Electrochemical Research On Semiconductor Roperties Of Oxide Films On Ni-base Alloys In High Temperature Water With Zn Ion Addition

Stress corrosion cracking and occupational radiation can be retarded effectively by zinc injection to the primary circuit of nuclear power plant. For simple understanding, the Zn ion cooperated with the other metallic oxide in the oxide film on the alloy and was instead of metallic hole. It is unclear the changes of the semiconductor properties of oxide films on alloy in high temperature water with zinc addition. The photoelectrochemical and capacitance responses(Mott-Schottky plots) were employed to investigate the semiconductor properties of the oxide films on Ni-based alloys in high temperature water with various Znion addition. And also the electrochemical analysis, surface morphology and component analysis were adopted. The results of the Znion addition to high temperature water were discussed by point defect model. Also the same experiment was introduced to SUS316L stainless steel. The semiconductor properties of oxide films on Ni-based and Fe-based alloys in high temperature water with Zn addition were fully discussed.The semiconductor properties of the passive film formed on pure Ni by anodic passivation in pH8.4borate buffer solution and the oxide film on pure Ni by thermally grown in air at500℃were investigated by photoelectrochemical response and Mott-Schottky plots analysis. The photocurrent spectra of the passive film on pure Ni were derived into two peaks for inner NiO and outer Ni(OH)2layers, respectively. The band gap energy Eg for the inner NiO was2.8eV and Eg for outer Ni(OH)2was1.6eV, respectively. Eg2.8eV of the inner NiO of the passive film on pure Ni was close to that2.4eV of the thermally grown oxide of pure Ni, indicating that the inner NiO in the passive film is crystalline structure. The Mott-Schottky plots for both the passive film and the thermal oxide film on pure Ni demonstrated that the two films exhibited p-type semiconductors with different values of flat band potential:0.40V for the passive film and0.15V for the thermally grown NiO. An electronic energy band model of both p-type semiconductors of inner NiO and outer Ni(OH)2layers was proposed to explain the photocurrent and Mott-Schottky plots for the passive film on pure Ni.The steady photocurrent response was employed to investigate the oxide films formed on Incone1600with various sulfate zinc addition. The photocurrent of the oxide film was plotted as a function of photon energy, for separating into several parts which can be derived from Fe2O3with a band gap energy2.2eV, Cr2O33.5eV, FexNi1-xCr2O44.1eV besides ZnO3.2eV which was firstly recorded in the oxide films of Incone1600by photoelectrochemical responses. For steady photoelectrochemical responses, the oxide film formed with zinc addition exhibited anodic photocurrent(n type semiconductor) at open circle potential while the film without zinc exhibited cathodic photocurrent(p type semiconductor). Mott-Schottky plots indicated a negative movement of the flat band potential of the oxide film on Incone1600with zinc addition to the film without zinc. At the same potential, the higher CSC-2(CSC, space charge capacitance) indicated a more compact oxide film of Incone1600with zinc addition in the high temperature water.A transient state photocurrent response was developed by coupling technique of potentiostat and lock-in amplifier and was also employed to investigate the semiconductor properties of oxide films on Ni-base alloys and stainless steel in high temperature water with ZnO addition. A compact structure oxide with formula ZnyFexNi1-x-yCr2O4of the outer layer, besides the chromium enrichment of the inner layer, of the oxide film on Incone1600in high temperature water with ZnO addition was studied. The semiconductor properties of the oxide films on Incone1600in high temperature water with ZnO addition suggested an untypical n-type semiconductor at anodic polarization with a negative movement of the flat band potential of the oxide films without ZnO. The value and dephasing angle of the transient state photocurrent response in function of the applied potential were also discussed. The relationship of the stability of the oxide film and the flat band potential and carrier density of the oxide film from Mott-Schottky plots were discussed by point defect model.The surface morphology and components of the corrosion oxide layers in high temperature water with Zn addition were examined by scanning electron microscopy(SEM) and X-ray photoelectron spectroscopy(XPS). The results revealed that smaller crystals on the alloys with Zn addition. And the Zn was detected on the surface and in the depth of the oxide film with both0valence and+2valence.