1. Fused zirconium corundum bricks manufactured under reducing atmosphere have poor corrosion resistance
When the glass phase of fused zirconium corundum bricks contacts the high-temperature glass liquid, a high viscosity layer will be generated, which is the key to the good corrosion resistance of zirconium corundum bricks. This requires a high softening temperature of the glass phase, so the bricks should have less components except Al2O3, ZrO2, SiO2, and Na2O. However, during melting in an electric furnace, a reducing atmosphere will be generated due to the use of graphite lining bricks and graphite electrodes. C and CO will reduce part of the Fe2O3, TiO2, and SiO2 in the melt to low-valent oxides, which increases the component elements. According to the basic principle of phase ratio, this will reduce the liquid phase limit temperature. When such bricks are used at high temperatures, the viscosity of the glass phase is greatly reduced, and the high-viscosity protective layer cannot be formed. The low viscosity of the glass phase makes it very easy to diffuse into the high-temperature glass liquid. Therefore, the crystal phase in the brick loses the binder and falls into the glass liquid, which causes streaks and stones in the glass liquid.
The fused cast AZS bricks produced by the oxidation method do not use graphite lining bricks. Although the electrodes still use graphite, they are melted by the long arc method, so that C combines with oxygen in the air in the arc to produce CO2 without entering the melt. The carbon content of bricks produced by this method is less than 0.005%, so the corrosion resistance is greatly increased.
At the same time, zirconium corundum bricks made by the reduction method will also produce bubbles in the glass. This is because the low-valent oxides and other substances such as C in the glass phase of the brick have strong reducing properties. When they come into contact with the glass liquid, they will seize the oxygen dissolved in the glass liquid. This changes the composition of the gas soluble in the glass and becomes a gas that is not easily soluble in the glass liquid and becomes bubbles. For example, SO3 dissolved in the glass liquid is reduced to SO2. SO2 has low solubility in molten glass and thus forms bubbles, which reduces the quality of the molten glass.
2. Irregular changes in thermal expansion
Fused cast AZS bricks are characterized by stable and dense organization and strong resistance to glass liquid erosion. There is abnormal expansion between 900 and 1200°C, which is caused by the transformation of ZrO2 monoclinic crystal to ZrO2 tetragonal crystal, which can be used as a reference for glass tank kiln baking and operation.
Due to the influence of other components in AZS bricks, the crystal transformation temperature fluctuates within ±50°C. Therefore, when used, the temperature change between 950 and 1150°C during heating and cooling should not be too large, generally not exceeding 15°C/h.
The abnormal expansion and contraction of zircon can be buffered by the glass phase to prevent cracks. In the late 1970s, 0.15% to 0.20% B2O3 was introduced into the composition, so that the glass phase contained in the AZS brick body not only has better thermal shock resistance, but also has a buffering effect on abnormal expansion. However, large temperature changes or repeated fluctuations within this temperature range will also cause cracks. Therefore, when heating the kiln, the temperature should be raised steadily within the range of 950-1150℃. When used in places where the temperature changes frequently (such as the charging port, etc.), other bricks should be used to protect the outside.
3. Electrical insulation
When using the full electric melting and electric boosting methods, the electrode bricks are required to have good electrical insulation at high temperatures. Zirconia corundum bricks have good electrical insulation, and the electrical insulation decreases with the increase of temperature. It can be seen that zirconium corundum bricks can be used as electrode bricks in the production of soda-lime glass tank furnace. However, when producing high borosilicate glass, AZS-41 bricks or zircon bricks should be used. Otherwise, not only will the power consumption be uncontrollable, but the bricks will also be melted, the electrodes will be damaged, and the glass liquid will be polluted.
4. Thermal conductivity
The thermal conductivity of zirconium corundum bricks is more than twice that of clay bricks. Therefore, when this type of tank wall brick is used, the cooling air volume required near the liquid surface should be twice that of clay bricks used as tank wall bricks. In order to achieve the effect of full cooling, the advantages of zirconium corundum bricks can be fully exerted.
5. The difference between AZS fused bricks and Al2O3 fused bricks
At high temperatures, the glass erosion resistance is as follows: AZS-41#>AZS-36#>AZS-33#>α-β-Al2O3, but the pollution resistance of AZS bricks is not as good as that of alumina electrocast bricks. This is because alumina electrocast bricks are very pure, and more than 90% of them are Al2O3. The viscosity of the nepheline metamorphic layer generated on the surface of the brick body in the glass liquid is not as high as that of the nepheline metamorphic layer containing ZrO2. It is easier to melt, so the corrosion resistance at high temperature is not as good as that of AZS fused bricks. However, because the difference between the viscosity of the impurities flowing into the glass liquid and the glass liquid is greater, it is more difficult to dissolve and eliminate, and the viscosity of the nepheline metamorphic layer of alumina bricks is small and easily soluble in the glass liquid, so the pollution to the glass liquid is small.
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