Corrosion behaviour of magnetron-sputtered Al1−x-Mnx coatings in neutral saline solution

Al-Mn coatings with different contents (0-41 at.%) were deposited on glass slides by magnetron co-sputtering. These coatings were characterised, before and after immersion tests, by X-ray diffraction, scanning electron microscopy (SEM) and electron probe microanalysis. The electrochemical measurements in a neutral saline solution showed that the pitting corrosion resistance of Al-Mn coatings increased with increasing Mn content as the pitting corrosion potentials are progressively shifted towards positive values. The immersion tests reveal that for all Mn contents, Al-Mn coatings keep a sacrificial character compared with steel. For Mn content above 26 at.%, XRD analysis showed the formation of an amorphous phase. This structure would be responsible for the high increase of the hardness of Al-Mn coatings and of the stabilisation of their open circuit potentials during the 48 h immersion tests.     

Subsolidus phase relation and crystal structure of the PrBa2−xSrxCu3O7±δ system

The PrBa_2−xSr_xCu₃O_7±δ solid solution was investigated by means of X-ray powder diffraction in combination with Rietveld analysis. The Sr-doped Pr123 single phase could be synthesized at 950 °C in air. The solubility of PrBa_2−xSr_xCu₃O_7±δ solid solution is 0.2≤x≤0.6. The structure of PrBa_2−xSr_xCu₃O_7±δ is orthorhombic for x=0.2. The structure transforms into tetragonal for 0.3≤x≤0.6. In the PrBa_2−xSr_xCu₃O_7±δ structure, Sr ions can replace Ba ions, the highest value is x=0.6 under our experimental condition. But Sr ions could not replace Pr ions. Furthermore Pr ions could not occupy the sites of Ba ions in the PrBa_2−xSr_xCu₃O_7±δ system. Both ionic radii and chemical properties play an important role in the mutual substitution of Pr, Ba and Sr ions in the Pr123 structure of the PrBa_2−xSr_xCu₃O_7±δ system.     

Phase behavior and some properties of LaMn1−xRhxO3 solid solution

Structure and magnetic and electrical properties of the polycrystalline compounds LaMn_1−xRh_xO₃ (0 < x ≤ 1) have been investigated. The samples were characterized by X-ray diffraction and Rietveld refinement which confirmed the space group Pnma (No. 62) for all compositions at room temperature. A transformation from O′- to O-type orthorhombic structure is seen near x = 0.6 tending to make the phase unstable. The electrical conductivity measurement shows semiconducting property above room temperature with a rather low activation energy for Mn-rich compositions. Compounds in the region 0.1 ≤ x ≤ 0.9 show ferromagnetic property but the substitution of Rh³⁺ ion for Mn³⁺ ion suppresses the ferromagnetism that results in reducing the Curie temperature, T_C.     

Interstitial solid solution Hf5GaxSn3 (x = 0-1)

Formation of an interstitial solid solution Hf₅Ga_xSn₃ (x = 0-1) based on the binary compound Hf₅Sn₃ (structure type Mn₅Si₃, Pearson symbol hP16, space group P6₃/mcm, a = 8.36562(6), c = 5.70775(4) Å from X-ray powder diffraction) was established at 600 °C. The crystal structure (structure type Hf₅CuSn₃, ordered derivative of Ti₅Ga₄, hP18, P6₃/mcm) was refined on X-ray single-crystal diffraction data for three compositions: Hf₅Ga_0.16(3)Sn₃ (a = 8.3288(12), c = 5.6988(11) Å), Hf₅Ga_0.53(2)Sn₃ (a = 8.4205(12), c = 5.7655(12) Å) and Hf₅GaSn₃ (a = 8.5564(12), c = 5.7859(12) Å). The Ga atoms occupy Wyckoff position 2b at the centres of Hf₆ octahedral interstices.     

Solubility of YbTe in Sb2Te3 and thermodynamic properties of the solid solution

The solubility of YbTe in Sb₂Te₃ is investigated by a combination of DTA, XRD, SEM, and EMF methods. The fragment of the T-x phase diagram of the YbTe-Sb₂Te₃ system is constructed for 0-25 mol.% YbTe. It is shown that the solubility limit for YbTe in Sb₂Te₃ is achieved at 15 mol.% YbTe at 300 K and at 17.5 mol.% YbTe at 855 K. From the EMF measurements with an YbTe electrode the partial thermodynamic functions of the YbTe pseudo-component are calculated for the alloys of different compositions. Also, the standard integral thermodynamic functions of the YbTe dissolution in Sb₂Te₃ as well as the standard thermodynamic functions of formation and the standard entropy of the solid solution are calculated from the experimental data.     

Synthesis and characterization of new pyrochlore solid solution Bi1.5Sb1.5Cu1−xMnxO7

A new pyrochlore solid solution with formula Bi_1.5Sb_1.5Cu_1−xMn_xO₇ has been synthesized using ceramic method at 1000 °C. The cell parameter decreases linearly with increasing manganese concentration. Rietveld refinements for (B_1.5Mn_0.5)(Sb_1.5Mn_0.5)O₇ compound using X-ray powder diffraction data confirmed an overall A₂B₂O₇ cubic pyrochlore structure with a = 10.42749 (4) Å and Fd-3m symmetry. The reliability factors are R_wp = 3.48%; R_p = 2.37%; R_exp = 1.65% and R_Bragg = 1.58%. The magnetic susceptibility measurements achieved between 4 and 300 K indicate a paramagnetic behaviour with an oxidation state “2+” of the manganese ion. The electric resistance measured using complex impedance spectroscopy method put in evidence a decrease of the electric resistance with the temperature, which reached 5 × 10² Ω at 675 K. Dielectric properties depend on the variation of frequency and temperature, results indicate a conductive compound.     

Thermodynamic properties and phase diagrams of the binary systems B2O3–Ga2O3, B2O3–Al2O3 and B2O3–In2O3

We calculated the binary phase diagrams B₂O₃–Ga₂O₃, B₂O₃–In₂O₃ and B₂O₃–Al₂O₃, and the Gibbs energy of formation of the binary compounds, using experimental liquidus data. The B₂O₃–Ga₂O₃ system is of industrial importance, because liquid B₂O₃, in which Ga₂O₃ is not very soluble, is used to protect GaAs during growth of single crystals of GaAs. During recovery of noble metals B₂O₃ is added to slags containing Al₂O₃ to lower the melting point and the viscosity. The B₂O₃–In₂O₃ system is of much less importance to industry. In all three systems we have a liquid miscibility gap, and also solid binary compounds, none of which melt congruently. The miscibility gaps are not surprising, because even in the B₂O₃–Bi₂O₃ system where four congruently melting compounds are present, a liquid miscibility gap exists close to B₂O₃.     

The effect of substitution of La for Tb on some physical properties of Tb1−xLaxNi2 solid solutions

The standard Gibbs energy of formation, , of MgLa in the temperature range from near absolute 0 to 525 K were determined by calorimetry. The heat capacities, C_p, from 2 K to 525 K were measured by the relaxation method and DSC. Also, a thermal anomaly at 5.9 K, which appeared to be a superconductive phase transition, was found in the obtained C_p values. The values were determined by combining the C_p data with the standard enthalpy of formation at 298 K which was measured by the Calvet-type calorimeter using hydrochloric acid solution. From 2 to 300 K, the increases gradually, and it can be evaluated as a linear function of temperature above 300 K as follows:

This result is expected to be useful as basic thermodynamic data of Mg-based alloys.     

EXAFS and Te spectroscopy study of the Yb1−xEuxTe, Pb1−xEuxTe and Yb1−xGdxTe solid solutions

We report EXAFS (Extended X-Ray Absorption Fine Structure) measurements on three solid solutions of rare-earth monotelluride in order to measure the x-dependence of the cation-anion distance and Debye-Waller factor. We find Yb_1−xEu_xTe is an ideal solid solution with a bimodal distribution of distances, accommodated by the Te sublattice, at contrast with the two other solid solutions Pb_1−xEu_xTe and Yb_1−xGd_xTe. The anomalous behaviour of the EXAFS parameters in the last system is related to the shallow nature of the Gd donor.     

Magnetic ordering and magnetic properties of ErAuxNi1−xIn (0 ≤ x ≤ 1) solid solution

The ErAu_xNi_1−xIn (0 ≤ x ≤ 1) quasiternary compounds crystallize in the hexagonal layered crystal structure of ZrNiAl-type. ErAuIn was reported to be an antiferromagnet with T_N = 3 K and magnetic moments having triangular arrangement within the basal plane (the magnetic order is described by the propagation vector ). On the contrary ErNiIn is a ferromagnet with T_C = 9 K and magnetic moments pointing along the c-axis. The magnetic ordering in ErAu_xNi_1−xIn (0 < x < 1) solid solution, has been investigated by neutron diffractometry in the temperature range between 1.5 and 15 K. Moreover, bulk magnetic measurements have been carried out in the range 1.72–400 K. All alloys of intermediate composition were found to be antiferromagnets with T_N between 4.6 and 7 K. Below 2 K their magnetic order is described by the propagation vector and magnetic moments are aligned along the c-axis. However, for alloys with 0.2 ≤ x ≤ 0.7 the propagation vector was found to turn into with increasing temperature.     

FeTiO3-Fe2O3固溶体合成及其碳热还原研究

为明确Fe₂O₃固溶对FeTiO₃还原过程的影响机理,本文基于粉末煅烧法合成(1-x)FeTiO₃?xFe₂O₃固溶体(0≤x≤1),研究了非等温碳热还原条件下固溶体的还原行为,并采用X射线衍射仪(XRD)和扫描电镜-能谱仪(SEM-EDS)对合成固溶体及还原产物进行表征。结果表明,实验合成固溶体质地均匀,纯度较高,且x越大,FeTiO₃晶格畸变程度越大。固溶体开始还原温度和还原速率(还原度α的增大速率)均随着x值的增加而增加。固溶Fe₂O₃能够促进FeTiO₃还原,且在还原过程中存在过渡相Fe₂TiO₄和Fe₃Ti₃O₁₀。固溶体-石墨交界面首先形成浮士体(FeO)、钛铁尖晶石(Fe₂TiO₄)和TiO₂,进一步还原生成金属Fe和Ti₂O₃。非等温碳热还原过程动力学计算分析,得出表观活化能为295.54 kJ/mol。     

Combustion synthesis of Ti3Si1−xAlxC2 solid solutions from TiC-, SiC-, and Al4C3-containing powder compacts

Preparation of the Ti₃Si_1−xAl_xC₂ solid solution with x = 0.2-0.8 was investigated by self-propagating high-temperature synthesis (SHS) using TiC-, SiC-, and Al₄C₃-containing powder compacts. Due to the variation of reaction exothermicity with sample stoichiometry, the combustion temperature and reaction front velocity decreased with increasing Al content of Ti₃Si_1−xAl_xC₂ for the TiC- and Al₄C₃-added samples, but increased for the samples with SiC. In contrast to the formation of Ti₃(Si,Al)C₂ as the dominant phase for the TiC- and SiC-added samples, TiC was identified as the major constituent in the final products of samples adopting Al₄C₃. In addition, the evolution of Ti₃(Si,Al)C₂ was improved by increasing the Al content of the TiC- and SiC-added powder compacts, but deteriorated considerably upon the increase of Al₄C₃ in the Al₄C₃-containing sample.     

Microwave-induced synthesis and characterization of nanometer Ce0.5Zr0.5O2 solid solution for the acidic catalytic reaction

Ce0.5Zr0.5O2 solid solution was successfully synthesized using cerium nitrate,zirconium nitrate,and urea as raw materials by the microwave irradiation method and charactefizde by X-ray diffraction,fluorescence spectrum,transmission electron microscopy,and infrared spectrum.Its acid catalytic activity was evaluated in the esterification reaction of acetic acid and n-butyl alcohol.The results show that Ce0.5Zr0.5O2 solid solution has cubic fluorite structure,and its particle diameter is in the nanometer scale.As a sort of solid acid,it possesses a higher acid catalytic activity and can be easily separated from reaction liquids.It can be used for several times,and basically,its activity keeps constant.The proton acid sites and Lewis acid sites exist in the structure of Ce0.5Zr0.5O2 solid solution.     

Luminescent properties of Na3Gd1−xEux(PO4)2 and energy transfer in these phosphors

A series of Eu³⁺ activated Na₃Gd_1−xEu_x(PO₄)₂ (0 ≤ x ≤ 1) phosphors were synthesized by solid-state reaction method. The structures and photo-luminescent properties of these phosphors were investigated at room temperature. The results of XRD patterns indicate that these phosphors are isotypic to the orthorhombic Na₃Gd(PO₄)₂. The excitation spectra indicate that these phosphors can be effectively excited by near UV (370-410 nm) light. The intensities of magnetic dipole transition ⁵D₀ → ⁷F₁ and forced electric dipole transition ⁵D₀ → ⁷F₂ are comparable, and the energy ratio (⁵D₀ → ⁷F₁/⁵D₀ → ⁷F₂) is 1.1. The emission spectra exhibit strong reddish orange performance (CIE chromaticity coordinates: x = 0.62, y = 0.38), which is due to the ⁵D₀ → ⁷F_J transitions of Eu³⁺ ions. The correlation between the structure and the photo-luminescent properties of the phosphors was studied. The energy transfer and concentration quenching of the phosphors were discussed. Na₃Gd_1−xEu_x(PO₄)₂ has a potential application for white light-emitting diodes.     

Synthesis and characterization of cobalt-free Ba0.5Sr0.5Fe0.8Cu0.2O3−δ perovskite oxide cathode nanofibers

The cobalt-free perovskite-oxide, Ba_0.5Sr_0.5Fe_0.8Cu_0.2O_3−δ (BSFC) is a very important cathode material for intermediate-temperature proton-conducting solid oxide fuel cells. Ba_0.5Sr_0.5Fe_0.8Cu_0.2O_3−δ nanofibers were synthesized for the first time by a sol-gel electrospinning. Process wherein a combination of polyvinylpyrrolidone and acetic acid was used as the spinning aid and barium, strontium, iron and copper nitrates were used as precursors for the synthesis of BSFC nanofibers. X-ray diffraction studies on products prepared at different calcination temperatures revealed a cubic perovskite structure at 900 °C. The temperature of calcination has a direct effect on the crystallization and surface morphology of the nanofibers. High porosity, and surface area, in addition to an electrical conductivity of 69.54 S cm⁻¹ at 600 °C demonstrate the capability of BSFC nanofibers to serve as effective cathode materials for intermediate-temperature solid oxide fuel cells.     

Self-propagating high-temperature synthesis of La(Sr)Ga(Mg)O3−δ for electrolyte of solid oxide fuel cells

This paper describes self-propagating high-temperature synthesis (SHS) of an electrolyte for solid oxide fuel (SOFC), in comparison to a conventional solid-state reaction method (SRM). Doped-lanthanum gallate: La_0.9Sr_0.1Ga_0.8Mg_0.2O_3−δ (LSGM9182) and LSGM9173 as the SOFC electrolyte, was prepared by the SHS and sintered at different temperatures, for measuring the electrical conductivity of the sintered LSGM and the power generating performance at 1073 K, in comparison to the SRM. In the SHS, the LSGM powders with smaller size were obtained and easily sintered at the 100 K-lower temperature, 1673 K, than in the SRM. Most significantly, the electrical conductivity of the sintered LSGM9182 was as high as 0.11 S cm⁻¹ and its maximum power density was a value of 245 mW cm⁻² in the cell configuration of Ni/LSGM9182 (0.501 mm in thickness)/Sm_0.5Sr_0.5CoO₃. The conclusion was that the proposed SHS-sintering method with many benefits of minimizing the energy requirement and the processing time in the production, easing temperature restriction for the sintering, and improving the electrolyte performance up to a conventional level is practicable for producing the LSGM-electrolyte of SOFC at an intermediate-temperature application.