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R-phase transformations in TiNi shape memory alloys (Nitinol) have various applications because of their small thermal hysteresis and low fatigue resistance. Adding a third element such as Fe or Al is one of the useful ways to induce R-phase transformation. Controlling the R-phase transformation temperature is crucial for industrial and bio-field applications. However, the effects of adding Fe have rarely been reported. In this study, the effects of Fe addition and heat treatment temperature on the Rphase transformation temperature of TiNiFe shape memory alloys were systematically investigated. Results showed that increasing Fe composition decreases the R-phase and martensitic transformation temperatures of 19K/1at%Fe and 51 K/1at%Fe, respectively. Additionally, in the Ti-49Ni-1Fe alloy, rather than a martensite transformation, the R phase transformation temperature was constant irrespective of heat treatment temperature and increasing number of thermal cycles. This means that the R-phase transformation temperature is not affected by dislocation density resulting from the heat cycling or cold working processes. This allows practical applications of R-phase transformation to be easily realized. Furthermore, this means that the R-phase transformation temperature is only affected by the Ni content of the matrix. (Received 6 October, 2023; Accepted 28 December, 2023)

keyword : Shape memory alloy, heat treatment temperature, R phase transformation, ternary system, Ti-Ni-Fe

In this study, novel non-skid Al-Al₂O₃ coatings with improved wear resistance were fabricated using twin wire arc spray (TWAS). TWAS Al coating was prepared as a reference sample and representative TWAS parameters (working distance, process gas pressure, arc current) were controlled to fabricate different Al-Al₂O₃ coatings. The Al-Al₂O₃ coatings showed a superior static coefficient of friction and higher surface roughness than the Al coating. The microstructural analysis of the Al-Al₂O₃ coatings revealed that the coatings contained Al splats, partially-melted Al₂O₃ particles, fully-melted Al₂O₃ splats and pores. The porosity and Al₂O₃ content of the Al-Al₂O₃ coatings varied with different process parameters. The Vickers hardness of the Al matrix showed a similar value in all samples, which means the deposition phenomena was the same. Ball-on-disc wear test with a Si3N4 ball was used to evaluate the wear resistance of the TWAS coatings. The weight loss of the Al-Al₂O₃ coatings were only 4.8 ~ 17.0 % of the Al coating, indicating that the wear resistance of the TWAS Al-Al₂O₃ coatings was superior. The TWAS coatings showed a complex wear mechanism, such as splat wear and abrasive wear. The distributed Al₂O₃ particles in Al-Al₂O₃ coating successfully suppressed the abrasive wear of the Al matrix, which contributed to the enhanced wear resistance. The results in this study indicated that the Al-Al₂O₃ composite coating has potential use as a novel non-skid coating. (Received 15 November, 2023; Accepted 19 January, 2024)

keyword : Twin wire arc spray, TWAS, Non-skid coating, Composite coating, Process optimization, Ball-on-disc test

It is known that Ni-based superalloys possess superior mechanical properties in high-temperature and high-pressure environments. One of the drawbacks of these alloys is their tendency to oxidize at high temperatures. Improving their oxidation properties and obtaining a fundamental understanding of the underlying mechanism of their oxidation behavior are critical for high temperature applications. In this work, we manufactured IN792 Ni-based alloys with two different grain sizes to examine the effect of grain size on oxidation behavior at 850℃ and 980℃. The oxidation rate became faster as the grain size became finer, and at 850℃, the oxide layer was composed of external oxides (TiO₂/NiO, Ni-Co-Cr-O, Cr₂O₃), internal oxides (TiTaO₄, non-oxidized layer, Al₂O₃) and a precipitate-free zone (PFZ). At 980℃, this structure became unstable due to the diffusion of Ni, and in particular, a lot of exfoliation of external oxides occurred in the coarse grain. Regardless of the structure of the oxide layers, the thickness of the PFZ increased significantly in the fine grains with a low γ fraction. Compared to the hardness of external Cr-rich oxides of ~500 HV, the hardnesses of the internal oxides consisting of Al-rich and Ni-Al-O were approximately 1000 HV and 1500 HV, respectively. Therefore, the most vulnerable position is expected to be the interfacial boundary between the external oxide and internal oxide, and this resulted in the ease of exfoliation of the external oxide in this location, by exposing the Ni-Al-O oxide to the surface in the coarse grain at 980oC. The current work can be a useful method in the design of Ni-based superalloys by controlling the grain size of the components. (Received 29 January, 2024; Accepted 2 February, 2024)

keyword : Ni-based superalloy, high-temperature oxidation, grain size

Concerns have arisen regarding the high concentrations of sodium sulfate in wastewater resulting from the waste Li-ion battery wet recycling process. In addressing this issue, Bipolar electrodialysis was employed to desalinate high-concentration sodium sulfate and recover it as sulfuric acid and sodium hydroxide. The investigation encompassed various experimental variables, such as applied voltage (maintained at a constant level), feed solution concentration, the initial concentrations of sulfuric acid and sodium hydroxide, and volume ratio (F/A/B). Optimal conditions were determined by assessing water migration (%), the recovery rates (%) of sulfuric acid and sodium hydroxide, concentration of the recovered substances, process time, and energy consumption. A higher applied voltage was found to reduce process time while increasing energy consumption, with the 25 V condition considered preferable. When utilizing a highconcentration feed solution, energy consumption rises; however, it decreases per unit of processed solution, rendering a 1.30 M Na₂SO₄ feed solution preferable. Increasing initial concentrations of sulfuric acid and sodium hydroxide substantially prolonged process time and increased energy consumption, emphasizing the advantage of commencing with low initial concentrations. Adjusting the volume ratio facilitated the concentration and recovery of sulfuric acid and sodium hydroxide with minimal impact on process time or energy consumption. Under the identified optimal conditions, the recovery of 1.70 M sulfuric acid and 2.44 M sodium hydroxide was achieved. (Received 14 November, 2023; Accepted 19 January, 2024)

keyword : LIBs recycling, Bipolar electrodialysis, Sodium sulfate recycling, Metal recovery, Membrane

This study investigates the influence of surfactant (sodium dodecyl sulfate, SDS) concentration on the size and optoelectronic properties of poly(3-hexylthiophene) (P3HT) nanoparticles (NPs) synthesized via the mini-emulsion technique. P3HT NPs were fabricated with varying SDS concentrations. The size dependent optoelectronic properties, including the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) levels, were analyzed through photoelectron spectroscopy in air, UVVis absorption spectroscopy and cyclic voltammetry. A clear trend of decreasing NP size with increasing SDS concentration was observed. Higher SDS levels resulted in smaller NPs with enhanced pi-pi stacking and shorter conjugation lengths. This structural change led to a noticeable shift in HOMO and LUMO levels, indicating a direct correlation between surfactant concentration and the electronic properties of the P3HT NPs. The absorption spectra revealed a decrease in the A0-0/A0-1 ratio with smaller NP size, suggesting a transition towards more pronounced H-aggregate characteristics. As the size of the P3HT NPs decreases, there is a notable increase in H-aggregate formation. This increase can be attributed to enhanced interchain interactions between the polymer chains. In smaller NPs, the surface area-to-volume ratio is higher, leading to more significant interactions between adjacent polymer chains. These interactions promote the formation of H-aggregates, characterized by their interchain pi-pi stacking, which differs from the intrachain coupling observed in J-aggregates. (Received 30 November, 2023; Accepted 22 December, 2023)

keyword : P3HT colloids, mini-emulsion, aggregates, surfactant, conjugation

Poly(3-hexylthiophene) (P3HT), a semiconducting polymer, is integral to the development of organic electronic devices. Its optoelectronic properties are significantly influenced by the nature of its intermolecular interactions, predominantly classified as J-type and H-type couplings. This study investigates the effect of sonication on the dielectric properties of P3HT, focusing on the transition from J-type (or less prominent H-type) to H-type intermolecular interactions, accompanied by disorder-order transformation. The research determined that sonication leads to a significant change in the dielectric properties of P3HT by forming distinct ordered regions interspersed within disordered or quasi-ordered areas. Specifically, there is an observable transition from J-type to H-type aggregation, which has profound effects on the material's electronic structure and optoelectronic performance. This transition was confirmed by changes in the absorption and photoluminescence spectra, indicating a more localized electronic character and the formation of non-emissive excitons in the case of H-aggregates. Increased dielectric constant after sonication is attributed to interface polarization, especially the Maxwell-Wagner-Sillars polarization. This effect is likely because new interfaces are created between the ordered regions and disordered/quasi-ordered regions within the P3HT material, where charges can accumulate as a result of disorder-order transformation. Our research contributes to the broader understanding of polymer physics and the development of organic electronic devices by showing how the manipulation of microstructural environments can control material properties. (Received 12 December, 2023; Accepted 8 January, 2024)

keyword : dielectric constant, disorder-order transformation, crystallinity, interface polarization

To improve the hydrogen-storage properties of Mg₂Ni, LiBH₄ was added by milling in hydrogen atmosphere (reactive mechanical milling, RMM). Mg₂Ni-10LiBH₄ was prepared with a composition of 90 wt% Mg₂Ni + 10 wt% LiBH4. The quantity of released hydrogen (H_r) versus temperature T curve for Mg₂Ni- 10LiBH₄ was obtained by heating at a rate of 4~5 K in 1.0 bar hydrogen. The hydrogen-storage properties of the sample were investigated. The phases formed were examined from the x-ray diffraction (XRD) patterns of the samples after RMM, and after hydrogen-absorption and release cycling. The XRD pattern of Mg₂Ni- 10LiBH₄ showed that this sample contained Mg₂Ni, Mg₂NiH₄, o-LiBH₄, h-LiBH₄, Ni, and MgH₂. The dHr/dT versus T curve exhibited three peaks at 325 K, 563 K, and 600 K, respectively. The peak at 325 K is for the hydrogen release from o-LiBH₄ and h-LiBH₄. The peak at 563 K is for the hydrogen release from Mg₂NiH₄ and the peak at 600 K is for the hydrogen release from Mg₂NiH₄ and MgH₂. The RMM of Mg₂Ni with added LiBH₄ creates defects and cracks. RMM facilitates nucleation, increases reactivity, and shortens the diffusion distances of hydrogen atoms. Expansion and contraction of lattices due to cycling has effects similar to, but weaker than, the effects of RMM. (Received 23 November, 2023; Accepted 6 January, 2024)

keyword : hydrogen-storage properties, Mg_{2Ni, LiBH4, XRD patterns, hydrogen absorption and release curves}

In this study, we enhanced the flexural strength of cordierite ceramics by incorporating h-BN (hexagonal boron nitride) nanoparticles, facilitated by the slip casting process. Initially, commercial cordierite powder with an average particle size of 10 mm underwent a ball-milling process to reduce the size to 2.5 mm and simultaneously achieve a narrower particle size distribution. The resulting slurry, composed of 67% solid content, exhibited improved stability during the slip casting process for both pristine cordierite and the mixture containing 1 - 2 wt% h-BN nanoparticles. After sintering, the bulk material containing 2wt% h-BN nanoparticles demonstrated a remarkable flexural strength of 174.8 MPa, a significant improvement compared to the initial 119.5 MPa obtained without the addition of h-BN. It is worth noting that the introduction of h-BN nanoparticles did not induce substantial changes in dielectric constant and thermal conductivity, indicating that the desired mechanical enhancement did not compromise other crucial material properties. This research demonstrates a successful approach to concurrently optimize the flexural strength, dielectric constants, and thermal conductivity of cordierite ceramics. This breakthrough opens up new avenues for advanced applications in a wide range of fields, from electronics to aerospace, where high-strength, thermally stable materials are in demand. (Received 7 November, 2023; Accepted 26 December, 2023)

keyword : flexural strength, cordierite, hexagonal boron nitride, slip casting

The effects of post-annealing times at 150℃ on the bonding strength and interfacial characteristics of Cu/Sn-3.0Ag-0.5Cu (SAC305)/Al were systematically evaluated. In the as-bonded sample, Cu₆Sn₅ intermetallic compound (IMC) was formed at the upper Cu/SAC305 interface, while Ag₃Al IMC was formed at the lower SAC305/Al interface, and a black layer of Al₂Cu IMC was formed at a distance of about 20 μm from the Al interface. The Al atoms from the Al pad diffused towards the SAC305 solder during the bonding process and reacted with Cu to form the Al₂Cu IMC. After post-annealing for 500 h at 150℃, the growth of Cu-Sn and Al₂Cu IMCs followed a linear relationship with the square root of the annealing time, which could be understood by a diffusion-dominant mechanism. To measure the bonding strength, the lap shear test was evaluated on the Cu/SAC305/Al structure with time during post-annealing at 150℃. Initial bonding strength of around 118.80 MPa decreased to 92.4MPa after post-annealing for 200h, and then remained constant until 500 h. And the fracture locus was the mixed mode of SAC305/Al₂Cu interface and cohesive inside SAC305 solder. Also, when the post-annealing time was increased from 150 h to 200 h, the fracture toughness decreased sharply from 438 J/m³ to 100 J/m³. This decrease seems to be closely related to an increase in the SAC305/Al₂Cu interface fracture mode. This is believed to be due to the increase in the SAC305/Al₂Cu interface fracture mode due to the growth of the Al₂Cu layer thickness.

keyword : post-annealing, lap shear test, intermetallic compound, bonding strength, toughness

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