The structure of chalcogenide glasses xSb//2S//3 center dot (1 minus x)As//2S//3 with 0 less than equivalent to x less than equivalent to 0.75 was studied by infrared reflectance spectroscopy. The absorption coefficient spectra, calculated from reflectance by Kramers-Kronig analysis, were deconvoluted in the high-frequency region from 250 to 450 cm** minus **1, and the frequency and relative intensity of the component bands were studied as a function of Sb//2S//3 content. Band assignments were based on the molecular model, and experimental relative intensities were compared with those calculated in terms of the random substitution and heterogeneous structure models proposed in the literature for such glasses. The results were found to be consistent with a glass structure formed by a random distribution of trigonal AsS//3/////2 and SbS//3/////2 pyramidal units bridged by sulfur atoms. A band resolved at ca. 360 cm** minus **1 was associated with mixed As-S-Sb bridges, in accordance with the composition dependence of its relative intensity which was found to be maximum at x equals 0.5. (Author abstract) 29 Refs.
Kamitsos, E.I. Kapoutsis, J.A. Culeac, I.P. Iovu, M.S.
Gel-glass dispersed liquid crystal (GDLC) films may be used as electro-optic devices. Films scatter light according to the number of droplets and the relative refractive indices of the LC and the silica matrix. LCs are birefringent; therefore their refractive index depends on the LC orientation and the optical angle of incidence. If the film is coated with transparent electrodes, and an electric field is applied, a reorientation of the LC director in the droplet occurs, producing a variation of the LC refractive index as `seen’ by the incoming light. If the refractive index of the sol – gel substrate matches the new LC index, the material changes from an opaque, scattering state to a transparent state. This feature can be used for preparing devices for visual presentation, i.e. displays. Unaltered GDLCs switch from white opaque to colourless transparent states. The contrast ratio, viewing angle and switching time of GDLC displays are presented. If these materials are to be used for displays, colour needs to be incorporated for many applications. The use of GDLCs associated to gel-glasses doped with fluorescent dyes for preparation of emissive `all sol – gel’ displays is presented, with the GDLC acting as an optical shutter for the RGB emission of the fluorescent dyes located at the backplane. A number of fluorescent dyes with high quantum yield for the chosen UV excitation, and appropriate colour coordinates, have been investigated.
D. Levy
no10
The essential condition for glasses and glass-ceramics to bond to living bone is the formation of a biologically active bone-like apatite layer on their surfaces in the body. In the present study, in order to investigate fundamentally the effect of B//2O//3 on the bioactivity of glasses and glass-ceramics, the compositional dependence of apatite formation on the surface of glasses in the system CaO-B//2O//3-SiO//2 was examined in the simulated body fluid. Substitution of small amounts of B//2O//3 for SiO//2 in CaO center dot SiO//2 formula increased the rate of apatite formation on the surface of the glass, while substitution of more than 30 mol% B//2O//3 for SiO//2 decreased it. The substitution of B//2O//3 for SiO//2 in CaO-SiO//2 binary glasses accelerated the dissolution of Ca(II) ion from the glasses, and hence enhanced the increasing rate of degree of supersaturation of the surrounding fluid with respect to apatite. The decrease in the apatite forming ability by substitution of large amounts of B//2O//3 for SiO//2 is attributed to the suppression of formation of silica hydrogel layer which plays an important role in apatite nucleation. (Author abstract) 22 Refs.
Ohtsuki, Chikara Kobayashi, Yukio Tsuru, Kanji Osaka, Akiyoshi
We propose a simple model of glass formation for various types of covalent and network glasses: binary covalent glasses, with the composition denoted by XnYm + x MpYq, with X an element of III-rd or IV-th group (e.g. B, Al, or Si, Ge), while MpYq is an alkali oxide or chalcogenide; next, the covalent network formers of the type AxB1-x, e.g. Gex Se1-x, Six, Te1-x etc. Finally, certain ternary glasses, with two different modifiers present, are also discussed. A simple formula relating the glass transition temperature Tg to the modifier consentration is derived. We give examples which show a good agreement of our formula with the experimental data.
Richard Kerner and Matthieu Micoulaut
Thermally stimulated luminescence has been observed in X-ray irradiated alkali borate and sodium silicate glasses doped with Ce**3** plus . The emission wavelength is about 360 nm which corresponds to the 5d-4f transition of Ce**3** plus . For the alkali borate glasses doped with Ce**3** plus , oxygen hole center and electron trapped nearby alkali ion induced by X-ray irradiation contribute to the thermally simulated luminescence, while Sm**3** plus acts as an electron acceptor in the thermally stimulated luminescence of alkali borate glasses codoped with Ce**3** plus and Sm**3** plus . In both cases, Ce**3** plus is ionized by X-ray to form Ce**4** plus and an electron which is trapped by an impurity level (oxygen hole center or Sm**3** plus in glasses with or without Sm**3** plus , respectively). The thermal stimulation excites the electron (electron trapped nearby alkali ion or Sm**3** plus ), which transfers to the 5d level of Ce**3** plus . The electronic transition from the 5d to the 4f levels gives rise to the emission observed. The temperature which gives the maximum emission intensity in the glow curve tends to decrease as the concentration of Na//2O increases in the sodium borate glasses doped with Ce**3** plus and Sm**3** plus . In contrast, the temperature corresponding to the maximum emission intensity is independent of the glass composition for the sodium silicate glasses doped with Ce**3** plus and Sm**3** plus . These facts suggest that the compositional dependence of local basicity for Sm**3** plus ion site in sodium borate glasses is different than that in sodium silicate glasses. (Author abstract) 15 Refs.
Tanaka, K. Hirao, K. Tanaka, H. Soga, N.
The corrosion of a ZrO//2 containing alkali resistant silicate glass, float glass and silica glass caused by the aqueous solution of NaOH was studied by use of correlation method with spectrophotometry. Effects of the corroding temperature, time and solution concentration on the rate of reaction and the degree of corrosion were investigated; effects of the apparent activation energy and the experimental value of frequency factor on the rate constant were discussed. (Author abstract) 6 Refs.
Wu, Zhengming Bu, Hengzhi
The glasses of B//2O//3 contents above 50% (mole percent) in PbO- Bi//2O//3-B//2O//3 system were prepared by conventional melt quenching technology. X- ray, SEM and IR methods were used to examine the structural features of these glasses. The results of X-ray diffraction analyses showed that the glass structure contains two kinds of matted crystals that related to the mole ratios of PbO versus Bi//2O//3 and to addition contents of B//2O//3. The compositions of the matted crystals with different mole ratios of PbO versus Bi//2O//3 ranged from 80:20 to 20:80 were determined. The analyses of IR showed that the structures of glasses with different mole ratios of PbO versus Bi//2O//3 contain different boron-oxygen rings such as boroxol rings or triborate rings. A structural model based on the results above- mentioned was presented. (Author abstract) 5 Refs.
Lu, Anxian Huang, Jiwu Lu, Renwei
The glasses of B//2O//3 contents above 50% (mole percent) in PbO- Bi//2O//3-B//2O//3 system were prepared by conventional melt quenching technology. The glass structure contains two kinds of matted crystal related to the mole ratios of PbO versus Bi//2O//3 and the addition contents of B//2O//3. Different boron- oxygen rings such as boroxol ring and triborate ring were found in the glass structure. (Edited author abstract) 5 Refs.
Lu, Anxian Huang, Jiwu Lu, Renwei
Various silica glasses were engraved deliberately by excimer laser radiation using wavelengths of 308 and 248 nm. The ablation of different samples was investigated by systematic variation of the processing parameters. The ablation rates were determined using profilometry and gravimetric measurements by evaluating the processing quality and the morphology of the processed surfaces was considered. The phenomenon of ablation is explained as a non-linear interaction of the laser beam and the glass. The experimental results show that the ablation behaviour of silica glass depends on the wavelength and the intensity of the laser radiation, on the surface quality and the degree of purity of the glass. Although high ablation rates were obtained, the suitability of excimer lasers for micromachining is restricted due to the rough surface morphology and poorly defined edges. (Author abstract) 18 Refs.
Hornberger, Helga Weissmann, Rudolf Lutz, Norbert
Optical microscopy, Scanning Electron Microscopy (SEM), X-Ray Diffraction analysis (XRD) and Energy dispersive electron Probe Micro Analysis (EPMA) were used to characterize surface and subsurface layers and areas on medieval church window glasses generated by weathering and contamination, respectively. Investigations were carried out at surfaces and at existing or at artificially created cross-sections as well. Altogether 30 samples (22 from the Katharinenkirche, Oppenheim (Germany), and eight from the Cathedral St. Gatien, Tours (France)) were at disposal for the investigations. Depending on possibilities, conceded by the decisions of the responsible curators of the named historical monuments, investigations were carried out to get as much information as possible about chemical and structural characteristics of defects of the authentic glasses caused by weathering processes. In case of their appearance and detectability so-called gel layers or gel areas were of special interest. With attention to the specific conditions, samples were characterized with respect to the documentation of topographic changes of their surfaces (SEM), the detection and characterization of crystalline phases (XDA), the determination of compositions of the genuine glasses as well as material areas caused by weathering (EPMA). Using records of element-specific mappings, information about depth-dependent element distribution profiles was accessible. (Author abstract) 5 Refs.
Braeutigam, Uwe Buerger, Herbert Voelksch, Guenter
