Tae-Whan Hong

Dehydrogenation properties of nano-/amorphous Mg2NiHx by hydrogen induced mechanical alloying

Abstract In recent years, nanocrystalline materials have been of interest for hydrogen storage applications. Especially, the great improvement of the hydrogenation properties of Mg alloys that can be achieved by nanocrystallization. In this study, nanocrystalline Mg2NiHx is fabricated from Mg and Ni chips by hydrogen induced mechanical alloying (MA) for 96 h under a high-pressure hydrogen atmosphere. The balls to chips mass ratios (BCR) are 30:1 and 66:1. The particles obtained are characterized by XRD and TEM, and absorbed hydrogen contents (AHC) were measured by TGA. For dehydrogenation kinetics, activation energies are calculated by isothermal thermogravimetry analysis (ITGA) and pressure–composition-isotherm (PCI) analysis. The results of XRD and TEM revealed that the Mg2NiHx peaks are broadened in the case of high BCR and the particles are composed of the nanocrystalline phases less than 10 nm with the amorphous phase. The results of ITGA and PCI analysis show that the dehydrogenation kinetics are greatly improved by nanocrystallization. The results show that BCR conditions mainly affect the size and fraction of the nanocrystalline phases, the resultant AHC and the dehydrogenation kinetics.

Synthesis and hydrogenation behavior of Mg-Ti-Ni-H systems by hydrogen-induced mechanical alloying

Mg and Mg alloys are attractive hydrogen storage materials because of their lightweight and high absorption capacity. Their range of applications could be further extended if their hydrogenation properties and degradation behavior could be improved. The main emphasis of this study was to find an economic manufacturing method for Mg–Ti–Ni–H systems, and to investigate their hydrogenation properties. (Mg10−xTix)–10, 20 mass% Ni systems were prepared by hydrogen-induced mechanical alloying (HIMA) using Mg and Ni chips and sponge Ti. The particles synthesized were characterized by X-ray diffraction, and their morphologies were observed by means of scanning electron microscopy (SEM) with energy dispersive spectrometry (EDS). The absorbed hydrogen capacity (AHC) was measured by using thermogravimetry analysis (TGA) after HIMA. In addition, the crystal structures were analyzed in terms of their bright-/dark field images and the selected area diffraction pattern (SADP) of transmission electron microscopy (TEM). In order to examine hydrogenation behavior, a Sieverts type automatic pressure–composition–isotherm (PCI) apparatus was used and the experiments were performed at 423, 473, 523, 573, 623 and 673 K. The results of TGA reveal that the absorbed hydrogen contents are around 2.5 mass% for (Mg9Ti1)–10 mass% Ni. With increased Ni content, the absorbed hydrogen content decreases to 1.7 mass%, whereas the dehydriding starting temperatures are lowered by some 70–100 K. The results of PCI on (Mg9Ti1)–20 mass% Ni show that its hydrogen capacity is around 5.3 mass% and its reversible capacity and plateau pressure are also excellent at 523 and 573 K. In addition, the reaction enthalpy, ΔHD.plateau, is −30.6±5.7 kJ/mol H2.

FABRICATION AND ELECTRICAL PROPERTIES OF PZT-PVDF 0–3 TYPE COMPOSITE FILM

ABSTRACT A film speaker was fabricated with 0–3 type piezoelectric composite. The 0–3 type composite was developed to incorporate the advantages of both ceramic and polymer. The pastes of PZT-PVDF composite were made with various mixing ratio. The paste was printed by conventional screen-printing method on ITO (Indium Tin Oxide) bottom electrode which was deposited on PET (polyethylene terephthalate) polymer film. The prepared composite film was about 80 μm in thickness. After printing the top-electrode of silver-paste, 4 kV/mm of DC field was applied at 120°C for an hour to align the electric dipole in the 0–3 composite film. The piezoelectric charge constant of d33 was increased with increasing the PZT weight percent. The maximum value was 24 pC/N at 70 wt% of PZT. But the piezoelectric voltage constant of g33 had the maximum value about 32 mV · m/N at 65 wt% of PZT. The SPL (Sound Pressure Level) of the speaker fabricated with the 65:35 composite film was tested at various driving voltages of 1 ∼ 100Vrms. The SPL was saturated at the driving voltage of 70Vrms and the value was about 68 dB at 1 kHz.

Investment casting of AZ91HP magnesium alloy

This paper describes AZ91HP magnesium alloy investment casting. The aim of this study is to optimize the process for magnesium investment casting. Special attention was given to evaluating the thermal stability of oxides against molten AZ91HP magnesium alloy. The oxides examined included CaO, CaZr03, and silica bonded A1203 and ZrSi04. Also, the microstructural features of the as-cast alloy were investigated, and the effect of the processing parameters on the microstructure and mechanical properties were evaluated describing the grain size, hardness and ultimate tensile strength of the as-cast alloy.

Fabrication and evaluation of hydriding/dehydriding behaviors of Mg–10 wt.%Ni alloys by rotation-cylinder method

Abstract Even if the Mg–Ni alloys have been studied as one of the good lightweight hydrogen storage materials, the alloys have strong difficulties on fabrication process of mass products, until now. The Rotation–Cylinder Method (RCM) was initiated and has been developed to magnesium based composites with moderate rotation under normal atmosphere. In this study, the Mg–(1, 5, 10) wt.%Ni alloys were easily manufactured by RCM and evaluated to hydrogenation properties by Sieverts-type automatic pressure–composition–isotherm (PCI) apparatus at 523, 573 and 623 K. The evolution of microstructure of as-cast specimens appeared to be typical hypoeutectic structure. From the results of backscattered electron imaging (BEI) and energy dispersive X-ray spectrometry (EDS), the difference of composition between α-Mg and Ni-rich eutectic region was distinguished clearly. The hydrogenation properties of Mg–Ni alloys depended on the behavior of nickel compositions. The hydrogen capacity of Mg–10 wt.%Ni was 6.0∼6.2 wt.%, and the plateau pressures were around 0.026, 0.18 and 0.67 MPa at 523, 573 and 623 K, respectively. Finally, in the Mg–Ni alloys produced by the RCM process, α-Mg phase was regarded as hydrogen storage system and the eutectic area acted as the catalytic system.

Hydrogen Brittleness on Welding Part for SDS Bottles

Abstract >> Tritium was attracted with high energy source in neutron fusion energy systems. A number of researchwas performed in tritium storage materials. The Korea was raised storage and delivery systems (SDS) of internationalthermonuclear experimental reactor (ITER) research. However, bottles of SDS would be important because of stability. The bottles have a welding zone, this zone will be vulnerable to hydrogen embrittlement. This zone havea high thermodynamic energy and heat deterioration. Therefore bottles were studied about hydrogen embrittlementto retain stability. The heat treatment of hydrogen was carried under pressure-composition-temperature (PCT) apparatus because of checking at real time. And then, mechanical properties were evaluated by tensile test andhardness test. In results of this study, hydrogen atmosphere condition is very important by tensile test and kineticstest. The samples were evaluated, that is more weak hydrogen pressure, increasing temperature and time. This results could be useful in SDS bottle designs.Key words : Hydrogen embrittlement(수소 취성 ), Hydrogenation(수소화), Tensile test(인장 시험 ), Hardness(경도),Tritium storage(삼중수소저장), SDS(저장 및 공급)

Fabrication and Thermophysical Properties of Al2O3-Based Multicomponent Composites by Sol-Gel Process

has received wide attention with established use as a catalyst and growing application in structural or functional ceramic materials. On the other hand, the boehmite (AlO(OH)) obtained by sol-gel process has exhibited a decrease in surface area during phase transformation due to a decline in surface active site at high temperature. In this work, -CuO/ZnO (ACZ) and -CuO/CeO (ACC) composite materials were synthesized with aluminum isopropoxide, copper (II) nitrate hemi (pentahydrate), and cerium (III) nitrate hexahydrate or zinc (II) nitrate hexahydrate. Moreover, the Span 80 as the template block copolymer was added to the ACZ/ACC composition to make nano size particles and to keep increasing the surface area. The ACZ/ACC synthesized powders were characterized by Thermogravimetry-Differential Thermal analysis (TG/DTA), X-ray Diffractometer (XRD), Field-Emmision Scanning Electron Microscope (FE-SEM), Bruner-Emmett-Teller (BET) surface analysis and thermal electrical conductivity (ZEM-2:M8/L). An enhancement of surface area with the addition to Span 80 surfactant was observed in the ACZ powders from 105 /g to 142 /g, and the ACC powders from 103 /g to 140 /g, respectively.

Fabrication and Evaluation of Hydorgenation Propeties on Mg 8 Ti 2- (10, 20 wt.%)Ni Composites

The hydrogen energy had recognized clean and high efficiency energy source. The research field of hydrogen energy was production, storage, application and transport. The commercial storage method was using high pressure tanks but it was not safety. However metal hydride was very safety due to high chemical stability. Mg and Mg alloys are attractive as hydrogen storage materials because of their lightweight and high absorption capacity (about 7.6 wt%). Their range of applications could be further extended if their hydrogenation properties and degradation behavior could be improved. The main emphasis of this study was to find an economical manufacturing method for Mg-Ti-Ni-H systems, and to investigate their hydrogenation properties. In order to examine their hydrogenation behavior, a Sievert`s type automatic pressure-compositionisotherm (PCI) apparatus was used and experiments were performed at 423, 473, 523, 573, 623 and 673 K. The results of the thermogravimetric analysis (TGA) revealed that the absorbed hydrogen contents were around 2.5wt.% for (Mg8Ti2)-10 wt.%Ni. With an increasing Ni content, the absorbed hydrogen content decreased to 1.7 wt%, whereas the dehydriding starting temperatures were lowered by some 70-100 K. The results of PCI on (Mg8Ti2)-20 wt.%Ni showed that its hydrogen capacity was around 5.5 wt% and its reversible capacity and plateau pressure were also excellent at 623 K and 673 K.

Fabrication of Mg-Ni Hydrogen Storage Alloys by Rotation-Cylinder Method

For many years, the Mg−Ni alloys have been studied as good lightweight hydrogen storage materials, however, the alloys present strong difficulties in the fabrication process of mass products. The rotation-cylinder method (RCM) has been developed for magnesium based composites with moderate rotation under a normal atmosphere. In this study, the Mg-3, 6, 9, 12 mass% Ni alloys were easily manufactured by RCM and their hydrogenation properties were evaluated with a Sieverts-type automatic pressure-composition-isotherm (PCI) apparatus at 523, 573 and 623K. The evolution of the microstructure of as-cast specimens appeared to be a typical hypoeutectic structure. From the results of the backscattered electron image (BEI) and energy dispersive spectrometry (EDS), the difference between the composition of the α-Mg and Ni-rich eutectic regions was distinguished clearly. The hydrogenation properties of Mg−Ni alloys depended on the behavior of the nickel compositions. Especially, the hydrogen kinetics of Mg-9 mass% Ni was more excellent than the others.

Life Cycle Assessment for Proton Conducting Ceramics Synthesized by the Sol-Gel Process

In this report, the environmental aspects of producing proton conducting ceramics are investigated by means of the environmental Life Cycle Assessment (LCA) method. The proton conducting ceramics BaZr0.8Y0.2O3-δ (BZY), BaCe0.9Y0.1O2.95 (BCY10), and Sr(Ce0.9Zr0.1)0.95Yb0.05O3-δ (SCZY) were prepared by the sol-gel process. Their material requirements and environmental emissions were inventoried, and their energy requirements were determined, based on actual production data. This latter point makes the present LCA especially worthy of attention as a preliminary indication of future environmental impact. The analysis was performed according to the recommendations of ISO norms 14040 and obtained using the Gabi 6 software. The performance of the analyzed samples was also compared with each other. The LCA results for these proton conducting ceramics production processes indicated that the marine aquatic ecotoxicity potential (MAETP) made up the largest part, followed by fresh-water aquatic ecotoxicity potential (FAETP) and Human Toxicity Potential (HTP). The largest contribution was from energy consumption during annealing and calcinations steps.