Zn-Ni alloy pulse electrodepositionand study of corrosion behavior

• Main Authors: Chi-Ming Huang, 黃啟明
• Other Authors: none
• Format: Others
• Language: zh-TW
• Published: 2003
• Online Access: http://ndltd.ncl.edu.tw/handle/84905098825368428279

碩士 === 國立雲林科技大學 === 工業化學與災害防治研究所 === 91 === Taiwan is located at the subtropical zone and surrounded by the sea. The marine wind entrains much sodium chloride and moisture from the sea toward the coastal regions, so a large amount of salinity and high humidity is in the coastal region atmospheres. Furthermore, due to a great many industrial areas located in the western coastal regions, SO2 is continuously emitted to the atmosphere. Therefore, high humidity, much sodium chloride and low pH causes severely metallic corrosion in the western coastal regions. In general, the metallic corrosion rate depends on corrosion factors such as the intensity of UV, the time of wetness and Cl- /SO2 deposition rates. The metallic corrosion rate is influenced not only by metallic anticorrosion but also by metallic surface coatings. Therefore, electrodeposition that makes a great effort to accomplish coatings once for all without future trouble is chosen to prepare different electrodeposited films on steel. Next, the steel and electrodeposited films on steel are used as the specimens for laboratory accelerated corrosion tests and then the corrosion rates of the specimens are obtained. In addition, the Cl- /SO2 collected in a marine industrial area are used to calculate the Cl- /SO2 deposition rates. At the same time and location, the steel and electrodeposited films on steel are used as the specimens for natural exposure tests and then the corrosion rate of the specimens are obtained. At last, the best electrodeposited film on steel for anticorrosion of the Cl- /SO2 is gotten according to the results of laboratory accelerated corrosion tests and natural exposure tests. The correlation model between laboratory accelerated corrosion rates and natural exposure corrosion rates can also be developed by the method of convertible coefficients. So, the correlation model and corrosion factors are utilized to estimate long term atmospheric corrosion without having to carry out natural exposure tests which involve long waiting time and considerable expenses. As the results, is the important parameter for Ni content in Zn-Ni alloy. We use parameters of electrodeposition(IP=150mA/cm2,T=40℃,Ton=1,Toff=4)to coating Zn-Ni alloy on steel, and from the results of in door accelerated corrosion tests and outdoor atmospheric, we find that the Zn-Ni alloy(Ni%=11.89%)has the minimum weight loss. In the other hand, we use the equation of corrosion rate to project the weight loss for atmospheric tests of sample(A,B,C)in Formosa Mai-Liao industrial park, the error of sample A(Ni=11.89%)is 21.2244%, the error of sample B(Ni=22.4%)is 19.1982%, the error of sample C(Ni=59.21%)is 21.2349%. We use Tafel curve to measure Ecorr and Icorr of different composition of Zn- Ni alloy. As the results, the Zn-Ni alloy(Ni=11.89%) has the maximum Ecorr(Ecorr = -0.458 volt) and the minimum Icorr(Icorr= 8.075E-7 A/cm2；reference to Ag/AgCl),the other hand, we also use AC Impedance to measure the polarization resistance(Rp) of Zn-Ni, we find that Zn-Ni alloy (Ni=11.89%) has the .maximum Rp(Rp=874.1 ohm). From the Nyquist diagram of different composition of Zn-Ni alloy, we find all Zn-Ni alloy have semicircle diagram, and it indicate that the all reactions are controlled by activation. The Bode diagram show that the range of phase degree is -50 to 0. At last, we use FT-IR to analysis the productions after corrosion tests, not only outdoor atmospheric corrosion tests but also indoor accelerated corrosion tests, the productions of corrosion tests are Zn(OH)2 and ZnCl2.