Transport of Nickel and Oxygen during the Oxidation of Nickel and Dilute Nickel/Chromium Alloy

Abstract

NiO films have been grown on high-purity Ni and Ni 0.1 weight percent (w/o) Cr alloy, at 700~ and 0.21 bar, by sequential oxidation in 1602 and 1802. The distributions of oxygen, Ni, and Cr isotopes in the films were analyzed using SIMS. For both materials, the rate controlling transport process was found to be the outward diffusion of Ni through the NiO. Inward oxygen gas transport also occurs and is responsible for the growth of new oxide within the films and for the growth of the inner layer of the well-developed duplex films which grow on the alloy. A mechanism whereby oxygen gas penetrates the films through fissures to form new oxide in available space is proposed to explain the observations and the growth of duplex films.The protective properties of oxide films formed by oxidation of metals depend on the transport of reactants (metal and oxygen) through the film and the structure of the film (including the microstructure). In general, the transport properties and structure of the oxide film are inter-related. In some cases, this relationship is relatively straightforward; for example, the oxidation of high-purity Co or Ni at high temperatures, when the classical singlelayer, single-phase compact oxide film grows by outward diffusion of metal ions through the oxide lattice. At the other extreme, the relationship is extremely complicated; for example, the oxidation of a multicomponent alloy in mixed gases at intermediate temperatures. The complicating factors include multiphase, multilayered, doped oxides containing voids, dislocations, and grain boundaries as additional potential routes for transport through the oxide.Between these two extremes is an important class of oxide film microstructures known as duplex films (or scales). Duplex films are formed under a wide variety of conditions on a large number of metal substrates. They can form on high-purity metals as well as on alloys. On high-purity metals, the inner and outer layers of the duplex film are distinguishable by their different grain size. The outer layer usually has a columnar structure, and the inner layer has an equiaxed structure of much finer grain size. The thickness of the inner layer, as a fraction of the total layer thickness, appears to depend on the system and the experimental conditions. However, the inner layer thickness never exceeds the thickness of metal converted to oxide (i.e., when the inner-layer/outer-layer boundary coincides with the position of the original metal surface). When duplex films form on dilute alloys, the inner-layer/ outer-layer boundary usually coincides with the position of original alloy surface, and the alloying elements are preferentially located in the inner layer (provided that the alloying elements have low mobility in the oxide).The transport processes which occur during duplex film growth have been studied using isotopically labeled oxygen tracers in a number of systems. The results of these experiments and their interpretation have recently been reviewed by Atkinson (1). The experiments have shown tha...

Temperature Effect on Oxidation Behavior of Ni-Cr Alloys in CO2Gas Atmosphere

“…External NiO growth has been well understood and its formation is controlled by Ni cation outward diffusion. 22,23 Increasing the chromium concentration of the alloys leads to the formation of a chromia band at the reaction front and eventually to a chromia layer (Figs. 7f and 10d).…”

Research Update: Ionotronics for long-term data storage devices

“…16 Furthermore, below 1000 • C, Ni oxidation is determined by the fast grain boundary diffusion of Ni in NiO. 24,25 We therefore expect that the optimization of the film microstructure by decreasing the oxide grain size will enhance the relevant diffusivity.…”

Enhanced Oxidation of Nickel at Room Temperature by Low-energy Oxygen Implantation

“…Ni 2+ cations diffuse through lattice defect sites (such as vacancies created within the oxide) to the surface where they react with adsorbed oxygen, following the parabolic rate law. [9][10][11][12] When a Ni vacancy is created, two neighbouring Ni 2+ atoms, in order to balance charges, each lose an electron forming two Ni 3+ ions (i.e. two electron holes).…”

“…As NiO is a metal deficient (Ni1-δO) p-type semiconductor, the subsequent oxidation of Ni at higher temperatures is expected to proceed by the outward migration of Ni cations and electrons with the growth of a single-phase oxide at the oxide/gas interface. [1] Indeed, the mass transport by diffusion of Ni cations, with a possible contribution from an inward diffusion of oxygen anions, has been identified in a number of oxidation studies of Ni, including the high temperature experiments (500 to 1400 °C), [7,[9][10][11][12] or oxidation during potentiostatic anodic polarization on pure Ni. [13] It is very important to gain information on the initial oxidation stage of Ni, as it represents the very first step of Ni reaction with the oxidizing environment.…”