Study of AC electrical properties of V2O5–P2O5–B2O3–Dy2O3 glasses

The AC conductivity of glass samples of composition 60V₂O₅–5P₂O₅–(35−x)B₂O₃–xDy₂O₃, 0.4≤x≤1.2 has been analyzed. The samples were prepared by the usual melt-quench technique. The prepared compounds were analyzed by X-ray diffraction (XRD) and thermo gravimetric–differential thermal analysis (TG/DTA). The activation energies were evaluated using glass transition temperature (T_g) and peak temperature of crystallization (T_c) from TG/DTA. The dependence of activation energy on composition was discussed. The electrical conductance and capacitance were measured over a frequency range of 20 Hz to 1 MHz and a temperature range of 303–473 K; these reveal semiconducting features based predominantly on an ionic mechanism. The dielectric and complex-impedance response of the sample is discussed. The relaxation time was found to increase with increasing temperature. Jonscher's universal power law is applied to discuss the conductivity. The electrode polarization was found to be negligible and confirmed from electrical modulus.     

Synthesis and characterization of MgAl2O4–ZrO2 composites

Different types of dense 5–97% ZrO₂–MgAl₂O₄ composites have been prepared using a MgAl₂O₄ spinel obtained by calcining a stoichiometric mixture of aluminium tri-hydroxide and caustic MgO at 1300 °C for 1 h, and a commercial yttria partially stabilized zirconia (YPSZ) powder as starting raw materials by sintering at various temperatures ranging from 1500 to 1650 °C for 2 h. The characteristics of the MgAl₂O₄ spinel, the YPSZ powder and the various sintered products were determined by X-ray diffraction (XRD), scanning electron microscopy (SEM), BET surface area, particle size analysis, Archimedes principle, and Vickers indentation method. Characterization results revealed that the YPSZ addition increases the sintering ability, fracture toughness and hardness of MgAl₂O₄ spinel, whereas, the MgAl₂O₄ spinel hampered the sintering ability of YPSZ when sintered at elevated temperatures. A 20-wt.% YPSZ was found to be sufficient to increase the hardness and fracture toughness of MgAl₂O₄ spinel from 406 to 1314 Hv and 2.5 to 3.45 MPa m^1/2, respectively, when sintered at 1600 °C for 2 h.     

Investigation of the effect of ZrO2 and ZrO2/Al2O3 additions on the hot-pressing and properties of equimolecular mixtures of α- and β-Si3N4

In this work, hot-pressing of equimolecular mixtures of α- and β-Si₃N₄ was performed with addition of different amounts of sintering additives selected in the ZrO₂–Al₂O₃ system. Phase composition and microstructure of the hot-pressed samples was investigated. Densification behavior, mechanical and thermal properties were studied and explained based on the microstructure and phase composition. The optimum mixture from the ZrO₂–Al₂O₃ system for hot-pressing of silicon nitride to give high density materials was determined. Near fully dense silicon nitride materials were obtained only with the additions of zirconia and alumina. The liquid phase formed in the zirconia and alumina mixtures is important for effective hot-pressing. Based on these results, we conclude that pure zirconia is not an effective sintering additive. Selected mechanical and thermal properties of these materials are also presented. Hot-pressed Si₃N₄ ceramics, using mixtures from of ZrO₂/Al₂O₃ as additives, gave fracture toughness, K_IC, in the range of 3.7–6.2 MPa m^1/2 and Vicker hardness values in the range of 6–12 GPa. These properties compare well with currently available high performance silicon nitride ceramics. We also report on interesting thermal expansion behavior of these materials including negative thermal expansion coefficients for a few compositions.     

Physical properties of pseudo quaternary Na2B4O7 – SiO2 – MoO3 – Dy2O3 glasses

Pseudo quaternary Na₂B₄O₇–SiO₂–MoO₃–Dy₂O₃ glasses with various concentrations of Dy₂O₃ were synthesized and characterized by ultrasound, DTA and X-ray diffraction (XRD). It was found that, the density, the molar volume and the elastic moduli increased while the ultrasonic velocities and the packing density decreased with increasing of Dy₂O₃ concentration. The lower values of the radii and the bond length of B₂O₃, compared to those of Dy₂O₃, decreased the interatomic forces between the reactant glass forming cations and oxygens inside the glassy network. Accordingly, this will increase the molar volume and in the same time will decrease the average cross-link density, the ultrasonic velocities, the glass transition temperature and the thermal stability. Also, this may result in a high density glass sample which will increase the elastic moduli. Based on Lasocka's model, a good correlation between the temperature of both glass transition ($T_{\mathit{gl}}$) and crystallization peak ($T_{\mathit{pc}})$was observed.     

The influence of In2O3 on electrical characteristics of iron mixed Li2O–PbO–B2O3–SiO2–Bi2O3 multi-component glass system

Glasses of the composition 19Li₂O–20PbO–20B₂O₃–30SiO₂–(10−x) Bi₂O₃–1Fe₂O₃: xIn₂O₃ with six values of x (0 to 5.0) were synthesized. Dielectric properties viz., dielectric constant, ε′(ω), loss, tan δ, ac conductivity, σ_ac, electric modulus, M(ω) over wide ranges of frequency and temperature and also dielectric break down strength have been studied as a function of In₂O₃ concentration. The temperature dispersion of real part of dielectric constant, ε′(ω) has been analyzed using space charge polarization model. The dielectric loss (and also the electric moduli) variation with frequency and temperature exhibited relaxation effects and these effects were attributed to the divalent iron ion complexes. The ac conductivity exhibited maximal effect, whereas the activation energy for the conductivity demonstrated minimal magnitude at about 1.0 mol% of In₂O₃. The conductivity mechanism is understood due to the polaronic transfer between Fe²⁺ and Fe³⁺ ions. The low temperature ac conductivity mechanism is explained following the quantum mechanical tunneling model. Spectroscopic studies viz., optical absorption and ESR spectra have revealed that the redox ratio (Fe²⁺/Fe³⁺) is maximal when the concentration of In₂O₃ is ~1.0 mol%. The higher values of dielectric parameters observed at 1.0 mol% of In₂O₃ are attributed to the presence of iron ions largely in divalent state and act as modifiers. The analysis of these results together with spectroscopic studies has indicated that when In₂O₃ is present in the glass matrix in higher concentrations (more than 1.0 mol%) iron ions predominantly exist in trivalent state, occupy substitutional positions and make the glass more rigid. Such enhanced rigidity of the network is causing the decrease of dielectric parameters with the concentration of In₂O₃. Finally it is concluded that In₂O₃ mostly participate in the glass network in octahedral positions and make act as reducing agent (for iron ions) in the studied glass matrix when its concentration is ≤1.0 mol%.     

Depolarization temperature and piezoelectric properties of (Bi1/2Na1/2)TiO3–(Bi1/2Li1/2)TiO3–(Bi1/2K1/2)TiO3 lead-free piezoelectric ceramics

The phase transition temperature and piezoelectric properties of x(Bi_1/2Na_1/2)TiO₃–y(Bi_1/2Li_1/2)TiO₃–z(Bi_1/2K_1/2)TiO₃ [x + y + z = 1] (abbreviated as BNLKT100y–100z) ceramics were investigated. BNLKT100y–100z ceramics were prepared by conventional ceramic fabrication. The depolarization temperature T_d was determined by the temperature dependence of the dielectric and piezoelectric properties. This study focuses on the effect of Li¹⁺ and K¹⁺ ions on T_d and the piezoelectric properties of BNT ceramics. BNLKT100y–100z (y = 0–0.08) has a morphotropic phase boundary (MPB) between rhombohedral and tetragonal phases at z = 0.18–0.20, and high piezoelectric properties were obtained at the MPB composition. The piezoelectric constant d₃₃ increased with increasing y; however, T_d decreased above y = 0.06. The d₃₃ and T_d values of BNLKT4-20 and BNLKT8-20 were 176 pC/N and 171 °C, and 190 pC/N and 115 °C, respectively.     

Investigation of phase separation of nano-crystalline anatase from TiO2SiO2 thin film

In this work, a set of SiO₂–TiO₂ mixed oxides was prepared by the polymeric sol–gel route and deposited on glass substrate through the dip coating technique. Then, the effect of different important preparation parameters (sol–gel stabilizers, Ti content, and heat treatment) on the phase separation was investigated. The developed films were heat treated at 500 °C and characterized using TGA/DTA, FTIR, XRD, SEM, and AFM. The results showed that TiO₂ segregation can be controlled by selecting an appropriate composition of diethanolamine (DEA) and methyl methacrylate (MMA) for preparation of polymeric silica–titania sol. Besides, anatase phase in the samples were crystallized without any stabilizers within heat treatment procedure at 500 °C; however, using appropriate composition of DEA and MMA crystallization rate significantly decreased.     

Crystallographic characterization of silicon nitride ceramics sintered with Y2O3–Al2O3 or E2O3–Al2O3 additions

Silicon nitride ceramics were sintered using Y₂O₃–Al₂O₃ or E₂O₃–Al₂O₃ (E₂O₃ denotes a mixed oxide of Y₂O₃ and rare-earth oxides) as sintering additives. The intergranular phases formed after sintering was investigated using high-resolution X-ray diffraction (HRXRD). The use of synchrotron radiation enabled high angular resolution and a high signal to background ratio. Besides the appearance of β-Si₃N₄ phase the intergranular phases Y₃Al₅O₁₂ (YAG) and Y₂SiO₅ were identified in both samples. The refinement of the structural parameters by the Rietveld method indicated similar crystalline structure of β-Si₃N₄ for both systems used as sintering additive. On the other hand, the intergranular phases Y₃Al₅O₁₂ and Y₂SiO₅ shown a decrease of the lattice parameters, when E₂O₃ was used as additive, indicating the formation of solid solutions of E₃Al₅O₁₂ and E₂SiO₅, respectively.     

The role of CeO2–ZrO2 as support in the ZnO–ZnCr2O4 catalysts for autothermal reforming of methanol

Autothermal reforming of methanol for hydrogen production was investigated over ZnO–ZnCr₂O₄ supported on a series of metal oxides (Al₂O₃, CeO₂, ZrO₂ and CeO₂–ZrO₂). CeO₂–ZrO₂ mixed oxides with Ce /Zr molar ratio of 4/1 was found to be the optimal support which showed significant effect on the catalytic activity and selectivity. The ZnO–ZnCr₂O₄/CeO₂–ZrO₂ and ZnO–ZnCr₂O₄ catalysts were characterized by XRD, TEM, H₂-TPR and XPS. The results show that CeO₂–ZrO₂ mixed oxides have significant effect on the catalytic performance and the supported catalyst shows more uniform temperature distribution in the catalyst bed which was mainly due to its reasonable redox properties.     

Phase stability and hot corrosion behavior of ZrO2–Ta2O5 compound in Na2SO4–V2O5 mixtures at elevated temperatures

For thermal barrier coating (TBC) applications, yttria stabilized zirconia (YSZ) is susceptible to hot corrosion. This paper examines the hot corrosion performance of ZrO₂/Ta₂O₅ compounds. Different compositions of ZrO₂–Ta₂O₅ samples in the presence of molten mixture of Na₂SO₄+V₂O₅ at 1100 °C were tested. The compositions were selected to form tetragonal and orthorhombic phases of zirconium-tantalum oxides. Results show that orthorhombic zirconium-tantalum oxide is more stable, both thermally and chemically in Na₂SO₄+V₂O₅ media at 1100 °C, and shows a better hot corrosion resistance than the tetragonal phase.     

Palladium(II) complexes with Pd2S2 rings. Synthesis and theoretical characterization of [Pd2(dppe)2(μ-S)2] and X-ray characterization of [Pd3(dppe)3(μ3-S)2]Cl2

The use of the dppe ligand and the fine tuning of the experimental conditions has allowed isolation of [Pd₂(dppe)₂)(μ-S)₂], whose structural characterization has been achieved by ab initio MP2 calculations, and of [Pd₃(dppe)₃(μ₃-S)₂]Cl₂, the X-ray structure of which is also reported.     

ICP-AES法测定矾土中Fe2O3、TiO2和SiO2

采用四硼酸锂熔融试样,电感耦合等离子体原子发射光谱法(ICP-AES法)测定矾土中Fe2 O3、TiO2和SiO2。通过对熔样方法选择、铝基体以及背景的研究,确定了分析条件。结果表明,该法具有良好的精密度和准确性,回收率在94%～108%。     

H2O2/Fe2(MoO4)3体系中H2O2吸附分解及NO氧化行为的DFT研究

为阐明H₂O₂/Fe₂(MoO₄)₃体系脱硝过程中H₂O₂吸附分解及NO氧化行为，基于DFT方法首次计算了H₂O₂和NO分子单独及二者同时在Fe₂(MoO₄)₃表面的吸附构型，并通过考察吸附能、Mulliken电荷及氧化路径等特性揭示H₂O₂催化分解和NO氧化的微观机制。结果表明：H₂O₂在Fe₂(MoO₄)₃表面易分解为活性自由基，而NO则以分子形式吸附；H₂O₂和NO共吸附时，H₂O₂优先吸附于催化剂表面并随后分解，NO则分别被H₂O₂分解产...     

Effect of yttrium and praseodymium on properties of Ce0.75Zr0.25O2 solid solution for CH4–CO2 reforming

Ce_0.75Zr_0.25O₂ solid solutions doped with Y³⁺ or Pr⁴⁺/Pr³⁺ were prepared by the co-precipitation method, and their physicochemical properties were characterized by means of N₂ adsorption, X-ray diffraction, X-ray photoelectron spectroscopy, FT-Raman, and H₂ temperature-programmed reduction and thermogravimetric analysis. Their performance in CH₄–CO₂ reforming was also tested in an atmospheric fixed-bed reactor. Ce_0.75Zr_0.25O₂ and Y³⁺ or Pr⁴⁺/Pr³⁺ doped Ce_0.75Zr_0.25O₂ solid solutions are of CaF₂ structure, and the thermal stability of Ce_0.75Zr_0.25O₂ is enhanced by doping Y³⁺ or Pr⁴⁺/Pr³⁺. Comparing with Ce_0.75Zr_0.25O₂, the migration of bulk lattice oxygen species become easier and the content of surface oxygen species is higher in the doped Ce_0.75Zr_0.25O₂, which is due to either oxygen vacancies or/and structural distortion resulted from the doping. The activity of the solid solutions in CH₄–CO₂ reforming is closely related to the surface oxygen species. Y³⁺ or Pr⁴⁺/Pr³⁺ doped Ce_0.75Zr_0.25O₂, especially the former, show higher activity than Ce_0.75Zr_0.25O₂, and Y³⁺ doped Ce_0.75Zr_0.25O₂ possesses better stability. All of the catalysts have good coke resistance. The catalyst deactivation is mainly due to the catalyst sintering.     

O1/A1/O2/A2工艺处理焦化废水试验研究

通过对短程硝化反硝化工艺的研究,开发了好氧/厌氧/好氧/缺氧(O1/A1/O2/A2)生物脱氮新工艺并用于焦化废水的处理。考察了NH4+-N、COD、TN对反应器运行效果影响。结果表明,当进水COD平均为3 012.9 mg/L,NH4+-N、TN、挥发酚、总氰平均质量浓度分别为590.5、608.4、361.8、34.5 mg/L;出水COD平均为81.7 mg/L,出水NH4+-N、TN、挥发酚、总氰的平均质量浓度分别为0.1、9.9、0.1、0.1 mg/L,出水指标达到国家污水综合排放一级标准,A/O工艺处理这种焦化废水TN偏高,而用O1/A1/O2/A2工艺可以解决这一问题,实现了TN脱除。考察了温度、DO、pH对短程硝化影响。结果表明,在DO质量浓度为1.0～1.5 mg/L、温度在30～35℃、pH 7.5～8.0,系统能够进行稳定短程硝化反硝化。     

Dehydrogenation of propane in the presence of N2O over In2O3―Al2O3 mixed oxide catalysts

Dehydrogenation of propane coupled with N₂O over a series of binary In₂O₃―Al₂O₃ mixed oxides was investigated. In contrast to the poor performance for sole N₂O decomposition, a remarkable synergy was identified between N₂O decomposition and propane dehydrogenation. Among the catalysts tested, the In₂O₃―Al₂O₃ sample containing a 20 mol% In₂O₃ showed the highest activity for propane dehydrogenation in the presence of N₂O. Moreover, stability far superior to those of the conventional iron-based materials was observed, attributable to the moderate surface acidity of the In―Al―O composite. The essential role of N₂O is suggested to generate active oxygen species facilitating propane dehydrogenation.     

MoS2/TiO2光催化降解甲基红

利用硫化钠与钼酸钠为原料,通过盐酸酸化,在TiO2上沉积MoS2纳米片。利用甲基红为降解对象,研究合成的片状纳米MoS2/TiO2复合物的光催化性能。结果显示该复合物具有优良的光催化降解甲基红的性能;催化剂用量、甲基红初始浓度与初始pH等条件对甲基红降解存在明显影响。该催化剂在重复使用3次时,甲基红2 h的脱色率接近65%,表明催化剂具有较好的重复使用性能。     

Microwave dielectric characteristics of Nb2O5-added 0.9Al2O3–0.1TiO2 ceramics

The sintering characteristics, phase composition, and microwave dielectric properties of Nb₂O₅-added 0.9Al₂O₃–0.1TiO₂ ceramics sintered at 1300–1500 °C have been investigated. Results show that Nb⁵⁺ and Al³⁺ can co-substitute for Ti⁴⁺ and form Ti_0.8Al_0.1Nb_0.1O₂, which can lower effectively the sintering temperature, and improve the quality factor of 0.9Al₂O₃–0.1TiO₂ ceramics.     

纳米TiO2/SiO2复合食品抗菌材料

以水玻璃和Ti(SO4)2为原料,制备出了多孔的纳米TiO2/SiO2复合粒子,在后处理过程中,利用无机包覆剂溶解度随温度的变化,在复合粒子表面包覆了一层无机结晶膜,经热处理除去包覆剂后,得到了以单分散纳米复合粒子组成的复合微粉.对复合微粉进行比表面和孔容测试,并运用XRD和TEM进行了表征,发现TiO2以12.6nm的纳米晶粒的形式被多孔的SiO2包覆,所形成的复合粒子则约为20nm.为了了解复合微粒的灭菌效果,运用纳米TiO2和复合粉末对4种保健食品进行对照灭菌实验,两个月以后,测得含复合微粒的样品中的菌落总数为50～120个/g,是相应保健食品企业标准许可菌落数的0.25%～0.7%,为相应空白样和纳米TiO2粉样品菌落数的0.52%～0.97%和33.3%～83.3%.