液相还原法并热压制备的纳米晶Ag-50Ni合金在含Cl^-介质中腐蚀电化学行为研究

ELECTROCHEMICAL CORROSION BEHAVIOR IN CHLORIDE ION CONTAINING MEDIA OF A NANOCRYSTALLINE BULK Ag-50Ni ALLOY

用液相还原法制备纳米尺寸Ag-50Ni粉末而后热压制得其纳米块体合金,并与传统粉末冶金法制备的粗晶Ag-50Ni合金对比研究了它们在含Cl-介质中的腐蚀电化学行为.结果表明:合金粉末平均粒径约为45nm,真空热压后,晶粒有所长大,但仍为纳米尺度;随Cl-浓度增加,两种尺寸Ag-50Ni合金的腐蚀电流密度均增加,腐蚀速度加快;晶粒尺寸降低后,腐蚀电流密度略有增加,腐蚀速度变快;当极化电位增到某一程度后,两种尺寸Ag-50Ni合金均出现钝化;纳米尺寸Ag-50Ni合金在含0.02mol/LCl-介质中的交流阻抗谱由双容抗弧组成,其余均由单容抗弧组成,腐蚀受电化学反应控制.

Precursory alloy powders with an average particle size of about 45nm were obtained by aqueous reducing method firstly and then a nanocrystalline Ag-50Ni bulk alloy was prepared through hot pressing the precursor at 620℃ under a pressure of 58 MPa. The grain sizes of the bulk alloy after hot pressing still remained in nano-size range. The electrochemical corrosion behavior of the nano-alloy was compared in chloride ion containing media with the corresponding coarse grained alloy prepared by conventional powder metallurgy. Corrosion current densities of nanocrystalline and coarse grained Ag-50Ni alloys increase and therefore corrosion rates become faster with the increment of chloride ion concentrations. However, the corrosion current densities of nanocrystalline Ag-50Ni are a little bigger than those of the corresponding coarse grained Ag-50Ni. Ag-50Ni alloys showed passivation behavior in media containing chloride ions with increment of polarization potentials. EIS plot of nanocrystalline Ag-50Ni is composed of single capacitive loop in a medium containing 0.05 mol/L Na2SO4 plus 0. 02 mol/L NaCl,while the others are composed of double capacitive loops. Thus, corrosion processes are controlled by electrochemical reactions.