Results from burial experiments with simulated medieval glasses
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Results from burial experiments with simulated medieval glasses Hannelore Roemich1 , Sandra Gerlach1 , Peter Mottner1 , Florias Mees2 , Patric Jacobs2 , Dirk van Dyck3 and Teresa Doménech Carbó4 ; 1 Fraunhofer-Institut fuer Silicatforschung (ISC), Bronnbach-Branch, D-98778 Wertheim, Germany; 2 University of Ghent, Belgium; 3 University of Antwerp, Belgium; 4 Polytechnical University of Valencia, Spain
ABSTRACT 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).
INTRODUCTION The interacting medium plays a dominant role during any kind of corrosion process. The reactions of glass in aqueous solutions have been well investigated. For weathering in the atmosphere, the experimental data are more difficult to interpret and do not always correlate with theoretical models. The reaction of glass in contact with soil is even more complex and only poorly investigated. Compared to corrosion in liquids or in humid air, corrosion in the soil renders more severe degradation, leading to thicker alteration layers (at least in humid soil) and a broader variety of alteration phenomena [1-4]. Archaeological glasses have been studied with emphasis on the structure of the alteration layer, the distribution of trace elements, the original glass composition and the environmental conditions [5-10]. Due to the large number of parameters involved and the long weathering periods, it has not been possible so far to draw conclusions, e.g. on the degradation of glasses as a function of the time of exposure in the soil [11, 12]. The long-term behaviour of glass in the soil or in contact with ground water is of interest to glass scientists with a background in archaeology [3, 13], but also to those with special interest in nuclear waste management [14-17]. Several attempts have been made to use ancient glasses as indicators for the performance of buried nuclear waste glasses [8, 18-20].
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In spite of differences in glass co
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