71 research outputs found
Structure of corrosion product formed on carbon steel covered with NiSO4-Added resin coating under sulfuric acid mist environment containing chloride
No full textShota Hayashida, Masamitsu Takahashi, Hiroshi Deguchi, Hiroaki Tsuchiya, Koushu Hanaki, Masato Yamashita, Shinji Fujimoto, Structure of Corrosion Product Formed on Carbon Steel Covered with NiSO4-Added Resin Coating under Sulfuric Acid Mist Environment Containing Chloride, Materials Transactions, 2021, Volume 62, Issue 6, Pages 781-787, Released on J-STAGE May 25, 2021, Advance online publication May 14, 2021, Online ISSN 1347-5320, Print ISSN 1345-9678, https://doi.org/10.2320/matertrans.C-M2021819.Corrosion resistance of carbon steel covered with resin coating containing nickel sulfate has been evaluated under chloride and sulfuric acid mist environment. The structure of corrosion products formed on steel surface was investigated by XRD and XAFS analyses using synchrotron radiation. Nickel sulfate promoted the formation of goethite and akaganeite. It was considered that this akaganeite was not tetragonal β-FeOOH but monoclinic akaganeite containing nickel
Uniaxial Magnetization and Electrocatalytic Performance for Hydrogen Evolution on Electrodeposited Ni Nanowire Array Electrodes with Ultra-High Aspect Ratio
No full textNi nanowire array electrodes with an extremely large surface area were made through an electrochemical reduction process utilizing an anodized alumina template with a pore length of 320 µm, pore diameter of 100 nm, and pore aspect ratio of 3200. The electrodeposited Ni nanowire arrays were preferentially oriented in the (111) plane regardless of the deposition potential and exhibited uniaxial magnetic anisotropy with easy magnetization in the axial direction. With respect to the magnetic properties, the squareness and coercivity of the electrodeposited Ni nanowire arrays improved up to 0.8 and 550 Oe, respectively. It was also confirmed that the magnetization reversal was suppressed by increasing the aspect ratio and the hard magnetic performance was improved. The electrocatalytic performance for hydrogen evolution on the electrodeposited Ni nanowire arrays was also investigated and the hydrogen overvoltage was reduced down to ~0.1 V, which was almost 0.2 V lower than that on the electrodeposited Ni films. Additionally, the current density for hydrogen evolution at −1.0 V and −1.5 V vs. Ag/AgCl increased up to approximately −580 A/m2 and −891 A/m2, respectively, due to the extremely large surface area of the electrodeposited Ni nanowire arrays
CPP-GMR Performance of Electrochemically Synthesized Co/Cu Multilayered Nanowire Arrays with Extremely Large Aspect Ratio
No full textAnodized aluminum oxide (AAO) films, which have numerous nanochannels ca. 75 nm in diameter, D and ca. 70 µm in length, L (ca. 933 in aspect ratio, L/D), were used as a template material for growing Co/Cu multilayered nanowire arrays. The multilayered nanowires with alternating Cu layer and Co layers were synthesized by using an electrochemical pulsed-potential deposition technique. The thickness of the Cu layer was adjusted from ca. 2 to 4 nm while that of the Co layer was regulated from ca. 13 to 51 nm by controlling the pulsed potential parameters. To get a Co/Cu multilayered nanowire in an electrochemical in-situ contact with a sputter-deposited Au thin layer, the pulsed potential deposition was continued up to ca. 5000 cycles until the nanowire reached out toward the surface of AAO template. Current-perpendicular-to-plane giant magnetoresistance (CPP-GMR) effect reached up to ca. 23.5% at room temperature in Co/Cu multilayered nanowires with ca. 3500 Co/Cu bilayers (Cu: 1.4 nm and Co: 18.8 nm). When decreasing the thickness of Co layer, the CPP-GMR value increased due to the Valet–Fert model in the long spin diffusion limit
Uniaxial magnetization reversal process in electrodeposited high-density iron nanowire arrays with ultra-large aspect ratio
No full textIn this study, magnetization reversal modes of iron nanowire arrays with large aspect ratios were investigated by Shtrikman's micromagnetic theory. The iron nanowire arrays were potentiostatically electrodeposited into anodized aluminum oxide nanochannels with average diameters, Dp, of ca. 33 nm, 52 nm, 67 nm, and 85 nm. The growth rate of the iron nanowires was ca. 105 nm s−1 at the cathode potential of −1.2 V (vs. an Ag/AgCl reference), and the axial length, Lw, reached up to ca. 60 µm. Maximum aspect ratio, Lw/Dw of the iron nanowires was found to be ca. 1800, and the axial direction coincided with 〈1 1 0〉 direction of the bcc-Fe crystal structure. The effect of the average diameter size on the coercivity of iron nanowire arrays corresponded well to the theoretical estimate, which was calculated by the magnetization curling mode in Shtrikman's micromagnetic theory. As the average diameter of the iron nanowires was decreased, coercivity and squareness of the nanowire arrays increased up to 1.63 kOe and 0.87, respectively
Microhardness and tensile strength of electrochemically synthesized nickel-cobalt binary alloy sheets exfoliated from a dumbbell-shaped titanium cathode
No full textNanocrystalline nickel–cobalt (Ni–Co) binary alloy sheets were fabricated through electroforming in an acidic aqueous bath using exfoliation from a metallic titanium cathode. Cobalt content in Ni–Co alloy sheets ranged from 28.8 at% to 72.0 at% depending on experimental parameters, such as cathodic overpotential and bath composition. The surface roughness ( R _a ) of the electroformed alloy sheets significantly decreased down to 1.5 μ m as saccharin sodium dihydrate was added as an additive to the acidic aqueous solution bath. X-ray diffraction profiles and transmission electron microscopy images indicated that the electroformed Ni–Co alloy sheets have a nanocrystalline structure (grain size ≈ 30 nm). The lattice constant of the electroformed Ni–Co alloy sheets increased with an increase in cobalt content (i.e. solute atom concentration). The mechanical properties were significantly improved because of the synergistic effects of crystal grain refinement and solid solution strengthening. The microhardness and tensile strength of the electroformed Ni–Co alloy sheets reached 609 kgf mm ^−2 and 1757 MPa ( X _Co = 49.9 at%), respectively. The tensile strength of the electroformed Ni–Co alloy sheets in this study significantly exceeded that of solidified Ni–Co alloys (approximately 370 MPa). Therefore, this study offers a technique to enhance the mechanical properties of electroformed Ni–Co alloy sheets
Effect of Ni addition on CPP-GMR response in electrodeposited Co-Ni/Cu multilayered nanocylinders with an ultra-large aspect ratio
No full textEffect of Co–Ni alloy composition on the current perpendicular-to-plane giant magnetoresistance (CPP-GMR) response of electrochemically synthesized Co–Ni/Cu multilayered nanocylinders was studied using anodized aluminum oxide membranes (AAOM) with nanochannel diameterD∼67 nm and length L∼70 μm. Co–Ni/Cu multilayered nanocylinders, which have an aspect ratio L/Dof ∼1,045, were fabricated in theAAOMnanochannel templates by utilizing a pulse-current electrochemical growth process in an electrolytic bath with Co2+,Ni2+ and Cu2+ ions. Co–Ni/Cu alternating structure with Co84Ni16 alloy layer-thickness of 9.6 nmand Cu layer-thickness of 3.8 nm was clearly observed in a nanocylinder with a diameter of 63 nm. The alternating structure was composed from crystalline layers with preferential orientations in hcp-CoNi (002) and fcc-Cu (111). The Co–Ni/Cu multilayered nanocylinders were easily magnetized in the long axis direction because of the extremely large aspect ratio L/D. InCo84Ni16/Cu multilayered nanocylinders, the coercivity and squareness were∼0.46 kOe and∼0.5, respectively. The CPP-GMR value was achieved up to 22.5% (at room temperature) in Co84Ni16/Cu multilayered nanocylinders.Materials Research Express, 9 (7), art. no. 075007; 2022journal articl
Determination of Cobalt Spin-Diffusion Length in Co/Cu Multilayered Heterojunction Nanocylinders Based on Valet–Fert Model
No full textAnodized aluminum oxide (AAO) nanochannels of diameter, D, of ~50 nm and length, L, of ~60 µm (L/D: approx. 1200 in the aspect ratio), were synthesized and applied as an electrode for the electrochemical growth of Co/Cu multilayered heterojunction nanocylinders. We synthesized numerous Co/Cu multilayered nanocylinders by applying a rectangular pulsed potential deposition method. The Co layer thickness, tCo, ranged from ~8 to 27 nm, and it strongly depended on the pulsed-potential condition for Co layers, ECo. The Cu layer thickness, tCu, was kept at less than 4 nm regardless of ECo. We applied an electrochemical in situ contact technique to connect a Co/Cu multilayered nanocylinder with a sputter-deposited Au thin layer. Current perpendicular-to-plane giant magnetoresistance (CPP-GMR) effect reached up to ~23% in a Co/Cu multilayered nanocylinder with ~4760 Co/Cu bilayers (tCu: 4 nm and tCo: 8.6 nm). With a decrease in tCo, (ΔR/Rp)−1 was linearly reduced based on the Valet–Fert equation under the condition of tF > lFsf and tN < lNsf. The cobalt spin-diffusion length, lCosf, was estimated to be ~12.5 nm.Nanomaterials, 11(1), art.no.218; 2021journal articl
Determination of Cobalt Spin-Diffusion Length in Co/Cu Multilayered Heterojunction Nanocylinders Based on Valet–Fert Model
No full textMechanical properties of Cu-Ni alloy thick films electrodeposited from aqueous solution containing pyrophosphate as a complexing agent
No full textCu-Ni alloy thick films with a thickness of approximately 170 µm were electrodeposited from an aqueous solution containing pyrophosphate as a complexing agent. The electrodeposited Cu-Ni alloy thick films with a dumbbell shape were exfoliated from a metallic titanium cathode to examine the crystal orientation, microhardness and tensile strength. The average crystallite size of electrodeposited Cu-Ni alloy thick films was around 30 nm. The microhardness increased up to 327 HV with increasing the Ni content up to ∼19 % while the maximum tensile strength reached 726 MPa at the Ni content of ∼13 %. The improvement of these mechanical properties can be explained by two strengthening mechanisms of solid solution alloying and crystallite size refining.Journal of Alloys and Compounds, 1026, art. no. 180398; 2025journal articl
Effect of Ni addition on CPP-GMR response in electrodeposited Co-Ni/Cu multilayered nanocylinders with an ultra-large aspect ratio
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