scholarly journals Understanding Cement Hydration of Cemented Paste Backfill: DFT Study of Water Adsorption on Tricalcium Silicate (111) Surface

Minerals ◽  
2019 ◽  
Vol 9 (4) ◽  
pp. 202 ◽  
Author(s):  
Chongchong Qi ◽  
Lang Liu ◽  
Jianyong He ◽  
Qiusong Chen ◽  
Li-Juan Yu ◽  
...  
Keyword(s):  
Water Molecule ◽  
Density Functional ◽  
Cement Hydration ◽  
Cementitious Materials ◽  
Dissociative Adsorption ◽  
Molecular Adsorption ◽  
Cemented Paste Backfill ◽  
Adsorption Mechanisms ◽  
Paste Backfill ◽  
Single Water Molecule

Understanding cement hydration is of crucial importance for the application of cementitious materials, including cemented paste backfill. In this work, the adsorption of a single water molecule on an M3-C3S (111) surface is investigated using density functional theory (DFT) calculations. The adsorption energies for 14 starting geometries are calculated and the electronic properties of the reaction are analysed. Two adsorption mechanisms, molecular adsorption and dissociative adsorption, are observed and six adsorption configurations are found. The results indicate that spontaneous dissociative adsorption is energetically favored over molecular adsorption. Electrons are transferred from the surface to the water molecule during adsorption. The density of states (DOS) reveals the bonding mechanisms between water and the surface. This study provides an insight into the adsorption mechanism at an atomic level, and can significantly promote the understanding of cement hydration within such systems.

scholarly journals Role of Mg Impurity in the Water Adsorption over Low-Index Surfaces of Calcium Silicates: A DFT-D Study

Minerals ◽  
2020 ◽  
Vol 10 (8) ◽  
pp. 665
Author(s):  
Chongchong Qi ◽  
Qiusong Chen ◽  
Andy Fourie
Keyword(s):  
Water Molecule ◽  
Density Functional ◽  
Water Adsorption ◽  
Dissociative Adsorption ◽  
Mg Doping ◽  
Calcium Silicates ◽  
Single Water Molecule ◽  
The Impact ◽  
Mg Doped

Calcium silicates are the most predominant phases in ordinary Portland cement, inside which magnesium is one of the momentous impurities. In this work, using the first-principles density functional theory (DFT), the impurity formation energy (Efor) of Mg substituting Ca was calculated. The adsorption energy (Ead) and configuration of the single water molecule over Mg-doped β-dicalcium silicate (β-C2S) and M3-tricalcium silicate (M3-C3S) surfaces were investigated. The obtained Mg-doped results were compared with the pristine results to reveal the impact of Mg doping. The results show that the Efor was positive for all but one of the calcium silicates surfaces (ranged from −0.02 eV to 1.58 eV), indicating the Mg substituting for Ca was not energetically favorable. The Ead of a water molecule on Mg-doped β-C2S surfaces ranged from –0.598 eV to −1.249 eV with the molecular adsorption being the energetically favorable form. In contrast, the Ead on M3-C3S surfaces ranged from −0.699 eV to −4.008 eV and the more energetically favorable adsorption on M3-C3S surfaces was dissociative adsorption. The influence of Mg doping was important since it affected the reactivity of surface Ca/Mg sites, the Ead of the single water adsorption, as well as the adsorption configuration compared with the water adsorption on pristine surfaces.

scholarly journals DFT Study into the Influence of Carbon Material on the Hydrophobicity of a Coal Pyrite Surface

Molecules ◽  
2019 ◽  
Vol 24 (19) ◽  
pp. 3534 ◽  
Author(s):  
Peng Xi ◽  
Donghui Wang ◽  
Wenli Liu ◽  
Changsheng Shi
Keyword(s):  
Carbon Atom ◽  
Water Molecule ◽  
Density Functional ◽  
Valence Bond ◽  
Covalent Bond ◽  
Point Of View ◽  
Pyrite Surface ◽  
Adsorbed Carbon ◽  
Single Water Molecule ◽  
The Impact

From the macroscopic point of view, the hydrophilicity of symbiotic carbon pyrite is weakened overall compared to that of pure pyrite. It is very important to explain the impact of elemental carbon accreted on a pyrite surface on the surface’s hydrophobicity from the perspective of quantum chemistry. To study the influence of adsorbed carbon atoms on the hydrophilicity of a coal pyrite surface versus a pyrite surface, the adsorption of a single water molecule at an adjacent Fe site of a one-carbon-atom-covered pyrite surface and a carbon atom monolayer were simulated and calculated with the first-principles method of density functional theory (DFT). The water molecules can be stably adsorbed at the adjacent Fe site of the carbon-atom-covered pyrite surface. The hybridization of the O 2p (H2O) and Fe 3d (pyrite surface) orbitals was the main interaction between the water molecule and the pyrite surface, forming a strong Fe–O covalent bond. The water molecule only slightly adsorbs above a C atom on the carbon-atom-covered pyrite and the carbon atom monolayer surfaces. The valence bond between the water molecule and the pyrite surface changed from an Fe–O bond to an Fe–C–O bond, in which the C–O bond is very weak, resulting in a weaker interaction between water and the surface.

scholarly journals Revisiting the reactivity between HCO and CH3 on interstellar grain surfaces

2020 ◽  
Vol 493 (2) ◽  
pp. 2523-2527 ◽  
Author(s):  
J Enrique-Romero ◽  
S Álvarez-Barcia ◽  
F J Kolb ◽  
A Rimola ◽  
C Ceccarelli ◽  
...  
Keyword(s):  
Water Molecule ◽  
Energy Barrier ◽  
Density Functional ◽  
High Energy ◽  
Functional Theory ◽  
Radical Coupling ◽  
High Energy Barrier ◽  
Single Water Molecule ◽  
Complex Organic

ABSTRACT The formation of interstellar complex organic molecules is currently thought to be dominated by the barrierless coupling between radicals on the interstellar icy grain surfaces. Previous standard density functional theory (DFT) results on the reactivity between CH3 and HCO on amorphous water surfaces showed that the formation of CH4 + CO by H transfer from HCO to CH3 assisted by water molecules of the ice was the dominant channel. However, the adopted description of the electronic structure of the biradical (i.e. CH3/HCO) system was inadequate [without the broken-symmetry (BS) approach]. In this work, we revisit the original results by means of BS-DFT both in gas phase and with one water molecule simulating the role of the ice. Results indicate that the adoption of BS-DFT is mandatory to describe properly biradical systems. In the presence of the single water molecule, the water-assisted H transfer exhibits a high energy barrier. In contrast, CH3CHO formation is found to be barrierless. However, direct H transfer from HCO to CH3 to give CO and CH4 presents a very low energy barrier, hence being a potential competitive channel to the radical coupling and indicating, moreover, that the physical insights of the original work remain valid.

scholarly journals Cost-Effective Treatment of Hemihydrate Phosphogypsum and Phosphorous Slag as Cemented Paste Backfill Material for Underground Mine

2019 ◽  
Vol 2019 ◽  
pp. 1-11 ◽  
Author(s):  
Xilong Xue ◽  
Yuxian Ke ◽  
Qian Kang ◽  
Qinli Zhang ◽  
Chongchun Xiao ◽  
...  
Keyword(s):  
Chemical Properties ◽  
Cost Effective ◽  
Strength Loss ◽  
Quality Standard ◽  
Cementitious Materials ◽  
Cemented Paste Backfill ◽  
Technical Requirements ◽  
Cost Effective Treatment ◽  
Paste Backfill ◽  
Phosphorous Slag

The environmental pollution caused by the discharge of phosphogypsum (PG) and phosphorous slag (PS) is a common issue for all countries. In order to fully utilize hemihydrate PG (HPG) and PS and treat goafs in mines, the HPG and PS were used as cementitious materials for cemented paste backfill (CPB). The physical and chemical properties of HPG and PS were first analyzed, and then, the characteristics of CPB were evaluated through fluidity tests, gas detection, uniaxial compressive strength (UCS) tests, bleeding tests, and scanning electron microscopy (SEM). After this, the underground environmental impact of CPB-based HPG and PS was investigated through a dynamic leachability experiment. The results show that (1) the UCS of CPB increases with the increase of the HPG content and mass fraction, and the addition of 3% quicklime can eliminate CO2, H2S, and SO2 generated from the slurry of CPB-based HPG-PS; (2) the addition of 3% quicklime and 5% cement to the HPG-PS mixtures can offset the strength loss of CPB in the late curing stage; (3) the UCS of the recommended specimen reaches 1.15–3.32 MPa after curing from 7 to 28 days, with their slump values varying from 15 mm to 26 mm, and the bleeding rates between 0.87% and 1.15%, which can meet the technical requirements of mining methods; (4) the UCS of CPB is the result of the cohydration reaction of hemihydrate gypsum (HG) in HPG and active Al2O3 and SiO2 in PS; and (5) the leaching indexes meet Category IV of the Chinese Groundwater Quality Standard (DZ/T 0290-2015). The results of this investigation provide a cost-efficient way for the efficient mining of phosphate resources and the comprehensive utilization of HPG and PS.

Influence of water on the CH3O˙ + O2 → CH2O + HO2˙ reaction

2019 ◽  
Vol 21 (28) ◽  
pp. 15734-15741 ◽  
Author(s):  
Subhasish Mallick ◽  
Amit Kumar ◽  
Brijesh Kumar Mishra ◽  
Pradeep Kumar
Keyword(s):  
Density Functional Theory ◽  
Electronic Structure ◽  
Water Molecule ◽  
Density Functional ◽  
Electronic Structure Calculations ◽  
Functional Theory ◽  
Influence Of Water ◽  
Single Water Molecule ◽  
Structure Calculations

Electronic structure calculations employing density functional theory have been used to study the effect of a single water molecule on the CH3O˙ + O2 → CH2O + HO2˙ reaction.

In situ measurements of cemented paste backfill at the Cayeli Mine

2012 ◽  
Vol 49 (7) ◽  
pp. 755-772 ◽  
Author(s):  
B.D. Thompson ◽  
W.F. Bawden ◽  
M.W. Grabinsky
Keyword(s):  
Cement Hydration ◽  
Time Pressure ◽  
Binder Content ◽  
Underground Mines ◽  
Cemented Paste Backfill ◽  
In Situ Data ◽  
Field Instrumentation ◽  
Rise Rate ◽  
Paste Backfill

Cemented paste backfill (CPB) is accepted as the optimal backfilling material for many underground mines. However, the lack of in-stope backfill pressure data poses fundamental problems from both operational and research standpoints. In response to the requirement for in situ data, a comprehensive field instrumentation project has been conducted. Results are presented here for two stopes at the Cayeli Mine, where geotechnical instruments were installed at the barricades and throughout the stopes. Measurements from a large (slow rise rate) stope with high binder content CPB demonstrated a rapid departure from hydrostatic loading, resulting in relatively low barricade pressures. Conversely, data from a smaller (fast rise rate) stope with lower binder content CPB demonstrated that when cement hydration is retarded, high barricade pressures occur. These examples illustrate the relationship between CPB rise rate and the moderating effect of cement hydration on in situ pressures, which ultimately control barricade pressures. Once CPB gains shear strength, arching of pressures occurs. In situ pressures were reduced with proximity to stope walls and further, under stope access brows, demonstrating that barricade location influences barricade loads. The application of real-time pressure monitoring of pastefill barricades has been demonstrated as an important tool in optimizing operational backfilling efficiency.

scholarly journals Analysis of damage failure in uniaxial compressive of cemented paste backfill by ultrasonic pulse velocity test

2021 ◽  
Vol 37 (2) ◽  
Author(s):  
B. Wang ◽  
L. Li ◽  
Y. Yu ◽  
B. Huo ◽  
J. Liu
Keyword(s):  
Mass Fraction ◽  
Damage Mechanics ◽  
Microstructural Analysis ◽  
Ultrasonic Pulse Velocity ◽  
Cementitious Materials ◽  
Ultrasonic Pulse ◽  
Pulse Velocity ◽  
Experimental Results ◽  
Cemented Paste Backfill ◽  
Paste Backfill

Cemented paste backfill (CPB) is prepared by mixing cementitious materials, tailings and water. Uniaxial compressive strength (UCS) is one of the most commonly used indicators for evaluating the mechanical performance of CPB. Ultrasonic pulse velocity (UPV) testing which is a non-destructive measurement, can also be applied to determine the mechanical properties of cement-based materials such as CPB. In order to study the failure mechanism of CPB,144 CPB samples prepared at different mass fraction and cement-tailing ratios were subjected to the UCS and UPV tests at 7,14 and 28 days of curing age. The effect of cement-tailing ratio and mass fraction on the UCS and UPV of CPB samples were obtained, the UCS values were correlated with the corresponding UPV data. Microstructural analysis was also performed on CPB samples to understand the effect of microstructure on the UCS data. The results show that the UCS and UPV values of CPB increased with cement-tailing ratio, mass fraction and curing time. Based on the experimental results, the damage constitutive equations and the damage evolution equations of different backfills were proposed on the basis of damage mechanics. Moreover, comparative analysis of constitutive model and experimental results were made to verify the reliability of the damage model. The results acquired by this paper provide a scientific basis for the rational strength design of backfill mine.

scholarly journals A first-principles characterization of water adsorption on forsterite grains

2013 ◽  
Vol 371 (1994) ◽  
pp. 20110582 ◽  
Author(s):  
Abu Md Asaduzzaman ◽  
Slimane Laref ◽  
P. A. Deymier ◽  
Keith Runge ◽  
H.-P. Cheng ◽  
...  
Keyword(s):  
First Principles ◽  
Density Functional ◽  
Water Adsorption ◽  
Gas Adsorption ◽  
Dissociative Adsorption ◽  
Single Site ◽  
Adsorption Mechanisms ◽  
Comprehensive Picture ◽  
Dual Site

Numerical simulations examining chemical interactions of water molecules with forsterite grains have demonstrated the efficacy of nebular gas adsorption as a viable mechanism for water delivery to the terrestrial planets. Nevertheless, a comprehensive picture detailing the water-adsorption mechanisms on forsterite is not yet available. Towards this end, using accurate first-principles density functional theory, we examine the adsorption mechanisms of water on the (001), (100), (010) and (110) surfaces of forsterite. While dissociative adsorption is found to be the most energetically favourable process, two stable associative adsorption configurations are also identified. In dual-site adsorption, the water molecule interacts strongly with surface magnesium and oxygen atoms, whereas single-site adsorption occurs only through the interaction with a surface Mg atom. This results in dual-site adsorption being more stable than single-site adsorption.

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