Many users have doubts when consulting ceramic fiber products. Obviously it is a standard ceramic fiber module at 1260°C. Why is the use temperature only about 1100? Did you use degraded materials? While screaming injustice in my heart, the editor deeply felt the need to tell everyone about the knowledge about the temperature of ceramic fiber modules.
In the continuous flame atmosphere heating furnace lining, the domestically produced aluminum silicate fiber, its long-term use temperature can also be said to be a safe use temperature: 1050 ordinary type is 950 ℃; 1260 standard type is 1050 degrees; 1260 high The pure type is 1100℃; the 1400 high-aluminum type is 1200℃; the 1430 zirconium-containing type is about 1350℃; kilns greater than 1250℃ can use chromium-containing aluminum silicate products or polycrystalline alumina fibers.
This is because during the long-term heating process of aluminum silicate fiber, once it exceeds its own withstand temperature, crystallization will occur. Popularly speaking, the internal fiber is broken and crushed, causing the product to pulverize and lose the thermal insulation performance. Cause production losses and even cause hidden safety hazards.
What is crystallization?
The crystallization process is that the atoms in the metastable state of the glass phase are ordered and formed, forming a lattice structure with the smallest internal energy. Aluminum silicate fiber belongs to amorphous refractory fiber, no matter what kind of composition structure, there is crystallization in the heating process.
Aluminum silicate fiber is divided into 5 conventional models, namely ordinary type, standard type, high purity type, high aluminum type and zirconium. These models have different degrees of crystallization at 1100℃ for 500h. This crystallization is proportional to the heating time. The crystallization temperature of the aluminum silicate fiber is 1100 ℃ for a long time and about 1200 ℃ for a short time.
Crystal heating process
After the mullite crystals are precipitated in the heating process of aluminum silicate fiber, the amount of crystallization increases with the increase of temperature or the extension of time.
At the same time as the crystallization process, the first fine grains should be gradually grown, and some grain growth processes are also the process of shrinking or eliminating other grains. As a result, the average grain size has increased. This grain growth is not the mutual bonding of small grains, but the result of grain boundary movement. As the mullite grains continue to grow, the microstructure of the fiber shrinks further. The shrinkage of the microstructure will appear in the macro, and the diameter of the refractory fiber rod will be unevenly “reduced in diameter”. When the refractory fiber grains merge and grow each other When it is close to the diameter of the fiber rod, the reduced diameter here is enough to break or powder the fiber. This temperature is the limit temperature of the refractory fiber.
Different grades of aluminum silicate fiber heating crystallization
Ordinary refractory fiber, due to high impurity content and low A1203 content, etc., crystal grains grow faster at the beginning of crystallization. It is the lowest temperature of glassy refractory fiber. The impurity content of high-purity refractory fiber is less than 1%, the crystallization temperature lags behind that of ordinary refractory fiber, and the crystal grain growth is relatively slow. Therefore, the use temperature of high-purity refractory fiber is higher than that of ordinary aluminum silicate fiber High-some.
The crystallization temperature of the high-alumina refractory fiber lags behind that of the high-purity refractory fiber during heating, and the growth rate of grains is slower. Its long-term use temperature is slightly higher than that of the high-purity refractory fiber. Zirconium-containing refractory fiber (or chromium-containing fiber), the microstructure of ZrO2 is absorbed in the matrix of high-purity refractory fiber, its main role is to inhibit the refractory fiber during the heating process crystal growth and grain growth. However, at (1200℃, ZrO2 will gradually burn or evaporate slowly. With the extension of time, its inhibitory effect will become smaller and smaller, and the crystallization and grain growth will also accelerate. Finally, the use temperature is basically the same as that of high-aluminum refractory fiber the same.
When the equipment is put into production, it can better achieve the effect of energy saving and heat insulation, and ensure the service life of the equipment. The materials must be selected strictly in accordance with the temperature of use of the product. According to the working conditions and operating temperature of the equipment, plus a certain temperature range, then select the corresponding grade of aluminum silicate fiber products.
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