| you are: Properties glin as raw materials for pottery
In the course of high-temperature roasting clay undergoes deep physical and chemical changes. Free water at first evaporates, then burn out organic substances. At temperatures 7G0-800°С there is a decomposition waterless metakaolini Al2O3-2SiO2 which was formed earlier (at 450-600°С) owing to degidratatsii kaolinita. Amorphous dioxide of silicon and okis aluminium at rise in temperature (900°С and above) again incorporate, forming an artificial mineral mullit 3Al2O3-2SiO2. Mullit gives to the burnt pottery water resistance, durability, thermal firmness. With its formation clay it is irreversible passes in kamnevidnoe a condition. Together with formation mullita rasplavljajutsja fusible components of clay, cementing and strengthening a material.
Roasting of a brick and other porous products usually comes to an end at temperature 950-1000°С. The further rise in temperature sharply intensifies formation and accumulation of a liquid phase - silicate rasplava which not only cements clay particles, but also condenses a ceramic material. As a result receive products with the dense ceramic crock, different small water absorption (less than 5%).
Quartz is present at clay in the form of quartz sand, it often add for otoshchenija vysokoplastichnyh glin. Quartz undergoes the polymorphic transformations accompanied by volume changes. R-quartz most often meeting in the nature at 573°С is reversible passes in a-quartz with increase in volume at 0,82%; this form is steady to 1050°С.
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