Development and application of alumina hollow ball firebrick for heat insulation products
With hollow alumina refractory ball and alumina powder as the raw material made of high purity alumina hollow brick has good heat insulation performance and high temperature resistant performance, using temperature up to 1800 ℃, alumina hollow ball is widely used in direct contact with high temperature melt not high temperature furnace lining, can also be used for high temperature furnace insulation materials.
Alumina hollow refractory ball
Brick, however, alumina bubble in the composition of corundum as aggregate and matrix phase, thermal expansion rate is bigger, lead to the poor thermal shock resistance of the product, greatly influence the service life of the alumina hollow brick, especially used in the temperature of the volatile environment prone to crack, flake, short service life, it is difficult to meet the requirements of the use of high temperature or ultra high temperature intermittent kiln.
Therefore, the mullite combined with alumina hollow ball firebrick below 1700 degrees Celsius and the alumina hollow ball brick with high thermal stability at 1800 degrees Celsius were developed to meet the requirements of high-temperature kilns under different conditions of use, which is in line with the national policy of energy conservation and emission reduction, and also conducive to the development direction of low-carbon economy.
Trial production of low temperature type (1700 ℃) high thermal shock stability thermal insulation products alumina hollow ball brick
Ordinary firebrick high purity alumina bubble because spherical alumina hollow ball aggregate particles, particles between points, could not form networks crisscross, mutually Mosaic structure of high strength and bonding force between particles is poorer, coupled with the ordinary alumina hollow ball matrix phase is corundum brick, lead to the poor thermal shock resistance of the product, the service life of refractory brick has greatly affected the alumina bubble. Through research and analysis on import alumina hollow ball firebrick in alumina hollow ball brick is introduced in the small expansion coefficient of the second phase mullite phase thermal shock stability, can effectively improve the products in the introduction of silica matrix, three stone and clay powder to replace part of sintering alumina powder, makes the mullite matrix petrochemical, mullite combined with the introduction of the phase can greatly improve the thermal shock resistance of alumina hollow brick, but as it reduces the noise introduced its highest use temperature.
Raw materials of alumina hollow ball has great influence on the high temperature performance of refractory brick, so in the light of the high purity raw materials, raw materials selection to minimize iron oxide, titanium dioxide content, such as mullite petrochemical test is to choose minerals containing silicon powder, alumina powder, and a moderate amount of mineralizer blend, join the pulp as a binder, alumina hollow brick manufacture alumina hollow ball as aggregate, mineral containing silicon and aluminum oxide powder mixed powder as the matrix, adding suitable amount of binder blended practice, after trapped material, on the pressure vibration molding machine molding 230 mm * 114 mm * 65 mm standard brick type alumina bubble. The bricks are dried and burned in a shuttle kiln at high temperature.
Test result can reflect, siliceous minerals increase ingredients, the zirconia mullite content in the hollow ball firebrick increase, thermal shock resistance of refractory brick with alumina bubble increase rapidly, but the content of mullite increases to more than 27%, alumina hollow ball no longer increases, the thermal shock resistance of refractory brick worse instead. Can be seen by SEM microstructure, 3 #, 4 # matrix of structure is similar, for porous network structure, the alumina hollow brick main crystal phase is well developed columnar mullite crystal, columnar mullite crystal form the continuous network skeleton, alumina hollow brick a small amount of glass phase between the columnar mullite crystal, residual traces of corundum phase in the matrix, the matrix good sintering, alumina mullite matrix in the hollow brick skeleton network contains more porosity is in the shape of a closed pores diameter of below 20 um, similar to tabular corundum grains in stomatal structure can reduce the thermal stress, It has a very good effect on improving the stability of thermal shock.
When a small amount of silicone-containing minerals is added, the thermal shock resistance stability of alumina hollow ball brick is not improved much. When a large amount is added, mullite is the main crystal phase in the hollow ball matrix, while corundum crystals are few. Mullite crystals are well developed and take on a columnar shape. The columnar mullite crystals form a continuous network structure, and the pores are isolated. The thermal shock resistance stability of alumina hollow ball bricks is greatly improved. When the amount of silicon-containing minerals continues to increase, although the mullite crystal in the matrix is well developed, it may be that the overburning of the matrix produces a large penetrating crack between the matrix and the hollow ball particles, which reduces the strength of the alumina hollow ball brick and the thermal shock stability. Therefore, the thermal shock stability of alumina hollow ball brick can be significantly improved by adding the right amount of silicone containing minerals.
