Refractory bricks thermal conductivity
The thermal conductivity of fire bricks is represented by the thermal conductivity that has the ability to transfer heat. Thermal conductivity represents the amount of heat per in unit area, unit time and unit temperature gradient in the energy transfer process.
At 1000 ℃The thermal conductivity of various refractory bricks rate as shown below. The thermal conductivity of different materials is often very different. At normal temperature, the thermal conductivity of various refractory bricks can be from a few percent to several tens (w／(m℃), which is nearly a thousand times lowst than the highest value. As the temperature rises, although the difference between the thermal conductivity of various refractory bricks tends to decrease, but the difference is still large. Such as 1000 degrees centigrade, the thermal conductivity of lightweight silica is only about 0.35W, recrystallized silicon carbide products is about 17.5W／(m℃), graphite can be up to 35W / (m℃).
In addition to temperature, the thermal conductivity of refractory material bricks is closely related to its chemical composition and structure. When refractory bricks are made of crystal, the properties of crystal have obvious influence on thermal conductivity. As we all know, the thermal conductivity of inorganic nonmetallic materials is generally much lower than that of metal. Because inorganic nonmetallic materials are different from metals with metal bonds, there are very few free electrons. The thermal conductivity caused by free electrons in this material is extremely limited, and the lattice vibration is mainly deviated from the degree of resonance. The greater the degree of deviation from the resonance, the thermal conductivity is smaller. The degree of lattice vibration deviation increases with the difference in the molar mass of the constituent components, so the thermal conductivity of the element is the largest. (So the thermal conductivity of graphite is relatively large).
China refractory bricks have a complex structure of crystals, the thermal radiation of the lattice is greater and the thermal conductivity is smaller, such as MgO, A12O3 and MgAl2O4 Such as MgO, A12O3 and MgAl2O4 are equiaxed, but the structure of MgAl2O4 is complex and the thermal conductivity is low. Non-coherent crystals, in the direction of dense particles along the crystal, thermal conductivity is larger. The quartz along the C axis has a dense accumulation of particles, and its thermal conductivity (13.6W／(m℃)) is about twice as high as that of the C axis. The layered structure of graphite, the thermal conductivity parallel to the direction of the level of about 4 times in the direction perpendicular to plane direction.
If the crystal is defective, the formation of substitutional solid solution, because the rules of the crystal structure of the destruction caused by thermal scattering phenomenon, resulting in a decrease in thermal conductivity. Other crystal defects such as vacancies, dislocations and so on, also has a similar effect. Due to the thermal scattering of the grain boundary, the thermal conductivity of the polycrystalline material is lower than that of the single crystal. The refractory raw material of fine grain is lower than that of coarse grain. The material contains impurities, the thermal conductivity is lowered due to the scattering effect.
When refractory bricks contain glass phase, due to the amorphous structure of the disorder, the probability of collision between atoms. So compared with the crystal, thermal conductivity is low. When the refractory brick contains pores, because the thermal conductivity of the gas is smaller than the solid, so with the increase in porosity, the thermal conductivity of the material decreases. This is the basic reason for the low thermal conductivity of porous materials.
FAQ:
What is a refractory brick?
Refractory materials are those that can withstand high temperatures without the heat damaging their structure, resistance, or thermal conductivity. In the case of bricks, the chemical composition of refractories is different from that of regular bricks, which also influences their color and thermal conductivity.
What are refractory bricks generally used for?
A fire brick or refractory is a block of ceramic material used in lining furnaces, kilns, fireboxes, and fireplaces. A refractory brick is built primarily to withstand high temperature, but will also usually have a low thermal conductivity for greater energy efficiency.
What raw material is used for refractory bricks?
The oxides of aluminium (alumina), silicon (silica) and magnesium (magnesia) are the most important materials used in the manufacturing of refractories. Another oxide usually found in refractories is the oxide of calcium (lime). Fire clays are also widely used in the manufacture of refractories.
How many types of refractory bricks are there?
Basic refractory bricks are basic in nature. They have good corrosion resistance and chemical resistance. They consist of Magnesite bricks, dolomite bricks and Bauxite bricks. Magnesite bricks contain 85% of magnesium oxide and 3 to 5% of iron oxide.