Bridging Oxygen Bonds Research Articles

Infrared spectroscopy in the investigation of oxide glasses structure

Results of FTIR study of glasses with polymeric network, containing SiO2, Al2O3, B2O3 and P2O5 as the network-forming compounds, Ca-aluminate glass and high PbO content glasses with SiO2, Al2O3 and B2O3 as admixtures stabilizing glassy state are presented. Coordination numbers of glass-network forming components with respect to oxygen and bridging oxygen bonds, linking the coordination tetrahedra in the multicomponent network glasses were determined.

A PM3 molecular orbital model of silica rings and their vibrational spectra

Abstract The PM3 molecular orbital model was applied to various silica rings from twofold to sixfold on size. From these optimized structures, the bridging oxygen (BO) and non-bridging oxygen (NBO) bond lenths, the SiOSi (φ) angles, the OSiO (θ) angles and final heats of formation were tabulated. These data were compared with earlier MNDO and ab initio molecular orbital calculations. The theoretical vibrational spectra were then calculated and compared with earlier work as well as the experimental IR response. The PM3 method was found to be a viable calculational tool for modeling silica structures.

Discrete bond model (DBM) of sodium silicate glasses derived from XPS, Raman and NMR measurements

In sodium silicate glasses, the fraction of differently bound Si species Q [ i] ( i = 0−4), depending on the number i of bridging oxygens bound to the quarternary silicon, is a function of stoichiometry and the Na/Si ratio. Sodium silicate glasses were investigated by high resolution X-ray photoelectron spectroscopy. To explain the differences in chemical shifts and linewidths of the O 1s signal of the bridging and the non-bridging oxygen as a function of alkali concentration, and extended glass model was developed. This new model takes into account the influence of the alkali concentration on the Q [ i] distribution and on the appearance and concentrations of differently bound bridging oxygens as well as non-bridging oxygens. In principle, four different bonds for the non-bridging oxygens (NaOQ [ i] , i = 0−3) and seven different bonds for the bridging oxygens (Q [ i] O Q [ j] , i, j = 1−4, | i − j| < 2), linking the different Q [ i] species could exist. According to this ‘discrete bond model’, for each glass composition the number of these possible bridging and non-bridging oxygen species is limited to a maximum of two for each of them. An approximation of the measured X-ray photoelectron O 1s signal by a superposition of O 1s signals as calculated on the basis of this model allows an excellent reproduction of the experimental results if the glasses are non-phase-separated. In the case of phase separation, the measured spectrum shows only Q [ i] OQ [ i] bonds (with i = 1−4) identical to the bonding behaviour in the corresponding well-known crystalline phases. The chemical shifts of the non-bridging oxygens relative to the brodging oxygens (as well as the absolute binding energies), as measured by X-ray photoelectron spectroscopy, can be explained by changes in the relative concentrations and intensities of the different oxygen bonds as a function of glass composition. The energy differences between two energetically neighbouring bridging oxygens (i.e., Q [ i] OQ [ i] and Q [ i] OQ [ j] with | i − j| = 1) are equal (within the experimental error) for all bridging oxygen bonds in sodium silicate glasses and can be correlated with the cation field strengths of the modifying cations.

Interaction between water and melt in the system CaAl 2O 4SiO 2H 2O

The interaction between dissolved H 2O and melt structure on the join CaAl 2O 4SiO 2H 2O has been studied with Raman spectroscopy. The total H 2O contents ranged from 3 to 10 wt.% with Al ( Al+Si) =0–0.333 . The spectra are consistent with formation of OH complexes that include all Ca 2+ and Al 3+ in addition to molecular H 2O. No direct evidence for (Si,Al)OH bonds can be discerned in the spectra of hydrous calcium aluminosilicate melt (the 970-cm −1 band from SiOH stretching observed in the spectra of SiO 2H 2O melts is not well resolved in aluminous samples). However, the spectral topology of the fundamental OH stretch bands near 3600 cm −1 can only be rationalized if some SiOH or (Si,Al)OH bonding exists in the melts. The melts become depolymerized as H 2O is dissolved to form Ca..OH and Al..OH complexes. Formation of Ca..OH complexes is a more efficient depolymerization mechanism than that of Al..OH complexes [6 vs. 2 3 nonbridging oxygen would be formed per mole H 2O dissolved as a Ca..OH complex of Ca(OH) 2 type vs. an Al..OH complex of Al(OH) 3 type]. With increasing Al ( Al+Si) of the melts complexing of OH with Al 3+ (Al..OH) probably becomes more important at the expense of complexes with Ca 2+ (Ca..OH). Thus, the effect of dissolved H 2O on melt polymerization diminishes with Al ( Al+Si) . However, the degree of polymerization of the melts (NBO/T) for a given total H 2O concentration is less than that expected by either the Ca..OH or the Al..OH complexing mechanism alone. The excess water is present as molecular H 2O and as (Si,Al)OH bonds that replace (Si,Al)O(Si,Al) bridging oxygen bonds in the melts.

Effect of pressure, temperature, and bulk composition on the structure and species distribution in depolymerized alkali aluminosilicate melts and quenched melts

The influence of pressure, temperature, and bulk composition on the structure of di‐ and tetra‐aluminosilicate melts and quenched melts have been studied with Raman spectroscopy. The melt polymerization and Al/(Al + Si) ranges represented are those typically found in quartz‐normative basaltic magmatic liquids. The reaction describing the equilibrium among coexisting coexisting units in the melts is T2O5 (2Q3) ⇔ TO3 (Q2)+TO2 (Q4), where T=Si+Al, and the superscripts on the alternative Q‐notations represent the number of bridging oxygen in the unit. The reaction shifts to the right with increasing temperature, pressure and Al/(Al+Si). The ΔG for the reaction (derived from molar abundances under the assumption of ideal mixing) decreases (becomes more negative), therefore, with increasing temperature, pressure, and bulk melt Al/(Al+Si). As the ionization potential of charge‐balancing and network‐modifying cations is increased at constant pressure, temperature, and Al/(Al+Si), the ΔG increases. The Al3+ exhibits a preference for the most polymerized of the coexisting structural units (TO2 or Q4) probably because among these units the TO2 units have the smallest average intertetrahedral angle. It is proposed that the difference in intertetrahedral angle between the coexisting units exerts an important control on the magnitude of the Al ‐ preference. The angle difference decreases as the network‐modifying cation becomes smaller and the Al3+ preference is less pronounced. The bulk compositional, temperature, and pressure effects leading to decreasing ΔG also weaken bridging oxygen bonds in the TO2 units. Transport properties (viscosity, diffusivity, and conductivity) are directly related to the strength and abundance of the bridging oxygen bonds. Increasing pressure results in enhanced cation diffusivity and decreased viscosity, and these trends will be more pronounced the larger the charge‐balancing and network‐modifying metal cation and the more aluminous the melt.

Preparation of multiple oxide BaTiO3 fibres by the sol-gel method

Multiple oxide BaTiO3 gel fibres were prepared by the sol-gel method from Ba(OC2H5)2-Ti(O-isoC3H7)4-H2O-C2H5OH-CH3COOH and Ba(CH3COO)2-Ti(O-isoC3H7)4-H2O-CH3COOH solutions. Relatively long gel fibres of 10cm length were obtained from both solutions in the limited composition region. The latter solution in particular showed a spinnability even when it contained no water. Therefore, the occurrence of spinnability of the solution was considered to be due to the formation of linear polymers composed of bridging acetate groups such as Ti←O-C(CH3)-O-Ti rather than metalloxane bonding as Ti-O-Ti. Addition of water to the solutions seems to break the bridging acetate bonds and replace some of them by bridging oxygen bonds. The as-drawn gel fibres which were X-ray amorphous crystallized into BaTiO3 ceramic fibres of 5mm average length upon heating above 600 ° C. However, the gel fibres drawn from the sols without water became powdery on heating because of the lack of Ti-O-Ti metalloxane bonds. The crystallization behaviour of the BaTiO3 gel fibres is discussed based on the infrared spectroscopy, X-ray diffraction analysis and thermogravimetric-differential thermal analysis.

Oxynitride glasses prepared from gels and melts

The structures of glasses prepared by melting mixtures of alkali borosilicate glass and silicon nitride powders and by ammonolysis of porous borosilicate gels were studied using Fourier transform infrared spectroscopy and combustion analysis. Whereas there was little evidence of nitride bond formation in the melt prepared glasses, SiN and BN bonding were observed in the gel-derived glasses. It is proposed that these differences occur because Na 2O and B 2O 3 are reduced by Si 3N 4 in the melt to form SiO 2 + N 2 + metal. In comparison, ammonolysis of gels is a low temperature process (<1000° C) which occurs by Lewis acid adsorption and Lewis base attack on bridging oxygen bonds.

Aqueous corrosion studies of a fluorozirconate glass

The effects of aqueous corrosion on a fluorozirconate glass containing ZrF 4, BaF 2, AlF 3, LaF 3 and LiF were investigated using soaking solution analysis, infrared transmission and reflectance spectroscopy and scanning electron microscopy. The dissolution of the glass was nearly congruent. The leached surface of the glass was covered with hydroxide crystals of Zr and Ba. The outer leached layer was thick, highly hydrated and cracked while the glass below was also hydrated and cracked indicating that no protective surface layer was formed. Drying studies of leached samples showed the appearance of an infrared absorptance peak at 7 μm (1440 cm −1) caused by bridging oxygen bonds formed during dehydration.

Electron Paramagnetic Resonance in R2O‐Al2O3−SiO2 Glass Systems

Systematic detection of an EPR signal was conducted for three alkali oxide‐Al2O3−SiO2 glass systems. Observed EPR spectra, having a main line with g=2.03 and a broad and anisotropic shape, are attributed to the unsaturated bridging oxygen bond resulting from the breakup of the SiO2 random network. This signal appears in the area AValkali atom ratio &gt;1 for the Na20 and K2O systems, indicating that the collapse of the Al 4‐coordinated structure begins at an equimolar ratio when alumina is substituted for the alkali oxide, whereas somewhat different behavior was observed for the Li2O system.