Evaluating Water Reactivity at Silica Surfaces Using Reactive Potentials

Mahadevan, Thiruvilla S.; Du, Jincheng

doi:10.1021/acs.jpcc.7b12653

Cited by 40 publications

(48 citation statements)

References 59 publications

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“…Depending on the reaction mechanism of how a silanol is formed, the product can be a hydroxyl ion or a hydronium . There was an insignificant amount of transient H 3 O + which indicates silanol formation through saturation of three coordinated silicon was statistically insignificant.…”

Section: Resultsmentioning

confidence: 99%

“…The pristine surface thus created was then subject to anneal at 498 K to relax the glass surface. Our earlier studies and trials thereafter had indicated that this annealing at 498 K is sufficient to relax the pristine surfaces in pure silica. Since sodium silicates have a T g lower than pure silica, this anneal should sufficiently relax all the compositions of sodium silicates also.…”

Section: Computational Proceduresmentioning

confidence: 92%

“…use of a reactive potential is critical for analyzing all the reactions and material transport inside the glass and solution. Recent improvements of reactive MD force fields have allowed for several advances in the modeling of silica‐water interactions . In one of the most recent studies of sodium silicate hydration with the ReaxFF, leaching of sodium into water and accumulation at the interface of the leached Na + ions was observed along with proton transport inside the glass in the first nanosecond of reaction.…”

Section: Introductionmentioning

confidence: 99%

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Hydration and reaction mechanisms on sodium silicate glass surfaces from molecular dynamics simulations with reactive force fields

Mahadevan

2020

J Am Ceram Soc

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Recent development of reactive force fields have enabled molecular dynamics simulations of interactions between silicate glasses and water at the atomistic scale. While multicomponent silicate glasses encompass a wide variety of compositions and properties, one common structural feature in these glasses is the combination of the network structure that is made up of silica tetrahedra linked through corner sharing interspersed with network modifiers like alkali and alkaline‐earth ions that break up the Si–O–Si linkages by forming nonbridging oxygen. In reactions with water, ion exchange between alkali ions in the glass and proton or hydronium in the solution, as well as hydrolysis reaction of the Si–O–Si linkages and subsequent silanol formation, is observed and well documented. We have used a set of recently developed reactive force field to investigate the reactions between water and the surfaces of silica and sodium silicate glasses of different compositions for reactions up to 8 nanoseconds. Our results indicate sodium leaching into water and diffusion of water molecules up to 25 Å into the glass surface. We examined the structural and compositional changes inside the glass and around the diffused ions and use these to explain the rates of silanol formation at the surface. We also observed proton transport in the glass which has an indirect influence on the silanol formation rates. While the surface of the glass was rough to start with, it undergoes further modification into a hydrated gel‐like structure in the glass for up to 5 Å in the higher alkali containing glasses. It was found that the leached sodium ions remain close to the interface and that fragments of silicate network from the surface is capable of dislodging from the bulk glass and enter the aqueous solution. These simulations thus provide insights into the formation and structure of an alteration layers commonly observed in multicomponent silicate glasses corroded in aqueous solutions.

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Section: Resultsmentioning

confidence: 99%

Section: Computational Proceduresmentioning

confidence: 92%

Section: Introductionmentioning

confidence: 99%

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Hydration and reaction mechanisms on sodium silicate glass surfaces from molecular dynamics simulations with reactive force fields

Mahadevan

2020

J Am Ceram Soc

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“…The complete details, for example, analytical form of potential function and implementations, of each potential can be found elsewhere. [45][46][47][48][49] ReaxFF is a reactive potential that is capable of modeling condensed phases and reproducing material properties. [56][57][58] This reactive potential employs a polarizable, geometry-dependent charge calculation method using the electronegativity equalization method (EEM), which allows a physically realistic charge distribution within the system of interest.…”

Section: Reaxff Teter and Mgffmentioning

confidence: 99%

Searching for correlations between vibrational spectral features and structural parameters of silicate glass network

et al. 2020

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Infrared (IR) and Raman spectroscopic features of silicate glasses are often interpreted based on the analogy with those of smaller molecules, molecular clusters, or crystalline counterparts; this study tests the accuracy and validity of these widely cited peak assignment schemes by comparing vibrational spectral features with bond parameters of the glass network created by molecular dynamics (MD) simulations. A series of sodium silicate glasses with compositions of [Na2O]x[Al2O3]2[SiO2]98−x with x = 7, 12, 17, and 22 were synthesized and analyzed with IR and Raman. A silica glass substrate and a crystalline quartz were also analyzed for comparison. Glass structures with the same compositions were generated with MD simulations using three types of potentials: fixed partial charge pairwise (Teter), partial diffuse charge potential (MGFF), and bond order‐based charge transfer potential (ReaxFF). The comparison of simulated and experimental IR spectra showed that, among these three potentials tested, ReaxFF reproduces the concentration dependence of spectral features closest to the experimentally observed trend. Thus, the bond length and angle distributions as well as Si–Qn species and ring size distributions of silica and sodium silicate glasses were obtained from ReaxFF‐MD simulations and further compared with the peak assignment or deconvolution schemes—which have been widely used since 1970s and 1980s—(a) correlation between the IR peak position in the Si–O stretch region (1050‐1120 cm−1) and the Si–O–Si bond angle; (b) deconvolution of the Raman bands in the Si–O stretch region with the Qn speciation; and (c) assignment of the Raman bands in the 420‐600 cm−1 region to the bending modes of (SiO)n rings with different sizes (typically, n = 3‐6). The comparisons showed that none of these widely used methods is congruent with the bond parameters or structures of silicate glass networks produced via ReaxFF‐MD simulations. This finding invokes that the adequacy of these spectral interpretation methods must be questioned. Alternative interpretations are proposed, which are to be tested independently in future studies.

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“…Therefore, understanding their interactions with adsorbed interfacial water molecules is critical to explain many surface properties of the glass. [3][4][5] It has been reported from previous investigations that soda lime silica (SLS, sodium calcium silicate) glasses exhibit enhanced wear resistance with increasing relative humidity (RH). 6,7 If one speculate that wear behaviors would follow the conventional stress corrosion theory, [8][9][10] it would be anticipated that a sliding contact between the two silicate materials would cause more wear in a humid condition than the dry condition; but the observed result is opposite.…”

Section: Introductionmentioning

confidence: 99%

Atomistic understanding of surface wear process of sodium silicate glass in dry versus humid environments

et al. 2020

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Understanding surface reactions of silicate glass under interfacial shear is critical as it can provide physical insights needed for rational design of more durable glasses. Here, we performed reactive molecular dynamics (MD) simulations with ReaxFF potentials to study the mechanochemical wear of sodium silicate glass rubbed with amorphous silica in the absence and presence of interfacial water molecules. The effect of water molecules on the shear‐induced chemical reaction at the sliding interface was investigated. The dependence of wear on the number of interfacial water molecules in ReaxFF‐MD simulations was in reasonable agreement with the experimental data. Confirming this, the ReaxFF‐MD simulation was used to find further details of atomistic reaction dynamics that cannot be obtained from experimental investigations only. The simulation showed that the severe wear in the dry condition is due to the formation of interfacial Sisubstrate–O–Sicounter_surface bond that convey the interfacial shear stress to the subsurface and the presence of interfacial water reduces the interfacial bridging bond formation. The leachable sodium ions facilitate surface reactions with water‐producing hydroxyl groups and their key role in the hydrolysis reaction is discussed.

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Evaluating Water Reactivity at Silica Surfaces Using Reactive Potentials

Cited by 40 publications

References 59 publications

Hydration and reaction mechanisms on sodium silicate glass surfaces from molecular dynamics simulations with reactive force fields

Hydration and reaction mechanisms on sodium silicate glass surfaces from molecular dynamics simulations with reactive force fields

Searching for correlations between vibrational spectral features and structural parameters of silicate glass network

Atomistic understanding of surface wear process of sodium silicate glass in dry versus humid environments

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