D.G. Li

Influence of passive potential on the electronic property of the passive film formed on Ti in 0.1 M HCl solution during ultrasonic cavitation

The influence of the applied passive potential on the electronic property of the passive film formed on Ti at different potentials in 0.1M HCl solution during ultrasonic cavitation, was investigated by electrochemical impedance spectra (EIS) and Mott-Schottky plot. The influence of the applied passive potential on the structure and composition of the passive film was studied by X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES). The results showed that the applied passive potential can obviously affect the electronic property of the passive film formed on Ti during ultrasonic cavitation. The resistance of the passive film increased, and the donor density of the passive film decreased with increasing the potential. The flat band potential moved to positive direction and the band gap of the passive film moved to negative direction with increasing potential. AES and XPS results indicated that the thickness of the passive film increased evidently with applying passive potential. The passive film was mainly composed of the mixture of TiO and TiO2. While the TiO2 content increased with increasing the applied passive potential, and the crystallization of the passive film increased with the increased potential.

Ultrasonic cavitation erosion of Ti in 0.35% NaCl solution with bubbling oxygen and nitrogen.

The influences of oxygen and nitrogen on the ultrasonic cavitation erosion of Ti in 0.35%NaCl solution at room temperature, were investigated using a magnetostrictive-induced ultrasonic cavitation erosion (CE) facility and scanning electron microscopy (SEM). The roles of oxygen and nitrogen in the composition and the electronic property of the passive film on Ti, were studied by Mott-Schottky plot and X-ray photoelectron spectroscopy (XPS). The results showed that the mass loss of Ti in 0.35%NaCl solution increased with increasing cavitation time. Bubbling oxygen can evidently increase the resistance of ultrasonic cavitation erosion comparing with bubbling nitrogen. XPS results showed that the thickness of the passive film on Ti in 0.35%NaCl solution in the case of bubbling oxygen for 3 weeks, was about 7 nm, and the passive film was mainly composed of TiO2 with an anatase structure. While TiO2 with a rutile structure was found to be the major component of the passive film on Ti in 0.35%NaCl solution in the case of bubbling nitrogen for 3 weeks, and the film thickness was 5 nm. The results extracted from Mott-Schottky plot showed that the passive film on Ti in the case of bubbling oxygen had more donor density than the passive film on Ti in the case of bubbling nitrogen.

The role of passive potential in ultrasonic cavitation erosion of titanium in 1 M HCl solution.

The influence of the applied passive potential on the ultrasonic cavitation erosion of Ti specimen in 1 M HCl solution was investigated by mass loss experiment, scanning electron microscopy (SEM), electrochemical impedance spectra (EIS) and Mott-Schottky plot. The results showed that Ti was in the passive state within the potential region from -0.3 VSCE to 1.5 VSCE under ultrasonic cavitation erosion. The applied passive potential can obviously decrease the mass loss of Ti caused by ultrasonic cavitation erosion in 1 M HCl solution. The resistance of the passive film increased, the flat band potential moved to positive direction, and the donor density of the passive film decreased with increasing the passive potential. Finally, a physical model was provided to explain the experimental results based on energy band and semi-conductive theories.

Enhancement of cavitation erosion resistance of 316 L stainless steel by adding molybdenum

The influence of Mo on ultrasonic cavitation erosion of 316 L stainless steel in 3.5% NaCl solution were investigated using an ultrasonic cavitation erosion (CE) facility. The morphologies of specimen after cavitation erosion were observed by scanning electron microscopy (SEM). The results showed that the addition of Mo can sharply decrease the mean depth of erosion (MDE) of 316 L SS, implying the increased resistance of cavitation erosion. In order to better understanding the influence of Mo on the cavitation erosion of 316 L SS, the semi-conductive property of passive films on 316 L SS containing different concentrations of Mo were studied by Mott-Schottky plot. Based on Mott-Schottky results and semiconductor physics, a physical model was proposed to explain the effect mechanism of Mo on cavitation erosion of 316 L SS.

Effect of ultrasonic cavitation on the diffusivity of a point defect in the passive film on formed Nb in 0.5 M HCl solution

This work primarily focused on the influence of ultrasonic cavitation on the transport property of the point defect in the passive film on formed Nb in 0.5M HCl solution via electrochemical techniques based on the point defect model (PDM). The influence of ultrasonic cavitation on the composition and structure of the passive film was detected by X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES). The transport property of a point defect in the passive film was characterized by the diffusivity of the point defect (D0). The influences of the ultrasonic cavitation power, passivated time and the distance between horn bottom and sample surface on D0 were analyzed. The results demonstrated that the passive film formed on Nb was an n-type semiconductor with a donor density (ND) ranging from 10(19) cm(-3) to 10(20) cm(-3) in the case of static state, while the order of ND increased one to two times by applying ultrasonic cavitation during film formation. The diffusivity of the point defect (D0) in the passive film formed on Nb at 0.5 V for 1 h in a 0.5 M HCl solution in the static state was calculated to be 9.704×10(-18) cm(2) s(-1), and it increased to 1.255×10(-16) cm(2) s(-1), 7.259×10(-16) cm(2) s(-1) and 7.296×10(-15) cm(2) s(-1) when applying the 180 W, 270 W and 450 W ultrasonic cavitation powers during film formation. D0 increased with the increment of the ultrasonic cavitation power, and decreased with the increased in formation time and distance between the horn bottom and sample surface. AES results showed the film structure and composition were changed by applying the ultrasonic cavitation. XPS results revealed that the passive film was mainly composed of Nb2O5 in the static state, and the low valence Nb-oxide (NbO) appeared in the passive film except Nb2O5 in the case of applying a 270 W ultrasonic cavitation power.

Effect of micro-particles on cavitation erosion of Ti6Al4V alloy in sulfuric acid solution

The influences of micro-particles on ultrasonic cavitation erosion of Ti6Al4V alloy in 0.1M H2SO4 solution were investigated using mass loss weight, scanning electron microscopy (SEM) and white light interferometer. Mass loss results revealed that the cavitation erosion damage obviously decreased with increasing particle size and mass concentration. Open circuit potential recorded during cavitation erosion shifted to positive direction with the decreased mass loss. Meanwhile, the mass loss sharply decreased with applying a positive potential during the entire ultrasonic cavitation erosion, and the relationship between the open circuit potential and the cavitation erosion resistance was discussed.

Influence of Molybdenum on Tribo-Corrosion Behavior of 316L Stainless Steel in Artificial Saliva

The influence of molybdenum on the tribo-corrosion behavior of 316L stainless steel in artificial saliva was investigated using potentiodynamic polarization curve, electrochemical impedance spectroscopy and sliding wear testing. The results showed that the passive capability of 316L stainless steel in artificial saliva was enhanced with increasing Mo. The anti-corrosion property of the passive film on 316L stainless steel was improved with increasing Mo via increasing transfer resistance of the passive film. Sliding wear testing results showed that the friction coefficient of 316L stainless steel in artificial saliva decreased with the increased Mo.