X.D. Bai

The establishment of a potential-pH diagram for phosphorous implanted iron in aqueous solutions

Abstract The corrosion behavior following phosphorous implantation into pure iron was investigated and the corresponding potential-pH diagrams were established by means of potentiodynamic polarization studies in aqueous solutions with pH ranging from 1.3 to 11.3. It was found that phosphorous implantation led to elevation of the corrosion potential and also extended the immunity and passivation range in comparison with that of the unimplanted iron. The mechanism of the corrosion resistance improvement of the phosphorous implanted iron is due to structural change and amorphous layer formation in the implanted surface.

ANNEALING-INDUCED BLUE SHIFT IN LUMINESCENCE BAND FROM SI-IMPLANTED SIO2 LAYER

The SiO2 layers thermally grown on Si wafers were implanted by 130 keV Si ions at liquid nitrogen temperature to a dose of 1×1017u2009ions/cm2. From the as-implanted samples, a visible photoluminescence band centered around 2.0 eV was observed. After postannealing at 1100u2009°C for 90 min another visible band in the range of 1.7 eV was detected. Interestingly, with increasing thermal annealing time, a blue shift in peak energy and an intensity variation of the 1.7 eV band were observed. A possible interpretation for the observations was discussed in terms of a so-called three-region model.

The effect of ion implantation of Ar on the aqueous corrosion resistance of Zr-4 alloy

Abstract The effect of ion implantation on the aqueous corrosion resistance of Zr-4 in deaerated 1N H 2 SO 4 was studied with the potentiokinetic technique. The Zr-4 alloy was bombarded with 5 × 10 14 – 2 × 10 16 Ar/cm 2 of 190 keV. It was found that the passive current density of Zr-4 decreases with increasing implantation dose. Photoelectrochemical results show that the ion implantation of Ar in Zr-4 raises the flatband potential of its passive film. AES was employed to analyze the surface of the passive film of Zr-4. The decrease in passive current density may be attributed to a thickening oxide layer on Zr-4 and a decrease in concentration of oxygen vacancies in its passive film.

Comparison of the air oxidation behaviors of Zircaloy-4 implanted with yttrium and cerium ions at 500 °C

Abstract As a valuable process for surface modification of materials, ion implantation is eminent to improve mechanical properties, electrochemical corrosion resistance and oxidation behaviors of varieties of materials. To investigate and compare the oxidation behaviors of Zircaloy-4, implantation of yttrium ion and cerium ion were respectively employed by using an MEVVA source at the energy of 40 keV with a dose ranging from 1×1016 to 1×1017 ions/cm2. Subsequently, weight gain curves of the different specimens including as-received Zircaloy-4 and Zircaloy-4 specimens implanted with the different ions were measured after oxidation in air at 500 °C for 100 min. It was obviously found that a significant improvement was achieved in the oxidation behaviors of implanted Zircaloy-4 compared with that of the as-received Zircaloy-4, and the oxidation behavior of cerium-implanted Zircaloy-4 was somewhat better than that of yttrium-implanted specimen. To obtain the valence and the composition of the oxides in the scale, X-ray photoemission spectroscopy was used in the present study. Glancing angle X-ray diffraction, employed to analyze the phase transformation in the oxide films, showed that the addition of yttrium transformed the phase from monoclinic zirconia to tetragonal zirconia, yet the addition of cerium transformed the phase from monoclinic zirconia to hexagonal zirconia. In the end, the mechanism of the improvement of the oxidation behavior was discussed.

Effect of cerium ion implantation on the oxidation behavior of zircaloy-4 at 500 °C

Abstract In order to investigate the oxidation behavior changes of zircaloy-4 induced by cerium ion implantation using a MEVVA source at an energy of 40 keV with a dose range from 1×10 16 to 1×10 17 ions/cm 2 at the maximum temperature of 130 °C, weight gain curves of the different specimens including as-received zircaloy-4 and cerium-implanted zircaloy-4 were measured after oxidation in air at 500 °C for 100 min. It was obviously found that a significant improvement was achieved in the oxidation behavior of cerium ion implanted zircaloy-4 compared with that of the as-received zircaloy-4. The depth profile of the element composition in the surface region of the samples was obtained by Auger electron spectroscopy, and the valence of the oxides in the scale was analyzed by X-ray photoemission spectroscopy. Glancing angle X-ray diffraction employed to examine the phase transformation in the oxide films showed that the addition of cerium transformed the phase from monoclinic zirconia to hexagonal zirconia. Finally, the mechanism of the improvement of the oxidation behavior is discussed.

Nonequilibrium alloy formation in the immiscible Cu–Mo system studied by thermodynamic calculation and ion beam mixing

For the equilibrium immiscible Cu–Mo system characterized by a positive heat of formation (+19u2002kJu2009mol−1), thermodynamic calculation showed that by adding an adequate interfacial free energy, the Gibbs free energy of the Cu–Mo multilayered films could be elevated up to a higher level than the convex-shaped free energy curve of the amorphous phase and supersaturated solid solutions. Accordingly, ion beam mixing of the Cu–Mo multilayered samples did result in forming a unique amorphous phase with an alloy composition around 80 at.u2009% Mo and two supersaturated solid solutions of fcc and bcc structures at around 27 at.u2009% and 90 at.u2009% Mo, respectively, matching well with the thermodynamic calculation.

Anodic and air oxidation of niobium studied by ion beam analysis with implanted Xe marker

Abstract Xe marker implantation and backscattering analysis were used to study the growth mechanism of anodic oxides on niobium. In 5 wt% aqueous ammonium citrate solution, analysis of the Xe marker movement demonstrated that the oxide was formed mainly within the existing oxide through the transport of both niobium cations and oxygen anions from each side when the anodic oxidation was carried out with a constant current density of 1.0 mA cm −2 and a limiting oxidation potential from 60 to 100 V. During anodization, the transport numbers of niobium increased with the elevation of potential. The air oxidation behavior of niobium and the profile of Xe ions at the temperature of 200–500°C were also studied. The growth law of niobium oxide was obtained and no movement of the peak position of Xe ions was observed when the temperature was below 350°C.

Cu-Zr-Nb Crystalline-Amorphous Composites Investigated by Thermodynamic Calculation and Ion Beam Mixing Experiments

The formation of Cu-Zr-Nb metallic glass was predicted by thermodynamic calculation and then five Cu-Zr-Nb ternary metallic multilayered films were designed and prepared by electron depositing. The metastable supersaturated solid solutions, amorphous phase as well as their composites were able to be obtained in these Cu-Zr-Nb metallic multilayered films upon ion beam mixing. The observations provided a clew to improve the ductibility of the metallic glasses. Some possible interpretations were presented concerning the formation of the crystalline-amorphous composite.

Luminescence band evolution in Si implanted SiO2 layer upon high temperature annealing

The SiO 2 layer thermally grown on Si was implanted by 130 and 160 keV Si ions at liquid nitrogen temperature or room temperature to a dose of I X 10 17 ions cm 2 . From the as-implanted samples, a visible photoluminescence band centered around 2.0 eV was observed. After post annealing at I 100°C, another visible band in the range of 1.7 eV was detected. Interestingly, with increasing the annealing time, a blue shift of the peak energy and intensity variation of the 1.7 eV band were observed. A possible interpretation for the observations is also discussed.

Si-ion implantation-induced luminescence from Si single crystals with a SiO2 overlayer

Abstract Si-ion implantation into Si single crystals with SiO 2 overlayers of various thicknesses was carried out to study the implantation-induced visible light emission. Some new characteristic luminescence bands associated with the thin SiO 2 overlayer were observed. A visible band peaked in the range of 1.7 eV was observed after post annealing at 1100°C in a flowing N 2 and this band appeared from the samples covered with a very thin layer (1000 A). A new luminescence band around 1.5 eV was detected in the samples with a thick SiO 2 (3000 A) layer after post annealing. Possible mechanisms responsible for the observed light emission were also discussed.