Gothic green glazed tile from Malbork Castle: multi-analytical study
Looking at the façade of a historical building, it is often difficult to distinguish between the original decoration and later additions. One such building is the Holy Virgin Mary Church at the Malbork Castle (Northern Poland), built between 1276 and 1406. During the latest restoration works, ceramic tiles with some remnants of the green glaze, decorating the Holy Virgin Mary Church façade, were studied in situ using portable X-ray fluorescence spectrometry. Micro-samples were analyzed in laboratory by scanning electron microscopy with energy dispersive X-ray spectrometry (SEM–EDS) and wavelength-dispersive X-ray spectrometry (SEM–WDS), micro-Raman spectroscopy and powder X-ray micro-diffraction. We found that what was originally thought to be a paint layer was in fact a heavily deteriorated SiO2–PbO glaze. White, yellow and black pigments were found to have been added into the glaze as opacifiers and colorants. Copper and iron were used as glaze colorants. The originally added pigments were transformed into new phases, such as antimony-doped tin oxide. The technology used to produce the glazed tiles was identified. All the results collectively confirmed the medieval origin of the green glazed tiles.Graphical abstractGothic green glazed tile from Malbork Castle: multi-analytical study.
Artificial lightning strike tests and coupled electrical–thermal analysis on roofing glazed tiles of ancient buildings
Lightning strike is one of the natural disasters to the roof components of ancient buildings. To investigate the causes and damage effects of lightning strikes on the roofing glazed tiles of ancient buildings, artificial lightning strike tests were carried out on glazed tiles. Based on the experiment results, a coupled electrical–thermal finite element model of mortar-containing glazed tiles was established and the Joule heat effect of lightning current was further investigated. The results show that when the lightning channel is attached to the surface of the enamel and body with a low electrical conductivity, the lightning current is mainly released in the form of surface flashover, and a minor damage is induced along the flashover path; when the lightning channel is attached to the mortar with a high electrical conductivity, the lightning current is injected into the mortar, resulting in significant tile damage. The spatial distributions of the temperature present clear gradient characteristics. The high-temperature area appears in the mortar while the high–thermal–stress area appears in the body connected to the grounding rail. As the peak of the lightning current increases, both the high-temperature and high–thermal–stress areas of the glazed tiles expand. The combination of the experiments and the numerical analysis results demonstrate that the damage mechanism of lightning Joule heat effect to glazed tiles may include two aspects. One is the internal explosive force generated from the sharp vaporization and expansion of the moisture inside the tiles due to rapid temperature increase, and the other is the thermal stress caused by the uneven temperature distribution.
Neutron Residual Stress Measurements on Rail Sections for Different Production Conditions
Rail sectioning with subsequent neutron diffraction experiments has been used to assess residual stresses in the rails. In this study we present the results of neutron stress measurements performed at the NIST Center for Neutron Research (NCNR) on rail sections from rails that were produced under various conditions. Specifically, these are air-cooled, air-cooled and roller-straightened, head-hardened and head-hardened and roller-straightened. More significantly, a head-hardened and roller-straightened rail was also studied after service to elucidate evolution of the service-induced residual stresses. In the latter case both a transverse-cut slice and the central region of a 0.53 m long piece were studied. Measurements on this piece are the first in which triaxial stresses have been determined for an intact rail. Neutron strain measurements with 3×3×3 mm3 spatial resolution were successfully employed for transversally cut slices to verify the difference in the stress state depending on the production process. Although examination of slices allows determination of only two-dimensional stresses in the plane of the slice, additional measurements on obliquely-cut slices, which were also carried out, and utilization of FEM gives the possibility of reconstructing the full triaxial stress distribution. Together, these approaches provide a better understanding of rail fabrication and the possibility of improving the durability and safety of rails in the future.Copyright © 2004 by ASME