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 the sample. The experimental conditions, maximal measured sample temperatures as well as calculated rotational temperatures are summarized in Tab. 1.

ConclusionFrom demonstrated results is visible that 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.

PLASMACHEMICAL REDUCTION OF BRASS CORROSION LAYERS

V. Mazankova , V. Sazavska, L. Radkova, F. Krcma  Faculty of Chemistry, Brno University of Technology, Purkynova 118, 612 00 Brno, Czech Republic

e-mail: mazankova@fch.vutbr.cz

Fig. 1: Dependencies of relative OH radical intensity (left) and sample temperature (right) on treatment time.

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

Tab. 1: Experimental conditions, measured sample temperature and calculated rotational temperature.

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.

Discharge power 200 W 300 W 300 W 400 W 500 W 500 W

Dutycycle 100 % 50 % 75 % 75 % 25 % 50 %

Sample temperature 430 K 400 K 360 K 450K 390 K 430 K

Rotational temperature 650 K 650 K 630 K 670 K 670 K 660 K

Acknowledgements This research has been supported by the Czech Ministry of Culture, project No. DF11P01OVV004.

Fig. 5: 500 W – 25% pulse.

Fig. 4: 400 W – 75% pulse.

Before treatment After treatment

Fig. 3: Experimental samples in dessicator with HCl.