Powder metallurgical production of 316L stainless steel/niobium composites for Proton Exchange membrane electrolysis cells

In this study, a composite made of a porous stainless steel (SS) 316L substrate coated with Nb was investigated as a novel porous transport layer (PTL) for proton exchange membrane electrolysis cells (PEMECs). The fabrication of such SS316L/Nb composites using scalable and automatable powder metallurgical techniques as tape casting, screen-printing and field assisted sintering technology/spark plasma sintering (FAST/SPS) was described. Sintering behaviour and the interdiffusion at the SS316L/Nb interface were investigated. Powder metallurgical techniques such as screen-printing are the preferred method to achieve a porous Nb coating, while FAST/SPS is the preferred method for a better control of the SS316L/Nb interface by lowered interdiffusion. First electrochemical performance tests with SS316L/Nb composites demonstrate they have potential to replace the state-of-the-art titanium-based PTLs. The use of SS316L is expected to decrease manufacturing costs of PTLs, while the addition of niobium layer, due to its excellent corrosion resistance in acid environment, aims to improve PEMECs lifetime and performance.     

三维原子探针对铌微合金化钢碳氮化物的析出研究

利用三维原子探针（3DAP）可以对不同元素的原子逐个进行分析,并给出纳米空间中不同元素原子的三维分布图形,分辨率接近原子尺度的优越性能,对含铌轿车横梁钢中的碳氮化物进行分析,结果表明,铌微合金化钢中存在尺寸为几个纳米大小的铌碳氮化物析出物,析出物呈薄片状,同时,铌碳氮化物在铁索体中析出是随机的。     

铌对高性能球墨铸铁微观组织的影响

利用图像分析软件定量分析了铌对球墨铸铁石墨球形态和铸态组织的影响。研究结果表明,添加铌能够使石墨化程度和球化率降低,圆度和石墨球大小增加,石墨球数量显著降低,但少量铌对球墨铸铁的石墨化、球化率、圆度、石墨球大小等影响不大。少量铌能显著增加珠光体数量。     

直接还原法在铌提取上的应用

利用直接还原法开辟从含铌铁矿中提铌的新途径：用ＣＯ／ＣＯ２混合气体选择性还原含铌铁矿，９０％以上的铁氧化物被还原为金属铁，而铌氧化物不被还原；磁选分离还原产物，去除金属铁，得到含铌矿物。其铌品位较原矿提高了近３倍。     

Microalloyed steels

This review considers the compositions, the main process routes, microstructure and structural properties of microalloyed steels. The background and brief history are followed by sections dealing with aspects of precipitation, which control grain size and dispersion strengthening in ferrite–pearlite steels, the approaches to modelling thermomechanical processing and the influence of multiple additions of transition metals on properties. High strength acicular ferrite/bainite steels used for linepipe are included and lead to super bainite steels. Around 12% of the world strip production is processed by the thin slab direct charging route, which is considered in some detail. The weldability of microalloyed steels now embraces joining using friction stir welding, which is discussed. Over the years, many approaches have been developed to predict the structural properties of these steels. They comprise several quantifiable microstructural features including possible atom clusters, relatively recently identified through atom probe tomography. A comprehensive collection of references is provided.     

Flotation of pyrochlore from low grade carbonatite gravity tailings with benzohydroxamic acid

The beneficiation of a low grade niobium tailings by flotation using benzohydroxamic acid (BHA) as a collector and sodium hexametaphosphate (SHMP) as a modifying agent has been studied. A concentrate containing approximately 3% Nb₂O₅ (with an upgrade ratio of 12) was obtained with nearly 80% Nb recovery in 6.5% of the mass after only one rougher flotation stage. After four rougher stages, a final concentrate containing 1.54% Nb₂O₅ with 93% Nb recovery in ∼15% of the mass was obtained. A Box–Behnken experimental design was employed to analyze the effects of collector dose and dispersant dose and pulp temperature and to model the concentrate grade and niobium recovery during rougher–scavenger flotation. The results indicate that temperature has no significant effect on recovery at the 95% or 90% confidence level. Statistical insignificance of the temperature effect has been attributed to the collector mechanism, which essentially does not require BHA species beyond a maximum monolayer capacity that is potentially achievable within the solubility limit at room temperature. SHMP plays an important role in the selective recovery of pyrochlore. Its dispersing function is distinguished from its depressing function in the rougher stages through a positive interaction term together with BHA in both the recovery model and the grade model. The main negative effect of SHMP on niobium recovery emerges in the scavenger stages as a result of depressing action (e.g., targeting primarily the middlings). The effect of reagent dose and temperature on the grade and recovery are presented using 3D graphs from statistical models developed. Negative quadratic terms of the statistical models are discussed in reference to possible overdosing of SHMP on the middlings (involving pyrochlore and gangue) as well as a postulated change of orientation mode of BHA, also due to its overdosing.     

铌欠缺对掺镧PZN基陶瓷的有序微区和介电性能的影响

研究了铌欠缺对掺镧 PZN基陶瓷相结构、有序微区以及介电性能的影响。铌欠缺消除了掺镧所产生的焦绿石相 ,使陶瓷试样恢复为百分之百的钙钛矿相结构。 Ram an散射光谱分析表明 ,铌欠缺使掺镧 PZN基陶瓷的有序微区增大 ,同时铌欠缺也提高了掺镧 PZN基陶瓷的介电常数。铌欠缺使介电常数增大的原因归结于焦绿石相的消除和“有效有序微区”尺寸的扩大     

Synthesis of Nb2O5 and Ta2O5 nanopowders by means of an endo-templating method

Finding efficient templates for the nanostructuring of materials is a key point. Here, the niobium (V) - and tantalum (V) oxide ceramics nanopowders have been synthesized by a hard-templating approach by using the tricalcium phosphate biomaterial (Ca₃(PO₄)₂.xH₂O) as template agent. The oxide ceramics were investigated by X-ray Diffraction (XRD), Fourier Transform Infrared (FTIR) spectroscopy, nitrogen physisorption and Scanning Electron Microscopy (SEM). It was observed that the surface properties (specific surface areas, pore volumes) of the Nb₂O₅ and Ta₂O₅ powders were strongly dependent of the amount of the Ca₃(PO₄)₂.xH₂O template previously used in the preparation of the [oxide ceramics/template] composites. For instance, with a Ca₃(PO₄)₂.xH₂O/ceramic salt weight ratio ranging from 0 to 1, the specific surface areas of Nb₂O₅ and Ta₂O₅ were gradually enhanced of 48–166 m²/g and 5–84 m²/g, respectively. The pore volumes were increased as well. The use of the eco-friendly tricalcium phosphate material (Ca₃(PO₄)₂.xH₂O) as template in the hard-templating approach may be suitable and efficient in the aim of synthesizing materials with enhanced surface properties.     

Improved ionic conductivity of zirconia-scandia with niobia addition

The ionic conductivity and the crystalline structure of ZrO₂−10 mol% Sc₂O₃- x mol% Nb₂O₅ solid electrolytes were investigated for x=0.25, 0.5 and 1. Dense specimens with relative densities higher than 95% were prepared by solid state reaction and sintered at 1500 °C for 5 h. Full stabilization of the cubic structure at room temperature was obtained for compounds with x=0.5 and 1, whereas the cubic and rhombohedric structures coexist for x=0.25. The highest ionic conductivity in codoped system was found for specimen containing 0.5 mol% niobium pentoxide, with the same order of magnitude as that of the parent solid electrolyte (zirconia-10 mol% scandia) in the high temperature range (above 600 °C). Preliminary investigation on phase stability shows that the isothermal conductivity of the new solid electrolyte remained constant up to 100 h at 600 °C. Niobium pentoxide addition was found to improve the overall ionic conductivity of zirconia-scandia solid electrolyte.     

o-Phenylenediamine adsorbed onto silica gel modified with niobium oxide for electrocatalytic NADH oxidation

A study of a modified carbon paste electrode employing o-phenylenediamine (PDA) adsorbed onto silica gel modified with niobium oxide (SN) for electrocatalytic oxidation of nicotinamide adenine dinucleotide (NADH) is described. The species adsorbed on SN was used to prepare a modified carbon paste electrode to investigate its electrochemical properties. The formal potential (E^0′) of the adsorbed PDA was −140 mV vs. SCE (saturated calomel electrode). The electrochemical behavior of the adsorbed PDA, compared to that of PDA dissolved in aqueous solution, was completely different. In solution, pH between 3.0 and 8.0, E^0′ remained almost constant and the response was very stable. A linear response range for NADH between 4.0×10⁻⁵ and 8.0×10⁻⁴ mol l⁻¹, at pH 7.0, was observed for the electrode, with an applied potential of −50 mV vs. SCE. The formation of an intermediate charge transfer complex is proposed for the charge transfer reaction between NADH and adsorbed PDA. The heterogeneous electron transfer rate, k_obs, was 5480 mol⁻¹ l s⁻¹ and the apparent Michaelis-Menten constant, 1.04×10⁻⁴ mol l⁻¹ at pH 7.0, evaluated with rotating disk electrode (RDE) experiments with an electrode with a coverage of PDA of 5.7×10⁻⁹ mol cm⁻². The slight increase in the reaction rate with the solution pH was assigned to the thermodynamic driving force.