Diffusion of nickel in single- and polycrystalline Cr₂O₃

Abstract

Chromia protective layers are formed on many industrial alloys to prevent corrosion by oxidation. Their role is to limit the inward diffusion of oxygen and the outward diffusion of cations. A number of chromia-forming alloys contain nickel as a component, such as steels, FeNiCr and NiCr alloys. To ascertain if chromia is a barrier to outward diffusion, nickel diffusion in chromia was studied in both single crystals and polycrystals in the temperature range 900-1100 C at an oxygen pressure of 10 À4 atm (argon þ 100 ppm O 2 ). A nickel film of $35 nm thick was deposited on the chromia surface and, after diffusing treatment, nickel penetration profiles were established by secondary ion mass spectrometry (SIMS). Two diffusion domains appear in polycrystals, the first domain is assigned to bulk diffusion and the second is due to diffusion along grain boundaries. For the bulk diffusion domain and diffusion in single crystals, using a solution of Fick's second law for diffusion from a thick film, bulk diffusion coefficients were determined at 900 and 1000 C. At the higher temperature, a solution of Fick's second law for diffusion from a thin film could be used. For the second domain in polycrystals, Le Claire's model allowed the grain boundary diffusion parameter (D gb ) to be established. Nickel bulk diffusion does not vary significantly according to the microstructure of chromia. The activation energy of grain boundary diffusion is slightly greater than the activation energy of bulk diffusion, probably on account of segregation phenomena. Nickel diffusion was compared with cationic self-diffusion and with literature data on Fe and Mn heterodiffusion in the bulk and along grain boundaries. All results were analyzed in relation to the oxidation process of stainless steel.

Oxidation kinetics and mechanisms of Ni-base alloys in pressurised water reactor primary conditions: Influence of subsurface defects

“…The second possible mechanism would involve the interface between the chromia nodules and the mixed chromite spinel due to cations diffusion via the chromium oxide nodules. From literature data [27] and [28] Ni SC D −24 cm 2 s −1 referring respectively to References [27] and [28], where α is the segregation factor) are significantly lower than the grain boundaries diffusion coefficient of oxygen in mixed chromite. However, when the density of Cr 2 O 3 nodules becomes significant, the cations diffusion via chromia nodules probably becomes the rate-controlling step of the growth of mixed chromite.…”

Influence of the Oxygen Partial Pressure on the Oxidation of Inconel 617 Alloy at High Temperature

“…However, for the longer oxidation time (28 days) nickel and manganese are found to be enriched in the outer part of the scale. This can be explain by the diffusion rates of these two elements in Cr 2 O 3 : Lobnig et al [39] showed that at 900°C manganese has a lattice-diffusion coefficient in a chromia layer grown on a Fe-20Cr-12Ni about two orders of magnitude higher than chromium (D = 1 9 10 -14 cm 2 s -1 for Mn and D = 8 9 10 -16 cm 2 s -1 for Cr autodiffusion for a 4 h annealing time), and work from Sabioni et al [40] showed that diffusion rate of nickel is higher than autodiffusion of chromium in chromine at 900°C.…”

Characteristics of Ba(Zr0.1Ce0.7Y0.2)O3-δ nano-powders synthesized by different wet-chemical methods for solid oxide fuel cells

“…Figure 5 (a) implies that the nickel ions in the anodes may diffuse into the interface between the cathode and electrolytes. The nickel seems to have penetrated through the grain boundary and the pores of the electrolyte to the cathode layer during the sintering in high temperature [23][24][25][26].…”