Corrosion resistance of zirconium and zirconium-titanium alloy in hot nitric acid

Since zirconium (Zr) has superior corrosion resistance to concentrated nitric acid (HNO3) at elevated temperature, it has been successfully used as a material for chemical plants to produce HNO3 or spent nuclear fuel reprocessing plants. However, the occurrence of stress corrosion cracking (SCC) has recently been reported in hot nitric acid conditions. The necessary conditions for SCC in Zr, and the preventive method against SCC by alloying were investigated. The slow strain rate technique test, electrochemical measurements, strain electrode tests, and analysis of corrosion products were carried out in this work. SCC does not occur in Zr in boiling HNO3 at concentrations less than 70%, whereas SCC is initiated in 6–94% HNO3 when a potential is applied above the critical potential for SCC. A new invention of Zr-15%Ti alloy is immune to SCC under applied potential conditions in hot HNO3; this alloy forms a stable passive film composed of ZrO2 and TiO2.