| you are: Properties glin as raw materials for pottery
Therefore at cooling ceramic a product, burnt to 1000°С, quartz again passes in quartz with corresponding reduction in volume. At temperature above 1050°С quartz passes in kristobalit which in turn in the range of temperatures 1400-1450°С passes in tridimit with volume change of 0,6%. Quartz plavitsja at 1723°С. Changes of volume of grains of the quartz, occurring in the course of roasting, influence durability and rastreskivanie pottery.
Caking glin name their property to be condensed at roasting and to form kamnepodobnyj a crock. On fig. 35 it is visible that with roasting rise in temperature degree of sintering increases and water absorption to a point decreases With as at temperature signs perezhoga - oplavlenie or vspuchivanie a material are marked.
The sintering Interval is equal tc - £4, where l - temperature of the beginning of sintering. Fusible clay (for brick manufacture, keramzita) have a sintering interval 50-100°С, at refractory clay it reaches 400°С.
Fire resistance name property of clay to resist to action of heats, not rasplavljajas.
Colour of clay after roasting has essential value for facing pottery (obverse a brick and ceramic stones, a terracotta tile), and also for thin ceramics. For reception of a white crock roasting conduct in the regenerative environment (in the presence of free WITH and Н2 in gases) and at certain temperatures that okis gland to translate in zakis. large grains pirita (Реч82) and iron oxides, forming on a crock after roasting black points are not desirable in clay. Allocation free okisi gland at heating between 450 and 800°С gives to a product reddish or yellowish colouring. Oxides of the titan cause deep bluish colouring of a crock.
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