Corrosion Resistance Evaluation of 304L Stainless Steel and MP35N Alloy in Thionyl-Chloride-Based MOFA-Battery Electrolytes

摘要

This paper describes an electrolyte compatibility study that was undertaken in support of the Multi-Option Fuze for Artillery (MOFA) Post-launch Battery. A new thionyl chloride electrolyte offering improved battery performance was evaluated for use in the MOFA battery. A laboratory study was initiated, under the sponsorship of ARDEC, to establish the compatibility and stability of the proposed electrolyte when stored in the battery. This paper presents the corrosion compatibility portion of the study. The corrosion resistance of the MOFA-battery structural materials to thionyl chloride electrolytes is one of the major characteristics to be considered for battery storage, performance, and reliability. Currently, type 304L stainless steel is used as an electrolyte reservoir material and MP35N alloy is used as a reservoir ball-seal material in the MOFA battery. In this study, electrochemical corrosion tests were performed to evaluate the corrosion resistances of 304L stainless steel and MP35N alloy in the thionyl-chloride-based electrolytes at approximately - 60 °F, room temperature, and 160 °F. Corrosion rates of the materials in the electrolytes were obtained by conducting polarization resistance tests with Tafel analysis and pitting susceptibilities of the materials were evaluated by conducting cyclic polarization tests. Due to the highly corrosive nature of the electrolytes and their high vapor pressures, a unique corrosion test cell and a reference electrode were developed to carry out the electrochemical tests. In this study, the stabilized corrosion rates of 304L stainless steel in the studied electrolytes at room temperature were found to be less than approximately 0.016×10~(-3) inch/yr, which was acceptable for the MOFA battery application. The analytical approach, novel corrosion test-cell configuration, and test results will be discussed in detail. The implications of the test data and results will be discussed in terms of the corrosion compatibility between the battery structural materials and the thionyl-chloride-based electrolytes.