Use of FTIR reflectance spectroscopy to monitor corrosion mechanisms on glass surfaces

Fourier transform infrared (FTIR) reflectance spectroscopy was used to monitor corrosion mechanisms on the surface of lithium disilicate (Li₂O-2SiO₂) glass samples exposed to an aqueous solution for short times. The traditional mechanisms of glass corrosion were observed but a spectral feature was resolved that was previously unreported. This feature consisted of a peak suspected to result partially from a silanol (Si-OH) vibration in the region 800-1050 cm⁻¹ that shifted and reappeared in a cyclic fashion throughout the corrosion process. The behavior of this peak tends to suggest that the creation and condensation of Si-OH groups is the reaction responsible for causing the shift of the main Si-O-Si and Si-O⁻ peaks, a phenomenon which has previously lacked a detailed explanation.     

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.     

Percolation transition of siloxane domain in partially phenylated organic/inorganic hybrid glass

Organic-inorganic hybrid glass undergoes a percolation transition of the organic or inorganic moiety at a certain volume fraction of either phase. At the percolation threshold, various properties of the hybrid glass exhibit an abrupt change. We attempted to evaluate the threshold volume fraction of the percolation transition in partially phenylated glass from the measurable or observable behavior at the percolation transition. The volume fraction of the phenyl moiety in the hybrid glass was varied by variation of the mixed fraction of two starting silicon alkoxides, TEOS (tetraethylorthosilicate) and PTES (phenyltriethoxysilane). The threshold volume fraction was estimated as the point at which the dye-colored state with hydrophilic/hydrophobic dye, the Vickers hardness and siloxane bonding length exhibited a significant change. The percolation threshold of the phenyl moiety was estimated to be approximately 50 vol.%. At this threshold, the Vickers hardness showed a abrupt and almost discrete decrease and noticeable elasticity appeared. At the same time, the siloxane bondings were stretched by approximately 20% on the percolation of the phenyl part. In partially phenylated glass prepared from mixture of TEOS and PTES, the siloxane bondings seem to have a strong tendency to form a percolated siloxane network, and as a result of that, only the percolation of the phenyl moiety could be captured from the experimentally measurable quantities.     

Evaluation of molecular volume of siloxane bonding and phenyl group in partially phenylated organic/inorganic hybrid glass

The molecular volume of the siloxane bonding and phenyl groups in partially phenylated organic/inorganic hybrid glass were evaluated from the density. The partially phenylated organic/inorganic hybrid glass were prepared by sol-gel method starting from TEOS (tetraethylorthosilicate) and PTES (phenyltriethoxysilane) mixed at various molar ratios. The molar volume of the hybrid glass exhibited a completely linear dependence on the molar fraction of PTES showing that the molecular volumes of the siloxane parts and phenyl groups are constant irrespective of the molar fraction of PTES. From the obtained dependence of the molar volume on the added molar fraction, the molecular volumes of the siloxane bonding and phenyl group were estimated. Finally, the percolation threshold of the volume fraction of phenyl group was estimated from using the obtained molecular volumes.     

Evolution of the local environment of lanthanum during simplified SON68 glass leaching

The evolution of the short- and medium-range local environment of lanthanum was determined by L_III-edge X-ray absorption spectroscopy (XAS) during leaching of simplified SON68-type glasses. In glass without phosphorus, lanthanum is found in a silicate environment, and its first coordination sphere comprises eight oxygen atoms at a mean distance of 2.51 Å. When this glass was leached at a high renewal rate, the lanthanum local environment was significantly modified: it was present at hydroxycarbonate and silicate sites with a mean La-O distance of 2.56 Å, and the second neighbors consisted of La atoms instead of Si for the glass. Conversely, in the gel formed at low renewal rates, lanthanum was found in a silicate environment similar to that of the glass. In phosphorus-doped glass, lanthanum is found in a phosphate environment, although the Si/P atomic ratio is 20:1. Lanthanum is surrounded by seven oxygen atoms at a mean distance of 2.37 Å. When phosphorus-doped glass is leached, regardless of the leaching solution flow rate, the short- and medium-range lanthanum local environment remains almost constant; the most significant change is a 0.05 Å increase in the La-O distance.     

Silicate nanoparticles by bioleaching of glass and modification of the glass surface

Bioleaching is examined as a low temperature (50 °C) soft chemical approach to nanosynthesis and surface processing. We demonstrate that fungus based bioleaching of borosilicate glass enables synthesis of nearly monodispersed ultrafine (∼5 ± 0.5 nm) silicate nanoparticles. Using various techniques such as X-ray diffraction, X-ray photoelectron spectroscopy and FTIR we compare the constitution and composition of the nanoparticles with that of the parent glass, and establish the basic similarities between the two. The bioleaching process is shown to enhance the non-bridging oxygen component and correspondingly influence the Si-O-Si network. The root mean square roughness of glass surface is seen to increase from 1.27 nm for bare glass to 2.52 nm for 15 h fungal processed case, this increase being equivalent to that for glass annealed at 500 °C.     

Nanomechanical properties of commercial float glass

The float process produces flat glass with a tin-rich surface due to contact with the molten metal bath. The incorporation of tin into the glass network is expected to modify the mechanical properties of the surface and the relative durability of the two sides of the material. In this work nanoindentation was used to evaluate the elastic modulus and hardness of a 2 mm thick commercial float glass. The near-surface elastic modulus (depths < 400 nm) of both sides of the glass was elevated by up to 10%, and could not be attributed solely to the presence of tin. However, slight differences in hardness (<10%) between the air and tin sides of the float glass were observed. These results suggest that tin may alter the flow properties of the glass, but the elastic modulus changes are masked by other structural and chemical differences between the air and tin sides of the float glass.     

Distributions of copper and CuBr in CuBr nanocrystallite-dispersed glasses prepared by copper staining

CuBr nanocrystallite-dispersed glasses were prepared by incorporation of copper into bromide ion-containing borosilicate glass using the technique of copper staining. The copper ion incorporation process was mainly controlled by ionic diffusion from the surface to the interior of the glass. The depth profiles of Cu and CuBr concentration were examined by energy dispersive X-ray analysis and by reference to the change in absorption intensity assigned to the CuBr exciton band along the depth. While the Cu concentration was found to decrease monotonically, the CuBr concentration profile showed a maximum at a distance of 10-50 μm from the glass surface. Although the depth reached by the copper ions became greater with increasing heat-treatment time, the depth at which CuBr was precipitated was found to be saturated. This means that regions were found in the glasses in which no CuBr crystallites precipitated, although migration of Cu ions to these regions had taken place.     

Sub-critical crack growth rate of soda-lime-silicate glass and less brittle glass as a function of fictive temperature

Sub-critical crack growth rates of soda-lime-silicate glass and less brittle glass with different fictive temperatures were compared using the DCDC method under both dry and humid atmospheres in order to investigate the origin of the unique mechanical features of the less brittle glass developed by Ito and his collaborators. In both dry and humid atmospheres, the crack velocity of the soda-lime-silicate glass was slower than that of the less brittle glass. For both glasses, the glass sample with higher fictive temperature showed a slower crack growth rate under both dry and humid atmospheres. These observations can be explained by the tendency for the plastic flow at the crack tip; the soda-lime-silicate glass is expected to show easier plastic flow under tension than the less brittle glass, and also the samples with higher fictive temperatures are expected to show easier plastic flow, leading to greater fracture toughness, K_IC, and slower crack growth rate.     

Nano-scale structural inhomogeneities of CuI-Cu2MoO4 superionic conducting glass observed by high resolution transmission electron microscopy

Nano-meter sized structural inhomogeneities of (CuI)_0.52-(Cu₂MoO₄)_0.48 superionic conducting glass were investigated by high resolution transmission electron microscopy. The as-quenched sample of CuI-Cu₂MoO₄ is a homogeneous glass, in which the CuI component is finely and uniformly dispersed among the oxyanions of Cu₂MoO₄ glassy matrix. A two-step crystallization, starting at 440 and 495 K, was observed in the glass. After the first step crystallization, precipitating nano-crystalline cubic CuI 2-3 nm in diameter, the electrical conductivity increases by about 50%. On the other hand, the electrical conductivity decreases with the second crystallization event forming crystalline phases of CuI, Cu₂O and others 20-30 nm in diameter.     

The ionic transition and the glass transition in ion-conducting glasses

In an ion-conducting glass, there may be the ionic transition which characterizes ‘melting’ of the modifying ions in a similar way as the glass transition characterizes ‘melting’ of the glass network former. The ionic transition can be observed, electrically, by the thermally stimulated depolarization current technique. It is demonstrated that the relaxation time for the ionic transition is the same (near 100 s) with that for the glass transition in so far as the heating/cooling rate lies within, say, 10⁻¹-10⁻⁵ K/s as adopted in our routine works.     

Various transmission electron microscopic techniques to characterize phase separation - illustrated using a LaF3 containing aluminosilicate glass

Various transmission electron microscopy techniques which are useful for the characterization of phase-separation phenomena in glass materials are exemplarily demonstrated at a 40 SiO₂-30 Al₂O₃-18 Na₂O-12 LaF₃ glass. It is shown that direct imaging of phase-separated regions possesses manifold advantages over the traditional replica technique, particular if the feature size approaches the nano-scale. Although surface replica can be accomplished effortless and made a great leap in glass structure research possible, the method is indirect, i.e. requires a deep understanding of the chemical attack leading to the surface topography eventually imaged. Moreover, surface replicas reach their limits for nanosized features due to the inherent structure of the deposited replica film.     

Physicochemical studies of phosphate based P2O5-Na2O-CaO-TiO2 glasses for biomedical applications

Glasses P₂O₅-Na₂O-CaO-TiO₂ with different TiO₂ contents and fixed P₂O₅ (45 wt%) and CaO (24 wt%) have been prepared employing the normal melting and annealing technique. Measurements such as ultrasonic velocity, attenuation, solubility and pH have been carried out in all the compositions of the glasses. It is interesting to note that the above measured ultrasonic parameters exhibit an abnormal behavior (minimum) at 0.5 wt% of TiO₂ content, beyond which an increase in these parameters with increasing TiO₂ content is observed. The maximum pH values and Ca²⁺ ion release have been observed for the TiO₂ free glass those compositions with and the low TiO₂(?1.0 wt%) content. As the content of the TiO₂ increases, the solubility of the glasses decreases. The observed weight loss reveals two stages of phosphate dissolution kinetics i.e. the first stage, in which the weight loss is proportional to t^1/2, and a second stage in which a linear behavior is observed.     

High resolution O MAS and triple-quantum MAS NMR studies of gallosilicate glasses

Gallosilicate (or ‘galliosilicate’) glasses have been widely studied as analogs of aluminosilicates, and the variations with composition in properties are known to be similar in both systems. We have applied ¹⁷O MAS and triple-quantum MAS (3QMAS) NMR spectroscopy to investigate the oxygen local environments in Na-, Li-, Ca- and Y-gallosilicate glasses. Signals due to several different oxygen species can be resolved and their concentrations quantified and NMR parameters determined. The NMR spectra generally resemble those of aluminosilicate glasses, indicating that the current model of gallium ions occupying the same types of sites as aluminum ions is a good first approximation. Quadrupolar coupling constants for the various oxygen sites tend to be larger than those for aluminosilicates, however, and vary less among different types of sites. Broader ¹⁷O spectra at low to medium external magnetic fields result. In detail, several types of differences between the observed oxygen species populations for gallosilicate and aluminosilicate are consistent with the larger radius of Ga³⁺ in comparison to Al³⁺, and possibly with a somewhat greater tendency for the former to form groups with oxygen coordination numbers greater than four. These include more Si-Ga disorder than Si-Al disorder in corresponding sodium gallo- vs. aluminosilicates, and more ‘non-stoichiometric’ non-bridging oxygen in a calcium gallosilicate than in a calcium aluminosilicate glass.     

Thermodynamics of the Cu/Cu-redox equilibrium in soda-silicate and soda-lime-silicate melts

The thermodynamics of the redox equilibrium of Cu⁺/Cu²⁺ were determined by square-wave voltammetry in glass melts with the base mol% compositions x Na₂O · (100 − x) SiO₂ (x = 15, 20, 26 and 33) and (26 − x) Na₂O · x CaO · 74 SiO₂ (x = 0, 5, 10 and 15) doped with 1 mol% CuO in the temperature range from 850 to 1150 °C. All recorded voltammograms showed two maxima attributed to the reductions of Cu²⁺ to Cu⁺ and Cu⁺ to metallic copper. Both peaks are shifted to smaller potentials with decreasing temperature. With increasing melt basicity, the [Cu⁺]/[Cu²⁺]-ratio first increases, and remains constant for optical basicities >0.56. The effect of composition on the redox equilibrium is explained by the incorporation of both Cu⁺ and Cu²⁺ in octahedral coordination into the melt structure.     

The glass transition temperature and infrared absorption spectra of: (70−x)TeO2 + 15B2O3 + 15P2O5 + xLi2O glasses

Glasses of the system: (70−x) TeO₂ + 15B₂O₃ + 15P₂O₅ + xLi₂O, where x = 5, 10, 15, 20, 25 and 30 mol% were prepared by melt quench technique. Dependencies of their glass transition temperatures (T_g) and infrared (IR) absorption spectra on composition were investigated. It is found that the gradual replacement of oxides, TeO₂ by Li₂O, decreases the glass transition temperature and increases the fragility of the glasses. Also, IR spectra revealed broad weak and strong absorption bands in the investigated range of wave numbers from 4000 to 400 cm⁻¹. These bands were assigned to their corresponding bond modes of vibration with relation to the glass structure.     

Signatures of an extended rigidity percolation in the photo-degradation behavior and the composition dependence of photo-response of Ge-Te-In glasses

Time dependent photocurrent measurements have been undertaken on bulk Ge₁₅Te_85−xIn_x (1 ? x ? 11) series of glasses. It is found that samples with x < 3 do not exhibit any photo-degradation whereas a decrease in photo-conductivity under illumination is observed in samples with x ? 3. Further, the photosensitivity of Ge₁₅Te_85−xIn_x glasses is found to reveal specific signatures at compositions x = 3 and 7. The observed composition dependent photo-degradation behavior and photo-response of these glasses have been understood on the basis of an extended rigidity percolation and its influence on network related properties.     

Nonlinear photosensitivity of photo-thermo-refractive glass by high intensity laser irradiation

Photo-thermo-refractive (PTR) glass is a material for high-efficiency phase volume hologram recording which possesses linear photosensitivity in the near UV region from 280 to 350 nm. In this paper nonlinear photosensitivity by 355 nm nanosecond pulses with intensity exceeding 1 MW/cm² and by 783 nm femtosecond pulses with intensity exceeding 1 TW/cm² is demonstrated. No photo-sensitizers are necessary in PTR glass for nonlinear photosensitivity. Photosensitivity by 355 nm nanosecond pulses is determined by glass matrix ionization resulting from two-photon absorption of incident radiation by glass matrix. Photosensitivity by 783 nm femtosecond pulses is determined by glass matrix ionization from nonlinear interaction of fundamental radiation and supercontinuum with modified glass matrix due to strong electric fields of incident radiation.     

Effect of antimony addition on the thermal and electrical-switching behavior of bulk Se-Te glasses

The thermal properties and electrical-switching behavior of semiconducting chalcogenide Sb_xSe_55−xTe₄₅ (2 ? x ? 9) glasses have been investigated by alternating differential scanning calorimetry and electrical-switching experiments, respectively. The addition of Sb is found to enhance the glass forming tendency and stability as revealed by the decrease in non-reversing enthalpy ΔH_nr, and an increase in the glass-transition width ΔT_g. Further, the glass-transition temperature of Sb_xSe_55−xTe₄₅ glasses, which is a measure of network connectivity, exhibits a subtle increase, suggesting a meager network growth with the addition of Sb. The crystallization temperature is also observed to increase with Sb content. The Sb_xSe_55−xTe₄₅ glasses (2 ? x ? 9) are found to exhibit memory type of electrical switching, which can be attributed to the polymeric nature of network and high devitrifying ability. The metallicity factor has been found to dominate over the network connectivity and rigidity in the compositional dependence of switching voltage, which shows a profound decrease with the addition of Sb.