Study on electrochemical properties of Zr60Cu20Ni8Al7HOTi2 bulk metallic glass in sulfuric acid solutions

摘要

Zr60Cu20Ni8Al7Hf3Ti2 bulk metallic glass (BMG) was produced by copper mold casting. X-ray diffraction pattern of as-sprayed BMG was obtained to demonstrate its amorphous structure. A typical broad peak is observed at the angle of 20 located at degree between 32° to 40°, and the second broad peak at the angle of 29 = 65°. Electrochemical properties of Zr60Cu20Ni8Al7Hf3Ti2 BMG in aerated sulfuric acid solutions with different concentrations (0.01 M, 0.1 M, 1 M) and different temperatures (20, 40, 60 Z) were investigated. Zr60Cu20Ni8Al7Hf3Ti2 BGM shows excellent corrosion resistance in tested conditions (temperature and concentration) as spontaneous passivation and wide passivate potential range are detected. In order to obtain the chemical composition of passive films and elucidate the corrosion mechanism of BMG in sulfuric acid solution, XPS analysis was performed for two kinds of samples. One is polarized at 0.5 V for 0.5 hours to get the passive film, and the other passive film is immersed for 8 hours in 0.01 M sulfuric acid solution at 20 . The high resolution scanning XPS spectra show the component of these two passive films are similar. The main composition of passive films is Z1O_2 and Al_2O_3 with a small quantity ofTiO_2, HiO_4, Cu and CuO. The Zr60Cu20Ni8Al7HBTi2 BMG possesses high corrosion resistance can be attributed to the enrichment of Zr and Al on the surface of alloy which is able to insulate the alloy substrate and the aggressive solutions by forming stable and compact oxides. The presence of minor amount of Hf and Ti elements on the surface also shows the role of advancing passivation stability, due to the formation of Hf~(4+) and Ti~(4+) oxides. In order to obtain more information about the properties of passive films, the Mott-Schottky curves were carried out. The formed passive films exhibit n-type semiconductor in diverse H2SO4 solutions open to air in the passivation potential district and p-type in the transpassivation potential. It is observed that the semiconductor type of passive films depends of applied potential. Different slopes at different potential regions indicate the existence of multiple oxides in the passive films. The slopes of Mott-Schottky curves are obviously susceptible to concentration and decrease with increasing concentration. Acceptor density N_a and donor density N_e of passive films increase with concentration and temperature of sulfuric acid solution, indicating the higher concentration and temperature aggravate impurity density of passive films.