Structure, phase formation, and wetting behavior of BaO–SiO2–B2O3 based glass–ceramics as sealants for solid oxide fuel cells

In the present study, glasses from the three different compositional triangles in the BaO–B₂O₃–SiO₂ system with fixed B₂O₃/SiO₂ ratio and different BaO/SiO₂ molar ratios (designated as Ba32, Ba37, and Ba42) were prepared, and suitability of them as sealant in solid oxide fuel cells were investigated. Structure of the glasses was characterized with Raman spectroscopy. According to the results, the structure of the glass with 32 % molar BaO (Ba32) predominantly consisted of Q² structural species. In glasses with 37 and 42 % molar BaO (Ba37 and Ba42), with the substitution of SiO₂ by BaO, distribution of Qⁿ units widened, silicate glass network depolymerized, and concentration of Q¹ structural units increased at the expense of Q² units. X-ray diffraction analyses revealed that in samples Ba32 and Ba37, initially, Ba₃Si₅O₁₃ and Ba₅Si₈O₂₁ phases were crystallized, respectively, and it seemed they acted as the sites for the subsequent growth of BaSi₂O₅ phase. In contrast, the dominant phase in sample Ba42 was Ba₂Si₃O₈. Sintering, wetting, and crystallization behavior of the glasses were studied using hot-stage microscopy and differential thermal analysis, respectively. Delay in the crystallization accompanied by depolymerization of the structure led into deformation at lower temperatures and greater wettability on the steel for Ba37 glass. All the glasses wetted AISI430 alloy at temperatures higher than 1,000 °C.     

The study of the structure and bioactivity of the B2O3 • Na2O • P2O5 system

In this study, we have investigated calcium and silicate‐free samples over a wide compositional range in the xB₂O₃·30 Na₂O·(70−x)P₂O₅ system, with 0 ≤ x ≤ 70 mol%, in order to determine the influence of the chemical composition on their structure and bioactive response in simulated body fluid. Information related to the chemical structures present in the network was obtained by means of Raman and infrared spectroscopy. For samples containing small amounts of P₂O₅, boron structures are preponderant. Upon increasing the phosphorus content, the samples' network is based on phosphate chains linked by boron groups through ‘P–O–B’ bridges. For high concentration of P₂O₅, the Q³ units form three‐dimensional network, whereas Q² units assist the chain formation. Regarding the in vitro assessment of bioactivity, the clear print of PO₄ asymmetric bending vibrations of apatite‐like layer in the 540–680 cm⁻¹ spectral domain, the scanning electron micrographs and energy dispersive x‐ray analysis spectra demonstrate that the studied borophosphate samples exhibit good bioactive response only for certain chemical compositions. More exactly, the highest bioactivity is obtained for 30% and 20% B₂O₃ (mol%) after 3 and 11 days of immersion, respectively. Therefore, the samples with 20–30 mol% boron content are valuable candidates that can be used as materials for tissue engineering applications. Copyright © 2013 John Wiley & Sons, Ltd.     

Study of structural modification of sodium aluminophosphate glasses with TiO2 addition through Raman and NMR spectroscopy

Structural modification of sodium aluminophosphate (NAP) glasses with TiO₂ addition has been investigated using Raman and MAS-NMR (³¹P and ²⁷Al) spectroscopy. TiO₂ incorporated NAP glasses having composition (mol%): 40Na₂O-10Al₂O₃-xTiO₂-(50−x)P₂O₅ (x=0-20), are prepared by conventional melt quench method. The low-frequency Raman spectrum suggests an increase in the average ionic character of phosphate glass network with addition of TiO₂. Raman and ³¹P MAS-NMR revealed that the glasses without TiO₂, consist mainly metaphosphate (Q²) structural units. These are gradually converted into pyrophosphate (Q¹) and orthophosphate (Q⁰) structural units along with the formation of P-O-Ti/P-O-Al linkages. ²⁷Al MAS-NMR revealed the change in coordination of Al from octahedral (AlO₆) to tetrahedral (AlO₄) for TiO₂ above 10 mol%. Raman spectra indicate that TiO₂ enters the network in the form of octahedral (TiO₆) and tetrahedral (TiO₄) structural units and at high concentration of TiO₂, tetrahedral structural units are more favourable. Various thermo-physical properties e.g. density (ρ), molar volume (V_m), glass transition temperature (T_g), microhardness (MH), and thermal expansion coefficient (TEC) have been measured as a function of TiO₂ content. Variations in the thermo-physical properties are correlated with these structural modifications in the phosphate structural units and consequently changes in the average ionic character of phosphate glass network.     

Spectroscopic Investigation of Tungsten Ions in Lead Scandium Phosphate Glass System

Lead scandium phosphate glasses (PbO-Sc₂O₃-P₂O₅) containing different concentrations of tungsten oxide (WO₃) ranging from 0 to 5 mol% were prepared. A number of studies, viz. differential thermal analysis (DTA), infrared spectra, optical absorption, and electron spin resonance (ESR) spectra, have been carried out. The results of DTA indicated the highest glass forming ability for the glass containing 5 mol% of WO₃. The results of spectroscopic studies have been analyzed in light of different oxidation states of tungsten ions.     

Conductivity and spectroscopic studies of Li<Subscript>2</Subscript>O-V<Subscript>2</Subscript>O<Subscript>5</Subscript>-B<Subscript>2</Subscript>O<Subscript>3</Subscript> glasses

Lithium vanadium-borate glasses with the composition of 0.3Li₂O–(0.7-x)B₂O₃–xV₂O₅ (x?=?0.3, 0.325, 0.35, 0.375, 0.4, 0.425, 0.45, and 0.475) were prepared by melt-quenching method. According to differential scanning calorimetry data, vanadium oxide acts as both glass former and glass modifier, since the thermal stability of glasses decreases with an increase in V₂O₅ concentration. Fourier transform infrared spectroscopy data show that the vibrations of [VO₄] structural units occur at V₂O₅ concentration of 45 mol%. It is established that the concentration of V⁴⁺ ions increases exponentially with the growth of vanadium oxide concentration. Direct and alternative current measurements are carried out to estimate the contribution both electronic and ionic conductivities to the value of total conductivity. It is shown that the electronic conductivity is predominant in the total one. The glass having the composition of 0.3Li₂O-0.275B₂O₃-0.475V₂O₅ shows the highest electrical conductivity that has the value of 7.4?×?10^?5 S cm^?1 at room temperature.     

OH-对磷酸盐铒玻璃光谱性质的影响

本文系统研究了Yb³⁺、Er³⁺共掺磷酸盐铒玻璃中OH^-含量与铒玻璃荧光寿命和光谱性质的关系.结果表明OH^-基团的存在使得Er³⁺离子的荧光强度显著降低,荧光寿命大大缩短.比较了三种不同Al₂O₃含量(5mol%,8mol%和13mol%)的铒玻璃在2.9μm波长处的红外吸收系数与铒离子荧光寿命的关系,发现玻璃中OH^-在2.9μm的吸收系数和Er³⁺的⁴Ⅰ_13/2能级离子衰减速率成线性关系,不同Al₂O₃含量的玻璃具有不同Er³⁺和OH^-基团的相互作用参量和不同的荧光寿命值及量子效率.并从玻璃结构上解释了Al₂O₃含量对除水机制和光谱性质的影响.经过充分除水后的铒玻璃荧光寿命可达到9.1ms.     

Structure,thermal behavior,and chemical durability of lead–calcium–phosphate glasses

ABSTRACT

Structure and physical properties of 25CaO–xPbO–(75–x)P₂O₅ (0≤x≤35) glasses are investigated in this paper. Substitution of PbO for P₂O₅ in the binary 25CaO–75P₂O₅ glass was found to increase the density and to decrease the molar volume. Fourier transform infrared (FTIR) and Raman spectroscopies show the evolution of the phosphate skeleton when the PbO content increases: Q³ to Q² species (0<x≤25) and Q² phosphate network (x = 25) to short phosphate groups (x > 25) such as (P₄O₁₃^6?) (x = 35). The glass transition temperature first decreases with x, then increases for x values larger than 10%. The evolution of the glass transition temperatures is interpreted from the structural data: the minimum point observed in T_g is attributed to the transition of the ultraphosphate network from the network containing the modifying cations at isolated sites to a network with modifier sub-structure sharing terminal oxygens. At higher PbO content, the large increase in T_g is due to the reticulation of the phosphate network by PbO₄ groups.     

Influence of Zn/Co ratio on dielectric behavior of Na<Subscript>2</Subscript>Zn<Subscript>1 ‐ x</Subscript>Co<Subscript>x</Subscript>P<Subscript>2</Subscript>O<Subscript>7</Subscript> glasses

A series of zinc phosphate glass doped with cobalt Na₂Zn_(1???x)Co_xP₂O₇ (x = 0, 1, 2 and 5 mol%) was synthesized. These glasses were characterized by both infrared and large broadband dielectric spectroscopy. Infrared spectra indicate the increase of Zn/Co ratio creates defect in phosphate network due to the depolymeration of phosphate anions. The dc conductivity increases and activation energy decreases with the amount of cobalt ions in the glass network. The impedance measurements reveal that the total conductivity follows Jonscher’s power law. The dielectric constant and dielectric loss increased with the temperature and decreased with the frequency whatever the cobalt proportion.     

57Fe Mössbauer spectroscopic study of (25−x)MnO–xZnO–15Fe2O3–60B2O3 glasses

The ⁵⁷Fe Mössbauer technique has been used to investigate the effect of zinc oxide substitution in (25???x)MnO–xZnO–15Fe₂O₃–60B₂O₃ glass system (x?=?0, 5, 10, 15 and 20 mol% of ZnO ). Mössbauer absorption spectra for all the samples recorded at room temperature suggest the existence of the two paramagnetic quadrupole doublets. The observed variations in hyperfine parameters have been explained on the basis of cations distribution and exchange interaction at the lattice sites and it is concluded that B–B interaction increases while the metal–metal interaction decreases due to replacement of manganese oxide by zinc oxide. These results suggest that the present glass system exhibits a paramagnetic behaviour that changes towards the weak paramagnetic when manganese oxide was replaced with zinc oxide.     

Optical properties of Yb3+ ions in fluorophosphate glasses for 1.0 μm solid-state infrared lasers

Yb³⁺-doped fluorophosphate glasses were prepared by melt-quenching technique and characterized their spectroscopic properties to assess the laser performance parameters. The magnitude of absorption (emission) cross-sections at 975 nm for all the studied Yb³⁺-doped glasses is found to be in the range of 0.29–1.50 × 10^?20 (0.59–1.99 × 10^?20 cm²) which is much higher than those of commercial Kigre QX/Yb: 1.06 × 10^?20 (0.5 × 10^?20 cm²) laser glass. The luminescence lifetimes of ²F_5/2 level decrease (1.15–0.45 ms) with increase in Yb₂O₃ concentration (0.1–4.0 mol%). Effect of OH^? content on luminescence properties of Yb³⁺ ions has also been investigated. The effect of radiative trapping has been discussed by using McCumber (McC) and Fuchtbauer–Ladenburge (F–L) methods. The product of experimental lifetimes and emission cross-sections for 0.1 mol% Yb₂O₃-doped glass is found to be 2.28 × 10^?20 cm² ms which indicates that the higher energy storage and extraction capability could be possible. The detailed spectroscopic results suggest that the studied glasses can be considered for high-power and ultrashort pulse laser applications.     

Optical,thermal, and structural properties of Nb2O5–TeO2 and WO3–TeO2 glasses

Glass samples from two systems, Nb₂O₅–TeO₂ and WO₃–TeO₂, were prepared at two melt quenching rates and characterized by density, DSC, UV-visible, and Raman spectroscopy. Addition of Nb₂O₅ decreased the density while increase in the WO₃ concentration increased the density. Glasses prepared at higher quenching rates had smaller densities than glasses of the same composition prepared at lower quenching rate although the short-range structure of both glasses were identical, as revealed by Raman spectroscopy. Optical studies found an intense absorption band just below the absorption edge in both the glass series. This band was attributed to electronic transitions of Nb⁵⁺ and W⁶⁺ ions and a lone pair of electrons on Te atoms. Glass transition temperature increased with increase in Nb₂O₅ and WO₃ mol% due to the increase in average bond strength in the glass network. Raman spectroscopy showed that the concentration of TeO₄ units decreased with the increase in Nb₂O₅ and WO₃ concentrations.     

Spectroscopic and dielectric studies on PbO–MoO3–B2O3 glasses incorporating small concentrations of TiO2

This paper deals with the investigation of a variety of physical properties including dielectric constant (over a wide range of frequency and temperature), optical absorption, luminescence, electron spin resonance (ESR) and infrared spectra of a TiO₂-doped lead molybdenum borate glass system. The composition chosen for the study is 30PbO–4MoO₃–(66–x)B₂O₃:xTiO₂ (with x ranging from 0.2 to 2.0). Quantitative analysis of the results of this study shows that, when the content of TiO₂ is around 0.8 mol%, the titanium ions exist predominantly in the tetravalent state and occupy substitutional positions in the glass network. A substantial increase in the insulating strength of these glasses on TiO₂ doping has also been observed. When the concentration of TiO₂ is increased beyond 0.8 mol%, it is observed that titanium ions exist primarily in the Ti³⁺ state and molybdenum ions in the Mo⁵⁺ state; analysis of the results further suggests that both of these ions participate in the depolymerization of the glass network.     

IR investigation of amorphous BaO-Fe2O3-B2O3 glasses prepared using 1 mol% TiO2

An infrared (IR) investigation of 35BaO-25Fe₂O₃-40B₂O₃glasses prepared by rapidly quenching the melts containing 1 mol% of TiO₂ at room temperature (25°C) is reported. The system is composed of BO₃ and BO₄ groups in the form of boroxol ring with tetraborate and diborate units forming the network structure. The iron oxide (Fe³⁺) possesses the positions in the network to occupying tetrahedral coordination sites. The TiO₂ (Ti⁴⁺) added by 1 mol% in the system probably maintain a tetrahedral (TiO₄) structure in the quenched glass, and thus induces growth of FeO₄ and BO₄ structural groups in the network. The network with latter groupings enhances the thermal stability as long as the sample does not crystallise significantly by given thermal treatments at temperatures upto 1000°C. A correlation with IR data has been made to account for the factors inhibiting the crystallisation of a system on addition of TiO₂.     

The transport and thermal properties of glassy LiPO<Subscript>3</Subscript>/crystalline Al<Subscript>2</Subscript>O<Subscript>3</Subscript> (ZrO<Subscript>2</Subscript>) composite electrolytes

Glassy LiPO₃/crystalline Al₂O₃ and glassy LiPO₃/crystalline ZrO₂ (0–12.5 vol.% of oxide fillers) composite solid electrolytes have been prepared by glass matrix softening. Their thermal and transport properties have been investigated by differential scanning calorimetry (DSC) and impedance spectroscopy methods. The addition of ZrO₂ leads to a decrease in the crystallization temperature of LiPO₃ glass. It was found that the conductivity behavior depends on the nature of the dispersed addition. In the case of the Al₂O₃ addition, the increase in the electrical conductivity is observed. The ionic conductivity of the LiPO₃/10% Al₂O₃ composite reaches 5.8 × 10^?8 S/cm at room temperature. In contrast, the conductivity in the LiPO₃/ZrO₂ composite system decreases.     

Electrical conductivity and local structure of lithium tin iron vanadate glass

A relationship between electrical conductivity (σ) and local structure of 15Li₂O·10Fe₂O₃·xSnO₂·(70–x)V₂O₅·5P₂O₅ glass (x = 0–20 mol%), abbreviated as xLFSVP glass, was investigated by ⁵⁷Fe- and ¹¹⁹Sn-Mössbauer spectroscopies, differential thermal analysis (DTA) and dc-four probe method. A small increase in quadrupole splitting (Δ) for Fe^III was observed from 0.70 to 0.74_{± 0.02} mm s^???1 with an increase of “x”, whereas isomer shift (Δ) values of 0.40_±0.01 mm s^???1 were independent of “x”. This result suggests that local distortion of Fe^IIIO₄ tetrahedra was slightly increased in SnO₂-containing vanadate glasses, which was reflected as an increase in glass transition temperature (T_g) from 266 to 285_±5 °C. A slope of 675 K / (mm s^???1) obtained in ‘T_g vs. Δ plot’ proved that Fe^III occupied the site of network former (NWF). An isothermal annealing of 10LFSVP glass at 500 °C for 100 min resulted in a marked decrease of Δ from 0.72 to 0.56_±0.02 mm s^???1, indicating that local distortion of FeO₄ tetrahedra was reduced by the structural relaxation of 3D-network. In contrast, identical δ and Δ values of 0.07_±0.01 and 0.53_±0.02 mms^???1, respectively, were observed in ¹¹⁹Sn-Mössbauer spectra of 10LFSVP glass before and after the annealing. These results indicate that Sn^IVO₆ octahedra are loosely bound in the glass matrix as a network modifier (NWM). A marked increase in σ from 7.4 × 10^???7 to 9.1 × 10^???3 S cm^???1 was observed in 20LFSVP glass after the isothermal annealing, indicating that structural relaxation of 3D-network evidently causes a marked increase in σ.     

Influence of surface modification by vanadium oxide and carbon on the electrochemical performance of LiFePO4/C

Surface modification with metal oxides is an efficient method to improve the performance of LiFePO₄. Carbon and V₂O₃ co-coated LiFePO₄ is synthesized by carbothermal reduction method combined with star-balling technique, and vanadium oxide is produced in situ. The structure and pattern of LiFePO₄/C modified with different amounts of vanadium oxide (0–5 mol%) were studied by X-ray diffraction, field-emission scanning electron microscopy, transmission electron microscopy, and micro-Raman spectroscopy. The electrochemical performance of material electrodes was analyzed by constant current charge–discharge and electrochemical impedance spectra (EIS). Electrochemical test results show that sample B (1.0 mol%) exhibits the best electrochemical performance, whose discharge capacity is up to 160.1, 127.2, and 88.4 mAh?g^?1 at 1, 5, and 10 °C, respectively. It indicates that V₂O₃ modification efficiently improves specific capacity and rate capability. The EIS experiment demonstrates that catalytic activity and reversibility of the cathode electrode are obviously increased by the surface modification of vanadium oxide.     

Optical and luminescence properties of Dy3+ ions in K–Sr–Al phosphate glasses for yellow laser applications

Trivalent dysprosium (Dy³⁺)-doped K–Sr–Al phosphate glasses have been prepared and investigated for their optical and luminescence properties. Judd–Ofelt theory has been used to derive radiative properties for the ⁴F_9/2 level of Dy³⁺ ions. The luminescence spectrum of 1.0 mol% Dy₂O₃-doped glass shows intense yellow emission around 572 nm ascribed to ⁴F_9/2 → ⁶H_13/2 transition with 78 % branching ratio and emission cross section of the order of 2.48 × 10^?21 cm². Moreover, the quantum efficiency of the ⁴F_9/2 level has been found to be 76 %. The luminescence decay curves for the yellow emission (⁴F_9/2 → ⁶H_13/2) have been measured and analyzed as a function of Dy³⁺ ion concentration. The results revealed that Dy³⁺-doped phosphate glasses could be useful for yellow laser applications.     

The influence of CdSe and ZnSe nanoparticles on the optical properties of Sm<Superscript>3+</Superscript> ions in lead borate glasses

The effect of glass composition and the presence of CdSe/ZnSe nanoparticles (NPs) on the optical absorption and fluorescence of Sm-doped lead borate glasses are studied. Three sets of glass samples xPbO:(99.5-x) B₂O₃:0.5Sm₂O₃, x = 29.5–69.5 mol%, xPbO:(96.5-x) B₂O₃:0.5Sm₂O₃: 3CdSe/ZnSe, x = 36.5, and 56.5 mol% are prepared. NPs are grown by annealing these glasses just below the glass transition temperature. Average size of both types of NPs increases with annealing time; however, CdSe NPs grew to a larger size range (2 to 20 nm) compared to ZnSe NPs (1 to 16 nm). We analyzed the hypersensitive transition, intensity parameters, radiative transition probability, stimulated emission cross section (σ_p), and the area ratio of the electric dipole/magnetic dipole transitions of Sm³⁺. The intensity parameters show a minimum at 11 h annealing for 36.5 mol% and a maximum for the same annealing duration in 56.5 mol% PbO containing CdSe NPs. The σ_p for 56.5 mol% of PbO with CdSe NPs is found to be a maximum when the average NP size is around 14 nm. ZnSe NPs containing glasses also show significant changes in σ_p when the average particle size is ~16 nm, for 36.5 mol% PbO. Our results suggest that the optical properties of Sm³⁺ in lead borate glasses are sensitive to its electronic environment which can be modified by varying the base glass composition and/or incorporating large NPs of CdSe/ZnSe. The large σ_p values that we observe for some of the glass compositions make them attractive materials for photonic devices and photovoltaic applications.

Open image in new window

Graphical abstract

     

Optical spectroscopic analysis of Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> doped CuO containing phosphate glass

The effect of Fe₂O₃ in sodium zinc phosphate glass system containing CuO with the chemical composition 40P₂O₅:38ZnO:1CuO:(21 ? x)Na₂O:xFe₂O₃ (where x = 1, 2, 3, 4, 5 and 6 mol%) has been studied. The glass formability of the prepared samples was examined by means of XRD which proved that there are no natural crystal contents. Archimedes method has been employed to measure the density of the prepared glass samples hence, the molar volume was calculated. The density and the molar volume were found to be increased by increasing Fe₂O₃ content. The optical spectroscopic analysis for the obtained glass samples has been carried out over the whole range (190–1000 nm) for studying the effect of bandpass absorption glass filter, its color peak center and UV cut-off. The center for bandpass filter is found to exhibit a red shift by increasing Fe₂O₃ content. Moreover, all glass samples showed a bandstop in UV-range which was increased by increasing Fe₂O₃ content. The results reveal the practicality of this glass composition in optical color glass bandpass filter for UV preventing applications such as UV-Laser protection.     

Assessment of role of iron ions on the physical and spectroscopic properties of multi-component Na2O−PbO−Bi2O3−SiO2 glass ceramics

Multi-component glass ceramics composition Na₂O?PbO?Bi₂O₃?SiO₂ doped with different concentrations of Fe₂O₃ as nucleating agent were characterised by XRD, SEM (scanning electron microscope) and DTA (differential thermal analysis) techniques. Optical absorption, EPR, FTIR and Raman studies are also carried out on these glass ceramics. Absorption bands observed at about 457, 489, 678 and 820 nm are the characteristics of Fe³⁺ ions whereas the band observed at about 964 nm is due to Fe²⁺ ions. EPR studies suggested that Fe³⁺ ions entered in the lattice as tetragonally distorted octahedral symmetry or rhombic sites at low concentration of Fe₂O₃, whereas at higher concentration of Fe₂O₃ (beyond 1 mol%), the super exchange type of interactions between multivalency iron ions begin to dominate. FTIR and Raman spectra have revealed the behaviour of various structural units in the glass ceramic matrix. The analysis of these spectroscopic studies indicates that iron ions do exist in Fe³⁺ and Fe²⁺ state.