Minoru Tomozawa

An infrared spectroscopic study of water-related species in silica glasses

Abstract Infrared (IR) spectroscopic measurements were made on types I, III and IV silica glass specimens before and after they were subjected to heat treatments at 80–1150°C in low-pressure steam, ambient air and dry air. In addition to the standard silanol band at 3672 cm−1, IR features attributed to free, hydrogen-bonded and structurally bound molecular water and to silanol which is hydrogen-bonded to neighboring silanol groups, water molecules and chlorine impurities were found to exist even in glasses with maximum total water concentrations of less than approximately 500 ppm H2O by weight. The existence of these species and their behaviors during heat treatments suggest a specific mechanism for the reaction between silica glass and molecular water. In addition, it is shown that the glass-water reaction does not attain equilibrium instantaneously at temperatures below 750°C.

A simple IR spectroscopic method for determining fictive temperature of silica glasses

Infrared spectroscopy was used to determine fictive temperature of silica glasses. Positions of both the fundamental structural band at ∼ 1122 cm−1 monitored in infrared (IR) reflection mode and an overtone of this band at ∼ 2260 cm−1 monitored in IR transmission mode were found to be directly correlated with the glass fictive temperature. At any particular fictive temperature, the equilibrium structural band positions were found to be independent of the impurity content, such as hydroxyl, in different types of silica glass. From band shifts, the average SiOSi bond angle was computed to decrease by about 1.3° when the fictive temperature increased from 950 to 1400°C. Using this method, fictive temperatures of various as-received silica glasses were determined.

Water diffusion into silica glass : structural changes in silica glass and their effect on water solubility and diffusivity

Abstract Infrared spectroscopy was used to measure structural changes, water surface concentrations and effective hydroxyl diffusion coefficients in silica glass during isothermal hydration heat-treatments at temperatures from 80 to 1150°C in 0.467 atm of water vapor. The observed glass structural changes were determined to be identical to relaxation during annealing, and it was found that infrared spectrometry may be used to measure glass fictive temperatures. Minute amounts of water had a pronounced accelerating effect on structural relaxation, and relaxation, in turn, affected the water content of the glass in three ways: (1) slow relaxation at low temperatures hindered the glass-water reaction or caused a slow increase of the reaction equilibrium constant; (2) expansion of the glass during water entry allowed an increase of the molecular water solubility; and (3) healing of the glass during bulk relaxation caused a decrease of the hydroxyl solubility. These processes occurred at different rates causing a peculiar increase and then decrease with time of both the surface hydroxyl concentration in thick specimens and total hydroxyl uptake in thin specimens. This observation was used to demonstrate that hydroxyl solubility measurements taken below 850°C by other researchers are not true equilibrium solubilities. Additionally, the kink at 550°C in the Arrhenius plot of Deff,OH as observed by Wakabayashi and Tomozawa in 1989 was found to be a time-dependent phenomenon which is explained in terms of slow glass-water reaction during relaxation. Diffusion of water into silica glass is therefore suggested to be bounded by two extremes: a high-temperature (> 850°C)/long-time extreme where relaxation and reaction are faster than diffusion and water diffuses according to the Doremus model and a low-temperature/short-time extreme in which relaxation and reaction are slower than diffusion and water penetration is limited only by the diffusion coefficient of molecular water in the glass.

Quantitative infrared spectroscopic measurement of hydroxyl concentrations in silica glass

Infrared (IR) spectroscopic analysis of high hydroxyl content silica glasses was compared with both weight loss measurements and nuclear reaction analysis (Helmich and Rauch, 1993) to obtain the molar absorptivity of the 3673 cm−1 hydroxyl band in silica glass. Agreement between the resulting molar absorptivity values (76.4 ± 2.8 and 77 ± 6 1glass/molOHcmglass for weight loss and nuclear reaction the experiments, respectively) and those from the literature gives a best estimate of the molar absorptivity to be 77.5 ± 1.5 1glass/molOHcmglass. Proportionality between the amplitudes of the fundamental OH stretching band at 3673 cm−1 and the combination SiOH bending-OH stretching band at 4522 cm−1 allowed the molar absorptivity of the combination band to be determined (1.53 ± 0.03 1glass/molOHcmglass) and comparison of the amplitudes and areas for both the 3673 and 4522 cm−1 bands gives the integrated molar absorptivities to be 10,100 ± 200 and 232 ± 5 1glass/molOHcmglass2, respectively. Nonlinear absorbance loss versus weight loss per surface area curves observed for some batches of type III silica glass suggest that hydroxyl can be simultaneously removed via multiple mechanisms.

Correlation of silica glass properties with the infrared spectra

Abstract Infrared (IR) spectroscopy has been used to interpret structural changes in silica glasses. Specifically, a shift of the Si–O stretching band in IR spectra is used to monitor changes in average Si–O–Si bond angle in the glass structure. A similar structural change is induced by the change of fictive temperature, hydrostatic pressure or compressive stress, with the average Si–O–Si bond angle decreasing with the increase of these parameters. It is anticipated that these similar structural changes would produce a similar change in glass properties. In order to confirm this expectation, HF etch rates of silica glasses were measured as a function of fictive temperature and stress. The experimental results on HF etch rates, together with changes in other glass properties in the literature, were compared with the change in glass structure revealed by IR spectroscopy. It was found that the similar structural change is accompanied by the consistent changes in a variety of glass properties. Monitoring the IR spectra of a silica glass sample, therefore, can be used to deduce changes in glass properties.

Barium zirconate-titanate/barium calcium-titanate ceramics via sol–gel process: novel high-energy-density capacitors

Lead-free barium zirconate-titanate/barium calcium-titanate, [(BaZr0.2Ti0.80)O3]1?x?[(Ba0.70Ca0.30)TiO3]x (x = 0.10, 0.15, 0.20) (BZT?BCT) ceramics with high dielectric constant, low dielectric loss and moderate electric breakdown field were prepared by the sol?gel synthesis technique. X-ray diffraction patterns revealed tetragonal crystal structure and this was further confirmed by Raman spectra. Well-behaved ferroelectric hysteresis loops and moderate polarizations (spontaneous polarization, Ps ~ 3?6??C?cm?2) were obtained in these BZT?BCT ceramics. Frequency-dependent dielectric spectra confirmed that ferroelectric diffuse phase transition (DPT) exists near room temperature. Scanning electron microscope images revealed monolithic grain growth in samples sintered at 1280??C. 1000/? versus (T) plots revealed ferroelectric DPT behaviour with estimated ? values of ~1.52, 1.51 and 1.88, respectively, for the studied BZT?BCT compositions. All three compositions showed packing-limited breakdown fields of ~47?73?kV?cm?1 with an energy density of 0.05?0.6?J?cm?3 for thick ceramics (>1?mm). Therefore these compositions might be useful in Y5V-type capacitor applications.

Correlation effects on alkali ion diffusion in binary alkali oxide glasses

Abstract The correlation factor in the Nernst-Einstei equation for low sodium Na2OGeO2 glass determined from dc conductivity and 22Na diffusion coefficient measurements was found to be near unity. Values of the correlation factor were also compiled from the literature for higher alkali content germanate glasses as well as for sodium borate and alkali silicate glasses. In all three systems the correlation factor was found to depend primarily on the alkali content in the glass. Specifically, uncorrelated ionic diffusion ( ƒ ⋍ 1 ) occurs in low alkali glasses while correlated motion ( ƒ ) takes place at higher alkali concentrations. This observation is consistent with the theory that many “holes” exist in low alkali glasses through which the diffusing cation can randomly jump.

Surface and bulk structural relaxation kinetics of silica glass

Abstract The structural relaxation kinetics of a silica glass were measured by following the IR structural band positions, which are directly correlated with the average Si–O–Si bond angle as well as with the fictive temperature of the glass, as a function of heat-treatment time, temperature and the water vapor pressure. Both surface relaxation and bulk relaxation kinetics were determined by measuring the IR reflection and absorption band positions, respectively. The surface relaxation was much faster than the bulk relaxation and had a smaller activation energy. Also, both relaxation kinetics were faster in the presence of water vapor. The apparent bulk relaxation time determined from the IR absorption band shift was a composite relaxation time consisting of both the relaxation time of the water-catalyzed near surface layer and the true bulk relaxation time of the glass interior which is unaffected by water vapor. The true bulk relaxation time was evaluated and found to have an activation energy consistent with that of the viscous flow.

Water in glass

Abstract Water in glass has drastic influence on glass properties. The structure of water in glass and selected water-related phenomena, i.e. water diffusion in glass, and glass—water phase separation are described. Their relation to glass properties, such as mechanical and chemical properties are discussed. Outstanding problems and the future are also discussed.

The nature of dissolved water in sodium silicate glasses and its effect on various properties

Abstract Sodium silicate glasses with a wide range of water contents were prepared. For water contents up to twelve wt% the specimens were prepared by melting Na 2 O·3 SiO 2 glass and varied amounts of water in hydrothermal pressure vessels. A few higher water content samples were synthesized by hydrating glasses in an autoclave under a steam atmosphere. The concentration of different species of water was analyzed by infrared spectroscopy. Density refractive index and the induced absorption due to γ-irradiation were analyzed in terms of the different water species present in the glasses. It has been observed that the effect of water on all these properties can be explained in terms of the different contributions of hydroxyls and molecular water.