The mobility of an organic volatile probe (1-n-propanol), incorporated in two types of amorphous carbohydrate glasses, was evaluated by measuring probe retention as a function of time. Retention was found to depend on temperature, moisture content and the degree of matrix collapse. In sucrose glasses, crystallization and probe release occur simultaneously and both crystallization and release depend on the temperature above Tg, as predicted by the William-Landel-Ferry (WLF) equation. In sucrose: raffinose systems held above Tg, initial rapid release of the probe (`fast′; release) is observed, coinciding with, and presumably due to, matrix flow during collapse, followed by a much slower diffusional release. Relaxation times for collapse (τc), and `fast′; release (τfr) above Tg were calculated. They were found to be dependent on T-Tg and moisture content. Dependence of relaxation times on (T-Tg) was found to be well predicted by the WLF equation.
Guy Levi and Marcus Karel
Department of Food Science and Center for Advanced Food Technology, Rutgers University, PO Box 231, New Brunswick, New Jersey 08903-0231, USA
Following interaction with simulated body fluid, apatite and calcite were identified on the surface of bioactive glasses. The phase composition of the glass surface layer after elution is affected by the experimental conditions. At a high ratio of sample surface area (S) to the volume of the leaching solution (V), calcite was identified in the surface layer, whereas a low ratio (a large volume of the solution) had led to the formation of apatite. From the point of view of crystallography, the apatite was not well developed, and its detection limit by the X- ray diffraction method was less than 5%. The calcite was well developed. Phosphorus- free glasses exhibited a higher tendency to calcite formation than the phosphorus containing ones. Suitable experimental conditions with respect to the S/V ratio have to be chosen in the ‘in vitro’ testing to ensure availability of phosphorus in the solution throughout the exposure, as otherwise calcite would eventually precipitate on a thin layer of apatite. (Author abstract) 10 Refs.
Rybarikova, Ludmila Had, Jiri Holubova, Irena
The mechanism of the adhesion of glass to metal is reviewed. The conventional theories for the adhesion of glass and metals, for example SiO//2-based glass and metal, SiO//2-PbO glass and Dumet metal, PbO low melting glass and alumina substrate, and the adhesion of magnetic metals, are introduced. Finally current work about the adhesion of PbO-based glass in low O//2 atmosphere is discussed. (Author abstract) 18 Refs.
Seki, H. Satoh, K. Satoh, H. Matusita, K. Sato, R.
Joining of alumina ceramics with glasses for high temperature applications was investigated. A range of glass formulations encompassing ternary (Al//2O//3-CaO-SiO//2, Al//2O//3-SiO//2-MgO), and quaternary (Al//2O//3-CaO-SiO//2- ZrO//2) glasses was selected. The glasses were selected so that they would reach chemical equilibrium with the alumina component during sealing at temperature above 1500 degree C. The results of wetting and joining experiments using five refractory glasses, and microstructural and microchemical analyses of the interfacial regions is presented. Wetting experiments suggest that four of the five glasses produced crack- free joint regions. A higher sealing temperature might have prevented cracking for the other glass. Interfacial microstructures were analyzed using optical and scanning electron microscopy. EDS and microprobe results were used to identify the phases that developed during sealing at 1600 degree C, and during cooling to room temperature. In all cases, there was a residual glass at the interface. In most cases, the crystalline phases are consistent with the equilibrium phase diagram, indicating that these diagrams provide a useful tool for selecting and modifying the compositions of glasses for joining applications. In conclusion, at least a subset of these glasses appear to be suitable for joining alumina assemblies intended for high temperature applications. (Author abstract) 8 Refs.
Tomsia, A.P. Glaeser, A.M. Moya, J.S.
Rare-earth aluminosilicate glasses were prepared from Shirasu (volcanic ash) and yttria concentrate as the main starting materials. Specific heats and elastic constants of these glasses were measured at room temperature. Using these values and previously measured values of thermal expansion coefficients and densities, Gruneisen constants were calculated from the Gruneisen relation. There is a good linear relation between specific heat and chemical composition of these glasses containing about 20 oxides. Observed values of specific heat coincide with calculated values within 3% error. Observed bulk moduli were quite high (about 80 GPa). Values of the Gruneisen constant mainly depend on SiO//2 content. (Author abstract) 7 Refs.
Kotani, Kazuo Mitsuhashi, Takefumi Makishima, Akio
The region of alpha prime – and beta prime -sialons in the Si//3N//4- Yb//2O//3-AlN system, glass forming region in the Yb//2O//3-AlN-SiO//2 system, the phase relation of the quasiternary Si//3N//4-(Yb//2O//3)//0//.//4(AlN)//0//.//6- SiO//2 system, and properties of oxynitride glasses have been studied. The region of alpha prime – and beta prime -sialons had some width in the Si//3N//4-Yb//2O//3-AlN system. Lattice parameters of alpha prime – and beta prime -sialons increased with increasing amount of additives. The solubility of Si//3N//4 in the liquid of Yb//2O//3-AlN-SiO//2 system was small. The glass transition temperature, softening temperature and Vickers hardness of oxynitride glasses in the Yb//2O//3-AlN-SiO//2 system were measured as a function of composition. Yb-sialons were suggested to coexist with liquid phase at temperatures higher than about 1460 degree C. (Author abstract) 22 Refs.
Murakami, Yuichiro Akiyama, Katsunori Yamamoto, Hirokazu
The effect of heat treatment on electrical properties of a quartz glass prepared by flame fusion was investigated and the following results were obtained. (1) When the glass was heated at 1000 degree C, the electrical conductivity increased irreversibly with time at first and then decreased. (2) The increase in conductivity went on uniformly in the interior of the glass. On the other hand, the decrease in the conductivity started at the surface layer of the glass and spread to the interior. (3) The glass approached finally a state in which the electrical conductivity changed reversibly between high and low conductive states depending on the secondary heat treatment conditions. Such irreversible and reversible changes can be explained by considering the chemical equilibrium between OH group and molecular water in silica glass, outward diffusion of molecular water and protonic conduction. (Author abstract) 8 Refs.
Yamamoto, Kazunao Namikawa, Hiroshi
Properties of (20-30) mol% CeO//2-(16-23) mol% Al//2O//3-(47-62) mol% SiO//2 glasses prepared in an atmosphere of N//2 have been investigated. Experimental results showed that the glass transformation temperature, dilatometric softening temperature and transmittance in the visible region decrease with increasing ceria content; and that the thermal expansion coefficient and microhardness increase with increasing ceria content. The cerous ions in cerium aluminosilicate glasses exhibited a broad fluorescence spectrum with a large Stoke shift at 450 nm from the excitation spectrum peak of 366 nm. The fluorescence peaks shifted to the shorter wavelength but cutoff wavelength of ultraviolet spectra shifted to the longer wavelength as cerium aluminosilicate glasses were prepared in air instead of in N//2 for the specimen of the same composition. (Author abstract) 30 Refs.
Lin, Sin-Lung Hwang, Chii-Shyang
The 70SnF//2 center dot 30P//2O//5 glasses containing 25-500 ppm of fluorescein exhibit change in color from light yellow to reddish orange (absorption maximum, lambda equals 500 nm) when heated at 240 degree C for 120-180 min. The fluorophosphate glasses also change the color from light yellow to reddish brown ( lambda equals 480 nm) when irradiated with **6**0Co gamma -rays of 5 multiplied by 10**4 Gy. The P-F stretching mode observed in the Fourier transformed infrared (FT- IR) spectra showed an increase in peak intensity along with the coloration, suggesting a cleavage of the weak chemical bond between fluoride ions (F** minus ) and fluorescein molecules. The coloration is ascribed to change of the molecular structure of fluorescein from non-crystalline to crystalline type. ESR spectra of gamma -ray irradiated 70SnF//2 center dot 30P//2O//5 glasses showed a poorly resolved doublet, which was ascribed to a hole-trapped PO//3F** minus center produced by electron scattering: PO//3F**2** minus yields PO//3F** minus plus e** minus . ( Author abstract) 17 Refs.
Nishida, Tetsuaki Sasaki, Shigeo Toma, Tetsuya Maeda, Yonezo
The thermooptic coefficients, i.e., the variation of refractive index with temperature (dn/dT), are analyzed in a physically meaningful model for two series ofsoda-lime-silica glasses, 25Na//2O·xCaO·(75-x)SiO//2 and (25-x)Na//2O·xCaO·75SiO//2. This model is based on three physical parameters—the thermal expansioncoefficient and excitonic and isentropic optical bands that are in the vacuum ultraviolet region—instead of on consideration of the temperature coefficient ofelectronic polarizability, as suggested in 1960. This model is capable of predicting and analyzing the thermopotic coefficients throughout the transmission regiion of the optical glasses at any operating temperature.