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During several hundred years of burial in the soil, glasses, especially those with medieval compositions, develop heavily corroded surfaces, showing phenomena such as local pitting, laminated layers and browning effects. For this study the damage phenomena have been characterised for three original glasses, using conventional methods (light microscopy and SEM of the surface and cross sections) and microfocus X-ray computed tomography (mCT), a new non-destructive analytical technique.The degradation of glass in the soil depends on a variety of parameters, concerned with the glass itself and with the burial environment. Since synergetic effects may complicate any mechanistic studies, laboratory experiments have been carried out under controlled conditions.Humid soil environments with a pH of 6.5 to 7.5 lead to the development of local microcracks on the surface, whereas more alkaline soil conditions (pH 8.0 to 9.0) favour the formation of laminated structures. The conclusions of the paper focus on the effect of glass composition (model glasses and archaeological glasses), soil conditions (variation of pH) and exposure time (23 months versus several centuries).

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Nuclear quadrupole interactions (NQI) were measured for several molybdenum-sulfur compounds by time differential perturbed angular correlation (TDPAC) spectroscopy using the 99Mo@-)99Tc probe. Compounds having the composition MoS2 of different origins and having different degrees of crystallinity, Li-intercalated MoS2, C00.5MoS2, and exfoliated single MoS2 slabs, were investigated. Crystalline and well-ordered 2H-MoS2 exhibits a characteristic NQI-frequency of 11 1 Mrads and axial symmetry. Dispersed MoSz prepared by thermal decomposition of various precursor compounds shows lower frequencies , and this effect is attributed to the presence of part of the Mo in octahedral coordination. Co0,sMoSz and Liintercalated MoS2 with Mo in octahedral coordination exhibit typical frequencies around 50 Mrad/s. Single MoS2 slabs prepared by exfoliation of Li,MoSz also give rise to a low frequency of 56 Mrads, this being indicative for octahedral Mo coordination. Highly disperse MoS2 samples typically contained additional minority species that have NQI-frequencies in the range 400 < w < 650 Mrads. These fractions were identified as Mo centers that have sulfur vacancies which are located along the edges of MoS2 platelets. These data are relevant for the interpretation of TDPAC spectra of sulfided supported Mo/Al2O3 catalysts. We show that formation steps of the sulfided phase and aging processes can be followed by TDPAC. Moreover, the observation of high-frequency fractions at 400 < w < 650 Mrads represents the first direct experimental detection of coordinatively unsaturated MoX+ sites at edges and comers of MoS2 slabs in these catalysts.

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