Plasmachemical removal of corrosion layers from Iron in pulsed RF discharge

Plasmachemical treatment of archaeological artefacts by RF hydrogen low pressure plasma is a relatively new technique developed during the 1980s. The corrosion removal process is very complex and its mechanism is not fully understood up to now and also optimal conditions are not known well. To study the process condition influence, the model corroded samples were prepared on iron with defined roughness using HCl, HNO3 and H2SO4 corrosion agents. The corrosion layers before and after plasma treatment were analyzed by electron microscopy including the study of corrosion layer profile. The experiment was done in Quartz reactor with outer electrodes creating capacitive coupled RF discharge in pure hydrogen at pressure of 170 Pa. The duty cycle was varied from continuous regime up to 1:25. The plasma treatment duration was 40-120 minutes depending on the duty cycle. The results showed that the application of pulsed discharge regime could maintain the corrosion removal process at lower mean power as well and thus the treated samples were affected by lower heating stress. On the other hand, the process was significantly longer.