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Investigations of synthetic magnesium silicate hydrate (M-S-H) samples have shown that M-S-H aged for 1 year can exhibit variable compositions with molar Mg/Si ratios in the range 0.7 ≤ Mg/Si ≤ 1.5. At lower Mg/Si ratio, additional silica is present whereas brucite is observed for Mg/Si ≥1.3. FT-IR and 29 Si NMR data reveal a high degree of silicate polymerisation, indicating the formation of silicate sheets. TGA shows the presence of bound water and of hydroxyl groups bound to Mg and as silanol groups in the M-S-H, in accord with 29 Si{ 1 H}CP/MAS and high-speed 1 H NMR measurements. Raman and XRD data suggest that the M-S-H structure is related to a disordered talc precursor at low Mg/Si and to a serpentine precursor at high Mg/Si ratio. Solubility products for M-S-H phases were calculated on basis of the compositions of the aqueous solutions and a solid solution model was suggested.

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The calcium silicate hydrate (C-S-H) phase resulting from hydration of a white Portland cement (wPc) in water and in a 0.3 M NaAlO(2) solution has been investigated at 14 and 11 hydration times, respectively, ranging from 6 h to 1 year by (27)Al and (29)Si MAS NMR spectroscopy. (27)Al MAS NMR spectra recorded at 7.05, 9.39, 14.09, and 21.15 T have allowed a determination of the (27)Al isotropic chemical shift (delta(iso)) and quadrupolar product parameter (P(Q) = C(Q)) for tetrahedrally coordinated Al incorporated in the C-S-H phase and for a pentacoordinated Al site. The latter site may originate from Al(3+) substituting for Ca(2+) ions situated in the interlayers of the C-S-H structure. The spectral region for octahedrally coordinated Al displays resonances from ettringite, monosulfate, and a third aluminate hydrate phase (delta(iso) = 5.0 ppm and P(Q) = 1.20 MHz). The latter phase is tentatively ascribed to a less-crystalline aluminate gel or calcium aluminate hydrate. The tetrahedral Al incorporated in the C-S-H phase has been quantitatively determined from (27)Al MAS spectra at 14.09 T and indirectly observed quantitatively in (29)Si MAS NMR spectra by the Q(2)(1Al) resonance at -81.0 ppm. A linear correlation is observed between the (29)Si MAS NMR intensity for the Q(2)(1Al) resonance and the quantity of Al incorporated in the C-S-H phase from (27)Al MAS NMR for the different samples of hydrated wPc. This correlation supports the assignment of the resonance at delta(iso)((29)Si) = -81.0 ppm to a Q(2)(1Al) site in the C-S-H phase and the assignment of the (27)Al resonance at delta(iso)((27)Al) = 74.6 ppm, characterized by P(Q)((27)Al) = 4.5 MHz, to tetrahedrally coordinated Al in the C-S-H. Finally, it is shown that hydration of wPc in a NaAlO(2) solution results in a C-S-H phase with a longer mean chain length of SiO(4) tetrahedra and an increased quantity of Al incorporated in the chain structure as compared to the C-S-H phase resulting from hydration of wPc in water.

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Mechanochemical synthesis using CeCl 3 -MBH 4 (M = Li, Na or K) mixtures are investigated and produced a new compound, LiCe(BH 4 ) 3 Cl, which crystallizes in a cubic space group I4̅ 3m, a = 11.7204(2) Å. The structure contains isolated tetranuclear anionic clusters [Ce 4 Cl 4 (BH 4 ) 12 ] 4− with a distorted cubane Ce 4 Cl 4 core, charge-balanced by Li + cations. Each Ce atom coordinates three chloride ions and three borohydride groups via the η 3 −BH 3 faces, thus completing the coordination environment to an octahedron. Combination of synchrotron radiation powder X-ray diffraction (SR-PXD), powder neutron diffraction and density functional theory (DFT) optimization show that Li cations are disordered, occupying 2/3 of the 12d Wyckoff site. DFT calculation indicates that LiCe(BH 4 ) 3 Cl is stabilized by higher entropy rather than lower enthalpy, in accord with the disorder in Li positions. The structural model also agrees well with the very high lithium ion conductivity measured for LiCe(BH 4 ) 3 Cl of 1 × 10 −4 Scm −1 at T = 20°C. In situ SR-PXD reveals that the decomposition products consist of LiCl, CeB 6 and CeH 2 . The Sieverts measurements show that 4.7 wt % H 2 is released during heating to 500°C. After rehydrogenation at 400°C and p(H 2 ) = 100 bar for 24 h an amount of 1.8 wt % H 2 is released in the second dehydrogenation. The 11 B MAS NMR spectra of the central and satellite transitions for LiCe(B(D/H) 4 ) 3 Cl reveal highly asymmetric manifolds of spinning sidebands from a single 11 B site, reflecting dipolar couplings of the 11 B nuclear spin with the paramagnetic electron spin of the Ce 3+ ions.

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