Direct calculation of Young's moidulus of glass

An equation has been derived for the direct calculation of the Young's modulus of oxide glasses from their chemical compositions. The method is based on a consideration of dissociation energy of the oxide constituents per unit volume and the packing density. For borate glasses, the ratio of four-coordinated to three-coordinated borons must be taken into consideration. Excellent agreement is obtained between calculated and measured values of Young's modulus for over thirty different glasses.     

Calculation of bulk modulus,shear modulus and Poisson's ratio of glass

Combining Grüneisen's equation with our Young's modulus equation of glass, new formulae were semi-empirically derived for the calculation of bulk modulus, shear modulus and Poisson's ratio of glass. Considering packing density of atoms and bond energy in unit volume the elastic moduli of glass can be calculated. The agreements between calculated and observed values of the moduli of glass are satisfactory for more than 30 glasses.     

A new method to characterize medium range order in metallic glasses

A new method was proposed to describe cluster packing in metallic glasses. This method has no limitation of solute concentration and characterizes cluster packing by Voronoi polyhedron. The application of this method to Cu₆₄Zr₃₆ metallic glass indicates that most of the styles of cluster packing have the preference of fivefold local environment but not a face-centered-cubic or an icosahedral packing. The linear correlation between the coordinate number and the average number of adjust clusters might give an indication of the fractal nature of medium range order in metallic glasses.     

The role of MgO on thermal properties,structure and bioactivity of bioactive glass coating for dental implants

The successful application of bioactive glasses as a coating for titanium implants to improve osseointegration is dependent on achieving a thermal expansion coefficient (TEC) match between the two phases. Many studies have indicated that magnesium affects the thermal and structural properties of a glass. However, its effect on bioactivity of bioactive glasses is still under debate. In this study, we characterize the effect of magnesium on the thermal properties, structure and bioactivity of glasses containing MgO. Seven glasses with different MgO concentrations have been synthesized by melt-derived technique. All these glasses contain SiO₂, CaO, MgO, ZnO, Na₂O, K₂O and P₂O₅ and have been characterized by X-ray diffraction (XRD), differential scanning calirometry (DSC) and dilatometry. Additionally, the oxygen density and bulk density have been investigated. The bioactivity of the MgO glass series was evaluated in simulated body fluid (SBF) and Tris-buffer solution. The results indicate that magnesium suppresses crystallization and decreases TEC, glass transition temperature (T_g) and softening (T_s) temperature. Oxygen density increases proportionally with MgO content; whereas glass density decreases. After different time points, XRD and Fourier transform infra-red spectroscopy (FTIR) show that magnesium does not inhibit the apatite forming ability of the glasses, but retards the time of apatite deposition. The glass coatings of this series exhibit clear clinical application for use as a functional barrier: osteoblastic attachment and growth was poor, however, fibroblastic biocompatibility was good.     

Dense amorphous packing of binary hard sphere mixtures with chemical order: The stability of a solute ordered approximant

Recently, Miracle proposed that the intermediate structure in metallic glasses could be usefully characterized as an ordered face centered cubic packing of solute-centered coordination clusters. In this paper we examine the stability of such solute ordered arrangements in binary hard sphere mixtures subject to density maximization through local particle moves.     

Vibrational spectral analysis of structural modifications of Cr2O3 containing oxyfluoroborate glasses

Infrared and Raman spectra of oxyfluoroborate glasses of the compositions 20CaF₂-20 ZnO-(60-x) B₂O₃-x Cr₂O₃ with 0 ≤ × ≤ 0.10 mol% (x = 0, 0.02, 0.04, 0.05, 0.06, 0.07, 0.08 and 0.1) have been analyzed in order to explain the role of Cr₂O₃ on the structure of these glasses. Density, molar volume, oxygen molar volume and oxygen packing density are determined to explain the packing of the atoms in the glasses. From these studies, the existence of different borate groups like di-, tri-, tetra-, penta-, ortho-, pyro- and metaborates in these glasses is established. With the increase in the concentration of Cr₂O₃ up to 0.06 mol%, conversion of BO₃ units into BO₄ units and above this mole fraction the reconversion of BO₄ units into BO₃ units is observed. The breaking and reforming of the boroxol ring is explained from the Raman spectral studies of these glasses.     

Bulk metallic glasses based on ytterbium and calcium

We report the formation of a family of bulk metallic glasses (BMGs) based on rare earth element of ytterbium and alkaline earth element of calcium. The glass-forming ability, atomic packing density and corrosion behaviors of the BMGs show an extremum around the eutectic point with the change of the concentration of Yb and Ca.     

Bond character and properties of the mixed alkali system Na2OK2OAl2O3SiO2

The mixed alkali glass system Na₂OK₂OAl₂O₃SiO₂ was investigated. Density, transformation temperature, refractive index, and chemical durability were studied. Optical absorption and ESR spectra of the CuO-doped glasses were determined.Calculations of the polarizability of O^2?, bonding parameters of the Cu²⁺ complex, and the packing density are presented. It was found that for the mixed alkali glasses, the oxygen- alkali bond has a more ionic character than expected from additivity. This fact enables the non-linear changes of the refractive index, of the shift of the Cu²⁺ absorption band, and of the covalency to be interpreted as the Na mole fraction is varied. It is also possible to explain qualitatively the density, T_g and chemical durability non-linear variations with change of the Na content by the ionicity deviations of the bond character and the postulated pairs of Na⁺ and K⁺ ions in the mixed alkali glasses.     

Synthesis of CuO---Al2O3---SiO2 glasses from the sol-gel method and properties

The synthesis of CuO---Al₂O₃---SiO₂ glasses by the sol-gel method was investigated and the thermal expansion of bulk glasses was measured. Phase separation was observed in these glasses and apparently consisted of a copper-rich dispersed phase and a network former-rich matrix phase. The low thermal expansion coefficient of these glasses was governed by the matrix phase.     

Considerations on the structure and physical properties of B2O3-SiO2 and GeO2-SiO2 glasses

Data of density, refractive index and thermal expansion coefficient for B₂O₃-SiO₂ and GeO_2-SiO₂ glasses have been analyzed. The volumes of the structural units are the same found for the vitreous B₂O₃, GeO₂ and SiO₂. The volume of any structural unit is constant over the entire composition region of the glass system. The same has been found for the differential refraction and unit refraction of the structural units in these glasses. Different features are observed for the differential expansion of the structural units. There is a considerable change with composition in the differential expansion of BO₃, GeO₄ and SiO₄ units. The effect is attributed to a change in the asymmetry of vibrations with the number of Si-O-B or Si-O-Ge linkages in the matrix. The thermal expansion coefficient is mainly determined by the contribution of B₂O₃ or GeO₂ in the concerned glasses.     

Packing as a probe of structure in alkaline earth glass systems

Packing is an intrinsic property of glass, defined as the ratio of ionic volume to molar volume, and is a useful parameter for analyzing structural changes with composition. Alkali based glasses show two trends in packing, one dominated by the oxygen covalent network for the small ions, Li and Na, and one ionically dominated by the metal cations for the large, K, Rb and Cs cases [S. Giri, C. Gaebler, J. Helmus, M. Affatigato, S.A. Feller, J. Non-Cryst. Solids 347 (2004) 87]. We have found that alkaline earth glasses do not display these behaviors, and in this paper we determined the packing fractions of these glasses and compared them with the alkali case. Further, we considered the structural implications of the packing trends.     

The application of small polaron theory to transition metal oxide glasses

A review of the experimental data on a range of transition metal oxide glasses shows a strong relationship between activation energy and site spacing for glasses based on V₂O₅. The behaviour confirms that transport in amorphous V₂O₅ and vanadate glasses is by adiabatic hopping with an appreciable polaron bandwidth, while non-adiabatic hopping between isolated centres is apropriate for glasses based on most other transition metal oxides. The behaviour of vanadium is linked to the retention of a well-defined VO^5? structural unit in the glass network and to optimisation of the packing of this unit within the glass.     

Mixed-alkali effect in alkali borate glasses

The spectral absorption of Cu²⁺ and Ni²⁺, the density, molar volume, refractive index, molar refraction, thermal expansion coefficient, transformation and dilatometric softening temperatures of mixed alkali borate glasses are reviewed. These results indicate that in borate glasses, mixed alkalis do not produce gross alterations of the glass network, and that the weak deviations observed may be related to the boric oxide anomaly.     

Quenched-in excess volume and structural relaxation in Ni- and FeNi based metallic glasses

The amount of quenched-in excess volume (ΔV_R) in various Ni- and FeNi based metallic glasses, which is defined by the volume change due to the structural relaxation, was estimated from measurements of length changes caused by isochronal annealing. It was found that the values of ΔV_R depend greatly on the kind of transition metals (Fe, Ni) and metalloids (Si, B, P) and their ratios (Fe/Ni, Si/B). In non-magnetic Ni-based metallic glasses, almost a linear relationship was observed between the changes in volume and electrical resistivity during the low temperature annealing below around 275°C. Furthermore, a large ΔV_R was observed in the metallic glasses which have a large thermal expansion coefficient such as Ni₇₅Si_12.5B_12.5 or which exhibit a well-defined glass transition such as Fe₂₇Ni₅₃P₁₄B₆, as a general trend. These results indicate that the amount of quenched-in excess volume is very sensitive to the local atomic arrangement and is attributed mainly to the distribution in bond lengths, angles and coordination numbers in the short range structure and the difference in packing of basic structural units between as-quenched and relaxed glassy states.     

Glass formation, physico-chemical properties, and structure of glasses based on Ga2S3-GeS2-Sb2S3 system

We prepared sulfide glasses based on a Ga₂S₃-GeS₂-Sb₂S₃ system and investigated the compositional dependences of their physico-chemical properties and structure. Additivities were observed for density and refractive index; i.e., these properties were presented by the summation of the contribution from each component. With the increase of Sb₂S₃ content, the density, refractive index, and thermal expansion coefficient increased while the glass transition and softening temperatures decreased, and the short-wavelength absorption edge shifted to the longer wavelength side. These variations are expected from the incorporation of a heavy element (Sb) into the glasses. On the other hand, the replacement of GeS₂ by Ga₂S₃ increased the density and refractive index, and shifted the short-wavelength absorption edge to the longer wavelength side. These variations were explained by the increase of the number densities of the cations with the replacement and the formation of metal-metal bonds. The latter was confirmed from the Raman spectra. We also investigated the effects of Ag₂S incorporation on the optical properties. The incorporation of Ag₂S increased the density and refractive index whereas the position of the short-wavelength absorption edge varied little. These results show the possibility of fabricating an optical waveguide by Ag incorporation into the glasses.     

Low expansion copper aluminosilicate glasses

The thermal expansion coefficients of Cu₂O---Al₂O₃---SiO₂ glasses have been measured. These glasses have very low expansion coefficients similar to that for SiO₂ glass, but their liquids temperatures are much lower. It was possible to reduce the liquids temperature by the addition of 2 mol% of Na₂O while maintaining low expansivity. In order to explain the low expansivity, the effects of cation size, valence, the Cu²⁺/Cu⁺ ratio, bond strength and phase separation were examined. Phase separation was observed in these glasses which probably consisted of a copper-rich dispersed phase and a network former-rich matrix phase. It was concluded that the overall expansion coefficients of the glasses were governed by the low expansion matrix phase.     

Dielectric breakdown in metal-anodic oxide film-metal sandwiches

This paper presents measured data on glass transition temperature, thermal expansion, density, hardness, refractive index and electron microscopy of GeAsSe glasses and bring together some literature data on viscosity and mechanical properties. Interpretation of this information to identify suitable compositions for bulk synthesis is discussed.     

The influence of Mg substitution for Al on the properties of SiMeRE oxynitride glasses

The thermal-mechanical properties of 60Si20Mg20RE (RE: rare earth) oxynitride glasses can be tailored by the substitution of rare earths of decreasing ionic size. The Young’s modulus, hardness, glass transition temperature and viscosity all increase with the substitution La by Gd and Gd by Lu while the thermal expansion coefficients decrease. Compared to the 55Si25Al20RE oxynitride glasses, replacement of Al by Mg lowers the glass transition temperatures and viscosities and raises the thermal expansion coefficients substantially. On the other hand, the Young’s moduli are higher in the Mg-bearing glasses. These behaviors are seen to be a result in changes in the nature of the bonding in the glass structure.     

Characterization of B2O3 and/or WO3 containing tellurite glasses

Characterization of B₂O₃ and/or WO₃ containing tellurite glasses was realized in the 0.80TeO₂–(0.20 ? x)WO₃ ? xB₂O₃ system (0 ≤ x ≤ 0.20 in molar ratio) by using differential scanning calorimetry, Fourier transform infrared spectroscopy, X-ray diffraction, scanning electron microscopy and energy dispersive X-ray spectrometry techniques. Glasses were prepared with a conventional melt-quenching technique at 750 °C. To recognize the thermal behavior of the glasses, glass transition and crystallization temperatures, glass stability value, glass transition activation energy, fragility parameter were calculated from the thermal analyses. Density, molar volume, oxygen molar volume and oxygen packing density values were determined to investigate the physical properties of glasses. Fourier transform infrared spectra were interpreted in terms of the structural transformations on the glass network, according to the changing B₂O₃ and/or WO₃ content. Crystallization behavior of the glasses was investigated by in situ X-ray diffraction measurements and microstructural characterization was realized by scanning electron microscopy and energy dispersive X-ray spectrometry analyses.