Earticle

CeO2 has been widely used for single buffer layer of coated conductor because of superior chemical and structural compatibility with ReBa2Cu3O7-δ(Re=Y, Nd, Sm, Gd, Dy, Ho, etc.). But, the surface of CeO2 layer showed cracks because of the large difference in thermal expansion coefficient between metal substrate and deposited CeO2 layer, when thickness of CeO2 layer exceeds 100 nm on the biaxially textured Ni-3%W substrate. The deposition rate has been limited to be less than 6 Å/sec in order to get a good epitaxy. In this research, we deposited CeO2 single buffer layers on biaxially textured Ni-3%W substrate with 2-step process such as thin nucleation layer(>10 nm) with low deposition rate(3 Å/sec) and thick homo epitaxial layer(>240 nm) with high deposition rate(30 Å/sec). Effect of deposition temperature on degree of texture development was tested. Thick homo epitaxial CeO2 layer with good texture without crack was obtained at 600 oC, which has Δφ value of 6.2 o, Δω value of 4.3 o and average surface roughness(Ra) of 7.2 nm within 10 ㎛ × 10 ㎛ area. This result shows the possibility of preparing advanced Ni substrate with simplified architecture of single CeO2 layer for low cost coated conductor.

금속 폐기물로부터의 유가금속 회수는 관련 원료의 수입 혹은 안정적 원료 수급을 위해서 매우 중요하다. 특히 폐리튬이차전지(LIBs)로부터 회수가 가능한 금속(Li, Co, Ni, Mn 등)의 재사용뿐만 아니라 폐리튬이차전지의 재활용 연구가 필수적이다. 폐리튬이차전지에서 회수된 수산화리튬(LiOH∙xH2O)은 촉매, 이산화탄소 흡수제 및 양극재의 전구체로 재사용이 가능하다. 본 연구에서는 폐리튬이차전지로부터 회수된 탄산리튬 전구체를 사용하였으며, 침전공정을 이용한 선택적인 리튬 분리를 통해 고순도 수산화리튬 분말의 제조 및 최적화 연구를 진행하였다. 수산화리튬 제조 조건으로는 교반을 기반으로 반응온도 90 ℃, 반응시간 3 시간, 탄산리튬과 수산화칼슘의 비율 1:1의 조건에서 수행하였으며, 순도 향상을 위해 2-step 수산화리튬 제조 공정을 추가적으로 진행하여 최종적으로 고순도의 수산화리튬∙제일수화물(LiOH∙xH2O)을 제조하였다.

A valuable metal recovery from waste resources such as spent rechargeable secondary batteries is of critical issues because of a sharp increase in the amount of waste resources. In this context, it is necessary to research not only recycling waste lithiumion batteries (LIBs), but also reusing valuable metals (e.g., Li, Co, Ni, Mn etc.) recovered from waste LIBs. In particular, the lithium hydroxide (LiOH?xH2O), which is of precursors that can be prepared by the recovery of Li in waste LIBs, can be reused as a catalyst, a carbon dioxide absorbent, and again as a precursor for cathode materials of LIB. However, most studies of recycling the waste LIBs have been focused on the preparation of lithium carbonate with a recovery of Li. Herein, we show the preparation of high purity lithium hydroxide powder along with the precipitation process, and the systematic study to find an optimum condition is also carried out. The lithium carbonate, which is recovered from waste LIBs, was used as starting materials for synthesis of lithium hydroxide. The optimum precipitation conditions for the preparation of LiOH were found as follows: based on stirring, reaction temperature 90 ℃, reaction time 3 hr, precursor ratio 1:1. To synthesize uniform and high purity lithium hydroxide, 2-step precipitation process was additionally performed, and consequently, high purity LiOH?xH2O powder was obtained.

Despite the therapeutic efficacy of exendin-4 for the treatment of type 2 diabetes, its application is still limited because of twice-a-day injection requirement. PEGylation, covalent conjugation of a PEG (polyethylene glycol) molecule to a peptide or protein, is known to prolong in-serum half-life as well as to improve pharmacokinetic and pharmacodynamic properties of a peptide or protein [1-3]. In this study, we attempted an aqueous-phase, two-step PEGylation process, in which amine groups of exendin-4 were first converted into thiol groups and then PEG-maleimide with different molecular weights (5 and 10kD) was conjugated via disulfide bridge. These reactions were performed in PBS buffer (pH 7.4) at 400C for overnight. The PEGylates were purified by cation exchange chromatography, using HiTrap SP HP column with a running buffer (10 mM citric acid, pH 3.5) and an elution buffer (10 mM citric acid with and 1 M NaCl). Then, conjugated peptides were separated by sizeexclusion chromatography (Superdex 75 PC 3.2/30 column), using 50 mM PBS (pH 7.0) with 0.15 M NaCl as an elution buffer.The overall conjugation efficiency was high, more than 70%. Maintenance of in-vitro bioactivity was measured by ELISA. This study demonstrates that exendin-4 can be more effectively PEGylated by the two-step process.

Multiferroic Pb(Zr0.52Ti0.48)O3/BiFeO3 multilayer thin films were fabricated by the spin-coating method on Pt/Ti/SiO2/p-Si(100) substrates alternately using Pb(Zr0.52Ti0.48)O3 and BiFeO3 metal alkoxide solutions. The PZT/BFO multilayer thin films show the formation of layers and a change of lattice constant caused by different structure of each other. The coating and heating procedure was repeated several times to form Pb(Zr0.52Ti0.48)O3/BiFeO3 multilayer films. All films showed the typical XRD patterns of the perovskite polycrystalline structure without the presence of a second phase such as Bi2Fe4O3. Pb(Zr0.52Ti0.48)O3/ BiFeO3 multilayer films showed a uniform and small grain size rather than pure Pb(Zr0.52Ti0.48)O3 and BiFeO3 films. We think that the crystal growth of the upper BiFeO3 layers can be influenced by the lower Pb(Zr0.52Ti0.48)O3 layers, and choosing the initial Pb(Zr0.52Ti0.48)O3 layer or a seeding layer has controlled the microstructural behavior of the resultant film. Leakage current density of the Pb(Zr0.52Ti0.48)O3/BiFeO3 multilayer film was 5.74 × 10-6 A/cm2 at 150 kV/cm.

The development of a new manufacturing process, a two-step temperature treatment, to modulate the physicochemical properties of nanoparticles including the size is critical. This is because its physicochemical properties can be key factors affecting the cellular uptake and the bioavailability of bioactive compounds encapsulated in nanoparticles. The aims of this study were to produce (beta-lactoglobulin) ${\beta}-lg$ nanoparticles and to understand how two-step temperature treatment could affect the formation and physicochemical properties of ${\beta}-lg$ nanoparticles. The morphological and physicochemical properties of ${\beta}-lg$ nanoparticles were determined using atomic force microscopy and a particle size analyzer, respectively. Circular dichroism spectroscopy was used to investigate the secondary structure of ${\beta}-lg$. The surface hydrophobicity and free thiol groups of ${\beta}-lg$ were increased with a decrease in sub-ambient temperature and an increase in mild heat temperature. As sub-ambient temperature was decreased, a decrease in ${\alpha}-helical$ content and an increase in ${\beta}-sheet$ content were observed. The two-step temperature treatment firstly involved a sub-ambient temperature treatment from 5 to $20^{\circ}C$ for 30 min, followed secondly by a mild heat temperature treatment from 55 to $75^{\circ}C$ for 10 min. This resulted in the production of spherically-shaped particles with a size ranging from 61 to 214 nm. Two-way ANOVA exhibited the finding that both sub-ambient and mild heat temperature significantly (p<0.0001) affected the size of nanoparticles. Zeta-potential values of ${\beta}-lg$ nanoparticles were reduced with increasing mild heat temperature. In conclusion, two-step temperature treatment was shown to play an important role in the manufacturing process - both due to its inducement of the conformational changes of ${\beta}-lg$ during nanoparticle formation, and due to its modulation of the physicochemical properties of ${\beta}-lg$ nanoparticles.

Recently, cesium tellurium iodine (Cs₂TeI₆) has emerged as an inorganic halide perovskite material with potential application in optoelectronic devices due to its high absorption coefficient, suitable bandgap and because it consists of nontoxic and earth-abundant elements. However, studies on its fabrication process as well as photoresponse characteristics are limited. In this study, a simple and effective method is introduced for the synthesis of Cs₂TeI₆ thin films by a two-step dry process. A Cs₂TeI₆-based lateral photosensor was fabricated, and its photoresponse characteristics were explored under laser illuminations of four different wavelengths in the visible range: 405, 450, 520, and 655 nm. The initial photosensing results suggest potential application and can lead to more promising studies of Cs₂TeI₆ film in optoelectronics.

Poly(methyl methacrylate) coated $BaF_2:Er^{3+}$ nanoparticles were prepared via a novel reverse-emulsion polymerization process using methyl methacrylate as continuous phase and water as dispersed phase. Preparation and coating of $BaF_2:Er^{3+}$ particles were processed in a single step. The resulting polymeric composites show the characteristic $Er^{3+}$ luminescence at excitation of 980 nm and may have potential applications in amplified optical networks.

The optical and electrical properties of indium tin oxide (ITO) thin films deposited at room temperature can be substantially enhanced by adopting a two-step process. In the first step, the films (50 nm thick) were grown by pulsed laser deposition (PLD) on glass substrate at room temperature and quickly annealed at $400^{\circ}C$ in nitrogen ambient for 1 minute by using rapid thermal annealing method. The process was completed by additional deposition (150 nm thick) on annealed film at room temperature. High quality ITO films grown by two-step process at room temperature could be obtained with the resistivity of $3.02{\times}10^{-4}{\Omega}cm$, the carrier mobility of 32.07 $cm^2/Vs$, and the transparency above 90 % in visible region mainly due to the enhancement of the film crystallinity and the increase of grain size.

금속 폐기물로부터의 유가금속 회수는 관련 원료의 수입 혹은 안정적 원료 수급을 위해서 매우 중요하다. 특히 폐리튬이차전지(LIBs)로부터 회수가 가능한 금속(Li, Co, Ni, Mn 등)의 재사용뿐만 아니라 폐리튬이차전지의 재활용 연구가 필수적이다. 폐리튬이차전지에서 회수된 수산화리튬($LiOH{\cdot}xH_2O$)은 촉매, 이산화탄소 흡수제 및 양극재의 전구체로 재사용이 가능하다. 본 연구에서는 폐리튬이차전지로부터 회수된 탄산리튬 전구체를 사용하였으며, 침전공정을 이용한 선택적인 리튬 분리를 통해 고순도 수산화리튬 분말의 제조 및 최적화 연구를 진행하였다. 수산화리튬 제조 조건으로는 교반을 기반으로 반응온도 $90^{\circ}C$, 반응시간 3 시간, 탄산리튬과 수산화칼슘의 비율 1:1의 조건에서 수행하였으며, 순도 향상을 위해 2-step 수산화리튬 제조 공정을 추가적으로 진행하여 최종적으로 고순도의 수산화리튬 제일수화물($LiOH{\cdot}xH_2O$)을 제조하였다.

A valuable metal recovery from waste resources such as spent rechargeable secondary batteries is of critical issues because of a sharp increase in the amount of waste resources. In this context, it is necessary to research not only recycling waste lithium-ion batteries (LIBs), but also reusing valuable metals (e.g., Li, Co, Ni, Mn etc.) recovered from waste LIBs. In particular, the lithium hydroxide ($LiOH{\cdot}xH_2O$), which is of precursors that can be prepared by the recovery of Li in waste LIBs, can be reused as a catalyst, a carbon dioxide absorbent, and again as a precursor for cathode materials of LIB. However, most studies of recycling the waste LIBs have been focused on the preparation of lithium carbonate with a recovery of Li. Herein, we show the preparation of high purity lithium hydroxide powder along with the precipitation process, and the systematic study to find an optimum condition is also carried out. The lithium carbonate, which is recovered from waste LIBs, was used as starting materials for synthesis of lithium hydroxide. The optimum precipitation conditions for the preparation of LiOH were found as follows: based on stirring, reaction temperature $90^{\circ}C$, reaction time 3 hr, precursor ratio 1:1. To synthesize uniform and high purity lithium hydroxide, 2-step precipitation process was additionally performed, and consequently, high purity $LiOH{\cdot}xH_2O$ powder was obtained.

In this study, to investigate the effects of 2-step shot peening at the surface of spring steel, crack growth tests are conducted on spring steel and shot peened specimens. And then the residual stresses and fractographs are examined. The crack growth equation that can describe the whole crack growth behavior is used to evaluate the experiment results. The results show that fatigue crack glows slowly in the shot peened specimen than in the unpeened. And in the case of the 2-step shot peened specimen the initial stress intensity factor range and the fracture toughness is higher than the unpeened specimen due to the compressive residual stress. Fractographs show that the compressive residual stress of the surface suppress the fatigue crack opening and consequently slow crack growth rates.