The past efforts to intensify the coke production by enlargement of the capacities of the coke oven batteries and by increase in the coking temperatures caused the need to improve silica building materials used for the construction of the coke batteries and the need for a perfect cognition of their high-temperature properties. The perfection of silica products was achieved by increase in their density with the simultaneous decrease in their specific gravity. The increase in density influences respectively increases the thermal conductivity. The decrease in specific gravity results in higher grade of quartz transformation to tridymite and cristobalite and thus in better volume stability of silica products in high temperatures, which is influenced by the additional transformation of the residual quartz linked with the increase in volume. The dimensional changes linked with the polymorphous quartz transformation and with the modification changes of the crystalline forms of SiO_2 have been examined by many researchers. For instance, it is generally known that the modification change of β-quartz to α-quartz is spontaneous at the temperature of 573°C but linked with the volume change of only 0.83%. The volume change is hardly visible on the thermal expansion curves when the content of the residual quartz in silica products is under 10%, and it can be considered as less important. On the contrary, the transformation of α-quartz to α-tridymite or to α-cristobalite is accompanied by increase in volume by approx. 15%. It is therefore much more important, even though it proceeds quite slowly at the temperatures under 1470°C and gains the spontaneous character only at higher temperatures.
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