Why the zirconium corundum brick manufactured in a reducing atmosphere has poor corrosion resistance

The contact between the glass phase of the fused zirconia corundum brick and the high temperature molten glass will generate a high viscosity layer, which is the key to the good corrosion performance of the zirconia corundum brick. This requires a high softening temperature of the glass phase, so in addition to Al2O3, ZrO2, SiO2, and Na2O, the other components in the brick are less. However, due to the use of graphite lining bricks and graphite electrodes when melting in an electric furnace, a reducing atmosphere will be generated. C and CO will reduce part of Fe203, TiO2, and SiO2 in the melt into low-priced oxides, which makes the component components increase. According to the basic principle of phase ratio, this will reduce the liquid limit temperature. When such a brick is used at high temperature, the viscosity of the glass phase is greatly reduced, and a high-viscosity protective layer cannot be formed. The low viscosity of the glass phase makes it easy to diffuse into the high-temperature glass liquid, so the crystal phase in the brick loses the binder. It will fall into the molten glass, which will cause streaks and stones in the molten glass. The fused zirconia corundum brick produced by the oxidation method does not use graphite lining bricks. Although the electrode uses graphite, it is melted by the long arc method, so that C is combined 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, the zirconium corundum brick manufactured by the reduction method will also generate 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 reducibility. When they come into contact with the molten glass, they will deprive the oxygen dissolved in the molten glass. This causes the gas soluble in the glass to change its composition and becomes a gas that is not easily soluble in the glass liquid and becomes bubbles. For example, SO3 dissolved in glass liquid is reduced to SO2. SO2 has a low solubility in molten glass and thus becomes bubbles. This degrades the quality of the molten glass.