Kinetic and thermal decomposition of ettringite synthesized from aqueous solutions.
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2016
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Resumo
The kinetics of the thermal decomposition of a
synthetic ettringite sample was studied between 298 and
820 K in an inert atmosphere for the present work. The
ettringite and its thermal decomposition products were
characterized using X-ray diffraction, infrared spectroscopy,
and scanning electron microscopy. Four
endothermic events were observed with thermogravimetry
curves, the maxima of which occurred at 366, 397, 537,
and 641 K. All events were associated with the loss of
water molecules with different degrees of interaction
within the ettringite structure. Chemical equations for each
decomposition step were proposed based on the percentages
of mass loss observed. In addition, for the first time,
the activation energies of each ettringite decomposition
events were determined by the isoconversional methods of
Ozawa–Flynn–Wall, Friedman, and Kissinger–Akahira–
Sunose. The modeling revealed that the activation energy
varied from *50 kJ mol-1, characteristic of mass transfer
control steps, to *150 kJ mol-1, which is typical of
chemical control, as the temperature increased and the
ettringite structure lost water. A total of 32 mol of water
was released equivalent to 43.1 % of the initial sample
mass.
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Ettringite, Thermal decomposition, Isoconversional method
Citação
GUIMARÃES, D.; OLIVEIRA, V. de A. A.; LEÃO, V. A. Kinetic and thermal decomposition of ettringite synthesized from aqueous solutions. Journal of Thermal Analysis and Calorimetry, v. 124, p. 1679-1689, 2016. Disponível em: <https://link.springer.com/article/10.1007/s10973-016-5259-3>. Acesso em: 29 set. 2017.