Abstract
Mixed metal oxide coated titanium anodes have been applied widely to cathodic protection as impressed current anodes in the oil/gas industry and for chlorine production in chlor-alkali industry. The anodic stability and service life are the main concerns in these applications. It has been known that oxide anodes have a very limited service life under operating conditions because of the severe corrosion of active component in the oxide mixture such as RuO2, leading to final deactivation of the anode.
To increase the effective life of anodes, this study considered alternative anode materials and concluded that the anode life is improved by doping the anode coating with IrO2. Therefore, corrosion behaviour of a RuO2-IrO2-TiO2/Ti oxide anode was investigated during an accelerated life test (ALT) in NaCl solution by use of cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and SEM/EDS. The service lifetime of IrO2 doped oxide coating is compared with RuO2/Ti and RuO2-TiO2/Ti anodes and a systematic evaluation is presented.
The life test indicated that the improved oxide anode has a long lifetime and appropriate activity. It was concluded that RuO2-IrO2- TiO2/Ti anodes last up to ten times longer than Ir-free anodes. An impedance model is then developed for this corrosion system and the model simulation compared to the experimental data. The model is shown to be in reasonable agreement with the experimental data. A comprehensive deactivation mechanism of titanium anodes has been proposed by the growth of an insulating TiO2 layer at coating-substrate interface.
The results presented in this paper are very promising and reveal that RuO2-IrO2-TiO2/Ti anode has a good potential to be used as mixed metal oxide anode in oil/gas and petrochemical industries.
