Clay refractory bricks are refractory products produced from refractory clay. It is widely used in industry. Clay bricks are divided into ordinary clay bricks, multi-cropped clay bricks, whole-cropped clay bricks and high-silice clay bricks.
(1) Chemical composition
Clay bricks vary greatly in chemical composition due to their different raw materials. Its main components are Al2O3 and SiO2.
(2) Crystal phase composition The clay brick crystal is mainly composed of mullite 3Al2O3·2SiO2 (Al2O371.8%, SiO228.2%) and SiO2. The SiO2 crystal is mainly composed of cristobalite and has a small amount of scaly quartz. The glass phase is mainly Al2O3, SiO2 and a small amount of other oxides. From the theoretical value of the phase diagram, it is calculated that when Al2O3 is 35%, mullite and SiO2 crystals each account for 50%. In fact, due to the presence of impurities such as Fe2O3 and R2O in the brick, the amount of mullite is less. this part
Al2O3, SiO2 and various other oxides make up the glass phase. The content of the glass phase is greatly affected by the type of raw material, chemical composition, and firing conditions. In general, when the content of SiO2, Fe2O3, and R2O is high, the glass phase is large.
(3) Properties and application of clay bricks Clay bricks have good thermal shock resistance and large fluctuation range, generally more than 10 times (1100 °C water cooling), which is not too large for the coefficient of linear expansion of clay products (the average coefficient of linear expansion between 201300 °C is 4.5×). 10-65.8×10-6/°C), and no polycrystalline transformation phenomenon and structure with obvious grain structure, so clay bricks are often used as big bricks at the bottom of the pool in glass furnaces.
Clay products are weakly acidic refractory products, and their acidity increases as the SiO2 content increases. It has a certain erosion resistance to acidity and a poor resistance to alkaline erosion. Therefore, clay products are suitable for use as refractory materials for acid furnaces. Large clay refractory bricks for glass kiln refer to clay refractory bricks with a weight of not less than 50kg for masonry glass kiln.
(4) Precautions for the use of clay bricks
1 different clay forming methods produced by different forming methods have different properties
In the clay bricks produced by various forming methods other than the high-pressure forming method, the content of the binder is relatively large, and thus the firing temperature cannot be too high. The brick has a low softening temperature, a large reburning shrinkage, and a high porosity. The structure of the clay brick produced by the mud casting method and the high pressure forming method is relatively uniform. However, the structure of the clay bricks produced by other molding methods is not uniform, and there are problems such as layered structure, directional cracking and internal cracks.
2 aggregates and combinations
Generally, the combination of refractory aggregates and conjugates has different erosion resistance. The aggregate is more resistant to erosion than the combination. When the difference in corrosion resistance between the two is large, the conjugate is first eroded, causing damage to the entire refractory material. However, in order to produce clay bricks with low porosity, a small amount of quartz and R2O are often added to the combination. The mechanical strength of such clay bricks is increased, but it also causes a decrease in the erosion resistance of the composite.
According to this feature, different clay bricks can be selected in different parts of the furnace due to different erosion conditions. The lower furnace strip and the lower lattice brick of the regenerator are less eroded by the dust and volatile matter of the batch material, the temperature is lower, and the load is heavy, mainly requiring high mechanical strength. Therefore, the binder in the brick may contain an appropriate amount of SiO2, Fe2O3, R2O. However, clay bricks used in high temperature parts mainly require high refractoriness, and the combination contains less impurities.