High Refractoriness Lightweight Mullite Thermal Insulation Bricks

With the development of industrialization, major industrial enterprises have begun to pay attention to the efficient application of energy. If energy efficiency can be achieved in high-temperature kilns, it will save a lot of fuel costs for enterprises. Manufacturers of refractory materials that have been committed to serving the high-temperature industry are also looking for refractory products that are more energy-saving and heat-resistant. At present, common insulation material products are nothing more than ceramic fiber insulation blankets, lightweight mullite refractory insulation bricks, mullite poly light bricks, alumina hollow ball bricks, etc. For lightweight mullite insulation bricks, Rongsheng refractory brick manufacturers also have their own unique advantages.

mullite insulation brick
Mullite Bricks

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    Lightweight Mullite Insulation Brick

    Mullite refractory bricks are made of artificially synthesized mullite, according to the specific gravity of the product, adding organic composite fillers, vacuum extrusion molding, and high-temperature sintering to form lightweight mullite products. With its lightweight and excellent thermal insulation properties, mullite lightweight refractory bricks are widely used in the hot surface refractory lining or insulation layer of various thermal equipment, creating conditions for improving the energy utilization rate of the equipment.

    Mullite lightweight refractory brick is a high-alumina refractory material with mullite as the main crystal phase, and the general alumina content is between 65% and 75%. The refractory temperature of mullite lightweight refractory bricks can reach above 1790°C. The starting temperature of softening under load is 1600-1700°C. Good thermal shock resistance.

    What are the Mullite Refractory Bricks?

    Mullite lightweight brick

    Mullite lightweight bricks are divided into JM23, JM26, JM28, and JM30 according to the grade. According to different use temperatures, it is mainly divided into 1350 lightweight mullite bricks, 1450 mullite insulation bricks, 1550 mullite lightweight bricks, etc.

    mullite bricks
    Mullite Insulation Bricks

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      Lightweight Mullite Bricks Properties

      1. Low thermal conductivity. It has a good heat insulation effect.
      2. Low heat melting. Due to the low thermal conductivity, mullite series lightweight heat insulation bricks accumulate little heat energy, and the energy-saving effect is obvious in intermittent operation.
      3. Low impurity content. Has a very low content of oxides such as iron and alkali metals. Therefore, the refractoriness is high, and the higher aluminum content makes it maintain good performance under reducing atmosphere.
      4. High compressive strength in a hot state.
      5. The appearance and size are regular, which can speed up the masonry and reduce the amount of refractory mud used. The strength and stability of the masonry are guaranteed, thereby prolonging the life of the lining.
      6. It can be processed into special shapes. To reduce the number of bricks and joints.

      Mullite Bricks Usage

      Mullite lightweight insulation bricks can be used as the backing insulation layer of hot face refractory lining or other refractory materials. Used in ethylene cracking furnaces, tubular heating furnaces, ammonia conversion furnaces, and gas generators in the petroleum and chemical industries. High-temperature shuttle kiln, tunnel kiln, ceramic roller kiln, push plate kiln, and other industrial furnaces refractory furnace insulation materials, etc.

      RS Zircon Mullite Bricks
      RS Zircon Mullite Bricks

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        Zircon mullite bricks

        By introducing ZrO2 into A12O3-SiO2 series bricks to improve the structure of mullite, the chemical corrosion resistance, thermal shock resistance and expansion coefficient of mullite can be improved. This kind of mullite brick containing ZrO2 is commonly known as zirconium mullite brick. It is generally produced by the electric melting method, and it is also produced by the sintering method. Sintered zircon mullite bricks are made of industrial alumina and zircon concentrates as raw materials. A special refractory material is made by introducing zirconia into the mullite matrix through the reaction sintering process. The introduction of zirconia into mullite bricks can greatly improve the high-temperature mechanical properties of mullite materials by using the phase transformation toughening of zirconia. Zirconia can promote the sintering of mullite materials. The addition of ZrO2 can accelerate the densification and sintering process of ZTM materials due to the generation of low melting point substances and the formation of vacancies. When the mass fraction of ZrO2 is 30%, the relative theoretical density of the body fired at 1530°C reaches 98%, the strength reaches 378MPa, and the toughness reaches 4.3MPa·m1/2.

        Using industrial alumina and zircon as raw materials, the zircon mullite bricks made by reaction sintering are difficult to control the process because the reaction and sintering are carried out at the same time. Usually, when firing, heat preservation at 1450°C to make it densified. Then the temperature was raised to 1600°C for reaction. ZrSiO4 decomposes into ZrO2 and SiO2 when it is greater than 1535 ° C, and SiO2 and Al2O3 react to form mullite. Since a part of the liquid phase appears when ZrSiO4 is decomposed, and the decomposition of ZrSiO4 can refine the particles and increase the specific surface area, thereby promoting sintering. Studies have shown that when the amount of zircon added is less than 54.7%. With the increase of zircon content, the microstructure of the sintered sample gradually transitions from the network structure of columnar corundum to the network structure of columnar mullite. The high-temperature flexural strength (1400°C) of the sample also increases with the increase of zirconia content, and a large value appears when the zirconia content is 23.7%, and then the strength decreases. The addition of zircon contributes to the improvement of thermal shock resistance.

        Sintered mullite brick

        Sintered mullite bricks are made of aluminum and silicon oxides or other compounds and aluminosilicate minerals. According to the chemical ratio, the synthetic mullite is made from the mixture and sintered at a high temperature, and then crushed and shaped, dried, and sintered at a high temperature to form a refractory brick.

        In good-quality synthetic mullite, the mullite content should reach 95%, which controls the requirements for the chemical purity of raw materials. When the sintering conditions are constant, the higher the purity of the raw materials, the more difficult it is for the crystals to grow, and the smaller the size of the mullite crystals. When it contains 5% to 10% glass phase, mullite can develop into columnar euhedral crystals with a length of about 10 μm.

        Synthetic mullite contains about 90% mullite, and there are glass phases and pores between mullite crystal phases. When the content of the glass phase increases (such as 20%), the mullite crystals develop well, and the mullite is cemented by the glass phase.

        Fused Mullite Brick & Fused Cast Mullite Brick
        Fused Mullite Brick vs Fused Cast Mullite Brick

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          Fused mullite brick

          Mullite bricks prepared by the melting-solidification crystallization process are called fused mullite bricks. Columnar mullite crystals in bricks can reach a millimeter scale. By changing the processing system, the size of mullite crystals can be controlled to be smaller.

          The analysis shows that although the design Al2O3/SiO2 is 3:2, the ratio of Al2O3/SiO2 in the composition of fused mullite is often close to 2:1. This is because fused crystal bricks contain 10% to 15% of the glass phase. If the ingredient composition is higher than 3:2 or close to 2:1, the intercrystalline glass phase will be reduced to less than 5%. Therefore, the fused mullite brick made of a mixture containing about 72% Al2O3 always contains a lot of glass phases. At the same time, the phase composition is also related to the melting system and atmosphere.

          Corundum Mullite Brick
          Corundum Mullite Bricks

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            Corundum mullite brick

            Corundum mullite bricks are high alumina refractory bricks composed of corundum and mullite main crystal phases. Corundum mullite bricks refer to refractory bricks made of high-purity or relatively pure raw materials. The presence of low-melting-point oxide impurities will reduce its high-temperature performance. Corundum mullite bricks are much more expensive than ordinary high alumina bricks. Properties of corundum mullite bricks. It has good high-temperature strength, high-temperature creep resistance, thermal shock resistance, and corrosion resistance. The physical and chemical properties of a typical corundum mullite brick are: Al2O3≥85%, Fe2O3 0.45%, and apparent porosity 19%. The compressive strength at room temperature is greater than 55MPa, and the softening temperature under load is greater than 1700°C. Heating line change (1600°C, 3h) -0.1%. Thermal shock resistance (1100°C water cooling) is greater than 30 times.

            Lightweight Mullite Insulation Brick with High Refractoriness

            The maximum service temperature of common mullite insulation bricks rarely reaches 1500°C. JM30 lightweight mullite insulation brick is one of them. Another one is alumina hollow ball brick. However, due to the limitation of the production process of these two types of bricks, the output of these two types of refractory insulation bricks is generally not very high. The technical team and project leader of Rongsheng refractory manufacturer have passed many experiments and external technical exchanges. We are also constantly looking for new production technology for lightweight mullite insulation bricks and other refractory insulation products. Rongsheng refractory brick manufacturer provides a variety of refractory brick products for industrial kilns, contact us for free samples and price information.

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