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Metal closo-borates are attractive electrolytes for solid state batteries. Here we present a detailed investigation of the polymorphism and thermal and electrochemical properties of Li 2B 10H 10 and Li 2B 12H 12 and their composites, (1 − x)Li 2B 12H 12-xLi 2B 10H 10. A new polymorph, β-Li 2B 10H 10, is identified with a cubic structure, a = 9.567(1) Å (Fm3̄m), with dynamically disordered B 10H 10 2− anions. A sub-stoichiometric compound denoted as γ-Li 2B 10H 10−y is prepared by thermal treatment (380 °C, 1 hour) in hydrogen and can be indexed to a cubic face-centered unit cell with a = 9.9224(5) Å. The 7Li MAS NMR spectra along with spin-lattice relaxation (T 1) measured by 7Li saturation-recovery NMR experiments clearly reveal a high degree of dynamics assigned to increasing amounts of γ-Li 2B 10H 10−y, which is in accordance with the measured Li + ionic conductivity. Thermal treatment (380 °C, 1 hour) of Li 2B 12H 12 in argon reveals the highest degree of dynamics and Li + conductivity. The (1 − x)Li 2B 12H 12-xLi 2B 10H 10 composites are found to be physical mixtures of γ-Li 2B 10H 10−y and Li 2B 12H 12 with minor amounts of α-Li 2B 10H 10, and their Li + conductivities are proportional to the amount of γ-Li 2B 10H 10−y. The highest Li + conductivity is observed for γ-Li 2B 10H 10−y: σ(Li +) = 7.6 × 10 −6 S cm −1 at 30 °C and 7.2 × 10 −3 S cm −1 at T = 330 °C. Cyclic voltammetry of γ-Li 2B 10H 10−y reveals an oxidative stability up to 2.8 V vs. Li/Li +, and a stable plating and stripping of lithium.

The partial replacement of Portland cement by aluminosilicate-rich supplementary cementitious materials (SCMs) represents a valuable approach to lower the CO2 footprint of concrete. However, SCMs alter the composition and structure of the principal binding component, calcium-alumino-silicate-hydrate (C-(A)-S-H), a less-crystalline aluminum-substituted calcium silicate hydrate. The uptake and structural impact of alkalis and aluminum are investigated for synthesized C-(A)-S-H phases with different Ca/Si and Al/Si ratios and alkali (Na+) contents, using solid-state Na-23, Al-27, and Si-29 NMR as principal analytical tools. Si-29{H-1} CP/MAS NMR data propose that the -87 ppm resonance originates from a second type of Q(2) pairing sites most likely in the middle of octameric or longer silicate units. This assignment along with constraints induced by the silicate dreierketten structure results in reliable simulations of the Si-29 NMR spectra. A quantitative 1:1 relation between the Al/Si ratios from Si-29 NMR and the content of fourfold-coordinated Al from Al-27 NMR is observed, which reveals that the Si-29 Q(p)(2)(1Al) resonance is only associated with Al(IV) in C-(A)-S-H. Combined analysis of the Al-27 and Si-29 NMR spectra can account for sixfold-coordinated AI being present in the bridging sites of the silicate chains as proposed very recently. The sodium uptake is found to decrease with increasing Ca/Si ratio. For C-(A)-S-H phases with high Ca/Si ratios (Ca/Si greater than or similar to 1.0), sodium promotes the incorporation of Al(IV) in the silicate chains but not at low Ca/Si ratios (Ca/Si less than or similar to 1.0). The results indicate that the mutual uptake of alkali and AI ions is governed by more than one mechanism and depends on the composition/structure of the C-(A)-S-H phase.

The RILEM technical committee 282-CCL: Calcined Clays as Supplementary Cementitious Materials, investigates all the aspects related to calcined clays, from clay exploration and characterization to calcination process, hydration reactions and concrete properties. This white paper focuses on the hydration mechanisms of calcined clay-blended Portland cements, covering both 1:1 and 2:1 calcined clays. The pozzolanic reaction of calcined clay is detailed, and the main reaction products are described. The differences observed depending on the clay type are also discussed, as well as the potential influence of the secondary phases present in calcined clay. The factors controlling and limiting the reaction of calcined clay are investigated, evidencing the role of porosity saturation and refinement of the microstructure. The complete characterisation of the hydration of calcined clay cements is made possible by the determination of the reaction degree of calcined clay. Several methods are compared to estimate the extent of calcined clay reaction. The influence of clinker and limestone mineralogy are also discussed. Finally, guidelines for optimising the mixture design of calcined clay blended cements are provided, with special attention to sulphate adjustment and clinker factor.

Demolished concrete is a large carbon sink which has not been utilized yet. Carbonation of hydrated cement paste from old concrete can effectively store CO2, and in addition, the resulting carbonated cement paste can be used as a pozzolanic material in new composite cements. This concept reduces the CO2 footprint of cement and promotes circularity and recycling. This work investigates a semi-dry gas-solid process for the carbonation of recycled cement paste. Decreasing gas humidity and hence the content of water adsorbed on the solid cement grains limits the transport of reactants from the dissolving hydrates and the overall reaction kinetics. It also leads to co-precipitation of the carbonation products, i.e., calcium carbonate and the alumina-silica gel, into a single dense matrix within the original grains. A decreasing water availability increases also the complexity and heterogeneity of the microstructure formed, since calcium carbonate precipitates as different polymorphs, including an amorphous form, and because the final phase assemblage comprises intermediate phases such as decalcified C-(A)-S-H, remains of the original hydrates in addition to the final carbonation products.

Reductions of CO2 emissions associated with Portland cement production represent currently the main challenge for the cement industry. A promising approach is to substitute the traditional hydration of cement by carbonation of cement clinker for the hardening of the material in concrete production. This work is a tailor-made experimental approach to explore the mechanisms of Portland clinker carbonation under wet conditions. The carbonation is found to be fast at the beginning of the reaction, provided enough CO2 is present in the system. Particularly, the calcium silicate phases react rapidly, where the kinetics is explained by the high undersaturation of these phases. Furthermore, the carbonation reaction can be divided into three stages when the reaction is limited by the different mechanisms: precipitation of products or dissolution of clinker or CO2. The main carbonation products are calcium carbonate and amorphous alumina silica gel. These phases precipitate in a different locations forming a special microstructural pattern.

Fast Li-ion conductivity at room temperature is a major challenge for utilization of all-solid-state Li batteries. Metal borohydrides with neutral ligands are a new emerging class of solid-state ionic conductors, and here we report the discovery of a new mono-methylamine lithium borohydride with very fast Li+ conductivity at room temperature. LiBH4⋅CH3NH2 crystallizes in the monoclinic space group P21/c, forming a two-dimensional unique layered structure. The layers are separated by hydrophobic −CH3 moieties, and contain large voids, allowing for fast Li-ionic conduction in the interlayers, σ(Li+)=1.24×10−3 S cm−1 at room temperature. The electronic conductivity is negligible, and the electrochemical stability is ≈2.1 V vs Li. The first all-solid-state battery using a lithium borohydride with a neutral ligand as the electrolyte, Li-metal as the anode and TiS2 as the cathode is demonstrated.

Design of new functional materials with fast Mg-ion mobility is crucial for the development of competitive solid-state magnesium batteries. Herein, we present new nanocomposites, Mg(BH

Design of new functional materials with fast Mg-ion mobility is crucial for the development of competitive solid-state magnesium batteries. Herein, we present new nanocomposites, Mg(BH4)2·1.6NH3-Al2O3, reaching a high magnesium conductivity of σ(Mg2+) = 2.5 × 10-5 S cm-1 at 22 °C assigned to favorable interfaces between amorphous state Mg(BH4)2·1.6NH3; inert and insulating Al2O3 nanoparticles; and a minor fraction of crystalline material, mainly Mg(BH4)2·2NH3. Furthermore, quasi-elastic neutron scattering reveals that the Mg2+-ion mobility in the solid state appears to be correlated to relatively slow motion of NH3 molecules rather than the fast dynamics of BH4- complexes. The nanocomposite is compatible with a metallic Mg anode and shows stable Mg2+ stripping/plating in a symmetric cell and an electrochemical stability of ∼1.2 V. The nanocomposite has high mechanical stability and ductility and is a promising Mg2+ electrolyte for future solid-state magnesium batteries.

Tricalcium aluminate (Ca

Dalton transactions 49(38), 13449 - 13461 (2020). doi:10.1039/D0DT02795B, Spinels are of essential interest in the solid-state sciences with numerous important materials adopting this crystal structure. One defining feature of spinel compounds is their ability to accommodate a high degree of tailorable point defects, and this significantly influences their physical properties. Standard defect models of spinels often only consider metal atom inversion between octahedral and tetrahedral sites, thereby neglecting other defects such as interstitial atoms. In addition, most studies rely on a single structural characterization technique, and this may bias the result and give uncertainty about the correct crystal structure. Here we explore the virtues of multi-technique investigations to limit method and model bias. We have used Pair Distribution Function analysis, Rietveld refinement and Maximum Entropy Method analysis of Powder X-ray Diffraction data, Zn edge Extended X-ray Absorption Fine Structure, and solid-state $^{27}$Al Nuclear Magnetic Resonance to study the structural defects in ZnAl$_2$O$_4$ spinel samples prepared by either microwave hydrothermal synthesis, supercritical flow synthesis, or spark plasma sintering. In addition, the samples were subjected to thermal post treatments. The study demonstrates that numerous synthesis dependent defects are present and that the different synthesis pathways allow for defect tailoring within the ZnAl$_2$O$_4$ structure. This suggests a pathway forward for optimization of the physical properties of spinel materials., Published by Soc., London

Reactivity of glasses is predominantly linked to the degree of depolymerization of the glass structure. In this work, eight calcium aluminosilicate glasses were synthesized with compositions reflecting the glassy phases of industrial fly ashes and slags. The chosen composition ranges allow for isolation and identification of the roles of Ca and Al. The reactivity of the glasses is found to be mainly dependent on the CaO content as calcium depolymerizes the glass structure and increases the rate of reaction of the glasses. The effect of Al 2 O 3 on glass reactivity is less pronounced and relies on chemical weakening of the glass structure. However, an increasing alumina content has a pronounced effect on the hydrate phase assemblage, bound water content, portlandite consumption and the heat of reaction. The resulting compressive strength of composite cement mortars incorporating the synthesized CaO-Al 2 O 3 -SiO 2 glasses is found to be a function of both the degree of glass reaction and the actual phase assemblage.

An approach based on enforced, wet carbonation of cement fines obtained from recycled concrete and its application as an SCM in new composite cements is presented as a new carbon capture and utilization technology. While the carbonation products are stable at a wide range of conditions, it is found that alkalis have a strong impact on product properties, as shown by carbonation in NaOH solutions in this study. Calcium carbonate precipitates mainly as calcite, regardless of the alkali concentration, however, the alkalis influence the size of the calcite crystals, which are smaller at low alkali concentrations. Alkalis modify also the structure of the alumina-silica gel, as a result of absorption of either sodium or calcium ions in this phase. Furthermore, alkali ions present in the solution influence directly the sulphate content of the carbonated cement paste, since a higher alkali concentration in the solution promotes leaching of sulphate.

The present work investigates the hydration and evolution of solid phase assemblage as a function of sulphate source in ternary Portland cement (PC), calcium aluminate cement (CAC) and calcium sulphate (CS¯HX) cement pastes. Two binders are compared, a PC‒rich and a CAC ‒ CS¯Hx ‒rich paste, containing gypsum and anhydrite as sulphate carrier, using a multi-method approach including calorimetry, XRD, TGA, MAS NMR spectroscopy, microscopy and thermodynamic modelling. The overall phase assemblage is very similar for the two-sulphate source in both PC-rich and CAC ‒ CS¯Hx−rich systems. However, the quantitative X-ray analysis, TGA and the 27Al, 29Si NMR show that the amounts of the crystalline hydrates and X-ray amorphous phases are influenced by the type of sulphate. In the long-term hydration, the anhydrite-bearing formulations exhibit the highest amount of ettringite, whereas the gypsum-containing samples develop a higher fraction of AFm phases and X-ray amorphous hydrates. This difference may relate to faster dissolution kinetics of gypsum compared to anhydrite in the studied ternary blends. For the CAC ‒ CS¯Hx −rich pastes, gehlenite from CAC (C2AS) shows hydraulic activity, which primarily results in the precipitation of strätlingite. Higher amounts of strätlingite are identified in the gypsum bearing samples, suggesting that the type of sulphate source impacts the hydration of silicate-bearing phases. Finally, the phase assemblages from thermodynamic modelling (using the GEMS software) are found to be in good agreement with those observed experimentally, although some differences occur as a result of kinetic effects.

CO2 mineralization using alkaline waste materials and by-products is a promising technology to reduce CO2 emissions. This work investigates the impact of alkali sulfates on the carbonation process. Detailed investigations of the carbonation reaction show that the sulfates are important phases impacting the mineralization. Alkalis alone accelerate the kinetics and change the morphology of the precipitated phases. Sulfates additionally reduce the amount of CO2 mineralized since a part of calcium precipitates as calcium sulfate. The mutual interaction between alkalis and sulfate ions provides a tool to control the mineralization kinetics and especially the extent of carbonation by preventing calcium sulfate precipitation at surplus of alkalis. Furthermore, sulfate-containing materials, which so far have not been considered as suitable for CO2 mineralization (e.g. gypsum), can now be considered for CO2 sequestration. A modification of the Steinour formula, used for calculations of the carbonation potential, is proposed to account for the observed effects.

In the present research, an alternative approach to produce supplementary cementitious materials (SCMs) based on the carbon capture and utilization is developed. The approach focuses on enforced carbonation of cement pastes obtained from recycled concrete and its application as SCM. This work focuses on the effect of alkalis in the starting solution on the carbonation mechanism of ground hydrated cement pastes in a wet reactor. The enforced carbonation of cement paste is a rapid process at ambient temperature and pressure being close to complete reaction within a few hours of carbonation, independently on alkali concentration. However, alkalis have a complex impact on the carbonation reaction as they accelerate the initial stages of the carbonation reaction, while the kinetics of the middle stages is retarded. The final degree of carbonation is only slightly affected by the alkali concentration in the solution. The origin of these effects can be explained by relating them to the evolution of solid and solution properties. Additionally, the alkali concentration has an impact on the morphology of the main carbonation products, that is, calcite and the alumina-silica gel.

Chemical science tbd, 1-12 (2021). doi:10.1039/D1SC05190C, The atomic structures, and thereby the coordination chemistry, of metal ions in aqueous solution represent a cornerstone of chemistry, since they provide first steps in rationalizing generally observed chemical information. However, accurate structural information about metal ion solution species is often surprisingly scarce. Here, the atomic structures of Ga$^{3+}$ ion complexes were determined directly in aqueous solutions across a wide range of pH, counter anions and concentrations by X-ray pair distribution function analysis and $^{71}$Ga NMR. At low pH ( 12 tetrahedrally coordinated gallium ions surrounded by ordered solvent are observed. The effects of varying either the concentration or counter anion were minimal. The present study provides the first comprehensive structural exploration of the aqueous chemistry of Ga$^{3+}$ ions with atomic resolution, which is relevant for both semiconductor fabrication and medical applications., Published by RSC, Cambridge

Isotropic and anisotropic couplings between the 11B nuclear spin and the electron spin of paramagnetic electrons are observed in 11B MAS NMR spectra of α-Pr(BH4)3 and LiCe(BH4)3Cl. The 11B NMR spectra of the central and satellite transitions are strongly influenced by the anisotropic nuclear spin-paramagnetic electron spin dipole-dipole interaction, which affects the spectra in a similar manner as the 11B chemical shift anisotropy. The 11B MAS NMR spectra are analyzed numerically, considering the quadrupole interaction and the anisotropic paramagnetic electron-nuclear spin dipole coupling along with the relative orientation of the two tensorial interactions. The observed isotropic shifts (δobs) show a linear dependency with the inverse temperature for both compounds, indicating that δobs is dominated by the contribution from the isotropic hyperfine shift. A similar temperature dependency is observed for the paramagnetic shift anisotropy for α-Pr(BH4)3. The isotropic and anisotropic paramagnetic interactions are approximately 5 and 4 times larger for α-Pr(BH4)3 as compared to LiCe(BH4)3Cl. This reflects mainly the difference in electron spin for the Pr3+ and Ce3+ ions and that the B site in α-Pr(BH4)3 has two Pr3+ ions within a 3 Å distance, whereas boron in LiCe(BH4)3Cl only has a single Ce3+ site within this distance.

Calcium aluminosilicate (CAS) glasses are the main reactive component in supplementary cementitious materials such as fly ashes and slags, which may also include significant amounts of magnesium. Eighteen CAS glasses have been synthesized in six series with 0, 25, and 50 mol% of Ca substituted by Mg. Their structure, pozzolanic reactivity and impact on Portland cement hydration are investigated by 29Si and 27Al NMR spectroscopy and TGA analysis. The aluminosilicate network is only slightly affected by the Mg for Ca substitution, although an increased distortion of the network is observed, which is ascribed to a lowering of the Mg coordination state relative to Ca. The glass reactivity is mainly governed by the network depolymerization, which increases with the MgO + CaO content, with Mg substitution only having a minor impact. Increasing Mg contents in the glasses lead to OH-hydrotalcite formation and a smaller fraction of Al incorporated in the C-A-S-H phase.

Hierarchical H-ZSM-5 zeolites are a promising class of heterogeneous catalysts that have shown encouraging results in lab-scale studies for the production of gasoline from dimethyl ether (DTG conversion). However, the influences of mesopore formation and shaping on various catalyst properties are still under debate. In this study, a series of H-ZSM-5 zeolites with hierarchical pore structures were prepared by modifying commercially available zeolites via alkaline treatment ("desilication"). The powdered zeolites were shaped into technical catalyst bodies by wet extrusion using either silica or alumina binders. All materials were extensively characterized. The different interactions during alkaline treatment were related to the observed modifications in the zeolite properties of the materials obtained. Although many properties of modified and untreated zeolite powders remained predominantly unchanged in their shaped catalyst equivalents, both binders affected certain material characteristics, particularly those related to their acidity. Finally, preliminary tests showed enhanced catalytic performance of hierarchical ZSM-5 catalysts in DTG conversion.

Spinels are of essential interest in the solid-state sciences with numerous important materials adopting this crystal structure. One defining feature of spinel compounds is their ability to accommodate a high degree of tailorable point defects, and this significantly influences their physical properties. Standard defect models of spinels often only consider metal atom inversion between octahedral and tetrahedral sites, thereby neglecting other defects such as interstitial atoms. In addition, most studies rely on a single structural characterization technique, and this may bias the result and give uncertainty about the correct crystal structure. Here we explore the virtues of multi-technique investigations to limit method and model bias. We have used Pair Distribution Function analysis, Rietveld refinement and Maximum Entropy Method analysis of Powder X-ray Diffraction data, Zn edge Extended X-ray Absorption Fine Structure, and solid-state 27Al Nuclear Magnetic Resonance to study the structural defects in ZnAl2O4 spinel samples prepared by either microwave hydrothermal synthesis, supercritical flow synthesis, or spark plasma sintering. In addition, the samples were subjected to thermal post treatments. The study demonstrates that numerous synthesis dependent defects are present and that the different synthesis pathways allow for defect tailoring within the ZnAl2O4 structure. This suggests a pathway forward for optimization of the physical properties of spinel materials.

Magnesium batteries are considered promising solutions for future energy storage beyond the lithium-ion battery era. However, the development of magnesium batteries is hindered by the lack of suitable electrolytes. Here we present solid Mg2+ electrolytes based on ammine magnesium borohydride composites, Mg(BH4)2·xNH3, which have conductivities ca. three orders of magnitude higher than the parent compounds (x = 1, 2, 3, and 6). A nanocomposite formed by the Mg(BH4)2·xNH3 composite and MgO nanoparticles exhibits outstanding Mg2+ conductivity of the order of 10-5 S cm-1 at room temperature and around 10-3 S cm-1 at moderate temperature (ca. 70 °C), with an activation energy for Mg2+ conduction of Ea ∼108 kJ/mol (1.12 eV) and high thermal stability (Tdec = 120 °C). Characterization using solid-state nuclear magnetic resonance, powder X-ray diffraction, and transmission electron microscopy reveals that the high Mg2+ conductivity is attributed to amorphization of Mg(BH4)2·xNH3 resulting in a highly dynamic state. This nanocomposite is compatible with a Mg metal anode and allows stable Mg plating/stripping (at least 100 cycles) in a symmetric cell. The results represent a major advancement of solid-state multivalent ion conductors here demonstrated for Mg2+.

Immobilized piperazine on the surface of graphene oxide (piperazine-GO) is synthesized and characterized by different methods such as FT-IR, solid-state 29Si{1H} and 13C{1H} CP/MAS NMR, elemental analysis, TGA, TEM, FE-SEM, XPS, and TPD. Subsequently, it is used as a heterogeneous bifunctional acid–base catalyst for the efficient multicomponent reaction of malononitrile, different active compounds containing enolizable C–H bonds and various aryl/alkyl aldehydes in aqueous ethanol. A wide variety of 2-amino-3-cyano-4H-chromenes are synthesized in the presence of this heterogeneous catalyst in good to high yields and with short reaction times. The catalyst is easily separated and reused for at least six times without significant loss of activity. The acidic nature of GO improves the catalytic activity of the supported piperazine and also provides heterogeneity to the catalyst. Use of aqueous ethanol as a green solvent, high turnover numbers (TON), facile catalyst recovery and reuse, simple work-up and generality of the method make this protocol an environmentally benign procedure for the synthesis of the title heterocycles. Financial support for this project by the University of Birjand Research Council and access to the solid-state NMR facilities at the Department of Chemistry, Aarhus University and the XPS facilities of the University of Alicante are acknowledged.

Ammine metal borohydrides show potential for solid-state hydrogen storage and can be tailored toward hydrogen release at low temperatures. Here, we report the synthesis and structural characterization of seven new ammine metal borohydrides, M(BH4)3·nNH3, M = La (n = 6, 4, or 3) or Ce (n = 6, 5, 4, or 3). The two compounds with n = 6 are isostructural and have new orthorhombic structure types (space group P21212) built from cationic complexes, [M(NH3)6(BH4)2]+, and are charge balanced by BH4-. The structure of Ce(BH4)3·5NH3 is orthorhombic (space group C2221) and is built from cationic complexes, [Ce(NH3)5(BH4)2]+, and charge balanced by BH4-. These are rare examples of borohydride complexes acting both as a ligand and as a counterion in the same compound. The structures of M(BH4)3·4NH3 are monoclinic (space group C2), built from neutral molecular complexes of [M(NH3)4(BH4)3]. The new compositions, M(BH4)3·3NH3 (M = La, Ce), among ammine metal borohydrides, are orthorhombic (space group Pna21), containing molecular complexes of [M(NH3)3(BH4)3]. A revised structural model for A(BH4)3·5NH3 (A = Y, Gd, Dy) is presented, and the previously reported composition A(BH4)3·4NH3 (A = Y, La, Gd, Dy) is proposed in fact to be M(BH4)3·3NH3 along with a new structural model. The temperature-dependent structural properties and decomposition are investigated by in situ synchrotron radiation powder X-ray diffraction in vacuum and argon atmosphere and by thermal analysis combined with mass spectrometry. The compounds with n = 6, 5, and 4 mainly release ammonia at low temperatures, while hydrogen evolution occurs for M(BH4)3·3NH3 (M = La, Ce). Gas-release temperatures and gas composition from these compounds depend on the physical conditions and on the relative stability of M(BH4)3·nNH3 and M(BH4)3

Ammine metal borohydrides show potential for solid-state hydrogen storage and can be tailored toward hydrogen release at low temperatures. Here, we report the synthesis and structural characterization of seven new ammine metal borohydrides

The carbonation mechanisms of ground, hydrated cement pastes that mimic recycled concrete fines are investigated under direct wet carbonation. The carbonation is a sequential processes including dissolution of the hydrates, transport of the dissolved material to the precipitation sites and precipitation of the reaction products. During the first stages of carbonation, when portlandite reacts, the reaction is limited by the amount of dissolved CO2 and potentially by the calcite precipitation rate. When portlandite is depleted, the kinetics is dominated by the dissolution of other hydrates and diffusion of calcium into the solution. The main carbonation products are calcite and an alumina-silica (hydrate) gel. The hydrotalcite-like phase appears to be stable towards carbonation under the experimental conditions employed in this work. The CO2 concentration and the paste composition have a limited influence on the reaction mechanisms as well as on products formed.

Octahydridoborate, i.e. [B3H8](-) containing compounds, have recently attracted interest for hydrogen storage. In the present study, the structural, hydrogen storage, and ion conductivity properties of KB3H8 have been systematically investigated. Two distinct polymorphic transitions are identified for KB3H8 from a monoclinic (alpha) to an orthorhombic (alpha ') structure at 15 degrees C via a second-order transition and eventually to a cubic (beta) structure at 30 degrees C by a first-order transition. The beta-polymorph of KB3H8 displays a high degree of disorder of the [B3H8](-) anion, which facilitates increased cation mobility, reaching a K+ conductivity of similar to 10(-7) S cm(-1) above 100 degrees C. beta-KB3H8 starts to release hydrogen at similar to 160 degrees C, simultaneously with the release of B5H9 and trace amounts of B2H6. KBH4 and K-3(BH4)(B12H12) are identified as crystalline decomposition products above 200 degrees C, and the formation of a KBH4 deficient structure of K3-x(BH4)(1-x)(B12H12) is observed at elevated temperature. The hydrogen-uptake properties of a KB3H8-2KH composite have been examined under 380 bar H-2, resulting in the formation of KBH4 at T >= 150 degrees C along with higher metal hydridoborates, i.e. K2B9H9, K2B10H10, and K2B12H12.

The structural arrangement of alkali-modified calcium aluminosilicate glasses has implications for important properties of these glasses in a wide range of industrial applications. The roles of sodium and potassium and their competition with calcium as network modifiers in peralkaline aluminosilicate glasses have been investigated by 27Al and 29Si MAS NMR spectroscopy. The 29Si MAS NMR spectra are simulated using two models for distributing Al in the silicate glass network. One model assumes a hierarchical, quasi-heterogeneous aluminosilicate network, whereas the other is based on differences in relative lattice energies between Si-O-Si, Al-O-Al, and Si-O-Al linkages. A systematic divergence between these simulations and the experimental 29Si NMR spectra is observed as a function of the sodium content exceeding that required for stoichiometric charge-balancing of the negatively charged AlO 4 tetrahedra. Similar correlations between simulations and experimental 29Si NMR spectra cannot be made for the excess calcium content. Moreover, systematic variations in the 27Al isotropic chemical shifts and the second-order quadrupole effect parameters, derived from the 27Al MAS NMR spectra, are reported as a function of the SiO 2 content. These observations strongly suggest that alkali ions preferentially charge-balance AlO 4 3- as compared to alkaline earth (calcium) ions. In contrast, calcium dominates over the alkali ions in the formation of nonbridging oxygens associated with the SiO 4 tetrahedra.

This paper investigates the effect of KOH and NaOH on C-S-H structure and solubility. Both KOH and NaOH have a similar effect, they increase pH values and silicon concentrations, and decrease calcium concentrations. At higher alkali hydroxide concentrations, more portlandite precipitates, while amorphous silica dissolves. This increases the Ca/SiC-S-H at low Ca/Sitarget but lowers the maximum Ca/SiC-S-H from 1.5 to 1.2 in 1 M KOH/NaOH. The amount of alkalis bound in C-S-H increases with increasing alkali hydroxide concentrations and is higher at low Ca/SiC-S-H. KOH/NaOH lead to a structural rearrangement in C-S-H, increasing the interlayer distance, number of layers stacked in c direction and shortening the silica chains. The mean chain lengths (MCL) estimated from FTIR and Raman spectroscopy agree well with the trends from 29Si NMR. Comparison with the independently developed CASH+ thermodynamic model showed a good agreement between the observed and modelled changes, including the shortening of the MCL.

A new potassium tetraamidoboranealuminate, K[Al(NH2BH3)4], has been synthesized by a mechanochemical reaction between KAlH4 and NH3BH3. The compound, K[Al(NH2BH3)4], crystallizes in a triclinic unit cell with space group symmetry P-1. The crystal structure consists of [K(NH2BH3)6]5 - octahedra which facilitate the bridging between K+ in 1D chains, while also bridging K+ to Al3+ to connect the 1D chains in a 3D network. Thermal analysis reveals that K[Al(NH2BH3)4] decomposes in two exothermic steps at T ~ 94 and 138 °C and releases primarily hydrogen. The total gas release amounts to ~6.0 wt% H2. The decomposition products are investigated ex situ by powder X-ray diffraction, infrared spectroscopy, and 11B and 27Al NMR and identified as KBH4 and amorphous phases, possibly BN3, N2BH, and/or NBH2 whereas aluminum is found in four-, five-, and six-fold coordination. Unfortunately, the decomposed sample shows no hydrogen absorption at T = 260 °C and p(H2) = 110 bar.

In this work, a new type of addition reaction between La(BH4)3 and LiX, X = Cl, Br, I, is used to synthesize LiLa(BH4)3Cl and two new compounds LiLa(BH4)3X, X = Br, I. This method increases the amounts of LiLa(BH4)3X and the sample purity. The highest Li-ion conductivity is observed for LiLa(BH4)3Br, 7.74 × 10-5 S/cm at room temperature (RT) and 1.8 × 10-3 S/cm at 140°C with an activation energy of 0.272 eV. Topological analysis suggests a new lithium ion conduction pathway with two new different types of bottleneck windows. The sizes of these windows reveal an opposite size change with increasing lattice parameter, that is, increasing size of the halide ion in the structure. Thus, we conclude that the sizes of both windows are important for the lithium ion conduction in LiLa(BH4)3X compounds. The lithium ion conductivity is measured over one to three heating cycles and with different contacts (gold or carbon) between the electrodes and the electrolyte. Moreover, 11B MAS NMR is used to verify the contents of the samples, whereas thermogravimetric analysis shows 4.8 and 3.6 wt % of hydrogen release for LiLa(BH4)3Cl and LiLa(BH4)3Br in the temperature range RT to 400°C. (Graph Presented).

Wet chemistry and spectroscopic investigations were conducted to study Fe(III) uptake by calcium silicate hydrate (C–S–H) at different Ca/Si ratios. Wet chemistry experiments were carried out by using a 55Fe radiotracer while 29Si NMR and XAS spectroscopy were performed on C–S–H phases loaded with different Fe(III) concentrations. Sorption kinetics experiments indicate that equilibrium was attained within 30 days. Over the studied concentration range, Fe(III) sorption was linear, irrespective of the difference in pH of the suspension and the Ca/ Si of C–S–H. In addition, Fe(III) sorption on C–S–H phases was significantly stronger than Al(III) sorption. The total Fe(III) uptake by C–S–H phases, however, was limited by the lower solubility of Fe(OH)3 compared to Al (OH)3; up to 1 mol Fe/kg C–S–H (molar Fe(III)/Si ~ 0.001) could be taken up. 29Si NMR and EXAFS data suggest Fe(III) uptake in octahedral coordination into the interlayer of the C–S–H phases with Ca/Si ratios 1.2 and 1.5. However, such an uptake mechanism appears unlikely in the case of the C–S–H phase with Ca/Si 0.8 because structural parameters of Fe(III) deduced from EXAFS are different., Applied Geochemistry, 113, ISSN:0883-2927, ISSN:1872-9134

A hydrophilic heterogeneous cobalt catalyst of chitosan, denoted as mTEG-CS-Co-Schiff-base, has been successfully prepared. This newly synthesized catalyst was characterized by different methods such as XRD, FE-SEM, TEM, TGA, FT-IR, 13C{1H} CP/MAS NMR, XPS and ICP analyses. The catalyst displayed excellent activity for the palladium and fluoride-free Hiyama, Suzuki, Heck and Hirao reactions of various aryl iodides, bromides and chlorides (i.e., the most challenging aryl halides which are cheaper and more widely available than aryl iodides and bromides) in water. The presence of triethylene glycol tags with hydrophilic character on the Co-complex supported on chitosan provides dispersion of the catalyst particles in water, which leads to higher catalytic performance and also facile catalyst recovery by successive extraction. It was reused for at least six successive runs without any discernible decrease in its catalytic activity or any remarkable changes in catalyst structure. The use of water as a green solvent, without requiring any additive or organic solvent, as well as use of a low cost and abundant cobalt catalyst instead of expensive Pd catalysts along with the catalyst recovery and scalability, make this method favorable from environmental and economic points of view for the C–C and C(sp2)–P coupling reactions. Notably, this is the first report on the application of a cobalt catalyst in Hiyama reactions. Financial support of this project by University of Birjand Research Council and Iran National Science Foundation (INSF, Grant Number: 96017097) is acknowledged.

Metakaolin can be considered as a model compound for an aluminosilicate-rich supplementary cementitious material (SCM) because of its composition and highly pozzolanic properties. This work presents a systematic investigation of the hydration of white Portland cement (wPc)–metakaolin (MK) blends cured at different temperatures by 29Si and 27Al MAS NMR with the main focus on the structure and composition of the C-(A)-S-H phase. White Portland cement–MK paste samples with wPc replacement levels of 0, 10, 20, and 30 wt% have been prepared and hydrated for 1–8 weeks at five different temperatures (5, 20, 40, 60, and 80 °C). Information on the degree of reaction for alite, belite, and MK is derived from the 29Si NMR spectra and shows that the hydration of the wPc–MK blends is accelerated with increasing temperature except for the blend with the highest MK level (30 wt%). The AlIV/Si ratio of the C-(A)-S-H phase is found to be independent on the hydration time but increases slightly with curing temperature. On the other hand, a significant increase in the average aluminosilicate chain lengths is observed for blends with increasing temperature, reflecting a decrease in the Ca/Si ratio for the C-(A)-S-H phase. Stratlingite is present in the wPc–MK blends at 20 °C and the fraction of this phase decreases with increasing curing temperature.

Calcined clays are attracting significant research attention because of their potential to partially replace CO2-intensive portland cement. This potential depends largely on their reactivity, especially dissolution under alkaline conditions. Identification and characterization of reactive sites in these amorphous calcined clays has so far not been reported. Here, we investigate kaolinite (1:1 clay) and montmorillonite (2:1 clay) calcined at different temperatures under alkaline conditions (0.1 mol/L NaOH). Solution compositions are determined in batch dissolution experiments, whereas 27Al and 29Si MAS and CP/MAS NMR are used to investigate the structure of the undissolved residues to identify sites that are reactive and undergo preferential dissolution. The highest Si and Al dissolution rates for kaolinite are observed for calcination at 700°C, corresponding to the temperature of optimum reactivity, whereas the rates decrease and become increasingly incongruent at higher temperatures. The Si and Al dissolution rates for optimally calcined kaolinite are 4 and 12 times larger than the corresponding rates for optimally calcined montmorillonite, in accord with the much higher reactivity of calcined kaolinite compared to calcined 2:1 clays. This superior performance of kaolinite is explained by novel 27Al NMR results, which show strong evidence for preferential dissolution of highly reactive pentahedral aluminum sites.

Ettringite (Ca-6[Al(OH)(6)](2)(SO4)(3)center dot 26H(2)O) is the first hydration product formed during Portland cement hydration. Al-27 MAS NMR has been used in a wide number of studies to detect and quantify ettringite in hydrated cement blends by the observation of a single, narrow resonance at 13-14 ppm. This work reports the first observation of resonances from two distinct Al sites in octahedral coordination for ettringite, employing Al-27 MAS and MQMAS NMR at an ultrahigh magnetic field (22.3 T). Thereby, the Al-27 NMR spectra are in agreement with the most accepted trigonal model for the ettringite structure. Al-27 quadrupole coupling parameters and isotropic chemical shifts for the two Al sites are determined from simulations and least-squares optimization of slow-speed Al-27 MAS NMR spectra of the satellite transitions. These data reveal that the local environments for the two octahedral Al sites are very similar, in accord with the most recent XRD refinements of the ettringite structure. Finally, the significant improvement in spectral resolution by the application of an ultrahigh magnetic field is illustrated by the detection of the two Al sites from ettringite in a hydrated cement mimicking the composition of a calcium sulfoaluminate cement.

In this paper, tris(hydroxymethyl) methylene ammonium acetate supported on GO as a new multifunctional heterogeneous catalyst was synthesized. After its characterization by different techniques such as FT-IR, TEM, FESEM, EDS, XPS, solid-state MAS NMR and elemental analysis, it was used as an efficient catalyst for the synthesis of hexahydroquinolines (HHQs) via a one-pot multi-component reaction. Different HHQs were synthesized in the presence of this heterogeneous metal-free catalyst in good to high yields at room temperature under solvent-free conditions. The catalyst was easily separated and reused at least five times without significant loss of activity. The acidic nature of GO improved the catalytic activity of the supported ILs and also provided heterogeneity to the ILs. This is the first report for the synthesis of HHQs in the presence of a multifunctional heterogeneous catalyst.

A new kind of solid gas chemical reactions has been investigated using solid-state powder H-2, C-13, and Si-29 NMR and EPR spectroscopies. These studies involve reactions between a silicate-created Si free-radical intermediate and a few ordinary gases such as isotopically H-2-, C-13-, and O-17-enriched methane ((CH4)-C-13 and CD4), carbon dioxide ((CO2)-C-13), hydrogen (H-2(2)) and oxygen (O-17(2)). The solid-state Si free-radical intermediate and gas reaction and silicate products are formed in a specially designed rotating apparatus, which by mechanical tumbling mimics the winds and collision speed of the mineral particles on Mars. It is shown that the "hard" quartz (SiO2) or corundum (alpha-AL(2)O(3)) grain particles, used to simulate the collision particles in a rotating Pyrex (borosilicate) reaction flask, act as an abrasive on the "soft" Pyrex flask and thereby create a silicate Si free-radical intermediate. EPR studies show that this radical is identical to the silicate radical intensively investigated by EPR from gamma-irradiation of Pyrex and other glasses and shown to constitute a submicrostructure of either silicate chains or helices. The intensity of the silicate Si free-radical EPR signal for the reaction product is strongly reduced or even disappears by performing the tumbling of the abrasive grain particles in an atmosphere of methane or other gases. C-13{H-1} and Si-29{H-1} CP/MAS NMR experiments of the reaction product with methane gas show the presence of one -bond CH3-Si equivalent to and HO-Si equivalent to covalent bonds in its structure and that sieving the product leads to a sensitivity enhancement by a factor of similar to 25. A flexible helical structure for the silicate Si free-radical intermediate is indicated by the preliminary results for the product resulting from the reaction with (CO2)-C-13, (encapsulation of the gas) and the indication of a congested methyl group in the product from reaction with methane.

The carbonation of Portland cement, metakaolin and limestone mortars has been investigated after hydration for 91 days and exposure to 1% (v/v) CO2 at 20 °C/57% RH for 280 days. The carbonation depths have been measured by phenolphthalein whereas mercury intrusion porosimetry (MIP), TGA and thermodynamic modeling have been used to study pore structure, CO2 binding capacity and phase assemblages. The Portland cement has the highest resistance to carbonation due to its highest CO2 binding capacity. The limestone blend has higher CO2 binding capacity than the metakaolin blends, whereas the better carbonation resistance of the metakaolin blends is related to their finer pore structure and lower total porosity, since the finer pores favor capillary condensation. MIP shows a coarsening of the pore threshold upon carbonation for all mortars. Overall, the CO2 binding capacity, porosity and capillary condensation are found to be the decisive parameters governing the carbonation rate.

Hydration kinetics for the principal phases of Portland cement blends have been incorporated in thermodynamic modeling (GEMS package), utilizing degrees of hydration from 29 Si MAS NMR. An empirical relationship for the reaction of these phases is established which includes three variable parameters that all can be estimated from the degrees of hydration. This approach is compared with thermodynamic equilibrium modeling (full hydration) for white Portland cement–metakaolin (0–30 wt.%) blends and for ternary blends of white Portland cement (65 wt.%)–metakaolin–limestone. The predicted phase assemblages have been compared with the phases identified by XRD, 27 Al and 29 Si MAS NMR which reveals that the incorporation of hydration kinetics improves the agreement between modeling and experiments. The results show also that the formation of stratlingite depends critically on the quantity of charge-balancing anions in the AFm phases, especially carbonate and sulfate anions, and on the degree of hydration for metakaolin.