Electrochemical Properties of Spark Plasma Sintered Tungsten

The increased use of spark plasma sintering (SPS) in powder metallurgy applications is mainly due to the benefits of faster heating rate, uniform heating condition, lower sintering temperature, and shorter dwell time. This method involves the Joule heating of specimens by a pulsed dc coupled with axial pressure. Tungsten cermets are prospective next generation nuclear materials, and SPS is a promising processing route for them. The corrosion resistance of these cermets will be influenced by the native oxide associated with tungsten. The behavior of tungsten in acidic environments has been shown to be associated with the dissolution of the outer layer of WO₃(H₂O)_x that rests on the compact inner layer of WO₃. The use of SPS temperatures in the range of 1300 ^oC to 1700 ^oC and dwell times of 5 to 30 minutes yielded bulk tungsten specimens with varying levels of porosity. Electrochemical impedance spectroscopic experiments were performed on these specimens under different acidic conditions in 0.1 M NaCl. The data were analyzed using an equivalent electrical circuit to determine the influence of porosity on the resistive and capacitive properties of the surface oxides.