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Cement is one of the most widely used structural materials and serves as the primary component of concrete. Among the various types, Portland cement is the most commonly utilized due to its excellent strength and corrosion resistance. Recently, efforts have been made to incorporate various functional additives into Portland cement to impart new properties; however, studies on the resulting changes in corrosion resistance remain insufficient. While the existing research has largely focused on impurities in cement, systematic studies on the effects of interstitial elements on the crystallization and electrochemical behavior of cement are scarce. This study investigates the influence of carbon (C) addition on the crystallographic structure and electrochemical properties of Portland cement. C concentrations from 0 to 10 wt.% were added. The microstructure and crystallographic structure with different C concentrations were analyzed using FE-SEM and XRD. The bonding characteristics of cement components according to the C composition were measured using XPS, hardness was measured using Vickers hardness, and electroconductivity was calculated using a 4-point probe. The electrochemical behavior was evaluated according to the ASTM G 61 standards through OCP, EIS, and potentiodynamic polarization tests. As the composition of C increased, the number of voids and cracks decreased, while the electrical conductivity increased from 1.7 × 10−4 to 4.3 × 10−2. Additionally, the resistance tended to decrease with the increase in C composition. Therefore, the concentration of C needs to be controlled depending on the required function of the cement. [ABSTRACT FROM AUTHOR]

Li-ion batteries are at risk of explosions caused by fires, primarily because of the high energy density of Li ions, which raises the temperature. Battery cases are typically made of plastic, aluminum, or SAF30400. Although plastic and aluminum aid weight reduction, their strength and melting points are low. SAF30400 offers excellent strength and corrosion resistance but suffers from work hardening and low high-temperature strength at 700 °C. Additionally, Ni used for plating has a low current density of 25% international copper alloy standard (ICAS). SAF2507 is suitable for use as a Li-ion battery case material because of its excellent strength and corrosion resistance. However, the heterogeneous microstructure of SAF2507 after casting and processing decreases the corrosion resistance, so it requires solution heat treatment. To address these issues, in this study, SAF2507 (780 MPa, 30%) is solution heat-treated at 1100 °C after casting and coated with Ag (ICAS 108.4%) using physical vapor deposition (PVD). Ag is applied at five different thicknesses: 0.5, 1.0, 1.5, 2.0, and 2.5 μm. The surface conditions and electrochemical properties are then examined for each coating thickness. The results indicate that the PVD-coated surface forms a uniform Ag layer, with electrical conductivity increasing from 1.9% ICAS to 72.3% ICAS depending on the Ag coating thickness. This enhancement in conductivity can improve Li-ion battery safety on charge and use. This result is expected to aid the development of advanced Li-ion battery systems in the future. [ABSTRACT FROM AUTHOR]

Lithium-ion batteries are superior energy storage devices that are widely utilized in various fields, from electric cars to small portable electric devices. However, their susceptibility to thermal runaway necessitates improvements in battery case materials to improve their safety. This study used electrochemical analyses, including open-circuit potential (OCP), potentiodynamic polarization, and critical pitting temperature (CPT) analyses, to investigate the corrosion resistance of super duplex stainless steel (SAF 2507) applied to battery cases in relation to post-weld heat treatment (PWHT) time. The microstructure during the manufacture, laser welding, and PWHT was analyzed using field-emission scanning electron microscopy, X-ray diffraction, and electron backscatter diffraction, and the chemical composition was analyzed using dispersive X-ray spectroscopy and electron probe micro-analysis. The PWHT increased the volume fraction of austenite from 5% to 50% over 3 min at 1200 °C; this increased the OCP from −0.21 V to +0.03 V, and increased the CPT from 56 °C to 73 °C. The PWHT effectively improved the corrosion resistance, laying the groundwork for utilizing SAF 2507 in battery case materials. But the alloy segregation and heterogeneous grain morphology after PWHT needs improvement. [ABSTRACT FROM AUTHOR]

High-entropy alloys (HEAs), a relatively new class of materials, have attracted significant attention in materials science owing to their unique properties and potential applications. High entropy stabilizes the phase of a solid solution over a wide range of chemical compositions, yielding unique properties superior to those of conventional alloys. Therefore, this study analyzed the microstructure and electrochemical behavior of HEAs (Cantor) to evaluate their corrosion resistance, according to their manufacturing process (casting, cold rolling, and annealing). The microstructural morphologies and sizes were analyzed using electron backscatter diffraction. The electrochemical behavior was examined using open circuit potential measurements, electrochemical impedance spectroscopy, potentiodynamic polarization tests, and critical pitting temperature measurements using a potentiostat. The casting process formed a nonuniform microstructure (average grain size = 19 μm). The cold rolling process caused the formation of fine grains (size = 4 μm). A uniform microstructure (grain size > 151 μm) was formed after heat treatment. The corrosion resistance of the HEAs was determined from the passivation layer formed by Cr oxidation. These microstructural differences resulted in variations in the electrochemical behavior. Microstructural and electrochemical analyses are crucial because HEAs have diverse potential applications. Therefore, this study contributes to future improvements in HEA manufacturing processes. [ABSTRACT FROM AUTHOR]

Li-ion batteries used in portable electronic devices and electric vehicles require high safety standards, necessitating the use of high-performance structural materials for battery casings. Super duplex stainless steel (SDSS) is a structural material suitable for portable electronic products owing to its excellent strength and corrosion resistance. SDSS AISI2507 was used to construct a Li-ion battery casing, a Ag coating was applied via physical vapor deposition (PVD) after the heat treatment of AISI2507 with or without a secondary phase, and the coating thickness was controlled by varying the PVD time. The thickness of the Ag coating layer increased proportionally with time, thereby enhancing the electrical conductivity. The structure and coating behavior were confirmed using FE-SEM, XRD, and GDS. The secondary phase was crystallized by the segregation of the alloy and formed a BCC structure. The FCC lattice structure exhibited excellent coating behavior on the austenite (FCC structure) of AISI2507. Conversely, the secondary phase exhibited low adhesion owing to differences in composition and crystal structure. However, the Ag coating layer on AISI2507 exhibited excellent electrical conductivity, outperforming conventional Ni-plated Li-ion battery casings comprising AISI304. However, the precipitation of the secondary phase must be controlled, as the formation of the secondary phase acts as a factor that decreases electrical conductivity from 58.8 to 53.6 (ICAS) %. The excellent performance of Ag-coated AISI2507 makes it suitable for the fabrication of enhanced Li-ion battery casings. [ABSTRACT FROM AUTHOR]

Super duplex stainless steel (SDSS) is a suitable structural material for various engineering applications due to its outstanding strength and corrosion resistance. In particular, its high-temperature strength can enhance the safety of electronic products and cars. SDSS AISI2507, known for its excellent strength and high corrosion resistance, was analyzed for its microstructure and electrochemical behavior at the ignition temperature of Li-ion batteries, 700 °C. At 700 °C, AISI2507 exhibited secondary phase precipitation values of 1% and 8% after 5 and 10 h, respectively. Secondary phase precipitation was initiated by the expansion of austenite, forming sigma, chi, and CrN phases. The electrochemical behavior varied with the fraction of secondary phases. Secondary phase precipitation reduced the potential (From −0.25 V to −0.31 V) and increased the current density (From 8 × 10−6 A/cm2 to 3 × 10−6 A/cm2) owing to galvanic corrosion by sigma and chi. As the fraction of secondary phases increased (From 0.0% to 8.1%), the open circuit potential decreased (From −0.25 V to −0.32 V). Secondary phase precipitation is a crucial factor in reducing the corrosion resistance of SDSS AISI2507 and occurs after 1 h of exposure at 700 °C. [ABSTRACT FROM AUTHOR]

The demand for Li-ion batteries has increased because of their extensive use in vehicles and portable electronic devices. This increasing demand implies greater interaction between batteries and humans, making safety a paramount concern. Although traditional batteries are fabricated using Al, recent efforts to enhance safety have led to the adoption of AISI304. The strength and corrosion resistance of AISI304 are greater than those of Al; however, issues such as stress-induced phase transformation and low high-temperature strength have been observed during processing. Duplex stainless steel SAF2507, which is characterized by a dual-phase structure consisting of austenite and ferrite, exhibits excellent strength and corrosion resistance. Although SAF2507 demonstrated outstanding high-temperature strength up to 700 °C, it precipitated a secondary phase. The precipitation of this secondary phase, believed to be caused by the precipitation of the carbides of Cr and Mo, has been extensively studied. Research on the precipitation of the secondary phase near 1000 °C has been conducted owing to the annealing temperature (1100 °C) of the SAF2507 solution. The secondary phase precipitates at approximately 1000 °C because of slow cooling rates. However, few studies have been conducted on the precipitation of the secondary phase at approximately 700 °C. This study analyzed the precipitation behavior of the secondary phase at 700 °C when SAF2507 was applied and assessed its safety during heat generation in Li-ion batteries. The precipitation behavior was analyzed using field emission scanning electron microscopy for morphology, energy-dispersive X-ray spectroscopy for composition, and X-ray diffraction for phase identification. [ABSTRACT FROM AUTHOR]

The development of Li-ion battery cases requires superior electrical conductivity, strength, and corrosion resistance for both cathode and anode to enhance safety and performance. Among the various battery case materials, super duplex stainless steel (SDSS), which is composed of austenite and ferrite as two-phase stainless steel, exhibits outstanding strength and corrosion resistance. However, stainless steel, which is an iron-based material, tends to have lower electrical conductivity. Nevertheless, nickel-plating SDSS can achieve excellent electrical conductivity, making it suitable for Li-ion battery cases. Therefore, this study analysed the plating behaviour of SDSS plates after nickel plating to leverage their exceptional strength and corrosion resistance. Electroless Ni plating was performed to analyse the plating behaviour, and the plating behaviour was studied with reference to different plating durations. Heat treatment was conducted at 1000 °C for one hour, followed by cooling at 50 °C/s. Post-heat treatment, the analysis of phases was executed using FE-SEM, EDS, and EPMA. Electroless Ni plating was performed at 60–300 s. The plating duration after the heat treatment was up to 300 s, and the behaviour of the materials was observed using FE-SEM. The phase analysis concerning different plating durations was conducted using XRD. Post-heat treatment, the precipitated secondary phases in SAF2507 were identified as Sigma, Chi, and CrN, approximating a 13% distribution. During the electroless Ni plating, the secondary phase exhibited a plating rate equivalent to that of ferrite, entirely plating at around 180 s. Further increments in plating time displayed growth of the plating layer from the austenite direction towards the ferrite, accompanied by a reduced influence from the substrate. Despite the differences in composition, both the secondary phase and austenite demonstrated comparable plating rates, showing that electroless Ni plating on SDSS was primarily influenced by the substrate, a finding which was primarily confirmed through phase analysis. [ABSTRACT FROM AUTHOR]

The demand for Li-ion batteries has significantly increased in recent years, driven by the growing need for electric vehicles and electronic devices like smartphones. Among various materials, super duplex stainless steel (SDSS) is considered a suitable material for Li-ion batteries due to its excellent strength and corrosion resistance. However, SDSS is sensitive to heat-treatment conditions, necessitating research on heat treatment and Ni plating for battery case usage. While extensive research has been conducted on SDSS and its heat-treatment conditions, there is a research gap concerning the Ni plating of SDSS. This study addresses this gap by performing Ni plating on heat-treated SDSS. Ni plating can be executed via two methods: electroless and electro-Ni plating. To achieve a uniform plating layer, Ni plating was conducted after heat treatment at temperatures ranging from 1000 °C to 1300 °C, followed by an analysis of the behavior of electroless Ni plating. The heat-treated SDSS displayed three primary characteristics: secondary phase precipitation, solution annealing, and ferritization (ferrite fractions of 61% and 73%). The presence of secondary phases led to a slower Ni plating rate due to its lower reactivity with Ni. Post-solution annealing, the texture of SDSS exhibited the thickest Ni plating layer at the same plating time. As the volume fraction of ferrite increased from 50% to 73% on electrochemical impedance spectroscopy, the resistance of the Ni plating layer decreased from 45 kOhms to 13 kOhms. The lowest resistance was observed when the ferrite fraction reached 73%, attributed to the lower reactivity of ferrite compared to austenite. Both secondary phases and ferrite contributed to reducing the thickness of the electroless Ni plating layer. Therefore, optimizing the volume fraction of SDSS using solution annealing proves beneficial for optimizing Ni plating and enhancing corrosion resistance. [ABSTRACT FROM AUTHOR]