Erosion mechanism
Chemical action on fused zirconium corundum bricks is more complex and severe, which can be divided into 4 aspects:
1. Precipitation of glass phase
The azs bricks on the pool wall are subjected to the action of high-temperature glass liquid for a long time (>1500℃). On the one hand, the glass phase in the brick will gradually melt and precipitate (the lowest precipitation temperature is about 1150℃); on the other hand, the alkaline glass liquid containing Na2O will invade the brick along the pores and cracks of the brick body, diffuse and penetrate each other with the precipitated glass phase, thereby reducing the viscosity of the precipitated glass liquid and increasing its fluidity, thereby intensifying the corrosion behavior and extending it in depth.
2. Damage to the skeleton
As the erosion of the glass liquid intensifies in depth, the skeleton minerals constituting the brick body are gradually infiltrated and surrounded by the glass liquid containing Na2O, and the skeleton begins to be eroded. First, the dissolved mullite decomposes into α-Al2O3 and SiO2, which in turn promotes the conversion of α-Al2O3 into β-Al2O3. As the temperature rises, β-Al2O3 is completely dissolved in the glass liquid, and the baddeleyite and corundum lattices are also destroyed, and then broken, disintegrated, and partially melted. β-Al2O3 gradually dissolves in the glass at high temperature, and very little is retained. As the glass continues to diffuse and penetrate, the baddeleyite microcrystals become free, part of which is taken away with the glass liquid and may become glass stones, and part of which is retained. Although baddeleyite can be dissolved in glass, its solubility is very small. As the temperature fluctuates, ZrO2 quickly crystallizes from the glass liquid to form skeleton-like or beaded baddeleyite crystals.
3. Crystallization of new minerals
Since the skeleton minerals of fused zirconium corundum bricks body are partially melted in the glass liquid, the composition of the original glass liquid is changed. Therefore, when the ratio of SiO2-Al2O3-Na2O in the glass liquid is close to the theoretical composition of nepheline, a large amount of nepheline crystals will precipitate. Al2O3+2SiO2+Na2O→2NaAlSiO4(nepheline)
4. Nepheline damage
Since the density of nepheline is less than that of the brick body, the precipitation of nepheline crystals is accompanied by a large volume expansion, making the brick body structure loose. Although the melting of part of the crystalline phase in the brick at this time will increase the viscosity of the glass liquid and have a certain bonding and protective effect on the loose structure, it still cannot completely block the airflow, material and glass liquid scouring and gravity in the kiln, and cracks and peels into the glass liquid to form glass stones. The wound surface after peeling continues to be eroded and scoured by the glass liquid and continues to peel. The result will inevitably lead to the erosion and disintegration of the electric fused zirconium corundum brick.
Extend the service life in the glass electric melting furnace
The glass pool kiln melts horizontally, the material liquid level moves horizontally, and the three-phase interface is severely eroded except for the flow hole. The glass electric melting furnace is vertical melting, most of which is cold top melting. The glass liquid surface is covered by a layer of raw material, and there are fewer three-phase interfaces. Due to vertical melting, the erosion of the pool wall bricks is no longer concentrated on the three-phase interface, but the overall erosion, so the weak link of the electric fused corundum brick is the breakthrough point of erosion. In view of the erosion mechanism of electric fused zirconium corundum bricks, the content of Na2O in the raw material components of electric fused zirconia corundum bricks must be strictly controlled first. The national standard requires that the content of Na2O in 33#WS is less than 1.45%, and the content of Na2O in 41#WS is less than 1.3%. The electric melting furnace standard requires that the content of Na2O in 33WS is less than 1.35%, and the content of Na2O in 41#WS is less than 1.05%. For the erosion part of Figure 2, the ratio of riser to brick material must reach 1.5:1. Through the pressure of the riser material, the residual pores in the brick material are effectively reduced, the anti-erosion ability of the brick material at the injection port is enhanced, and the injection port is required to have no obvious shrinkage cavity residue.
For the eroded parts, the brick joints are strictly inspected during the assembly of fused zirconium corundum bricks, and are required to be less than 0.3mm. The expansion differences of various parts are strictly controlled during the kiln baking process to ensure the tightness of the brick joints during the process, thereby reducing gas entry, preventing the formation of a three-phase interface at the brick joints, and reducing the erosion of the parts in Figure 3. For the erosion of the parts in Figure 4, the width of the brick is required to be less than 400mm during the design process. Too wide will cause the bricks to have many shrinkage holes and loose inside; the ratio of the riser to the brick must reach 1.5:1, and the internal quality of the bricks can be improved through pressure and exhaust gas rate; the insulation is reduced in the later stage of kiln operation, and the erosion rate is reduced by lowering the temperature of the bricks.
