Tetsuji Yano

Structural investigation of sodium borate glasses and melts by Raman spectroscopy. I. Quantitative evaluation of structural units

Abstract Short-range and intermediate range structures of the sodium borate glass system were investigated using Raman spectroscopy to quantify their dependence on Na 2 O concentration. High-resolution spectra were collected by Raman spectroscopy using the Q-switched, second-harmonic pulse of a Nd:YAG laser as an excitation source. The system was designed for measurement of the spectra of glasses and melts up to temperatures over 1000 °C with high signal to noise ratio. Use of polarized light and the simultaneous analysis of HH and VH spectra allowed deconvolution of Raman spectra into appropriate bands with high reproducibility. The deconvoluted bands in the high-frequency region of 1100–1600 cm −1 could be assigned to the vibration modes due to the short-range structures of BO 3 and BO 2 O − units in the glasses. The band intensity ratios showed a simple linear relationship with the molar ratio, symmetric BO 3 triangle unit, N 3s , to asymmetric BO 2 O − triangle unit, N 3a , obtained from 11 B-NMR results. These results allowed a quantitative measure for normalizing the spectra leading to a direct comparison of the band intensities. The ring-structures of intermediate range order, boroxol, pentaborate, tetraborate and diborate groups, could be quantified from the spectra in the middle-frequency region. Their trends with Na 2 O concentration showed a good consistency with 10 B-NMR results and also Krogh-Moe’s model.

Structural investigation of sodium borate glasses and melts by Raman spectroscopy. II. Conversion between BO4 and BO2O− units at high temperature

Abstract Raman scattering spectra were recorded for pure boron oxide and sodium borate glasses and their melts at the temperature ranging from room temperature to 1200 °C to investigate the structural changes occurring in the melts. The amounts of short-range order structures (SRO), BO 2 O − and BO 3 , were estimated from the high frequency bands at 1100–1600 cm −1 . The ratio of 4-fold coordinated boron oxide BO 4 , N 4 , at high temperature could be derived for the glass melts as a function of Na 2 O concentration. In Na 2 O ⩽20 mol% region, N 4 showed a slight decrease while the remarkable decrease of N 4 was found in the region of Na 2 O ⩾25 mol% with increasing temperature. The enthalpy of the equilibrium reaction, BO 4 ↔ BO 3 + NBO monotonously increased from 20 to 80 kJ/mol with an increase in Na 2 O. A characteristic temperature T X SRO was found to exist, which defines the temperature sensitive–nonsensitive transition point of the above conversion of the structures of SRO, and did not necessarily coincide with the glass transition temperature. T X SRO plots were located between the liquidus line and the immiscibility dome in the phase diagram. Using this temperature and composition relationship, anomalous behavior of isothermal viscosity and strong-fragile characteristics of melts could be explained quantitatively.

Chemisorption of water and carbon dioxide on nanostructured BaTiO3–SrTiO3(001) surfaces

The interaction of water and carbon dioxide with nanostructured epitaxial (Ba,Sr)TiO3(001) thin film and bulk single crystal SrTiO3(001) surfaces was studied using x-ray photoemission spectroscopy (XPS), thermal desorption spectroscopy (TDS), and density functional theory (DFT). On both surfaces, XPS and TDS indicate D2O and CO2 chemisorb at room temperature with broad thermal desorption peaks (423–723 K) and a peak desorption temperature near 573 K. A comparison of thermal desorption Redhead activation energies to adsorption energies calculated using DFT indicates that defect surface sites are important for the observed strong adsorbate-surface reactivity. Numerical calculations of the competetive adsorption/desorption equilibria for H2O and CO2 on SrTiO3(001) surfaces show that for typical atmospheric concentrations of 0.038% carbon dioxide and 0.247% water vapor the surfaces are covered to a large extent with both adsorbates. The high desorption temperature indicates that these adsorbates have the pote...

Structural investigation of sodium borate glasses and melts by Raman spectroscopy. III. Relation between the rearrangement of super-structures and the properties of glass

The structure of the intermediate range order (IRO) of sodium borate glasses and melts were quantitatively investigated by the analysis of high-temperature Raman scattering spectra. Raman bands at the middle frequency region of 700–950 cm−1 were normalized using the bands at high frequency spectra and their intensities were compared among the spectra collected from the melts with different composition at various temperature. Bands at 805, 780, 750 and 720 cm−1 were focused and their intensity changes were quantified. The exceeds of temperature over the glass transition temperature did not necessarily cause the decrease of all the band intensities. At Na2O<15 mol%, 805 cm−1 band was the most sensitive to temperature, while at 15<Na2O<30, it was switched to 780 cm−1 band and 805 cm−1 band became insensitive. When Na2O concentration exceeded 30 mol%, 750 and 720 cm−1 bands were decreased with temperature. Accompanying the previous analysis on the structures of short range-order (SRO) of boron atoms [J. Non-Cryst. Solids, in this issue], some models of the structural rearrangement along with temperature were proposed. The combination of the obtained structural informations of IRO and SRO was found to explain the mechanisms causing various characteristic properties of borate glasses and melts, especially immiscibility and boron oxide anomaly of thermal expansion coefficient from the microscopic and dynamic points of view of the vitrification process in melt.

Structure of glasses in the system SnPbPFO

A quantitative structural model of oxyfluoride glasses in the system SnPbPFO is proposed on the basis of IR, XPS, NMR and Mossbauer spectroscopy. The main structure of the glass is that phosphorus tetrahedra [PO4−xFx] (x = 0, 1, 2) including PF bonds connected to each other by intervening Sn(Pb) or SnO(PbO). This gives rise to the network of the OPOSn linkage. Besides, there are Sn(Pb)F bonds in this structure. The existence of covalent and less polar PF bonds results in the molecular nature in the structure of the glasses. This enables one to introduce organic molecules into the glasses.

An innovative energy-saving in-flight melting technology and its application to glass production.

Abstract The conventional method used for glass melting is air-fuel firing, which is inefficient, energy-intensive and time-consuming. In this study, an innovative in-flight melting technology was developed and applied to glass production for the purposes of energy conservation and environmental protection. Three types of heating sources, radio-frequency (RF) plasma, a 12-phase alternating current (ac) arc and an oxygen burner, were used to investigate the in-flight melting behavior of granulated powders. Results show that the melted particles are spherical with a smooth surface and compact structure. The diameter of the melted particles is about 50% of that of the original powders. The decomposition and vitrification degrees of the prepared powders decrease in the order of powders prepared by RF plasma, the 12-phase ac arc and the oxygen burner. The largest heat transfer is from RF plasma to particles, which results in the highest particle temperature (1810 °C) and the greatest vitrification degree of the raw material. The high decomposition and vitrification degrees, which are achieved in milliseconds, shorten the melting and fining times of the glass considerably. Our results indicate that the proposed in-flight melting technology is a promising method for use in the glass industry.

Structural evolution during Ag+Na+ ion exchange in a sodium silicate glass

The structural evolution during Ag+Na+ ion exchange in a sodium silicate glass has been investigated by micro infrared reflectance spectroscopy (IRRS) and 29Si MAS-NMR spectroscopy. The IRRS spectrum varied depending on the Ag concentration in the glass. The spectrum for the original glass had two distinct peaks corresponding to SiOSi and SiO− stretching vibrations in the wavelength region from 1500 to 700 cm−1. The spectrum at a depth of 0.05 mm from the surface of ion-exchanged glass having Ag2O concentration of about 31 mol% had one peak and two shoulders, whereas the spectrum at a depth of 0.13 mm having Ag2O concentration of about 15 mol% had only one peak and the shoulders were not resolved. This change in the IRRS spectra was attributed, from 29Si MAS-NMR spectroscopy, to the structural change induced by the Ag+Na+ ion exchange to from Q4 and Q2 species at the expense of Q3 species, which is responsible for the reduction in glass transition temperature.

Structure and phase transformation of alkali silicate melts analysed by Raman spectroscopy

Raman spectra of binary alkali silicates were measured at various temperatures from 1300°C to room temperature to investigate the relation between structural change and phase transformation phenomena. Distribution of structural units of Q n was estimated at each temperature by the deconvolution of spectra based on the equilibrium 2Q3 ↔ Q2 + Q4. The Q n distributions of sodium and potassium silicate systems strongly depend on temperature and the equilibrium shifts to the left-hand side with decreasing temperature, but those of lithium silicate system were less sensitive to the temperature variation. In alkali disilicates (33 mol% R2O–67 mol% SiO2, where R=Li, Na or K), the Q n distributions near the melting point were independent of alkali ion species, and they held the relation [Q2] = [Q4] ≈ [Q3]/4. This means that two of 6Q3 units (six-memberd ring) in crystals are transformed into a pair of Q2 and Q4 in the melting process. Below the melting point, the Q n distribution in lithium disilicate melt remained while, in sodium and potassium disilicate melts, [Q3] increased with decreasing temperature. Crystallization of the alkali disilicate melts is discussed considering the configuration entropy of Q n units. In 25 mol% Li2O–75 mol% SiO2, which is in the range of the immiscibility dome, the Q n distribution was maintained even when phase separation occurs in the cooling process.

Cation site occupation by Ag+/Na+ ion-exchange in R2O–Al2O3–SiO2 glasses

Ag+/Na+ ion-exchanged R2O–Al2O3–SiO2 glasses with uniform concentration profile of Ag+ and Na+ were prepared by heat treatment in molten silver salt followed by holding at the same temperature in an ambient atmosphere. Their glass transition temperature (Tg) and thermal expansion coefficient (TEC) were measured and structures were investigated using 29Si-MAS NMR, 27Al-MAS NMR, IR and Raman spectroscopies. Both Tg and TEC decreased with increase of the exchange ratio, but Tg was still above the ion-exchange temperature of 400°C even for the fully exchanged sample. The 29Si- and 27Al-MAS NMR spectra were mostly unchanged and no sign of the structural alteration of the glass network was observed. On the other hand, the vibrational spectra showed remarkable peak shifts depending on the exchange ratio. From these structural results, it was found that when the exchange ratio was low, the introduced Ag+ ions were stabilized at the non-bridging oxygen (NBO) site, and then Na+ ions in AlO4 site were exchanged by Ag+ ions after full replacement of NBO sites, where O represents the bridging oxygen.

Anomalous chemical shifts of Cu 2p and Cu LMM Auger spectra of silicate glasses

Abstract Chemical states of copper ions in various kinds of silicate glasses were investigated by X-ray photoelectron spectroscopy (XPS) and X-ray-induced Auger electron spectroscopy (XAES). Cu 2p photoelectron peaks of the melt-quenched Cu2O–Al2O3–SiO2 and Cu+/Na+ ion-exchanged Cu2O–Na2O–Al2O3–SiO2 glasses have the same binding energy assigned to Cu(I) state. On the other hand, Cu LMM Auger spectra show different spectral shapes in the respective glasses. Compared with the crystalline compounds Cu2O and CuO and metallic Cu, the chemical shifts of the Cu LMM Auger lines are considered to represent the difference of the relaxation effect of the two-hole final state of Cu due to the electron donation ability of the surrounding elements around Cu in the glasses. Analysis of the spectra of Cu 2p and Cu LMM lines of the melt-quenched Cu2O–Na2O–SiO2 glass shows remarkable X-ray irradiation effects. X-ray induces the Cu 2p peak shifts towards the lower binding energy side and finally it has a lower binding energy than that of metallic Cu. It is assigned to Cu(I) in octahedral coordination as found in the spinel structure. From the detailed analysis of Cu 2p spectra, the changes of the redox of Cu ion and the structural evolution on the glass surface are discussed.