Experiment

1. PLASMACHEMICAL REDUCTION OF BRASS CORROSION LAYERS V. Mazankova , V. Sazavska, L. Radkova, F. KrcmaFacultyofChemistry, Brno University of Technology, Purkynova 118, 612 00 Brno, CzechRepublice-mail: mazankova@fch.vutbr.cz Introduction Influence of RF low-pressure hydrogen plasma on corroded brass samples was investigated. The method is based on a partial reduction of the incrustation and corrosion layers by RF low pressure hydrogen plasma. It induces changes in structure and constitution of corrosion layers on metal objects. Fig. 1: Dependencies of relative OH radical intensity (left) and sample temperature (right) on treatment time. Experiment It is well known that brass is an alloy of copper and zinc. Due to this fact the treatment temperature must not exceed 450 K. The rotational temperature is an important parameter of plasma, and it corresponded to temperature of neutral gas. Rotational temperature was more or less independent on the discharge regime, and it was significantly higher than temperature of thesample.The experimental conditions, maximal measured sample temperatures as well as calculated rotational temperatures are summarized in Tab. 1. Tab. 1: Experimental conditions, measured sample temperature and calculated rotational temperature. Fig. 3: Experimental samples in dessicator with HCl. Before treatment After treatment Fig. 4: 400 W – 75% pulse. Fig.2 Experimental set-up: 1 – quartz discharge reactor (90 cm long, i.d. 95 mm); 2 – corroded sample; 3 – quartz grate; 4 – outer copper electrodes; 5 –air-inlet valve; 6 – mass flow controller; 7 – RF power supply and matching network; 8 –pressure gauge; 9, 10 – valves; 11 – rotary oil pump; 12 – optical fibre cable; 13 - thermocouple Fig. 5: 500 W – 25% pulse. Conclusion From demonstrated results isvisiblethat there is only a very slow corrosion removal at sample temperature lower than 400 K. A decrease of intensity of OH radicals was observed at sample temperatures higher than 400 K. However, changes of corrosion layers composition were observed by a thermogravimetric and element analysis in all cases. The presented results clearly demonstrated that there was a relatively narrow sample temperature interval in which the corrosion removal was effective. The most significant advantages of the presented method, as compared to conventional ones, are the efficient removal of chlorides and significant reduction of treatment time. For archeological practice it is important that finer surface details and a memory of instruments which were used for object creation can be preserved. Acknowledgements This research has been supported by the Czech Ministry of Culture, project No. DF11P01OVV004.