Cathodic protection is widely recognized as the most cost effective and technically appropriate corrosion prevention methodology for the port, offshore structures, ships. When applying the cathodic protection method to metal facilities in seawater, on the surface of the metal facilities a compound of calcium carbonate(CaCO 3 ) or magnesium hydroxide(Mg(OH) 2 ) films are formed by Ca 2+ and Mg 2+ ions among the many ionic components dissolving in the seawater. And calcareous deposit films such as CaCO 3 and Mg(OH) 2 etc. are formed by the surface of the steel product. These calcareous deposit film functions as a barrier against the corrosive environment, leading to a decrease in current demand. On the other hand, the general calcareous deposit film is a compound like ceramics. Therefore, there may be some problems such as weaker adhesive power and the longer time of film formation uniting with the base metal. In this study, we tried to determine and control the optimal condition through applying the principle of cathodic current process to form calcareous deposit film of uniform and compact on steel plate. The quantity of precipitates was analyzed, and both the morphology, component and crystal structure were analyzed as well through SEM, EDS and XRD. And based on the previous analysis, it was elucidated mechanism of calcareous deposit film formed in the sacrificial anode type (Al, Zn) and current density (1, 3, 5 A/m 2 ) conditions. In addition, the taping test was performed to evaluate the adhesion.
To improve the corrosion resistance of an electro-galvanized steel sheet, we deposited magnesium film on it using a vacuum evaporation method and annealed the films at 250–330°C. The zinc–magnesium alloy is consequently formed by diffusion of magnesium into the zinc coating. From the anodic polarization test in 3% NaCl solution, the films annealed at 270–290°C showed better corrosion resistance than others. In X-ray diffraction analysis, ZnMg 2 was detected throughout the temperature range, whereas Mg 2 Zn 11 and FeZn 13 were detected only in the film annealed at 310°C. The depth composition profile showed that the compositions of Mg at 270–290°C are evenly and deeply distributed in the film surface layer. These results demonstrate that 270–290°C is a proper temperature range to produce a layer of MgZn 2 intermetallic compound to act as a homogenous passive layer.
Most reports on the fabrication of high-quality Gallium nitride (GaN) are typically based on physical techniques that require very expensive equipment. Therefore, the electrodeposition was adopted and examined to develop a simple and economical method for GaN synthesis. GaN films are synthesized on aluminum substrates that are heat-treated at various temperatures using a low-cost and low-temperature electrochemical deposition technique. The electrochemical behavior of source ions in aqueous solutions is examined by cyclic voltammetry (CV). In the solution at pH 1.5 containing 0.1M Ga(NO 3 ) 3 , 2.5 M NH 4 NO 3 and 0.6 M H 3 BO 3 , reduction of gallium and nitrate ions are observed in CV. The presence of hexagonal GaN and gallium oxide (Ga 2 O 3 ) phases is detected for the films deposited on Al substrates at −3.5 mA•cm -2 for 3 h. The energy dispersive X-ray and mapping results reveal that Ga, O, and N coexist in these films. Raman analysis shows hexagonal GaN formation on Al substrates. The changes in the morphology and preferred orientation of GaN were found, which was caused by the reactivity of aluminum surface and the aluminum oxide layer formed by the heat treatment.
This study was intended to investigate the effect of the amount of magnesium addition and heat treatment in the Al-Mg coating film in order to improve corrosion resistance of aluminum coating. Al-Mg alloy films were deposited on cold rolled steel by physical vapor deposition sputtering method. Heat treatment was fulfilled in an nitrogen atmosphere at the temperature of 400°C for 10 min. The morphology was observed by SEM, component and phase of the deposited films were investigated by using GDLS and XRD, respectively. The corrosion behaviors of Al-Mg films were estimated by exposing salt spray test at 5 wt.% NaCl solution and measuring polarization curves in deaerated 3 wt.% NaCl solution. With the increase of magnesium content, the morphology of the deposited Al-Mg films changed from columnar to featureless structure and particle size was became fine. The x-ray diffraction data for deposited Al-Mg films showed only pure Al peaks. However, Al-Mg alloy peaks such as Al 3 Mg 2 and Al 12 Mg 17 were formed after heat treatment. All the sputtered Al-Mg films obviously showed good corrosion resistance compared with aluminum and zinc films. And corrosion resistance of Al-Mg film was increased after heat treatment.
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