Search

The paper deals with possibilities of using solid residues from fluidized bed combustion of coal, bed and filter ash in the production of composite Portland cements. The ash from fluidized bed combustion contains a high amount of CaO, in the form of free lime or CaSO4 (anhydrite), so it could be used as a possible donor of sulfates to the Portland clinker instead of usually used gypsum. At first, the chemical composition of collected ashes was determined by X-Ray Fluorescence and the ongoing hydration process was monitored by isoperibolic calorimetry. Then samples containing mixtures of Portland clinker and ash were prepared. Their respective compressive strength and flexural strength were analyzed and observations were made on the hydration and composition of products of the hydration reaction detected by X-Ray diffraction. Finally, the results of selected mixtures were verified with prepared standardized mortars.

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-1

Water composition during cement hydration can be changed due to migration of ions from the cement matrix to the solution. The storage of various materials together can lead to transfer of various ions and distortion of results. This article is aimed on the influence of storage environment on the Portland cement hydration and hydrated samples composition. Test specimens were prepared and stored in different environments. Storage environments were ultrapure water and solutions having alkaline and acidic pH value. The mechanical properties were measured after 1, 7 and 28 days. Composition of samples stored in different environment was tested by X-ray diffraction and DTA analysis. (C) 2016 Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license.

The kinetics, the mechanism and the thermodynamics of activated state of formation of primary strontian feldspar via sinter-crystallization of non-equilibrium melt during the thermal treatment of ceramic body was investigated in this work via differential thermal analysis using isoconversional Kissinger kinetic equation. The process of formation of non-equilibrium melt and subsequent crystallization of primary strontian feldspar requires the activation energy of 631±3 and 664±2 kJ mol1, respectively. The investigation of mechanism of formation of primary strontian feldspar reveals that the process is driven by the surface nucleation and diffusion controlled growth of the new phase. The nucleation rate decreases with the time of process and non-equilibrium melt can be formed only in metastable equilibrium with activated state of strontian feldspar. Deep consideration of kinetic data leads to the deduction of new kinetic approach that enables single calculation of activation energy and frequency factor of heterogeneous processes as well as the dependence of thermodynamic parameters of activated state on temperature. Further consideration of kinetic data reveals that the activation energy is directly proportional to the function of csch (z)+1. For z=e, this term enables to derive the value for the parameter B(x) in empirical equation for Arrhenius temperature integral p(x) proposed by Doyle to be 1.0642.

The paper deals with possibilities of using solid residues from fluidized bed combustion of coal, bed and filter ash in the production of composite Portland cements. The ash from fluidized bed combustion contains a high amount of CaO, in the form of free lime or CaSO4 (anhydrite), so it could be used as a possible donor of sulfates to the Portland clinker instead of usually used gypsum. At first, the chemical composition of collected ashes was determined by X-Ray Fluorescence and the ongoing hydration process was monitored by isoperibolic calorimetry. Then samples containing mixtures of Portland clinker and ash were prepared. Their respective compressive strength and flexural strength were analyzed and observations were made on the hydration and composition of products of the hydration reaction detected by X-Ray diffraction. Finally, the results of selected mixtures were verified with prepared standardized mortars.

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-1

Water composition during cement hydration can be changed due to migration of ions from the cement matrix to the solution. The storage of various materials together can lead to transfer of various ions and distortion of results. This article is aimed on the influence of storage environment on the Portland cement hydration and hydrated samples composition. Test specimens were prepared and stored in different environments. Storage environments were ultrapure water and solutions having alkaline and acidic pH value. The mechanical properties were measured after 1, 7 and 28 days. Composition of samples stored in different environment was tested by X-ray diffraction and DTA analysis. (C) 2016 Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license.

The kinetics, the mechanism and the thermodynamics of activated state of formation of primary strontian feldspar via sinter-crystallization of non-equilibrium melt during the thermal treatment of ceramic body was investigated in this work via differential thermal analysis using isoconversional Kissinger kinetic equation. The process of formation of non-equilibrium melt and subsequent crystallization of primary strontian feldspar requires the activation energy of 631±3 and 664±2 kJ mol1, respectively. The investigation of mechanism of formation of primary strontian feldspar reveals that the process is driven by the surface nucleation and diffusion controlled growth of the new phase. The nucleation rate decreases with the time of process and non-equilibrium melt can be formed only in metastable equilibrium with activated state of strontian feldspar. Deep consideration of kinetic data leads to the deduction of new kinetic approach that enables single calculation of activation energy and frequency factor of heterogeneous processes as well as the dependence of thermodynamic parameters of activated state on temperature. Further consideration of kinetic data reveals that the activation energy is directly proportional to the function of csch (z)+1. For z=e, this term enables to derive the value for the parameter B(x) in empirical equation for Arrhenius temperature integral p(x) proposed by Doyle to be 1.0642.

Water composition during cement hydration can be changed due to migration of ions from the cement matrix to the solution. The storage of various materials together can lead to transfer of various ions and distortion of results. This article is aimed on the influence of storage environment on the Portland cement hydration and hydrated samples composition. Test specimens were prepared and stored in different environments. Storage environments were ultrapure water and solutions having alkaline and acidic pH value. The mechanical properties were measured after 1, 7 and 28 days. Composition of samples stored in different environment was tested by X-ray diffraction and DTA analysis. (C) 2016 Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license.

The paper deals with possibilities of using solid residues from fluidized bed combustion of coal, bed and filter ash in the production of composite Portland cements. The ash from fluidized bed combustion contains a high amount of CaO, in the form of free lime or CaSO4 (anhydrite), so it could be used as a possible donor of sulfates to the Portland clinker instead of usually used gypsum. At first, the chemical composition of collected ashes was determined by X-Ray Fluorescence and the ongoing hydration process was monitored by isoperibolic calorimetry. Then samples containing mixtures of Portland clinker and ash were prepared. Their respective compressive strength and flexural strength were analyzed and observations were made on the hydration and composition of products of the hydration reaction detected by X-Ray diffraction. Finally, the results of selected mixtures were verified with prepared standardized mortars.

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-1