J.M Hu
,
J.X. Wu
,
H.M Meng
,
YR. Zhu
,
D.B. Sun and D.J. Yang(Beijing Corrosion and Protection Center
,
Open Laboratory of Corrosion
,
Erosion and Surface Technology
,
University of Science and Technology Beijing
,
Beijing 100083
,
China)
金属学报(英文版)
Titanium based IrO2 +Ta2O5 oxide anodes with different compositions and pyrolysis temperatures were prepared by termodecompoisition method. By using X-ray diffraction (XRD), the structure and texture coefficient of the coatings, TC(hkl), of IrO2 rutile crystal have been tested. It showed that, the crystallization processes of IrO2 and Ta2O5 in xIrO2 +(100-x) Ta2 O5 (x is in mol%) films affected and confined each other.In the mixed system, IrO2 rutile phase existed as a solid solution with Ta, and attained the maximum solubility when x=70mol%, i.e. for the coating of 70% IrO2 +Ta2O5.For the coatings of low iridium content or at low preparing tem pemture, (110) and (101) pwtered orientations were dominant. However, preferred growth of IrO2 weakened with increasing either iridium content or temperature. Three typical surface morphologies were observed by using scanning electron tnicroscopy(SEM). The crystallite size of the mixed oxide coatings were finest for the the film of 70%IrO2 +30%Ta2O5,and decreased with the pyrolysis tempemture. As the results of the finest crystallite segregating on sudece and the maxitnum solid solubility of Ir and Ta component in deposits, the coatings with the composition of 70%IrO2 +Ta2O5 prepared at 450℃ presented the mdrimutn electrocatalgtic activitg for O2 evolution in 0. 5M H2SO4 solution.UP to 550℃, Ti base suffered to oxidation resulting in decreasing anode conductivity,therefore, coatings performed a low activity.
关键词:
titanium based coating anode
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Progress in Organic Coatings
Sol-gel coatings were prepared using 3-glycidoxypropyltrimethoxysilane (GPTMS) and tetraethoxysilane (TMOS) as precursors, diethylentriamine as curing agent. Inhibition effect of 2-methyl piperidine on AZ91D in 0.005%, 0.05% and 0.5% (wt.%) NaCl solution is investigated. Potentiodynamic polarization tests revealed that 2-methyl piperidine significantly decreased the anodic activity of AZ91D especially at high concentration. Corrosion behaviors of sol-gel coatings incorporated with 2-methyl piperidine on AZ91D in the Harrison's solution were analyzed using electrochemical impedance spectroscopy (EIS). EIS results showed the corrosion resistance of sol-gel coatings and sol-gel sealed phosphate conversion coating on AZ91D were significantly improved through addition of 2-methyl piperidine. Fourier transform infrared spectra (FT-IR) confirmed that the 2-methyl piperidine was compatible with sol-gel matrix. (C) 2009 Elsevier B.V. All rights reserved.
关键词:
Sol-gel coatings;Magnesium alloy;Inhibitor;Corrosion;parameters;resistance;inhibitors;aa2024-t3;films
Corrosion Science
The corrosion of die cast AZ91D was studied and related to its microstructure. For comparison and to more fully understand the behaviour of die cast AZ91D, corrosion studies and microstructural examinations were also carried out using slowly solidified high purity AZ91, Mg-2%Al, Mg-9%Al, low purity magnesium and high purity magnesium. Corrosion was studied in 1N NaCl at pH 11 by (1) observing the corrosion morphology, (2) measuring electrochemical polarisation curves and (3) simultaneously measuring both the hydrogen evolution rate and the magnesium dissolution rate. The skin of die cast AZ91D showed better corrosion resistance than the interior. This is attributed to a combination of(1) a higher volume fraction of the beta phase, (2) a more continuous beta phase distribution around finer alpha grains, and (3) lower porosity in the skin layer than in the interior of the die casting. This study showed that the casting method can influence the corrosion performance by its influence on the alloy microstructure. (C) 1999 Elsevier Science Ltd. All rights reserved.
关键词:
magnesium alloys;AZ91D;diecasting;corrosion;microstructure;magnesium;alloys
Electrochimica Acta
Corrosion behavior of cast, homogenized (T4) and microcystallized (mc) AZ91D alloy was investigated in NaCl aqueous solution by gas collection and electrochemical measurement. The capacitance property of the product films formed on mc alloy and cast alloy was studied by Mott-Schottky approach. The results implied that the grain size have a significant influence on the corrosion resistance of AZ91D alloy as well as P phase. The product films behaved as P-type semiconductor with the increasing of anodic potential. TEM observation indicated that the particle size of the product film on the me alloy (< 10 nm) was far smaller than that on the cast alloy (200 nm), which might be beneficial to the widening of energy band and the decreasing of acceptor concentration in the product film on me alloy. (c) 2005 Elsevier Ltd. All fights reserved.
关键词:
magnesium alloy;microcrystallization;sputtering;corrosion;TEM;small semiconductor crystallites;magnesium;behavior;heterogeneity;oxidation;films;size;electron;chloride;sulfate
Applied Surface Science
High corrosion resistance Cu/Ni-P coatings were electrodeposited on AZ91D magnesium alloy via suitable pretreatments, such as one-step acid pickling-activation, once zinc immersion and environment-friendly electroplated copper as the protective under-layer, which made Ni-P deposit on AZ91D Mg alloy in acid plating baths successfully. The pH value and current density for Ni-P electrodeposition were optimized to obtain high corrosion resistance. With increasing the phosphorous content of the Ni-P coatings, the deposits were found to gradually transform to amorphous structure and the corrosion resistance increased synchronously. The anticorrosion ability of AZ91D Mg alloy was greatly improved by the amorphous Ni-P deposits, which was investigated by potentiodynamic polarization curve and electrochemical impedance spectroscopy (EIS). The corrosion current density (I(corr)) of the coated Mg alloy substrate is about two orders of magnitude less than that of the uncoated. (C) 2011 Elsevier B. V. All rights reserved.
关键词:
AZ91D Mg alloy;Electrodeposition;Ni-P;Corrosion resistance;phosphorus incorporation;pure magnesium;thin-films;ni;pretreatment;deposits;behavior;copper
Acta Physico-Chimica Sinica
The corrosion behavior of anodized AZ91D magnesium alloy in neutral 1% (w) NaCl aqueous solution was investigated by salt spray test, polarization Curve, electrochemical impedance spectroscopy (E-IS), electrochemical noise (EN) and scanning electron microscope (SEM). The results showed that the corrosion behavior of Mg alloy presented characteristic changes due to anodization. For example, the unsealed anodic film Could be sustained in 5% NaCl salt spray beyond 200 h, E-corr of anodized magnesium alloy shifted up and the inductive period for pitting corrosion was obviously prolonged, and the impedance modules in high frequency of anodized alloy were several thousand times those of unanodized alloy. All these proved that anodization process made the alloy gain excellent property of anti-corrosion. The evolution of fractal dimension (D-r) was first utilized to depict the corrosion process of anodized AZ91D magnesium alloy and shown as rapid increasing in the initial, fluctuating in the medium and decreasing in the last. This evolution was related with the three different corrosion stages of anodized AZ91D magnesium alloy in 1% NaCl solution.
关键词:
AZ91D magnesium alloy;Anodization;EN;EIS;Fractal dimension;mg-al alloys;electrochemical noise;impedance spectroscopy;atmospheric;corrosion;sodium-chloride;pure al;dimension;coatings
Corrosion Science
For better understanding of the roles of beta phase in the corrosion processes of AZ91D alloy, corrosion behavior of a cast (alpha + beta phase) and a homogenized (beta phase) AZ91D alloy was investigated in NaCl aqueous solution by gas collection and electrochemical measurements. According to the hydrogen evolution properties during corrosion, two different types of corrosion tend might be differentiated. For type I, hydrogen diffused into alloy, which evoked the decreasing of hydrogen evolution rate (HER) and the weakening of negative difference effect (NDE). For type II, in the corrosion process, hydrogen in the alloys diffused into the product film (P-type semiconductor), which suggested that hydrogen entering the film would be ionized. The generated electrons during ionization decreased the concentration of vacancies in the valence band of the product films, indicating an improvement of corrosion resistance of AZ91D alloy. (c) 2005 Elsevier Ltd. All rights reserved.
关键词:
magnesium alloy;beta phase;effect of hydrogen;corrosion;EIS;310 stainless-steel;anodic-dissolution;hydrogen;behavior;chloride;film;mg
International Journal of Electrochemical Science
A plasma electrolytic oxidation (PEO) ceramic coating F-B-A with excellent compactness was prepared on magnesium alloy AZ91D in acidic KF solution with dihydric phosphate by applying a bipolar pulse voltage. For comparison, two other coatings F-M and F-M-A were prepared in the same solution with and without addition of dihydric phosphate by applying a mono-polar pulse voltage. The composition and microstructure of the coatings were characterized by XRD, XPS and SEM. While their corrosion performance in 3.5% NaCl solution was examined by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). Results showed that the F-B-A coating was uniform and compact without fissures on surface, and its porosity was around 4.8%; while the other coatings were loose and porous with porosity around 45.6% and 27.9%, respectively. The F-B-A coating showed a bi-layered microstructure, of which the outer consisted mainly of KMgF(3) and MgF(2) with seldom MgO, whereas, the inner mainly of MgF(2), Mg(3) (PO4)(2), MgHPO(4) and little MgO. The magnesium alloy with F-B-A coating exhibited corrosion resistance about three orders higher than the sample with the F-M coating. EIS tests indicated that this bi-layered coating slowed down the penetration rate of chlorine ions and postponed the initiation of pitting corrosion on substrate.
关键词:
PEO coating;magnesium alloy;KF based electrolyte;bipolar mode;corrosion behavior;plasma electrolytic oxidation;electrochemical impedance spectroscopy;silicate-containing electrolytes;microarc oxidation;nacl solution;mg;alloy;resistance;films;behavior;aluminum
材料科学技术（英文）
By combination of magnetron sputtering deposition and vacuum annealing, an aluminum diffusion coating was prepared on the substrate of AZ91D alloy to improve its corrosion resistance. The microstructure and composition of the diffusion coating was investigated by scanning electron microscopy and X-ray diffraction. The diffusion coating was mainly comprised of beta phase-Al12Mg17. The continuous immersion test in 3.5 wt pct neutral NaCl solution indicated that the specimen with diffusion coating had better corrosion resistance compared with the bare AZ91D alloy specimen. The potentiodynamic polarization measurement indicated that the diffusion coating could function as an effectively protective layer to reduce the corrosion rate of AZ91D alloy when exposed to 3.5 wt pct NaCl solution.
关键词:
AZ91D;magnesium alloy;corrosion;diffusion coating;protection
