Pattern formation during electropolishing

Abstract

Using atomic force microscopy, we find that the surface morphology of a dissolving aluminum anode in a commercial electropolishing electrolyte can exhibit both highly regular and randomly packed stripe and hexagonal patterns with amplitudes of about 5 nm and wavelengths of 100 nm. The driving instability of this pattern formation phenomenon is proposed to be the preferential adsorption of polar or polarizable organic molecules on surface ridges where the contorted double layer produces a higher electric potential gradient. The enhanced relative coverage shields the anode and induces a smaller dissolution rate at the ridges. The instability is balanced by surface diffusion of the adsorbate to yield a length scale of 4(D s /k d) 1/2 , where D s is the surface diffusivity and k d is the desorption coefficient of the adsorbate, which correlates well with the measured wavelength. A long-wavelength expansion of the double-layer field yields an interface evolution equation that reproduces all of the observed patterns. In particular, bifurcation analysis and numerical simulation yield a single voltage-dependent dimensionless parameter that measures a balance between smoothing of adsorbate concentration by electric-field-dependent surface diffusion and fluctuation due to interfacial curvature and stretching. Randomly oriented stripes are favored at large ͑low voltage͒, while random hills dominate at small ͑high voltage͒ with perfectly periodic stripes and hexagonal hill patterns within a small window near ϭ1. These predictions are in qualitative and quantitative agreement with our measurements. ͓S0163-1829͑97͒04744-9͔

The role of the Ti surface roughness in the self-ordering of TiO2 nanotubes: a detailed study of the growth mechanism

“…This shallow ripple-like structure is an EP characteristic of metals 40 and can be used as a pre-pattern prior to anodization to obtain highly ordered oxide nanostructures, as shown in the case of Al. 36,40,[42][43][44][45] The electrochemical polishing of Ti is usually achieved in sulphuric acid-based electrolytes, which results in smooth surfaces. 46 However, in this work the EP conditions used (electrolyte type and voltage) resulted in organized dimple patterns, 40 with an interripple spacial period = 97 nm [ Fig …”

Fundamental mechanisms of focused ion beam guided anodization

“…One example is creating shallow strips, spots, or both kinds of features on the metal surface before the anodization from different electropolishing conditions. 5 These shallow surface features are generally on the scale of several nanometers. However, they are not effective in guiding the anodization and the relationship between the electropolished features and the anodized patterns is unclear.…”

Ordered nano-scale dimple pattern formation on a titanium alloy (Ti-6Al-4V)

“…Electronic mail: pkruse@mcmaster.ca 2158-3226/2012/2(3)/032101/12 C Author(s) 2012 2, 032101-1 windows of the optimized electrolyte and the optimized potential are narrow, and if experimental conditions are not at optimum for dimple formation, the surface will exhibit random nanoscale roughness 21 or other patterns). [22][23][24][25][26] So far, this method has successfully generated dimples on pure metals (tantalum, titanium, tungsten and zirconium). 19 Here, we demonstrate for the first time that the same pattern can also be achieved on an alloy surface, namely titanium alloy (Ti-6Al-4V) in addition to tunable microscale roughness.…”