Glasses Tech

April 6, 2009

Role of AgI for ionic conduction in AgI-AgPO//3 glasses

Filed under: Glasses 1997 — admin @ 11:44 am

Eyeglasses

Using frequency and temerpautre-depenent conductivity data for x AgI · (1-x) AgPO//3 glassess in he compsoition k range form kx = 0.10 to x = 0.55, we find that the number density fo mboile ions as wel as the ionci relaxation emchanism are independent of tmeperature and compsoition. We belveve that this result si important in roder to clarify the contrversial ole f AgI for the ion transport in these glasses. Mloreover, ur observation should gerally impact on he understanding fo fast ion codncution in glass. In kthe freqency range convered in korur sudy, i. e., at freqenceis belwo a few MHz a sueprlinear dependence of the condcutivity on freqency as reproted recently has not been observed.

Roling, B. Ingram, M. D. 
no.10

Nonlinear acoustic and microwave absorption in glasses

Filed under: Glasses 1997 — admin @ 11:41 am

A theory of weakly nonlienar low-temperture relaxational absorption f acosutic and electromagnetic wdaves in dielectric and metallic glasses isdevleoped. Basedupon te mdoel fo two-level tuneling systems we sdhwo that the nonienar contriubtion to the adbsorption k can be anomalously large. Tis is the case at wo enough frequencies, ωτ//0(T)<<1, where τ//0(T) is the miniml relaxation tiemf fortwo-level systems with te itnelrevel splitting ~k//BT. in dielectric glasses, the lwoest-roder noninear contribution is proportional to the wave's intenstiy. It i negativ eand exhbitis anomalous frequency and tmeruatre dependenes, ΔΓ/Γ//0∝[ωτ//0(T)]^-1/2 T^-2. in metallic glasses, the nonienar contribution is also negative, and it i proportional to the square root of the wav'es intensity and independent of the frequency. Nuemrical estiamtes shwo that the rpedicted nonlienar conribution can be measured experiemtnally. Kirkengen, M. Galperin, Yu. M.

Photochromic behavior in the fluorescence spectra of 9-anthrol encapsulated in Si-Al glasses prepared by the sol-gel method

Filed under: Glasses 1997 — admin @ 11:36 am

The fluorescence spectra of 9-anthrol during the sol-gel-xerogel transitions of 13 systems containing different silicon and aluminum ratios and catalysts have been observed at a constant temperature (300 K) as a function of the sol-gel reaction time. Fluorescence decay curves for typical xerogel samples also have been observed. 9-Anthrol in the sol-gel systems showed four different fluorescence bands originating from the hydrogen-bonded, the complex, the ion pair, and the anion form species. Continuous light irradiation of the xerogels at 360 nm led to an increase in the fluorescence at 480 nm. These findings indicate that anthrone transforms to 9-anthrol by the photoinduced intermolecular proton transfer in these matrixes. The most effective and remarkable tautomerization occurred in the Si:Al equals 90:10 system, and it was concluded that this photochromic behavior occurs by the photoinduced proton transfer from a proton at the surface Bronsted acid site on the-O-Si-O-Al-O- network to the anthrone molecule. (Author abstract) 39 Refs.

Fujii, Tsuneo Kodaira, Kazuhiko Kawauchi, Osamu Tanaka, Nobuaki Yamashita, Hiromi Anpo, Masakazu

Structure and bonding in As-Sb-S chalcogenide glasses by infrared reflectance spectroscopy

Filed under: Glasses 1997 — admin @ 11:23 am

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.

A model of glass transition in binary and ternary glasses

Filed under: Glasses 1997 — admin @ 11:04 am

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

Structure model of glasses for PbO-Bi//2O//3-B//2O//3 system containing higher B//2O//3

Filed under: Glasses 1997 — admin @ 10:32 am

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

Structure model of glasses for PbO-Bi//2O//3-B//2O//3 system

Filed under: Glasses 1997 — admin @ 10:30 am

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

The influence of alkali and alkaline earths on the working range for bioactive glasses

Filed under: Glasses 1997 — admin @ 10:27 am

Viscosity-temperature dependence has been investigated for glasses in a system where bioactive compositions are found. A glass is called bioactive when living bone can bond to it. In this work, high-temperature microscopy was used to determine viscosity-temperature behavior for 40 glasses in the system Na2O-K2O-MgO-CaO-B2O3-P2O5-SiO2. The silica content in the glasses was 39-70 wt %. All glasses containing <54 mol % SiO2 devitrified during the viscosity measurements. Generally, glasses that devitrified contained more alkali but less alkaline earths than glasses with a large working range. A working range is the temperature interval at which forming of a glass can take place. This temperature interval can, for bioactive glasses, be enlarged by decreasing the amount of alkali, especially Na2O, in the glass and by increasing the amount of alkaline earths, especially MgO. Optionally, B2O3 and P2O5 can be added to the glass. An enlarged working range is a prerequisite for an expanded medical use of bioactive glasses as, e.g., sintered and blown products, and fibers.

Compositional dependence of bioactivity of glasses in the system Na2

Filed under: Glasses 1997 — admin @ 9:39 am

The bioactivity, i.e., bone-bonding ability, of 26 glasses in the system Na2O-K2O-MgO-CaO-B2O3-P2O5-SiO2 was studied in vivo. This investigation of bioactivity was performed to establish the compositional dependence of bioactivity, and enabled a model to be developed that describes the relation between reactions in vivo and glass composition. Reactions in vivo were investigated by inserting glass implants into rabbit tibia for 8 weeks. The glasses and the surrounding tissue were examined using scanning electron microscopy (SEM), light microscopy, and energy-dispersive X-ray analysis (EDXA). For most of the glasses containing < 59 mol % SiO2, SEM and EDXA showed two distinct layers at the glass surface after implantation, one silica-rich and another containing calcium phosphate. The build-up of these layers in vivo was taken as a sign of bioactivity. The in vivo experiments showed that glasses in the investigated system are bioactive when they contain 14-30 mol % alkali oxides, 14-30 mol % alkaline earth oxides, and < 59 mol % SiO2. Glasses containing potassium and magnesium bonded to bone in a similar way as bioactive glasses developed so far. J Biomed Mater Res, 37, 114-121, 1997. Maria Brink1, Tia Turunen

Compositional dependence of bioactivity of glasses in the system Na//2O- K//2O-MgO-CaO-B//2O//3-P//2O//5-SiO//2

Filed under: Glasses 1997 — admin @ 9:34 am

The bioactivity, i.e., bone-bonding ability, of 26 glasses in the system Na//2O-K//2O-MgO-CaO-B//2O//3-P//2O//5-SiO//2 was studied in vivo. This investigation of bioactivity was performed to establish the compositional dependence of bioactivity, and enabled a model to be developed that describes the relation between reactions in vivo and glass composition. Reactions in vivo were investigated by inserting glass implants into rabbit tibia for 8 weeks. The glasses and the surrounding tissue were examined using scanning electron microscopy (SEM), light microscopy, and energy-dispersive X-ray analysis (EDXA). For most of the glasses containing less than 59 mol % SiO//2, SEM and EDXA showed two distinct layers at the glass surface after implantation, one silica-rich and another containing calcium phosphate. The build-up of these layers in vivo was taken as a sign of bioactivity. The in vivo experiments showed that glasses in the investigated system are bioactive when they contain 14-30 mol % alkali oxides, 14-30 mol % alkaline earth oxides, and less than 59 mol % SiO//2. Glasses containing potassium and magnesium bonded to bone in a similar way as bioactive glasses developed so far. (Author abstract) 30 Refs.

Brink, Maria Turunen, Tia Happonen, Risto-Pekka Yli-Urpo, Antti

Glasses Tech