Application of Silica Sol in Corundum Mullite Castables

July 18, 2022

    At present, the lining of furnaces such as heating furnaces, soaking furnaces, and ignition furnaces mostly use low-cement and high-alumina castables. Cement-bonded high-alumina castables generally require about 2 days of curing and demolding time and more than a week of oven time during construction. When the material is used, because the cement contains CaO, CaO will react with Al₂O₃ and SiO₂ in the material to form low melts such as mayenite at high temperature, resulting in a decrease in the softening temperature of the material under load and poor thermal shock resistance. The service life of the furnace lining.

 

     Because silica sol is a kind of nano-silica gel, it has strong specific surface area and adsorption, and ionization in water makes the colloidal particles have the same negative charge, resulting in repulsion between particles, which makes the use of silica sol as the binding agent. The castable of the agent has excellent flow properties. After heat treatment, the colloidal particles are combined with chemical bonds Si-O-Si to form a stable spatial network structure. At the same time, the silica sol covers the surface of the solid particles to form a firm silica gel film, thereby enhancing the bonding, curing and bonding strength of the material.

 

     Therefore, the castable with silica sol as binder has high bonding strength at medium and low temperature, which meets the requirements of industrial furnace lining construction; and at high temperature, a ceramic bond can be formed inside the material, that is, the highly active SiO₂ in the silica sol is very high. It is easy to react with Al₂O₃ in the raw material to form needle-like and columnar mullite in the matrix to produce high bonding strength. In addition, due to the staggered distribution of acicular and columnar mullite bodies, an interwoven network structure is formed, which can improve the strength, toughness and thermal shock resistance of the castable.

 

     The corundum-mullite castable combined with silica sol has been used in the heating furnaces of several large steel mills in China since the beginning of 2010, and has achieved better construction and application results than the previous use of pure aluminate cement combined castable. At the beginning of 2010, during the construction of a heating furnace in a factory, the temperature in the furnace was low, the thickness of the furnace wall was more than 300mm, and the thickness of the furnace roof was more than 400mm. The strength of the sol combined with the castable increases rapidly after construction. The mold is removed after only 12 hours of curing. The gas oven is implemented immediately after the mold is removed. The entire construction and baking process is reduced by half compared with the original time. The castable is used normally. At present, the heating furnace is still in use.

 

     The corundum mullite castable combined with silica sol is also used for the working lining of the permanent layer of the ladle. On a 300t ladle in a large steel plant, the service life of the silica sol combined corundum mullite castable exceeds 1500 furnaces, which is more than the original cement-bonded castable. Lifetime with 1000 furnaces increased by 50%. This is mainly a corundum mullite castable combined with silica sol, which has good physical properties and high temperature performance, and its service life will definitely exceed the current conventional cement-bound castable lining.

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