Filip Delalieux

Cultural heritage and the environment

Air pollution can have a significant influence on the weathering of monuments and on the deterioration of museum objects and prehistoric cave paintings. Three important mechanisms of stone weathering will be discussed, and an overview of analysis techniques invoked for the assessment of the degradation processes will be given. The effects of several air pollutants on works of art are reviewed, illustrated with examples of the micro-analysis of aerosols in two European museums. The influence of tourism on the preservation of prehistoric rock art is also addressed.

Environmental conditions controlling the chemical weathering of the Madara Horseman monument, NE Bulgaria

Abstract The conditions that led to the deterioration of the Madara Horseman sculpture, a relief carved in a sandy limestone cliff in north-east Bulgaria, were studied, with most emphasis on the chemical weathering at the stone–atmosphere interface. Total deposition sampled close to the monument contains high concentrations of NH 4 + and K + , which shows the influence of the dense vegetation in the area, and Ca 2+ , which reflects the cliffˈs weathering products. Ca 2+ is also one of the most important constituents (next to aluminosilicates) of the atmospheric particulate collected at the monument. S-rich particles are the most abundant particles in the size range – , K + and NO 3 – , is formed in the rain-sheltered areas of the monument. Secondly, karstic dissolution in the interior of the rock substrate leads to the formation of a hard carbonate crust at the surface of the sculpture. This natural surface hardening leads to a state of ‘auto-conservationˈ of the monument. The atmospheric composition seems to have only a limited influence on the deterioration of the Madara Horseman. Far more important are the micro-climatic conditions and the action of lichens.

Feasibility study of three-dimensional XRF spectrometry using μ-X-ray beams under grazing-exit conditions

Abstract Grazing-exit XRF (GE-XRF), where the X-ray fluorescence is measured at small take-off angles, is a method related to TXRF. It has been demonstrated that GE-XRF is useful for surface, thin-film and particle analyses. In GE-XRF, it is possible to use a μ-X-ray beam at a normal incidence. Thus, a laboratory GE-XRF instrument was developed in combination with a μ-XRF setup. A μ-X-ray beam was produced by the combination of a single capillary and a pinhole aperture. It was demonstrated that depth information could be obtained by using this setup and changing the exit angle. Therefore, this instrument enables measurement of surface-sensitive line scanning and elemental mapping under grazing-exit conditions. In principle, measuring the elemental X-ray mappings at different exit angles enables the reconstruction of three-dimensional elemental distributions. To confirm the feasibility of three-dimensional XRF, a type of Japanese lacquerware, ‘Tamamushi-nuri’, which has a layered structure near the surface, was measured.

DAMAGE FUNCTIONS AND MECHANISM EQUATIONS DERIVED FROM LIMESTONE WEATHERING IN FIELD EXPOSURE

In this article damage functions and mechanism equations areelaborated for Massangis limestone, exposed to ambientatmospheric conditions. Limestone slabs were placed in fivedifferent environments in Belgium and run-off water wascollected for chemical analyses, over a 3 yr period. Toelucidate the weathering mechanism and the relativecontributions of different deleterious factors, calciumconcentrations in run-off water were regressed versus thetotal (wet + dry) deposition of ions onto the stone, gaseousatmospheric pollutant concentrations and meteorological parameters. The data matrix (30 000 analytical results) was interpreted using Multiple Linear Regression (MLR) and PartialLeast Squares Regression (PLS). Mechanism equations and damagefunctions were first established for each of the five studiedsites separately and subsequently pooled regressions were calculated. A damage function is proposed and compared with limestone damage functions found in the literature, after introducing the field data presented in this work into the respective functions. Massangis limestone mass loss is bestpredicted with a PLS model. Rainwater volume is the most decisivefactor in causing mass loss at all sites, and sulphate andbicarbonate are the most important weathering products.Models established using MLR result in less reliablepredictions of mass loss compared to PLS.

Micro X-ray fluorescence using a pinhole aperture in quasi-contact mode

A cone shaped pinhole aperture (inner diameter, 0.3 mm and outer cone slope, 60 degrees) was developed to reduce the primary X-ray beam size of a conventional XRF setup. This aperture was used in combination with a single capillary. The pinhole was placed very close to the sample surface, that is, in quasi-contact mode. The gap size between the aperture and the sample was adjusted to be less than 0.5 mm. The X-ray fluorescence produced by the sample was measured from this gap at a small takeoff angle. The lateral resolution was evaluated using a tungsten wire placed at different gap sizes. The best resolution, which is almost equal to the pinhole size, was obtained in quasi-contact mode. The X-ray fluorescence signals of Au Lα and Co Kα from a Au-Co grating were analyzed while scanning the sample in front of the conical aperture. From this line scan, it was evident that the best resolution and the highest intensities of X-ray fluorescence were obtained in quasi-contact mode.

Weathering of dolomitic sandstone under ambient conditions

Abstract The weathering of White Mansfield dolomitic sandstone has been studied under ambient atmospheric conditions. Specially constructed sampling devices, called “micro-catchment units”, were installed to sample the runoff water, i.e. the rain water that flows over the stones. In a first part of the study, the bulk run-off water was studied (some 500 samples), as well as individual particles in the runoff. The second part of the study was focussed on the stone material after three years of exposure. A whole range of modern analytical techniques has been used. An outline of the work and the results is given.

Localized thin-film analysis by grazing-exit electron probe microanalysis

Abstract We have studied the application of grazing-exit electron probe microanalysis (GE-EPMA) for surface and thin-film analysis. In this method, characteristic X-rays are measured at small take-off angles of less than 1°. Under grazing-exit conditions, the X-rays emitted from deep inside the sample are not detected because they are stopped by a slit mounted in front of the energy-dispersive X-ray detector. Hereby, it becomes possible to perform localized surface analysis with GE-EPMA. We applied this method to thin-film analysis of a small surface area. The exit-angle dependence of the characteristic X-ray intensities was measured for thin films of Cr and Ti. Thickness and density of thin films were determined by fitting the experimental plots with theoretically calculated curves. Differences were found in the densities of two Cr thin films deposited by magnetron sputtering and vacuum evaporation. The advantage of GE-EPMA is that non-destructive thin-film analysis of small surface areas can be incorporated in simple scanning electron microscope (SEM) analysis.