Enhancement of oxidation resistance of zirconium alloy with anodic nanoporous oxide layer in high-temperature air/steam environments

Park, Yang Jeong,Kim, Jung Woo,Ali, Ghafar,Cho, Sung Oh Elsevier 2018 Corrosion science Vol.140 No.-

<P><B>Abstract</B></P> <P>Highly-ordered and hexagonally close-packed nanoporous zirconium oxide layer is formed on the surface of zirconium alloy by anodization, and the anti-oxidation behavior of the zirconium alloy with the nanoporous oxide layer has been investigated. The oxidation experiments were carried out in both air and steam environments at 1000 °C. Interestingly, zirconium alloy with the nanoporous oxide layer exhibits dramatic improvement in the oxidation resistance compared to bare zirconium alloy without the nanoporous oxide layer. Analysis using several characterization tools reveals that large single-crystalline columnar zirconium oxide grains are formed beneath the nanoporous oxide layer and these grains prevent further oxidation.</P> <P><B>Highlights</B></P> <P> <UL> <LI> By anodization, highly-ordered and hexagonally close-packed nanoporous oxide layer formed on the surface of Zr-Nb-Sn alloy. </LI> <LI> Anodic nanoporous oxide film decreases the corrosion of the Zr-Nb-Sn alloy. </LI> <LI> Tetragonal zirconia dominate at 500 ℃ for the specimens that have anodic nanoporous oxide film. </LI> <LI> Large columnar oxide grains formed after oxidation of the specimens that have anodic nanoporous oxide film. </LI> </UL> </P>

A comparison between self-ordering of nanopores in aluminium oxide films achieved by two- and three-step anodic oxidation

F. Nasirpouri,M. Abdollahzadeh,M.J. Almasi,N. Parvini-Ahmadi 한국물리학회 2009 Current Applied Physics Vol.9 No.11

We report on the enhancement of naturally-occurred self-ordering of nanopores in anodic aluminium oxide (AAO) membrane by performing three step anodic oxidation. Two and three step anodic oxidation methods were used to achieve self ordering of nanopores and the ordering of nanopores obtained by the methods were compared. The current–time curves, recorded during anodization, elucidate an almost similar features for all three steps in both methods. Scanning electron micrographs (SEM) show hexagonally arranged nanopores in a way which forms highly ordered areas or ordered domains. Domains are placed beside each other like a polycrystalline structure after two and three step anodizing, while larger ones are clearly observed over the surface after three step anodizing. More uniform nanopores with narrower size distribution are observed for AAO films of three step anodic oxidation. We report on the enhancement of naturally-occurred self-ordering of nanopores in anodic aluminium oxide (AAO) membrane by performing three step anodic oxidation. Two and three step anodic oxidation methods were used to achieve self ordering of nanopores and the ordering of nanopores obtained by the methods were compared. The current–time curves, recorded during anodization, elucidate an almost similar features for all three steps in both methods. Scanning electron micrographs (SEM) show hexagonally arranged nanopores in a way which forms highly ordered areas or ordered domains. Domains are placed beside each other like a polycrystalline structure after two and three step anodizing, while larger ones are clearly observed over the surface after three step anodizing. More uniform nanopores with narrower size distribution are observed for AAO films of three step anodic oxidation.

<i>In Situ</i> Determination of the Pore Opening Point during Wet-Chemical Etching of the Barrier Layer of Porous Anodic Aluminum Oxide: Nonuniform Impurity Distribution in Anodic Oxide

Han, Hee,Park, Sang-Joon,Jang, Jong Shik,Ryu, Hyun,Kim, Kyung Joong,Baik, Sunggi,Lee, Woo American Chemical Society 2013 ACS APPLIED MATERIALS & INTERFACES Vol.5 No.8

<P>Wet-chemical etching of the barrier oxide layer of anodic aluminum oxide (AAO) was systematically investigated by using scanning electron microscopy (SEM), secondary ion mass spectrometry (SIMS), and a newly devised experimental setup that allows accurate <I>in situ</I> determination of the pore opening point during chemical etching of the barrier oxide layer. We found that opening of the barrier oxide layer by wet-chemical etching can be significantly influenced by anodization time (<I>t</I><SUB>anodi</SUB>). According to secondary ion mass spectrometry (SIMS) analysis, porous anodic aluminum oxide (AAO) samples formed by long-term anodization contained a lower level of anionic impurity in the barrier oxide layer compared to the short-term anodized one and consequently exhibited retarded opening of the barrier oxide layer during the wet-chemical etching. The observed compositional dependence on the anodization time (<I>t</I><SUB>anodi</SUB>) in the barrier oxide layer is attributed to the progressive decrease of the electrolyte concentration upon anodization. The etching rate of the outer pore wall at the bottom part is lower than that of the one at the top part due to the lower level of impurity content in that region. This indicates that a concentration gradient of anionic impurity in the outer pore wall oxide may be established along both the vertical and radial directions of cylindrical pores. Apart from the effect of electrolyte concentration on the chemical composition of the barrier oxide layer, significantly decreased current density arising from the lowered concentration of electrolyte during the long-term anodization (∼120 h) was found to cause disordering of pores. The results of the present work are expected to provide viable information not only for practical applications of nanoporous AAO in nanotechnology but also for thorough understanding of the self-organized formation of oxide nanopores during anodization.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/aamick/2013/aamick.2013.5.issue-8/am400520d/production/images/medium/am-2013-00520d_0010.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/am400520d'>ACS Electronic Supporting Info</A></P>

양극산화와 열산화 처리로 형성된 티타늄 산화막의 표면 특성과 생체활성에 관한 연구

박영준,송호준,이용렬 大韓齒科器材學會 2004 대한치과재료학회지 Vol.31 No.4

The purpose of this study was to evaluate the surface characteristics of titanium oxide films formed by anodization and thermal oxidation techniques, and to investigate its effects on formation of calcium phosphate. As experimental specimen groups, naturally oxidized film (AS-R), thin anodic oxidation film (ANO-L), thick anodic oxidation film (ANO-H) treated up to dielectric breakdown voltage, and thermal oxidation films of TH-L and TH-H treated at 530℃ and 800℃ in the air, respectively, were prepared. Surface characterization was performed using field emission-scanning electron microscopy (FE-SEM), X-ray diffractometry (XRD), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS) in order to evaluate the micro-morphology, crystalline structure, chemical composition, and binding structure of the oxide films. Bioactivity of specimen groups was investigated by evaluating the degree of calcium phosphate formation after immersing the samples in MEM for 7 days. The results were as follows: 1. Nanometer sized granular oxide particles were distributed on the surface of TH-L samples and sub-micrometer sized large crystallites were formed on TH-H samples. Irregularly shaped oxides were observed in ANO-L, and homogeneously porous oxide film having average pore size of about 0.5 ㎛ was formed in ANO-H. 2. Titanium oxide films having anatase crystalline structure were formed on ANO-L and TH-L sample surfaces. However, the preferred orientation crystal planes of ANO-L and TH-L were different to be (101) and (004) plane, respectively. Rutile crystalline structure was dominantly shown on TH-H sample, and anatase and rutile crystals were co-existed on ANO-H sample surfaces. 3. The amounts of hydroxyl group, which is related to the bioactivity of titanium implant, were higher in thermally treated specimen groups than in other groups. This result was analyzed to have close relation to the preferred orientation crystal plane and surface area of oxide films. The content of hydroxyl group increased as the density of surface titanium atoms increased, and that was least in specimen group having rutile and anatase crystalline structure in coexistence. 4. Immersion test in MEM showed that the capacity of calcium phosphate formation was dependent on total content of hydroxyl group and surface morphology of titanium oxides.

Effects of anodic spark oxidation by pulse power on titanium substrates

Park, Il Song,Lee, Min Ho John Wiley Sons, Ltd. 2011 Surface and interface analysis Vol.43 No.7

<P><B>Abstract</B></P><P>The characteristics of the oxide layer of titanium generated by anodic spark oxidation are affected significantly by the process variables. In this study, electrochemical treatments were performed while applying a direct current, a pulse current, and a reverse pulse current during anodic spark oxidation. A mixed solution of 0.015 <SMALL>M</SMALL> DL‐α‐GP (DL‐α‐glycerophosphate disodium salt) and 0.2 <SMALL>M</SMALL> CA (calcium acetate) was used as the electrolyte. The pore size generated after anodic spark oxidation was smallest in the group exposed to the reverse pulse current followed in order by the pulse current and direct current. Anatase was the major crystal phase of the TiO<SUB>2</SUB> produced on the surfaces subjected to 280 V, and the rutile phase was additionally detected in the group subjected to 320 V. The crystals precipitated on the surface after the hydrothermal treatment were hydroxyapatite (HA) crystals that had a polygonal bar‐shaped needle structure. Good activity was observed in the 320‐V pulse treated group, in which very thin needle‐shaped crystals were observed after immersing the samples in Hanks' solution for 4 weeks. The cell viability was increased greatly by anodic spark oxidation, and the surface roughness was also increased. It is believed that the surface treated using a pulse current has excellent characteristics, making it suitable for applications in biomaterials. Copyright © 2010 John Wiley & Sons, Ltd.</P>

Effects of anodized oxidation or turned implants on bone healing after using conventional drilling or trabecular compaction technique: histomorphometric analysis and RFA

Kim, Shin Koo,Lee, Han Na,Choi, Yong Chang,Heo, Seong-Joo,Lee, Cheol Won,Choie, Mok Kyun Blackwell Publishing Ltd 2006 Clinical oral implants research Vol.17 No.6

<P>Abstract</P><P>Objectives</P><P>The aim of this study was to compare the bone healing characteristics adjacent to anodic oxidation and turned surfaces after implant installation using the trabecular compaction technique or the conventional drilling technique in the soft bone area.</P><P>Material and methods</P><P>A total of 72 implants (36 anodic oxidation surface and 36 turned surface implants) were inserted into the distal end of the femur head of 12 dogs by two different surgical techniques. There were four experimental groups: (1) DT group; drilling+turned, (2) DO group; drilling+oxidation, (3) CT group; compaction+turned, and (4) CO group; compaction+oxidation. The resonance frequency was measured and six specimens/treatment group were obtained at 0, 3 and 8 weeks, postoperatively. Undecalcified ground sections were prepared for histologic and histomorphometric examinations.</P><P>Results</P><P>At week 0, the trabecular compaction groups showed a higher bone to implant contact ratio (BIC) than the conventional drilling groups, regardless of surface types. The CT group showed a higher implant stability quotient (ISQ) than the DT group. At week 3, the oxidation groups showed a higher BIC than the turned groups regardless of the surgical technique used. The CO group showed higher ISQ than the CT group. At week 8, there was no statistically significant difference in BIC and ISQ between the groups.</P><P>Conclusions</P><P>Surgical technique and implant surface state have an effect on the initial bone response to two-stage implants inserted into trabecular bone regions.</P>

Comparative Study of Pore Characterizations of Anodized Al–0.5 wt.% Cu Thin Films in Oxalic and Phosphoric Acids

Alaa M. Abd-Elnaiem,S. Moustafa,T. B. Asafa 성균관대학교(자연과학캠퍼스) 성균나노과학기술원 2019 NANO Vol.14 No.11

Porous anodic alumina (PAA) thin films, having interconnected pores, were fabricated from Cu-doped aluminum films deposited on p-type silicon wafers by anodization. The anodization was done at four different anodizing voltages (60 V, 70 V, 80V and 90 V) in phosphoric acid and two voltages (60V and 70 V) in oxalic acid. The aluminum and PAA samples were characterized by SEM and XRD while the pore arrangement, pore density, pore diameter, pore circularity and pore regularity were also analyzed. XRD spectra confirmed the aluminum to be crystalline with the dominant plane being (220), the Cu-rich phase have an average particle size of 15 ffi 5nm uniformly distributed within the Al matrix of 0.4-μm grain size. The steady-state current density through the anodization increased by 117% and 49% for oxalic and phosphoric acids, respectively, for 10V increase (from 60 to 70 V) in anodization voltage. Similarly, the etching rate increased by 100% for oxalic acid and by 40% for phosphoric acid which are responsible for 47% and 29% decreases in anodization duration, respectively. The highest value of circularity obtained for anodized Al–0.5wt.% Cu formed in oxalic acid at 60V was 0.86, and it was 0.80 for the phosphoric acid at 90 V. Anodization of Al–0.5wt.% Cu films allows the formation of circular pores directly on p-type silicon wafers which is of importance for future nanofabrication of advanced electronics. The results of anodized Al–0.5wt.% Cu thin film were compared with other anodized systems such as anodized pure Al and Al doped with Si.

Anodic aluminum oxide supported Cu-Zn catalyst for oxidative steam reforming of methanol

김정현,장영신,김재창,김동현 한국화학공학회 2019 Korean Journal of Chemical Engineering Vol.36 No.3

Oxidative steam reforming of methanol (OSRM) is autothermal and therefore well suited for hydrogen production. The exothermic part of OSRM generates heat at the reactor inlet to be used as the reaction heat for the endothermic methanol steam reforming in the rest of the reactor. With conventional particle catalysts, a hot spot is formed at the reactor inlet because of the poor thermal conductivity in the catalyst bed. The catalyst at the hot spot is deactivated by thermal sintering. Side reactions such as the reverse water gas shift reaction and methanol decomposition reaction become active at the hot spot. We developed a high-thermal-conductivity Al plate catalyst to suppress the formation of the hot spot in the catalyst bed during OSRM. In particular, a strongly bonded layer of anodic aluminum oxide as a catalyst support was grown on the Al plate surface via anodic oxidation in oxalic acid solution, and the internal surface area of the support was increased by pore widening and hot water treatments. To obtain a catalyst with high activity, multiple impregnations (>three times) and an anodization time of 24 h was needed. The catalyst was deactivated when operated at an elevated temperature of 623 K, but the activity was completely restored by a simple oxidation. Notably, OSRM was proven to be a combination of methanol combustion and methanol steam reforming reactions, and the kinetics of these two reactions were studied in detail.

Sonochemical assisted synthesis of nano-structured titanium oxide by anodic oxidation

Neupane, M.P.,Park, I.S.,Bae, T.S.,Lee, M.H. Elsevier Sequoia 2013 Journal of alloys and compounds Vol.581 No.-

This work describes the effect of electrolyte agitation conditions on the anodic growth of nano-structured titanium oxide on titanium samples of size 20mmx10mm (thickness 2mm) in an electrolyte containing 0.02M calcium glycerophosphate (Ca-GP) and 0.15M calcium acetate (CA). Magnetic stirring and different intensities of ultrasonic waves were applied during anodization. The application of ultrasonic waves during anodization was found to increase the reaction rates; the higher the ultrasonic irradiation power, the faster the growth rate of nano-structured titania. The diameters of the pores created under ultrasonic wave conditions were found to be larger than those of the pores created under magnetic stirring conditions in the corresponding nano-structured titania. An increase in the sonication power to 180, 250, and 350W resulted in an increase in the density, uniformity and diameters of the pores, respectively. The surface roughness and Ca/P ratio also increased with an increase in the sonication power. It was found that the applied ultrasonic wave could determine the surface morphology, properties and compositions of the anodic oxide films. We believe that sonoelectrochemistry is a simple method to design and synthesize nanostructured titanium oxide for implant applications.

카복실산 용액에서 양극산화에 의해 형성된 나노다공성 금 표면상의 전기화학적 글루코오스 산화

노성진,정화경,이금섭,김민주,김종원,Roh, Seongjin,Jeong, Hwakyeung,Lee, Geumseop,Kim, Minju,Kim, Jongwon 한국전기화학회 2013 한국전기화학회지 Vol.16 No.2

세 가지 종류의 카복실산(포름산, 아세트산, 프로피온산) 용액 하에서 양극산화 반응을 통한 나노 다공성 금(nanoporous gold, NPG) 구조의 형성과 NPG 전극 표면 상의 전기화학적 글루코오스 산화반응을 관찰하였다. 세 가지 카복실산 용액 조건 중에서 포름산 용액 조건하의 양극산화를 통해 형성된 NPG 전극에서 글루코오스의 산화 활성이 가장 우수하였다. 포름산 용액 조건하의 양극산화 과정에서 가장 우수한 글루코오스 산화 활성을 얻기 위한 최적 조건은 인가전위 5.0 V와 반응시간 4시간이었다. 카복실산 용액 하에서 형성된 NPG 상의 전기화학적 글루코오스 산화 활성을 염소이온의 부재 및 존재 하 조건에서 관찰하고, 이를 옥살산 용액 하에서 형성된 NPG 상의 거동과 비교 분석하였다. 포름산 용액 하에서 최적 조건으로 형성된 NPG 전극상에서 글루코오스의 전류법 검출 응용을 제시하였다. We investigate the formation of nanoporous gold (NPG) surfaces by anodization in three carboxylic acid (formic acid, acetic acid, and propionic acid) solutions and the electrochemical oxidation of glucose at NPG surfaces. Among three carboxylic acids, formic acid provided the most efficient conditions for NPG formation towards glucose oxidation. The optimized conditions during anodization in formic acid for glucose oxidation were 5.0 V of applied potential and 4 hour of reaction time. Electrocatalytic activities for glucose oxidation at NPG surfaces prepared by anodization in carboxylic acids were examined under the absence and presence of chloride ions, which were compared to those observed at NPG prepared in oxalic acid solutions. The application NPG prepared by optimized anodization conditions in formic acid to the amperometric detection of glucose was demonstrated.