Low Porosity Clay Bricks for Glass Kilns

Low porosity clay bricks for glass kilns are clay bricks with low porosity. A small amount of quartz and R2O are often added to the binder. In this way, the mechanical strength of the clay brick is increased. But this also causes the corrosion resistance of the binder to decrease. Of course, low porosity will also compensate for the reduction in corrosion resistance caused by changes in the chemical composition of the binder.However, in general, the high temperature performance and corrosion resistance of this brick have decreased. Therefore, low porosity cannot be blindly pursued. Generally speaking, when the porosity of clay bricks is less than 10%, the amount of SiO2, R2O, and Fe2O3 contained in them is relatively high. If the porosity is controlled at about 20%, less of the above substances can be added. At this time, the high temperature performance and corrosion resistance of the brick are better.

 

Chemical composition

Due to the different raw materials, the chemical composition of clay bricks varies greatly. Its main components are SiO2 and Al2O3. The range of various components is as follows: SiO2 50~70%,

Al2O3 25~45%, Fe2O3 1.0←3.0%, TiO2 1.0~2.5%, R2O+RO 1.0~4.0%.

Crystal phase composition

The crystals of low-porosity clay bricks for glass kilns are mainly mullite 3Al2O3·2SiO2 (Al2O3 71.8%, SiO2 28.2%) and SiO2 crystals. SiO2 crystals are mainly cristobalite, with a small amount of tridymite. The glass phase is mainly SiO2, Al2O3 and a small amount of other oxides. Mullite and SiO2 crystals are very small and difficult to identify with an optical microscope. In particular, mullite crystals must be observed with X-ray analysis or electron microscopes. Therefore, it is difficult to determine the proportions of various crystal phases in bricks. It is calculated from the theoretical value of the phase diagram that when Al2O3 is 35%, mullite and SiO2 crystals each account for 50%. In fact, due to the presence of impurities such as Fe2O3·R2O in the brick, the amount of mullite generated is less. This part of Al2O3, SiO2 and other various oxides form a glass phase. The content of the glass phase is greatly affected by the type of raw materials, chemical composition, and firing conditions. In general, there is more glass phase when the content of SiO2, Fe2O3, and R2O is high.

The thermal expansion rate of low-porosity clay bricks for glass kilns is the smallest among commonly used refractory materials, except for semi-acidic clay bricks with high SiO2 content. Its expansion curve changes linearly without special parts. At the same time, due to the fine crystals and small and evenly distributed pores of clay bricks, stress can be buffered more easily. Therefore, low-porosity clay bricks for glass kilns have strong thermal shock resistance in a wide range. This is not very meaningful in glass tank furnaces. The tank furnace is in continuous production and the temperature changes very little. However, refractory accessories near the feeder, such as punches and bowls, require good thermal shock resistance, and clay bricks can fully play their role.

Low-porosity clay bricks for glass kilns have low porosity, large bulk density, high conductivity and good corrosion resistance. Clay bricks used in heat storage chambers are of this type.

The erosion of low-porosity clay bricks for glass kilns is mainly affected by the following two aspects. The first is the type of erosion and the chemical reaction rate. The second is the concentration of the reaction product. Of course, this is also related to the structure of the clay bricks and the temperature, time, physical and chemical erosion conditions. The following mainly studies the erosion of clay bricks from the perspective of the types of corrosive agents.

Glass molten metal erosion of clay bricks

When low-porosity clay bricks used in glass kilns are eroded by glass molten metal, a metamorphic layer will be generated. Various oxides react with clay bricks to different degrees. Analysis of the composition of the metamorphic layer found that it contained the most K2O, followed by Na2O and GaO, while BaO and B2O3 were the least. This metamorphic layer is grayish white and generally 0.5 to 3 mm thick. The main crystal phase in the metamorphic layer is mullite. Due to the long time at high temperature, the original needle-shaped mullite in the brick will grow in the glass phase. This mullite will be eroded by R2O and other factors to form feldspar. After further erosion, it will melt into the glass molten metal and become high-aluminum stripes or bumps.

This erosion is most intense at the glass molten surface. Not only is the temperature high here, but it is also at the junction of gas, liquid and solid phases, and it will be affected by sodium carbonate and mirabilite in the batch. Sometimes there is also nitrate water. Nitrate water has a very low viscosity and reacts with clay bricks to produce SiS₂. When this substance decomposes, it produces gas that will cause the deteriorated layer of the brick to foam, thereby accelerating erosion.

Erosion of clay bricks in the regenerator

The low-porosity clay bricks for glass kilns are eroded by the dust of the batch material in the regenerator to form a layer of glassy glaze. In addition to the glass phase, the glaze also contains complex twinned nepheline (Na2O·Al2O3·2SiO2), leucite (K2O·Al2O3·4SiO2), feldspar (K2O·Al2O3·6SiO2) and mullite (3Al2O3·2SiO2). This glaze layer will flow away at higher temperatures. The flowed material solidifies at the lower temperature of the lattice bricks, blocking the lattice holes, which will greatly reduce the efficiency of the regenerator.

The low-porosity clay bricks for glass kilns produced by our company are of many varieties and specifications, mainly three-low clay bricks, low-porosity clay bricks and other professional clay bricks, which can be widely used in thermal equipment such as glass kilns, blast furnaces, hot air furnaces, cement kilns, chemical kilns, etc.

Note: The indicators in the table are typical values of standard bricks.

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