Tea tree extract, containing antioxidant constituents α-terpineol, terpinen-4-ol, and α-terpinene, has a wide range of applications in the cosmetic, food, and pharmaceutical industries. In this study, tea tree extract showed an anticorrosive effect under 1 M HCl solution on mild steel (MS) and 304 stainless steel (STS). Uniform corrosion for MS and pitting corrosion for STS at 298 K were retarded, with inhibition efficiencies of 77% and 86%, respectively. The inhibition of uniform and pitting corrosion was confirmed by scanning electron microscopy and laser scanning confocal microscopy in terms of surface roughness and pitting morphologies. The most effective constituent contributing to the inhibitory performance of tea tree extract was revealed to be α-terpineol, with an inhibition efficiency of 83%. The adsorption of tea tree extract was confirmed by surface characterization analysis using Fourier transform infrared spectroscopy, Raman spectroscopy, and Electrochemical impedance spectroscopy. Interestingly, G- and D-peaks of Raman spectra were detected from the inhibited steels, and this finding is the first example in the corrosion inhibition field. The anticorrosion mechanism can be explained by the formation of organic-Fe complexes on the corroded steel surface via electron donor and acceptor interactions in the presence of an oxygen atom of the hydroxyl group or ether of organic inhibitors.

Double-pass Friction Stir Processing (FSP) was applied to fabricate an AZ31/CNT nano-composite for surface hardening of lightweight structural components. The effects of double-pass FSP as well as groove depth (i.e., volume fraction of CNT) on the CNT distribution, dynamically recrystallized grain size, and resulting microhardness were studied. Double-pass FSP was performed for the CNT-filled plate-type specimen with different groove depths of 2, 3, and 4 mm. By applying double-pass FSP, the average size of CNT clusters decreased, implying a more homogeneous distribution. Compared with the FSPed specimen without CNT, grain size was refined from 19 μm to 3 μm and microhardness increased from 52 Hv to 83 Hv (i.e., 71% increase).

Since flexible devices are being used in various states of charge (SoCs), it is important to investigate SoCs that are durable against external mechanical deformations. In this study, the effects of a mechanical fatigue test under various initial SoCs of batteries were investigated. More specifically, ultrathin pouch-type Li-ion polymer batteries with different initial SoCs were subjected to repeated torsional stress and then galvanostatically cycled 200 times. The cycle performance of the cells after the mechanical test was compared to investigate the effect of the initial SoCs. Electrochemical impedance spectroscopy was employed to analyze the interfacial resistance changes of the anode and cathode in the cycled cells. When the initial SoC was at 70% before mechanical deformation, both electrodes well maintained their initial state during the mechanical fatigue test and the cell capacity was well retained during the cycling test. This indicates that the cells could well endure mechanical fatigue stress when both electrodes had moderate lithiation states. With initial SoCs at 0% and 100%, the batteries subjected to the mechanical test exhibited relatively drastic capacity fading. This indicates that the cells are vulnerable to mechanical fatigue stress when both electrodes have high lithiation states. Furthermore, it is noted that the stress accumulated inside the batteries caused by mechanical fatigue can act as an accelerated degradation factor during cycling.