Thermal Expansion of Alkali Borate Glasses

The thermal expansion behavior of lithium, sodium, potassium, and rubidium borate glasses was measured. The results indicate that the "borate anomaly" in the thermal expansion coefficient occurs at ∼20 mol% alkali oxide. A maximum in the glass transformation and dilatometric softening temperatures also occurs at ∼27 mol% alkali oxide. No evidence for phase separation was observed in this study. These effects are related to the structural changes reported for these glasses by Bray and coworkers.     

Optimized structural and mechanical properties of borophosphate glass

A series of phosphate glasses composed of (65-x)P₂O₅–15BaO–5Al₂O₃–5ZnO–10Na₂O-xB₂O₃ (x = 0, 2, 4, 6, and 8 mol%) were successfully prepared using the melt-quenching method. The effects of the addition of boron trioxide (B₂O₃) on the physical, structural, and mechanical properties of the glasses were investigated. As the added content of B₂O₃ increased from 0 to 6 mol%, the glass exhibited increased density and transition temperature, and decreased molar volume, indicating optimization of the glass stability. Raman spectroscopy revealed that the introduction of B₂O₃ transformed the glass from a chain structure to a three-dimensional network structure, which enhanced the chemical stability of the glass by the cross-linking of long phosphate chains with boron ions. Regarding the mechanical properties, when the boron content was 6 mol%, the flexural strength of the glass was 41% higher than that of the undoped boron, while the Vickers hardness and Knoop hardness values increased by 20.58% and 7.05%, respectively, and the fracture toughness was slightly decreased. In general, improving the mechanical properties of phosphate glass is of great significance for increasing the applications of this glass.     

Properties of Calcium, Strontium, and Barium Galliosilicate Glasses

Glasses in three alkaline-earth (Ca, Sr, and Ba) galliosilicate systems were prepared, and the density, viscosity, thermal expansion coefficient, and glass transformation temperature were measured. All glasses contain 30 mol% alkaline-earth oxide. It is suggested that alkaline-earth ions can play a role in the glass structure which is similar to that of an intermediate ion.     

Sol-Gel Synthesis of High-Quality Heavy-Metal Fluoride Glasses

Fluoride glasses are excellent laser hosts and are very well suited for a broad spectrum of optical applications. However, current fluoride glass synthesis is expensive. The solgel method is an affordable alternative for producing highperformance, optical-quality heavy-metal fluoride glasses. The method involves forming a hydrous oxide gel of the constituent metal alkoxides and salts, polymerizing the solution to form a gel, fluorinating the gel with anhydrous HF, melting the amorphous material in an oxidizing atmosphere of SF₆, and casting the melt into desired shapes. ZBLA (57ZrF₄·36BaF₂·4LaF₃·3AlF₃, in mol%) and Nd-doped (0.3 mol%) ZBLA glass rods were prepared by this process and their properties were measured. The solgel-based glasses had thermal and optical properties similar to those found in the literature for conventionally prepared fluorides.     

Phosphate content affects structure and bioactivity of sol-gel silicate bioactive glasses

Bioactive glasses can heal bone defects and bond with bone through formation of hydroxyl carbonate apatite (HCA) surface layer. Sol-gel derived bioactive glasses are thought to have potential for improving bone regeneration rates over melt-derived compositions. The 58S sol-gel composition (60 mol% SiO₂, 36 mol% CaO, and 4 mol% P₂O₅) has appeared in commercial products. Here, hydroxyapatite (HA) was found to form within the 58S glass during sol-gel synthesis after thermal stabilization. The preformed HA may lead to rapid release of calcium orthophosphate, or nanocrystals of HA, on exposure to body fluid, rather than the release of separate the calcium and phosphate species. Increasing the P₂O₅ to CaO ratio in the glass composition reduced preformed HA formation, as observed by XRD and solid-state NMR. Instead, above 12 mol% phosphate, a phosphate glass network (polyphosphate) formed, creating co-networks of phosphate and silica. Nanopore diameter of the glass and rate of HCA layer formation in simulated body fluid (SBF) decreased when the phosphate content increased.     

Comparative studies on the bioactivity of some borate glasses and glass–ceramics from the two systems: Na2O–CaO–B2O3 and NaF–CaF2–B2O3

Combined FTIR spectroscopy and X-ray diffraction analysis have been employed to investigate the bone-bonding ability or bioactivity of some prepared borate glasses and their glass–ceramic derivatives from the two systems (Na₂O–CaO–B₂O₃) and (NaF–CaF₂–B₂O₃). The present study includes the mentioned FTIR spectral and X-ray analytical techniques before and after immersion of the glasses and glass–ceramics for 2 weeks in 0.025 M sodium phosphate (Na₂HPO₄) solution. Also, the work extends to evaluate the corrosion behavior for specified grains of the studied samples (0.3–0.6 mm) after immersion in phosphate solution for 2 weeks at 37 °C. The FTIR spectra of the two glass systems after immersion show some changes in the vibrational bands than before immersion. The generation of the characteristic peaks at about 580 and 680 cm⁻¹ after immersion confirms the bone bonding ability by the formation of hydroxyapatite phase. The X-ray diffraction studies show the separation of (CaF₂) which is known to be an efficient nucleator. Weight loss data show a difference in solubility in the sodium phosphate solution between fluoride and oxide glass systems due to the strong action of the leaching solution and ease of solubility of fluoride glasses than corresponding oxide glasses in this solution. SEM data indicate the formation of small rounded or nodular shape crystals which are characteristics for the formation of hydroxyapatite layer and complete agreement with X-ray data.     

Magnetic Behavior and Microstructure of Vanadium Phosphate Glasses

The magnetic properties and microstructures of the vanadium phosphate glass system over the composition range 60 to 90 mol% V₂O₅ were investigated to study magnetic ordering in the glass and the effect of microstructure on its magnetic properties. Direct antiferromagnetic coupling between V⁴⁺ ions in the glassy matrix exists, and a transition temperature near - 70°C was observed. As-cast glasses with high V₂O₅ concentrations separated into two glassy phases; this separation increased the ESR line width as a result of inhomogeneity broadening. The separation, which concentrated the vanadium ions in a vanadium-rich phase, caused a hysteresis in the plot of ESR line intensity vs temperature at the transition temperature. Reduction of the vanadium ions by dextrose added to the melt enhanced phase separation and resulted in weak antiferromagnetic transitions at +70° and -120°C, the Neel temperatures of VO₂ and V₂O₃, respectively.     

Effect of magnesium content on bioactivity of near invert phosphate-based glasses

A series of phosphate glasses 40P₂O₅-(40−x)CaO-xMgO-(20−y)Na₂O-yTiO₂ (where 0 ≤ x ≤ 24 and y = 0 or 1) with varying MgO contents were investigated for their in vitro calcium phosphate (CaP) formation. Thermal analysis of these glass compositions was conducted and a significant decrease in glass transition temperature from 448°C to 430°C was seen with reducing MgO content from 24 to 8 mol%. Degradation studies were performed in phosphate buffered saline (PBS) at 37°C, where the 8 mol% MgO glass showed the highest mass loss of around 3.4% after 28 days of immersion. Cation release studies were conducted via ion chromatography, using ultrapure water at 37°C as the degradation medium. The highest release of Ca²⁺ and Na⁺ ions was observed with the 8 mol% MgO glass. In vitro CaP formation studies were conducted using glass discs immersed in simulated body fluid (SBF) at 37°C for up to 28 days. The amorphous phase and chemical composition of deposited CaP layers on the glass discs were confirmed via X-ray diffraction (XRD) and energy-dispersive X-ray spectroscopy (EDX) analysis, respectively. CaP layers with Ca/P ratio 0.8-1.1 were found to be deposited on the lower MgO content (8 to 2 mol%) glass surface after 28 days of SBF study.     

Structural and thermal influence of niobia in aluminoborosilicate glasses

The addition of small amounts of niobia (Nb₂O₅) in borosilicate glasses was explored. By analysis on thermal and structural changes, we found evidences that niobium integrates the glass structure in octahedral NbO₆ coordination. Adding up to 8.0 mol% of Nb₂O₅, the oxide partially ruptured the glass structure, interfering in the BO₃/BO₄ ratio, but the predominant network configuration was maintained. Thermally, there was an increase in the processing interval and the glasses became more resistant against crystallization, with the presence of niobia. Also, the oxide contributed to a notable decrease in the viscosity of the melts. The improvement of such properties were obtained by the controlled dispersion of the oxide in the glass network structure, avoiding large areas of phase-to-phase separation to preserve the desired ability of these glasses to incorporate a wide range of elements.     

Li2O-CuO-P2O5玻璃的电性能

本文采用一种新的成形工艺制备20Li2O-30CuO-50P2O5(摩尔比)玻璃,并在玻璃转变温度之上对样品进行了不同时间的热处理后测试了其电性能。结果发现,随热处理时间的延长电导率会出现峰值,且所有样品电导率与温度之间的关系都能很好地遵从Arrhenius关系,结合SEM、XPS和XRD分析,对这一现象作出了初步的解释。     

Preparation and Properties of Silver Borate Glasses

Silver borate Basses containing 0 to 30 mol% Ag₂O were formed. Properties measured include density, thermal expansion coefficient, glass transformation and dilatometric softening temperatures, transformation-range viscosity, dc electrical conductivity, and helium permeability and diffusivity. Optical spectroscopy revealed that the color of these glasses results from absorption bands at ∼407, ∼310, and ∼250 nm. Each band increased in intensity as the silver oxide content of the glass was increased. The properties of these glasses were consistent with the structural model currently used to describe the structure of alkali borate glasses. No evidence for the existence of phase separation was found for the conditions of the present study.     

Glass transition and crystallization of ZnO-B2O3-SiO2 glass doped with Y2O3

The effect of Y₂O₃ on the glass transition kinetics, crystallization kinetics, phase separation and crystallization behavior of 60ZnO–30B₂O₃–10SiO₂ glass has been investigated by non-isothermal differential thermal analysis, scanning electron microscopy (SEM) and X-ray powder diffraction (XRD). The glass transition activation energies E_g calculated by using both Kissinger and Moynihan model decrease from 668?kJ/mol to 573?kJ/mol for Kissinger model, and 682?kJ/mol to 587?kJ/mol for Moynihan model with the increase of yttrium oxide doping content from 0 to 6?mol%. And the glass crystallization kinetics parameters, crystallization activation energy E_c and Avrami exponent n stands for crystal growth, are also obtained on the basis of several well developed equations. Increase of about 58?kJ/mol in Ec values obtained by different theoretical equations is caused by addition of 6?mol% yttrium oxide into 60ZnO–30B₂O₃–10SiO₂ glass, and the Avrami exponent (n close to 2) suggests that crystal growth in 60ZnO–30B₂O₃–10SiO₂ glass doped with or without yttrium is mainly one-dimensional growth of crystals. The results on the phase separation and crystallization behavior occurred at 893?K and 993?K respectively for base and doped glass, are well consistent with the glass transition and crystallization kinetics results. Hence, addition of yttrium oxide into 60ZnO–30B₂O₃–10SiO₂ glass decrease the glass transition activation energy while increase the crystallization activation energy of glass, thereby the stability of glass structure is improved. Phase separation phenomenon and crystallization behavior occurred at glass surface provide some useful information for preparing glass ceramics with micro- or nano-crystals in surface.     

Joining of Calcium Phosphate Invert Glass-Ceramics on a β-Type Titanium Alloy

A bioactive calcium phosphate invert glass-ceramic containing β-Ca₃(PO₄)₂ crystals could be joined strongly with a Ti–29Nb–13Ta–4.6Zr alloy consisting of a β-titanium phase by heating the metal on which the mother glass powders with a composition 60CaO·30P₂O₅·7Na₂O·3TiO₂ (mol%) were placed, at 800°C for 1 h in air; the tensile joining strength was estimated to be ∼26 MPa on average. A compositionally gradient layer was developed on the metallic substrate during the heating. When the metal with glass powders on it was heated at 850°C in air, the phosphate glassy phase flowed viscously, permeating the oxide layer formed around the surface of the metal, which was thicker than that formed by heating at 800°C; a compositionally gradient layer was not developed, and a strong joining was not realized. The joining between the glass-ceramic and the metal is suggested to be controlled by viscous flow of the glassy phase in the glass-ceramic and by reaction of the glassy phase with the oxide phase formed around the surface layer of the metal.     

纳米二氧化钛薄膜光催化剂的合成及特性

研究采用溶胶-凝胶技术以载玻片为基质制备了纳米TiO2薄膜,向溶胶中添加乙酰丙酮后改善了溶胶的稳定性及薄膜的牢固性。用扫描探针显微镜(DFM)、X射线衍射(XRD)、红外光谱(IR)及X射线光电子能谱(XPS)对薄膜进行了表征。结果表明:扫描探针显微镜(DFM)观察到薄膜中颗粒的粒径为20~40nm,X射线衍射(XRD)表明TiO2为锐钛型,用红外光谱(IR)表征了溶胶及粉末样品的物性并探讨了反应的机理,X射线光电子能谱(XPS)结果显示薄膜中除含有Ti、O元素外,还有少量从玻璃表面扩散至薄膜中的Na和Si元素。TiO2薄膜对光降解甲基橙水溶液具有很好的光催化性,通过掺SnO2、酸处理途径明显提高了其性能。     

Effect of Nucleating Agents on the Crystallization of Calcium Phosphate Glasses

Phase evolution in calcium phosphate-based glass ceramics has been examined. Pure CaO:P₂O₅ readily formed a glass which surface nucleated upon annealing, but volume nucleation at 680°C was observed only after the addition of the nucleating agents, TiO₂ and A1₂O₃. Phase separation of Ti and Al occurred along with the nucleation and growth of a calcium phosphate phase, similar to β-Ca₂P₂O₇. Heat treatments at higher temperatures and/or for longer times resulted in crystallization of A1- and Ti-rich, phase-separated regions. A glass with a higher CaO:P₂O₅ ratio (approximately 2:1) could be prepared only when a total of 25-35 mol% of TiO₂, A1₂O₃, and SiO₂ were present in the batch. The glass phase-separated into respective SiO₂- and CaO/P₂O₅-rich regions on cooling. The SiO₂-rich regions did not influence crystallization and remained amorphous throughout the heat treatments. In the CaO/P₂O₅-rich regions, homogeneous volume nucleation of a Ti-rich phase readily occurred followed by the heterogeneous nucleation and growth on these nuclei of a calcium phosphate phase. Although this phase was macroscopically composed of spherulites, TEM revealed that they consisted of intertwined nanodendrites whose individual arms were approximately 20 nm wide and 50 nm long.     

Integration Between Optical and Structural Behavior of Heavy Metal Oxide Glasses Doped with Multiple Glass Formers

Heavy metal oxide glasses (composition 60 PbO, 20 Bi₂O₃ mol%) and containing 20 mol% conventional glass formers SiO₂, B₂O₃, and P₂O₅ were prepared. Combined optical and Fourier transform infrared absorption spectra were measured for the prepared glasses to justify the role of glass formers in the optical spectra together with the network structural groups in such glasses. Also, the density and molar volume values were calculated to obtain some insight on the compactness and arrangement in the network. Optical measurements have been used to determine the optical band gap (E_g), Urbach energy (ΔE) and the refractive index (n). Optical spectra of all the samples reveal strong UV absorption which is related to the presence of unavoidable trace iron impurities (Fe ³⁺ ions) contaminated within the raw materials which were used for the preparation of the studied glasses. Additional near visible bands are observed in all prepared glasses due to characteristic absorption of Pb ²⁺ and Bi ³⁺ ions. Furthermore, The variations of the luminescence intensity, values of the optical band gap, band tail, and refractive index can be understood and related in terms of the structural changes that take place in the glass samples. The infrared absorption spectra of the prepared glasses show characteristic absorption bands related to the borate or silicate or phosphate network (BO₃, BO₄, SiO₄, PO₄ groups) together with vibrational modes due to Bi-O and Pb-O groups.     

Crystallization in 70Ga2S3.30La2S3(mol%) Glasses as a Function of Oxide/Hydroxide Concentration

The crystallization of 70Ga₂S₃^.30La₂S₃(mol%) glasses has been studied using X-ray diffraction and transmission electron microscopy. Two of the glasses were prepared from raw materials with nominally different oxide concentrations. The third was prepared from raw materials aged in an oxygen-depleted, argon-flushed glove box for more than 1 yr. Their oxide/hydroxide impurity content was qualitatively ranked using Fourier transform infrared spectroscopy. The lowest oxide content composition (≤0.5 wt%, supplied information) devitrified readily close to the glass transition temperature, T _g, forming crystallites of a new (GLS) phase with a monoclinic Bravais lattice and a lathlike internal structure. Ga₂S₃was observed in small quantities between the laths. Samples prepared from nonaged, high oxide (1–3 wt%) content precursors produced the most stable glass. On crystallization, these samples exhibited spherulites composed of intergrown laths of melilite-structured La_3.33Ga₆S₁₄and the new monoclinic GLS phase. Whiskers of Ga₂S₃were found in the residual glass between crystallites. Samples prepared from aged raw materials produced spherulites of La_3.33Ga₆S₁₄on crystallization with no identifiable regions of the new GLS phase.     

Immiscibility and Crystallization in A12O3-SiO2 Glasses

Metastable glass-in-glass separation was observed on rapid quenching of A1₂O₃-SiO₂ melts containing from 10 to 50 mol% A1₂O₃. Nucleation and subsequent crystallization of mullite within the high-alumina-dispersed glass phase may occur either during cooling from the melt or on reheating. The metastable binary two-liquid region is compositionally defined, and a structural interpretation of the phase separation and the effects of small oxide additions on it is offered. Evidence for both classical and possible spinodal nucleation mechanisms during liquid segregation in this system is presented.     

Crystallization Behavior of CaO–P2O5 Glass with TiO2, SiO2, and Al2O3 Additions

TiO₂ above 4 mol% is an effective nucleating agent for CaO–P₂O₅ glass which also contains substantial SiO₂ and Al₂O₃ additions. Glass ceramics can be made from this glass using a single slow heating ramp with no need for a nucleating heat treatment step. Powder of this composition crystallizes rapidly to β-Ca₂P₂O₇, whereas bulk glass crystallizes from diphasic nuclei consisting of a central cubic Ca-P-Ti-Si-Al oxide phase surrounded by impure AlPO₄ dendrites. Metastable calcium phosphate grows on the AlPO₄ dendrites and later transforms to β-Ca₂P₂O₇.     

Comparison of the Formation of Calcium and Barium Phosphates by the Conversion of Borate Glass in Dilute Phosphate Solution at near Room Temperature

The formation of phosphates of calcium or barium at near room temperature by the direct conversion of borate glass in dilute phosphate solution was investigated. Borate glass particles (150–300 μm), with the composition 20Na₂O·20AO·60B₂O₃ (mol%), where A is the alkali-earth metal Ca or Ba, were prepared by conventional processing, and immersed in 0.25 M K₂HPO₄ solution at 37°C and with a starting pH value of 9.0 or 12.0. The effects of the borate glass composition and the solution pH on the rate of formation, the chemical composition, and the structure of the phosphate products formed in the conversion reaction were investigated using weight loss and pH measurements, X-ray diffraction, X-ray fluorescence, scanning electron microscopy, and Brunauer–Emmett–Teller surface area. At both pH values, the calcium borate glass particles were completely converted to hydroxyapatite, Ca₁₀(PO₄)₆(OH)₂, with a high surface area (160–170 m²/g). At pH=9.0, the barium borate glass particles converted completely to a barium phosphate product that was isostructural with BaHPO₄, whereas at pH=12.0, the barium phosphate product was isostructural with Ba₃(PO₄)₂, with both products having much lower surface areas (4–8 m²/g). The formation of the phosphate products was pseudomorphic, retaining the external shape of the original glass particles.