How to Make Silica Bricks
How to Make Silica Bricks
To create high quality silica bricks, the manufacture process must first select the raw material. The chemical purity of the quartzite used in the raw material must be high. Then, the manufacturer must choose the type of firing process that will result in the highest degree of transformation. Then, the bricks must undergo a specific firing time to develop their volume stability and transformation properties. Using local raw materials is the most convenient way to manufacture silica bricks.
The raw materials for silica bricks are typically quartz and pure quartzites. These materials are heated between 1400 and 1500degC and transformed into a mixture of a-cristobalite, a-tridymite, and b-quartz. The latter is more stable than the former, as it exhibits low thermal expansion and is resistant to shock. But this characteristic makes silica bricks less suitable for use in low-temperature kilns.
The invention is a method for manufacturing silica bricks. The firing conditions are shown in FIG. 1 and FIG. 2. The temperature and firing time are related to each other. Symbols on FIG. 2 correspond to the symbols shown in Table 3. The yield of silica bricks for different firing conditions are indicated in FIG. 3. Depending on the degree of oxygen concentration and the rate of temperature elevation, the bricks can be classified as low-porosity silica.
The properties of silica bricks are closely related to the type of silicon dioxide that it contains. One important quality index to look for in silica bricks is the true specific gravity, which should be less than 2.38. The lower the true specific gravity, the less likely it is that there is cristobalite, residual quartz, or tridymite in the brick. High-quality silica bricks will exhibit a high specific gravity and resist refractoriness. Impurities should be avoided, such as Al2O3, K2O, and Na2O.
Another type of brick is a periclase brick. Periclase bricks contain a glassy phase and 18-25% alumina. They exhibit excellent thermal expansion and load-bearing properties to 1300 degrees Celsius. Most naturally occurring fireclays have alumina content of 25 to 45%. The more alumina in a brick, the more refractoriness it has. The highest-purity magnesia bricks are obtained from sea water.
As the silica stone in silica bricks is heated, it forms a stable structure. This stable structure results in a brick that is refractorily stable and resistant to thermal shock. It is also possible to incorporate a silicon compound that is 0.5 to 10% by weight in the silica bricks, such as silicon nitride or silicon carbide. Then, the bricks are fired at temperatures of 1200 to 1400 degrees C., i.e., above line ABC in FIG.1.
A study involving soda vapor confirmed that silica bricks do have a liquid phase, which helps explain the process of frost formation. The liquid phase starts at a temperature of 1450 degrees Fahrenheit. As the flux increases, the liquid phase gradually permeates the interior of the brick, promoting growth of tridymite crystals. However, as the bricks are filled with tridymite, the ability of the bricks to absorb liquid decreases.
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