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Microscopic properties of passive films on Ti and Zr from optical, electrochemical and SXM‐measurements
Author(s) -
Schweinsberg M.,
Kudelka S.,
Michaelis A.,
Schultze J. W.
Publication year - 1998
Publication title -
materials and corrosion
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.487
H-Index - 55
eISSN - 1521-4176
pISSN - 0947-5117
DOI - 10.1002/(sici)1521-4176(199803)49:3<161::aid-maco161>3.0.co;2-p
Subject(s) - materials science , crystallinity , microstructure , substrate (aquarium) , ellipsometry , amorphous solid , composite material , thin film , nanotechnology , crystallography , chemistry , oceanography , geology
A combined application of several microtechniques is presented and discussed with the Ti/TiO 2 and Zr/ZrO 2 ‐systems as an example. All measurements were carried out on single grains of technical materials in order to detect and quantify the effect of substrate microstructure on the properties of anodic passive films formed potentiodynamically in 0.5 M H 2 SO 4 (dU/dt = 20 mVs −1 ). Anisotropy‐Micro‐Ellipsometry (AME) was employed to determine the crystallographic orientation of the substrate grains along with passive film thickness and crystallinity in dependence on the anodization potential. Both the isotropic (amorphous) TiO 2 ‐ and the anisotropic (crystalline) ZrO 2 ‐films exhibit a systematic dependence of film thickness on the grain orientation. Local LASER‐scanning photocurrent measurements (λ=257 nm) on the same grains likewise show a heterogeneity of the photoelectrochemical reactivity in all cases. This is quantitatively explained by the results from local electro‐chemical measurements on single grains using photoresist‐microelectrodes. From oxide formation charges and Mott‐Schottky evaluation of capacitance data, differences in reactivity due to different donor densities are found from grain to grain and are a strong function of the substrate packing density. Additional information on corresponding topographical and mechanical properties of different grains is obtained from Scanning Probe Microscopy (SXM) techniques, i.e. AFM‐measurements. The grain topography is dominated by the material loss during electropolishing, which decreases with increasing packing density. The mechanical properties (stiffness) of the passive film as obtained from AFM‐Force modulation techniques are correspondingly related to the substrate texture. In all cases investigated here, a systematic correlation of optical, structural, electronic and mechanical properties of the passive oxides on the substrate grain orientation is found, thus proving a strong texture‐dependence of anodic film growth.