Nanoscale Niobium Research Articles

Nanoscale niobium coatings including superior conducting and corrosion resistance on titanium foil materials for PEMFC bipolar plates

In this work, the nanoscale Nb coating for titanium is fabricated by high power impulse magnetron sputtering technology to enhance its conductivity and corrosion resistance, which is utilized as bipolar plates material. The surface morphology, composition, corrosion resistance and conductivity of specimens with various deposition times were characterized. The results demonstrate that the thickness and roughness of nanoscale coatings increase with deposition time and all the Nb-coated titanium specimens exhibit superior corrosion resistance in 0.5 M H2SO4 solution with 5 ppm HF at 80 °C. The corrosion current density increases and then decreases with deposition time, reaching its smallest value at 600 s (3.07 μA cm−2), which is reduced by 3 orders of magnitude compared to the substrate (387.98 μA cm−2). After potentiostatic polarization experiment (PP) for 12 h, the polarization current density (ipp) of coatings reduces as deposition time increases, with values of 1.54, 0.58, 0.45 and 0.27 μA cm−2, respectively. Furthermore, a low ICR is obtained for fresh Nb-coated titanium specimens, with values of 8.45, 8.95, 3.62 and 3.04 mΩ cm2, respectively. After PP for 12 h, the ICR slightly increase to values of 9.83, 9.63, 6.76 and 6.15 mΩ cm2, which still satisfy the demand of 2025 DOE requirements (≤10 mΩ cm2).

Evolution of the Structure and Properties of Cu–6% Nb Microcomposite Wire during Long-Term Temperature Tests

The electrical conductivity, mechanical strength and crystal structure of Cu–6 wt % Nb microcomposite wire upon exposure to a temperature of 450°C for up to 2000 hours are investigated. Structural changes are compared with the ultimate strength and electrical conductivity. Several mechanisms of strength degradation with different time constants are identified. Within long times, the ultimate strength decreases by 32% from the initial value while the electrical conductivity increases by no more than 2%. Strength degradation is accompanied by the relaxation of microstresses in the copper matrix and structural changes in the nanoscale niobium component.

Microstructure and wear characteristics of in-situ micro/nanoscale niobium carbide reinforced copper composites fabricated through powder metallurgy

In this work, a highly wear-resistant cooper matrix composite reinforced by in situ formed nano-NbC particles was synthesized by hot pressing mechanically alloyed Cu+Nb+C powders. The composite possesses a smaller friction coefficient and displays a wear rate (2.6 × 10−5 mm3N−1 m−1) two orders of magnitude lower than the micro-NbC reinforced Cu composites (123.5 × 10−5 mm3N−1 m−1). Such property enhancement is attributed to the hardness improvement and the solid lubricating effects induced by nanoscale niobium carbides/oxides as well as iron oxides. The oxidation and pulverization of NbC during friction have played a key role in increasing the wear resistance and their mechanisms are discussed. The findings provided a strategy for developing other wear-resistant composite materials.

Nanoscale niobium oxides anode for electrochemical lithium and sodium storage: a review of recent improvements

In recent years, Nb-based oxides, especially Nb2O5, due to their unique structural advantages, have stimulated scholars’ extensive research enthusiasm in the field of energy storage systems including lithium ion batteries (LIBs) and sodium ion batteries (SIBs), excellent chemical stability and outstanding rate capability dominated by pseudocapacitive nature. In addition, Nb-based oxides usually have a higher operating voltage (> 1.0 V vs Li+/Li), which can effectively prevent the decomposition of organic electrolytes and the formation of solid electrolyte interface films in batteries. This review systematically summarizes the different crystal structures of Nb2O5 and the lithium storage mechanism based on theoretical calculations, as well as the comparison of various synthesis strategies. In addition, the advanced research progress of niobium-based oxides as anode materials in LIBs and SIBs is summarized from the perspective of nanostructure control engineering that affects electrochemical performance. It also puts forward reasonable cognition and challenges for future research, which is conducive to the design of energy storage equipment that meets the needs of sustainable development. The design and optimization of various synthesis methods facilitate the formation of a variety of heterogeneous nanostructures, leading to reversible storage of Li and Na ions.

Comparison of Precipitates and Texture Evolution in Nb-Bearing Grain-Oriented Silicon Steel Produced by Conventional Processing and Novel Twin-Roll Casting

The Nb-bearing grain-oriented silicon steel sheets were produced by conventional route and novel twin-roll casting route, respectively. The microstructure, texture and precipitate evolution were comparatively investigated by using electron backscattered diffraction (EBSD) and transmission electron microscope (TEM). The findings revealed that the precipitation behavior and the texture evolution were totally different between the two processing routes. In the conventional route, a great number of nanoscale niobium nitride particles (NbN), which acted as mainly grain growth inhibitors were precipitated during hot rolling, while in the twin-roll casting route, due to the rapid solidification, the precipitation of NbN were suppressed and a new type Nb-bearing precipitate enriched with sulfur element was observed in the as-cast strip. Besides, the primary recrystallized texture of conventional specimens was characterized by strong γ-fiber with a peak at {111} <110>, together with very few Goss components. While in the case of twin-roll casting specimens, the strongest primary recrystallized texture was {111} <112> texture and the area fraction of Goss component was much higher than that of conventional specimens. After final high temperature annealing, complete secondary recrystallization was obtained in twin-roll casting specimens and the magnetic induction of B8 was 0.1 T higher than that of conventional specimens.

Synchrotron Investigation on the Precipitation Behaviour of Niobium Microalloyed Steel

The precipitation and dissolution behavior of niobium carbo-nitrides is of particular interest for many technical applications. Niobium-microalloyed high strength low alloy (HSLA) steels are widely used in civil construction, automobile and line pipe applications. These steels rely on thermomechanical processing. In this context, coupled processes like thin slab casting and thermomechanical rolling of microalloyed steel grades require most precise information on the precipitation state at the individual processing steps. Reasonable equations for the solubility product at thermal equilibrium can be taken from literature but kinetics is largely unknown. Conventional X-ray technology is not able to detect small volume fractions below 0.1% of nanoscale precipitates. Investigation of nanoscale niobium precipitates by transmission electron microscopy (TEM) analysis or chemical extraction methods is common practice. However, TEM suffers from statistical relevance and chemical extraction will not give information on particle distribution and orientation. Investigation by high energy synchrotron X-ray of about 100 keV offers statistical relevance as volumes of several cubic millimeters are regarded. This large reflecting sample volume allows to detect nanometer-sized particles and provides very high angular resolution leading to an exact determination of the reflection peaks. The wavelength of around 0.12 Å is able to analyze nanometer-sized particles. Due to the high energy of the applied synchrotron radiation, precipitation and dissolution reactions could be observed during thermal treatment inside a soaking furnace. The results establish this technology for analysis of nanoscale niobium carbo-nitride precipitates

Sub-100 fJ and sub-nanosecond thermally driven threshold switching in niobium oxide crosspoint nanodevices

We built and measured the dynamical current versus time behavior of nanoscale niobium oxide crosspoint devices which exhibited threshold switching (current-controlled negative differential resistance). The switching speeds of 110 × 110 nm2 devices were found to be ΔtON = 700 ps and ΔtOFF = 2.3 ns while the switching energies were of the order of 100 fJ. We derived a new dynamical model based on the Joule heating rate of a thermally driven insulator-to-metal phase transition that accurately reproduced the experimental results, and employed the model to estimate the switching time and energy scaling behavior of such devices down to the 10 nm scale. These results indicate that threshold switches could be of practical interest in hybrid CMOS nanoelectronic circuits.

Anodically formed oxide films on niobium: Microstructural and electrical properties

The electrical and structural properties of nanoscale niobium pentoxide (Nb 2O 5) dielectric layers in niobium-based solid electrolyte capacitors were studied. The Nb 2O 5 layers are formed by anodic oxidation of Nb-powder compacts. Capacitance measurements show a strong bias-voltage dependence of the capacitance after anodization. Heat treatments at temperatures up to 320 °C, which are applied in the capacitor-production process, lead to an increase of the capacitance and a reduction of the bias dependence. Based on the electrical and structural properties, which are characterized by electron microscopic techniques, a model is presented which explains the behavior of the specific capacitance after the various processing steps.