Conventional Melting Method Research Articles

Proton infiltration of phosphosilicate glass-electrolytes for intermediate temperature fuel cell

ABSTRACTA fast proton conducting glass with proton transport number tH = 1 was successfully prepared by using conventional melting method. In-situ FTIR (Fourier transform infrared) measurements under hydrogen atmosphere, temperature of 300°C and applying 1 V between Pt electrodes were carried out in order to monitor the proton concentration. The electrode reaction on Pt in these conditions is similar to that under intermediate-temperature fuel cell operation. It was found from the in-situ FTIR measurements that the absorbance around 2900 cm-1 increases clearly after applying 1 V, whereas no significant change was observed around 3400 cm-1. Proton infiltration into the glass is discussed based on the in-situ FTIR and impedance results.

Comparative Investigation of Optical Properties in Tm<sup>3</sup><sup>+</sup>/Er<sup>3</sup><sup>+</sup>/Yb<sup>3</sup><sup>+</sup> Co-Doped Oxyfluoride Tellurite and Germanate Glasses

Tm3+/Er3+/Yb3+co-doped oxyfluoride tellurite and germanate glasses have been synthesized by conventional melting method. Intense up-conversion (UC) luminescence emissions were simultaneously observed under 980 nm excitation at room temperature in two glasses. The possible UC mechanisms are discussed and estimated. However, in the studied Tm3+/Er3+/Yb3+co-doped oxyfluoride glasses, tellurite glass showed weaker UC emissions than germanate glass, which is inconsistent with the prediction from the difference of maximum phonon energy between oxyfluoride tellurite and germanate glasses. Absorption spectrum and Raman spectroscopy were employed to investigate the origin of the difference in UC luminescence in two glasses. Our results confirm that, besides the maximum phonon energy, the phonon density of host glasses is another important factor in determining the UC efficiency.

Survey and research on up-conversion emission character and energy transition of Yb3+/Er3+/Tm3+ co-doped phosphate glass and glass ceramic

By conventional high-temperature melting method, Yb3+/Er3+/Tm3+ co-doped phosphate glass was synthesized. After annealing the precursor glass, the phosphate glass ceramic (GC) was obtained. By measuring the X-ray diffraction (XRD) spectrum, it is proved that the LiYbP4O12 and Li6P6O18 nano-crystals have existed in the phosphate GC. The up-conversion (UC) emission intensity of the GC is obvious stronger compared to that of the glass. The reason is that the shorter distance between rare earth ions in the glass ceramic increases the energy transitions from the sensitized ions (Yb3+) to the luminous ions (Er3+ and Tm3+). By studying the dependence of UC emissions on the pump power, the 523 and 546nm green emissions of Er3+ ions in the glass are two-photon processes. But in the glass ceramic, they are two/three-photon processes. The phenomenon implies that a three-photon process has participated in the population of the two green emissions. Using Dexter theory, we discuss the energy transitions of Er3+ and Tm3+. The results indicate the energy transition of Tm3+ to Er3+ is very strong in the GC, which changes the population mechanism of UC emissions of Er3+.

Sintering, crystallization and dielectric properties of CaO-B2O3-SiO2 system glass ceramics

CaO-B2O3-SiO2 (CBS) glass powders are prepared by conventional glass melting method at different melting temperatures, whose properties and microstructures are characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). It is found that there are SiO2 and some unknown phases in CBS glass melting liquid from 1 300 °C to 1 500 °C and the amount of these phases decreases with the increase of the melting temperature. The CBS glass melted at 1 450 °C could be sintered from 830 °C to 930 °C and the bulk densities of the samples are all higher than 2.4 g/cm3. From the points of the properties and energy conservation, the melting temperature of 1 450 °C is the optimal melting temperature. The glass ceramic sintered at 850 °C exhibits better dielectric properties: ɛr=6.33, tan δ=2.2×10−3 at 10 GHz, and the major phases of the samples are CaSiO3, CaB2O4 and SiO2.

Gamma Radiation Effects on the Optical Properties of Yb-doped Silicate Glasses

A series of Yb-doped silicate glasses were prepared by a conventional melting method under normal proc- essing conditions. The effects of gamma-ray (from a 60 Co γ source) radiation on the absorption and emission properties of all glass samples were investigated. The radiation exposure leaded to the formation of color centers in glass samples. Such radiation-induced photodarkening caused a strong broad optical absorption band, which had a maximum wave- length centered at around 400 nm and the tail extended into the near infrared region. In addition, a minor part of the

Gamma radiation effects on absorption and emission properties of erbium-doped silicate glasses

A series of Er-doped silicate glasses is prepared by a conventional melting method under normal processing conditions, and the effects of gamma-ray radiation on absorption and emission properties of all samples are investigated. The radiation-induced darkening causes a strong broad optical absorption band that has a maximum around 400 nm and extends to the near infrared region. The point defects generated in the silicate matrix by irradiation around the Er3+ ion favor the activation of non-radiative relaxation channels thus modifying the photoluminescence quantum efficiency from specific excited levels, such as those emitting at 520 and 650 nm. Photobleaching effects are observed in Er-doped silicate glasses pumped by 980 nm LD at room temperature.

Bi-doped germanium niobate glasses with near-infrared broad-band emission

The Bi2O3 doped glasses with concentrations of (0.9-x) GeO2-xNb2O5-0.1BaO (x=0.04, 0.07, 0.1) glasses are prepared by the conventional melting method. The differential thermal analysis (DTA) curves, the absorption spectra, the fluorescence decay curve and the X-ray photoelectron spectra are measured. The difference between glass crystallization onset temperature and transition temperature (Tx-Tg) of the glasses is up to 200℃ from the DTA curve. Absorption peaks at 500, 700, and 1000 nm are observed. The absorption edges show a red-shift with the increase of Nb2O5 content x. The emission band at 1300 nm with the full width at half maximum near 200 nm is observed under the excitation of 808 nm laser. The fluorescence intensity increases with the increase of the concentration of Bi2O3. The fluorescence intensity reaches a maximal value when the concentration of Bi2O3 is about 0.01. The peaks of binding energy in XPS are located at 159.6 and 164.7 eV respectively. The binding energy peaks are located between those of Bi3+ and Bi5+ by comparing with those of Bi2O3 (Bi3+) and NaBiO3 (Bi5+). According to the XPS results, one may conclude that Bi3+ and Bi5+ ions co-exist in the glass. The near infrared broadband emission may be assigned to Bi5+ ion based on the results of emission spectra and X-ray photoelectron spectra. The broadband intensity is gradually weakened as the Nb2O5 content x increases from 0.04 to 0.1. As GeO2 is substituted by Nb2O5, complex NbGe defects are formed and the lower valence state of Bi ions will be inevitably formed to compensate the extra electric charge from Nb5+, thus resulting in the inhibition of Bi5+ and weakening the fluorescence aforementioned.

Structure and optical properties of TeO2-Nb2O5-BaCl2 glass

Oxygen-chlorine tellurite glasses: (90-x)TeO2-10Nb2O5-xBaCl2 (x=10, 20, 30) are prepared using the conventional melting method. The influences of component on the density, structure, optical properties, refractive index and dispersion of the glasses are studied using density specific gravity balance, Raman spectroscopy, infrared-visible-UV spectrophotometer and Prism Coupler. The results show that the glass density first increases and then decreases with the increase of content of BaCl2. Furthermore, the structural units are converted from [TeO4] trigonal bipyramid into [TeO3] trigonal pyramid. Moreover, glass refractive index gradually decreases. In addition, new tellurite glass has high linear refractive index n (2.02259), nonlinear refractive index N2 (6.8× 10-12 esu) and third-order nonlinearpolarizability χ(3)(3.7× 10-13 esu). The new tellurite glass exhibits a high transmittance in the visible and infrared spectral region and possesses an cut-off edge in the near UV spectral region, and they each undergo an obvious blue shift with the increase of content of BaCl2. The direct and indirect transition optical band gaps of the samples are calculated according to the Tauc equation, and they increase with the content of BaCl2 increasing.

Investigation of the melting characteristic, forming regularity and thermal behavior in lead-free V 2O 5–B 2O 3–TeO 2 low temperature sealing glass

Lead-free glasses in V 2O 5-B 2O 3-TeO 2 ternary system were fabricated by the conventional melting method. The melting characteristic, glass forming regularity, sealing temperature and characteristic temperature of V 2O 5-B 2O 3-TeO 2 ternary system were investigated, respectively. The results show that V 2O 5-B 2O 3-TeO 2 ternary system glasses have a region of low melting temperature, three different crystallizing areas and a wide glass forming area. The system glasses possess the lowest sealing temperature (335 °C), when the system consists of 40 mol% V 2O 5 and 60 mol% TeO 2. In addition, the glass with composition of 10% V 2O 5, 30% B 2O 3, 60% TeO 2 has low thermal expansion coefficient (106 × 10 − 7 °C − 1 ) and sealing temperature (355 °C). Both of above two compositions would be potential materials for low temperature sealing glass.

Characterization of emission properties of Er 3+ ions in TeO 2–CdF 2–WO 3 glasses

TeO 2–CdF 2–WO 3 glasses with various compositions and Er 3+ concentrations were prepared by conventional melting method. Their optical properties were studied by measuring the absorption, luminescence spectra and the decay patterns at room temperature. From the optical absorption spectra the Judd-Ofelt parameters ( Ω t ), transition probabilities, branching ratios of various transitions, and radiative lifetimes were calculated. The absorption and emission cross-section spectra of the 4I 15/2 to 4I 13/2 transition of erbium were determined. Emission quantum efficiencies and the average critical distance R 0 which provides a measure for the strength of cross relaxation were determined.

Shape Memory NiTi Alloys Obtained by Powder Metallurgy Route

The effect of Fe, respective Cu, additions as substitute for Ni in NiTi shape memory alloys (SMAs) on the delaying of its phase transition and narrowing hysteresis are well known, NiTi-Fe and NiTi-Cu SMAs having applications especially to the actuators that require such properties. These SMAs are currently produced by conventional melting methods, which are energo-intensive and impose very severe processing conditions to avoid contamination. The results of researches presented in this paper prove the possibility of these SMAs obtaining by powder metallurgy via reactive sintering – more advantageous from both technical and economic point of view. A beneficial effect on both sintering and homogeneity of the obtained SMAs proved to have a controlled mechanical alloying applied to powder mixture before compacting and sintering.

Preparation of transparent cobalt doped glass ceramic and application as saturable absorber Q switch for 1.54 μm Er-glass laser

Glass with composition of 51SiO 2–24.5Al 2O 3–23MgO–1.5K 2O doped with Co 2+ ions was prepared by conventional melting method. The glass sample was heated at 900 °C for 360 min under atmosphere, and the powder XRD measurement showed that crystalline phase successfully precipitated in the sample. As is compared with standard JCPDS card, the crystalline phase identified as a mixture of zirconium titanate (ZrTiO 4) and one of the compounds of magnesium aluminum oxide. The crystallite size was confirmed by transmission electron microscope (TEM) observation; it could be estimated as 30 nm in diameter from the TEM image. Based on the area ratio of crystalline phase and residual glass phase, the precipitated crystallite phase volume ratio can be estimated to be not higher than 30% in the Co 2+ doped glass ceramic sample. The absorption coefficient at 1.54 μm for transparent glass ceramic sample is clearly higher than that in base glass, which can be explained by the fact that Co 2+ ions entered into the precipitated nano-sized crystal phase and led to higher absorption coefficient at 1.54 μm for tetrahedral coordinated Co 2+ ion. Consequently, the Co 2+ doped transparent glass ceramic sample with thickness of 0.35 mm was used as a saturable absorber for 1.54 μm Er-glass laser oscillation, and Q switched pulses with pulse energy of 40 mJ, pulse width of 42 ns, and peak power of 0.95 mW were shown in the experiments.

Effect of BaF2 Addition on Crystallization Kinetics and Dielectric Properties of B2O3-Nb2O5-SrO-BaO Glass-Ceramics

A series of strontium barium niobate-based B2O3 system glass–ceramics have been prepared by conventional melting and heat-treated crystallization method. The effect of BaF2 addition in nucleation and crystallization kinetics has been explored for dielectric applications. BaF2 addition decreased the activation energy of crystallization obviously and changed microstructure of glass–ceramics significantly. The dielectric constant and breakdown strength of glass–ceramics were improved significantly by adding BaF2. The glass–ceramic with a relative dielectric constant of 337 and a breakdown strength of 52.7 kV/mm was achieved.

Structure and physical properties of Bi 2O 3–B 2O 3–Ga 2O 3 glasses

Glasses with compositions xBi 2O 3–35B 2O 3–(65 − x)Ga 2O 3 (x = 45, 50, 55, 60 mol%) were prepared by conventional melting method. The thermal properties were investigated by differential thermal analysis (DTA) and the structures of the glasses were probed by infrared, Raman and X-ray photoelectron spectroscopies (XPS). The results show that both density and refractive index increase with increase of Bi 2O 3. The glass transition temperature (T g), onset crystallization temperature (T x) and ΔT (T x − T g) decrease with the content of Bi 2O 3. The glass network is mainly constituted by the [BiO 6] octahedron, [BO 3] triangle, [BO 4] tetrahedron and steady [GaO 4] tetrahedron structural units. Borate oxide exists mainly in [BO 3] units in the glass. [BO 4] units are converted into [BO 3] with increasing Bi 2O 3 by producing more non-bridging oxygens. Raman and XPS investigation indicates that Bi 5+ ions may be formed in the glass containing 60 mol% Bi 2O 3.

Infrared, Raman and XPS spectroscopic studies of Bi 2O 3–B 2O 3–GeO 2 glasses

Glasses with composition 50Bi 2O 3–(50 − x) B 2O 3– xGeO 2 ( x = 0, 5, 10, 15 mol%) were prepared by conventional melting method. The thermal properties were investigated by differential thermal analysis (DTA) and the structures of the glasses were probed by Infrared, Raman and X-ray photoelectron spectroscopy (XPS). The results show that density, refractive index and optical basicity increase with the increase of GeO 2. The glass transition temperature ( T g), onset crystallization temperature ( T x) and Δ T ( T x − T g) increase as well. The cut-off edges in ultraviolet and infrared shift to longer wavelength by the addition of GeO 2. Infrared, Raman and XPS results indicate that the glass network consists of [Bi–O 6] octahedron, [BO 3] triangle, [BO 4] tetrahedron and [GeO 4] tetrahedron and borate oxide mainly exists in [BO 3] units. XPS result indicates Ge 4+ ions form steady [GeO 4] tetrahedra units in the glass network and the number of non-bridging oxygens decreases with the addition of GeO 2.

2 μm mid-infrared optical spectra of Tm 3+-doped germanium gallate glasses

Glasses with the composition of 65GeO 2-12Ga 2O 3-10BaO-8Li 2O-5La 2O 3 (molar ratio) doped with 1.526 wt.%, 3.006 wt.%, 5.836 wt.%, 11.028 wt.%, and 15.678 wt.% Tm 2O 3, respectively, were fabricated by conventional melting method. According to the absorption spectra and the Judd-Ofelt theory, the J-O strength parameters ( Ω 2, Ω 4, Ω 6) were calculated, with which the radiative transition probabilities, branching ratios and radiative lifetimes were obtained. The infrared emission spectra (with 808 nm LD excitation) at ∼1.47 and ∼1.8 μm of various concentrations of Tm 3+-doped glasses were studied. The emission intensity at ∼1.8 μm reached to the maximum when the Tm 2O 3-doping concentration was near to be ∼3.006 wt.% (1.0 mol.%), and then decreased as doping concentration increased further. The mechanism of the fluorescence intensity change was explained with the cross-relaxation effect and the concentration quenching effect of Tm 3+. Meanwhile, according to McCumber theory, the absorption and emission cross-sections corresponding to the 3F 4→ 3H 6 transitions of Tm 3+ at 1.8 μm was obtained. For Tm 3+-doped germanate glasses, the maximum emission cross-section reached a value higher than that reported for fluorozircoaluminate glasses. It is expected to be a favorable candidate host for ∼2.0 μm mid-infrared laser because the glass shows favorable optical spectra.

Infrared, Raman and XPS spectroscopic studies of Bi 2O 3–B 2O 3–Ga 2O 3 glasses

Glasses with compositions 60Bi 2O 3–(40−x)B 2O 3–xGa 2O 3 ( x = 5, 10, 15, 20 mol%) are prepared by conventional melting method. The thermal properties are investigated by differential thermal analysis (DTA) and the structures of the glasses were probed by Infrared, Raman and X-ray photoelectron spectroscopy (XPS). The results show that density, refractive index and optical basicity increase with the increase of Ga 2O 3. The glass transition temperature ( T g), the onset crystallization temperature ( T x), Δ T ( T x− T g) decrease with the content of Ga 2O 3. The cut-off edges in ultraviolet and infrared shift to longer wavelength with the increase of Ga 2O 3. On the other hand, the addition of Ga 2O 3 causes a progressive coordination number change of the boron atom from 3 to 4. XPS result indicates both Bi 5+ and Bi 3+ exist in 5 mol% Ga 2O 3 content, while Bi 5+ amounts decrease with the increase of Ga 2O 3 contents. The glass is mainly composed of [BiO 6], [BO 3], [BO 4] and [GaO 4] polyhedra. Glasses are supposed to have layer structure. [BO 3] triangle and [BO 4] tetrahedra may be located between the [GaO 4] tetrahedral and [BiO 6] octahedra to prevent crystallization and to compensate electric charge.

Effect of Bi2O3 content on properties of (Na2O, K2O)–SiO2–CaO–Al2O3–B2O3 glass system

(Na2O, K2O)–SiO2–CaO–Al2O3–B2O3 glass system with 25–60 wt-% in concentration variations of Bi2O3 was fabricated in the laboratory scale using the conventional melting method. The values of refractive index, density and dielectric constant of the glass samples were measured at room temperature. It was found that the values of refractive index and density increased with increase in Bi2O3 content. The dielectric constant decreased with addition of Bi2O3 content up to 35 mol.-% and increased beyond this concentration. The colours of the glass samples changed from colourless to yellow when Bi2O3 concentration increased. The relationship between the properties such as, refractive index, density, dielectric constant and Bi2O3 content was also analysed and discussed. The results suggested that the bismuth bearing glass can be used as a suitable candidate to replace lead and/or barium based glasses.

Microstructure and mechanical properties of rapidly solidified FeAlCr intermetallic compound

In this work results regarding microstructural characterization of a melt‐spun intermetallic compound Fe40Al5Cr (% at.) produced by rapid solidification employing the melt spinning technique at three different tangential wheel speeds (12, 16 and 20 ms‐1) are presented. Melt spun ribbons were characterized by optical and scanning electron microscopy (SEM) in order to observe morphology, grain size, ribbon thickness and also fracture surfaces after tensile tests. EDS coupled to SEM was employed to perform punctual and scan line chemical analyses on samples, x‐ray diffraction (XRD) was utilized to identify crystal structure and phases. Transmission electron microscopy (TEM) was employed to confirm crystal structure and also to characterize nanopores formed in the specimens by vacancy clustering. With regard to mechanical properties, micro hardness Vickers measurements as well as tensile tests at room temperature were applied to the rapidly solidified ribbons.The grain size of rapidly solidified Fe40Al5Cr ribbons suffered a drastic reduction as compared with alloys of the same composition produced by conventional melting and casting methods, and in melt‐spun ribbons it decreases as the wheel speed increases. Punctual and line‐scanning chemical analyses revealed that Cr enters in solid solution in FeAl matrix. Hardness measurements revealed a softening in rapidly solidified FeAlCr ribbons as compared with FeAl alloys and tensile test exhibited a (transgranular + intergranular) mode of fracture, reaching up to 3 % of elongation in FeAlCr alloys. The presence of porous (meso and nano) were also characterized.

Effect of 1-methyladenine on thermodynamic stabilities of double-helical DNA structures

1-Methyladenine (m1A) alters T·A Watson–Crick to T·m1A Hoogsteen base pair. Owing to its conversion to N6-methyladenine (m6A) at higher temperatures, thermodynamic studies of m1A-containing DNAs using conventional melting methods are subject to the influence of m6A species. In this study, we applied nuclear magnetic resonance spectroscopy to determine the base pairing modes and effect of m1A on thermodynamic stability of double-helical DNA. The observed base pairing modes account for the destabilizing trend which follows the order T·m1A ∼ G·m1A < A·m1A < C·m1A, providing insights into the m1A flipping process and enhancing our understandings of the mutagenicity of m1A.