The zone refining method is a physical method for effectively purifying metals. Increasing yield and reducing impurity content have always been the focus of its research. This article systematically summarizes the relevant research on the production of high-purity metals by zone refining, including mechanisms, parameter optimization, zone refining types, analysis methods, limitations, and future development directions, and it provides relevant theoretical foundations for the production of high-purity metals as well.

Steel fiber-reinforced ultra-high-performance concrete (UHPC) is becoming an important type of concrete reinforcement. After mixing with the reinforced steel fibers, the UHPC has perfect flex resistance, shear strength, crack resistance, shock resistance, and anti-seepage. In this study, the influence of straight, corrugated, and hooked brass-coated steel fibers (BCSFs) on the microstructure, mechanical properties, and crack expansion mechanism of ultra-high-performance concrete (UHPC) with varying content of 1–6 wt.% under different curing times were investigated. Field emission scanning electron microscopy and energy dispersive X-ray spectrometry were employed to characterize the microstructure of the BCSF-reinforced UHPC mix specimens. X-ray computed tomography was employed to determine the porosity of the BCSF-reinforced UHPC mix specimens. The obtained results indicate the flexural strength and compressive strength of BCSF-reinforced UHPC mix specimens are enhanced, along with increasing the content of BCSFs reinforcement with different shapes (straight, corrugated, and hooked). The embedded BCSFs play a major role in the adhesive property and stress transfer of the BCSFs–UHPC matrix interface. Different from many studies, the flexural strength of mix UHPC with straight BCSFs is higher than those with corrugated and hooked BCSFs. However, the compressive strength of UHPC with corrugated BCSFs is higher than those with straight and hooked BCSFs. The flexural strength of mix UHPC with 6 wt.% straight BCSFs at 28 days reaches the maximum value of 26.2 MPa, and the compressive strength of UHPC with 6 wt.% corrugated BCSFs at 28 days reaches the maximum value of 142.3 MPa. With the increase in straight BCSF content from 1 wt.% to 6 wt.%, the porosity in mix UHPC reduces gradually from 18.4% to 8.3%. The length of average crack spacing is dependent on the straight BCSF content. With the increase in straight BCSF content from 1 wt.% to 6 wt.%, the average crack length reduces gradually from 34.2 mm to 12.1 mm, and the average crack width reduces gradually from 0.78 mm to less than 0.1 mm. During crack extension, part of the energy in the UHPC mixture specimen with the 6 wt.% BCSF content flows into the crack tip region converted into the work dissipated during the bridging process. The crack propagation resistance of the UHPC mixture with straight BCSFs was improved compared with those with corrugated and hooked BCSFs. The bond strength between the BCSFs and UHPC matrix was enhanced by using vibrational mixing, and the brass film coated on the BCSFs contributes to increase the flexural and compressive strength of the UHPC mixture.

Understanding the infiltration and solidification processes of liquid 5083Al alloy into Al₂O₃ three-dimensional reticulated porous ceramic (Al₂O_3(3D) RPC) is essential for optimizing the microstructure and properties of Al₂O_3(3D)/5083Al interpenetrating phase composites (IPCs) prepared by low-pressure infiltration process (LPIP). This study employs ProCAST software to simulate the infiltration and solidification processes of liquid 5083Al with pouring velocities (PV) of 0.4 m/s infiltrating into Al₂O_3(3D) RPC preforms with varying porosities at different pouring temperatures (PT) to prepare Al₂O_3(3D)/5083Al IPCs using LPIP. The results demonstrate that pore diameter of Al₂O_3(3D) RPC preforms and PT of liquid 5083Al significantly influence the of the infiltration. Solidification process analysis reveals that the Al₂O_3(3D) RPC preform with smaller pore diameters allows the lower pouring velocity of 5083Al to solidify faster compared to the preform with larger pore diameters. Al₂O_3(3D)/5083Al IPCs were prepared successfully from Al₂O_3(3D) RPC porosity of 15 PPI with liquid 5083Al at PV 0.4 m/s and PT 800 °C using LPIP, resulting in nearly fully dense composites, where both Al₂O_3(3D) RPCs and 5083Al interpenetrate throughout the microstructure. The infiltration and solidification defects were reduced under air pressure of 0.3 MPa (corresponding to PV of 0.4 m/s) during LPIP. Finite volume method simulations are in good agreement with experimental data, validating the suitability of the simplified model for Al₂O_3(3D) RPCs in the infiltration simulation.

Interface problems and the destruction of the continuity of the oxide film in the Al matrix usually reduce the corrosion resistance of the material. In this paper, the corrosion resistance of Al matrix composites (AMCs) was improved by introducing the silicon carbide skeletons (SiC_3D) obtained with polymer replica technology. SiC_3D/6061Al was fabricated by infiltrating molten 6061Al alloy in the oxidized SiC_3D using the low-pressure casting method. The corrosion resistance performances of 6061Al and SiC_3D/6061Al in NaCl solution were studied by electrochemical, neutral salt spray corrosion (NSS), and salt leaching (SL) tests. Results show corrosion resistance of SiC_3D/6061Al is higher than that of 6061Al alloys by open circuit potential (OCP), potentio-dynamic polarization (PDP), and electrochemical impedance spectroscopy (EIS) tests. However, NSS and SL tests show the corrosion resistance of SiC_3D/6061Al is lower than that of 6061Al alloy. The reason is a corrosion resistant and anti-oxidation network macrostructure with large interface recombination, few concentrated interfaces, and a small specific area that formed in SiC_3D/6061Al. SiC_3D cannot damage the continuity of the Al₂O₃ passivating film, and the network macrostructure greatly improves the corrosion resistance performance.

In this study, an Al₂O₃3D/5083 Al composite was fabricated by infiltrating a molten 5083 Al alloy into a three-dimensional alumina reticulated porosity ceramics skeleton preform (Al₂O₃3D) using a pressureless infiltration method. The corrosion resistance of 5083 Al alloy and Al₂O₃3D/5083 Al in NaCl solution were compared via electrochemical impedance spectroscopy (EIS), dynamic polarization potential (PDP), and neutral salt spray (NSS) tests. The microstructure of the two materials were investigated by 3D X-ray microscope and scanning electron microscopy aiming at understanding the corrosion mechanisms. Results show that an Al₂O₃3D/5083 Al composite consists of interpenetrating structure of 3D-continuous matrices of continuous networks 5083 Al alloy and Al₂O₃3D phase. A large area of strong interfaces of 5083 Al and Al₂O₃3D exist in the Al₂O₃3D/5083 Al composite. The corrosion development process can be divided into the initial period, the development period, and the stability period. Al₂O₃3D used as reinforcement in Al₂O₃3D/5083 Al composite improves the corrosion resistance of Al₂O₃3D/5083 Al composite via electrochemistry tests. Thus, the corrosion resistance of Al₂O₃3D/5083 Al is higher than that of 5083 Al alloy. The NSS test results indicate that the corrosion resistance of Al₂O₃3D/5083 Al was lower than that of 5083 Al alloy during the initial period, higher than that of 5083 Al alloy during the development period, and there was no obvious difference in corrosion resistance during the stability period. It is considered that the elements in 5083 Al alloy infiltrated into the Al₂O₃3D/5083 Al composite are segregated, and the uniform distribution of the segregated elements leads to galvanic corrosion during the corrosion initial period. The perfect combination of interfaces of Al₂O₃3D and the 5083 Al alloy matrix promotes excellent corrosion resistance during the stability period.

In this study, the effect of sintering temperature and the addition of kaolin, a sintering agent, on the microscopic, phase, and mechanical properties of ceramics were investigated using secondary aluminum dross (SAD) as the main component in the manufacturing of ceramics. The basic phases of the ceramics were Al₂O₃, MgAl₂O₄, NaAl₁₁O₁₇, and SiO₂ without the addition of kaolin. The diffraction peaks of MgAl₂O₄, NaAl₁₁O₁₇, and SiO₂ kept decreasing while those of Al₂O₃ kept increasing with an increase in temperature. In addition, the increase in temperature promoted the growth of the grains. The grains were uniform in size and regular in distribution, with a shrinkage of 2.2%, porosity of 72.5%, bulk density of 1.076 g/cm³, and compressive strength of 1.12 MPa. When the sintering temperature was 1450°C, the basic phases of the ceramic after the addition of kaolin were Al₂O₃, MgAl₂O₄, NaAl₁₁O₁₇, and SiO₂. With the increase of kaolin, the diffraction peaks of NaAl₁₁O₁₇ and SiO₂ decreased until they disappeared, while the diffraction peaks of Al₂O₃ increased significantly. When kaolin was added at 30 wt.%, the ceramics obtained had shrinkage of 18%, a porosity of 47.26%, a bulk density of 1.965 g/cm³, and compressive strength of 31.9 MPa. Cracks existed inside the ceramics without the addition of kaolin, while the addition of kaolin significantly changed this defect. It is shown that SAD can obtain porous ceramics with good properties at a sintering temperature of 1450°C and a kaolin addition of 30 wt.%.