During the glass melting process, refractory materials and glass liquid interact at high temperatures, causing refractory materials to be corroded and damaged, and even causing defects in glass liquid. In the tank furnace, the corrosive effect of the batch components on the refractory materials is much greater than that of the glass liquid. The corrosive effect of the mirabilite batch is stronger than that of the alkali batch. Usually, the corrosive effect of molten soda ash is limited to the vicinity of the feed port, while mirabilite can corrode almost all tank walls. The glass liquid containing compounds such as boric acid, phosphoric acid, fluorine, chlorine, lead, and barium and high alkali content has a particularly strong corrosive effect on refractory materials. Although the kiln arch, breast wall, small furnace, and regenerator in the flame space of the tank kiln are not in direct contact with the glass liquid, they are also corroded to varying degrees by the batch dust and volatiles on the glass liquid surface.
The corrosive intensity of glass liquid on refractory materials mainly depends on the physical properties of the glass liquid such as viscosity and surface tension, and the chemical reaction during the erosion process has only a subordinate effect. Molten glass with low viscosity and low surface tension can easily infiltrate refractory materials, and it can penetrate into refractory materials along the capillary system on the surface of refractory materials. Glass with more alkali content has lower viscosity, and borosilicate glass has lower surface tension, so they will corrode refractory materials strongly.
During the heating process of the batch, fusible polyacid compounds begin to form and flow on the surface of the glass liquid. Then, these melts gradually dissolve with the more refractory components, so the refractory materials in the melting zone of the tank furnace are corroded by polyalkali silicates. Especially when melting the glass of the Glauber's salt batch, the molten nitrate water floating on the surface of the glass liquid directly reacts with the refractory materials. Sodium sulfate melts at 885℃ and participates in the glass formation reaction until the reaction is complete at about 1440℃. Nitrate water, alkali solution and polyalkali silicates are easily absorbed into the capillary pores on the surface of the refractory materials, causing the refractory materials to be strongly corroded.
When the refractory materials for tank furnaces are subjected to physical and chemical erosion, the erosion rate is a function of temperature. The erosion rate increases logarithmically with increasing temperature.
Raising the melting temperature reduces the viscosity of the molten glass, which accelerates the erosion of the refractory material, thus greatly shortening the service life of the refractory material. In a pool kiln, every increase in the melting temperature by 50-60°C will shorten the life of the refractory material by about 1/2. In a crucible kiln, as long as the melting temperature increases by 20-40°C, the service life of the crucible will be shortened by 1/2.
The resistance of refractory materials to physical and chemical erosion is mainly determined by the type of its constituent phases and their distribution and bonding state. Generally, refractory materials are composed of one or more crystalline phases, glass phases and gas phases (pores). The chemical stability of the glass phase is poorer than that of the crystal, and the pores are channels (especially open pores) for the corrosive agent to penetrate into the refractory material. The depth of the glass liquid or the components of the batch material penetrating into the pores of the refractory material is proportional to the fourth power of the pore diameter. The corrosive agent first acts on the glass phase in the refractory material and reacts with each other. After the solution penetrates into the refractory and dissolves the glass phase, the crystals in the refractory will be eroded by the glass flow, and new parts that continue to be eroded may continue to appear. Most of the pores and glass phases exist in the combination of sintered refractory materials, so the combination becomes the weak link of the refractory material's resistance to physical and chemical erosion.
The greater the viscosity of the melt formed by the erosion of the refractory material, the denser the material, the fewer open pores, and the less erosion it will suffer. As the viscosity of the glass liquid increases due to the dissolution of the refractory material, a protective film that rarely moves can be formed on the surface of the refractory material, thereby reducing the erosion.
In order to obtain a refractory material with good erosion resistance, in addition to having a stable crystal phase, a high softening temperature, a high melt viscosity, a small glass phase and a low porosity, it is also required that the crystal phase has a small crystal form and is evenly distributed in the glass phase, with a uniform structure and a tight combination, so that the glass phase can be enhanced.
The uneven surface of the refractory material, gaps and cracks will deepen the erosion, especially the transverse joints. The denser the masonry and the finer the gaps, the less erosion the glass liquid has on the pool wall bricks.
The convection of glass liquid and the instability of the glass liquid surface can aggravate the erosion of refractory materials. This is mainly because the liquid flow will accelerate the physical and chemical interaction between the glass liquid and the refractory material. However, the friction between the glass liquid and the refractory material is very small, so the mechanical wear effect is relatively light.
During the erosion process, the refractory material is dissolved and a thin film is formed on the surface. When it is washed by the glass liquid flow, the protective film that was rarely active moves, exposing the new surface part of the refractory material, which provides favorable conditions for further erosion. When clay pool wall bricks are eroded by sodium-calcium silicate glass, the damage to the glass surface is much faster than that not too deep below the liquid surface, and deep grooves are easily formed.
The fluctuation of the glass liquid surface will strengthen the scouring effect on the damaged refractory layer. When the glass liquid level drops, the softened film can no longer remain on the inner surface of the refractory material, and when the glass liquid level rises again, the peeled film cannot return to its original position and is carried away by the liquid flow. A new layer of refractory material is exposed again, and is further eroded by the rising glass liquid again, which accelerates its destruction. Sometimes, the high-viscosity glass liquid layer generated by the dissolution of the refractory material is peeled off, and there is no time to diffuse and homogenize, which will cause streaks in the glass.
Due to the temperature difference of the glass liquid, the glass liquid flow near the pool wall moves downward, and the erosion and dissolution of the refractory material of the pool wall will change the density of the glass liquid, which will affect the speed of the liquid flow near the pool wall and strengthen the erosion. Ventilation and cooling of the pool wall can help reduce erosion, but it is only possible when the thickness of the pool wall bricks is not large. Sometimes, the convection circulation of the glass liquid at the pool wall can also be enhanced, which will in turn strengthen the erosion of the refractory material.
Temperature fluctuations in the pool kiln will cause the destruction of the balance of the refractory-glass liquid system. For example, when the temperature rises, the viscosity of the protective film covering the surface of the pool wall bricks decreases, and it is easy to be washed away by the glass liquid flow, which will also accelerate its erosion and damage.
Modern pool kilns mostly use auxiliary electric melting and bubbling clarification processes to increase the melting rate. However, it also strengthens the convection of the glass liquid and increases the temperature of the deep glass liquid, which also strengthens the erosion of the refractory materials.
When adding batch materials to the pool kiln, the material powder is easily carried away by the gas flowing in the kiln. The dust contains a lot of alkali, which often deposits on the upper surface of the pool wall bricks to form glaze and flow down along the surface of the bricks, forming deep grooves on the brick surface, and even falling in drops into the glass liquid, causing the glass liquid to have defects such as stripes.
The upper structure of the pool kiln is often eroded by batch dust and volatiles. However, the dust reacts chemically with the refractory material, and its products are mostly left on the surface of the refractory material to form a thin film, which has a protective effect and can prevent the batch dust from further eroding the refractory material.
The volatiles of batch and glass liquid also chemically erode the refractory materials. The volatile components are mainly alkali metal oxides and boron compounds, as well as fluorides, chlorides and sulfides. These volatiles react chemically with the refractory materials in the gas phase and penetrate into the pores or gaps of the refractory materials. They condense into liquid phase in the lower temperature parts and react chemically with the refractory materials. The condensed liquid of these compounds erode the refractory materials more strongly. They penetrate deeply into the pores of the refractory materials through infiltration and diffusion, especially when there are cracks and gaps in the upper structure, which will cause great damage to the refractory materials.
Batch dust and volatiles erode the refractory materials together under most clear conditions. The farther away from the feed port, the less batch dust there is, while the upper structure of the working pool and the feed trough is only eroded by the volatiles of the glass liquid.
The atmosphere in the kiln also affects the erosion of refractory materials. For example, when working in a reducing atmosphere or using generator gas, CO and H2 in the gas will reduce the iron oxide in the bricks, thereby accelerating the erosion of the refractory materials.
The dust of the batch material, the volatiles of the glass liquid and their condensates, as well as the atmosphere in the kiln, also play a considerable destructive role in the refractory materials of the regenerator.
The replacement reaction between molten glass, powder and volatiles and refractory materials is mainly carried out by diffusion in the presence of a solid phase. Since molten glass has a large viscosity, it is usually difficult to reach equilibrium and the reaction rate is slow. During the alteration process, dissolution, recrystallization and the formation of new phases occur. The erosion process of refractory materials of different properties is not the same. The erosion process of various refractory materials is mainly related to the type of corrosive, the chemical reaction rate, the concentration of the reaction products, the structure and temperature of the bricks, the action time, and the physical and chemical erosion conditions.