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ZnO nanotubes with a wall thickness on the order of nanometers were produced by utilizing an organic template and atomic layer deposition (ALD). The organic template was removed by an O 2 plasma process and a thermal annealing process, with the wall structure of the ZnO nanotubes maintained during the removal of the template. We investigated the response of a ZnO nanotube to ethanol gas as a function of its wall thicknesses. The ZnO nanotubes with a wall thicknesses of 10 nm showed the highest gas response (defined as the ratio of electrical resistances, R air / R gas , under air atmosphere to the mixed air atmosphere with ethanol vapor) of 1184 toward 100 ppm at 450 °C. The ZnO nanotube with a wall thickness of 10 nm was wholly depleted and thus highly responds to the adsorption of chemical species on its surface. Accurate control of the wall thickness of the ZnO nanotubes is crucial to make ZnO nanotube sensors with high response.

From a Mg–23.5 wt%Ni–5 wt%Cu alloy synthesized by the gravity casting method in a large quantity (7.5 kg), Mg–23.5 wt%Ni–x wt%Cu (x = 2.5, 5 and 7.5) samples for hydrogen storage were prepared by melt spinning and crystallization heat treatment. The samples were ground under H2 in order to obtain a fine powder. These alloys contained crystalline Mg and Mg2Ni phases. The Mg–23.5Ni–2.5Cu alloy had the highest hydriding and dehydriding rates after activation among these alloys. The dehydriding curve under 1.0 bar H2 at 573 K exhibits two stages; the dehydriding rate is high for about 2.5 min (the decomposition of Mg2Ni hydride and Mg hydride in small particles), and then it becomes lower (the decomposition of Mg hydride). The hydriding and dehydriding properties of another sample 88 wt%(87.5Mg–10Ni–2.5Cu)–5 wt%Nb2O5–7 wt%NbF5 were also investigated.

The variations of the amount of hydrogen generated with the kind of powders and the condition of the magnesium and magnesium hydride powders were investigated. By the reaction of Al, TiH2 and unmilled and milled Mg powders with water, the H2 generation rates were very low and the quantities of H2 generated were extremely small. The quantity of H2 generated by the reaction of unmilled MgH2 powder with water was greater than those generated by the reactions of Al, TiH2, and unmilled and milled Mg powders with water. The MgH2 powder milled for 2 h, with finer particles, generated much more H2 by its reaction with water than unmilled MgH2 powder. The MgH2 + 5%MgO powder milled for 2 h generated much more H2 by its reaction with water than the Al, TiH2, unmilled Mg, milled Mg, unmilled MgH2, and milled MgH2 powders.

Nickel and purchased Fe2O3 or Fe2O3 synthesized by spray conversion were added to Mg via reactive mechanical grinding (mechanical grinding in H2). Samples with compositions of 71.5 wt%Mg–23.5 wt%Ni–5 wt%Fe2O3 (purchased) and 71.5 wt%Mg–23.5 wt%Ni–5 wt%Fe2O3 (synthesized by spray conversion) were prepared, and the phase changes in the samples were examined using X-ray diffraction analysis following hydriding–dehydriding cycling, as well as following reactive mechanical grinding. Both samples contained an Mg(OH)2 phase after hydriding–dehydriding cycling, as well as after reactive mechanical grinding. To the best of our knowledge, the formation of Mg(OH)2 phase is not reported in Mg-Ni-Fe2O3 system hydrogen storage materials.

3-Dimensionally porous tin oxide (SnO 2 ) foams were fabricated by an electrochemical deposition and their application for gas sensors was investigated. The electrochemical deposition was carried out in an electrolyte containing sulfuric acid and tin sulfate, and Sn film-coated SiO 2 /Si substrate was used as a cathode instead of conventional metal foil, which was deposited by a thermal evaporation. The porous Sn foam structure was formed during electrodeposition and its pore wall was composed of self-supported networked dendrites. The annealing at 700 °C converted the Sn foam into the corresponding metal oxide (SnO 2 ) foam with preserving the structural integrity and pore structure. The porous SnO 2 foam sensors responded to H 2 , CO, NH 3 , NO x , and C 2 H 5 OH gases. In particular, the foam sensors showed a significantly higher gas response toward C 2 H 5 OH, and the response time and working temperature were improved due to the rapid gas diffusion through 3D interconnected open porous structure.

Mg-based materials have a high potential for commercialization due to the large hydrogen storage capacity, low cost and abundance in the Earth's crust. Despite these advantages, reaction kinetics of Mg with hydrogen is slow. Various investigations to increase the hydriding kinetics of Mg were performed. Although LaNi5 has a low hydrogen storage capacity, it can store hydrogen at a low temperature. In this study, a Mg–23.5Ni–5Cu alloy was prepared by gravity casting method in a large quantity (approximately 7.5 kg), and then melt-spun and heat-treated. LaNi5, Nb2O5 or LaNi5 + Nb2O5 were added to the Mg–23.5Ni–5Cu alloy by reactive mechanical grinding in a planetary mill. The hydrogen storage capacity and hydriding behavior of the Mg–23.5Ni–5Cu alloys with LaNi5, Nb2O5 or LaNi5 + Nb2O5 added were then investigated.

Copper chip scrape has been occurred by cutting of copper pipe. The feasibility of copper chip scrape into the copper powder by milling was studied. Two milling type such as rod milling and horizontal balling milling were applied in this research. Copper chip can not fragmented into powder by using rod milling. In contrast to rod milling, copper chip can be changed into powder by horizontal ball milling for above 36 hours. It was found that recycling of copper chip scraps into copper powder by horizontal ball milling is possible and powder fraction percent () of milled copper chip for 48 hours is 25.3%.

Heteroepitaxial indium tin oxide (ITO) films were grown on three differently oriented yttria-stabilized zirconia (YSZ) substrates ((1 0 0), (1 1 0), (1 1 1)) by rf magnetron sputtering, and their structural characteristics and electrical and gas sensing properties were investigated. The initially formed ITO exhibited an island structure on the very thin layer and became a continuous film after the prolonged deposition. The heteroepitaxial relationships between ITO films and YSZ substrates were confirmed by X-ray diffraction, pole figure, and high resolution transmission electron microscopy (HRTEM). The chemical composition, determined by X-ray photoelectron spectroscopy (XPS), was slightly different at early stage depending on the substrate orientation, but it became similar after the longer deposition. Hall measurements indicated that the electrical resistivity of ITO films decreased with increasing the deposition time (or film thickness) irrespective of the film orientation. The ITO film deposited on (1 1 0) YSZ for 10 s showed the highest electrical resistivity. The gas sensor fabricated from the ITO film on (1 1 0) YSZ deposited for 10 s showed the highest NO2 gas response at relatively low temperature (100 °C), which was attributed to the higher Sn concentration and higher surface roughness of that film.

Vertically aligned TiO 2 nanotube arrays for H 2 gas sensor were fabricated by using atomic layer deposition combined with anodic aluminum oxide template. Morphology and crystalline structure of the TiO 2 nanotubes were characterized, and gas sensing properties at low temperatures ( 2 nanotubes with anatase phase were synthesized to be vertically aligned on the substrate and electrically interconnected with each other. The TiO 2 nanotube sensors were operated in air environment, and the highest magnitude of the gas response ( R air / R gas ) was determined to be ∼100 toward 1000 ppm H 2 /air at 100 °C. The sensor showed a very short response time ( 2 gas against several reducing gases including NH 3 , CO, and C 2 H 5 OH.

Mg-5wt%Ni-2.5wt%Fe-2.5wt%V (named Mg-5Ni-2.5Fe-2.5V) powder was prepared by reactive mechanical grinding using a planetary ball mill. The activation process, the changes in phase and microstructure with hydriding-dehydriding cycling, and the variations in the hydriding and dehydriding rates with temperature were investigated. The rate-controlling step for the dehydriding reaction of Mg-5Ni-2.5Fe-2.5V was analyzed by using a spherical moving boundary model. As the temperature increased from 473 K through 623 K, the initial hydrogen absorption rate under 12 bar H 2 decreased, while the hydrogen desorption rate under 1.0 bar H 2 increased.

Yttria stabilized zirconia (YSZ) coating was formed on AA1050 Al alloys by aerosol deposition (AD), and its electrochemical corrosion properties were investigated in 3.5 wt% NaCl and 0.5M H 2 SO 4 solutions. The crack-free, dense, and ~5 μm thick YSZ coating was successfully obtained by AD. The as-deposited coating was composed of cubic-YSZ nanocrystallites of ~10 nm size. The potentiodynamic test indicated that the YSZ coated Al alloy had much lower corrosion current densities (2 nA/㎠) by comparison to uncoated sample and exhibited a passive behavior in anodic branch. Particularly, a pitting breakdown potential could not be identified in H 2 SO 4 . EIS tests revealed that the impedance of YSZ coated sample was ~10 6 Ω㎠ in NaCl and ~10 7 Ω㎠ in H 2 SO 4 , which was about 3 or 4 orders of magnitude higher than that of uncoated sample. Consequently, the corrosion resistance of Al alloy had been significantly enhanced by the YSZ coating.

Divalent ytterbium-doped Ca-α-SiAlON phosphors were synthesized by a spark plasma sintering (SPS) method without a reducing gas. A single phase Ca-α-SiAlON:Yb2+ was successfully achieved at relatively low temperature of 1600 °C. Its photoluminescence excitation spectrum showed a broad band peaking at 450 nm due to the 4f135d1 → 4f14 transition of Yb2+ ions, while a corresponding green emission band was observed at 545 nm. The post-annealing in a reduced atmosphere significantly improved the luminescent properties by increasing the crystallinity, reducing the carbon contamination, and changing the residual Yb3+ to Yb2+ in as-synthesized samples. The post-annealed powders, compared to commercial YAG:Ce3+ and silicate phosphors, showed a low thermal quenching due to the rigid crystal structure.

Ga2O3/SnO2 core–shell nanowires were synthesized by combining thermal evaporation and atomic layer deposition (ALD), and nanowire network sensors were fabricated by directly depositing them on the substrate with interdigitated Pt electrodes. Crystalline Ga2O3 nanowires of ∼20 nm diameter were grown on Au-catalyzed substrate at 800 °C. ALD-grown SnO2 shell layer was composed of interconnected nanoparticles of

The magnesium prepared by mechanical grinding under H 2 (reactive mechanical grinding) with transition elements or oxides showed relatively high hydriding and dehydriding rates when the content of additives was about 20 wt%. Ni and Fe were chosen as transition elements to be added. Ti was also selected since it was considered to increase the hydriding and dehydriding rates by forming Ti hydride. Samples Mg–14Ni–6Fe 2 O 3 , Mg–14Ni–6Ti, Mg–14Ni–3Fe 2 O 3 –3Ti, and Mg–14Ni–2Fe 2 O 3 –2Ti–2Fe were prepared by reactive mechanical grinding, and their hydrogen storage properties were examined. Among these samples, Mg–14Ni–6Ti had the highest hydriding and dehydriding rates.

Epitaxial SnO 2 thin films were grown on (1 1 0) (a-cut) and (1 0 0) (m-cut) sapphire substrates using plasma enhanced atomic layer deposition (PEALD) with dibutyltindiacetate (DBTDA) as a precursor. X-ray diffraction, X-ray pole figure, and high resolution TEM analyses revealed that SnO 2 film deposited on a-cut sapphire was (1 0 1) oriented with a small component of (2 0 0) orientation, and the (1 0 1) planes were slightly tilted due to the presence of (2 0 0) plane and/or twinning. SnO 2 film on m-cut sapphire was strongly (0 0 1) oriented with a small amount of the (3 0 1) orientation. The determined in-plane orientation relationships were [0 1 0]SnO 2 //[0 0 1]Al 2 O 3 and [1 0 1]SnO 2 //[1 1 0]Al 2 O 3 (a-cut) and [0 1 0]SnO 2 //[0 0 1]Al 2 O 3 and [1 0 0]SnO 2 //[0 1 0]Al 2 O 3 (m-cut) consistent with the previous reports.

Mg-23.5 wt%Ni-xwt%Cu (x=2.5, 5 and 7.5) samples for hydrogen storage were prepared by melt spinning and crystallization heat treatment from a Mg-23.5 wt%Ni-5 wt%Cu alloy synthesized by the gravity casting method. They were then ground under H2 to obtain a fine powder. Among these samples the Mg- 23.5Ni-2.5Cu sample had the highest hydriding and dehydriding rates after activation. The Mg-23.5Ni-2.5Cu sample absorbed 3.59 and 4.01 wt%H for 10 and 60 min, respectively, at 573K under 12 bar H2. The activated 88(87.5Mg-10Ni-2.5Cu)-5Nb2O5-7NbF5 sample absorbed 2.93 wt%H for 10 min, and 3.14 wt%H for 60 min at 573K under 12 bar H2.

Red emitting nano-sized Y(P,V)O 4 :Eu 3+ phosphors were prepared by liquid phase precursor (LPP) method followed by grinding in planetary ball mill, and their photoluminescence (PL) properties were investigated. A single phase Y(P,V)O 4 :Eu 3+ phosphor was successfully synthesized by LPP process, and as-synthesized phosphor exhibited an elongated morphology of ∼2 μm long and ∼400 nm wide. The planetary ball milling yielded a spherical nano-powder of ∼100 nm size and its PL intensity decreased to 17% of as-synthesized phosphor due to some degree of amorphization. The subsequent annealing at 1100 °C produced a well-crystallized, polygonal shaped Y(P,V)O 4 :Eu 3+ nano phosphor of ∼300 nm size and its PL intensity increased to 120% compared to both as-synthesized and commercial Y(P,V)O 4 :Eu 3+ phosphors.

A Mg-23.5wt%Ni-5wt%Cu alloy was synthesized by the gravity casting method in a large quantity (7.5 kg). From this alloy, Mg-23.5wt%Ni-xwt%Cu (x = 2.5, 5 and 7.5) samples for hydrogen storage were prepared by melt spinning and crystallization heat treatment. The samples were ground under H2 in order to obtain a fine powder. These alloys contained crystalline Mg and Mg2Ni phases. The Mg-23.5Ni-2.5Cu alloy had the highest hydriding and dehydriding rates after activation among these alloys. The dehydriding curve under 1.0 bar H2 at 573 K exhibits two stages; the dehydriding rate is high for about 2.5 min (the decomposition of Mg2Ni hydride and Mg hydride in small particles), and then it becomes lower (the decomposition of Mg hydride).

Mg–15 wt%Ni–5 wt%Fe 2 O 3 (Mg155) was prepared by reactive mechanical grinding (RMG). Mg155 exhibited high hydriding and dehydriding rates even at the first cycle, and its activation was completed after only two hydriding–dehydriding cycles. The activated Mg155 absorbed 5.06 and 5.38 wt% of hydrogen, respectively, for 5 and 60 min at 573 K under 12 bar H 2 . It desorbed 1.50 and 5.28 wt% of hydrogen, respectively, for 5 and 60 min at 573 K under 1.0 bar H 2 . The initial hydrogen absorption rate decreased, but the hydrogen desorption rate increased rapidly with an increase in temperature from 563 K to 603 K. The rate-controlling step for the dehydriding reaction in a range from F ≃ 0.20 to F ≃ 0.75 is considered to be the chemical reaction at the Mg hydride/α-solid solution interface. The absorption and desorption PCT curves exhibited two plateaus at 573 K. The hydrogen-storage capacity of the activated Mg155 was about 6.43 wt% at 573 K.

The fabrication of nano-porous SnO 2 films with 1-D nano-channels by anodic oxidation has been a challenge due to a collapse of pore structure during annealing process and an existence of non-porous upper barrier layer. A new approach is developed to synthesize the nano-porous SnO 2 films by employing Sn thin film instead of Sn foil and a reactive ion etching (RIE) process. The integrity of nano-porous structure was maintained by anodizing the Sn thin film deposited on SiO 2 /Si substrate, and 1-D nano-channels were opened up by removing the non-porous layer by RIE. As a potential application to gas sensor, CuO was impregnated to the nano-porous SnO 2 films and their gas sensing properties were investigated. The nano-porous CuO–SnO 2 film sensors exhibited the enhanced sensitivity and selectivity toward H 2 S gas, and their H 2 S sensing mechanism was discussed in terms of the formation/disruption of resistive p-CuO/n-SnO 2 junction based on the variation of XPS binding energy and electrical resistance during gas exposure.

Highly aligned single crystal SnO2 (101) nanowires were epitaxially grown on TiO2 (101) substrates by thermal evaporation via Au-catalyzed vapor−liquid−solid (VLS) growth. The orientation relationship and interface structure between the nanowires and the substrate were determined by X-ray pole figure and high resolution transmission electron microscopy (HR-TEM) combined with the focused ion beam (FIB) lift-out technique. Epitaxially grown SnO2 (101) nanowires exhibited three angular growth directions ([101], [011], and [011]) with different inclination angles to the substrate due to a tetragonal crystal structure. An atomic stacking model was proposed to describe the angular growth of SnO2 (101) nanowires with ⟨101⟩ growth directions. The obtained results are expected to provide an understanding of the growth direction of nanowires and heteroepitaxial relationships between nanowires and substrate to synthesize the well-aligned SnO2 nanowires, which can be integrated into the electronic devices and lead t...

Specimen charging that is associated with the electron bombardment on the sample is a practical hindrance to high-resolution transmission electron microscopy (HRTEM) analysis because it causes a severe loss of resolution in either diffraction or image data. Conductive thin film deposition on an insulating specimen has been proposed as an effective approach to the mitigation of the specimen charging; however, this method is generally not useful in HRTEM imaging of materials because the deposited film induces another artifact in the HRTEM image contrast. In this study, we propose practical methods to mitigate the specimen charging that takes place during the HRTEM of materials. For bulk-type specimens prepared by either an ion-thinning or focused-ion beam (FIB) process, a plasma cleaning treatment is significantly effective in eliminating the charging phenomenon. In the case of low-dimensional nanomaterials such as nanowires and nanoparticles, the plasma cleaning is not feasible; however, the charging effect can be effectively eliminated by adjusting the electron illumination condition. The proposed methods facilitate a decrease in the buildup of specimen charging, thereby enhancing the quality of high-resolution images significantly.

The activated 76.5 wt%Mg–23.5 wt%Ni (Mg–Ni) has a lower hydriding rate, compared with Mg–23.5 wt%Ni heat-treated after melt spinning, due to the nonhomogeneous distribution of Ni particles in the mixture and the larger sizes of the particles. Among 76.5 wt%Mg–23.5 wt%Ni (Mg–Ni), 71.5 wt%Mg–23.5 wt%Ni–5 wt%Fe2O3 (Mg–Ni–O), and 71.5 wt%Mg–23.5 wt%Ni–5 wt% Fe2O3(spray conversion) (Mg–Ni–Osc) samples, Mg–Ni–Osc has the highest hydriding and dehydriding rates. The reactive mechanical grinding of Mg with Ni, purchased Fe2O3 or Fe2O3(spray conversion) is considered to facilitate nucleation and shorten diffusion distances of hydrogen atoms. After hydriding–dehydriding cycling, all the samples contain Mg2Ni phase. The samples with Fe2O3 and Fe2O3(spray conversion) as starting materials contain Mg(OH)2 phase after hydriding–dehydriding cycling as well as after reactive mechanical grinding.

The need for high performance electrochemical energy storage devices has increased due to the fast development of portable electronics and electric vehicles. For decades, lithium ion batteries (LIBs) have been considered as one of the most attractive examples in many electric applications, because of their high energy density and good power performance. However, its limited resource restricts the application of LIBs for large-scale energy storage systems. Among many other candidates, sodium ion batteries (SIBs) have been demonstrated as a promising alternative for its high abundance in earth crust and sea water. In recent years, there were numerous attempts to find new anode materials for high performance SIBs, including carbonaceous materials, metal oxides, phosphides, and alloy-based materials. Transition metal sulfides have received much interests as promising SIB anode materials because of their high theoretical capacity and good electrical conductivity. Numerous researches have been reported about iron sulfide, cobalt sulfide, and many others with good electrochemical properties. Among them, nickel sulfides have great advantages such as high theoretical capacity, low cost, and environmental friendliness. Especially, nickel disulfide (NiS2) delivers a theoretical capacity of 873 mAh/g, according to conversion reaction (NiS2 + 4Na = Ni + 2Na2S). However, like other conversion-type transition metal sulfides, NiS2 suffers from large volume changes which cause structural pulverization problem. To overcome this hindrance, synthesizing the composite with carbon or forming 3D network has been generally adopted. Such modifications help the active material to buffer volume changes and ensure its structural integrity. Herein, we report the electrochemical properties of NiS2 nanospheres synthesized by hydrothermal process as an anode for SIB. Compared to micro sized particles, nanospheres have superior rate capability due to shorter Na ion and electron diffusion path during the electrochemical process by offering large contact areas between electrode and electrolyte. Also, it is well known that nanoscale particles prevent the accumulation of internal stresses during volume changes. Therefore, they show the improved cyclability by additional inhibition of crack formation within the particles. NiS2 powders were synthesized via a simple hydrothermal method. Ni nitrate hexahydrate (Ni(NO)36H2O) and L-cysteine (C3H7NO2S) were used for nickel and sulfur source respectively. First, they were dispersed in DI water and hexadecyltrimethylammonium bromide (CTAB, C19H42BrN) was added as surfactant. Then the mixture solution was transferred to stainless steel autoclaves and maintained at 160 °C for 12 h. After they were cooled to room temperature, the mixture was filtrated and the separated black precipitate was dried at 50 °C under vacuum. The resulting powder was confirmed to be NiS2 by XRD with particle size of ~120 nm. The first discharge and charge curves are shown in Fig. 1. The first discharge capacity achieved was 837 mAh/g, which is 96 % of the theoretical value. The first charge capacity was 696 mAh/g, corresponding to the coulombic efficiency of 83%. Based on these results, we tried various methods such as carbon coating, to improve electrochemical properties of NiS2 nanospheres. Figure 1

Lithium ion batteries (LIBs) has been the main energy storage medium for portable electronics since the commercialization by Sony Corporation since 1991. Ever growing demand for large-scale energy storage devices such as electrical vehicles requires the high energy density and long cycle life LIBs that could not be attained by the currently used battery. Graphite is the most common anode material in commercial LIBs, but its specific capacity is relatively low (372 mAh g-1) with a poor rate capability, which does not meet the high demand for large-scale applications. Silicon (Si) is one of the most promising anode candidates due to its high theoretical specific capacity (3579 mAh g-1 for Li15Si4), relatively low discharge potential (~0.4V vs Li+/Li), and abundance in nature. However, Si goes through a dramatic volume change during cycling and thus undergoes a drastic structural deformation, which induces loss of electrical contact between Si and current collector, breakdown of solid electrolyte interphase (SEI) layer, and Si aggregation during cycling, eventually resulting in failure of cyclic performance. Although design a various nanostructure forms or introduction of secondary phase layers has been realized as a method to achieve high-performance Si anode, these methods require complex reactions such as hydrothermal or template-assisted synthesis and usually involve hazardous reagents like SiH4 or HF, which eventually result in cost and barrier to scale up. From the practical view, use of commercial Si is the most promising, where the commercial production of Si has been benefitted from the development in semi-conductor industry. Conventionally, battery is prepared by mixing active materials and binder with conducting agent in organic solvent to produce viscous slurry and blading onto copper current collector. Recently, the selection of binder has turned out to play critical role in the battery performance as maintaining the structural integrity of electrode film. It has been revealed that carboxylic acid or hydroxyl functional groups terminated binders which is commercially available, such as polyacrylic acid (PAA), carboxymethyl cellulose (CMC or Na-CMC) or alginate (Alg or Na-Alg) binder, can result in enhanced cycling performance utilizing the hydrogen bonding interactions with the native oxide on Si, compared to that of conventional PVDF binder which has no functional group and bonds weekly with Si through a week Van der Waals interaction. Nonetheless, due to the linear chain characteristic of these binders, susceptible sliding upon the continual volume change of Si results in the contact loss between binder and Si, which eventually results in the irreversible capacity failure. Herein, we propose a novel concept that can achieve stable Si anode by transitioning the bonding nature between binder and Si from hydrogen bond to mechanically robust covalent bond, which can effectively restrain any large movement of Si, and eventually prevent the destruction of the electrical network during cycling. Inducing the esterification reaction between binder and Si can be an efficient method to form a covalent bond between those two materials. (eq. (1)) R-COOH+HO-R’ -> R-COO-R’+ H2O -------- (1) To induce an esterification reaction between binder and Si, three crucial points have to be addressed. First, as carboxylate (–COO-) functional group terminated binder such as Na-CMC can hardly react with the hydroxyl functional group (-OH), PAA binder which is terminated with the carboxylic acid functional group (-COOH) has been selected in our system. Second, while commercially purchased Si has a –OH functional group by a partially hydrolyzed SiO2 layer covering the Si particles, its functional group density is insufficient for an esterification reaction to take place. Therefore, terminating –OH functional group at the surface of Si is crucial factor to increase the site to react with PAA binder. Third, due to kinetically sluggish characteristic of esterification reaction, proper usage of esterification catalyst is required. Experimental procedure is as follows; firstly, as-received Si was pretreated in piranha solution to terminate –OH. Then, –OH terminated Si was prepared into slurry by mixing with Super-P and PAA binder, casted onto copper foil, dried overnight and punched for a coin-type cell. To induce the esterification reaction, punched cell was dipped into sodium hypophosphite catalyst solution and then annealed in 180 °C for 1 h. Three counter groups are denoted as HB-Cell (punched cell with no annealing process), PE-Cell (annealed cell without usage of sodium hypophosphite), and FE-Cell (annealed cell with addition of sodium hypophosphite.) The fabricated FE-Cell exhibits superior cycle stability (2200 mAh g-1 at 100 cycles) compare to HB-Cell or PE-Cell, demonstrating the effect of covalent bond on obtaining the high-performance Si anode. Figure 1

Blue emitting CaAl 2 O 4 :Eu 2+ (CA:Eu 2+ ) phosphors were prepared by combining Pechini method and planetary ball milling, and their photoluminescence (PL) properties were investigated. A single phase monoclinic CA:Eu 2+ phosphor was synthesized by Pechini process using two-step annealing; first annealing at 1400 °C in air and second annealing at 1450 °C in 5% H 2 /N 2 atmosphere. The obtained CA:Eu 2+ phosphor exhibited a blue emission at 440 nm under the excitation of λ exc = 340 nm, but the particle size was unexpectedly large with irregular shape (5–50 μm). The subsequent planetary ball milling and two-step re-annealing produced more rounded powders (2–3 μm) with smoother surfaces. Its PL intensity increased to 135% compared to the phosphor synthesized by Pechini process and comparable to that of the commercial BaMgAl 10 O 17 :Eu 2+ (BAM) phosphor.

Epitaxial SnO2 films were deposited on TiO2 single crystals with various orientations by plasma enhanced atomic layer deposition (PEALD), and their structural characteristics and gas sensing properties were investigated, particularly focusing on the crystallographic orientation dependence of H2 gas response. Dibutyltindiacetate (DBTDA) was used as Sn source, and (1 0 0), (0 0 1), (1 1 0), and (1 0 1) TiO2 were employed as substrates for SnO2 deposition. All the SnO2 films were ∼90 nm thick after 1000 ALD cycles and epitaxially grown on TiO2 substrates, which were confirmed by X-ray pole figure and high resolution transmission electron microscopy (HRTEM). Differently oriented epitaxial SnO2 films showed the different H2 gas response and different temperature dependence of gas response. The (1 0 1) SnO2 films grown on (1 0 1) TiO2 exhibited the highest H2 gas response of ∼380 toward 1000 ppm H2/air at 400 °C, which was associated with the different temperature dependence of resistance in (1 0 1) film rather than the microstructural characteristics and chemical composition compared to the other films.

The influence of grain size on the wear behavior of zirconia ceramics was investigated when slided against steel in dry unlubricated conditions. Fully densified Y-TZP ceramics (≥98% of theoretical density) with a wide range of grain size from 75 to 1470 nm were developed using spark plasma sintering (SPS), microwave sintering (MS), and conventional pressureless sintering (CS) methods. SPS was effective in producing fully densified nanocrystalline zirconia at low temperature and short sintering time. The steady state coefficient of friction (COF) varied in a range of 0.35–0.44, but the wear rate reduced from 3.5 to 0.88 × 10−6 mm3/Nm with decreasing grain size. The plastic deformation and microcracking lead to a mild wear for the nanocrystalline zirconia, whereas the delamination/spalling results in the increased wear for the coarser zirconia.

The nano-sized cobalt powders were prepared using a pulsed wire evaporation method. The cobalt powder had a spherical shape with a diameter of less than 200 nm. A cobalt electrode was prepared from the nano-sized cobalt powder, acetylene black and polyvinylidene fluoride. During the first discharge, the Li/Co cell showed a plateau potential of 0.7V and a capacity of 440mAh/g. The nano-sized Co electrode had a stable reversible lithium storage capacity of approximately 280mAh g−1 after 30 cycles.

Hybrid coatings of poly( L -lysine) and apatite were formed on the micro-arc oxidized titania through a biomimetic process. Phosphorous (P)-containing titania films were prepared by micro-arc oxidation (MAO) of titanium (Ti) substrates in an electrolyte solution containing β-glycerol phosphate disodium salt pentahydrate. The hybrid coatings were grown by immersing MAO titania in the poly( L -lysine)-containing simulated body fluid (SBF) solution. After 72 h immersion, the globular precipitates appeared on the surface of titania films and grew up to ~ 10 µm. These precipitates consisted of 100–200 nm nano-flakes with a distorted (less straight) morphology. XRD and FT-IR confirmed that these precipitates were poly( L -lysine)-containing apatite nanocomposite.

Cobalt (Co) and tantalum (Ta) co-substituted BiFeO3 polycrystalline ceramics were prepared by a solid-state reaction and their magnetic and dielectric properties were investigated. Magnetic hysteresis loops were clearly observed in co-substituted specimens and magnetization was greatly improved. The co-substitution decreased the electrical conductivity by six orders of magnitude along with the reduction of grain size. The magnetoelectric coupling was estimated in co-substituted BiFeO3 by determining the changes of the dielectric constant with an external magnetic field.

In this study, bulk nano-crystalline Si₃N₄ ceramics were fabricated by spark plasma sintering (SPS) and their mechanical properties, in particular wear, were investigated. A wide range of grain sizes, from 80 ㎚ and 250 ㎚ were obtained by varying sintering conditions (1550℃-5 min to 1650℃-20 min). The elastic modulus of obtained ceramics was ~250 ㎬ and hardness was in the range of 13~14 ㎬. The indentation fracture toughness increased from 2.58 ㎫·m 1/2 to 3.24㎫·m 1/2 with increasing sintering temperature possibly due to the elongated grains. Sliding wear tests revealed at least an order magnitude improvement in wear resistance with grain refinement. Microstructure analysis indicated that nano-Si₃N₄ specimens worn mainly through delamination and microcracking, while that of coarser specimens revealed severe wear with grain debonding and fracture.

Y(P,V)O4:Eu phosphor prepared by liquid phase precursor(LPP) method was modified by planetary ball milling and nano-sized powder with spherical shape was successfully obtained. A post-annealing was conducted at 1100 ° for 1 h to enhance the crystallinity and photoluminescence property.

MoO3 nanoparticles were prepared by thermally oxidizing the MoO2 nano-crystallites synthesized by solvothermal reaction, and their gas sensing properties were investigated. Ethanol and water mixed solvents were used in the solvothermal synthesis, and it was observed that the phase, size, and morphology of the products were strongly dependent on the composition of solvents. Well-crystallized and spherical MoO2 nano-crystallites (~20 nm) were obtained in the mixed solvent (water:ethanol = 40:10 in vol), and subsequent heat treatment at 450 °C produced the well-separated, slightly elongated MoO3 nano-particles of ~100 nm. The nano-particle MoO3 gas sensor responded to both oxidizing and reducing gases, but it exhibited the extremely high gas response toward H2S with a short response time (

The green emitting Ca 2 SiO 4 :Eu 2+ (C 2 S:Eu) phosphors were synthesized by the polymeric precursor process (Pechini-type), and the effects of calcination temperature and europium (Eu) doping concentration on the luminescent properties were investigated. The crystalline β-C 2 S was obtained in the calcination temperature of 1100°―1400°C, and Eu was reduced into Eu 2+ by annealing in 5% H 2/ N 2 atmosphere. The obtained C 2 S:Eu 2 + phosphors exhibited a strong emission at 504 nm under the excitation of λ exc = 350 nm. The highest photoluminescence (PL) intensity was observed in the C 2 S:Eu 2+ phosphors either calcined at 1300°C or doped with 3 mol% Eu. The obtained PL properties were discussed in terms of crystal structure, particle size and shape, surface roughness, and effect of concentration quenching.

Melt spun Mg–23.5Ni and 90%(ms Mg–23.5Ni)–10%Nb 2 O 5 alloys were prepared by reactive mechanical grinding. The activated 90%(ms Mg–23.5Ni)–10%Nb 2 O 5 alloy has higher hydriding and dehydriding rates than the activated melt spun Mg–23.5Ni alloy. The activated 90%(ms Mg–23.5Ni)–10%Nb 2 O 5 alloy absorbs 4.70 wt% H for 10 min at 573 K under 12 bar H 2 , and desorbs 4.75 wt% H for 25 min at 573 K under 1.0 bar H 2 . The added Nb 2 O 5 and/or their pulverization during mechanical grinding are considered to make Mg particles finer. This is considered to make the activated 90%(ms Mg–23.5Ni)–10%Nb 2 O 5 alloy has higher hydriding and dehydriding rates than the activated melt spun Mg–23.5Ni alloy. The hydrogen-storage properties of the 90%(ms Mg–23.5Ni)–10%Nb 2 O 5 alloy were compared with those of other alloys prepared under similar conditions.

Mg and its alloys have attracted an extensive attention in the field of structural materials such as automobile components, aerospace components, and computer parts due to high strength/weight ratio, good electromagnetic shielding, high thermal conductivity and good recycling ability (1). Furthermore, the use of magnesium alloys with a low density in the automotive industry is predicted to be continuously expanded because of the demands for reducing environmental burden and improving energy efficiency (2). However, magnesium and its alloys are extremely susceptible to corrosion resulting in decreased mechanical stability and surface contamination, so this point greatly restricts their applications (3). To enhance the poor corrosion resistance, various physical and chemical surface treatments have been performed. Among the various techniques, chemical-conversion coating is widely used, but conventional conversion coatings are gradually restricted because it is based on chromium compounds that have been shown to be highly toxic carcinogens (1,4). Thus, micro-arc oxidation (MAO), which is an environmental friendly process and is capable of protecting the magnesium alloys from corrosion and wear condition, has been attracting a renewed interest over the last few years(5). The extensive researches have been carried out in evaluating the effect of electrolyte composition and applied potential on the properties of MAO films. However, the effect of electrolyte compositions on the corrosion behavior of MAO films has not yet been discussed in detail. Thus, the aim of this work is to develop a proper MAO films on AZ91D magnesium alloy in various electrolyte solution. Corrosion behavior of these oxide films was evaluated in terms of electrolyte composition and concentration, and we examine relation between electrolyte condition and corrosion behavior. In this study, the protective oxide coatings were formed on AZ91D magnesium alloys by micro-arc oxidation (MAO) in several aluminate electrolytes containing potassium hydroxide, potassium fluoride, and sodium hydroxide. MAO was conducted in the range of current density between 13 – 21 A/dm using a pulse power supply for 10 – 60 min. The corrosion resistance of MAO films was performed by EG&G potentiostat/galvanostat model 273 with model 352 corrosion software in 3.5 % NaCl solution at pH 7.0. The crystalline MgO and MgAl2O4 spinel phases along with amorphous phase were detected by XRD (Fig. 1). With increase of electrolyte concentrations, the content of crystalline MgO and MgAl2O4 phases decreased and coating layers became more porous (Fig. 2). While using a less conductive electrolyte raises the breakdown voltage, it also increases the arc duration. In addition, all MAO specimens exhibited superior corrosion resistance compared to untreated AZ91D. The results indicate that the phase, morphology, thickness, and corrosion resistance of MAO films were found to be strongly dependent on electrolyte concentration and surface current density. Surprisingly, MAO films composed of amorphous phase showed much better corrosion resistance than MAO films with crystalline MgO and MgAl2O4 (Fig. 3).

95%(gravity cast Mg–23.5Ni)–-5%Nb 2 O 5 alloy was prepared by horizontal ball milling in n-hexane of gravity cast Mg–23.5wt%Ni with Spex milled Nb 2 O 5 . Melt spun Mg–23.5wt%Ni after heat treatment at 523 K for 1 h was also ground by planetary ball milling with finer Nb 2 O 5 prepared by milling with NaCl. The activated 90%(melt spun Mg–23.5Ni)–10%Nb 2 O 5 alloy shows higher hydriding and dehydriding rates than the activated 95%(gravity cast Mg–23.5Ni)–5%Nb 2 O 5 alloy, thanks to the homogeneous distribution of fine Mg 2 Ni phase in melt spun Mg–23.5Ni and the finer Nb 2 O 5 addition to melt spun Mg–23.5Ni, which leads to the effective diminution of the Mg particle size. The activated 90%(ms Mg–23.5Ni)–10%Nb 2 O 5 alloy absorbs 4.70 wt%H at 573 K under 12 bar H 2 for 10 min, and desorbs 4.75 wt%H at 573 K under 1.0 bar H 2 for 25 min.

SnO2 porous structure was fabricated by anodic oxidation. The Sn coated SiO2/Si wafer was used as an anode and it was anodized in 0.3 M oxalic acid aqueous solution using DC power supply. The phase of formed oxide was rutile and the morphology showed a nano porous structure. The porous SnO2 with nano-channel was obtained at 6V in 0.3 M oxalic acid and the pore diameter was approximately 20 nm. A post annealing was performed at 500 ° for 3 h to enhance the crystallinity. To evaluate the gas sensing properties, a comb like Pt pattern was deposited on the anodized and annealed specimen and its gas sensing properties were measured as a function of gas concentration and working temperature

The 90 wt.% (Mg–23.5 wt.% Ni)–10 wt.% Ta2O5 alloy (designated as (Mg–23.5Ni)–10Ta2O5) was prepared by pulverizing the melt spun and heat treated Mg–23.5 wt.% Ni alloy with the Ta2O5 prepared by spray-conversion in a planetary ball mill. The activated (Mg–23.5Ni)–10Ta2O5 alloy had a higher hydriding rate than the activated Mg–23.5Ni alloy but a similar dehydriding rate. The activated (Mg–23.5Ni)–10Ta2O5 alloy absorbed 4.64 wt.% H for 5 min (i.e., a hydriding rate of 0.93 wt.% H/min) at 573 K, and desorbed 5.02 wt.% H for 5 min (i.e., a dehydriding rate of 1.00 wt.% H/min) at 623 K. The activated (Mg–23.5Ni)–10Ta2O5 alloy exhibited a hydrogen-storage capacity of 6.68 wt.% H.

The effects of Nb and Co ion substitution on the dielectric and magnetic properties of the multiferroic BiFeO₃ thin films have been investigated. Heteroepitaxial BiFeO3 thin films were deposited by Pulsed Laser Deposition method. Nb substitution decreased the leakage current by 6 orders of magnitude and Co substituted BiFeO₃ thin films showed an enhanced magnetization, 2 times larger than that of un-substituted BiFeO₃. Through the co-substitution of Co and Nb, BiFeO₃ thin films with a low leakage current and an enhanced magnetization could be obtained.

Mg-10wt%Ni-5wt%Fe-5wt%Ti powder was prepared by reactive mechanical grinding using a planetary ball mill. The Mg-10wt%Ni-5wt%Fe-5wt%Ti powder exhibited high hydriding and dehydriding rates even at the first cycle, and its activation was completed after two hydriding–dehydriding cycles. After the reactive mechanical grinding, the particle size of the powder was reduced, as compared with those of the starting materials. The hydrogen storage properties were measured at temperatures of 473 K, 573 K and 623 K. The activated Mg-10wt%Ni-5wt%Fe-5wt%Ti powder absorbed 5.31 wt% and 5.51 wt% of hydrogen for 5 min and 1 h, respectively, at 573 K under 12 bar H2. It desorbed 5.18 wt% of hydrogen at 573 K under 1.0 bar H2 for 1 h. The initial hydrogen absorption rate increased when passing from 473 K to 573 K, but decreased at 623 K. The hydrogen desorption rate increased rapidly with increasing temperature from 473 K to 623 K. The hydrogen storage capacity was about 6.72 wt% at 573 K.

Mg–23.5 wt.%Ni–(5, 10 and 15 wt.%)La alloys were prepared by gravity casting and their hydrogen-storage properties were examined after pulverizing. The gravity cast Mg–23.5Ni–(5, 10 and 15)La alloys consist of α-Mg, Mg2Ni and Mg17La2 phases. The activated Mg–23.5Ni–10La alloy has the highest hydrogen-storage capacity of 4.96 wt.%H (from P–C–T curve) and the highest initial hydriding rate (hydrogen content 3.83 wt.%H at 10 min) with an initial hydrogen pressure in the channel of 11 bar H2 at 573 K. This is attributed to its containing the largest amount of the Mg17La2 phase, which is easily dissociable during the hydriding reaction.

The effects of the crystallographic orientation on the H2 gas sensing properties were investigated in highly oriented polycrystalline Pd-doped SnO2 films, which were obtained using rf magnetron sputtering of a Pd (0.5 wt%)-SnO2 target on various substrates (a-, m-, r-, and c-cut sapphire and quartz). All the films had a similar thickness (∼110 nm), root-mean-square (rms) roughness (∼1.3 nm), surface area, and chemical status (O, Sn, and Pd). However, the orientation of the films was strongly affected by the orientation of the substrates. The (1 0 1), (0 0 2), and (1 0 1) oriented films were grown on ( 1 1 2 ¯ 0 ) (a-cut), ( 1 0 1 ¯ 0 ) (m-cut), and ( 1 1 ¯ 0 2 ) (r-cut) Al2O3 substrates, respectively, and rather randomly oriented films were deposited on (0 0 0 1) (c-cut) Al2O3 and quartz substrates. In addition, the oriented Pd-doped SnO2 films were highly textured and had in-plane orientation relationships with the substrates similar to the epitaxial films. The (1 0 1) Pd-doped SnO2 films on ( 1 1 2 ¯ 0 ) and ( 1 1 ¯ 0 2 ) Al2O3 showed a considerably higher H2 sensitivity, and their gas response decreased with increasing sensing temperature (400–550 °C). The films deposited on ( 1 0 1 ¯ 0 ) and (0 0 0 1) Al2O3 showed the maximum sensitivity at 500 °C. The comparison of the H2 gas response between undoped and Pd-doped SnO2 films revealed that the Pd-doping shifted the optimum sensing temperature to a lower value instead of improving the gas sensitivity.

Ultrafine TiC-5%Co powders were synthesized by spray drying of aqueous solution of TiO slurry and cobalt nitrate, followed by calcination and carbothermal reaction. The oxide powders with carbon powder was reduced and carburized at under hydrogen atmosphere. During reduction, CO gas was mainly evolved by reducing reaction of oxides. Ultrafine TiC-5%Co powders were easily formed by carbothermal reaction at due to using ultrafine powders as raw materials. The ultrafine WC-TiC-Co alloy prepared by sintering of mixed powder of ultrafine WC-13%Co powder and ultrafine TiC-5%Co powder has higher sintered density and mechanical properties than WC-TiC-Co alloy prepared by commercial WC, TiC and Co powders.

A nano-sized Co3O4 powder was prepared using a spray conversion method that could be applied for mass production. The spray-conversion process consisted of spray drying of a metallic liquid solution, a calcination treatment, and a ball milling process. The calcined Co3O4 powder consisted of agglomerated spherical clusters with nano-sized particles. After milling for 24 h, agglomerated powders were fragmented into fine powders sized below 60 nm. The lithium/cobalt oxide cell was charge-discharged at a constant current density of 0.2 mAcm−2 and showed a first discharge capacity of 1100 mAhg−1. The discharge capacity of the Li/Co3O4 cell drastically decreased with cycle number. By increasing the carbon content of the anode, the cycle life was improved. For a Co3O4 electrode containing 40 wt.% carbon, the discharge capacity was over 400 mAhg−1 after 50 cycles. The spray conversion method might be a useful method to prepare nano-sized Co3O4 powder for the anode material of lithium batteries.

Mg–23.5 wt% Ni and Mg–23.5 wt% Ni–5 wt% Cu alloys for hydrogen storage were prepared by melt spinning and crystallization heat treatment. The alloys were ground by a planetary ball mill for 2 h in order to obtain a fine powder. The activated Mg–23.5Ni and Mg–23.5Ni–5Cu alloys absorbed 4.34 and 4.84 wt% H, respectively, at 573 K under 12 bar H 2 for 60 min. The activated Mg–23.5Ni and Mg–23.5Ni–5Cu alloys desorbed 4.27 and 4.81 wt% H, respectively, at 573 K under 1.0 bar H 2 for 30 min. The hydriding rates of the alloys are quite high, even at 473 K, while the dehydriding rates of the samples at 473 K are nearly zero.

Phosphorous (P)-containing titania films were prepared by micro-arc oxidation (MAO) of titanium (Ti) in an electrolyte containing β-glycerol phosphate disodium salt pentahydrate (β-GP, C 3 H 7 Na 2 O 6 P . 5H 2 O), and their apatite inducing ability in a simulated body fluid (SBF) was investigated. Macro-porous titania films were formed, consisting of only anatase phase, and the P content in the films increased up to 8 at.% with an increasing applied voltage. During hydrothermal treatment, the P in the films was diffused out to the surface and hydrolyzed to form the hydrogen phosphate (HPO 4 2− ) group. When immersed in SBF, no apatite was induced in any of the P-containing MAO specimens for up to 28 days. However, after a hydrothermal treatment at 250 °C, apatite was induced on the titania surfaces as early as 9 h immersion, and the entire exposed surface was covered with the apatite globules after 36 h immersion, which was much faster than the apatite induction on Ca-containing titania. The higher apatite-inducing ability of P-containing titania after hydrothermal treatment was believed to be due to the crystal structure (anatase) and presence of HPO 4 2− group on the surface.