Experimental Study on the Origin of Dropwise Condensation of Steam on Ion Implanted Metallic Surfaces

The presented work provides new perspectives on the origin of dropwise condensation of steam on ion implanted metallic surfaces. For the experimental study metallic samples made of different materials implanted with various ion species were used. Condensation experiments with saturated steam and surface analysis via contact angle and surface free energy measurements, atomic force microscopy and scanning electron microscopy were performed. It could be shown that available explanation approaches for the appearance of dropwise condensation based on a reduction of the metal surface free energy by ion implantation have to be discarded. Our results rather suggest a nucleation mechanism proceeding on surfaces featuring nano-scale surface roughness and chemical inhomogeneity. These characteristics seem to be induced by nano-particles precipitated due to supersaturation of the metal substrate with the doping elements. On unimplanted high-alloyed materials like stainless steel, dropwise condensation was found to develop spontaneously because of strong oxidation effects. Obviously the latter naturally produce surface modifications which are similar to those obtained artificially by ion implantation.