to cracking, deformation or even destruction of the thermal insulation brick. Therefore, in the design process, it is necessary to take into account the role of various loads, and select the appropriate type and thickness of heat-insulating bricks.
Lightweight heat-insulating bricks will also undergo aging phenomena in the process of use, such as surface chalking, cracking, peeling and so on. These phenomena will affect the performance and service life of the heat insulation brick. Therefore, in the process of use, measures need to be taken to prevent the occurrence of aging phenomena, such as regular maintenance, painting protection and so on.
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