Journal of Central South University of Technology

Xing, Shi-wen; Li, Cai-xia; Li, Chao; Zhao, Xi-tong; Liu, Hong-xu

doi: 10.1007/s11771-022-5192-5pmid: N/A

Mg−6Al−2Sr alloys with different Sm contents (0%, 0.5%, 1%, 1.5%, 2%, mass fraction) were prepared by melting and casting method. The effects of Sm on the microstructure and mechanical properties of as-cast Mg−6Al−2Sr alloys were studied by optical microscope, scanning electron microscope, energy dispersive spectrometer, transmission electron microscope, X-ray diffraction and tensile test. The results show that the microstructure of as-cast Mg−6Al−2Sr alloy is composed of α-Mg, Mg17Al12, Mg13Al3Sr and lamellar acicular Al4Sr phase. After adding Sm element, granular block Al2Sm phase appears in the grain. With the increase of Sm content, the discontinuous long strip reticular Mg17Al12 phase and the lamellar acicular Al4Sr phase gradually decrease, and the Al2Sm phase increases and distributes more dispersedly, so the alloy microstructure is continuously refined. The average grain size of the alloys decreases at first and then increases with the increase of Sm content. When the Sm content is 1.5 wt%, the average grain size reaches the minimum value of 94.6 µm. With the increase of Sm content, the mechanical properties of the alloy at room temperature first increase and then decrease. When the Sm content is 1.5 wt%, the alloy has the best comprehensive mechanical properties at room temperature.

Yang, Kun; Wang, Jian; Yang, Guang-yu; Jia, Liang

doi: 10.1007/s11771-022-5203-6pmid: N/A

As the next generation biomedical titanium alloy, β-type titanium alloys are excellent candidates for biomedical applications due to the relative low elastic modulus and the contained non-toxic elements. However, the relative low strength and unsatisfactory tribological property are undesired for load-bearing implant applications. In this study, 0–5 at% Si was added to the classic Ti−35Nb−5Ta−7Zr alloy to improve its strength and wear resistance, and the (Ti−35Nb−5Ta−7Zr)1−x−Six (x=0, 1 at% and 5 at%) alloy were fabricated by selective electron beam melting (SEBM) technology. The results indicated that Si addition significantly increases in compressive yield strength, which is mainly due to grain refinement strengthening. At the same time, the wear rate of the as-built TNTZ-5Si alloy in SBF solution was only ∼30% of the Ti−6Al−4V alloy. Consequently, the TNTZ-5Si alloy showed an excellent combination of compressive yield strength, elastic modulus and wear resistance for potential load-bearing implant applications.

Yi, Tie; Liu, Sheng-dan; Fang, Chen; Jiang, Geng-duo

doi: 10.1007/s11771-022-5218-zpmid: N/A

The role of oxides in the formation of hole defects in friction stir welded joint of 2519-T87 aluminum alloy has been investigated by using optical microscope, scanning electron microscope, electron backscatter diffraction and electron probe microanalyzer to examine the distribution of oxides and the features of hole defects, and using ABAQUS 3D thermo-mechanical coupling finite element model based on arbitrary Lagrangian-Eulerian method to simulate the material flow behavior. Oxides exist at the edge of tunnel hole and in the micropores in the joint. Based on distribution of oxygen and material flow behavior, it is believed that the oxides on the surface of the alloy tend to flow down into the bulk along the flow direction of plastic material during friction stir welding, aggregate in the weak region of material flow at the intersection of the shoulder affected zone and the stir pin-tip affected zone, and consequently prevent the material from contacting and diffusing. Due to the insufficient material flow and therefore the small plastic deformation, the pressure is not high enough to compress the accumulated oxides, resulting in hole defects.

Xiao, Jing-jing; Yao, Chen; Wu, Ya-xin; Li, Chang-zhu

doi: 10.1007/s11771-022-5217-0pmid: N/A

The adsorption mechanism of O-isopropyl-S- [2- (hydroxyimino) propyl] dithiocarbonate ester (IPXPO) to chalcopyrite was investigated by using contact angle, in-situ atomic force microscopy (in-situ AFM), cyclic voltammetry (CV) and X-ray photoelectron spectroscopy (XPS). The results of contact angle and in-situ AFM demonstrated that IPXPO adsorbed on chalcopyrite increases surface hydrophobicity and roughness. It was found by CV experiments that a layer passive film was formed. The results of XPS spectra further revealed that the thiol S atom, oxime N atom, and O atom in the IPXPO molecule might react with copper atoms to form Cu-S, Cu-N, and Cu-O bonds, respectively. An artificial mixed minerals flotation test indicated that under the condition of pH=6.79 and IPXPO initial concentration 5×10−5 mol/L, the flotation recovery of chalcopyrite reached about 90%, while for pyrite only 25%, suggesting that IPXPO is an excellent collector for flotation separation and enrichment of chalcopyrite.

Sun, Jing; Ma, Jin-fang; Li, Qian; Li, Guang-yue; Shi, Wen-ge; Yang, Yu; Hu, Peng-fei; Guo, Zhi-min

doi: 10.1007/s11771-022-5216-1pmid: N/A

The role of Fe/S ratios (ω, g/g) in the uranium bioleaching from a complex uranium ore by Acidithiobacillus ferrooxidans and Acidithiobacillus thiooxidans consortium was investigated. The results showed good uranium extraction with over 90% at the Fe/S ratio of 5:0.5, 5:1 and 5:5, while poor extraction (<46%) at the Fe/S ratio of 5:0 and 5:10. Furthermore, the bacterial community analysis based on species-specific gyrB numbers indicated that, absent sulfur or excessive sulfur would be not conducive to the synergistic growth for A. ferrooxidans and A. thiooxidans, and then not conducive to the uranium dissolution. Meanwhile, the sulfur-oxidizers could play an important role in the process of uranium synergistic bioleaching by mixed bacterial consortia. Additionally, the characteristics of mineral residue was detected by SEM-EDS. The results showed appropriate sulfur dosage would change the structure and improve the porosity of passivation substance. Lastly, the uranium dissolution kinetics and biochemical reaction mechanism was analyzed. It indicated that the biochemical reaction coupling iron and sulfur had a pleiotropic effect on the uranium dissolution from the ore particles, appropriate Fe/S ratio is the key factor for uranium bioleaching by chemoautotrophic acidophiles.

Dang, Rui; Xu, Xiu-feng; Xie, Meng-meng

doi: 10.1007/s11771-023-5243-6pmid: N/A

Non-precious electro catalysts with high-efficiency, cheapness and stablility are of great significance to replace noble metal electro catalysts in the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). In this work, triangular Cu@CuO nanorods on Cu nanosheets were fabricated by a novel in-situ oxidation approach using Cu nanosheets as self-template and conductive nano-substrate in an aqueous solution of NaOH/H2O2, and then by low-temperature phosphorization treatments. The experimental results show that the phosphating temperature has a significant effect on the morphology, composition and number of active sites of Cu@Cu3P nanorods. The Cu@Cu3P-280 electrode exhibits a good HER catalytic activity of achieving a current density of 10 mA/cm2 at 252 mV in acid electrolyte. After catalysis for 14 h, the current density can still reach 72% of the initial value. Moreover, the Cu@Cu3P-280 electrode also shows an excellent OER catalytic activity in basic electrolyte, reaching a current density of 10 mA/cm2 at the overpotential value of 200 mV. After catalysis for 12 h, the current density remained more than 93% of the initial value. This work provides a theoretical basis for the directional design and preparation of sustainable, low-cost, bifunctional electrocatalytic materials.

Wang, Chong-qing; Yang, Jia-peng; Huang, Rong; Cao, Yi-jun

doi: 10.1007/s11771-022-5199-ypmid: N/A

Natural minerals receive growing attention as inexpensive, green, and efficient catalysts for degradation of organic pollutants. Mechanical activation of natural chalcopyrite was conducted for improving the catalytic performance. Tetracycline degradation was evaluated in the presence of hydrogen peroxide and mechanically activated chalcopyrite. Tetracycline degradation at 100 min is 55.52% (Chp10), 68.97% (Chp30), 77.79% (Chp60), and 86.43% (Chp120), respectively, and the rate constant of pseudo-first-order kinetics is 0.0079, 0.0109, 0.0137 and 0.0192 min−1, respectively. Chalcopyrite samples were examined by multiple characterizations. Mechanical activation of natural chalcopyrite induces the decline of particle size and slight increase of surface area, smaller grain size, lattice strain, and partial sulfur oxidation. The relationship between catalytic activity and property change manifests that the improved catalytic ability is mainly ascribed to the increase of surface area and surface oxidation induced by mechanical activation. This work provides novel insights into the improvement of catalytic performance of natural minerals by mechanical activation.

Eliwa, Ahmed Atef; Mubark, Amal Essam; Abdelfattah, Nasr Abelaziz; El Gawad, Ebrahim Abd

doi: 10.1007/s11771-022-5209-0pmid: N/A

Phosphogypsum (PG), the main by-product of phosphoric acid production industries, is considered one of the most important secondary sources of rare earth elements (REEs). The current study focuses on the recovery of REEs content and the residual phosphate content existing in the PG with preserving on the CaSO4 skeleton to be used in other various applications. These attainments are carried out using citric acid leaching process via soaking technique. Several dissolution parameters for REEs using citric acid were studied, including soaking time, soaking temperature, citric acid concentration, solid-to-liquid ratio, and recycling of the citrate leaching solutions in the further REEs dissolution experiments. The best-operating conditions were 14 d of soaking time, 7.5% citric acid concentration, and the solid-to-liquid ratio of 1/5 at ambient temperature. About 79.57% dissolution efficiency of REEs was achieved using the optimal conditions. Applying four soaking stages by mixing different fresh PG samples with the same citrate solution sequentially, cumulative dissolution efficiency for REEs was found to be 64.7% under optimal soaking conditions. REEs were recovered using Dowex 50X8 resin from citrate solutions with 96% extraction efficiency. Dissolution kinetics proved the pseudo-first-order nature, reversible reactions, and two activation energies for all REEs.

Adeel, Ahmad; Maria, Athar; Yasir, Khan

doi: 10.1007/s11771-022-5219-ypmid: N/A

This article studies the influence of polymers on drag reduction and heat transfer enhancement of a nanofluid past a uniformly heated permeable vertically stretching surface. Our prime focus is on analyzing the possible effects of polymer inclusion in the nanofluid on drag coefficient, Nusselt number and Sherwood number. Dispersion model is considered to study the behavior of fluid flow and heat transfer in the presence of nanoparticles. Molecular approach is opted to explore polymer addition in the base fluid. An extra stress arises in the momentum equation as an outcome of polymer stretching. The governing boundary layer equations are solved numerically. Dependence of physical quantities of engineering interest on different flow parameters is studied. Reduction in drag coefficient, Nusselt number and Sherwood number is noticed because of polymer additives.

Tang, Xue-yang; Cai, Xiao-pei; Peng, Hua; Ma, Chao-zhi; Chang, Wen-hao; Yao, Yu-fei

doi: 10.1007/s11771-022-5179-2pmid: N/A

The cause and treatment of rail corrugation for the metro have always been a popular and challenging issue. In this work, the field measurements were carried out on rail corrugation, track stiffness, and the track dynamic response. A three-dimensional finite element model was developed to investigate the cause of rail corrugation. The constraints on rail vibration from two wheelsets and adjacent wheel-rail interactions were taken into account in the model. According to experimental and simulation results, the suppression measure for rail corrugation was proposed and the suppression mechanism was discussed. It was found that the cause of rail corrugation is related to vertical and lateral vibration of the rails outside the two wheelsets at around 380 Hz. The increased stiffness of the fasteners reduces the vibration energy of the rail and the wheel-rail force. However, simply increasing the stiffness of the fasteners may not be effective in the suppression of rail corrugation. If necessary, the rails need to be grinded to reduce the roughness to a certain level, so that increasing the fastener stiffness can effectively suppress the rail corrugation.