Silica brick is an acid refractory, which has good acid slag corrosion resistance. The load softening temperature is as high as 1640 ~ 1670 ℃, and the volume is relatively stable under high temperature for long-term use. The mineral facies of silica brick are mainly scaly quartz and cristobalite, as well as a small amount of quartz and glassy.
Silica Brick Introduction
The mineral facies of silica brick are mainly scaly quartz and cristobalite, as well as a small amount of quartz and glassy. The volume of scaly quartz, cristobalite and residual quartz changes greatly due to the change of crystal form at low temperature, so the thermal stability of silica brick at low temperature is very poor.
During use, it shall be heated and cooled slowly below 800 ℃ to avoid cracks. Therefore, it should not be used in kilns with rapid temperature change below 800 ℃. It is mainly used for the partition wall of the carbonization chamber and combustion chamber of the coke oven, the regenerator and sediment chamber of the steel-making open hearth furnace, the refractory silica brick material of the soaking furnace, the glass furnace and the firing kiln of ceramics, etc. It is also used for the high-temperature load-bearing part of hot blast stove and the top of acid open hearth furnace.
Silica Brick Characteristics
Silica brick is the main type of silica refractory, in which the mass fraction of SiO2 is not less than 93%. Silica brick is a typical acid refractory brick.
It has good resistance to acid slag and oxides such as Al2O3, FeO and Fe2O3, but it has poor resistance to alkaline slag and is easy to be damaged by oxides such as Cao, K2O and Na2O. The load softening temperature of silica brick is as high as l640-1680 ℃, and the volume is relatively stable after long-term use at high temperature.
However, the thermal shock resistance of silica brick is poor and the fire resistance is not high enough. The properties of silica brick, including chemical mineral composition, true density, bulk density, fire resistance, load softening temperature, high temperature volume stability, thermal shock resistance and slag resistance, are closely related to the properties of raw materials, crystal transformation and manufacturing process.
Silica Brick Detailed Specification and Advantages
(1) Chemical mineral composition.
The mass fraction of SiO2 in silica brick shall be greater than 93%. In general, the crystalline phase of silica brick is scaly quartz, cristobalite and a small amount of residual quartz, and the matrix is glass phase.
(2) True density and bulk density.
The true density of silica brick is one of the important symbols to judge the degree of crystal transformation. The true density of general silica brick is less than 2.388/cm3, and the true density of high-quality silica brick is 2.33-2.34g/cm3. Silica is 2.65g/cm3. The higher the degree of scale quartification, the smaller the true density of fired silica brick. Therefore, the mineral composition of silica brick can be judged according to the true density of silica brick. The bulk density of silica brick is related to porosity. In general, the apparent porosity of silica brick is 17% – 25%, and the bulk density is 1.8-1.95g/cm3. The higher the forming pressure of silica brick, the greater the bulk density. Increasing the bulk density can improve the structural strength, thermal conductivity and slag resistance of silica brick.
(3) Fire resistance.
The fire resistance of silica brick is low, 1670-1730 ℃. With the different mass fraction, crystal form, impurity type and quantity of SiO2, it changes slightly, but fluctuates little. The higher the mass fraction of SiO2 and the lower the mass fraction of impurities, the higher the fire resistance. Especially when the mass fraction of A12O3, K2O and Na2O increases, the fire resistance of silica brick decreases. In short, the fire resistance of silica brick is not high and can not meet the requirements of intensive smelting.
(4) Load softening temperature.
The load softening temperature of silica brick is relatively high, generally 1620-1670 ℃, which is close to its fire resistance. This is mainly because the main crystal phase of silica brick is the network structure formed by scaly quartz with spearhead bicrystal and the glass phase with high matrix viscosity. When the silica brick is heated under load, the temperature interval from the beginning of softening deformation to its failure is small. Once the softening temperature is reached, it will be destroyed rapidly, resulting in a very narrow temperature range of load softening deformation. The initial softening temperature is close to its fire resistance, which is a special property of silica brick.
(5) Volume stability.
During the heating process of silica brick, in addition to the general thermal expansion, crystal transformation and volume expansion also occur. If there is unconverted residual quartz in the brick, it will continue to transform into scaly quartz or cristobalite at high temperature, resulting in large volume expansion. When ordinary silica brick is heated from normal temperature to 1450 ℃, the volume expansion rate is 1.5% – 2.2%, while when it is cooled from 1450 ℃ to 250 ℃, the volume shrinks, and the final residual expansion rate is 0.1% – 0.9%. The residual expansion of high-quality silica brick shall not exceed 0.3% – 0.4%.
(6) Thermal shock resistance.
When the temperature changes dramatically, the crystallization inside the silica brick changes rapidly, and the volume expands or shrinks suddenly, resulting in large internal stress, which makes the silica brick crack or peel off. Therefore, the thermal shock resistance of silica refractory brick is very poor, and the water cooling at 850 ℃ is only 1-2 times. However, when the service temperature of silica brick fluctuates above 600 ℃, it has good thermal shock resistance because the crystallization does not change rapidly.
(7) Slag resistance.
As acid refractory brick, silica brick has strong corrosion resistance to acid and weak acid slag and furnace gas containing corrosive gas. It also has a certain resistance to the erosion of slag containing ciao and FeO. This is because when Si02 coexists with CaO or FeO, after absorbing a certain amount of Cao and FeO, Si02 generates two immiscible liquid phases with high viscosity at high temperature, which is not easy to form droplets or penetrate into the pores of refractory bricks.Although the fire resistance of silica brick is not very high, it has high load softening temperature, high temperature structural strength, good stability when used above 600 ℃ for a long time, and can resist the erosion of acid slag. Therefore, it is mainly used for building glass furnace and coke oven. The partition wall of coke oven carbonization chamber built with silica brick has good stability and air tightness at high temperature, and the service life can reach 10-15 years. If used properly, it can reach more than 25 years. Silica brick has been used as lining brick of acid converter. Silicon brick was also widely used in electric furnace roof, reverberatory arch roof, regenerator and sediment chamber in the past, but now it has been gradually replaced by high alumina brick and magnesia alumina brick.In the process of heating and baking, the furnace built with silica brick shall be heated slowly to avoid damage to the masonry due to excessive expansion.
