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Sintering behaviour as dependence of water absorption, flexural strength and firing shrinkage of dry pressed test samples made from three different types of feldspar rocks on the firing temperature (1120­1300°C) was determined. Potassium, potassiumsodium and sodium-calcium industrially milled feldspars with similar granulometry according to equivalent mean spherical diameter of the grains d(0.5) in the range of 16.6­20.8 ̄m were used. The sintering process was described according to changes in mineralogical composition of the fired test samples too. During the sintering process, feldspars gradually disappear in phases­first of all alkali feldspars (albite, microcline); anorthite (calcium feldspar) is more resistant to melting thanks to its higher melting temperature and it increases the sintering temperature of feldspar. Sodium-potassium feldspar Z43NaK50 with the lowest content of alkalis (3.35% of K2O and 2.67% of Na2O) and the highest equivalent mean spherical diameter d(0.5) showed the most intensive sintering activity. An explanation of this unexpected fact can be found in the equilibrium phase diagrams and in the formation of low melting eutectic mixtures.

Sintering of feldspar rocks from czech quarries