• Journal of Surface Science and Engineering
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• v.55 no.1
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• pp.32-37
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• 2022

In a carbon-zero social atmospher, research is underway to reduce the use of fossil fuels. Interest in cleaner energy sources and their storage system is growing, and among them, research on effective energy storage is being actively conducted. Energy storage system(ESS) can be divided into secondary batteries, fuel cells, and capacitors, and the superiority of energy density of secondary batteries has a dominent influence on the ESS market. However, as problems with secondary batteries, charge/discharge speed, safety, and deterioration of electrodes are being highlighted. In this study, an electrode for supercapacitor with superior charge/discharge speed and specific capacitance is manufactured. The manufactured spinel nickel cobalt electrodes had specific capacitances of 1018.8 F/g, 690.8 F/g, and 475.1 F/g at 1 A/g in 1 M KOH electrolyte, and shows a performance retention rate of 77.48%, 63.30%, and 58.16% after 2000cycles at 7 A/g.

• The korean journal of orthodontics
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• v.53 no.2
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• pp.89-98
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• 2023

Objective: This study aimed to compare the mechanical and thermal properties in the anterior and posterior segments of new and retrieved specimens of a commercially available multizone superelastic nickel-titanium (NiTi) archwire. Methods: The following groups of 0.016 × 0.022-inch Bioforce NiTi archwires were compared: a) anterior and b) posterior segments of new specimens and c) anterior and d) posterior segments of retrieved specimens. Six specimens were evaluated in each group, by three-point bending and bend and free recovery tests. Bending moduli (Eb) were calculated. Furthermore, the new specimens were evaluated with scanning electron microscopy/energy-dispersive X-ray spectrometry. A multiple linear regression model with a random intercept at the wire level was applied for data analysis. Results: The forces in the posterior segments or new specimens were higher than those recorded in the anterior segments or retrieved specimens, respectively. Accordingly, Eb also varied. Higher austenite start and austenite finish (Af) temperatures were recorded in the anterior segments. No statistically significant differences were found for these temperatures between retrieved and new wires. The mean elemental composition was (weight percentage): Ni, 52.6 ± 0.5; Ti, 47.4 ± 0.5. Conclusions: The existence of multiple force zones was confirmed in new and retrieved Bioforce archwires. The retrieved archwires demonstrated lower forces during the initial stages of deactivation in three-point bending tests, compared with new specimens. The Af temperature of these archwires may lie higher than the regular intraoral temperature. Even at 2 mm deflections, the forces recorded from these archwires may lie beyond biologically safe limits.

• Journal of the Korean Society for Marine Environment & Energy
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• v.17 no.4
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• pp.257-267
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• 2014

The distributions of trace metals in the East Sea were investigated during the R/V Lavrentyev cruise (July 2009) in which four transects from Russia shore to South were conducted to collect 25 surface water samples. The total dissolved concentrations of Cu and Ni were measured using ICP-MS, DRC-e. In the coastal area, their concentrations of Russia shore (Cu, 1.51; Ni, 1.82 nM) were 1.9 times for Cu and 2.0 times for Ni lower than Korea shore (Cu, 2.87; Ni, 3.71 nM). In the subregion, their concentrations of Warm region (Cu, 3.03; Ni, 2.28 nM) were higher for Cu than Cold region (Cu, 2.04; Ni, 2.28 nM). The distributions of Cu and Ni concentrations were divided by lowest level at $10^{\circ}C$ of water temperature. In this study period, the surface water temperatures of Russia shore and Japan basin were lower than $10^{\circ}C$ and them of Ulleung basin and Sakhalin shore were higher. Below $10^{\circ}C$, Cu and Ni concentrations increased when surface water temperatures decreased. Above $10^{\circ}C$, their concentrations increased with temperature, which showed highest concentrations in the Ulleung basin, directly influenced by flux from East Korean Warm Current. By comparing with other sea areas (Western Mediterranean, Atlantic), Cu concentrations in the East Sea were a little higher and Ni concentrations were lower. Particularly as the level of Cu in the offshore in the Ulleung basin were higher than in the coastal area, We can suggest that the atmospheric flux of Cu is relatively important in this area.

• Journal of the Microelectronics and Packaging Society
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• v.28 no.2
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• pp.71-79
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• 2021

In this study, we have successfully fabricated the Sn-Ni paste and evaluated the bonding properties for high-temperature endurable EV (Electric Vehicle) power module applications. From evaluating of the micro-structural changes in the TLPS (Transient Liquid Phase Sintering) joints with Sn and Ni contents in the Sn-Ni pastes, a lack of Ni powders and Ni particle agglomerations by Ni surplus were observed in the Sn-20Ni and Sn-50Ni joints (in wt.%), respectively. In contrast, relatively dense microstructures are observed in the Sn-30Ni and Sn-40Ni TLPS joints. From differential scanning calorimetry (DSC) thermal analysis results of the fabricated Sn-Ni paste and TLPS bonded joints, we confirmed that the complete reactions of Sn with Ni to form Ni-Sn intermetallic compounds (IMCs) at bonding temperatures occurred, and there is no remaining Sn in the joints after TLPS bonding. In addition, the interfacial reactions and IMC phase changes of the Sn-30Ni joints under various bonding temperatures were reported, and their mechanical shear strength were investigated. The TLPS bonded joints were mainly composed of residual Ni particles and Ni₃Sn₄ intermetallic phase. The average shear strength tended to increase with increasing bonding temperature. Our results indicated a high shear strength value of approximately 30 MPa at a bonding temperature of 270 ℃ and a bonding time of 30 min.

• Restorative Dentistry and Endodontics
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• v.28 no.1
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• pp.41-49
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• 2003

There are increasing usage of Nickel-Titanium rotary files in modern clinical endodontic treatment because it is effective and faster than hand filing due to reduced step. This study was conducted to evaluate the effect of canal preparations using 3 different rotary Nickel-Titanium files that has different cross sectional shape and taper on the maintenance of canal curvature. Simulated resin block were instrumented with Profile(Dentsply, USA), GT rotary files(Dentsply, USA), Hero 642(Micro-Mega France), and Pro-Taper(Dentsply, USA). The image of Pre-instrumentation and Post-instrumentation were acquired using digital camera and overspreaded in the computer. Then the total differences of canal diameter, deviation at the outer portion of curvature, deviation at the inner portion of curvature, movement of center of the canal and the centering ratio at the pre-determined level from the apex were measured. Results were statistically analyzed by means of ANOVA, followed by Scheffe test at a significance level of 0.05. The results were as follows； 1. Deviation at the outer portion of curvature, deviation at the inner portion of curvature were showed largest in Pro-Taper so also did in the total differences of canal diameter(p＜0.05). 2. All the groups showed movements of center Profile combined with GT rotary files and Hero 642 has no difference but Pro-Taper showed the most deviation(p＜0.05). 3. At the 1, 2, 3mm level from the apex movements of center directed toward the outer portion of curvature, but in 4, 5 mm level directed toward the inner portion of curvature(p＜0.05). As a results of this study, it could be concluded that combined use of other Nickel-Titanium rotary files is strongly recommended when use Pro-Taper file because it could be remove too much canal structure and also made more deviation of canal curvature than others.

• Journal of the Korean Magnetics Society
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• v.9 no.4
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• pp.217-222
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• 1999

The pick up impurity was studied for preparing the NiCuZn ferrite powder by a ball milling method that usually uses in the industrial ceramic process. The raw materials of NiO, CuO, ZnO, and $Fe_2O_3$ powder were weighted according to various spinel composition and mixed for 18 hrs by a wet ball milling method after that the slurry was followed by spray dried and calcined at $700^{\circ}C$ 3 hrs. The calcined NCZF powder was finally ball milled during 65 hrs as same method. The stainless steel ball and jar are used as mixing and milling equipment and the solid concentration of the slurry was 25 vol%. The impurities, stainless steel pickup, were effected by the composition of raw materials especially iron oxide, nickel oxide in the mixing process and by the rate of calcine of NiCuZn ferrite in final milling process. The empirical equation of stainless steel pickup was driven in the wet ball milling system. Finally, the composition of NiCuZn ferrite could be controlled by the empirical equation.

• Journal of environmental and Sanitary engineering
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• v.18 no.3 s.49
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• pp.35-42
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• 2003

The electric resistance and constant current were investigated on the nickel-thallium-phosphorus alloy deposits by electroless-plating. The Ni-Tl-P alloy deposits were achieved with a bath using sodium hypophosphit as the reducing agent and sodium citrate as the comlexing agent. The basic plating solution is composed of 0.1M NiSO$_4$, 0.005${\sim}$0.0IM Tl$_2$S0$_4$, 0.1${\sim}$O.2M sodium hypophosphite and 0.02${\sim}$O.IM sodium citrate and the plating condition were pH 5${\sim}$6, temperrature 80$_4$90${\circ}$C. The results obtained are summarized as follows: 1) The crystal structure of deposit was amorphous structure as deposited state, became microcrystallized centering on Ni(111) plane by heat treatment at 200${\circ}$C, and grew as polycrystalline Ni, Ni$_3$P, Ni$_5$p$_2$,Tl, etc. by heat treatment higher than 350${\circ}$C. The grain size of plated deposits was grown up to 28.3~42.0nm by heat treatment for 1hour at 500${\circ}$C. 2) The electrical resistivity showed a comparatively high value of 192.5$_4$208.3 ${\mu}$${\Omega}$Cm and its thermal stability was great with resistivity value less than 0.22% in the thermal surroundings of 200${\circ}$C. 3) Ni-Tl-P alloy deposit showed such good constant current-making-effect in the variation of electric voltage, heat treatment temperature, and the composition of the deposit that it can be put to practical use as the matter of constant current device.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.19 no.4
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• pp.184-189
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• 2009

We characterized the growth behavior of nano NiO crystals synthesized by heat-treatment in air at the elevated temperatures using nickel nitrate ($Ni(NO_3)_2{\cdot}6H_2O$). The crystals had the octahedral shape and the length of 200${\sim}$500 nm. The truncation was observed when the NiO powder was heated up to $900^{\circ}C$ for 2 hours. but not be seen at under $600^{\circ}C$. It was observed that nano NiO crystals synthesized at $900^{\circ}C$ made up the networks, the coalescence of the nano crystals through the neck formation between the crystals appeared as the first stage in the sintering mechanism.

• Journal of the Korean Electrochemical Society
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• v.19 no.3
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• pp.57-62
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• 2016

The over-discharging phenomena in sodium-nickel chloride batteries were investigated in relation to decomposition of molten salt electrolyte and consequent metal co-deposition. From XRD analysis, the material deposited on graphite cathode current collector was revealed to be by-product of molten salt electrolyte decomposition. In particular, the result showed that the Ni-Al alloys ($Al_3Ni_2$, $Ni_3Al$ and $Al_3Ni$) were electrochemically deposited on graphite current collectors in line with over-discharging behaviors. It is assumed that the $NiCl_2$ solubility in molten salt electrolytes leads to the co-deposition of Ni-Al alloys by increasing metal deposition potential above 1.6 V (vs. $Na/Na^+$). The cell tests have revealed that the composition of molten salt electrolytes modified by various additives makes a decisive influence on the over-discharging behaviors of the cells. It was revealed that NaOCN addition to molten salt electrolytes was advantageous to suppress over-discharge reactions by modifying the characteristics of molten salt electrolytes. NaOCN addition into molten salt electrolytes seems to suppress Ni solubility by maintaining basic melts. The cell using modified molten salt electrolyte with NaOCN (Cell D) showed relatively less cell degradation compared with other cells for long cycles.

• Journal of the Korean Ceramic Society
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• v.49 no.2
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• pp.135-141
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• 2012

To improve the visible-light induced photocatalytic application performances of $TiO_2$, in this study, the $NiS_2$ modied $TiO_2$ composites were prepared by two methods: hydrothermal method and sol-gel method. The composites were denoted as hs-$NiS_2$/$TiO_2$, and sg-$NiS_2$/$TiO_2$ and characterized by XRD, UV-vis absorbance spectra, SEM, TEM, EDX, and BET analysis. The photocatalytic activities under visible light were investigated by the degradation of methyl orange (MO). The photodegradation rate of methyl orange under visible light with $NiS_2$/$TiO_2$ composites was markedly higher than that of pure $TiO_2$, and the effect of hs-$NiS_2$/$TiO_2$ composites was better than that of sg-$NiS_2$/$TiO_2$. The results indicate that the hydrothermal process could partly inhibit the agglomeration of $NiS_2$/$TiO_2$. Thus, the dispersion of nanoparticles was improved, and that the promoting effect of $NiS_2$ could extend the light absorption spectrum toward the visible region.