Effect of Fluorine Ion on the Electrical Properties of Glasses in the Na2O–P2O5 System

The temperature–concentration dependence of the electrical conductivity of glasses in the NaPO₃–NaF system has been investigated. The regularities revealed are interpreted from the standpoint of the structural microinhomogeneity of glasses, which is due to the formation of polar structural units of the Na⁺[O^–POO_2/2], Na₂ ⁺[O^– ₂POO_1/2], Na⁺[F^–POO_2/2], and Na⁺F^– types. It is shown that the concentration dependence of the electrical conductivity is governed by the ratio between the concentrations of these structural units.     

Effect of Tungsten Oxide on the Crystallization Properties of Glasses of the B2O3–La2O3–Nb2O5 System

Glass Physics and Chemistry - The effect of tungsten oxide on the crystallization properties of glasses of the 37.5B2O3 22.5La2O3 (40 – x)Nb2O5 xWO3 (where x = 10, 15, 20, 30, 40 mol %)...     

P2O5-B2O3-V2O5无铅低熔玻璃形成能力和结构

以取代用作封接玻璃和电子浆料粘接相含铅低熔玻璃为目的,实验研究了P2O5-B2O3-V2O5体系玻璃的形成能力,结构和低熔性能.P2O5-B2O3-V2O5体系中,组成在B2O35%～30%、V2O50%～45%、P2O35%～50%(物质的量浓度,下同)区域内的玻璃具有较强的玻璃形成能力,较低的转变温度、良好的重熔流动性和抗析晶性能.优选玻璃组成为:15P2O5-35V2O5-25B2O3-3SiO2-2Al2O3-10ZnO-5SnO-7BaO-3Bi2O3,玻璃转变温度为308℃,在450℃玻璃细粉重熔熔体流动性好,适合用作在450～500℃烧结的封接玻璃和电子浆料的粘接相.红外光谱分析表明:玻璃结构是由大量孤立的[PO4]、[BO3]、[VO2]和[VO3]基团形成的层状结构,在层与层之间有少量的诸如B-O-B、P-O-P、P-O-V、P-O-B等桥氧键连接.     

Effect of V2O5 Loading on Propane Combustion over Pt/V2O5–Al2O3 Catalysts

Propane combustion was studied on Pt(0.4%)/V₂O₅–Al₂O₃ catalysts containing up to 20% V₂O₅. The density, strength and nature of surface acid sites were determined by TPD of NH₃ and FTIR spectra of adsorbed pyridine. The sample acidity increased with the vanadium content, essentially because the addition of vanadium oxide generated Brønsted acid sites. The Pt dispersion as determined by H₂ chemisorption increased with increasing V₂O₅ loading. The sample activity for propane combustion was evaluated through both conversion versus temperature (light-off curves) and kinetically-controlled conversion versus time catalytic tests. The propane combustion turnover rate on Pt/V₂O₅–Al₂O₃ increased with the amount of vanadium, probably because the intrinsic Pt oxidation activity increases with the sample acidity.     

Effect of P2O5 on evolution of microstructure of MgO–Al2O3–SiO2 glass ceramics

Abstract

MgO–Al₂O₃–SiO₂ (MAS) cordierite based glass ceramics were prepared by volume crystallisation. X-ray diffraction, Scanning electron microscopy and Energy diffraction scanning were used to investigate crystallisation behaviour and the influence of P₂O₅ on microstructure MAS based glass ceramics. The results showed that P⁵⁺ could promote the phase separation of MAS glass and that the glass was divided into two areas, such as Mg₄Al₂Ti₉O₂₅ and the containing P⁵⁺ area at <900°C. Mg₄Al₂Ti₉O₂₅ and Mg₃(PO₄)₂ in the area were both advantageous to the precipitation of μ cordierite, which further transformed to α cordierite due to P⁵⁺ in the residual glassy phase. However, P⁵⁺ inhibited the presence of cordierite when the heat treatment temperature was >900°C.     

Sb2O5和Bi2O3添加剂对Ag(Nb1-xTax)O3陶瓷结构、形貌和性能的影响

研究了Sb2O5和Bi2O3添加剂对Ag(Nb1-xTax)O3陶瓷材料的结构、形貌和介电性能的影响.结果表明:当Sb2O5和Bi2O3的质量分数较少(＜2.5%)时,不会影响Ag(Nb1-xTax)O3的钙钛矿结构,但能促进其烧结,使所得陶瓷样品更均匀致密.添加适量的Sb2O5和Bi2O3均可使Ag(Nb1-xTax)O3的介电常数(ε)增大,介电损耗(tgδ)减小,介电性能的温度稳定性得到改善.Bi2O3较Sb2O5对降低Ag(Nb1-xTax)O3陶瓷损耗及改善温度稳定性的效果更佳.     

Effect of a Bi–Cr–O synthetic multi-phase on the microstructure and electrical properties of ZnO–Bi2O3 varistor ceramics

ZnO–Bi₂O₃–MnO₂ (ZBM)-based varistors were fabricated via doping a novel synthetic multi-phase (SMP) additive produced by calcining the mixture of 18Bi₂O₃·Cr₂O₃ at a given temperature. The effects of the SMP on the microstructural and electrical properties of ZBM varistors were investigated. It was found that the SMP dopant was a compound crystalline phases including Bi–Cr–O phases (Bi_7.38Cr_0.62O_12+x and CrBi₁₈O₃₀) and small amounts of Bi₂O₃ rather than a synthesized polycrystal. The Bi–Cr–O phases were not emerged for samples with x=1, indicating that the amount of it is tiny and the small Bi₂O₃ may accelerate ZnO grain growth. With more SMP doping (x>1) in the ZBM ceramics, it acted as a barrier inhibiting grain growth. For samples with x=5, excellent electrical properties were obtained: the nonlinear coefficient α increased up to 50.19 corresponding to the highly barrier height of 2.62 eV; the leakage current I_L reduced to 0.3 μA. The dielectric constant ε_a is proportional to the ratio of the grain size d to the thickness of the depletion layer width t, which explained the ε_a increased at f=1 kHz for the samples with x=1 and 5. The improvement of the electrical properties can be explained by the oxygen absorption mechanism.     

Glass forming region and bonding mechanism of low-melting V2O5–TeO2–Bi2O3 glass applied in vacuum glazing sealing

As a new kind of energy-saving glass, vacuum glazing has excellent thermal and sound insulation properties and is widely used in building, household appliances and solar photovoltaic. The edge sealing material, along with sealing method, is key to the fabrication of vacuum glazing. Low transition temperature (T_g) and good fluidity at sealing temperature (T_s) make low-melting glass of V₂O₅–TeO₂–Bi₂O₃ (VTB) system perfect to be the edge sealing material for vacuum glazing. The glass forming region of VTB ternary system was mapped for the first time in this work. Low-melting VTB glass of 40V₂O₅–50TeO₂–5Bi₂O₃–3ZnO–2Na₂O (wt%) was optimized to be the sealing material. Glass powder of this composition could be used to seal the edges of vacuum glazing at an extremely low temperature of 360°C. With the assistance of anodic-bonding method, the bonding strength of vacuum glazing was dramatically enhanced. Vacuum glazing fabricated under the optimized process parameters of 420°C, 600 V, and 60 min possesses a highest bonding strength of 4.31 MPa. Furthermore, anodic-bonding mechanism of low-melting VTB glass applied in vacuum glazing sealing has been thoroughly researched.     

Effect of TiO2 on crystallization and mechanical properties of MgO–Al2O3–SiO2 glasses containing P2O5

MgO–Al₂O₃–SiO₂ glass-ceramics have been widely used in military, industrial, and construction applications. The nucleating agent is one of the most important factors in the production of glass-ceramics as it can control the crystallization temperature or the grain size. In this study, we investigated the effect of replacing P₂O₅ with different amounts of TiO₂ on the crystallization, structure, and mechanical properties of an MgO–Al₂O₃–SiO₂ system. The crystallization and microstructure were investigated by differential scanning calorimetry, Raman spectroscopy, X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The mechanical properties were investigated by measuring the Vickers hardness, Young's modulus, and fracture toughness. The results showed that adding TiO₂ favored the precipitation of fine grains and significantly increased the Vickers hardness, Young's modulus, and fracture toughness of the glasses. Introducing an appropriate amount of TiO₂ can make a glass structure more compact, promote crystallization, and improve the mechanical properties of MgO–Al₂O₃–SiO₂ glass-ceramics.     

The effect of Si–Bi2O3 on the ignition of the Al–CuO thermite

The ignition temperature of the Al–CuO thermite was measured using DTA at a scan rate of 50 °C min^?1 in a nitrogen atmosphere. Thermite reactions are difficult to start as they require very high temperatures for ignition, e.g. for Al–CuO thermite comprising micron particles it is ca. 940 °C. It was found that the ignition temperature is significantly reduced when the binary Si–Bi₂O₃ system is added as sensitizer. Further improvement is achieved when the reagents are nano-sized powders. For the composition Al + CuO + Si + Bi₂O₃ (65.3:14.7:16:4 wt.%), with all components nano-sized, the observed ignition temperature is ca. 613 °C and a thermal runaway reaction is observed in the DTA.     

P2O5对Bi2O3-B2O3-ZnO体系玻璃结构及热性能的影响

采用传统的熔融冷却的方法制备了(40-x)Bi2O3-30B2O3-30ZnO-xP2O5(0≤x≤15mo1％)体系玻璃.使用红外光谱、拉曼光谱、DSC和热膨胀仪研究了封接玻璃的结构和热性能.红外光谱及拉曼光谱结果表明,P2O5作为网络形成体,以[PO4]进入到玻璃的网络结构中,玻璃的网络结构性增强.玻璃结构中[BO3]三角体结构单元相对含量有增多趋势,[BO4]四面体、[BiO3]三角体、[BiO6]八面体结构单元相对含量减少.随着P2 O5含量的增加,玻璃化转变温度和玻璃的初始析晶温度升高;玻璃的密度减小.Bi2O3-B2O3-ZnO-P2O5体系封接玻璃热膨胀系数减小,从8.289×10-6℃-1减小到6.354×10-6℃-1.玻璃的软化点逐渐增大,从416℃升高到524℃.     

Effect of pH on the Catalytic Properties of Mo–V–Te–P–O Catalysts for Selective Oxidation of Isobutane

Mo–V–Te–P mixed oxide catalysts, prepared by a dry-up method at various pHs (in the range of about 1.0–9.0), have been tested in the partial oxidation of isobutane. The best catalytic performance was achieved over a catalyst prepared at a pH about 7.0. In this case, high selectivity to methacrolein (37.0%) at an isobutane conversion of 12.7% has been obtained at 380 °C. The surface V⁴⁺/V⁵⁺ ratios of the calcined samples were strongly influenced by the pH in the synthesized solution, which is one of the key factors in the catalytic performance for selective oxidation of isobutane.     

Effect of CaO doping on the properties and crystallization behavior of Y2O3–Al2O3–SiO2 glass

Nowadays, Y₂O₃–Al₂O₃–SiO₂ (YAS) glass joining is considered to be a promising scheme for nuclear-grade continuous silicon carbide (SiC) fiber reinforced SiC matrix composites (SiC/SiC). CaO has great potential for nuclear applications since it has low reactivity and low decay rate under nuclear irradiation. In this paper, the effect of CaO doping on the structure, thermophysical properties, and crystallization behavior of YAS glass was systematically studied. As the CaO doping content increased, the number of bridge oxygens and the viscosity at high temperatures reduced gradually. After heat treatment at 1400 °C, the main phases in YAS glass were β-Y₂Si₂O₇, mullite, and SiO₂ (coexistence of crystalline and glass phases), while that with 3.0% CaO doping turned into a single glassy phase under the same treatment conditions. Moreover, a structural model and the modification mechanism were proposed, which provided a theoretical basis for the subsequent component design and optimization.     

Subsolidus phase equilibria in the La2O3–Fe2O3–Sb2O5 system and characterization of layered ternary oxide LaFe0.5Sb1.5O6

Phase equilibria in the La₂O₃-Fe₂O₃–Sb₂O₅ system have been studied. The isothermal section was constructed at T=900 °С. The existence of the ternary oxide LaFe_0.5Sb_1.5O₆ was confirmed. The structure of this compound was solved using Rietveld refinement of synchrotron radiation-based powder XRD data. LaFe_0.5Sb_1.5O₆ crystallizes in a trigonal layered structure relating to PbSb₂O₆ type (space group P-31m, a=b=5.2446(3) Å, c=5.1930(3) Å, Z=1). The fine powder of LaFe_0.5Sb_1.5O₆ was prepared by molten salt synthesis. The compound was characterized by diffuse reflection and Mossbauer spectroscopy, magnetic measurements, scanning electron microscopy and photocatalytic tests. The magnetic behavior of LaFe_0.5Sb_1.5O₆ in the applied magnetic field H=5000 Oe is entirely paramagnetic. By contrast, in the small magnetic field H=100 Oe the magnetic data of LaFe_0.5Sb_1.5O₆ indicates an unusual critical behavior near phase transition at T<2 K.     

The influence of microstructure and phase composition of glass ceramics in the VO2–V2O5–P2O5–Cu2O–SnO2 system on the electrical properties related to the metal–semiconductor phase transition

Phase composition, microstructure and electrical conductivity of glass ceramics in the VO₂–V₂O₅–P₂O₅–SnO₂ and VO₂–V₂O₅–P₂O₅–Cu₂O–SnO₂ systems have been studied. Only crystalline phases VO₂, SnO₂ and vanadium phosphate glass of the V₂O₅–P₂O₅ system have been found in glass ceramic compositions in the VO₂–V₂O₅–P₂O₅–SnO₂ system. Besides the above-mentioned phases, probably the X-ray lines of V₃O₅, V₄O₇, V₅O₉, V₆O₁₁, V₇O₁₃, V₄O₉, V₆O₁₃, V₂O₅, SnO₂, SnO, Sn₂O₃, Sn₃O₄ and CuO phases are observed in the X-ray spectra of glass ceramics in the VO₂–V₂O₅–P₂O₅–Cu₂O–SnO₂ system. According to SEM/EDS data, these phases were observed as submicrometer fine-crystalline inclusions in glass on the surface of VO₂ crystallites and between them. The formation of these phases was caused by the redox processes in the liquid phase during glass ceramics synthesis. The important role of tin oxides possessing high electrical conductivity and vanadium oxides exhibiting a low temperature of metal–semiconductor phase transition in the stabilization of glass ceramics electrical properties related to the phase transition in VO₂ has been established.