Scanning Microscopy


Electron probe X-ray micro-analysis (EPXMA) and Laser microprobe mass analysis (LAMMA), were applied to characterize the leachate of sandy limestones of a Belgian cathedral.

Individual suspended particles, found in water that was sprayed over the cathedral walls ("1 each ate water"), were sized and analyzed by automated EPXMA-analysis, and classified with hierarchical cluster methods. LAMMA was used to gather more information about particles, present in the solution, as well as in suspension.

It was found that the leachate from black walls, had a high sulphate concentration and a large variety of particles in suspension, with different morphology and composition, with silicates as most abundant group. The leachate from white walls is characterized by a predominant Ca-rich suspension, with both original and recrystallized calcite particles, and by a much lower sulphate-ion concentration in the solution.

LAMMA-analysis revealed that the "organic" group of the EPXMA-analysis, consists mostly of carbon-containing fly-ash particles.

Hence, in general, it could be concluded that walls which are not subject to direct rainfall are generally covered with a gypsum crust, that turns black due to adhesion of soil dust and fly-ash particles, while white walls become thinner due to rainwater erosion of weathering products and original stone components.

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