Atomic occupancy mechanism in brownmillerite Ca<sub>2</sub>FeAlO<sub>5</sub> from a thermodynamic perspective

Tao, Yong; Zhang, Wenqin; Li, Neng; Wang, Fazhou; Hu, Shuguang

doi:10.1111/jace.16711

Cited by 18 publications

(13 citation statements)

References 52 publications

(91 reference statements)

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“…To understand the impact of Fe incorporation on the stability of the AFt crystal, supercells of AFt with Fe dosage is set of 25%, 50%, 75%, and 100% are constructed to calculate the defect formation energy. Previous research on the C 4 AF crystals finds that the occupancy of Al and Fe follows the “homogeneous layer principle,” namely Al and Fe ions tend to occupy a layer individually rather than mix with each other within a layer 37 . The same principle is adopted for the substitution site selection in this work.…”

Section: Resultsmentioning

confidence: 97%

The impact of Fe dosage on the ettringite formation during high ferrite cement hydration

et al. 2021

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Illustrating the influence of Fe dosage and temperature on the formation of sulfoaluminate hydrates is of great significance to understand the early hydration process of high ferrite cement under steam curing. Herein, the impact of Fe dosage on the ettringite formation at different temperatures was revealed through the combination of experiments and computational simulations. A Fe dosage no more than 20% conspicuously accelerated the crystal growth of ettringite by increasing the surface energy in the (0 0 1) direction, whereas a higher dosage suppressed the formation of ettringite as the high incorporation of Fe ions into the ettringite crystal was energetically unstable. The chemical environment analysis of Fe in products shows that Fe(OH) 6 3− , compared with Al(OH) 6 3− , prefers to participate in the formation of Al 2 O 3 -Fe 2 O 3 -mono than ettringite, which is also confirmed by the calculated thermodynamic properties' results. The understanding of the impact and mechanism of Fe on the formation of ettringite under steam curing conditions plays a pivotal role in the utilization of high ferrite cement. K E Y W O R D S crystal stability, ettringite, high ferrite cement, molecular dynamics, monosulfate| 3653 WAN et Al.stable phase, AFm, which gradually retransforms into AFt (delayed ettringite) with the internal temperature of concrete decreasing after steam curing. 9-12 Hydrates of C 4 AF possess superior sulfate resistance ability than that of C 3 A owing to the different characteristics between their hydrates. 4 During the C 4 AF hydration, the Fe-bearing AFt and amorphous Fe(OH) 3 formed at the beginning when the solution was rich in gypsum and the Fe-bearing AFm precipitated as the gypsum was consumed. 13 Comparing the reaction of Al-AFm (traditional AFm) with Al/Fe-AFm (Al 3+ is partially replaced by Fe 3+ ) in the presence of gypsum, respectively, Huang et al. 4 found that Al/Fe-AFm rapidly transformed into Al/Fe-AFt after 168 h, while Al-AFm remained, which implies that there was a lower risk of delayed ettringite formation in HFC than OPC for the reason that the proportion of C 4 AF is much higher. When the cement is enriched in the ferrite phase, the hydration product AFt has not only higher but also varied Fe content, 4,6,14,15 making it even more difficult to associate the chemical composition of AFt with its physical properties in the cement system. Therefore, Möschner et al. 16,17 synthesized Fe-ettringite (Ca 6 [Fe(OH) 6 ] 2 (SO 4 ) 3 •26H 2 O) and Fe-bearing ettringite (Ca 6 [Al x Fe 1-x (OH) 6 ] 2 (SO 4 ) 3 •26H 2 O)with different iron-to-aluminum ratios at room temperature, the solubility of Fe-AFt was obtained, and a continuous solid solution of Al/Fe-AFt was observed when the ratio of Al content is between 0.3 and 0.6. To date, the effect of Fe on the formation and conversion of AFt and AFm during steam curing largely remains behind a blindfold, although works have been published on the crystal structure and physical properties of Fe-bearing Aft. 16,17 In this work, we synthesized AFt with...

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Section: Resultsmentioning

confidence: 97%

The impact of Fe dosage on the ettringite formation during high ferrite cement hydration

et al. 2021

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“…The red area has higher adsorption energy, which indicates a higher tendency for adsorption, while the blue area is the opposite A survey of the published literature modeling of CMCs has been studied by a n ers. Processes that have been modeled CVD, 17,18 CVI, [19][20][21][22] and Sol-Gel Infiltrat of alumina matrix in eight-harness satin has been studied numerically in Ref. [ proaches used in the above work general ing the flow of a high viscosity resin thr and modeling the chemical reactions and during processing.…”

Section: Methodsmentioning

confidence: 99%

“…The mechanism of the leaching of Ca 2+ ions and the interaction between the products of CO 2 dissolved in water and the calcium silicates are still not clear due to the experimental limitations. The density functional theory (DFT) has been applied to reveal the interaction of calcium silicate and its hydration products with water from the atomic scale 16–23 . Therefore, the adsorption of the H 2 CO 3 and H 2 O molecule on the γ‐C 2 S surface is investigated in this work with DFT calculations, which provides novel insights into the mechanism of carbonation on the γ‐C 2 S surface.…”

Section: Introductionmentioning

confidence: 99%

Adsorption behavior of carbonic acid on γ‐dicalcium silicate surface from molecular simulations

et al. 2021

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This paper aims to investigate the adsorption of carbonic acid and water molecules on the (010) surface of γ‐dicalcium silicate (γ‐C2S) at an atomic scale using density functional theory (DFT) and ab initio molecular dynamics. It provides novel insights into the mechanism of carbonation on the surface of γ‐C2S. The electrons transfer and interfacial reactions between the carbonic acid (H2CO3) molecule and the γ‐C2S surface are characterized by adsorption configuration, bond order, electron density difference, and partial density of states. There exist strong interactions between H2CO3 and γ‐C2S surface, including two types of chemical adsorption and one type of physical adsorption. This work confirms that water in the carbonation of γ‐C2S is to react with CO2 to provide the reactants, and protons transfer of the carbonic acid molecule plays a crucial role in the carbonation process. The adsorption of the carbonic acid molecule is more favorable with respect to that of the water molecule, which may be the initial step of the carbonization of γ‐C2S.

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“…However, in the case of ferrite, this problem may be more complex and related to the specific distribution of Fe and Al atoms in the Ca2FeAlO5 structure, as they could be located in octahedral or tetrahedral layers (about 75% of octahedral and tetrahedral sites are occupied by Fe and Al, respectively). This implies a mixed substitution of Mg for both Fe and Al and similarly of Si for Al and Fe, but with a preference according to the order give (i.e., Mg for Fe and Si for Al; [40,41]). Their chemical composition is variable; except, aggregates mostly composed of Si, Ca and O, particles, also containing Ca, Al and Fe, could be noted as well, as shown in Table 1 and Figure 9.…”

Section: Cement Mortar Between Stony Blocks Of the Subwall Below The Pavement Levelmentioning

confidence: 99%

Cement Render and Mortar and Their Damages Due to Salt Crystallization in the Holy Trinity Church, Dominicans Monastery in Cracow, Poland

2020

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The investigations focused on the façade of the 17th-century Myszkowskis chapel at the 13th-century Church of the Holy Trinity in Cracow, Poland. Most of the chapel’s façade is made of rusticated limestone blocks, but its lower part is covered with cement render, and the basement consists of irregular pieces of limestone and sandstone, bound and partly replaced with cement mortar. The façade exhibited clearly visible damages: gray soiling of the surface, cracks, scaling, and efflorescence. The study presents characteristics of the cement render and mortar used for stone repair and/or substitution, as well as efflorescence from the lower part of the Myszkowskis chapel façade. The materials were analyzed with optical microscopy, scanning electron microscopy (SEM-EDS), Raman microspectroscopy, X-ray diffractometry (XRPD), and mercury intrusion porosimetry. The analyses demonstrated that the render covering some of the decayed limestone blocks was prepared using Portland cement (residual clinker grains represent alite and belite) as a binding agent, mixed with crushed stone as an aggregate. The cement mortar consisted of rounded quartz grains, rock fragments, and feldspars in very fine-grained masses of calcite and gypsum, also containing relics of cement clinker (alite, belite, ferrite, and aluminate). All these components point out the use of the ordinary Portland cement. Analyses of the efflorescence allowed us to distinguish several secondary salts, among others, thenardite, aphthitalite, and darapskite. The appearance of these phases is related to the composition and physicochemical properties of the building materials, atmospheric alteration agents, air pollution, and some other anthropogenic factors.

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Atomic occupancy mechanism in brownmillerite Ca₂FeAlO₅ from a thermodynamic perspective

Cited by 18 publications

References 52 publications

The impact of Fe dosage on the ettringite formation during high ferrite cement hydration

The impact of Fe dosage on the ettringite formation during high ferrite cement hydration

Adsorption behavior of carbonic acid on γ‐dicalcium silicate surface from molecular simulations

Cement Render and Mortar and Their Damages Due to Salt Crystallization in the Holy Trinity Church, Dominicans Monastery in Cracow, Poland

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Atomic occupancy mechanism in brownmillerite Ca2FeAlO5 from a thermodynamic perspective

Cited by 18 publications

References 52 publications

The impact of Fe dosage on the ettringite formation during high ferrite cement hydration

The impact of Fe dosage on the ettringite formation during high ferrite cement hydration

Adsorption behavior of carbonic acid on γ‐dicalcium silicate surface from molecular simulations

Cement Render and Mortar and Their Damages Due to Salt Crystallization in the Holy Trinity Church, Dominicans Monastery in Cracow, Poland

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Atomic occupancy mechanism in brownmillerite Ca₂FeAlO₅ from a thermodynamic perspective