Window glass fragments from four Belgian sites were studied and for a set of eighty-five samples the UV-VIS-NIR transmission spectra were analyzed. This collection contains historical and archaeological finds originating from religious buildings namely the Basilica of Our Lady of Hanswijk in Mechelen (17th-20thc) and the Church of Our Lady in Bruges (16th-20thc) as well as from secular buildings as a private house/Antwerp (18th-1948) and the castle of Middelburg-in-Flanders (1448-17thc). All sites contain material on the hinge point between the medieval and the industrial tradition. The variation in composition of the analyzed samples can be explained by the use of different glassmaking recipes, more specifically the use of different raw materials. The composition of window glass differs essentially in the type of flux, using a potash rich fluxing agent until the post-medieval times and industrial soda from the 19th century onwards. A second difference concerns the iron impurities in the glass. For all fragments a clear compositional classification could be made based on the iron concentration. These conclusions were based on archaeological research and drawn after submitting samples to expensive, complex, time-consuming and destructive chemical analyzing methods. Our study indicates that similar conclusions could be made applying the proposed optical based methodology for plain window glass. As a whole, the obtained results make it possible to cluster the fragments for a particular site based on three different sensing parameters: the UV absorption edge, the color and the presence of characteristic absorption bands. This information helps in identifying trends to date window glass collections and indicating the use of different raw materials, production technologies and/or provenance.
This study presents the active protective properties of lithium‐leaching coatings for a range of aluminium alloys. Coatings with and without lithium carbonate as leachable inhibitor were applied on the aluminium alloys, artificially damaged and exposed to the neutral salt spray. A combined approach of scanning electron microscopy and electrochemical measurements revealed that the lithium carbonate leaching coating provided effective corrosion inhibition on AA2024, AA7075, AA5083, and AA6014 by the formation of a protective layer in the defect area and preventing local corrosion processes despite the different intrinsic electrochemical activity of the alloys.
Electrochemical processesing can be used to obtain aluminium surfaces with a well defined roughness. This is based on the use of DC or AC of polarisation of aluminium in an acid eletrolyte containing either chloride or nitrate anions. The roughness is obtained by a controlled pitting process. This DC or AC electrograining process is used for the preparation of aluminium litho material or for the production of Al capacitor foil. In the case of aluminium litho the water retentive properties and the adhesion of the polymer film are important. In the case of capacitor foil it is important to create a very high specific surface area. In the paper the electrochemical process is introduced and the link between the basic electrochemical parameters, such as aluminium alloy composition, current density, electrolyte composition, type of the anion in relation to the obtained morphology is discussed.
The major optical technique applied in this paper is spectroscopic ellipsometry. Ellipsometry measures the polarization change of the light due to interaction with the sample surface. It is called ‘spectroscopic’ if the measurement is performed at various wavelengths within a spectral interval. Spectroscopic ellipsometry performed in the visual spectrum allows the characterization of very thin films on metals, e.g. anodic oxide films or conversion layers on Al. In this contribution the optical modelling that leads to accurate thickness measurements of such films is shown. Visual spectroscopic ellipsometry (VISSE) fails to give chemical information due to the absence of absorption peaks in the spectrum. Therefore, an original approach has been followed by the use of the new infrared spectroscopic ellipsometry (IRSE) technique. This method combines the advantages of VISSE to the characteristic information revealed by Fourier transform infrared spectroscopy. In this paper we used IRSE on the anodic oxide and chromium phosphate films. The infrared optical modelling is discussed and calculated thickness values are compared to thickness measurements obtained by VISSE. Copyright © 2000 John Wiley & Sons, Ltd.
Electrochemical impedance spectroscopy (EIS) was used to investigate the corrosion resistance of the chromate conversion coating (CCC) formed on two different substrates, namely bare and clad 2024 aluminum alloys, and after different surface preparation procedures, namely acid pickling with or without desmutting. The impedance data were fitted using previously published equivalent circuits, which were developed on the basis of a physical model of the CCC. The evolution of the network parameters during exposure to the chloride solution enabled the correlation of the differences in the film morphology, which are caused by the variation in the substrate microstructure, with the corrosion protection provided by the conversion film. Specifically, the CCC corrosion resistance is strongly decreased by the presence of both intermetallic particles and copper smut on the Al surface, since the former are locations of defects in the conversion layer and the latter inhibits the film growth and lowers its adherence to the substrate. The corrosion resistance of the CCC formed on the different substrates and after the different surface preparation treatments can be clearly differentiated using the EIS technique and fitting the data with the proposed equivalent circuits, which represent the conversion film as a nonhomogeneous system containing large defects where the corrosion attack principally occurs. © 2004 The Electrochemical Society. All rights reserved.
Non‐destructive optical investigations (SE and FTIRS) of chromium phosphate conversion layers on aluminium are correlated to AES and TEM investigations. The AES results support the duplex model of the structure. FTIR‐spectra provide a non‐destructive characterization in agreement with the Auger data. Fitting the SE‐data with a proper model makes it possible to determine the thickness accurately. A correlation is made between the thickness obtained with SE, FTIRS and AES. It is shown that for thin layers a good agreement is obtained.
