... Rapid anodic growth of TiO2 and WO3 nanotubes in fluoride free electrolytes R. Hahn, J.M. Macak, P. Schmuki*Department of Materials Science, WW4-LKO, University of Erlangen-Nuremberg, ... length of 30 lm, and a wall thickness of about10 nm. Fig. 1c and d shows SEM images of nanoporousWO3prepared in ClOÀ4 and ClÀcontaining electrolytes. In this case, bundles of WO3nanopore ... explore the general feasibility of this princi-ple and to gain some insight into the growth mechanism of this novel growth approach.2. Experimental partTitanium and tungsten foils (0.1 mm, 99.6%...