Characteristics of Silica Brick Used in Coke Oven
(1) The chemical composition of silica brick varies with different silica raw materials. In general, the content of SiO2 is 93%~98%, and other impurities, such as SiO2, Fe2O3 and CaO, are 2.0%~7.0%.
(2) The mineral composition of silica brick, the common silica brick is mainly squamous quartz, accounting for 30%~70%; The high silica and high density silica bricks mainly consist of square quartz, accounting for 20%~80%. Residual quartz and amorphous quartz glass are in small quantities in any silica brick.
The refractoriness of silica brick mainly depends on SiO2 content and impurity content and its properties. The higher the SiO2 content, the less the impurity content and the closer the refractoriness is to the melting point of SiO2; On the contrary, the lower the refractoriness, the refractoriness of silicon brick is generally 1690~1730℃.
(4) The softening temperature of silica brick under load is relatively high, about 1650℃, because the crystal network structure of scaly quartz plays a skeleton role in silica brick. Some impurities, though, have lower melting points. However, as the skeleton has a certain bearing capacity, its softening temperature under load is close to its refractoriness, which is a significant characteristic of silicon brick.
(5) Slag resistance of silica brick, the main chemical composition of silica brick is typical acid oxide SiO2, which determines that it has a strong resistance to acid slag. At the same time, Fe2O3, CaO and SiO2 can form new compounds, so the silica brick still has a certain resistance to the alkaline oxides Fe2O3 and CaO in the slag.
(6)The true density of silica brick reflects the degree of quartz transformation in silica brick, so that mineral composition can be judged. The smaller the true density, the better. The smaller the true density means that the quartz transformation is complete and the residual expansion generated in the actual use is small.
(7)The porosity of silica brick represents the density of silica brick. The smaller the porosity, the denser the structure. The apparent porosity of silica brick is generally 21%~25%. The size of porosity, in addition to raw materials mainly depends on its technological conditions.
(8)The residual expansion of silica brick refers to the irreversible volume expansion of silica brick after being calcined again, which is called residual expansion of silica brick. The reason is that there are still unconverted quartz or residual quartz in the silica brick to continue to transform. The smaller the residual expansion of silicon brick is, the better. Otherwise, when it is used in the kiln, it will cause the destruction of the kiln structure due to its excessive expansion, and even cause accidents. The silicon brick with low true density has a small residual expansion. The size of residual expansion of silica brick mainly depends on firing conditions. When the silicon brick is burned to 1450℃ and kept warm, the residual expansion is generally 0.3%~0.8%.
(9) The normal temperature compressive strength of silicon brick is mainly used to determine the advantages and disadvantages of the structure of silicon brick. The compressive strength at room temperature is often closely related to porosity and true density. It also depends on the nature of raw materials and technological conditions. The compressive strength of silicon brick is 19.6~29.4MPa at normal temperature.