Experimental Study of Structural Materials for Prolonged Venus Surface Exploration Missions

Abstract

Materials used in the fabrication of landers for Venus exploration need to be carefully selected to assure functional durability throughout anticipated prolonged future mission durations in the harsh conditions that include 460°C and 9.2 MPa pressure with supercritical CO 2 and trace corrosive gases. Previous work has shown the adverse effects that trace quantities of the atmospheric sulfide and halogen Venus gas constituents have on some materials used in sensor and electronic component fabrication. In this study, a limited, systematic evaluation of several pure elemental metals as well as Ti-6Al-4 V is conducted to determine on an elemental level the constituents of structural materials that could survive prolonged Venus exploration. The metals are characterized before and after exposure to a simulated Venus surface atmosphere using X-ray photoelectron spectroscopy, Auger electron spectroscopy, energy-dispersive spectroscopy, and field-emission-scanning electron microscopy. Ti-6Al-4 V, titanium, and molybdenum all demonstrate stability when exposed to the simulated Venus surface environment. In contrast, cobalt, palladium, and to some extent chromium have adverse reactions to the sulfur constituents. The 96% supercritical CO 2 leads to the complete oxidation of niobium and zirconium, as well as spalling oxide layers on tantalum and formation of a thick oxide layer on tungsten.xM yCOg MxOy yC s R1xM yCO 2 g MxOy yCOg R22COg CO 2 g C s Boudouard reaction

Experimental Weathering of Rocks and Minerals at Venus Conditions in the Glenn Extreme Environments Rig (GEER)

“…The behavior of Zn in our magnetite ore sample is consistent with the summary of element reactivity presented in Figure 13 of Lukco et al. (2020) that states zinc forms sulfides under Venus‐like conditions in GEER. Due to the presence of Zn, we cannot use this sample to speak to the fate of pure magnetite under our experimental conditions, however, the fact that S was observed only in scattered areas of the magnetite surface, as opposed to discrete grains of a Fe,S phase, suggests that if any iron‐based reaction was occurring, it was doing so slowly relative to the reaction involving zinc, which did produce distinct mineral grains.…”

“…In a previous GEER experiment, silver was found to separate out of a sample containing Ag‐Cu braze sealing the end of a Kovar (Fe 53%, Ni 29%, Co 17%) tube, with the Cu forming copper sulfide, although the Ag was not seen to form a chloride phase (Lukco et al., 2018). Copper is known to be highly reactive in the GEER environment, reacting to form copper sulfides (Lukco et al., 2018, 2020), suggesting that it may have diffused through the chalcopyrite to form a copper‐rich sulfide mineral at the surface.…”

Surface-passivated Cu conductors for high-temperature sulfurous environments

“…3 However, if the structural integrity is compromised in harsh environments, such as those found on Venus with its reactive sulfuric environment and high average surface temperature, corrosion could occur at high rates, destabilizing the structure and electrical conductivity of the metal components in electronic devices. 4–7 Another strategy is to utilize high-temperature metallic materials for corrosion-resistant electronics, 8 including noble metals, such as gold, 9 silver, 10 and palladium, 11 and passive metals, such as nickel. 12 Such high-temperature conductors offer high melting points, good electrical performance, and low heat expansion coefficients.…”