In situ EXAFS investigation of carbon-supported Pt clusters under potential control.

The transformation of carbon supported Pt clusters under potential control in 1M HClO4 solution was investigated by in-situ X-ray absorption spectroscopy measurements. Both XANES and EXAFS data are used to show the structure evolution of the Pt clusters at various potentials. It showed that the white line area and the edge energy increase with the applied potential in the range 0.1-1.5V. The coordination number of oxygen and platinum on the Pt/C electrode increases and decreases, respectively, with the applied potential. It is found that the size of Pt cluster does not grow during the electrode fabrication. However, the crystallization of Pt cluster occurs during the potential cycling.

Passive film on orthopaedic TiAlV alloy formed in physiological solution investigated by X-ray photoelectron spectroscopy.

The passive film formed by electrochemical oxidation on TiAlV alloy in physiological solution was studied using X-ray photoelectron spectroscopy (XPS) and electrochemical impedance spectroscopy (EIS). The alloy was polarised at different oxidation potentials in the electrochemical chamber attached to the spectrometer. Thus the composition of the layer formed by oxidation was analysed by XPS without prior exposure to air (quasi-in situ). The oxide layer was predominantly TiO2, which contained a small amount of suboxides TiO and Ti2O3 closer to the inner metal/oxide interface. With increasing potential the content of Ti4+ species increased and that of Ti3+ and Ti2+ decreased. The content of titanium in TiO2 was lower than theoretically predicted due to the incorporation of Al2O3 in TiO2 matrix. Vanadium oxide was not identified by XPS. Angular resolved XPS analysis confirmed that Al2O3 is located mainly at the outer oxide/solution interface. The thickness of the oxide layer was dependent on the oxidation potential and after oxidation at 2.5 V reached 9 nm. EIS measurements were used to in situ characterise electronic properties of passive films over seven decades of frequency. A link between electronic, electrochemical and physiochemical properties was established.

The behavior of stainless steels in physiological solution containing complexing agent studied by X-ray photoelectron spectroscopy.

The passive film formed by electrochemical oxidation on two different stainless steels differing in molybdenum (Mo) content in physiological solution with and without the addition of complexing agent, i.e., citrate, was studied using X-ray photoelectron spectroscopy. The alloys were polarized at different oxidation potentials in the electrochemical chamber attached to the spectrometer. Thus, the composition of the film formed by oxidation was analyzed by X-ray photoelectron spectroscopy without prior exposure to air (quasi in situ). The passive film formed in physiological solution consists of two predominant oxides, i.e., chromium and iron oxides. Oxides of alloying elements nickel and Mo are also detected in the film. It seems that the strong enrichment of oxidized chromium and Mo in the passive layer, and strong enrichment of Mo and depletion of iron at the metal surface underneath the passive layer, are responsible for the outstanding corrosion resistance of orthopedic stainless steel in physiological solution. Commercial AISI 304 is not suitable for orthopedic applications. The addition of complexing agent affects significantly the passivation behavior of orthopedic stainless steel, because it changes the distribution of the elements within the passive layer and at the metal surface underneath.