We have examined the bonding arrangements in Na–P–O–F and Na–Al–P–O–F glasses using 19F, 27Al, and 31P solid-state magic angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy. For the Al-free series of glasses, the 19F NMR spectra are dominated by peaks near +90 ppm, representative of F terminating P-chains. The formation of these bonds has little effect on the 31P chemical shifts, indicating that F preferentially replaces bridging oxygen on the phosphate tetrahedra, consistent with previous NMR studies of crystalline fluorophosphates and other spectroscopic studies of fluorophosphate glass. For the Na–Al–P–O–F glasses, 27Al NMR detects only octahedral Al-sites, the 19F NMR spectra include a second peak near −12 ppm due to F bonded to Al, and the 31P NMR spectra contain signals due to Q1-sites with one or more Al next-nearest neighbors. The relative intensity of the two 19F peaks correlates well with previous spectroscopic studies and shows that a greater fraction of F–P bonds forms when the base glass is remelted in NH4HF2.

Inelastic neutron scattering is applied for the first time to monitor directly the concentration of calcium hydroxide formed during the hydration of tricalcium silicate. Results taken between 10 and 40 °C show that the onset of calcium hydroxide formation is delayed at lower temperatures but that the final quantity formed appears to be converging to a temperature-independent value. At 20°C, the 28 day value is 1.3 moles per mole of tricalcium silicate. Combining these results with previous measurements of the free water index made using quasielastic neutron scattering reveals that the hydrogen content of the C–S–H gel decreases significantly at increased curing temperature.

We describe a new multistate empirical valence bond (MS-EVB) model of OH(-) in aqueous solutions. This model is based on the recently proposed "charged ring" parameterization for the intermolecular interaction of hydroxyl ion with water [Ufimtsev, et al., Chem. Phys. Lett., 2007, 442, 128] and is suitable for classical molecular simulations of OH(-) solvation and transport. The model reproduces the hydration structure of OH(-)(aq) in good agreement with experimental data and the results of ab initio molecular dynamics simulations. It also accurately captures the major structural, energetic, and dynamic aspects of the proton transfer processes involving OH(-) (aq). The model predicts an approximately two-fold increase of the OH(-) mobility due to proton exchange reactions.

Green rust (GR, Fe4Fe 3+ 2(OH)12-SO4·xH2O) nanoparticles have the potential to provide effective solutions for contaminated groundwater remediation (e.g., permeable reactive barriers). Structural Fe within GR can reduce adsorbed trace elements (e.g., Se) and significantly lower their solubility and bioavailability. GR forms in suboxic environments and when exposed to oxic conditions rapidly transforms (minutes) to various iron (oxyhydr)oxide phases. The kinetics and mechanisms of these reactions and the fate of associated trace elements are poorly understood. Synchrotron-based in situ time-resolved Small/Wide Angle X-ray Scattering (SAXS/WAXS) and Energy Dispersive X-ray Diffraction (EDXRD) were used to characterise the crystallisation and oxidative transformation of GR nanoparticles via the oxidation of a Fe-sulphate solution, utilizing advanced environmental cells. The speciation of associated trace elements (i.e., Zn and Se) were analyzed by X-ray Absorption Spectroscopy (XAS). Results showed that initially Fe(OH)2 formed which then transformed to GR-sulphate (GRII). With continued oxidation GRII transformed to lepidocrocite (L) and goethite (G) (Fig. 1).

Diffusion coefficients of water in hydrated cement pastes and mortars obtained from proton field cycling NMR spin lattice relaxation over three orders of magnitude in magnetic field strength are in good agreement with values from molecular dynamics simulations of water on the surface of tobermorite. The level of agreement from these two independent approaches provides mutual support for their validity.

Molecular dynamics (MD) simulation of the Mg/Al (3:1) layered double hydroxide (LDH), hydrotalcite (HT), containing citrate, C6H5O7(3-), as the charge balancing interlayer anion provides new molecular scale insight into the interlayer structure, hydrogen bonding, and energetics of the hydration and consequent swelling of LDH compounds containing organic and biomolecules. Citrate-HT exhibits affinity for water up to very high hydration levels, in contrast to the preferred low hydration states of most LDHs intercalated with small, inorganic anions. This result is consistent with the recent experimental observation of the delamination of lactate-HT. The high water affinity is rationalized in terms of the preference of citrate ion for hydrogen bonds (H-bonds) donated from water molecules rather than from the hydroxyl groups of the metal hydroxide layer and the need to develop an integrated interlayer H-bond network among the citrate ions, water, and -OH groups of the hydroxide layers. The changes in the orientation of citrate molecules with progressive hydration are also intimately related to its preference to accept hydrogen bonds from water.

P. KOMADEL, 1 J. MADEJOVA, 1 M. JANEK, 1 W. P. GATES, 2'4 R. J. KIRKPATRICK, 3 AND J. W. STUCKI 2 1 Institute of Inorganic Chemistry, Slovak Academy of Sc iences , 842 36 Bratislava, Slovakia 2 Department of Natural Resources and Environmental Sciences, University of Illinois, Urbana, Illinois 61801, USA 3 Department of Geology, University of Illinois, Urbana, Illinois 61801, USA 4 Present address: Savannah River Ecology Laboratory, P.O. Drawer E, Aiken, SC 29801, USA

X-ray diffraction, compositional analysis, and 29Si and 27Al MAS NMR spectroscopy of Al-substituted tobermorite-type C–S–H made by precipitation from solution provide significant new insight into the structural mechanisms of Al-substitution in this important and complicated phase. Al occurs in 4-, 5-, and 6-coordination (Al[4], Al[5], and Al[6]) and plays multiple structural roles. Al[4] occurs on the bridging tetrahedra of the drierkette Al–silicate chains, and Al[5] and Al[6] occur in the interlayer and perhaps on particle surfaces. Al does not enter either the central Ca–O sheet or the pairing tetrahedra of the tobermorite-type layers. Al[4] occurs on three types of bridging sites, Q3 sites that bridge across the interlayer; Q2 sites that are charge balanced by interlayer Ca+2, Na+, or H+; and Q2 sites that are most likely charge balanced by interlayer or surface Al[5] and Al[6] through Al[4]–O–Al[5,6] linkages. Although the data presented here are for relatively well-crystallized tobermorite-type C–S–H with C/S ratios ≤ 1.2, comparable spectral features for hydrated white cement pastes in previously published papers[30], [31], [32] [M.D. Andersen, H.J. Jakobsen, J. Skibsted, Incorporation of aluminum in the calcium silicate hydrate (C–S–H) of hydrated Portland cements: a high-field 27Al and 29Si MAS NMR investigation Inorg. Chem. 42 (2003) 2280–2287; M.D. Andersen, H.J. Jakobsen, J. Skibsted, Characterization of white Portland cement hydration and the C–S–H structure in the presence of sodium aliminate by 27Al and 29Si MAS NMR spectroscopy, Cem. Concr. Res. 43 (2004) 857–868; M.D. Andersen, H. J. Jakobsen, J. Skibsted, A new aluminum-hydrate phase in hydrated Portland cements characterized by 27Al and 29Si MAS NMR spectroscopy, Cem. Concr. Res., submitted for publication.] indicate the presence of similar structural environments in the C–S–H of such pastes, and by implication OPC pastes.

Molecular dynamics (MD) simulations of water confined in nanospaces between layers of talc (system composition Mg(3)Si(4)O(10)(OH)(2) + 2H(2)O) at 300 K and pressures of approximately 0.45 GPa show the presence of a novel 2-D ice structure, and the simulation results at lower pressures provide insight into the mechanisms of its decompression melting. Talc is hydrophobic at ambient pressure and temperature, but weak hydrogen bonding between the talc surface and the water molecules plays an important role in stabilizing the hydrated structure at high pressure. The simulation results suggest that experimentally accessible elevated pressures may cause formation of a wide range of previously unknown water structures in nanoconfinement. In the talc 2-D ice, each water molecule is coordinated by six O(b) atoms of one basal siloxane sheet and three water molecules. The water molecules are arranged in a buckled hexagonal array in the a-b crystallographic plane with two sublayers along [001]. Each H(2)O molecule has four H-bonds, accepting one from the talc OH group and one from another water molecule and donating one to an O(b) and one to another water molecule. In plan view, the molecules are arranged in six-member rings reflecting the substrate talc structure. Decompression melting occurs by migration of water molecules to interstitial sites in the centers of six-member rings and eventual formation of separate empty and water-filled regions.

This paper reviews the results of recent molecular dynamics (MD) modelling studies of the interaction of water and solute species with mineral surfaces and their behaviour in mineral interlayers. Emphasis is on results for single and double hydroxide phases. Computational results are presented for water and anions in the interlayers of the Ca2Al, Mg2Al, and LiAl2 layered double hydroxides and on the surfaces of the Ca2Al phase. Detailed results for water on the (001) surface of brucite (Mg(OH)(2)) are presented and compared to published results for other phases. In all these cases, hydrogen bonding and the development of a hydrogen-bond network involving the H2O molecules and the solid substrate play very significant roles. The MD methods are especially effective for investigating the structure and dynamics of mineral-fluid interfaces and mineral interlayers, because they can be applied to systems containing hundreds to thousands of atoms and for extended durations of the order of nanoseconds.

Clay-PEO nanocomposites can have large electrical conductivities that make them potential electrolyte materials for rechargeable lithium batteries, but the origin of these large conductivities, especially for Li-containing materials, is poorly understood. This paper presents X-ray diffraction (XRD), TGA-DTA, and (7)Li and (23)Na NMR data for PEO nanocomposites made with natural (SWy-1) and synthetic (MNTS) montmorillonite clays that provide new insight into interlayer structure. An increase in basal d(001)-spacings demonstrates successful intercalation of PEO in all samples, and X-ray line narrowing shows that this intercalation improves the layer stacking order. The basal spacings of 17.9-19.4 A are consistent with a helical or bilayer structure of PEO in the interlayer. TGA-DTA provides quantitative results for the hydration state of the nanocomposites, demonstrates PEO intercalation, and shows that the composites prepared from the synthetic montmorillonite are less stable than those made with SWy-1. (7)Li NMR shows that the nearest neighbor hydration state of Li(+) is unaffected by PEO intercalation and suggests weak interaction of Li(+) with PEO. (23)Na NMR shows that PEO intercalation results in the conversion of the multiple Na(+) hydration states observed for the pristine clay into inner sphere sites most likely formed through coordination with the basal oxygens of the clay. These differences between lithium and sodium suggested that tighter binding of the Na to the clay may be the origin of the conductivity of Li-montmorillonite-PEO nanocomposites being as much as 2 orders of magnitude larger than those of Na-montmorillonite-PEO nanocomposites. The results confirm the idea that polymer oxygen atoms do not participate in sequestering the exchangeable cations and agree with the jump process for cation migration advanced by Kuppa and Manias (Kuppa, V.; Manias, E. Chem. Mater. 2002, 14, 2171).

Molecular dynamics (MD) modeling is an effective tool for studying the structure, dynamics and energetics of cement materials at the molecular level, and is especially useful when used in conjunction with experimental data that allows detailed definition of the systems to be modeled. Here we present a combined MD and experimental study of the swelling behavior of kanemites (hydrous alkali layered silicates) and alkali silicate hydrate (A-S-H) gels that leads to testable hypotheses concerning the mechanisms of water incorporation into the gels produced during the alkali silica reaction (ASR) in concrete. The MD computational results show that entry of water into the interlayer spaces of kanemite [Na,K)HSi 2 O 5 · n H 2 O] is structurally and energetically limited and, thus, suggest that expansion of A-S-H gels produced during the alkali silica reaction (ASR) is due principally to incorporation of water molecules between nano-particles, rather than within kanemite-like interlayer galleries. Kanemite-like volumes appear to be a significant component of A-S-H gels with compositions in the range observed for in-service concrete. XRD data suggest that these nano-particles have coherent diffraction lengths of the order of 10 nm perpendicular to the silicate layers. The MD-computed structures of Na- and K-kanemite are in excellent agreement with those determined from X-ray diffraction data. Likewise, the computed energetics of water sorption are in excellent agreement with the observed X-ray diffraction, water sorption, TGA/DTA, and 29 Si NMR data for kanemites and A-S-H. The water sorption and TGA/DTA behaviors of the kanemites and A-S-H gels show many similarities but also significant differences.

Molecular dynamics (MD) computer simulations of liquid water adsorbed on the muscovite (001) surface provide a greatly increased, atomistically detailed understanding of surface-related effects on the spatial variation in the structural and orientational ordering, hydrogen bond (H-bond) organization, and local density of H2O molecules at this important model phyllosilicate surface. MD simulations at constant temperature and volume (statistical NVT ensemble) were performed for a series of model systems consisting of a two-layer muscovite slab (representing 8 crystallographic surface unit cells of the substrate) and 0 to 319 adsorbed H2O molecules, probing the atomistic structure and dynamics of surface aqueous films up to 3 nm in thickness. The results do not demonstrate a completely liquid-like behavior, as otherwise suggested from the interpretation of X-ray reflectivity measurements and earlier Monte Carlo simulations. Instead, a more structurally and orientationally restricted behavior of surface H2O molecules is observed, and this structural ordering extends to larger distances from the surface than previously expected. Even at the largest surface water coverage studied, over 20% of H2O molecules are associated with specific adsorption sites, and another 50% maintain strongly preferred orientations relative to the surface. This partially ordered structure is also different from the well-ordered 2-dimensional ice-like structure predicted by ab initio MD simulations for a system with a complete monolayer water coverage. However, consistent with these ab initio results, our simulations do predict that a full molecular monolayer surface water coverage represents a relatively stable surface structure in terms of the lowest diffusional mobility of H2O molecules along the surface. Calculated energies of water adsorption are in good agreement with available experimental data.

Investigation of a series of synthetic alkali silicate gels and gels produced by the alkali silica reaction (ASR) in field concrete using 29Si NMR spectroscopy, X‐ray diffraction, and bulk chemical analysis shows that local structures of the synthetic and field gels are quite similar. The most abundant Si sites for the field and synthetic gels with similar compositions have Q3 polymerization, and the number of non‐bridging oxygens per Si is similar for these samples. These samples also yield a basal X‐ray diffraction peak near 8–12 Å, suggesting that the structure is dominated by sheet‐like units, consistent with the dominant Q3 polymerization. Calculations based on the relative site abundances of the sites observed by 29Si NMR and the bulk chemical compositions indicate that there is insufficient alkali to charge‐balance all the non‐bridging oxygens and that there is a significant concentration of Si–OH linkages. The results provide strong support for the basic structural concepts of the so‐called kanemite model for ASR gel proposed by Wieker and coworkers, although the overall gel structure is likely to be more complex.