The formation of feldspar strontian (SrAl2Si2O8) via ceramic route: Reaction mechanism, kinetics and thermodynamics of the process

Abstract

The reaction mechanism, the equilibrium composition, the temperature range of stability of formed intermediates as well as the kinetics and thermodynamics of activated state during the formation of monoclinic strontium-aluminum-silicate feldspar stroncian (SrAl2Si2O8) via the ceramic route from the mixture of SrCO3, Al2O3 and SiO2 is described in this work. Strontian does not appear up to the temperature of 1150 degrees C and is the only stable phase at the temperature >= 1600 degrees C. Three independent reactions lead to two parallel reaction pathways, i.e. the formation of strontian from single or binary oxides (1) and with Sr-gehlenite as the intermediate (2). Since the reaction rate constants ratio is higher than one (k(1)/k(2) > 1), the first reaction route is favored according to the Wegscheider principle. The kinetics of chemical reaction of 1.5 order corresponding to the kinetic function F-2/3 ((1 - alpha)(-1/2) - 1) was determined as the rate determining the mechanism of formation of strontian. The integral and differential methods show that the process requires average apparent activation energy of 229.3 kJ mol(-1). The determined average value of frequency factor is 2.1 x 10(5) S-1The reaction mechanism, the equilibrium composition, the temperature range of stability of formed intermediates as well as the kinetics and thermodynamics of activated state during the formation of monoclinic strontium-aluminum-silicate feldspar stroncian (SrAl2Si2O8) via the ceramic route from the mixture of SrCO3, Al2O3 and SiO2 is described in this work. Strontian does not appear up to the temperature of 1150 degrees C and is the only stable phase at the temperature >= 1600 degrees C. Three independent reactions lead to two parallel reaction pathways, i.e. the formation of strontian from single or binary oxides (1) and with Sr-gehlenite as the intermediate (2). Since the reaction rate constants ratio is higher than one (k(1)/k(2) > 1), the first reaction route is favored according to the Wegscheider principle. The kinetics of chemical reaction of 1.5 order corresponding to the kinetic function F-2/3 ((1 - alpha)(-1/2) - 1) was determined as the rate determining the mechanism of formation of strontian. The integral and differential methods show that the process requires average apparent activation energy of 229.3 kJ mol(-1). The determined average value of frequency factor is 2.1 x 10(5) S-1