The Corrosion Effect of Dynamic Liquid Metal Galinstan on Stainless Steel S31600/SS316 in the Presence of Selected Refrigerants at Temperatures up to 150 °C

Abstract

A corrosion study examined stainless steel S31600/SS316 after exposure to the liquid metal galinstan and gases including nitrogen, n-pentane, isobutane and R245fa at 150 °C under dynamic conditions for 3.5, 9.5 and 20.5 days. Ampules partly filled with galinstan and the gas were continuously stirred to create regions of gas-only, gas-liquid, and liquid-only exposure. Post test examinations used a variety of qualitative and quantitative methods (visual observation, scanning electron microscopy with energy dispersive X-ray spectroscopy, surface profilometry and chemical analysis) to evaluate coupons and galinstan samples for evidence of corrosion. In the gas-exposed region, no corrosion was detected in any coupon. In the liquid region, galinstan constituents were found to be localized to grain boundaries for nitrogen and isobutane coupons but dispersed on n-pentane coupons; a gallium oxide layer was found on R245fa coupons. In the liquid-gas interface region, severe corrosion was found on the n-pentane 20.5-day and the isobutane 9.5 and 20.5-day coupons; fine scattered corrosion on the R245fa 9.5-day coupon but not on the 20.5-day coupon was observed. Profilometry results indicated the least roughness change for coupons in n-pentane, a higher change in nitrogen, then in isobutane, and the highest in R245fa. In the presence of refrigerants and under dynamic conditions, intergranular attack on stainless steel may be enhanced by chemical reactions combined with microsegregation of galinstan or gallium oxide elements on stainless steel grain boundaries. Further work is required to confidently identify and explain this corrosion mechanism.