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.     

VC- and Cr3C2-doped WC–NbC–Co hardmetals

This study compares the microstructure and mechanical properties of plain and 0.9 or 3.6 wt% VC- or Cr₃C₂-doped WC–12 wt% Co hardmetals with 40 wt% NbC, prepared by pulsed electric current sintering (PECS) in the solid state for 4 min at 1240 °C and conventional pressureless liquid phase sintering (CS) for 1 h at 1420 °C. The addition of VC or Cr₃C₂ was found to inhibit grain growth of the residual WC grains, whereas the size of the solid solution (Nb,W,V/Cr)C grains was hardly influenced. The type of grain growth inhibitor and densification temperature however, strongly influenced the composition of the NbC solid solution formed, which was thermodynamically and experimentally assessed.     

Production of niobium carbide ceramic composites derived from polymer/filler mixtures: preliminary results

Studies have shown that Al₂O₃–NbC composites present a good potential to be used for metalworking. Manufacturing of composite ceramic material derived from polymer reactive filler mixtures were investigated. The present study reports the preliminary results of reaction bonded niobium carbide derived from polymer (polysiloxane), inert filler (Al₂O₃) and reactive filler (Nb). Niobium powder, alumina and polysiloxane mixtures were homogenized in a planetary ball milling and pressureless sintered in inert atmosphere at temperatures up to 1600 °C. Depending on the niobium content and pyrolysis conditions, ceramic materials with a porosity of 20–40%, a weight loss of 5–15%, a linear shrinkage of 2–4% and a flexural strength of maximum 80 MPa were obtained. X-ray diffraction (XRD) of a sample containing 60 wt% polymer + 40 wt% Nb showed the presence of new crystalline phases such as NbC, Nb₃Si and Nb₅Si₃.     

Nb521铌合金电子束焊工艺研究

对Nb521铌合金进行了电子束焊工艺试验研究,优化了工艺参数,分析了焊缝表面成形及焊接接头组织、常温和高温力学性能.结果表明:Nb521具有良好的电子束焊接性能,焊缝常温拉伸强度、屈服强度均能达到母材的95％以上,延伸率达到母材的86.7％,在1600℃以下焊缝性能良好.     

Phase evolution in plasma sprayed Nb2O5 coatings

Nb₂O₅ polymorphism and defect chemistry depend on the temperature, pressure, atmosphere composition and the initial crystallography. Plasma spray of Nb₂O₅ is a pathway to form coatings with in-situ metastable and nonstoichiometric phases, however so far unexplored. This study aimed to understand the phase evolution of plasma sprayed Nb₂O₅ coatings, and its effect on their morphology and properties. Phase evolution from H-Nb₂O₅ in the feedstock, to T-Nb₂O₅, TT-Nb₂O₅, N-Nb₂O₅, H-Nb₂O₅, Nb₁₂O₂₉ and NbO₂ in the coatings depends on the plasma Ar/H₂ ratio and its related enthalpy. The microstructure shows a layered distribution of nonstoichiometric phases at the splat boundaries and splat cores composed of T-Nb₂O₅ or TT-Nb₂O₅. The presence and distribution of these phases are related to the thermomechanical and electrical properties. The mechanisms driving the formation of these coatings are based on the Nb₂O₅ incongruent vaporization which promote retention of nonstoichiometric phases and the rapid solidification of metastable phases.     

NbCl5的制取工艺研究

本文主要介绍了铌粉氯化制取ＮｂＣｌ５的工艺，其中包括温度，氯气流速等变量对铌粉氯化反应的影响。结果指出：当温度低于４５０℃时，平均反应速率随着温度的升刘而增大；在４００－６５０℃范围内，反应速率符合一级反应；升高温度能提高氯化效率的氯气利用率；加大氯气流速，可增加反应速率，但却降低了氯化效率。     

快淬Nd—Fe—B粘结磁体在步进电机上的应用研究

本文主要报道快淬Nd-Fe-B粘结磁体在36BY_(02)型永磁式步进电机中作为24极转子磁钢的应用研究,分析磁体性能与工作点设计及电机性能参数关系。     

Niobium and divalent‐modified titanium dioxide ceramics: Colossal permittivity and composition design

Colossal permittivity (CP) (ε_r=10⁴~10⁵) is attained in (A_1/3Nb_2/3)_xTi_1‐xO₂ (A=Ba²⁺, Ca²⁺, Zn²⁺, Mg²⁺) ceramics. Here, (Ca_1/3Nb_2/3)_xTi_1‐xO₂ material was studied as a typical example, and effects of Ca and Nb on their microstructure, dielectric properties and stability were studied. Both backscattering and elements mapping strongly confirmed the formation of secondary phases due to the addition of Ca and/or Nb. Secondary phases‐induced by Ca cannot affect dielectric properties of the ceramics when low Ca and Nb contents were doped, while secondary phases formed by Ca and Nb strongly affected their dielectric properties in a high doping level. In particular, their dielectric properties can be well modified by the optimization of sintering temperatures. In addition, the (Ca_1/3Nb_2/3)_xTi_1‐xO₂ ceramics with x=0.01 exhibited the optimum dielectric properties (ε_r=130500 and tan δ=0.19). Electron‐pinned defect‐dipoles may be suitable to explain CP phenomenon of this work. We believed that this profound investigation can benefit the development of new TiO₂ ceramics as a CP material.