Corrosion Properties of Tantalum, Columbium, Molybdenum and Tungsten

Abstract

The corrosion resistance properties of tantalum, columbium (niobium), molybdenum and tungsten as they are affected by the nature of the corrosive medium, its concentration and its temperature are presented. Tantalum, the most resistant, is inert to all acids except HF and free SO3 at temperatures usually encountered in industrial processes. It is attacked by strong alkalis at room temperature. The resistance to gases depends upon the temperature of exposure. Columbium in general is less resistant than tantalum in all media. Molybdenum shows good resistance to non-oxidizing acids and to alkaline solutions over a wide range of temperatures and concentrations, and is attacked only slightly by hydrofluoric acid. Tungsten’s resistance to acid corrosion is equal to or better than that of molybdenum. All four are extremely resistant to the liquid metals at elevated temperatures. The structural and fabrication limitations of each metal are discussed and the useful fields of application are indicated. 6.3.1