A Modular Concept of Crystal Structure Applied to the Thermal Transformation of α‐<scp><scp>C</scp></scp><sub>2</sub><scp><scp>SH</scp></scp>

Garbev, Krassimir; Gasharova, B.; Stemmermann, Peter

doi:10.1111/jace.12921

Cited by 16 publications

(18 citation statements)

References 39 publications

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“…Compositional changes in the silicate matrix due to the presence of H 2 O during the hydration/dehydration tests at 450/550ºC were observed by XRD. These changes are consistent with the hydration of Ca 2 SiO 4 to form different hydrated silicates (Garbev et al 2014;Mitsuda et al 1985;Roßkopf et al 2015;Speakman et al 1967;Yanagisawa et al 2006), being Ca 5 (SiO 4 ) 2 (OH) 2 the main compound identified in our samples (Criado et al 2015). Although these hydrated silicates only represent a small fraction of the total amount of silicates present in the composite material, the formation of these hydrates could play a role in the deterioration of the mechanical properties over cycling.…”

Section: Observations On the Decay Of Crushing Strengthsupporting

confidence: 90%

Enhancement of a CaO/Ca(OH)2 based material for thermochemical energy storage

2016

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The application of hydration/dehydration reactions of CaO/Ca(OH) 2 to thermochemical energy storage systems can be facilitated by the development of Ca-based materials with improved mechanical properties when compared to the natural Ca-precursor, while maintaining good chemical activity. For this purpose, we are developing composite materials for fluidized bed or fixed bed applications synthesized using sodium silicate to bind fine CaO/Ca(OH) 2 particles. In this work, the mechanism of decay in the mechanical properties of the resulting CaO/Ca-silicates composites over hundreds of hydration/dehydration cycles has been investigated. Based on the observed mechanism, improvements to the method of synthesis of the materials have been introduced, in order to retain the original carbonate grain volumes, which are larger than those of the equimolar quantity of the expanding Ca(OH) 2 during hydration. A noticeable improvement in the mechanical stability of the resulting pellets was observed when the material was exposed to temperatures of around 880ºC in pure CO 2 before calcination in order to avoid the decomposition of CaCO 3 during the formation of the hard Ca-silicates that provide mechanical strength to the composite. Further gains in mechanical stability 2 were achieved by avoiding the complete hydration of the CaO grains in the composites. These results confirm the primary role of Ca(OH) 2 anisotropic expansion as the main cause of the reduction in crushing strength of the pellets. It can be concluded that the formation of calcium silicates as binders of CaO rich grains is a promising route for the development Ca-based composite materials. However, more effort is still needed to overcome the decay in performance observed after several hundreds of cycles.

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Section: Observations On the Decay Of Crushing Strengthsupporting

confidence: 90%

Enhancement of a CaO/Ca(OH)2 based material for thermochemical energy storage

2016

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“…Other reflections are observed at angles close to 16, 32.3, 50 and 55 in 2. Similar observations have previously been reported in XRD studies of synthesized C-S-H and C-(A)-S-H systems (Taylor et al, 2010;Renaudin et al, 2009;Garbev et al, 2008). In C-S-H samples, it has been observed that the intensity of the main reflection at 29.5 2 increases with increasing Ca/Si ratio and there is a rightward shift of the peak to higher 2 angles.…”

Section: Direct Decomposition Of Hydrating Slagsupporting

confidence: 87%

“…In C-S-H samples, it has been observed that the intensity of the main reflection at 29.5 2 increases with increasing Ca/Si ratio and there is a rightward shift of the peak to higher 2 angles. The other reflection at 32.3 also increases with increasing Ca/Si ratio (Renaudin et al, 2009;Garbev et al, 2008). In C-(A)-S-H systems, incorporation of aluminium takes place by substitution of tetrahedral bridging sites of Si 4+ with Al 3+ .…”

Section: Direct Decomposition Of Hydrating Slagmentioning

confidence: 99%

Quantitative phase analysis of slag hydrating in an alkaline environment

Reddy

Subramaniam

2020

J Appl Crystallogr

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An X‐ray diffraction (XRD)‐based evaluation of the crystalline and amorphous phases in slag hydrating in an alkaline environment is presented. A method is developed for the quantification of the amorphous phases present in hydrating slag in a sodium hydroxide solution. In hydrating slag, the amorphous reaction product is identified as calcium aluminosilicate hydrate. A water‐soluble sodium‐based amorphous reaction product is also produced. The XRD‐based quantification method relies on the direct decomposition of the XRD intensity pattern of the total amorphous phase present in partially hydrated slag into the intensity patterns of the amorphous unreacted slag, the hydrate and the sodium‐based product. The unreacted slag content in partially hydrated slag is also determined from the decomposition of the intensity signature of the total amorphous phase. An independent verification of the amorphous unreacted slag content in hydrating slag is obtained from measurements of blends of unhydrated and partially hydrated slag. The XRD‐based phase‐quantification procedure developed here provides a basis for evaluating the extent of reaction in hydrating slag.

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“…This use has been very elegantly employed to follow the evolution of a single crystal (grain) of α-C 2 SH on heating. [136] The exact transformation mechanism of dehydration remained controversial but this work showed conclusive evidences of the formation of Dellaite at about 350°C. Figure 16 shows diffractionlimited IR images of a thin α-C 2 SH crystallite, thickness ≈ 3 µm, showing the spatially resolved intensity evolution with temperature of selected vibration bands to highlight the appearance and disappearance of the phases.…”

Section: Scanning Synchrotron Radiation Microscopiesmentioning

confidence: 76%

Recent studies of cements and concretes by synchrotron radiation crystallographic and cognate methods

Aranda

2015

Crystallography Reviews

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The portfolio of available synchrotron radiation techniques is increasing notably for cements and pastes. Furthermore, sometimes the terminology is confusing and an overall picture highlighting similarities and differences of related techniques was lacking. Therefore, the main objective of this work is to review recent advances in synchrotron techniques providing a comprehensive overview. This work is not intended to gather all publications in cement chemistry but to give a unified picture through selected examples. Crystallographic techniques are used for structure determination, quantitative phase analyses and microstructure characterization. These studies are not only carried out in standard conditions but synchrotron techniques are especially suited to non-ambient conditions: high temperatures and pressures, hydration, etc., and combinations. Related crystallographic techniques, like Pair Distribution Function, are being used for the analysis of ill-crystalline phase(s). Furthermore, crystallographic tools are also employed in imaging techniques including scanning diffraction microscopy and tomography and coherent diffraction imaging. Other synchrotron techniques are also reviewed including X-rays absorption spectroscopy for local structure and speciation characterizations; small angle X-ray scattering for microstructure analysis and several imaging techniques for microstructure quantification: full-field soft and hard X-ray nano-tomographies; scanning infrared spectro-microscopy; scanning transmission and fluorescence X-ray tomographies. Finally, a personal outlook is provided.

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A Modular Concept of Crystal Structure Applied to the Thermal Transformation of α‐C₂SH

Cited by 16 publications

References 39 publications

Enhancement of a CaO/Ca(OH)2 based material for thermochemical energy storage

Enhancement of a CaO/Ca(OH)2 based material for thermochemical energy storage

Quantitative phase analysis of slag hydrating in an alkaline environment

Recent studies of cements and concretes by synchrotron radiation crystallographic and cognate methods

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A Modular Concept of Crystal Structure Applied to the Thermal Transformation of α‐C2SH

Cited by 16 publications

References 39 publications

Enhancement of a CaO/Ca(OH)2 based material for thermochemical energy storage

Enhancement of a CaO/Ca(OH)2 based material for thermochemical energy storage

Quantitative phase analysis of slag hydrating in an alkaline environment

Recent studies of cements and concretes by synchrotron radiation crystallographic and cognate methods

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A Modular Concept of Crystal Structure Applied to the Thermal Transformation of α‐C₂SH