(1) Different content of glass phase
The content of brick glass phase in foreign countries is about 25%, while that in domestic brick only contains a small amount of glass phase. This difference is mainly caused by the different Al2O3 and R2O contents: Al2O3 in foreign bricks is 38% ~ 40%, R2O is 0.9% ~ 1.5%; Al2O3 content in domestic bricks is as high as 43% ~ 48%, while R2O content is lower than 0.85%.
(2) Apparent porosity
The apparent porosity of overseas machine pressed brick is as high as 20% ~ 23%, while that of domestic similar brick is generally less than 19%, mostly between 16% ~ 18%.
(3) Strain rate
Foreign brick has high strain rate. The main way to get high strain rate is to keep high porosity, so the apparent porosity of non vacuum pouring brick abroad is more than 20%. Vacuum pouring is a special technology. Although the apparent porosity of the bottom brick produced by this technology is low, the structure of the brick is even, and there are many closed pores. When loading, the internal stress concentration point is less, so the strain rate is very high. There is a big difference in this index between domestic bricks, the elasticity of bricks is poor, and they are easy to break or even float when they are used. Because the advantages and disadvantages of large expansion joint reserved at the bottom of the tank are not well understood in the domestic float industry, the method of large expansion joint has been used for safety, so that the bottom bricks do not squeeze each other at high temperature, so there is no special requirement for the strain rate index of the bottom bricks. In the future, if we learn from foreign experience and use small expansion joint in design, we must work hard to improve the strain rate index of domestic bricks.
(4) Anti nepheline peeling
The main difference between domestic and foreign brick in anti nepheling is the mechanism of anti nepheling. From the use effect, the domestic brick is no worse than the imported brick, and even better than the foreign brick.
Because the imported brick emphasizes high strain rate, more air holes must be introduced. The side effect of high porosity is poor impermeability. Na2O released from the glass band is easy to penetrate into the brick and react with the brick components to form nepheline. With the volume expansion of about 20%, the expansion shear force causes the reaction product to peel off and float up. In order to solve this problem, it is necessary to increase the content of glass phase in the brick. When the reaction product expands, the glass phase is squeezed into the air hole. On the one hand, it compensates the volume expansion of Xiashi petrochemical, on the other hand, it blocks the channel for Na2O to penetrate further, so that Xiashi Petrochemical can be limited within the extremely thin thickness range of the brick surface, so as to minimize the expansion shear force caused by the reaction and prevent the reaction from peeling and floating up.
The resistance of domestic bricks to nepheline is mainly due to the low porosity. Na2O is difficult to penetrate into the interior of the bricks, and only a thin layer of nepheline is formed on the surface of the bricks, which will not peel off and float up. However, if there are cracks, angle drop and other defects in the brick, the structure of the brick near the defect is generally loose, Na2O is easy to invade, and the nepheline layer is relatively thick. The phenomenon of arching, even curling and peeling can be observed.
