Multicomponent phosphate invert glasses with improved processing

Owing to their structure of small phosphate units, phosphate invert glasses have high crystallisation tendencies, which make processing of the melt challenging. The aim was to improve their processing by (1) increasing the number of glass components and (2) incorporating intermediate oxides (TiO₂, MgO and ZnO). Glasses (P₂O₅–CaO–MgO–Na₂O) were produced by a melt-quench route. In series 1, TiO₂ was partially substituted for Na₂O, and the number of components was increased by partially substituting strontium for calcium, zinc for magnesium and potassium for sodium on a molar base. In series 2, the MgO + ZnO content in the multicomponent glass was varied between 0 and 20 mol% in exchange for CaO + SrO. Differential scanning calorimetry showed a significant increase of the processing window in the multicomponent glasses, explained by an increased energy barrier for crystallisation owing to increased entropy of mixing. The MgO + ZnO content also significantly improved the processing window from 117 K (0 mol% MgO + ZnO) to 185 K (20 mol%), owing to their large field strength. These results show that the processing of phosphate invert glasses for biomedical applications can be improved significantly by incorporating ions such as strontium or zinc which are also known to have therapeutic effects.     

Linear and nonlinear optical properties of glasses doped with Bi nanoparticles

Transparent glass samples doped with bismuth nanoparticles are prepared by heat treatment of as-made glass samples. According to the results of X-ray diffraction, transmission electron microscopy, and energy-dispersive X-ray spectra, Bi nanoparticles are well distributed inside glasses after heat treatment. The average size of Bi nanoparticles increases with the increasing of heat treatment temperature. Because of the size effect and multiple scattering of nanoparticles, the fundamental absorption edge shows a red-shift behavior with the increasing of heat treatment temperature. Nonlinear optical properties of Bi nanoparticles doped glasses are investigated by using Z-scan technique. The maximum value of χ⁽³⁾ of the glasses is estimated to be 2.49 × 10^? 7 esu at 800 nm. These results indicate that Bi nanoparticles doped glasses may be promising as material for optical switching.     

Effect of aluminum ions on intrinsic sub-critical crack growth in metaphosphate glasses

Sub-critical crack growth in various kinds of metaphosphate glasses was investigated by using DCDC (Double Cleavage Drilled Compression) technique. The crack growth measurements were only being made in Region III, or in an inert environment. In order to evaluate intrinsic crack growth behaviors in Region III, crack propagation tests were performed in dehydrated heptane, and the crack velocity, v, was plotted as a function of the stress intensity factor, K_I. Fracture toughness of glass was also estimated from a stress intensity factor at a given crack velocity. For binary metaphosphate glasses (50MO · 50P₂O₅, M = Zn, Mg, Ca, Ba), fracture toughness increases in the order of Mg > Ca > Zn > Ba. However, the slope of K_I–v curve is almost unchanged. In the case of aluminum containing metaphosphate glasses, with increasing aluminum content, fracture toughness increases and the slope of K_I–v curve becomes smaller, regardless of the type of divalent cations in glass. It is concluded that an addition of aluminum ions into metaphosphate glass results in both high toughness and easy fatigue. In addition, the structural role of aluminum ions on the intrinsic sub-critical crack growth is discussed in terms of the models of atomistic bond rupture.     

Photoinduced redox-reactions and transmission changes in glasses doped with 4d- and 5d-ions

(Fluoride)phosphate and borosilicate glasses of high intrinsic transparency in the deep ultraviolet (UV), were doped with 50–5000 ppm of the 4d- and 5d-ions Zr, Nb, Ta, Mo, or W. All of these ions absorb strongly in the UV. Samples plates were irradiated by UV lasers and the as a consequence generated various extrinsic and intrinsic defects were characterized by optical and EPR spectroscopy. The laser induced transmission changes depend not only on the glass matrix, but also on the valence of the dopants. Only fully oxidized d⁰-ions are observed in fluoroaluminate glasses. Laser irradiation photoreduces the d⁰-ions to extrinsic electron-centers (EC). Laser induced transmission changes extend from the UV up to 600 nm in the visible. The dopants are easily reduced to lower valences in metaphosphate glasses. Extrinsic hole centers (HC) replace intrinsic HC in samples containing the reduced transition metal ions. The strong transmission changes seen below 300 nm arise from intrinsic EC and extrinsic HC. The few remaining intrinsic HC (300–600 nm) recombine rapidly with EC or transform into more stable extrinsic HC. Borosilicate glasses show the formation of intrinsic boron oxygen hole center in the EPR spectra and of intrinsic HC and EC in the optical spectra. The d¹-ion Mo⁵⁺ is the only identified reduced dopant species in the borosilicate glasses. The band intensity of intrinsic EC in relation to intrinsic HC is correspondingly highest for the Mo-doped samples, in which extrinsic HC are generated.     

UV–visible and infrared absorption spectra of transition metals-doped lead phosphate glasses and the effect of gamma irradiation

Undoped and transition metals (TM 3d)-doped lead phosphate glasses were prepared. Ultraviolet–visible absorption spectra were measured in the range 200–1100 nm before and after successive gamma irradiation. Experimental results indicate that the undoped lead phosphate glass reveals before irradiation strong and broad ultraviolet absorption which is related to the co-sharing of absorption due to both trace iron impurities and lead ions (Pb²⁺). In the TM-doped glasses, characteristic absorption bands are obtained in both the UV and/or visible regions due to each respective TM ion in addition to that observed by the base undoped UV absorption. Gamma irradiation produces with the undoped glass a prominent induced ultraviolet broad band centered at about 300 nm originating mostly from the contribution of trace iron impurities and the visible spectra reveal markedly high shielding behavior towards successive gamma irradiation, due to the presence of both high content of heavy Pb²⁺ ions and the sharing of phosphate as a partner. With TM-doped samples, the observed induced bands are virtually varying and related to the type of the sharing TM ions. Infrared absorption spectra reveal in the undoped and TM-doped glasses characteristic structural phosphate groups mainly consisting of metaphosphate and pyrophosphate units. Transition metals are assumed to cause depolymerization of the phosphate glass network with different ratios but the changes in IR spectral data are limited due to the low doping level. Gamma irradiation of the samples is assumed to cause changes in the bond angles or bond lengths of the structural phosphate units within network as evident in the variation of the intensities of the IR bands.     

Manufacturing of porous niobium phosphate glasses

Niobium phosphate glasses with composition 33P₂O₅ · 27K₂O · 40Nb₂O₅ are usually very stable with regard to crystallization resistance, with a relatively high glass transition temperature (T_g ∼ 750 °C), and are potentially suitable for nuclear waste immobilization. Porous niobium phosphate glasses were prepared by the replication method. The porous glasses were produced via the dip-coating of an aqueous slurry containing 20 wt% powdered glass into commercial polyurethane foams. The infiltrated foams were oxidized at 600 °C for 30 min to decompose the polymeric chains and to burn out the carbon, leading to a fragile glass skeleton. Subsequent heating above the glass transition temperature in the range of 780–790 °C for 1 h, finally resulted in mechanically stable glass foams, which maintained the original interconnected pore structure of the polyurethane foam. The struts showed the neck formation between particles, evidencing the initial stage of sintering. The open and interconnected porosity of the glassy foams lies in the range of 85–90 vol.%. It was concluded that porous niobium phosphate glasses are potential candidates for immobilizing liquid nuclear waste.     

Crystallization of barium magnesium phosphate glasses determined by differential thermal analysis and X-rays diffraction

The scope of this work is to determine the crystalline phases of devitrified barium magnesium phosphate glasses and the glass composition which presents the best resistance to crystallization. Barium magnesium phosphate glasses with composition xMgO · (1 ? x)(60P₂O₅ · 40BaO) mol% (x = 0, 0.15, 0.3, 0.4, 0.5, and 0.6) were analyzed by differential thermal analysis (DTA) to evaluate the thermal stability against crystallization, and X-ray diffraction (XRD) to identify the crystalline phases formed after devitrification. The glass transition temperature (T_g) increases as the MgO content increases. The maximum temperature attributed to the crystallization peak in the DTA curve (T_c) increases when x increases in the range 0 ? x ? 0.3, and it decreases for x > 0.3. The most thermally stable glass composition against crystallization is for x = 0.3. After the devitrification, the number of coexisting crystalline phases increases as the MgO content increases. For x = 0.3 there is the coexistence of γBa(PO₃)₂ and Ba₂MgP₄O₁₃ phases for devitrified glasses. The trend of the T_c is explained based on the assumptions of changes in the Mg²⁺ coordination number and the amphoterical features of MgO.     

Thermal and mechanical properties of rare earth aluminate and low-silica aluminosilicate optical glasses

Aluminate glasses containing 45–71.5 mol% alumina, 10–40 mol% rare earth oxide, and 0–30 mol% silica were synthesized from precursor oxides. The glass transition and crystallization temperatures were determined by differential scanning calorimetry; the structural and mechanical properties were investigated by Raman and Brillouin spectroscopy. The range of the supercooled liquid region varies from ∼40 °C to 200 °C, providing a useful working range for compositions with 5–30 mol% silica. Raman scattering showed the presence of isolated SiO₄ species that strengthen the network-forming structure, enhance glass formation, and stabilize the glass even when they are present at fairly low concentrations. Sound velocities were measured by Brillouin scattering. From these and other values, various elastic moduli were calculated. The moduli increased with both aluminum and rare earth content, as did the hardness of the glasses. Young’s modulus was in the range 118–169 GPa, 60–130% larger than that for pure silica glass.     

Synthesis and characterization of M2O–MgO–WO3–P2O5 (M = K, Rb, Cs) glass system

Transparent glasses of the composition M₂O–MgO–WO₃–P₂O₅ (M = K, Rb, Cs), corresponding to the crystalline phases of M₂MgWO₂(PO₄)₂, have been prepared and studied by Raman and IR spectroscopy as well as DTA. Moreover, the thermally stimulated depolarization and dc conductivity have been measured. The glass transition temperature is 797, 795 and 773 K for the K-, Rb- and Cs-containing glass, respectively. Raman and IR studies have shown that these glasses have very similar structure. The main building blocks are pyrophosphate groups, WO₆ octahedra and magnesium–oxygen polyhedra. The dc conduction in these glasses is controlled by hopping of small polarons. The potassium containing glass was shown to be very stable whereas the rubidium and cesium glasses have significantly higher tendency for crystallization and phase separation. It seems, therefore, that the potassium containing glass is a suitable material for the preparation of samples containing non-linear and ferroelectric nanocrystals of the K₂MgWO₂(PO₄)₂ phosphate.     

Structure of rare-earth phosphate glasses by X-ray and neutron diffraction

Previous diffraction studies of the structures of rare-earth phosphate glasses (R₂O₃)_x(P₂O₅)_1−x are extended to glasses with smaller R³⁺ ions with R = Sm, Gd, Dy, Er, Yb, Y for x = ∼0.25 and with R = Nd, Sm, Gd for x = ∼0.15. Parameters for the P–O, R–O and O–O first-neighbor peaks were obtained by Gaussian fitting. P–P and R–P distances were estimated from the positions of peak maxima. Effects of residual silica or alumina contents present as a result of glass processing were taken into account for selected samples. The P–O coordination number, N_PO, and the P–O, O–O, P–P distances are consistent with the presence of phosphate tetrahedra and are insensitive to the R species and the R₂O₃ content. Rare-earth coordination numbers, N_RO, decrease from ∼8 to ∼6.5 when x is increased from ∼0.15 to ∼0.25. N_OO and N_PP decrease with increasing R₂O₃ content indicating the network disintegration. The numbers N_RO of the metaphosphate glasses (x = ∼0.25) decreases from ∼7 to ∼6 when R is changed from La to Yb. This change is also indicated by the behavior of the R–O distances and by constant number densities of atoms. The decrease in N_RO with increasing R₂O₃ content is due to the reduction in the number of terminal O (O_T) available for coordination of the R³⁺ ions (six at metaphosphate composition). Especially for smaller R³⁺ ions sharing O_T between two R sites is not favored. The decrease by ∼0.04 nm of the prominent R–R first-neighbor distance with a change of R from La to Yb at the metaphosphate composition is indicated by a shift to higher magnitude of scattering vector of the shoulder occurring in front of the first main diffraction peak.     

Catalysis and proton-conduction of novel phosphate glasses

The performance of phosphate glasses as a catalyst for water decomposition and a proton conductor was investigated. Glasses with a composition of 30Na₂O–10BaO–30P₂O₅–(30?x)WO₃–xNb₂O₅ (5 < x < 25) decompose water vapor and generate hydrogen at 500 °C. The best decomposition performance was observed on a specimen with the Nb₂O₅ composition of x = 15. A part of hydrogen produced on the glass surface changes to protons by reducing W⁶⁺ ions and penetrates into the glass. The electron is the dominant charge carrier in the electric conduction of W-rich glasses, whereas proton conduction is predominant in Nb-rich glasses in hydrogen atmosphere. A Raman scattering experiment revealed that Nb contributes to depolymerize the –P–O–P– chains in the phosphate glass producing non-bridging oxygen. A possible model was proposed for the water decomposition and proton conduction processes.     

Spectroscopic studies of gamma irradiated Nd doped phosphate glasses

Ultra violet-visible (UV-Vis) and Fourier transform infrared (FT-IR) spectra of Nd doped phosphate glasses have been studied before and after gamma irradiation in order to understand the changes in the optical properties of glasses as well as to find the characteristics frequencies of the vibrational modes of chemical bonds, which decide the structural and spectral changes. UV, Vis, IR absorption and photoluminescence spectra of these glasses show changes depending on the composition of glass matrix. These changes are correlated on the basis of oxygen (O) and neodymium (Nd) concentration ratio obtained from energy dispersive X-ray spectroscopic (EDX) measurement. Gamma irradiation shows decrease in transmission below 700 nm for all the Nd³⁺ absorption lines from all the samples. Differential absorption spectra (UV-vis) of the samples before and after gamma irradiation show generation of some new bands below 700 nm along with dips (decrease) in the spectrum at the location of main Nd³⁺ absorption lines. This is attributed to the generation of different types of defects in the glass matrix along with possibility of change in the valence state of Nd³⁺ to Nd²⁺. IR absorption spectra of these glasses are found dominated mainly by the characteristics phosphate groups and water (OH) present in the glass network. The effects of gamma irradiation on IR absorption are observed in the form of bond breaking and possible re-arrangement of bonding. EDX and X-ray photoelectron spectroscopic (XPS) measurements indicate decrease in the relative concentration of oxygen in the glass samples after γ-irradiation.     

Structure-property correlation in (50 − x)Na2O–50P2O5–xCoCl2 glassy systems

Ternary sodium–cobalt–phosphate glasses of the composition (50 − x)Na₂O–50P₂O₅–xCoCl₂ with x varying between 0 and 15 mol% prepared by melt quenching have been characterized by Fourier transform infrared (FT-IR) spectroscopy and X-ray diffraction (XRD) techniques. Thermal (T_g, T_c) and electrical properties have been investigated. Infrared spectra reveal the formation of metaphosphate glasses (Q² tetrahedral units) with symmetric bridging oxygen (P–O–P) and non-bridging oxygen (P–O⁻). The spectra also indicate the formation of P–O–Co bonds in the metaphosphate glasses that replace P–O⁻–Na⁺ bonds. The results of thermal studies correlate with these FT-IR findings and support the formation of P–O–Co bonds and an increased cross-link density with increasing CoCl₂. This results in enhanced chemical durability and increased T_g and T_c of the glasses. The electrical conductivity parameters upon changing the composition have been correlated with structural changes in the glass matrix.     

Properties of sodium-based ternary phosphate glasses produced from readily available phosphate salts

Three series of phosphate glasses were produced by melting together sodium phosphate salt (NaH₂PO₄) and the phosphate salts of either calcium (CaHPO₄), magnesium (MgHPO₄ · 3H₂O) or iron (FePO₄ · 2H₂O) in a 5% gold/95% platinum crucible at 1200 °C. The glass compositions were confirmed by EDX and XRD analysis. Glass transition temperature (T_g), density and durability in water were determined for all the compositions. Maximum metal oxide contents before devitrification were between 55% and 59% for CaO + Na₂O and 59% and 62% for MgO + Na₂O. The normalized equivalent for Fe₂O₃ + Na₂O was between 55% and 61%. Density values for the glasses lay between 2.49 and 2.75 g cm⁻³. T_gs lay between 295 °C and 470 °C. Degradation rates in deionized water at 37 °C lay between 0.03 g cm⁻² h⁻¹ for Na phosphate glasses and 9 × 10⁻⁶ g cm⁻² h⁻¹ for Ca phosphate glasses, 3 × 10⁻⁶ g cm⁻² h⁻¹ for Mg phosphate glasses and <3 × 10⁻⁶ g cm⁻² h⁻¹ for Fe phosphate glasses. The effect of metal addition on properties goes as Fe > Mg > Ca for degradation rates and T_g and Fe > Mg ≈ Ca for density. The change in properties with metal addition was seen to be linear for Fe and Ca additions but not with Mg addition. This is in agreement with the anomalous behavior of magnesium phosphate glasses.     

Ion conducting phosphate glassy materials

Fast ion conducting (FIC) phosphate glasses have become very important due to a wide range of applications in solid-state devices. We present an overview on silver based fast ion conducting phosphate glasses. Silver phosphate glasses containing chlorides of some metals viz; Li, Na, Mg, Pb and Cu [Ag₂O–P₂O₅–xMCl_y, where x = 0, 1, 5, 10 and 15 wt% and y = 1 when M = Li or Na and y = 2 when M = Mg, Pb or Cu] have been synthesized by melt quenching technique. Studies on these glassy materials characterized by X-ray diffraction, Fourier transform infrared spectroscopy, differential scanning calorimetric techniques and ion transport measurements are presented. The FT-IR studies support the formation of P–O–M linkages. The values of glass transition temperature (T_g) of the glassy materials containing lithium or sodium chloride have been found to decrease with increasing dopant concentrations indicating expansion of the glassy network. On the other hand, the T_g values increase with increasing magnesium, lead or copper chloride concentrations in silver phosphate glasses. This indicates an increase in cross–link density and enhanced chemical durability of these glassy materials. Ion transport studies suggest that the values of electrical conductivities of the metal chloride doped glassy materials are higher than those of the undoped ones and, at a particular dopant concentration, the following trend is observed.σ (–LiCl) ≥ σ (–NaCl) > σ (–MgCl₂) > σ (–PbCl₂) > σ (–CuCl₂)These results are supported by the experimental results of FT-IR spectral and thermal studies.     

Influence of the partial substitution of CaO with MgO on the thermal properties and in vitro reactivity of the bioactive glass S53P4

The influence of up to 4 mol% substitution of MgO for CaO on the properties of the bioactive glass S53P4 was studied. Thermal analysis, hot stage microscopy and X-ray diffractometry were utilized to measure the thermal properties and the crystallization characteristics of the glasses. The in-vitro bioactivity was measured by immersing the glasses for 4 h to one week in simulated body fluid. The formation of silica rich and hydroxyapatite layers was assessed from FTIR spectra analysis and SEM images of the glasses surface. Increasing substitution of MgO for CaO decreased the glass transition, the onset and endset of melting and the fusion temperatures. The activation energies for glass transition and crystallization also decreased from (790 ± 30) to (407 ± 30) kJ/mol and from (283 ± 30) to (145 ± 30) kJ/mol, respectively, indicating a decrease in bond length and an increase in bond strength with progressive MgO at the expense of CaO. All glasses dissolved identically in SBF during the first 24 h of immersion with subsequent formation of hydroxyapatite at the grain surfaces. The thickness of the surface layers decreased with increasing MgO content. For longer duration of immersion, the glasses with the highest MgO contents exhibited a slower reaction tendency, with simulated body fluid, than the Mg-free glass. These changes in the glass structure and in-vitro properties may be of interest for products from bioactive glasses with large surface area to volume ratio.     

Novel Bi-doped glasses for broadband optical amplification

Broadband infrared luminescence is observed in various Bi-doped oxide glasses prepared by conventional melting-quenching technique. The absorption spectrum of the Bi-doped germanium oxide glass consists of five broad peaks at below 370, 500, 700, 800 and 1000 nm. The fluorescence spectrum exhibits a broad peak at about 1300 nm with full width at half maximum (FWHM) of more than 300 nm when excited by an 808 nm laser diode. The fluorescence lifetime at room temperature decreases with increasing Bi₂O₃ concentration. Influence of the glass composition and melting atmosphere on the fluorescence lifetime and luminescent intensity is investigated. The mechanism of the broadband infrared luminescence is suggested. The product of stimulated emission cross-section and lifetime of the Bi-doped aluminophosphate glass is about 5.0 × 10^?24 cm² s. The glasses might be promising for applications in broadband optical fiber amplifiers and tunable lasers.     

Luminescent properties and applications of Tb3+ doped silicate glasses with industrial scales

Tb³⁺ doped X-ray conversion glassy screen with an industrial scale (50 mm × 50 mm × 12 mm) was successfully fabricated, and its luminescent properties and applications in CCD imaging system were investigated. Results showed that Tb³⁺ doped silicate glasses mainly emit weak blue (400–460 nm) and strong green (480–570 nm) fluorescence. With the increase of Tb³⁺ ion concentration, the intensity of green emission increases, but that of blue emission decreases. Gd³⁺ ions can sensitize the luminescence of Tb³⁺ ions among silicate glasses. With the increase of CeO₂ concentration, the luminescent intensity of Tb³⁺ doped silicate glasses at 550 nm quickly decreases. However, the irradiation resistance of Tb³⁺ doped silicate glasses can be effectively improved by CeO₂ addition. The imaging quality of the luminescent glass screen is more excellent than that of Gd₂O₂S polycrystalline screens.     

The densities of mixed glass former 0.35 Na2O + 0.65 [xB2O3 + (1 − x)P2O5] glasses related to the atomic fractions and volumes of short range structures

The mixed glass former effect (MGFE) is defined as a non-linear and non-additive change in the ionic conductivity with changing glass former fraction at constant modifier composition between two binary glass forming compositions. In this study, mixed glass former (MGF) sodium borophosphate glasses, 0.35 Na₂O + 0.65 [xB₂O₃ + (1 ? x)P₂O₅], 0 ≤ x ≤ 1, which have been shown to have a strong positive MGFE, have been prepared and their physical properties, density and molar volume, have been examined as predictors of structural change. The density exhibits a strong positive non-linear and non-additive change in the density with x and a corresponding negative non-linear and non-additive change in the molar volume. In order to understand the structural origins of these changes, a model of the molar volume was created and best-fit to the experimentally determined molar volumes in order to determine the volumes of the short range order (SRO) structural units in these glasses, how these volume change from the molar volumes of the binary glasses, and how these volumes change across the range of x in the ternary glasses. The best-fit model was defined as the model that required the smallest changes in the volumes of the ternary phosphate and borate SRO structural groups from their values determined by the densities of the binary sodium phosphate and sodium borate glasses. In this best-fit molar volume model, it was found that the volumes of the various phosphate and borate SRO structural groups decreased by values ranging from a minimum value of ~ 1% for x = 0.1 and 0.9 to a maximum value of ~ 6% for the phosphate and ~ 9% for the borate SRO groups at the minimum in molar volume at x = 0.4. The free volume was found to have a negative deviation from linear which is unexpected given the positive deviation in ionic conductivity.     

Effect of Al2O3 addition on the formation of perovskite-type NaNbO3 nanocrystals in silicate-based glasses

The crystallization behavior of 30Na₂O–25Nb₂O₅–(45 ? x) SiO₂–xAlO_1.5 (x = 0, 2.5, and 5) (mol%) glasses was examined and the effect of Al₂O₃ addition on the formation of perovskite-type NaNbO₃ crystals was clarified. It is found from X-ray diffraction analyses and transmission electron microscope observations that NaNbO₃ nanocrystals are formed in all glasses and the size of NaNbO₃ crystals decreases with the substitution of Al₂O₃ for SiO₂. A crystallized (heat-treated at 684 °C for 5 h) glass with x = 5, which contains NaNbO₃ nanocrystals with an average size of 50 nm, shows good optical transparency in the wavelength region of 500–2000 nm and a small hysteresis loop in the polarization–electric field curve. The lines containing NaNbO₃ crystals were patterned on the surface of NiO-doped glass with x = 5 by irradiations (power: 1.3–1.4 W, scanning speed: 10 μm/s) of Yb:YVO₄ fiber laser (wavelength: 1080 nm). The formation mechanism of NaNbO₃ nanocrystals in aluminosilicate glasses was also discussed.