Breakdown of Passivity of Nickel by Fluoride: II . Surface Analytical Studies

Abstract

Passive layers on nickel and their change by the action of fluoride have been studied by surface analyses such as x‐ray photoelectron spectroscopy (XPS) and low energy ion scattering (ISS). The thickness of the layers is deduced from the height of the XPS signals normalNi2normalp3/2 , O1s, and F1s and their attenuation by covering layers. Argon sputtering gives information on the in‐depth structure of the passivating films in combination with XPS and the higher depth resolution of ISS. Their thickness and chemical composition change with the electrode potential and the time of exposure to HF . A multilayer structure is found with an inner oxide and outer hydroxide film and, in a higher potential range, a fluoride layer in between. The layer structure shows a close correspondence to the results of the electrochemical examination.

XPS characterization of the corrosion film formed on the electroless nickel deposit prepared using different stabilizers in NaCl solution

“…This model is supported by X-ray photoelectron spectroscopy (XPS) investigations. 1 -5 The XPS data reveal two fairly well resolved O 1s peaks at 529.8 eV and 531.6 eV, and these two peaks correspond well to the positions of oxygen in NiO and Ni(OH) 2 . 1 However, these spectral features may also be interpreted differently since Ni 3C can give rise to spectral features very similar to those of Ni(OH) 2 .…”

“…9 In addition, the structure of the inner oxide layer did not vary with the time or potential of passivation. 9 A nearly saturated layer of hydroxyl groups with a 1 ð 1 epitaxy can be formed on NiO(111), and further exposure to water leads to the formation of a nearly complete monolayer of nickel hydroxide similar to that found inˇ-Ni(OH) 2 . 12 Further investigation of this bilayer structure indicated that hydroxylation of the NiO thin film on Ni(111) was structurally sensitive.…”

“…The 99.5% pure Ni metal was sputtered at 4 keV for 60 seconds to remove surface oxide prior to the acquisition of XP spectra. Indium foil was used to hold NiO (100), Ni(OH) 2 powder, and Ni 3 PO 4 2 ÐxH 2 O powder to enhance the conductivity and minimize the charging effects. The specimen was covered with a nickel screen to reduce the generation of secondary electrons.…”

“…1 -12 A bilayer model, composed of a top layer of nickel hydroxide [Ni(OH) 2 ] and a base layer of nickel oxide (NiO), is thought to be present. This model is supported by X-ray photoelectron spectroscopy (XPS) investigations.…”

“…The S atoms remain on the outermost layer of the Ni(100) surface, and anodic dissolution proceeds by a layer by layer mode. 11 In situ STM investigation of passive films revealed a bilayer structure composed of an Ni(OH) 2 outer layer and an NiO inner layer on the Ni(111) surface. 9 In addition, the structure of the inner oxide layer did not vary with the time or potential of passivation.…”