• Journal of the Korean Society for Precision Engineering
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• v.22 no.6 s.171
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• pp.199-206
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• 2005

In this work, a theoretical investigation on the energy harvesting is undertaken using one of potential smart materials; piezoelectric material. The energy equations fur both square and circular types of the piezoelectric material are derived, and the energy generated from two commercially available Products: $PZT (Lead/Zirconium/Titanium: Pb(Zr,\;Ti)O_3)$ and PVDF (polyvinylidene fluoride) are investigated in terms of the thickness and area. In addition, a finite element analysis (FEA) is undertaken to obtain the generated energy due to the uniform pressure applied on the surface of the piezoelectric materials. A comparative work between the theory and the FEA is made followed by the brief discussion on the usage of the harvested energy for Bio MEMS.

• Proceedings of the Materials Research Society of Korea Conference
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• 2003.03a
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• pp.147-147
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• 2003

• Journal of Powder Materials
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• v.30 no.6
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• pp.521-527
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• 2023

Piezoelectric technology, which converts mechanical energy into electrical energy, has recently attracted drawn considerable attention in the industry. Among the many kinds of piezoelectric materials, BaTiO₃ nanotube arrays, which have outstanding uniformity and anisotropic orientation compared to nanowire-based arrays, can be fabricated using a simple synthesis process. In this study, we developed a flexible piezoelectric energy harvester (f-PEH) based on a composite film with PVDF-coated BaTiO₃ nanotube arrays through sequential anodization and hydrothermal synthesis processes. The f-PEH fabricated using the piezoelectric composite film exhibited excellent piezoelectric performance and high flexibility compared to the previously reported BaTiO₃ nanotube array-based energy harvester. These results demonstrate the possibility for widely application with high performance by our advanced f-PEH technique based on BaTiO₃ nanotube arrays.

• Journal of Powder Materials
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• v.10 no.6
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• pp.430-435
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• 2003

The phenomenon of electrical explosion of conductors is considered in the context of the changes in the energy and structural states of the metal at the stages of energy delivery and relaxation of the primary products of EEC. It is shown that these changes are related to the forced interaction of an intense energy flux with matter and to the subsequent spontaneous relaxation processes. The characteristics of nano-sized metal powders are also discussed. The preferential gas media during EEC is Ar+$H_2$. An increase in $e/e_s$ (in the range of values studied) leads to a reduction in the metal content. For reactive powders obtained with high metal content, it is necessary to separate the SFAP fractions, which settled on the negative electrode of the electric filter.

• Ceramist
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• v.22 no.4
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• pp.402-416
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• 2019

The development of next-generation secondary batteries, including lithium-ion batteries (LIB), requires performance enhancements such as high energy/high power density, low cost, long life, and excellent safety. The discovery of new materials with such requirements is a challenging and time-consuming process with great difficulty. To pursue this challenging endeavor, it is pivotal to understand the structure and interface of electrode materials in a multiscale level at the atomic, molecular, macro-scale during charging / discharging. In this regard, various advanced material characterization tools, including the first-principle calculation, high-resolution electron microscopy, and synchrotron-based X-ray techniques, have been actively employed to understand the charge storage- and degradation-mechanisms of various electrode materials. In this article, we introduce and review recent advances in in-situ synchrotron-based x-ray techniques to study electrode materials for LIBs during thermal degradation and charging/discharging. We show that the fundamental understanding of the structure and interface of the battery materials gained through these advanced in-situ investigations provides valuable insight into designing next-generation electrode materials with significantly improved performance in terms of high energy/high power density, low cost, long life, and excellent safety.

• Corrosion Science and Technology
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• v.19 no.2
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• pp.75-81
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• 2020

To reduce structural weight, light metals, including aluminum and magnesium alloys, have been widely used in various industries such as aircraft, transportation and automobiles. Recently, composite materials such as Carbon Fiber Reinforced Plastics (CFRP) and Graphite Epoxy Composite Material (GECM) have also been applied. However, aluminum and its alloys suffer corrosion from various factors, which include aggressive ions, pH, solution temperature and galvanic contact by potential difference. Moreover, carbon fiber in CFRP and GECM is a very efficient cathode, and very noble in the galvanic series. Galvanic contact between carbon fiber composites and metals in electrolytes such as rain or seawater, is highly undesirable. Notwithstanding the potentially dangerous effects of chloride and temperature, there is little research on galvanic corrosion according to chloride concentration and temperature. This work focused on the effects of chloride concentration and solution temperature on AA7075T6. The increased galvanic corrosion between CRFP and AA7075T6 was evaluated by electrochemical experiments, and these effects were elucidated.

• Corrosion Science and Technology
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• v.20 no.1
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• pp.26-36
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• 2021

Pipes operating in the seawater environment faces cavitation degradation and corrosion of the metallic component, as well as a negative synergistic effect. Cavitation degradation shows the mechanism by which materials deteriorate by causing rapid change of pressure or high-frequency vibration in the solution, and introducing the formation and explosion of bubbles. In order to rate the cavitation resistance of materials, constant conditions have been used. However, while a dynamic cavitation condition can be generated in a real system, there has been little reported on the effect of ultrasonic amplitude on the cavitation resistance and mechanism of composites. In this work, 3 kinds of epoxy coatings were used, and the cavitation resistance of the epoxy coatings was evaluated in 3.5% NaCl at 15 ℃ using an indirect ultrasonic cavitation method. Eleven kinds of mechanical properties were obtained, namely compressive strength, flexural strength and modulus, tensile strength and elongation, Shore D hardness, water absorptivity, impact test, wear test for coating only and pull-off strength for epoxy coating/carbon steel or epoxy coating/rubber/carbon steel. The cavitation erosion mechanism of epoxy coatings was discussed on the basis of the mechanical properties and the effect of ultrasonic amplitude on the degradation of coatings.

• 한국신재생에너지학회:학술대회논문집
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• 2009.11a
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• pp.383-383
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• 2009

Silicon is commercially prepared by the reaction of high-purity silica with wood, charcoal, and coal, in an electric arc furnace using carbon electrodes, so called the metallurgical refining process, which produces ~98% pure Si (MG-Si). This can be further purified to solar grade silicon (SoG-Si) by various techniques. The most problematic impurity elements are B and P because of their high segregation coefficients. In this study, we explored the possibility of the using Cat-CVD for Si purification. The existing hot-wire CVD was modified to accommodate the catalyzer and the heating source. Mo boat (1.5 cm ${\times}$ 1 cm ${\times}$ 0.2 cm) was used as a heating source. Commercially available Si was purchased from Nilaco corporation (~99% pure). This powder was kept in the Mo-boat and heated to the purification temperature. In addition to the purification by cat-CVD technique, other methods such as thermal CVD, plasma enhanced CVD, vacuum annealing was also tried. It is found that the impurities are reduced to a great extent when treated with cat-CVD method.

• Proceedings of the Korean Vacuum Society Conference
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• 2016.02a
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• pp.422.1-422.1
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• 2016

Graphene quantum dots (GQDs), a new kind of carbon-based photo luminescent nanomaterial from chemically modified graphene oxide (CMGO) or chemically modified graphene (CMG), has attracted extensive research attention in the last few years due to its outstanding chemical, optical and electrical properties. To further extended its potential applications as optoelectronic devices, solar cells, bio and bio-sensors and so on, intensive research efforts have been devoted to the CMG. However, the CMG, a suspension of aqueous, have problematic since they are prone to agglomeration after drying a solvent. In this study, we synthesized the GQDs from graphite and deposited on silicon substrate by kinetic spray. The photo luminescent properties of deposited GQD films were analyzed and compared with initial GQDs suspension. In addition, its carbon properties were investigated with GQDs solution properties. The properties of deposited GQD films by kinetic spray were similar to that of the GQDs suspension in water. We could provide a pathway for silicon-based silicon based device applications. Finally, the well-adjusted GQD films with photo luminescence effects will show Energy-Down-Shift layer effects on silicon solar cells. The GQD layers deposited at nozzle scan speeds of 40, 30, 20, and 10 mm/s were evaluated after they were used to fabricate crystalline-silicon solar cells; the results indicate that GQDs play an important role in increasing the optical absorptivity of the cells. The short-circuit current density (Jsc) was enhanced by about 2.94 % (0.9 mA/cm2) at 30 mm/s. Compared to a reference device without a GQD energy-down-shift layer, the PCE of p-type silicon solar cells was improved by 2.7% (0.4 percentage points).

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.36 no.6
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• pp.620-626
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• 2023

Energy harvesting technology, which converts wasted energy sources in everyday life into usable electric energy, is gaining attention as a solution to the challenges of charging and managing batteries for the driving of IoT sensors, which are one of the key technologies in the era of the fourth industrial revolution. Hybrid energy harvesting technology involves integrating two or more energy harvesting technologies to generate electric energy from multiple energy conversion mechanisms. In this study, a hybrid energy harvesting device called TMPPEG (thermo-magneto-piezoelectric-pyroelectric energy generator), which utilizes low-grade waste heat, was developed by incorporating PVDF polymer piezoelectric components and optimizing the system. The variations in piezoelectric output and thermoelectric output were examined based on the spacing of the clamps, and it was found that the device exhibited the highest energy output when the clamp spacing was 2 mm. The voltage and energy output characteristics of the TMPPEG were evaluated, demonstrating its potential as an efficient hybrid energy harvesting component that effectively harnesses low-grade waste heat.