A kinetic and mechanistic study of the dehydroxylation of calcium hydroxide

Galwey, Andrew K.; Laverty, Genevieve M.

doi:10.1016/0040-6031(93)80304-s

Cited by 56 publications

(43 citation statements)

References 30 publications

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“…24,26 As discussed in the introduction, the formation of such a structure, which is likely to be permeable, can be expected to play an important role in controlling the migration of molecular water from the bulk to the surface of the crystal and so is of interest for this study. Such a delay can be expected to lead to the temporary existence of an intermediate structure, perhaps in the form of a defective CaĲOH) 2 lattice.…”

Section: Evolution Of Caĳoh) 2 Intensity and Intermediate Structurementioning

confidence: 99%

“…acetic acid 19 or water vapour. 19,21,24 Chaix-Pluchery et al postulated that the coalescence of water-rich zones would provide a network of fast diffusion pathways through the crystal, thus triggering the onset of rapid dehydration. by inducing a donation of protons to the lattice which delayed the onset of formation and ordering of molecular water.…”

Section: Introductionmentioning

confidence: 99%

“…24 This observation led Blamey et al to propose that the dehydration reaction was inhibited in the presence of CO 2 because of the formation of an impermeable CaCO 3 layer blocking the transfer of H 2 O from the particle centre to the surface. Hence, the kinetics of dehydration were found to vary significantly with factors affecting this step such as reaction pressure, water vapour or the packing of the samples and this step was identified as the limiting kinetic step in a number of studies, explaining large differences in measured energies of activation.…”

Section: Introductionmentioning

confidence: 99%

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In situ synchrotron XRD investigation of the dehydration and high temperature carbonation of Ca(OH)₂

2015

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The dehydration and high temperature carbonation reactions of CaĲOH) 2 are an essential part of a number of existing schemes aiming to apply the thermochemical CaO-CaCO 3 cycle ('Ca Looping') in emerging energy industries such as CO 2 capture, gasification and thermal energy storage. However, the underlying chemical mechanisms are poorly understood and the reaction kinetics exhibit a number of strange features such as the increased thermal stability of CaĲOH) 2 , dubbed "superheating", observed in the presence of CO 2 . In this work, in situ X-ray diffraction (XRD) measurements using a synchrotron source are coupled with full pattern fitting analysis to provide high-resolution and high-accuracy data on the evolution of CaĲOH) 2 crystalline structural parameters during the dehydration and carbonation reactions. This method has allowed new observations to be made that provide insight into the studied reaction mechanisms and disprove existing hypotheses as to the origin of superheating. A new hypothesis, involving the formation of an intermediate and permeable CaĲOH) 2 structure was formulated which can explain the growing body of observations in this area. 7306 | CrystEngComm, 2015, 17, 7306-7315 This journal is

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Section: Evolution Of Caĳoh) 2 Intensity and Intermediate Structurementioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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In situ synchrotron XRD investigation of the dehydration and high temperature carbonation of Ca(OH)₂

2015

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“…Kinetic behaviour was interpreted [28] as water loss under diffusion control. The dehydrated material later recrystallized, apparently [28] by a nucleation and growth process, but the water elimination and product phase generation did not coincide in space.…”

Section: Ca(oh)2mentioning

confidence: 99%

Structures and functions of reaction interfaces developed during solid-state dehydrations

Brown

Galwey

Guarini

1997

Journal of Thermal Analysis

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The literature reveals that the mechanisms of some solid-state dehydrations are more complicated than has been generally accepted. Reactions at a thin advancing reactant-product interface provide the geometric models on which the most widely employed rate equations are based. For some systems, this "thin interface" model is a simplification of observed behaviour. Elimination of water from crystallographic sites may occur to a significant extent within a much thicker zone of reactant towards which the active interface is progressing. Consequently the region of chemical change may not coincide with the region of structural transformation. Limited initial dehydration may occur across all crystal faces prior to the onset of a nucleation and growth process that is usually regarded as the dominant rate process in the dehydrations of many large crystals. Experimental observations for solid-state dehydrations are discussed and reaction mechanisms with different rate controlling processes are distinguished. Studies of dehydrations have contributed substantially to the theory of solid-state reactivity, and advances in understanding may have wider application to other solid-state reactants.

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“…25) In contrast, it is thought that the diffusive loss of water from within the Ca(OH)2 crystal is an important reaction control. 26) Also, it has been reported that 5% addition of Fe2O3 at 800°C has little effect during the decomposition of the calcium carbonate, but subsequently enhances lime sintering because of its low Tammann temperature which allow rapidly permitting diffusion into the lime cracks and fissures. 27) Nevertheless, no direct evidence were found in this study to reveal the mechanism that Fe2O3 involvement influence the decomposition process and the following sinter behavior.…”

Section: Comparison For the Two Different Cao Sourcesmentioning

confidence: 99%

Influence of CaO Source on the Formation Behavior of Calcium Ferrite in Solid State

Yin

Xiang

et al. 2013

ISIJ Int.

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Calcium hydroxide and Calcium carbonate were used as CaO source to investigate the formation behavior of calcium ferrite in solid state below 1 200°C. The density change of CaO-Fe2O3 samples with temperature were in-situ and off-line determined, with linear shrinkage rate test for mixed powders at a heating rate of 10°C/min and with Archimedes method for the pellets isothermal roasted at various temperatures and time, respectively. Phase composition of roasted samples was determined with X-ray powder diffraction method, and TG-DSC analysis was used to understand the decomposition behavior and formation of calcium ferrites in different heating rates. As a result, the formation of Ca2Fe2O5 could occur much earlier when calcium hydroxide was used as raw material; however, the formation rates of CaFe2O4 tend to be faster when calcium carbonate was used when the temperature is higher than 1 100°C. In addition, the formation of Ca2Fe2O5 was supposed to be prior to CaFe2O4 in this study when the temperature is lower than 900°C.

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A kinetic and mechanistic study of the dehydroxylation of calcium hydroxide

Cited by 56 publications

References 30 publications

In situ synchrotron XRD investigation of the dehydration and high temperature carbonation of Ca(OH)₂

In situ synchrotron XRD investigation of the dehydration and high temperature carbonation of Ca(OH)₂

Structures and functions of reaction interfaces developed during solid-state dehydrations

Influence of CaO Source on the Formation Behavior of Calcium Ferrite in Solid State

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A kinetic and mechanistic study of the dehydroxylation of calcium hydroxide

Cited by 56 publications

References 30 publications

In situ synchrotron XRD investigation of the dehydration and high temperature carbonation of Ca(OH)2

In situ synchrotron XRD investigation of the dehydration and high temperature carbonation of Ca(OH)2

Structures and functions of reaction interfaces developed during solid-state dehydrations

Influence of CaO Source on the Formation Behavior of Calcium Ferrite in Solid State

Contact Info

Product

Resources

About

In situ synchrotron XRD investigation of the dehydration and high temperature carbonation of Ca(OH)₂

In situ synchrotron XRD investigation of the dehydration and high temperature carbonation of Ca(OH)₂