Indium doped niobium phosphates as intermediate temperature proton conductors

Indium doped niobium phosphates were prepared from precursors of trivalent indium oxide, pentavalent niobium oxide and phosphoric acid. The obtained materials were characterized by X-ray diffraction, impedance spectroscopy, FT-IR spectroscopy and scanning electron microscopy. It was found that the indium doping promoted formation of the cubic Nb₂P₄O₁₅ phase instead of the monoclinic Nb₅P₇O₃₀ phase in the pristine niobium phosphates and enhanced the preservation of OH functional groups in the phosphates. The preserved OH functionalities in the phosphates after the heat treatment at 650 °C contributed to the anhydrous proton conductivity. The Nb_0.9In_0.1 phosphate exhibited a proton conductivity of five times higher than that of the un-doped analog at 250 °C. The conductivity was stabilized at a level of above 0.02 S cm⁻¹ under dry atmosphere at 250 °C during the stability evaluation for 3 days.     

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通过采用扫描电镜、透射电镜及电子能谱等分析测试技术,研究了高铌管线钢的显微组织特征和析出相种类、大小及形态.结果表明,采用控轧控冷工艺(TMCP)生产的高铌管线钢具有细化的显微组织和多种类型的析出相,显微组织主要为高位错密度的针状铁素体、少量多边形铁素体和MA岛;第二相粒子主要包括板坯再加热过程中未溶解的TiN、以TiN为核心的高温析出NbC、形变诱导析出的NbC和低温弥散析出的细小NbC.细化的有效晶粒尺寸,以及高密度位错与弥散析出相间的交互作用,确保了高铌管线钢获得高的强度和韧性.     

Three Nb single crystals processed by equal-channel angular pressing—Part II: Mesoscopic bands

Three high-purity Nb single crystals with different orientations are deformed by equal-channel angular pressing (ECAP) at room temperature for one pass. Large misorientation bands (LM-bands) are observed in two single crystals, but with different appearances. An analysis of slip activity is carried out to link the primary slip systems to the observed microstructures. It is found that the LM-bands are parallel to the primary slip systems at the beginning of deformation. Further characterization of the bands shows that their end orientations tend to have a stable configuration with respect to the simple shear plane and the direction. Based on these results and comparison with earlier works, the forming process of the LM-bands during ECAP is proposed.     

Nb2O5掺杂对BaTiO3基介电陶瓷瓷料性能的影响

研究了Nb2O5掺杂对细晶BaTiO3陶瓷的微观形貌和介电性能的影响,并利用XRD、SEM对掺杂后陶瓷的相组成和微观形貌进行了表征.实验表明:掺杂2%(质量分数)Nb2O5的试样达到最优的性能(ε25℃=1 395,αε=4%),满足X8R特性;XR.D分析表明,Nb5+取代B位形成了固溶体-BaNb0.5Ti0.5O...     

钛、铌对16%Cr超低碳氮铁素体不锈钢的再结晶和力学性能的影响研究

实验室研究了钛、铌对16%Cr超低碳氮铁素体不锈钢的高温塑性、再结晶温度以及冷轧板力学性能的影响。结果表明,变形温度和应变速率对变形抗力的影响十分显著,而不同含量的钛、铌对钢的变形抗力影响很小。当变形温度达到1 350℃时,三种成分钢的抗拉强度和塑性急剧下降。钛、铌的加入对钢板的完全再结晶温度有一定的影响,即加钛或加铌均延迟再结晶。不加钛、铌的钢在拉伸时有明显的屈服现象,且屈服强度较高,r值较低,而加钛或钛、铌复合加入的钢没有明显的屈服现象,r值较高均达1.50以上。     

Distribution Behavior of Nb,Ta, and Pa as Homologues of Db in Cation Exchange and Solid-Liquid and Liquid-Liquid Extractions by Aliquat 336 from Hydrochloric Acid

Detailed chemical studies on transactinide elements will clarify their characteristic properties caused by strong relativistic effect. In this work, to realize chemical study on transactinide element ₁₀₅Db, cation exchange, and solid-liquid and liquid-liquid extractions of micro amounts of Nb, Ta (homologues of Db), and Pa (pseudo homologue) by Aliquat 336 were performed employing hydrochloric acid. Clearly different chloride complex formations and distribution reaction kinetics were observed among these elements, and the present results are useful for studying the chemical properties of Db. Based on these results, we propose suitable experimental conditions for Db.     

Niobium diffusion modified austenitic stainless steel bipolar plate for direct methanol fuel cell

An austenitic stainless steel with a niobium diffusion protective layer is evaluated for bipolar plate of direct methanol fuel cell (DMFC). Corrosion resistance of niobium diffusion modified AISI 304 stainless steel (niobized 304 SS) is investigated in simulated DMFC cathodic environment (0.5 M H₂SO₄ + 2 ppm HF + 0.1 M methanol solution at 50 °C) and anodic environment (0.5 M H₂SO₄ + 2 ppm HF + (1 M, 10 M and 20 M) methanol solution at 50 °C), respectively. Potentiodynamic, potentiostatic as well as electrochemical impedance spectroscopy tests show that, comparing with a bare 304 SS, the corrosion current density of niobized 304 SS is reduced greatly while the polarization resistance is raised in the simulated DMFC cathodic environment. Corrosion tests in the simulated anodic environment are applied to examine the effect of methanol on the corrosion behaviour of niobized 304 SS. It is interesting to find that the niobized 304 SS shows better corrosion resistance in the higher methanol concentration solutions.     

热轧参数对粗奥氏体晶粒铌钢变形抗力的影响

通过Thermecmastor-Z热模拟试验机,在900-1 050℃以变形速率1-20 s-1、真应变0-0．7研究了晶粒尺寸800μm的铌钢(％:0．05C、1．44Mn、0．13Nb)奥氏体控轧过程的变形抗力,并建立了变形抗力的回归方程。试验结果表明,随温度增高,铌钢在奥氏体区变形抗力递减;在同一温度下,随变形程度增加,钢的变形抗力增加;同时在给定变形程度下,变形抗力随变形速率增大而增大;变形抗力回归方程计算值与实测值相差≤5 MPa。     

Influence of air oxidation on the properties of decorative NbOxNy coatings prepared by reactive gas pulsing

In this work the oxidation resistance of DC reactive sputtered niobium oxynitrides and its influence on the properties of the films are studied. The depositions have been carried out by DC magnetron sputtering with a reactive gas pulsing process. The nitrogen flow was kept constant and the oxygen flow was pulsed. Pulse durations of 10 s produced multilayer coatings with a period of λ = 10 nm. Three sets of films with increasing duty cycle (= on-time of high oxygen flow / pulse duration) have been deposited. The films were subsequently annealed in air at 400, 500 and 600 °C, respectively.X-ray diffraction measurements showed a clear and progressive change from a roughly amorphous nature of the films to a crystalline oxide-type compound for those annealed at 600 °C, which was consistent with the composition analysis. For annealing temperatures of 500 and 600 °C, the coatings presented a significant reduction in hardness, approaching the values characteristic of Nb₂O₅-type films. Moreover, the residual stress measurements performed by using the deflection method revealed low values in all the coatings nearly independent on the annealing temperature.Color variation in the CIE − L^?a^?b^? color space and the reflectance in the UV-visible spectrum range of these niobium oxynitrides were investigated and correlated to their chemical composition and structural features. For both properties, the variation tendencies are quite similar, showing the transition from a nitride-type alloy to an oxide-type one with increasing annealing temperature.     

High surface area niobium oxides as catalysts for improved hydrogen sorption properties of ball milled MgH2

We report, high surface area (up to 200 m²/g) nanocrystalline niobium oxide (so called p-Nb₂O₅) synthesized by ‘chimie douce’ route and its importance in enhancing the hydrogen sorption properties of MgH₂. p-Nb₂O₅ induces faster kinetics than commonly used commercial Nb₂O₅ (c-Nb₂O₅) when ball milled with MgH₂ (named (MgH₂)_catalyst) by reducing the time of desorption from 35 min in (MgH₂ )_c-Nb2O5 to 12 min in (MgH₂ )_p-Nb2O5 at 300 °C. The BET surface area of as-prepared Nb₂O₅ was tuned by heat treatment and its effect on sorption properties was studied. Among them, both p-Nb₂O₅ and Nb₂O₅:350 (p-Nb₂O₅ heated to 350 °C with a BET specific surface area of 46 m²/g) desorb 5 wt.% within 12 min, exhibiting the best catalytic activity. Furthermore, thanks to the addition of high surface area Nb₂O₅, the desorption temperature was successfully lowered down to 200 °C, with a significant amount of desorbed hydrogen (4.5 wt.%). In contrast, the composite (MgH₂ )_c-Nb2O5 shows no desorption at this “low” temperature.