Earticle

The electrical/thermal stabilities and magnetic field controllability of a no-insulation (NI) high-temperature superconducting magnet are characterized by contact resistance between turn-to-turn layers, and the contact resistance characteristics are determined by properties of conductor surface and winding tension. In order to accurately predict the electromagnetic characteristics of the NI coil in a design stage, it is necessary to control the contact resistance characteristics within the design target parameters. In this paper, the contact resistance and critical current characteristics of a rare-earth barium copper oxide (REBCO) conductor were measured to analyze the effects of surface treatment conditions (roughness and oxidation level) of the copper stabilizer layer in REBCO conductor. The test samples with different surface roughness and oxidation levels were fabricated and conductor surface analysis was performed using scanning electron microscopes, alpha step surface profilers and energy dispersive X-ray spectroscopy. Moreover, the contact resistance and critical current characteristics of the samples were measured using the four-terminal method in a liquid nitrogen impregnated cooling environment. Compared with as-received REBCO conductor sample, the contact resistance values of the REBCO conductors, which were post-treated by the scratch and oxidation of the surface of the copper stabilizer layer, tended to increase, and the critical current values were decreased under certain roughness and oxidation conditions.

희토류 영구자석(Rare earth magnet)은 사용량이 급격하게 증가하고 있으며, 이와 맞물려 폐희토류 자석의 발생량도 급격히 증가할 것으로 예측된다. 폐희토류 자석의 재활용은 주로 자석에 포함되어 있는 희토류 원소를 침출/분리하여 회수하는 공정으로 이루어지고 있으나, 침출 공정에 투입되는 폐희토류 자석의 분쇄 특성에 대한 연구는 전무한 실정이다. 따라서 본 연구에서는 폐희토류자석을 이용하여 효과적인 파분쇄 공정 및 분쇄특성에 대한 연구를 진행하였다. NdFeB 폐자석을 조크러셔로 파쇄한 결과 급격한산화 없이 효과적으로 입도가 감소는 하였지만, 롤크러셔의 경우 지속적인 압축에 의해 증가하는 표면과 대기 중의 산소가 반응하여 불꽃을 내며 급격한 산화가 발생하였다. 또한 파쇄 공정을 통해 생산된 시료를 볼밀에 투입하여 분쇄 특성을 파악한 결과, 일반적인 광물과 다르게 분쇄가 잘 이루어지지 않고 분쇄 16분 이후에 정상적인 분쇄가 이루어졌다. 또한 일반적인 광물에 비해 매우낮은 분쇄율(S)과 미분이 발생이 매우 높은 분쇄분포(B)를 보임을 확인하였으며, 이는 향후 NdFeB 폐자석 파분쇄 공정 설계 시 기초자료로 사용될 수 있을 것으로 판단된다.

Due to the increasing demand of rare earth magnet for various application, it is predicted that the amount of waste rare earth magnet will increase sharply. The process of waste rare earth magnet recycling is mainly consisted of leaching and separation of rare earth element contained in the magnet. However, there is no study on the breakage characteristics of the waste rare earth magnet for production of magnet powder. Therefore, in this study, effective crushing/grinding process and breakage characteristics were investigated for waste rare earth magnet. In the case of jaw crusher, the particle size of magnet was effectively reduced without rapid oxidation. In ball mill grinding test, it was found that the grinding process was not performed properly at the early stage of grinding. Moreover, waste rare earth magnet showed very low specific rate of breakage(S) and high fraction of fine particle breakage distribution(B) compared to ordinary minerals. These results can be used as a basic data for developing crushing/grinding circuit of waste rare earth magnet.

Purpose: This study was to observe characteristic of metal oxidation and bonding strength according tocomposition of Ni-Cr alloy for porcelain fused to metal crown. The three kinds of Ni-Cr alloy with differentcomposition ratio of parent metal were observed general properties and chemical properties of each alloy surface andmeasured the shear bonding strength between ceramic and each alloys. The aim of study was to suggest the materialfor design of parent metal’s composition ratio to development of alloy for porcelain fused to metal crown. Methods: The three kinds of alloy as test specimen was Ni(59wt%)-Cr(24wt%), Ni(67wt.%)-Cr(16wt.%) alloyand Ni(71wt%)-Cr(12wt%)alloy. The oxide on surface was observed by EDX. And the shear test was performed byMTS. Results: The surface property and oxide characteristic analysis of oxide layer, weight percentage of Element Owithin Ni59Cr24 alloy measured 23.03wt%, Ni67Cr16 alloy measured 21.13wt% and Ni71Cr12 alloy was measured48.55wt%. And the maximum shear bonding strength was measured 58.02Mpa between Ni59Cr24 alloy and vintagehalo(H2 group). Conclusion: The surface property and oxide characteristic three kind of Ni-Cr alloy was similar. and shearbonding strength showed the highest bonding strength in H2 specimens.

Expressed as insoluble forms in E. coli, native CWPO_C (cell wall peroxidase from poplar tree) and mutated variants were successfully reactivated throughout refolding experiments and used for elucidating the previously presumed existence of electron transfer pathway in CWPO_C structure. Their catalytic properties were fully characterized through analysis such as steady state kinetics, direct oxidation of lignin macromolecules respectively accompanying with their stabilities during polymerization reactions, which proved strongly that the 74th residue on the CWPO_C structure plays the important role in catalyzing the macromolecules throughout electron transfer mechanism. This study also contributed deeper understanding about role of aromatic amino acids in electron transfer mechanism usually manipulated by peroxidase/H2O2 catalyst system. Furthermore, we also successfully synthesize the highly bioactive poly(catechin) by applying radical robust CWPO_C mutant in extension of poly(catechin). Anti-oxidation activity of synthesized poly(catechin) was confirmed by xanthine oxidase assay. The elucidation of uniquely catalytic mechanism in CWPO_C may improve applicability of peroxidase/H2O2 catalyst in conducting green polymer chemistry.

The chemical, electrical, and optical properties of ZnO and Al-doped ZnO films after high temperature annealing were studied. The resistivity increased significantly after annealing at $600^{\circ}C$ under $10^{-10}$ Torr atmosphere. The mechanism of the resistivity change was explored using photoemission spectroscopy and photoluminescence spectrometer. The results indicated that the amount of oxygen deficient region O-Zn bonds decreased and oxygen vacancy was decreased after the high temperature vacuum annealing. The increase in the resistivity of ZnO and Al-doped ZnO films was resulted from the decrease in carrier concentration due to a decrease in the amount of oxygen deficiency.

In continuous hot dip galvanizing process, oxide formation on steel surface has an influence on Zn wetting. High strength automotive steel contains high amount of Si and Mn, where Si-Mn composite oxides such as $Mn_2SiO_4$ or $MnSiO_3$ covers the surface after annealing. Zn wetting depends on how the aluminothermia reaction can reduce the Mn-Si composite oxides and then form inhibition layer such as $Fe_2Al_5$ on the steel surface. The outward diffusion of metallic ions such as $Mn^{2+}$, $Si^{2+}$ in the steel matrix is very important factor for the formation of the surface oxides on the steel surface. The surface state and grain boundaries provide an important role for the diffusion and the surface oxide reactions. Some elements such as P, Sb, and B have a strong affinity for the interface precipitation, and it influence the diffusivity of metallic ions on grain boundaries. B oxide forms very rapildly on the steel surface during the annealing, and this promote complex oxides with $SiO_2$ or MnO. P has inter-reacted with other elements on the grain boundaries and influence the diffusion through on them. Small addition of Sb could suppress the decarburization from steel surface and retards the formation of internal and external selective oxides on the steel surface. Interface control by the trace elements such as Sb could be available to improve the Zn wettability during the hot dip galvanizing.

Novel ultra-high molecular weight polyethylene (UHMWPE)/zirconia composites were previously prepared by the in situ polymerization of ethylene using a Ti-based Ziegler-Natta catalyst supported on to the surface of zirconia, as a bearing material for artificial joints. Tribological tests revealed that a uniform dispersion of zirconia in UHMWPE markedly increased the wear resistance. The effects of zirconia content on the oxidation behavior of the ${\gamma}$-ray-treated UHMWPE/zirconia composite surfaces were examined. The oxidation index that estimates the oxidation degree as the content of total carbonyl compounds was monitored using Fourier transform infrared spectroscopy-attenuated total reflectance. The changes in the surface composition due to the oxidation were confirmed by electron spectroscopy for chemical analysis. The extent of oxidation decreased with increasing zirconia content, which was attributed to the increased crystallinity as well as the decreased polymer portion of the UHMWPE/zirconia composites.

The effects of surface oxidation on magnetic properties were investigated at high frequencies (10k-100MHz) for $7-18\mu\textrm{m}$ thick $Co_{70}Fe_{5}Si_{15}B_{10}$ amorphous ribbons with controlled domain structure. Oxidation was accelerated by acid-treatment or anodic oxidation treatment, and the insulation layers were prepared on the surfaces of the ribbons. The acid-treatment was effective in improving permeability and magnetic loss. Although the anodic oxidation treatment was effective in both making oxide layer and thinning, the magnetic properties were not improved compared with the case of the acid-treatment.

In the current paper, we are reporting the results from an investigation of the surface and sub-surface oxidation of a TRIP steel containing 2 wt.% Mn and 0.5 wt.% Al with and without 0.03 wt.% Sb. The oxidizing conditions in the gas were successively varied in terms of the linear gas flow-rate and dew-point, from conditions were gas-phase mass transport limited conditions prevailed, to those were solid state processes became the rate determining conditions. It was found, that at sufficient low oxidizing conditions (defined as flow-rate/dew-point), the metal surfaces were clear of any external oxides, and as the oxidizing conditions were increased, Mn- and Si- oxide nodules formed along with magnetite. As the oxidizing conditions were increased further, a dense magnetite layer was present. The limits of the various regions were experimentally quantified and a proposed hypothesis for their occurrences is presented. No obvious effect of Sb was noted in this micro-structural research of the oxides that results from the various conditions investigated in this study.

This paper presents a brief summary on a relatively new plasma aided electrolytic surface treatment process for light metals. A brief discussion regarding the advantages, principle, process parameters and applications of this process is discussed. The process owes its origin to Sluginov who discovered an arc discharge phenomenon in electrolysis in 1880. A similar process was studied and developed by Markov and coworkers in 1970s who successfully deposited an oxide film on aluminium. Several investigation thereafter lead to the establishment of suitable process parameters for deposition of a crystalline oxide film of more than $100{\mu}m$ thickness on the surface of light metals such as aluminium, titanium and magnesium. This process nowadays goes by several names such as plasma electrolytic oxidation (PEO), micro-arc oxidation (MOA), anodic spark deposition (ASD) etc. Several startups and surface treatment companies have taken up the process and deployed it successfully in a range of products, from military grade rifles to common off road sprockets. However, there are certain limitations to this technology such as the formation of an outer porous oxide layer, especially in case of magnesium which displays a Piling Bedworth ratio of less than one and thus an inherent non protective oxide. This can be treated further but adds to the cost of the process. Overall, it can be said the PEO process offers a better solution than the conventional coating processes. It offers advantages considering the fact that he electrolyte used in PEO process is environmental friendly and the temperature control is not as strict as in case of other surface treatment processes.

This paper presents a brief summary on a relatively new plasma aided electrolytic surface treatmentprocess for light metals. A brief discussion regarding the advantages, principle, process parameters andapplications of this process is discussed. The process owes its origin to Sluginov who discovered an arcdischarge phenomenon in electrolysis in 1880. A similar process was studied and developed by Markovand coworkers in 1970s who successfully deposited an oxide film on aluminium. Several investigationthereafter lead to the establishment of suitable process parameters for deposition of a crystalline oxide filmof more than 100μm thickness on the surface of light metals such as aluminium, titanium and magnesium. This process nowadays goes by several names such as plasma electrolytic oxidation (PEO), micro-arcoxidation (MOA), anodic spark deposition (ASD) etc. Several startups and surface treatment companieshave taken up the process and deployed it successfully in a range of products, from military grade riflesto common off road sprockets. However, there are certain limitations to this technology such as theformation of an outer porous oxide layer, especially in case of magnesium which displays a PilingBedworth ratio of less than one and thus an inherent non protective oxide. This can be treated further butadds to the cost of the process. Overall, it can be said the PEO process offers a better solution than theconventional coating processes. It offers advantages considering the fact that he electrolyte used in PEOprocess is environmental friendly and the temperature control is not as strict as in case of other surfacetreatment processes.

A new 80Ti-15Ta-5Zr wt% alloy surface was protected by anodic oxidation in phosphoric acid solution. The protective oxide layer (TiO2, ZrO2 and Ta suboxides and thickness of 15.5 nm) incorporated $PO{_4}^{3-}$ ions from the solution, according to high resolution XPS spectra. The AFM analysis determined a high roughness with SEM detected pores (20 - 50 nm). The electrochemical studies of bare and anodically oxidized Ti-15Ta-5Zr alloy in Carter-Brugirard saliva of different pH values and saliva with 0.05M NaF, pointed to a nobler surface for the protected alloy, with a thicker electrodeposited oxide layer acting as a barrier against aggressive ions. The oxidized alloy significantly decreased corrosion current densities and total quantity of ions released into the oral environment in comparison with the bare one, at higher polarisation resistance and protective capacity of the electrodeposited layer. The impedance data revealed a bi-layered oxidation film formed by: a dense, compact, barrier layer in contact with the metallic substrate, decreasing the potential gradient across the metal/oxide layer/solution interface, reducing the anodic dissolution and a more permissive, porous layer in contact with the electrolyte. The open circuit potential for protected alloy shifted to nobler values, with thickening of the oxidation film signifying long-term protection.

Micro-arc discharge oxidation (MDO) is a cost-effective plasma electrolytic process which can be used to improve the wear and corrosion resistance of Al-alloy parts by forming a alumina coating on the component surface. However, the MDO coated Al-alloy components often exhibit relatively high friction coefficients and low wear resistance fitted with many counterface materials, additionally, the pitting corrosion for the MDO coated AI-alloy components, especially for a thinner alumina coating, often occurs in atmosphere circumstance due to the porous alumina coats. Therefore, a duplex treatment, combining a MDO coated ahumina thin layer with a TiN coating, prepared by magnetron sputtering (MS), has been investigated. The Vicker's microhardness, pin-on-disc, electrochemical measurement, salt spray, XRD and SEM tests were used to characterize and analyze the treated samples. The work demonstrates that the MDO/MS coated samples have a combination of a very low friction coefficient and good wear resistance as well as corrosion since the micro-holes on alumina coating are partly or fully covered by TiN material.

Oxidation-reduction cycling (ORC) procedures are widely used for cleaning nanoparticle surfaces when investigating their electrocatalytic activities. In this work, the effect of ORC on the surface structures and electrocatalytic oxygen reduction activity of Au electrodes is analyzed. Different structural changes and variations in electrocatalysis are observed depending on the initial structure of the Au electrodes, such as flat bulk, nanoporous, nanoplate, or dendritic Au. In particular, dendritic Au structures lost their sharp-edge morphology during the ORC process, resulting in a significant decrease in its electrocatalytic oxygen reduction activity. The results shown in this paper provide an insight into the pretreatment of nanoparticle-based electrodes during investigation of their electrocatalytic activities.

Very initial stage of oxidation process of Si (001) surface was investigated using large scale molecular dynamics simulation. Reactive force field potential was used for the simulation owing to its ability to handle charge variation associated with the oxidation reaction. To know the detail mechanism of both adsorption and desorption of water molecule (for simulating wet oxidation), oxygen molecule (for dry oxidation) and their atom constituents, interaction of one molecule with Si surface was carefully observed. The simulation is then continued with many water and oxygen molecules to understand the kinetics of oxide growth. The results show that possibilities of desorption and adsorption depend strongly on initial atomic configuration as well as temperature. We observed a tendency that H atoms come relatively into deeper surface or otherwise quickly desorbed away from the silicon surface. On the other hand, most oxygen atoms are bonded with first layer of silicon surface. We also noticed that charge transfer is only occur in nearest neighbor regime which has been pointed out by DFT calculation. Atomic structure of the interface between the oxide and Si substrate was characterized in atomic scale.

Zirconium diboride is widely applied because of some excellent properties. The effect of the oxidation temperature on the surface microdomain of ZrB2-YAG multi-phase ceramics was studied, it helps to improve the performance of ultra-hightemperature ceramics. The results show the oxidation layer thickness is increased with an increase in the oxidation temperature, the oxidation layer thickness is decreased by increasing the density of multi-phase ceramics at the same oxidation temperature. The ceramic surface shows the (m)ZrO2, YAG, B2O3 and ZrB2 phases below the the oxidation temperature at 1300 ο C, but the ceramic surface do not show the ZrB2 phase above the oxidation temperature at 1300 ο C that is to say, the ZrB2 phase of the ceramic suface is entirely oxidized. The oxidation layer thickness is increased with an increase in the oxidation time, however, the ratio of increasing thickness is less and less. The oxidation layer shows a loose structure during the initial stage of the oxidation, which lacks a barriers for the diffusion of the oxygen.