The anodic polarization of Ni electrode in 0.5 M aqueous KOH solution at various polarization potential (Ep), time (tp) and temperature (T) values leads to the formation of β-Ni(OH)2 films. The growth of the hydroxide layers are irreversible and cannot be reduced electrochemically to metallic Ni. The hydroxide layer becomes thicker at higher values of Ep and/or tp and/or T. The thickness of β-Ni(OH)2 hydroxide were determined using ex–situ XPS and depth–profile techniques. Application of the oxide growth theories to our data indicate that the development of the β-Ni(OH)2 layer follows inverse logarithmic growth kinetics. The driving force of the process is the strong electric field that is established across the oxide layer. The strength of electric field is in the range of 0.015 – 0.197 x 109 V m–1. The oxidation mechanism of the Ni(II) surface compound to Ni(III) is electrochemically irreversible and the process is treated according to Randles–Sevcik equation. A linear relation was determined between the peak current density (jp) and the square root of the potential scan rate (v1/2) for the entire range of Ep, tp and T. The diffusion coefficient (D) values calculated for anodic and cathodic processes are 8.1 ± 0.2 x 10–12 and 4.3 ± 0.2 x 10–12 cm2 s–1, respectively. The activation energy (Ea) values for the diffusion process are 23 ± 2 kJ mol–1 (anodic) and 26 ± 2 kJ mol–1 (cathodic). The D and Ea values calculated from chronoamperometry measurements are comparable with those calculated from jp vs. v1/2 plots. The electro–reduction of PtO electrochemically pre–formed on Pt electrode in 0.5 M aqueous H2SO4 solution was also investigated. A well–controlled reduction conditions (Er, tr and T) were applied to determine the amount of the reduced PtO oxide. The reduction of the PtO requires much less time once ca. 1 monolayer (ML) of the oxide has been removed (ca. 1 ML of PtO remains). As expected, the longer tr and/or lower Er values, the greater the amount of the reduced oxide and consequently the smaller the amount of the remaining PtO oxide. / Thesis (Ph.D, Chemistry) -- Queen's University, 2011-02-08 10:58:54.114

No description available.

No description available.

An experimental investigation to study the influence of base metal composition on the time required to achieve complete isothermal solidification (tf) during TLP bonding of three Ni-base superalloys was performed. Alloys IN 738, DS Rene80 and DS IC 6 show similar behaviour when bonded at 1100 oC, with comparable tf. However, at higher temperatures, IN 738 requires extended period of time (as compared to DS Rene80 and DS IC 6) to achieve complete isothermal solidification. The prolonged tf in IN 738 appears to be caused by a more pronounced reduction in concentration gradient of the diffusing solute within the material during bonding. In contrast, the shorter complete isothermal solidification time experienced by alloy DS IC6 is attributable to its capability to better accommodate the diffusing solute, through the formation of densely packed second-phase precipitates in the diffusion affected zone (DAZ).

No description available.

No description available.

No description available.

No description available.

No description available.

No description available.