Alteration of fused zirconium corundum bricks in glass kiln

Alteration of fused zirconium corundum bricks in glass kiln

Electro-fused cast zirconium corundum (AZS) bricks are mostly used in high-temperature parts of the kiln and in parts severely corroded by glass liquid. Different brick models are usually marked by the amount of ZrO2. The brick is mainly composed of two crystal phases of a-corundum, multiple pieces of stone, and a glass phase. Except for baddeleyite and a-corundum eutectic, the rest are free. The more ZrO2 there is in the brick, the more free baddeleyite there is. The corrosion resistance of these two crystal phases is very good, and the two crystal phases are closely integrated and have a uniform and dense structure, so they have stronger corrosion resistance. Since a small amount of Na2 is introduced into the brick, the mullite crystallization area is reduced, and the mullite crystal phase is difficult to precipitate, and a glass phase is formed to fill between the above crystal phases. This glass phase is eroded by high-temperature glass liquid to form albite glass with greater privacy, which has a higher viscosity due to a certain amount of ZrO2 dissolved in it. This layer of high-viscosity glass stays on the brick surface and is not easy to spread, thus protecting the brick body. If the crystals of the bricks are coarse and it is difficult to form a high-viscosity layer after being corroded, the glass liquid will easily penetrate into the bricks and erode the bricks faster.

The alteration process of zirconium corundum bricks begins with the interaction between the molten glass bricks and the original glass phase in the bricks, gradually diffusing and dissolving. After that, the a-corundum and clinoclinite in the brick slowly dissolved in sequence. The viscosity of the glass liquid near the brick surface increases, forming a protective layer against erosion. At the same time, the metasomatic reaction will produce a-corundum, nepheline, skeleton baddeleyite, etc. Usually, for bricks near the liquid level on the upper part of the pool wall, the glass liquid in the metamorphic layer has obviously penetrated into the brick body, but the corundum and baddeleyite eutectic are still connected by the remaining glass. The surface of the bricks at the lower part of the pool wall is composed of Q-corundum, clinoplastite residues and a turbid glass phase. Due to the reaction between the glass phase in the bricks and the glass liquid, a nepheline liquid phase is generated, which dissolves part of the haoyingite, forming a high Anvil degree metamorphic layer. When the temperature decreases, the dissolved ZrOZ will precipitate star-shaped or dendritic crystals, which is the secondary crystallization of Leteguite. In the high-privacy layer at the lower part of the pool wall, there are mostly secondary crystals of Gao Shi and nepheline crystals coexisting. With the prolongation of use time, these two crystal phases may be taken away by the glass liquid flow, and then gradually diffuse toward the glass liquid. The more difficult-to-melt brake stone may be partially dissolved and remain in the glass liquid as stones in the finished product.

In some cases, the pool wall bricks are not one piece for the entire depth of the pool, but are laid in layers, which results in horizontal joints. Erosion is prone to occur at horizontal joints. The corrosion conditions of electrofusion cast corundum bricks and sintered anvil bricks are different. The private soil bricks are basically subject to the same erosion above and below the horizontal joints, while the corundum bricks are seriously eroded above the horizontal joints and slightly eroded below the horizontal joints, as shown in Figure 1. This upward drilling-like erosion process has another problem: there is a gap in the horizontal seam of the pool wall, and the molten glass can easily take advantage of it. At this time, the bricks above the horizontal seam will be corroded by the glass liquid below to form high Anvil's protective layer. This protective layer tends to flow downward under the influence of gravity. Due to the loss of this high-privacy layer, the exposed new brick surface will be subject to new corrosion. At this time, there will be some bubbles at the upper end of the eroded layer, thus intensifying the erosion. As a result of this repeated action, the bricks above the horizontal joints are subject to strong upward drilling erosion. The protective layer of bricks with horizontal joints will not be lost; there are no air bubbles staying on the lower surface, so they will be less corroded. Now due to the increase in kiln temperature and the adoption of auxiliary electric fusion and bubbling technology, the erosion above the horizontal joints is more serious. Therefore, the design of the entire pool wall tile is often used.

Zirconium corundum bricks prepared in a reducing atmosphere have poor corrosion resistance. This is because the electric furnace uses graphite electrodes and graphite furnace linings to create a reducing atmosphere. C and CO will reduce part of FeZO3, TiO2, and SiO2 in the melt to low-priced oxides, increasing the components and softening the glass phase in the bricks. The temperature will drop by 100 to 150℃. When this kind of brick is used at high temperature, the viscosity of the glass phase is low and it is easier to diffuse into the high-temperature glass liquid, causing the crystal phase in the brick to lose its binding material and enter the glass liquid, forming stripes and stones.

Corundum bricks made in a reducing atmosphere will also produce bubbles in the glass. This is because the low-valent oxides and other reducing substances (such as C) in the glass phase in the brick have strong reducing properties. When they interact with the glass, they take away the oxygen dissolved in the glass and make the soluble gas in the glass liquid less soluble. And become bubbles. For example, SO3 dissolved in the glass liquid is reduced to SO2. The solubility of SO2 in the glass liquid is low, so it becomes bubbles and reduces the quality of the glass. Nowadays, the hydrogenation method is used to make zirconium corundum bricks, which can improve its performance and prevent the above defects.