International audienceAlthough the characteristic time constant for viscous relaxation of glass is so large at room temperature that viscous flow would be hardly detectable, a permanent deformation can be easily achieved at ambient temperature by applying a sharp contact loading-a Vickers indenter for instance-for few seconds only. We provide direct evidence for densification and volume conservative shear flow by means of atomic force microscopy topological analysis of the indentation profile and volume on as-quenched and densified specimens (pressure up to 25 GPa). We show that both possible mechanisms contribute to different extents depending on the glass composition. A major finding is that densification predominates in glasses with relatively low atomic packing density but that shear flow relays on once densification is achieved. (c) 2010 American Institute of Physics. [doi:10.1063/1.3407559

Atomic force microscopy is used to investigate the possibility of cavity formation during crack growth in silicate glasses. Matching areas on both fracture surfaces were mapped and then compared. For silica glass, and soda-lime-silicate glass, the fracture surfaces matched to a resolution of better than 0.3 nm normal to the surface and 5 nm parallel to the surface. We could find no evidence for cavity formation in our study and suggest that completely brittle fracture occurs in glass.

Ge-Se chalcogenide glasses are characterized by relatively low hardness (0.39 -2.35 GPa) and low fracture toughness (0.1-0.28 MPa⅐m 1/2 ). Actually, the hardness of chalcogenrich glasses is low enough so that the brittleness parameter, B ‫؍‬ H/K c , is lower than that of silicate glasses. Whereas hardness and Young's modulus increase with increasing germanium contents, fracture toughness follows a trend similar to that of the density and exhibits a maximum for the Ge 20 Se 80 composition, which corresponds to the rigidity percolation threshold. Optical microscopy and atomic force microscopy observations suggest that the indentation deformation proceeds by a localized shear deformation phenomenon. Glasses in the chalcogen-rich region behave viscoelastically at room temperature. As a consequence, an increase of the loading time results in a decrease of hardness and toughness.

International audienceThe highly visible and infrared (up to 6 mu m) transparent Sr3Al2O6 polycrystalline ceramic was obtained by full crystallization of the corresponding glass composition. The glass synthesis and the direct congruent crystallization processes are described, and the material transparency is discussed in light of its microstructure. This new transparent ceramic exhibits a high density (i.e., complete absence of porosity) and micrometer-scale crystallites with very thin grain boundaries. These microstructural characteristics, inherent to the preparation method, minimize light scattering and demonstrate the advantages of this synthesis route compared to the high-pressure process used for the few reported transparent polycrystalline materials. This Sr3Al2O6 ceramic shows a H = 10.5 GPa hardness, a E-r = 150 GPa reduced elasticity modulus, and a 9.6 x 10(-6) K-1 thermal expansion coefficient. Such a transparent strontium aluminate ceramic opens the way to a wide range of applications, especially photonics when doped by various doping agents. As examples, the luminescence of Sr3Al2O6:Eu3+ and Sr3Al2O6:Er3+, which show strong emissions in the visible and infrared ranges, respectively, is presented. Moreover, the Sr3Al2O6:Ce3+ material was found to exhibit scintillation properties under X-ray excitation. Interestingly, the analogous Sr3Ga2O6 transparent polycrystalline ceramic material could equally be prepared using the same elaboration method, although its hygroscopicity prevents the preservation of its high transparency under normal conditions. The establishment of the key factors for the transparency of this economical and innovative synthesis method should enable the prediction of new classes of technologically relevant transparent ceramics

Abstract:The primary objective of this study is the development of transparent thin film materials in the IR enabling strong infrared absorption of organic compounds in the vicinity of metal nanoparticles by the surface plasmon effect. For developing these optical micro-sensors, heterostructures combining gold nanoparticles and chalcogenide planar waveguides are fabricated and adequately characterized. Single As 2 S 3 and Ge 25 Sb 10 Se 65 amorphous chalcogenide thin films are prepared by radiofrequency magnetron sputtering. For the fabrication of gold nanoparticles on a chalcogenide planar waveguide, direct current sputtering is employed. Fabricated single layers or hetero-structures are characterized using various techniques to investigate the influence of deposition parameters. The nanoparticles of gold are functionalized by a self-assembled monolayer of 4-nitrothiophenol. Finally, the surface enhanced infrared absorption spectra of 4-nitrothiophenol self-assembled on fabricated Au/Ge-Sb-Se thin films hetero-structures are measured and analyzed. This optical component presents a ~24 enhancement factor for the detection of NO 2 symmetric stretching vibration band of 4-nitrothiophenol at 1336 cm −1 . 232-239 (1999). 19. L. Tichý, H. Ticha, P. Nagels, R. Callaerts, R. Mertens, and M. Vlcek, "Optical properties of amorphous As-Se and Ge-As-Se thin films," Mater. Lett. 39(2), 122-128 (1999). 20. J. Charrier, M. L. Anne, H. Lhermite, V. Nazabal, J. P. Guin, F. Charpentier, T. Jouan, F. Henrio, D. Bosc, and J. L. Adam, "Sulphide GaxGe25-xSb10S65(x=0,5) sputtered films: Fabrication and optical characterizations of planar and rib optical waveguides," J. Appl.

A B S T R A C T This paper presents a new method to determine both the magnitude and the sign of the surface stresses that develop as a consequence of sodium/hydrogen ion exchange in soda-lime-silicate glass immersed in water. At 90 • C, very thin layers that develop at the surfaces of polished glass specimens are found to have extremely high compressive stresses, −2.4 GPa. The negative sign of the stress is consistent with earlier findings that the ion-exchange process involves hydronium ions (H 3 O + ) and not bare protons (H + ). I N T R O D U C T I O NSilicate glasses are inert to attack by water or water vapour at room temperature and, hence, are used in a wide variety of commercial applications. Their chemical reaction rate with water is so slow that glass windows, hundreds of years old, are still being used in many countries today without apparent degradation. Despite this excellent resistance to attack, water does react with silicate glasses, even the most resistant of compositions. Modern reviews of the subject of glass corrosion may be found in Refs [1,2]. A review that laid the foundations of this subject was published by Douglas and Isard 3 in 1949. The present paper is concerned with soda-lime-silicate glasses, the most common type of glass in use today. Soda-lime-silicate glasses are very corrosion resistant at room temperature, but do react with water to form a thin hydration layer on the glass surface. According to Lanford et al., 4 two types of reactions occur in this type of glass: an ion exchange between alkali ions in the glass and hydrogen ions in solution, and a congruent dissolution, in which glass dissolves in the water in concentrations equal to their ratio in the dry glass. In the glass studied by Lanford et al., congruent dissolution only occurred after exposure at 90 • C for 400 h.exchange leads to a compressive stress because H 3 O + is larger than Na + . Measurement of the hydrogen and soda profiles 4 revealed a ratio between the hydrogen concentration in the surface of the hydrated glass and the sodium concentration in the unhydrated glass of 2.9 ± 0.3. This three-to-one replacement of Na + by H + suggests that Na + is replaced by H 3 O + . The stress state in the ionexchange layers is of great importance to the understanding of the behaviour of cracks in soda-lime-silicate glasses, for these stresses can either retard or enhance the rate of crack growth and thus affect the strength of glass. The first attempts at measuring surface stresses due to ion exchange were carried out by Bunker and Michalske 5 and Michalske et al., 6 who used an interferometer technique to quantify the bending of thin plates of an alkaliborosilicate glass that was subjected to a water exposure on one side of the plate. From this bending and the elastic constants of the glass, the surface stresses were determined. As the thickness of the ion-exchanged layer in the glass plates was not known exactly, the stresses determined in these experiments were only approximate. These authors also used a fracture mechani...

No abstract

No abstract