Chulwoong Han

This study investigates the formation mechanism and functional behavior of carbon-encapsulated nickel powders synthesized via RF thermal plasma processing. The plasma environment enables simultaneous melting of nickel particles and thermal dissociation of methane, leading to the incorporation of reactive carbon species into molten Ni under non-equilibrium conditions. Upon rapid quenching, the temperature-dependent solubility of carbon in the Ni-C system decreases sharply, resulting in supersaturation-driven outward diffusion and precipitation of carbon, forming a conformal graphitic shell.Microstructural analysis confirms the formation of a continuous core-shell structure with nanoscale carbon layers exhibiting partially ordered sp² bonding. The presence of the carbon shell significantly influences the oxidation and sintering behavior of the powders. Under ambient conditions, the shell acts as an effective diffusion barrier, suppressing oxygen ingress. Thermogravimetric analysis reveals a pronounced shift in oxidation onset temperature, indicating enhanced oxidation resistance. This behavior is attributed to an increase in the apparent activation energy due to diffusion limitations imposed by the carbon shell.At elevated temperatures, however, carbon oxidation and structural degradation lead to the breakdown of the shell, resulting in accelerated oxidation of the nickel core. In addition, the carbon shell suppresses sintering by reducing interparticle contact and limiting atomic diffusion, thereby inhibiting neck growth and grain coarsening.Overall, the results demonstrate that the formation and performance of carbon-encapsulated nickel powders are governed by a non-equilibrium dissolution–precipitation mechanism in the Ni-C system. The study provides a comprehensive understanding of the process-structure-property relationship and offers design guidelines for developing oxidation-resistant and sintering-resistant metallic powders for high-temperature applications.

The W/Cu binary system is characterized by its mutual insolubility and excellent wettability, making W/Cu composite materials ideal for managing thermal and electrical properties in electronic components. To optimize material properties, control over the microstructure is crucial, and nanocomposites with uniform dispersion offer significant advantages. In this study, W/Cu composite nanoparticles were synthesized by feeding a blended feedstock of tungsten trioxide (WO₃) micro-powder and cupric oxide (CuO) micro-powder into a reactive radio frequency (RF) argon–hydrogen thermal plasma system. Cu-coated W nanocomposite particles were obtained through the vaporization, reduction, and condensation processes. The resulting nanocomposite particles were composed of body-centered cubic (BCC) α-W, A15 β-W, and face-centered cubic (FCC) Cu phases, with a chemical composition closely matching theoretical calculations. The phase evolution and morphological changes of the synthesized particles were analyzed as a function of heat treatment temperatures up to 1000 °C in a reducing atmosphere. Up to 600 °C, the phase composition and morphology remained stable. At 800 °C, localized diffusion and coalescence of Cu led to the formation of particulate Cu, and a significant phase transformation from metastable β-W to α-W was observed. Additionally, extensive Cu segregation due to long-range diffusion resulted in distinct Cu-rich and Cu-depleted regions. In these regions, notable sintering of W particles and the complete disappearance of β-W occurred. The results showed that the temperature-dependent redistribution of Cu plays a crucial role in the phase transformation of W and the morphology of W/Cu composite particles.

This study investigated the effect of flux type and amounts on recovery behavior of aluminum alloy during the melting process of Al can scrap. The heat treatment was conducted to remove the coating layer on the surface of can scrap at 500°C for 30 min. The molten metal treatment of the scrap was performed at 750°C in a high-frequency induction furnace with different flux types and amounts. It was observed that the optimum condition for recovery of Al alloy was to add about 3 wt.% flux with a salt and MgCl2 mixing ratio of 70:30 during melting process. The mechanical properties of recovered Al alloy were about 254.8 MPa, which is similar to that of the virgin Al5083 alloy.

This study investigated the recovery behavior of valuable metals (Co, Ni, Cu and Mn) in spent lithium ion-batteries based on Al2O3-SiO2-CaO-Fe2O3 slag system via DC submerged arc smelting process. The valuable metals were recovered by 93.9% at the 1250℃ for 30 min on the 20Al2O3-40SiO2-20CaO-20Fe2O3 (mass%) slag system. From the analysis of the slag by Fourier-transform infrared spectroscopy, it was considered that Fe2O3 and Al2O3 acted as basic oxides to depolymerize SiO4 and AlO4 under the addition of critical 20 mass% Fe2O3 in 20Al2O3-40SiO2-CaO-Fe2O3 (CaO + Fe2O3 = 40 mass%). In addition, it was observed that the addition of Fe2O3 ranging between 20 and 30 mass% lowers the melting point of the slag system.