Wetting of lithium on nanostructured surfaces for first wall components

Liquid metals are garnering increased attention as an alternative divertor solution to tungsten divertors. While tungsten suffers from a myriad of potentially critical issues, such as bulk erosion, melting under significant transient heat loads, and nanostructuring colloquially referred to as fuzz, liquid metals avoid many of these entirely. In order to implement liquid metal concepts, the interactions between the liquid metal and the substrate it is deposited upon must be characterized. One such critical interaction is the wetting of a liquid metal on the surface of the PFC structure. The wetting ability of a substance determines many significant properties, including the thickness of the liquid film and the propensity of a flowing liquid to break into rivulets. A previous study conducted at the University of Illinois [1] characterized wetting as a measurement of the contact angle of lithium when deposited as liquid droplets onto a surface. The dependence of the contact angle on temperature was measured, finding a transition between non-wetting and wetting at a critical temperature. For example, at 215 °C, stainless steel registers a contact angle of 137°, whereas above its wetting temperature of 315 °C, the contact angle is less than 80°. The impact of nanostructuring of the surface is detailed herein. A novel method of rapid laser nanostructuring was developed to create the samples. To further the knowledge of liquid metal PFC surface interactions, results of experiments on the relationships between material and temperature and the contact angle of lithium are presented for a variety of nanostructured surfaces.