Irina Sieber

Self-assembled porous tantalum oxide prepared in H2SO4/HF electrolytes

The formation of porous Ta2O5 on tantalum was investigated in H2SO4 electrolytes containing low concentrations of HF (0.15 wt %). Under optimized electrochemical conditions, porous Ta2O5 consisting of self-assembled pore arrays with single pore diameters of ~20 nm and a pore spacing of ~15 nm forms. The pore structure and the pore distribution depend on the concentration of HF, the anodization voltage, and the time for anodic oxidation. Porous layers ~400 nm thick with a regular pore distribution can be formed. For thicker layers cracking and a tendency for delamination was observed.

Porous Tantalum Oxide Prepared by Electrochemical Anodic Oxidation

It has recently been demonstrated [I. Sieber, B. Kannan, and P. Schmuki, Electrochem. Solid-State Lett., 8, J10 (2005)] that Ta can be porosified by anodic oxidation in diluted HF electrolytes. Pore morphology strongly depends on the HF concentration in the electrolyte and anodization time. In the present article, we investigate various factors that affected the process of self-assembled porous Ta 2 O 5 formation. The parameters studied are the HF concentration, the oxidation time, the anodization potential, and the potential scan rate. By optimizing the parameters, the porous tantalum oxide could be obtained that consists of highly regular pore arrays with single pore diameters of about 20 nm and pore spacing of about 15 nm. A steady-state porous film formation/film dissolution mechanism controls the time scale of the development of the porosity, the ordering effects, and the thickness of the formed oxide layer, which are similar to those operative for Ti and Nb.

Anodic Porous Zirconium Oxide Prepared in Sulfuric Acid Electrolytes

We report the formation of self-organized porous ZrO2 layers by anodization of Zr in H2SO4 electrolytes. Anodization at 20 V after a potential sweep from open-circuit potential with a defined sweep rate results in tube-like porous ZrO2. In particular, under optimized electrolyte condition and polarization, a highly ordered porous structure is obtained. Furthermore, sponge-like porous ZrO2 is also fabricated under a specific electrochemical condition.

Electron Beam Induced Writing of Corrosion Protection

Carbon patterns (C layers) were deposited on iron surfaces by electron-beam induced contamination decomposition writing. Chemical and electrochemical etching were used to investigate the protective nature of these C layers against metal corrosion. The results clearly show that E-beam written C patterns can be very corrosion resistant. The key factor controlling the degree of protectiveness, under given conditions of attack, is the deposition dose, i.e., the layer thickness. For sufficiently high doses, the iron surface can be completely protected against corrosion. Therefore, this direct masking approach opens new perspectives for highly precise and controlled local corrosion suppression.

Self-Organized Nanoporous Valve Metal Oxide Layers

The present work examines that formation of self-organized nanoporous oxide layers can be achieved on a whole series of valve metals directly via anodization in fluoride-containing electrolytes. In particular, nanoporous layers on IVB valve metals - Ti, Zr and Hf - are presented. The remarkable difference between the metals is the thickness, which may be essentially ascribed to the difference in chemical dissolution rates of each oxide. Morphology, structure and thickness are strongly affected by the electrolyte pH.