A molecular dynamics study of Li-doped borate glasses

The objective of this work is to investigate the effect of alkali content and temperature on the microstructure of lithium borate glasses, xLi₂O · (1 − x)B₂O₃. We have applied the molecular dynamics technique with Ewald summation and periodic boundary conditions to a collection of ca. 256 particles confined within a primitive cubic cell and interacting through a BornMayer-Huggins type of potential augmented with three-body angular terms. The results of this study have been discussed in relation to experimental structural data obtained by NMR and infrared spectroscopies.Метою даної роботи є дослідження впливу лужного вмісту і температури на мікроструктуру xLi₂O · (1 − x)B₂O₃. Ми застосували метод молекулярної динаміки з пересумовуванням за Евальдом до набору з 256 частинок, розміщених в примітивній кубічній комірці, що взаємодіють з потенціалом типу Борна-Майєра-Хаггіна, доповненим членами тричастинкової кутової взаємодії. Результати цих досліджень обговорюються в зв’язку з експериментальними даними, отриманими методами ядерного магнітного резонансу і інфрачервоної спектроскопії

Second-order nonlinear optical properties induced by thermal poling in photonic oxide glasses and transparent glass-ceramics

In recent years there has been a resurgence of interest in oxide glasses due to advances in lasers for information transport. Oxide glasses combine low cost of fabrication and good compatibility with silica glass fibers, which offer the opportunity for developing structures with nonlinear optical properties in integrated optical devices. The creation of an axial symmetry under thermal poling is currently necessary to induce Second-Order NonLinear (SONL) optical properties in glasses. A description of theoretical models which have been proposed for charge migration during thermal poling is presented. A review of SONL efficiencies which have been obtained for different glass compositions by this method is reported. Correlations between SONL properties and structural modifications under poling are also presented. Finally, we focus on the challenging fabrication of transparent glass-ceramic composites, especially when they are obtained by the precipitation of ferroelectric nanoparticle phases in the glassy matrix which adds the advantageous SONL properties of ferroelectric crystals

Influence of thermal treatment on the water release and the glassy structure of perlite

The effect of slow and rapid thermal treatment on water release and the structure of perlite was investigated by employing complementary techniques including X-ray diffraction, infrared spectroscopy and scanning electron microscopy. The study of several perlite samples, with different grain size and origin, has shown that rapid heating has a more pronounced effect on the glassy structure and that this is the only process capable of leading to perlite grain expansion. This process was simulated in a laboratory furnace allowing the careful control of temperature and time of treatment, and, thus, the description of their influence on the expansion process. The results show that molecular water released between 250 and 550 °C affects mostly the expansion process. Infrared spectroscopy provides evidence for additional water release, through dehydroxylation of Si-OH bonds, that may contribute also to expansion with a simultaneous development of the silicate network. The grain morphology was found to correlate with the expansion ratio. The presence of crystallites in raw perlite was shown to affect also the expansion process

Technology and Provenance Analysis of Glass Fragments from an Ottoman Bathhouse (Hamam) in Kyparissia, Peloponnese, Greece

This study focuses on the analysis of a post-medieval assemblage of glass vessels and tableware, recovered from an Ottoman bathhouse in Kyparissia, SW Peloponnese, Greece. The chemical composition of the samples was estimated using SEM/EDS, whereas minor and trace elements were identified by qualitative XRF analysis. Raman spectroscopy was applied in order to examine the connectivity of the silicate glass matrix in more detail. The acquired data indicate significant chemical variations among the samples, especially in regards to the alkali source and the decolourant used. Moreover, one high-lead glass has also been identified. The provenance analysis, which was based on the statistical treatment of the resulted and published analytical data, indicated that the different glass types originated both from the eastern regions of the Ottoman Empire and from glassmaking centres in central and northern Europe. The determination of technology and provenance of the assemblage provided with valuable new information regarding the production and trading network of glass in mainland Greece during the Ottoman rule

Spectroscopic studies of Manduca sexta and Sesamia nonagrioides chorion protein structure

The secondary structure of Manduca sexta and Sesamia nonagrioides chorion proteins has been studied in intact chorions using laser-Raman and Fourier transform infra-red (FTIR) spectroscopy and in a solution containing extracted and reassembled chorion proteins using circular dichroism (CD) spectroscopy. Laser-Raman and IR spectra suggest the predominance of antiparallel β-pleated sheet structure in intact chorion proteins of both Lepidoptera species. The bands at 1673, 1674 cm-1 (amide I) and 1234-1238 cm-1 (amide III) in the laser-Raman spectra can best be interpreted as resulting from abundant antiparallel β-pleated sheet structure. Analysis of the amide I band suggests that chorion proteins consist of 60-70% antiparallel β-pleated sheet and 30-40% β-turns. Supporting evidence for the prevalence of antiparallel β-pleated sheet in chorion proteins was supplied using FTIR spectroscopy by the observation of a very intense absorption band at 1635 cm-1(amide I) and of a weak band at 1530, 1525 cm-1 (amide II) from chorions of both species. Surprisingly, analysis of the CD spectra of extracted and reassembled chorion proteins suggests that, in solution, they retain a regular secondary structure most probably dominated by β-pleated sheet. We therefore suggest that the prominent regular β-sheet structure of chorion proteins may exist in solution and dictate the aggregation and polymerization process in vivo. © 1995

Studying a Funerary Roman Vessel Glass Collection from Patras, Greece: An Interdisciplinary Characterisation and Use Study

In a rescue excavation of a Roman funerary complex located at the city of Patras, Achaia, Greece, an assemblage of high quality glass vessels of the 2nd-3rd c. AD was recovered. Here we present the results from the physicochemical examination of the collection using a combination of non-destructive techniques, namely optical microscopy, portable X-Ray Fluorescence, Scanning Electron Microscopy and Infrared spectroscopy (IR) techniques. The analyses resulted in the chemical characterization of the glass samples and the identification of a rare example of soda plant-ash glass. Moreover, madder lake was identified as the original content of several glass vessels. Finally, the effect of the original content on the corrosion processes was investigated, along with issues of biocorrosion. Statement of significance The interdisciplinary study of an assemblage of 2nd-3rd c. AD Roman funerary vessel glasses from Patras, Greece is reported. The archaeological and archaeometric study of Roman glass in south and central Greece has so far been limited. The present work is the first attempt to examine the complete chaîne opératoire of Roman funerary glass vessels, using a multi-technique approach. More specifically, the basic aims of the study were (1) the chemical characterization of the glass and the determination of the raw materials used; (2) the determination of the original content of the vessels; and (3) the examination of the corrosion effects on the glass