In the production process of lightweight refractory materials, the following six raw materials are often used as refractory aggregates. Their performance characteristics are as follows:
01 hollow ball
1. Alumina, zirconia hollow balls
Alumina hollow balls are made of industrial alumina and blown by high-temperature electrofusion. Its main crystal phase is α-Al2O3, its chemical composition is α-Al2O3 greater than 98.5%, and SiO2 and Fe2O3 are less than 0.5% respectively. Hollow ball particles are white, hollow, thin-walled spheroids. The natural grading is generally 5~3mm7%~10%, 3~2mm10%~17%, 2~1mm22%~32%, 1~0.5mm26%~36 %, 0.5~0.2mm15%~28%, the corresponding bulk density is 540~600kg/m3, 600~650kg/m3, 650~750kg/m3, 750~850kg/m3 and 850~950kg/m3. The long-term use temperature of this ball is 1800℃.
Zirconia hollow balls are made of zirconia by high-temperature electric melting and blowing. Its main crystal phase is cubic ZrO2, with a content of ≥80%; its chemical composition is ZrO2+CaO≥99%. The particle size of hollow spheres is 0.2~5mm, the bulk density is 1500~2500kg/m3, and the maximum operating temperature is 2200℃.
2. Floating beads
Floating beads are aluminum silicate glass beads floated from fly ash in thermal power plants. They are gray-white, thin-walled, hollow, and have a closed and smooth surface. The performance of floating beads also varies greatly due to different coal quality, combustion conditions and other conditions. Suitable for floating beads of refractory materials, the chemical composition is AI2O3 30%~43%, SiO2 50%~61%, Fe2O3 1.1%~3.8%, CaO 0.5%~1.8%, MgO 0.2%~1.3%, R2O 0.4%~ 1.6%, burning loss 0.2%~1.5%. Refractory degree ≥1610℃. The particle size of floating beads is <200μm, and the bulk density is 0.3~0.4g/cm3. It is characterized by light body, strong shell and low thermal conductivity. It is a good raw material for lightweight refractory materials.
02porous clinker
Porous clinker is made by processing and calcining hard clay ore or bauxite ore. First, the ore is ground and the burnt waste and binding agent are added to form balls on the balling disk; secondly, the balls with a certain strength are loaded into the kiln and calcined at 1350~1460°C to obtain porous clinker. The material is divided into two types: clay-based and high-aluminum. Both are used as refractory aggregates and can be used directly or after crushing and grading.
Chemical composition of clay porous aggregate: Al2O3 40-~42%, SiO2 50-~52%, Fe2O3 32.1%%2.7%, RO 1.0%~1.7%, R2O 0.5%~1.1%, loss on ignition 0.3%~0.6 %. The loose bulk density is 0.55~0.85g/m3, the particle bulk density is 1.1~1.6g/m3, the cylinder pressure strength is ≥6MPa, the water absorption is 10%~20%, and the refractoriness is greater than 1670℃; the chemical composition of high-aluminum porous aggregate is Al2O3≥ 55%, SiO2 35%~40%, Fe2O3≤2.5%. The loose bulk density is 0.9~1.2g/cm3, and the refractoriness is greater than 1690℃.
03Porous mullite
Porous mullite is made from natural raw materials fired at high temperatures. Most of its crystalline phase is mullite and the crystals are well developed. Its needle-shaped crystals intersect with each other to form a network structure, which becomes porous mullite. The cylinder pressure strength is 2~3MPa.
04ceramsite
Ceramsite is a spherical porous particle made by calcining fusible clay, shale, fly ash, coal gangue and other raw materials. Its surface is rough and hard, similar to ceramics, and its interior is honeycomb-shaped with no interconnections. of tiny pores. Ceramsite is characterized by small bulk density, low thermal conductivity and high strength. It is an excellent artificial lightweight aggregate with a wide range of applications. It is mainly used as refractory aggregate in amorphous refractory materials.
Ceramsite varieties are divided into clay ceramsite, shale ceramsite, fly ash ceramsite and gangue ceramsite. According to its particle shape and size, it is divided into two types: coarse ceramsite (particle diameter greater than 10mm) and ceramsite sand (particle diameter equal to or less than 10mm). Its loose bulk density is not more than 1000kg/m3 and 1200kg/rn3 respectively. The cylinder compressive strength should be Greater than 1.4MPa.
Among amorphous refractory materials, shale ceramsite is preferred. Its chemical composition: α-Al2O3 19%~22%, SiO2 58%~62%, Fe2O3 7%~8%, SO3 0.2%~0.4%, loss on ignition 0.8%~1.2%. The cylinder compressive strength is 2.5MPa, the solidity (weight loss rate) is 1.7%, and the refractoriness is 1290°C. The raw shale ceramsite sand particles are divided into 10~5mm, 5~3mm, 3~1.2mm and 1.2~0.3mm, and their loose bulk density is correspondingly 400kg/m3, 440kg/m3, 480kg/m3 and 540kg/m3.
05expanded perlite
Expanded perlite is produced by calcining perlite. It is white, porous particles, with a smooth surface, thin walls, and a honeycomb structure inside. Therefore, the bulk density of expanded perlite is small, generally 40~550kg/m3; the thermal conductivity is low, 0.028~0.048W/(m·K at 200~500℃); the refractoriness is 1280~1360℃; it has both sound insulation and resistance Freezing performance. Its chemical composition is SiO2 72%~77%, α-Al2O3 10%~15%, Fe2O3 0.7%~1.2%, CaO 0.7%~1.8%, MgO 0.2%~0.5%, K20 3%~5%, Na20 3.0 %~4.2%, burning loss 0.2%~0.8%.
06 expanded vermiculite
Expanded vermiculite is made from calcined vermiculite. Its bulk density is 80~300kg/m3. When the calcination is not good and there are many impurities, the volume will be heavy. The particles are composed of extremely thin flakes, and the spaces between each flake are filled with air, so the thermal conductivity is low and the water absorption rate is high. Chemical composition of expanded vermiculite: Si0237.5%~43.5%, α-Al2O3 14.5%~18.9%, Fe2033.5%~23.4%, Mg011.1%~22.6%, Ca00.8%~2.8%, lost on combustion 3.4%~12.2%. The refractoriness is 1300~1370℃.
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