Corrosion of Common Heat Exchanger Materials by Lithium Nitrate Trihydrate

Lithium nitrate trihydrate (LNH) is promising as a thermal energy storage material with one of the largest specific and volumetric enthalpies of fusion for materials with a near-room temperature melting point. In order to integrate this material into high cooling power energy storage modules, it is necessary for heat exchanger materials to be compatible with LNH. However, understanding of corrosion of metals and polymers in high salt content solutions (wH2O < 0.50) is relatively limited. Here, we report the effects of six month immersion corrosion studies on nine common polymeric materials and twelve metallic alloys in molten LNH along with likasite, a common nucleation agent, to determine materials compatibility and degradation mechanisms. No degradation was observed in nylon, PVC, or fluorinated polymers, nor was corrosion observed in stainless steel, nickel, or titanium alloys. Copper alloys did corrode in the LNH and likasite solution, experiencing both uniform surface corrosion and localized pitting corrosion. Aluminum alloys experienced localized corrosion with LNH, which was more severe in cases with likasite present. Thus, aluminum is not recommended as a viable option for use in this system without further investigation into possible corrosion inhibitors. Potential corrosion mechanisms are discussed, and initial results of corrosion inhibitors on the corrosion rate of aluminum in LNH are presented