Properties and Morphology of Barium Germanate Glasses

The density, thermal expansion behavior, and transformation-range viscosity of barium germanate glasses containing 0 to 9 mol% BaO were measured. The addition of BaO to Ge0₂ resulted in phase separation at all BaO concentrations. The results of the property measurements indicate that glasses containing up to 3 mol% BaO consist of a matrix of essentially pure GeO₂ with barium-rich droplets. Glasses containing 6 mol% BaO or more consist of two interconnected vitreous phases. The morphology of glasses containing between approximately 3.5 and 5.5 mol% BaO can be altered from the droplet/matrix form to that of two continuous phases by the appropriate heat treatment.     

Viscosity and Thermal Expansion of Alkali Germanate Glasses

Transformation-range viscosities are reported for Na₂O-, K₂O-, Rb₂O-, and Cs₂O-GeO₂ glasses. A minimum in viscosity occurs between 1 and 5 mol% alkali oxide and a maximum between 17 and 22 mol% alkali oxide. The thermal-expansion coefficients of the Na₂O-GeO₂ glasses also exhibit a minimum at < 5 mol% Na₂O. The accepted structural model for alkali germanate glasses does not predict the minimum at low R₂O concentrations. A modification of this model is suggested to explain these data.     

Thermal, Structural, and Dielectric Properties of Cu-Doped Ge-S Glasses

Glasses of GeS_1.5+y at.% Cu and GeS 1.375 +z at.% Cu were analyzed by DTA. For concentrations y ≊2.5 and z ≊4, new exothermic transformations and an initial small endothermic effect appear. All these transformations occur below the glass transition temperature of the original Ge:S glass, Analysis by X-ray and electron diffraction showed that this devitrification process is connected with crystallization of a Cu₂GeS₃ phase. Electron transmission microscopy showed that this crystalline phase is dispersed in a glassy matrix as disconnected aggregates with irregular symmetry. Near the maximum copper concentration y ≊5, z ≊6) at the boundary of the glass-forming region, there is one additional exothermic transformation in the system GeS_1.5+y at.% Cu and two in the system GeS_1.375+z at.% Cu, one of them corresponding to crystallization of the Cu₃GeS₄ phase. X-ray diffraction patterns of the crystalline phases are shown. The spectrum of ionic thermocurrents in such glassyceramic material shows a new peak at 120 K which is probably related to interfacial polarization associated with the crystalline phase-glassy matrix boundary.     

Composition Effects on Thermal and Crystallization Properties of Glasses in Sb–S–I System

The effect of composition variations on thermal and crystallization properties of Sb–S–I glass system is investigated by differential thermal analysis (DTA) and X-ray diffraction (XRD). In general, the glass transition temperature ( T _g) and the temperature corresponding to the maximum crystallization rate ( T _p) are found to decrease with increasing iodine concentration for a fixed Sb/S ratio. However, precipitation of SbSI phase is sensitive to the Sb/S ratio for a given iodine fraction. The optimal composition and its devitrification behavior for forming only the ferroelectric SbSI phase are established on the basis of DTA curves and XRD patterns.     

Optical Properties of Rare-Earth Ions in Lead Germanate Glasses

Glasses of composition ( x - 1)PbO(100 - x )GeO₂1Ln₂O₃, with x = 30 mol% (Ln = Nd, Eu, Er), 40 mol% (Ln = Pr, Nd, Sm, Eu, Dy, Ho, Er, Tm), and 50 mol% (Ln = Eu, Er), have been prepared by quenching the oxidic melts. From the optical absorption and emission spectra in the ultraviolet-visible-near-infrared (UV-VIS-NIR) region, the intensity parameters, spontaneous emission probabilities, branching ratios, radiative lifetimes, and, for selected NIR transitions, peak stimulated emission cross sections have been obtained. The trends observed in the intensity parameters have been discussed, as a function of the number of f electrons as well as a function of the lead content. As the amount of lead increases, the covalency of the Ln-O bond increases, the symmetry of the rare-earth site increases, and the dopant site distribution narrows. The peak stimulated emission cross sections rank among the highest found for oxide glasses.     

铋掺杂锗酸盐玻璃超宽带近红外发光性质及机理

采用传统的高温熔融法制备了80GeO2–20RO (R=Ca, Sr, Ba)掺铋锗酸盐玻璃。研究了铋掺杂锗酸盐玻璃超宽带近红外发光性质,探讨了铋离子掺杂玻璃超宽带发光机理。结果表明：在808 nm激光激发下,铋掺杂锗酸盐玻璃随着碱土金属离子半径增加,中心波长为1300 nm的发射强度逐渐降低;在690 nm激光激发下,铋掺杂锗酸盐玻璃的近红外发射覆盖从900 nm到2000 nm波段但不呈现正态分布,荧光半高宽达428 nm。随着碱土金属离子半径的增加,其近红外发射中心位置逐渐向长波方向移动,推测近红外发光可能源于两种不同形式铋的发光中心。铋掺杂的锗酸盐玻璃具有良好的光学性能,较宽的荧光半高宽,将成为未来超宽带光纤放大器的增益介质。     

Dy3+掺杂Ge-Ga-Sb-S-CsI硫卤玻璃的热学特性及析晶动力学研究

采用熔融急冷法制备了系列Dy3+掺杂的70GeS2-10Ga2S3-5Sb2S3-10CsI硫卤玻璃样品.测试了样品的可见-近红外和红外透过光谱,分析了Dy3+的光谱吸收及杂质吸收.测试了样品的DTA曲线,分析了样品的热学特性.利用修正Kissinger方程分析了玻璃转变活化能Et、析晶活化能Ec,根据Johnson-Mehl-Avrami方法计算了结晶动力学参数n.研究结果表明:随着Dy3+掺杂浓度的增加,玻璃吸收光谱增强,转变活化能和析晶活化能先增加后减小,x=0.3wt%的玻璃样品最稳定.析晶过程中为两维晶体生长.     

硫氮玻璃的析晶性能与结构分析

通过对二元（Ｇｅ－Ｓ）和三元（Ａｓ－Ｇｅ－Ｓｅ）系统硫系基玻璃和引入Ｓｉ３Ｎ４的硫氮玻璃试样析晶性能的比较,对硫氮玻璃的析晶行为与其结构之间的关系进行了较深入的探讨。试验结果表明,随着Ｓｉ３Ｎ４的引入,硫系玻璃的析晶温度得以提高或伴随析晶放热峰的消失。这表明氮原子的引入加强了硫系基玻璃微观结构的连缀度,使硫氮玻璃的析昌能力有所下降。此外还在经过析晶热处理的硫氮玻璃试样的ＸＲＤ中发现两个新衍射峰,且     

Radiation,Crystallization, and Physical Properties of Cadmium Borate Glasses

Silicon - The melt-quenching method has been used to fabricate Na2B4O7 - CdO glass system. The XRD diffractometer procedure was used to check the status of these samples. Inter-ionic distance (Ri)...     

Nucleation and Crystallization of New Glasses from Fly Ash Originating from Thermal Power Plants

The nucleation and crystallization kinetics of new glasses obtained by melting mixtures of a Spanish carbon fly ash with glass cullet and dolomite slag at 1500°C has been evaluated by a calculation method. These glasses, whose microstructure was examined by TEM carbon replica, were susceptible to controlled crystallization in the 800°–1100°C range. The resulting glass-ceramics developed acicular and branched wollastonite crystals or a network of dendritic pyroxene mixed with anorthite feldspar (SEM and EDX analysis). The time–temperature–transformation curves (processing of the XRD data) showed the crystallization kinetics and the critical cooling rate to be in the 12°–42°C/min range.     

Properties and Crystallization Behavior of Sodium Iron Phosphate Glasses

Ternary Na₂O–Fe₂O₃–P₂O₅ (NFP) glasses with varying Na₂O/Fe₂O₃, Na₂O/P₂O₅, and Fe₂O₃/P₂O₅ ratios were prepared. The properties and crystallization tendencies were systemically investigated. It is shown that both density and chemical stability of the glass increase with Fe₂O₃. In contrast the Na₂O/P₂O₅ ratio has little effect on the glass properties for a fixed Fe₂O₃ content. The crystallization behavior of the glasses was analyzed by DTA and XRD. Unlike Li₂O–Fe₂O₃–P₂O₅ glasses NFP glasses were found to be stable against crystallization. 15Na₂O–27Fe₂O₃–58P₂O₅ glass was found to have the highest chemical stability among the studied NFP samples; the influence of TiO₂, ZrO₂ on crystallization in this composition was studied. It is found that addition of 3.4 mol% TiO₂ or 2.2 mol% ZrO₂ had little effect on the crystallization behavior of this glass. However, when the amounts of TiO₂ or ZrO₂ were increased to 8.4 or 5.5 mol% respectively the glass readily devitrified. Furthermore the addition of fluorine (introduced by replacing Na₂CO₃ with NaF in the glass batch) leads to amorphous glasses which could be crystallized to form NaFeP₂O₇ upon controlled thermal treatment. With increasing NaF additions the activation emergy for crystallization decreased from 428 to 381 kJ/mol.     

Effect of BaF2 Content on Luminescence of Rare‐Earth Ions in Borate and Germanate Glasses

Rare‐earth‐doped oxyfluoride germanate and borate glasses were synthesized and next studied using spectroscopic methods. Influence of fluoride modifier on luminescence properties of rare earths in different glass hosts was examined. The excitation and emission spectra of Pr³⁺ and Er³⁺ ions in the studied glasses were registered. The emission spectra of Pr³⁺ ions in germanate and borate glasses are quite different and depend strongly on the glass host. In samples doped with Er³⁺ ions emission bands located around 1530 nm corresponding to the main ⁴I_13/2→⁴I_15/2 laser transition were registered, independently of the glass host. Quite long‐lived near‐infrared luminescence of Er³⁺ ions was observed for germanate glasses with low BaF₂ content, while in borate glass systems influence of barium fluoride on luminescence lifetimes is not so evident. The Judd–Ofelt calculations were used in order to determine quantum efficiencies of excited states of rare‐earth ions in germanate and borate glasses.     

Crystallization and Nonlinear Optical Properties of Potassium Niobium Silicate Glasses

The crystallization of the xK₂O · xNb₂O₅· (1 – 2x)SiO₂(x= 0.167–0.250) glasses and glasses close in composition to K₂O · Nb₂O₅· 4SiO₂at the ratio K₂O : Nb₂O₅ 1 is investigated. In high-silica glasses, the metastable phase separation followed by the bulk multiphase crystallization are observed at temperatures close to the glass transition point T _g. The nanostructured transparent glasses that exhibit the optical second harmonic generation (SHG) effect are formed at the early stages of phase separation. The surface crystallization of glasses with the precipitation of the KNbSi₂O₇noncentrosymmetric phase occurs at higher temperatures.     

Crystallization of Yttria–Alumina–Silica Glasses

Bulk nucleation has been studied for glasses within the Y₂O₃–Al₂O₃–SiO₂ system, using a two-stage nucleation and growth heat treatment. The crystalline phases formed have been identified. Annealing in an inert atmosphere is required in order to prevent surface nucleation from dominating the results. Despite this, the phases observed are in general agreement with those observed in previous studies done in air. The nucleation kinetics of the y -Y₂Si₂O₇ phase have been measured and the optimum nucleation temperatures have been identified. The kinetic data have been analyzed using two existing models based on classical nucleation theory. The results of this study have been compared with crystallization results of a previous study of glass of similar composition within sintered silicon nitride samples. A two-stage heat treatment is suggested as a process that may lead to improved devitrification of grain boundary glass in such materials.     

Properties and Crystallization of Rare-Earth Si–Al–O–N Glasses Containing Mixed Trivalent Modifiers

Thirteen glasses of the general formula (M1, M2)_9.33Si₁₄Al_5.33O_41.5N_5.67 where M1=La or Nd and M2=Y or Er have been prepared with M1/(M1+M2) fractions of 1, 0.75, 0.5, 0.25, and 0. Data for molar volume (MV), glass compactness ( C ), Young's modulus ( E ), microhardness ( H ), glass transition temperatures ( T _g), and dilatometric softening temperatures ( T _d) have been recorded. In addition, temperatures at which crystallization exotherms arise have also been determined as well as crystalline phases present after the glasses had been heat treated to 1300°C in nitrogen. The results clearly demonstrate that glass properties vary linearly with effective cation field strength (CFS) of the combined modifiers (M1, M2), which is calculated from the atomic fractions of M1 and M2 and their associated CFSs. Glass stability in both the La–Y and La–Er systems reaches a maximum at M1 and M2 fractions of 0.5 because of the relative stability of different oxynitride and disilicate phases with changes in ionic radius. Furthermore, La appears to stabilize the α polymorph of yttrium disilicate because of combined La–Y ionic radius effects.     

Physical Properties,Crystallization, and Thermal/Hydrolytic Degradation of Poly(L‐lactide)/Nano/Micro‐Diamond Composites

The effects of incorporated nano/micro‐diamond (NMD) on the physical properties, crystallization, thermal/hydrolytic degradation of poly(L ‐lactic acid) (PLLA) were investigated for a wide NMD concentration range of 0–10 wt.‐%. Incorporated NMD increased the tensile modulus and strength of PLLA films but decreased the elongation at break of PLLA films. Incorporated NMD accelerated the crystallization of PLLA during heating and cooling and increased the absolute crystallization enthalpy of PLLA films (except for an NMD concentration of 10 wt.‐% during cooling) but did not alter the crystallization mechanism. Incorporated NMD increased and decreased the thermal stability of PLLA films for NMD concentrations of 1–5 and 10 wt.‐%, respectively, and increased the hydrolytic degradation resistance of PLLA films.

     

Structural and Thermal Expansions in Alkali Silicate Binary Glasses

Two volume-changing processes that should be considered in detail are (1) distention of networks by added oxides which may swell glass volumes in proportion to the added oxide volumes and (2) angular change in intertetrahedral bonding which may take place at and above annealing temperatures in proportion to the number of metal ions introduced by the modifications. Accordingly, the partial molar volumes of modifiers, ν _R , are assumed as those of their crystal or liquid states and the partial molar volumes of silica are computed from (1/ν_S) = 2.20 + 0.00057 ( r_m – 0.12) (1723 – t ). Tentative glass volumes are then computed as V_g= S_mν_S+ r_mν_R by use of the mole fractions S_m and r_m for silica and nonsilica, respectively. The excess of computed glass volumes, V₀ , over V as derived from observed densities is taken as a measure of the penetration of modifiers into the network cavities without corresponding distention of the network. By using the computed density of 1.95 for vitron, the value 2.20 for silica glass, and 2.30 as reported for irradiated silica, one can estimate that silica glass consists of 28% vitron and 72% disordered silica in the intervitron tissues. The values of V_g , – V mentioned are found to be in fair accord with expectations computable from the vitron theory.