Iron oxide-Palladium core-shell nanospheres for ferromagnetic resonance-based hydrogen gas sensing

Interfaces of ferromagnetic transition metals such as Iron, Cobalt, and Nickel with non-magnetic palladium are of interest due to their unique magnetic and spintronic properties. These interfaces enable ferromagnetic resonance (FMR) based sensing of hydrogen gas. In the present work, we synthesized Fe₃O₄–Pd core-shell nanospheres via a one-pot synthesis method using the thermal decomposition of Fe³⁺ acetylacetonate in the presence of a reducing agent to produce the Fe₃O₄ core, followed by the reduction of a Pd²⁺ precursor to form the pure Pd shell. We found that our in-situ synthesized core-shell nanostructure is magnetically active and shows excellent H₂ gas sensing properties. The effect of reversible hydrogen gas absorption on the magnetism of Fe₃O₄–Pd core-shell nanospheres was investigated. The hydrogen-induced ferromagnetic-resonance (FMR) peak shift amounted to 30% of the peak linewidth for the virgin state of the sample. In addition, in the presence of hydrogen gas, we observed a fully reversible decrease in the FMR peak linewidth by about two times. This was accompanied by a nearly doubling of the FMR peak height. Response and recovery times of about 2 and 50 s, respectively, were extracted from the measurements. All the data was collected using a mix of just 3% hydrogen in a nitrogen carrier gas.     

Mechanical behavior of electrochemically hydrogenated electron beam melting (EBM) and wrought Ti–6Al–4V using small punch test

The influence of electrochemical charging of hydrogen at j = ?5 mA/cm² for 6, 12, 48 and 96 h on the structural and the mechanical behavior of wrought and electron beam melting (EBM) Ti–6Al–4V alloys containing 6 wt% β and similar impurities level was investigated. The length of the α/β interphase boundaries in the EBM alloy was larger by 34% compared to that in the wrought alloy. The small punch test (SPT) technique was used to characterize the mechanical behavior of the non-hydrogenated and hydrogenated specimens. It was found that the maximum load and the displacement at maximum load of the wrought alloy remained nearly stable after 6 h of charging, showing a maximum decrease of ～32% and 11%, respectively. Similarly, hydrogenation of the EBM alloy resulted in a gradual degradation in mechanical properties with charging time, up to ～81% and 86% in pop-in load and displacement at the “pop-in” load, respectively. The mode of fracture of the wrought alloy changed from ductile to semi-brittle with mud-cracking in all hydrogenated specimens. In contrast, the mode of fracture of the EBM alloy changed from a mixed mode ductile-brittle fracture to brittle fracture with star-like morphology. The degraded mechanical properties of the EBM alloy are attributed to its α/β lamellar microstructure which acted as a short-circuit path and enhanced hydrogen diffusion into the bulk as well as δ_a and δ_b hydride formation on the surface. In contrast, a surface layer with higher concentration of δ_a and δ_b hydrides in the wrought alloy served as a barrier to hydrogen uptake into the bulk and increased the alloy resistivity to hydrogen embrittlement (HE). This study shows that EBM Ti–6Al–4V alloy is more susceptible to mechanical degradation due to HE than wrought Ti–6Al–4V alloy.     

某铁矿强磁尾矿反浮选回收试验研究

针对我国西部某铁矿强磁选尾矿进行了反浮选回收铁资源的试验研究, 探讨了pH值、抑制剂可溶性淀粉用量、阳离子捕收剂十二胺用量对浮选指标的影响。结果表明, 在矿浆pH=10、可溶性淀粉用量2 400 g/t、十二胺用量400 g/t条件下进行一粗一精(精选药剂用量减半)闭路反浮选, 可获得铁品位43.88%、回收率50.93%的铁精矿产品。     

Influence of hexagonal to orthorhombic phase transformation on diffusion-controlled dendrite evolution in directionally solidified Sn–Ni peritectic alloy

The hexagonal to orthorhombic (HO) transformation from β-Ni₃Sn₂ (hexagonal) phase to α’-Ni₃Sn₂ (orthorhombic) phase was confirmed in directionally solidified Sn–Ni peritectic alloys. It is shown that the remelting/resolidification process which is caused by both the temperature gradient zone melting (TGZM) and Gibbs?Thomson (G?T) effects can take place on secondary dendrites. Besides, the intersection angle between the primary dendrite stem and secondary branch (θ) is found to increase from π/3 to π/2 as the solidification proceeds. This is the morphological feature of the HO transformation, which can change the diffusion distance of the remelting/ resolidification process. Thus, a diffusion-based analytical model is established to describe this process through the specific surface area (S_V) of dendrites. The theoretical prediction demonstrates that the remelting/resolidification process is restricted when the HO transformation occurs during peritectic solidification. In addition, the slope of the prediction curves is changed, indicating the variation of the local remelting/resolidification rates.     

Effects of sintering in a high magnetic field on properties of vitrified bond and vitrified CBN composites

Vitrified bond CBN grinding wheels are being widely used due to their superior performance. Also, advantages of vitrified grinding wheels are high elastic modulus, stable chemical property, and low thermal expansion coefficient. Brittleness and low strength are key factors restricting the development of vitrified bond CBN grinding wheels. In this paper, the sintering in a high magnetic field was innovatively introduced into the manufacturing of vitrified bond CBN grinding wheels, and the effects of sintering in a high magnetic field on properties on vitrified bond and vitrified CBN composites were systematically investigated. Vitrified bond was characterized using three-point bending, scanning electron microscopy, X-ray diffraction. It was observed that microstructure of vitrified bond could be changed, grain orientation could be controlled and average grain size could be decreased in a high magnetic field, while vitrified bond strength could be simultaneously improved. High quality vitrified bond could be obtained by appropriately adjusting the strength and direction of high magnetic field. Results demonstrated that vitrified bond properties were improved when the magnetic field strength was 6?T. In order to highlight the high magnetic field effect on the vitrified CBN composites, the ordinary CBN abrasives and nickel plated CBN abrasives were used respectively. Microstructures, bending strengths of vitrified CBN composites were compared in different high magnetic fields. When the magnetic field strength was appropriate (less than 6?T), the binding characteristic of vitrified bond CBN composites with nickel plated CBN abrasives was greatly improved. The highest bending strength value of vitrified CBN composites was 79.5?MPa in 6?T high magnetic field.     

Detailed Insight into the Interaction of Bicyclic Somatostatin Analogue with Cu(II) Ions

Somatostatin analogues are useful pharmaceuticals in peptide receptor radionuclide therapy. In previous studies, we analyzed a new bicyclic somatostatin analogue (BCS) in connection with Cu(II) ions. Two characteristic sites were present in the peptide chain: the receptor- and the metal-binding site. We have already shown that this ligand can form very stable imidazole complexes with the metal ion. In this work, our aim was to characterize the intramolecular interaction that occurs in the peptide molecule. Therefore, we analyzed the coordination abilities of two cyclic ligands, i.e., P1 only with the metal binding site and P2 with both sites, but without the disulfide bond. Furthermore, we used magnetic circular dichroism (MCD) spectroscopy to better understand the coordination process. We applied this method to analyze spectra of P1, P2, and BCS, which we have described previously. Additionally, we analyzed the MCD spectra of P3 ligand, which has only the receptor binding site in its structure. We have unequivocally shown that the presence of the Phe-Trp-Lys-Thr motif and the disulfide bond significantly increases the metal binding efficiency.     

玻璃熔体表面张力特性在配方设计中的考量

本文从配方角度,探讨在玻璃配方设计与调整中,组分对表面张力和配合料熔化进程的影响。     

Effect of Cu addition on microstructural evolution and hardening of mechanically alloyed Al−Ti−O in-situ composite

The microstructure formation and strengthening of an Al−5wt.%TiO₂ composites with additions of 5 wt.% Cu and 2 wt.% stearic acid (as a process control agent, PCA) during mechanical alloying and subsequent thermal exposure were studied. The powder composites were prepared by high-energy ball milling for up to 10 h. Single line tracks of the powders were laser melted. Optical and scanning electron microscopy, XRD analysis and differential scanning calorimetry were used to study microstructural evolution. The results showed that the Cu addition promotes an effective mechanical alloying of aluminum with TiO₂ from the start of milling, resulting in higher microhardness (up to HV 290), while the PCA, on the contrary, postpones this process. In both cases, the composite granules with uniform distribution of TiO₂ particles were formed. Subsequent heating of mechanically alloyed materials causes the activation of an exothermic reaction of TiO₂ reduction with aluminum, the start temperature of which, in the case of Cu addition, shifts to lower values, that is, the transformation begins in the solid state. Besides, the Cu-added material after laser melting demonstrates a more dispersed and uniform structure which positively affects its microhardness.     

Corrosion and wear properties of micro-arc oxidation treated Ti6Al4V alloy prepared by selective electron beam melting

In order to analyze the effect of voltage during micro-arc oxidation (MAO) on corrosion and wear properties of Ti6Al4V (TC4), the MAO technology was employed to treat TC4 samples fabricated by selective electron beam melting (SEBM) at the voltages of 400, 420 and 450 V. The results show that the metastable anatase phase gradually transforms to rutile phase with oxidation time and temperature increasing. The surface morphology of coating contains numerous micropores with uniform size distribution. Cracks and pores over 10 μm are found on MAO-TC4 sample with applied voltage of 450 V. The thickness of MAO coating is positively correlated with the voltage. The corrosion resistance and wear resistance are related to phase composition, micropore size distribution on the surface and film thickness. When the voltage is 420 V, the coating shows the smallest corrosion current density (0.960×10⁻⁷ A/cm²) and the largest resistance (7.17×10⁵ Ω·cm²). Under the same load condition, the coating exhibits larger friction coefficient and wear loss than the TC4 substrate. With the increase of voltage, the wear mechanism of the coating changes from abrasive wear to adhesive wear, and the adhesive wear is intensified at applied voltage of 450 V, with a maximum friction coefficient of 0.821.     

Facile synthesis of tubular magnetic carbon nanofibers by hypercrosslinked polymer design for microwave adsorption

In this study, a simple and efficient method for fabrication of tubular magnetic carbon nanofibers (TMCF) has been developed. Firstly, tubular polymer nanofiber precursors are synthesized by confined self-condensation method. After carbonization of polymer and in situ transformation of FeCl₃ at high temperature, TMCF loaded with Fe nanoparticles is obtained. It has been found that carbonization temperature has significant effects on conductivity, specific surface area, pore volume, defects number in carbon component, and magnetic content of TMCF. The influence of composition, structure, and filler content on microwave absorption properties is revealed. Meanwhile, the microwave absorption mechanism has been analyzed in depth, which benefits from the designed unique structure. The TMCF obtained at 700°C exhibited best performance with the filler content of 15%. The minimum reflection loss is −47.33 dB@2.2 mm, the effective absorption bandwidth is 6.5 GHz (RL < 10 dB), and the matching frequency is 14.1 GHz. The obtained TMCF is lightweight and possess excellent microwave absorption ability, which can be widely used as highly efficient microwave absorber.