What are the raw materials used in silica brick production and how to improve the thermal conductivity of silica brick?

Refractory Raw materials Ladle Silica 

component
Silica brick is refined by calcining high-purity quartz stone, and then mixed with a small amount of lime milk. Some of its aggregates can be used after crushing waste silica brick. Advanced silica brick raw materials need special chemical treatment to remove impurities. The chemical composition of silicon brick is generally [% (mass)]: sio294 ~ 98, Al2O3 2〜2,CaO1. 5〜3.5,Fe2O30. 3〜3,R2O0〜0.5。
Crystal composition.
From the chemical composition of silica brick, it is not difficult to see that the phase composition of silica brick is mainly silicate crystallization, such as SiO2 and a small amount of calcium silicate. There are many crystal types, including quartz, squamous quartz and cristobalite. Brick crystal phase composition (%): scaly quartz 30 ~ 70, cristobalite 20 ~ 80, quartz 3 ~ 15, glass phase 4 ~ 40.
In the crystalline phase of silicon brick, the SiO2 crystal of silicon brick with high melting point is 1713deg; It is impossible for silicon bricks to be completely composed of SiO2. Not because the purity of raw materials is difficult to achieve, but because the crystallization of SiO2 cannot be combined, all other components exist. The crystalline phase and a small amount of glass phase composed of these components have a low melting point and can combine SiO2 crystal particles, so they are called conjugates. However, the large particles of SiO2 in bricks are called aggregates. The corrosion resistance and high temperature resistance of the binder are worse than those of the aggregate. However, too little binder will loosen the bond of aggregate, so the binder should be selected correctly.
1. Silica brick uses natural silica as raw material and adds an appropriate amount of mineralizer to promote the transformation of quartz in the green body. Slow sintering at 1350 ~ 1430 ℃ in reducing atmosphere. When the temperature reaches 1450 ℃, the total volume expansion is about 1.5 ~ 2.2%. This residual expansion will make the cutting joint very dense and ensure the air tightness and structural strength of the masonry body.
(1) Mineral chemical composition. The mass fraction of silica in silicon brick should be greater than 93%. The crystal phase of ordinary silica brick is flake 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 an important index to judge the degree of crystal transformation. The true density of ordinary silica brick is less than 2.388/cm3, and that of high-quality silica brick is less than 2.33/cm3. The content of silicon is 2.65g/cm3. The higher the degree of britannization of lepidolite, the smaller the true density of fired silica brick. Therefore, the mineral composition of silica brick can be judged by the real density of silica brick.
The density of silicon brick is related to porosity. Ordinary silicon brick has a porosity of 17% - 25%, and its bulk density is 1.8-1.95g/cm3. The higher the molding pressure of silica brick, the greater the density; Increasing the bulk density of silica brick can improve the structural strength, thermal conductivity and slag resistance.
3. Fire resistance. The fire resistance of silica brick is poor, 1670-1730 ℃. With the change of SiO2 content, crystal form, impurity type and quantity, the fluctuation range is small; The higher the mass fraction of sulfide, the lower the mass fraction of impurities and the better the fire resistance. Especially when the content of A12O3, K2O and Na2O increases, the fire resistance of silica brick is worse. Silica brick has poor fire resistance and can not meet the requirements of intensive smelting.
4) Load softening temperature. The softening temperature of silica brick under load is generally between 1620 ~ 1670 ℃, which is close to the fire resistance rating. The main reason for this phenomenon is that the main crystal phase of silica brick is the network structure formed by spear double crystal scale quartz and the glass phase with high matrix viscosity. When the silica brick is heated under load, the temperature interval between softening deformation and failure is small. Once the softening temperature is reached, it will be destroyed rapidly, resulting in a narrow temperature range of softening deformation under load. A special characteristic of silica brick is that the temperature at which it begins to soften is close to its fire resistance.
5. Volume stability. During the heating process of silicon brick, in addition to the general thermal expansion, the crystal form transformation occurs with the volume expansion. If unconverted quartz remains in the brick, it will continue to be transformed into scaly quartz or cristobalite at high temperature, resulting in large volume expansion. When ordinary silica brick is heated to 1450 ℃ at room temperature, the volume expansion rate is 1.5% - 2.2%; When it is cooled from 1450 ℃ to 250 ℃, the volume shrinks, and the final remaining expansion rate is 0.1% - 0.9%. The residual expansion of high-quality silica brick shall not exceed 0.3% - 0.4%.
Thermal shock resistance: under the condition of rapid temperature change, the crystallization in the silica brick will change rapidly, and the volume will suddenly expand or contract, resulting in large internal stress, leading to the rupture or spalling of the silica brick. The results show that the thermal shock resistance of silica refractory brick is poor, and the water is cooled at 850 ℃ only once or twice. However, when the service temperature of silica brick is higher than 600 ℃, its thermal shock resistance is good because there is no rapid crystallization transformation.
(7) Slag prevention. Because silica brick is acid refractory brick, it has strong corrosion resistance to slag with weak acidity and furnace gas containing corrosive gas. At the same time, it also has certain slag erosion resistance and certain fire resistance. The reason is that when SiO2 coexists with CaO or FeO, after SiO2 absorbs a certain amount of Cao and FeO at high temperature, two interphase liquid phases with high viscosity will be produced, which is not easy to form droplets or penetrate into the pores of refractory bricks.
Silica bricks - Determination of water content - Gravimetric method.
Scope this recommended method uses gravimetric method to determine the moisture content in silica brick. The method is suitable for the determination of moisture in silica brick with mass fraction greater than 0.1%. In principle, the sample is dried at 105 ~ 110 ℃ to a certain temperature, and the moisture content is calculated based on the water loss mass. Operation step 3.1 weigh and weigh 1.00G of wet sample, with particle size less than 0.088mm, accurate to. 0.0001g. 3.2 in the oven without bottle cap, put the sample into a constant weighing bottle and dry it at 105 ~ 110 ℃ for 1 hour. Cover the lid (a small piece of paper should be padded at the bottle mouth), then take it out and put it into a dryer to cool to room temperature (waste paper), and weigh it. Repeat the operation until it is put into the dryer, cooled to room temperature (waste paper), and weighed. This repeated GUI constant (15 mA per drying). The moisture is calculated according to the following format and expressed by mass fraction:
Om-h2o = (m1-m2) / m * 100m2: om-h2o-water mass fraction,%; M1 - mass of sample weighting bottle before drying, G; M2 - mass of sample weighting bottle after drying, G;