Surface Treatment Strategies to Produce Hydrophilic Porous Titanium Wicks for Heat Pipes

Titanium–water heat pipes have been identified as a promising solution for mass-efficient high temperature (500–600 K) heat distribution in thermal radiator panels for fission surface power and nuclear electric propulsion space platforms. However, titanium surfaces rapidly passivate and become hydrophobic in most environments. Therefore, treatment strategies are needed to process titanium heat pipe wicks to achieve durable hydrophilic conditions. This study evaluates several thermal and chemical treatment strategies to produce hydrophilic commercially pure titanium (CP-Ti) wicks. A promising approach is identified that applies concentrated H2O2 solution treatment, followed by thermal treatment in an air furnace at 600°C. Additively manufactured CP-Ti wick coupons processed with this approach are characterized for permeability and effective pore radius in a rate-of-rise experiment. High performing wick geometries are embedded in full additively manufactured heat pipe radiator (HPR) prototypes. The chemical treatment process is adapted for these complex enclosed heat pipe wicking networks. Prototype CP-Ti-water HPRs are evaluated for thermal radiation performance in a cryogenically cooled vacuum chamber at relevant heat input temperatures. Results indicate successful activation of wick networks and nearly isothermal heat pipe surfaces.