The refractory fire bricks are made from fireclays (chamotte), unfired refractory-bond clay and fired-refractory clay. The fireclay bricks usually have 2 main components that include 18% to 44% of alumina and 50% to 80% of silica. The clay varieties and the manufacturing methods allows for the production of many brick types that are appropriate for particular applications. The fireclay uses are mainly due to presence of a mineral mullite, that is formed during firing which is characterized by low-thermal expansion and high refractoriness.
The https://cheapfirebricks.com/fire-clay-bricks/ is made up of hydrated aluminum-silicates along with minor levels of other mineral types. A general formula for the aluminum silicates is AI203.2SiO2.2H20 which corresponds to 39.5% alumina, 46.5% silica and 14% water. Kaolinite is a more common member for these groups.
At the higher temperatures, the water drives off, while the residue will theoretically be made up of 45.9% alumina and 54.1% silica. But, even pure clays still contain other constituents in small amounts like compounds of magnesium, titanium, iron, lithium, potassium, sodium, calcium, and even free silica. The total quantities of these agents, that lower melting points, should not exceed levels of 5% to 6%.
The word Fireclay brick is used for groups of refractory clays that are typically able to withstand temperatures that are above PCE (pyrometric cone equivalent) values of 19. Plasticity and refractoriness are the 2 main properties that are required in fireclay to ensure it is suitable for manufacturing refractory bricks. The better fireclays have fusion points that are high along with good plasticity. The fireclay that contains high alumina along with low lime, iron oxide, alkalis and magnesia are usually preferable when it comes to producing refractory bricks.
The kaolinitic (aluminous) varieties of fireclay are more refractory due to its density and hardness along with an absence in iron, which gives it a white-burning color. Absence of alkali also provides these bricks with a very high fusion-temperature.
One of the characteristic properties of clay is how it behaves with water. When it is combined with water, the clay turns into a plastic which can then be molded and shaped. The plasticity occurs due to clay minerals that become surrounded by a liquid film, which lowers cohesion forces that occur between the particles. As the strength of bonds between these layers starts to reduce due to enough water layers, the mixture of clay can then be shaped or formed under a pressure while still retaining its shape.
During the process of heating up to a temperature of 500 degrees C or 600 degrees C, the kaolin minerals lose the crystallization water, and it is in this intermediate-phase that metakaolin forms. This phase still has a crystalline order that is low. The kaolin lattice will not completely disintegrate until around 925 degrees C. To begin with there are no reaction that occur between the alumina and silica in the decomposed-clay. At a temperature of 950 degrees C the mullite starts to form. Above a temperature of 1100 degrees C, only the glassy or/and cristobalite and mullite will be present. The glassy phase approximate composition is 80% silica, 10% alumina and around 5% of earth alkalis and alkalis. Read more on this page: WWW.cheapfirebricks.com