• Journal of Electrochemical Science and Technology
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• 제10권1호
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• pp.1-13
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• 2019

Na-ion batteries are being considered as promising cost-effective energy storage devices for the future compared to Li-ion batteries owing to the crustal abundance of Na-ion. However, the large radius of the Na ion result in sluggish electrode kinetics that leads to poor electrochemical performance, which prohibits the use of these batteries in real time application. Therefore, identification and optimization of the anode, cathode, and electrolyte are essential for achieving high-performance Na-ion batteries. In this context, the current review discusses the suitable high-voltage cathode materials for Na-ion batteries. According to a recent research survey, sodium vanadium fluorophosphate (NVPF) compounds have been emphasized for use as a high-voltage Na-ion cathode material. Among the fluorophosphate groups, $Na_3V_2(PO_4)_2F_3$ exhibited the high theoretical capacity ($128mAh\;g^{-1}$) and working voltage (~3.9 V vs. $Na/Na^+$) compared to the other fluorophosphates and $Na_3V_2(PO_4)_3$. Here, we have also highlighted the classification of Fluorophosphates, NVPF composite with carbonaceous materials, the appropriate synthesis methods and how these methods can enhance the electrochemical performance. Finally, the recent developments in NVPF for the application in energy storage devices and its outlook are summarized.

• 구강회복응용과학지
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• 제25권2호
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• pp.183-190
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• 2009

본 연구의 목적은 NaF와 $H_3PO_4$를 사용하여 양극산화과정을 통해 나노튜브 제작 조건을 찾는 것이다. 절삭된 직경 15 mm, 두께 1.5 mm의 티타늄 디스크를 양극에, 백금을 음극에 연결하고 전극간의 거리는 10 mm가 되도록 하였다. $H_3PO_4$와 NaF 용액을 전해질로 하여 양극산화를 시행하였는데 전압, 전해질 농도, 산화시간을 달리하여 티타늄 디스크에 나노튜브를 형성하였다. 양극산화 후 24시간 동안 증류수로 세척한 후 24시간 동안 $40^{\circ}C$ 오븐에서 건조하고 시편의 표면구조 형상을 관찰 분석하였다. 실험 결과 0.5 wt % NaF에서 전압과 시간이 증가함에 따라 pore 형태의 초기 나노튜브 형성되었다. 1.0 wt % NaF에서 20 V, 20 분과 25 분에서 나노튜브가 생성되었고, 30 V에서 튜브의 형태가 커지면서 터지는 양상을 보였다. 2.0 wt % NaF에서 전압과 시간에 상관없이 적절한 나노튜브형태가 형성되지 않았다. $1M\;H_3PO_4$, 1.0 wt % NaF 전해용액, 20 V, 20분 양극산화 조건에서 티타늄 디스크 상에 가장 잘 정렬된 형태의 나노튜브 구조가 형성되었다. 양호한 형태의 나노튜브 형성을 위해서는 전해질의 종류에 따라 적절한 농도, 전압, 시간의 형성조건이 필요할 것으로 사료된다.

• Journal of Electrochemical Science and Technology
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• 제4권3호
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• pp.113-118
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• 2013

Fluorophosphate, $Na_2MnPO_4F$ as new cathode material was synthesized by carbothermal treatment method. Prepared $Na_2MnPO_4F$ has particle size under 100 nm and residual carbon exists in surface of $Na_2MnPO_4F$. Additional carbon coating was performed in order to increase the electrochemical properties. Even capacity and overpotential were improved by carbon coating using mechanical ball milling, the reduced crystallinity limited the drastic improvement of the electrochemical properties. To solve this problem, re-heat treatment was involved to recover crystallinity and then notable improvement of electrochemical properties was obtained. Specific amount of $Li^+$ that participates in electrochemical $Li^+$ insertion / extraction reaction, was x = 1 in $Li_xNa_{2-x}MnPO_4F$ within the voltage range of 2.0 to 4.8 V. The doubled capacity by 2 electron reaction can be obtained when NMPF is charged to higher voltage over 4.8 V.

• 한국표면공학회:학술대회논문집
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• 한국표면공학회 2017년도 춘계학술대회 논문집
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• pp.155-155
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• 2017

Surface modifications are commonly utilized to adjust the properties of the titanium and its alloy surface to the specific needs of the medical applications, but there are disadvantages such as poor osteoconductive properties and low adhesion of bone cell to implant surface. In order to improve these disadvantages, changes in surface properties have an important effect on osseointegration during implantation. In this paper we applied new technological method for improving a unique surface modification using the characteristic of an electrolytic Solution. Thus, in the electrolyte containing NaF in Na2SO4, TiO2 nanoporous was uniformly formed, and HAp nanoparticles were electrodeposited around the TiO2 nanopores, but in the electrolyte containing NH4F in (NH4)H2PO4, the coarse protrusions including HAp nano particles were regularly deposited onto the TiO2 barrier layer. The surface characteristics and the distributed elements and have been investigated by EDS analysis, and ultra-fine structure of surface are carried out using FE-SEM. To investigate the behavior of the anion, the analysis of chemical states was performed by XPS, and the narrow spectrums for Ti2P, Ca 2p, and P 2p seems to be almost similar depending on the characteristics of the electrolyte solution respectively. In addition, Ca 2p spectrum could be resolved into two peaks for Ca 2p3/2 and 2p1/2 at 347.4 and 351.3 eV, which are related to hydroxyapatite. And, the P peak can also be deconvoluted into two peaks for P1/2 and P3/2 levels with binding energy 134.2 and 133.4 eV, respectively. From the result of soaking test, the apatite morphologys were well-formed onto the modified surface according to the different conditions.

• 전기화학회지
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• 제25권1호
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• pp.22-31
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• 2022

Carbon nanomaterials are considered to be the materials of choice for the fabrication of electrochemical energy storage devices due to their stability, cost-effectiveness, well-established processing techniques, and superior performance compared to other active materials. In the present work, reduced graphene oxide (rGO) has been synthesized and used for the fabrication of a symmetric supercapacitor. The electrochemical performance of the fabricated supercapacitors with three different aqueous electrolytes namely 0.5 M H₂SO₄, 0.5 M H₃PO₄, and 1.0M Na₂SO₄ have been compared and analyzed. Among the three electrolytes, the highest areal specific capacitance of 14 mF/cm² was calculated at a scan rate of 5 mV/s observed with 0.5M H₃PO₄ electrolyte. The results were also confirmed from the charge/discharge results where the supercapacitor with 0.5M H₃PO₄ electrolyte delivered a specific capacitance of 11 mF/cm² at a current density of 0.16 mA/cm². In order to assess the stability of the supercapacitor with different electrolytes, the cells were subjected to continuous charge/discharge cycling and it was observed that acidic electrolytes showed excellent cyclic stability with no appreciable drop in specific capacitance as compared to the neutral electrolyte.

• 한국표면공학회:학술대회논문집
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• 한국표면공학회 2018년도 춘계학술대회 논문집
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• pp.75-75
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• 2018

Commercially pure titanium (CP-Ti) and Ti-6Al-4V alloys have been widely used in implant materials such as dental and orthopedic implants due to their corrosion resistance, biocompatibility, and good mechanical properties. However, surface modification of titanium and titanium alloys is necessary to improve osseointegration between implant surface and bone. Especially, when titanium oxide nanotubes are formed on the surface of titanium alloy, cell adhesion is greatly improved. In addition, plasma electrolytic oxide (PEO) coatings have a good safety for osseointegration and can easily and quickly form coatings of uniform thickness with various pore sizes. Recently, the effects of bone element such as magnesium, zinc, strontium, silicon, and manganese for bone regeneration are researching in dental implant field. The purpose of this study was researched on the surface morphology of PEO-treated Ti-6Al-4V alloy after anodic titanium oxide treatmentusing various instruments. Ti-6Al-4V ELI disks were used as specimens for nanotube formation and PEO-treatment. The solution for the nanotube formation experiment was 1 M $H_3PO_4$ + 0.8 wt. % NaF electrolyte was used. The applied potential was 30V for 1 hours. The PEO treatment was performed after removing the nanotubes by ultrasonics for 10 minutes. The PEO treatment after removal of the nanotubes was carried out in the $Ca(CH_3)_2{\cdot}H_2O+(CH_3COO)_2Mg{\cdot}4H_2O+Mn(CH_3COO)_2{\cdot}4H_2O+Zn(CH_3CO_2)_2Zn{\cdot}2H_2O+Sr(CH_2COO)_2{\cdot}0.5H_2O+C_3H_7CaO_6P$ and $Na_2SiO_3{\cdot}9H_2O$ electrolytes. And the PEO-treatment time and potential were 3 minutes at 280V. The morphology changes of the coatings on Ti-6Al-4V alloy surface were observed using FE-SEM, EDS, XRD, AFM, and scratch tester. The morphology of PEO-treated surface in 5 ion coating solution after nanotube removal showed formation or nano-sized mesh and micro-sized pores.

• 한국표면공학회:학술대회논문집
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• 한국표면공학회 2016년도 추계학술대회 논문집
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• pp.119-119
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• 2016

Over the last years the anodic formation of ordered $TiO_2$ nanotube layers has created significant scientific interest. Titanium oxide nanotube formation on the titanium or titanium alloy surface is expected to be important to improve cell adhesion and proliferation under clinical conditions. It should be possible to control the nanotube size and morphology for biomedical implant use by controlling the applied voltage, alloying element, current density, anodization time, and electrolyte. $TiO_2$ nanotubes show excellent biocompatibility, and the open volume in the tubes may be exploited as a drug release platform and so on. Therefore, in this study, Nanotube shape on the Ti-29Nb-xHf alloys with applied potentials was reserched. $TiO_2$ nanotube formation on Ti-29Nb-xHf alloys was carried out using anodization technique as a function of applied DC potential (10 V to 30 V and 30 V to 10 V) and anodization time for 60~120 min in $1MH_3PO_4$ with small additions of (0.8 wt. %, to 1.2 wt. %) NaF. The morphology change of anodized Ti-29Nb-xHf alloys was determined by FE-SEM, XRD, and EDS.

• 한국표면공학회:학술대회논문집
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• 한국표면공학회 2018년도 춘계학술대회 논문집
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• pp.74-74
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• 2018

Ti-6Al-4V alloys have been widely used as orthopedic materials because of their excellent corrosion resistance and mechanical properties. However, it does not bind directly to the bone, so it requires a surface modification. This problem can be solved by nanotube and micropore formation. Plasma electrolytic oxidation (PEO) treatment for micropore, which combines high-voltage spark and electrochemical oxidation, is a new way of forming a ceramic coating on light metals such as titanium and its alloys. This method has excellent reproducibility and can easily control the shape and size of the Ti alloy. In this study, formation of bioactive surface by PEO-treatment after $2^{nd}$ ATO technique of Ti-6Al-4V alloy was invesgated by various instrument. Nanotube oxide surface structure was formed on the surface by anodic oxidation treatment in 0.8 wt.% NaF and 1M $H_3PO_4$ electrolytes. After nanotube formation, nanotube layer was removed by ultrasonic cleaning. PEO-treatment was carried out at 280V for 3 minutes in the electrolytic solution containing the bioactive substance (Mg, Zn, Mn, Sr, and Si). The surface of Ti-6Al-4V alloy was observed by field emission scanning electron microscopy (FE-SEM, S-4800 Hitachi, Japan). An energy dispersive X-ray spectrometer (EDS, Inca program, Oxford, UK) was used to analyze the spectra of physiologically active Si, Mn, Mg, Zn, and Sr ions. The PEO film formed on the Ti-6Al-4V alloy surface was characterized using an X-ray diffractometer (TF-XRD, X'pert Philips, Netherlands). It is confirmed that bioactive ions play an essential role in the normal bone growth and metabolism of the human skeletal tissues.

• 한국표면공학회:학술대회논문집
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• 한국표면공학회 2015년도 춘계학술대회 논문집
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• pp.106-106
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• 2015

In this study, we investigated electrochemically formed nanotube shape on ternary Ti-25Ta-xHf alloys with Hf contents. Ti-25Ta-xHf (x=0~15 wt.%) alloys were manufactured by vacuum arc-melting furnace. The obtained ingots were homogenized in an argon atmosphere at $1050^{\circ}C$ for 2h and then water quenching. The specimens were cut from ingots to 4 mm thickness and first ground and polished using SiC paper (grades from #100 to #2000). The anodization treatments on Ti-25Nb-xHf alloys were carried out at room temperature for experiments. The formation of nanotubular film was conducted by electrochemical method in mixed electrolytes with 1 M $H_3PO_4$ + 0.8 wt. % NaF at 30 V for 2 h. The morphologies of nanotube depended on the Hf content in Ti-25Ta-xHf ternary system.

• Spatial Information Research
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• 제14권1호
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• pp.129-150
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• 2006

본 연구에서는 GIS 및 확률 기법을 이용하여 광상의 위치와 지질, 지화학 및 지구물리 자료들 간의 상관관계를 분석하고, 광상부존가능도(Mineral potential map) 작성 및 검증을 수행하였다. 연구지역은 1:25만 강릉도폭지역 a이며, 구축된 데이터베이스 자료는 1:25만 광상분포도, 지화학도, 지질도, 부우게 중력이상도, 자력이상도이다. 본 연구에 사용된 광상은 퇴적기원의 비금속광상(고령토, 도석, 규석, 운모, 연옥, 석회석, 납석)이다. 원소별 지화학도 작성은 채취된 각 시료 3,595개의 원소별 분석치를 이용하여 IDW 보간법으로 만들었다. 구축된 지화학도는 Al, Alkalinity, As, Ba, Ca, Cd, Co, Cr, Cu, Fe, K, Li, Mg, Mn, Mo, Na, Ni, Pb, Si, Sr, V, W, Zn, $Cl^-,\;F^-,\;{NO_2}^-,\;{NO_3}^-,\;{PO_4}^{3-},\;{SO_4}^{2-}$, pH, Eh 및 Conductivity로 총 32개이다. 이러한 광상과 관련 요인들 간의 상관관계는 확률기법인 weight of evidence를 적용하여 계산하였고, 이를 바탕으로 광상부존가능도를 작성하였다. 광상부존가능도는 wieght of evidence의 W+와 W- 값을 GIS 중첩분석에 적용하여 작성하였다. 계산된 광상부존가능지수는 기존 광상부존가능성을 정량적으로 설명하고 표현하며 검증할 수 있는 값이다. 각 기법을 이용하여 작성한 광상부존가능도의 검증결과는 85.66%의 정확도를 나타내었다.