Characterization of Plasmachemical Treatment of Archaeological Artifacts

journal article - other

English

Plasmachemical treatment of archaeological artifacts is a relatively new technique. Up to now, it has been used more or less intuitively in practice, but for a widespread application an exact characterization of the process is necessary. The process is based on using low-pressure hydrogen plasma in which the artifacts (in this case silver coins and some pieces of iron) are treated for several hours, usually in more steps. The problem is how long period of the plasmatic treatment is optimal and how to characterize its efficiency. From the kinetic point of view, the oxide and chloride molecules reduction is the main process. Significant, but not very intense radiation of the $\cdot $OH radical was observed in the optical emission spectra. Due to the fact that in pure hydrogen plasma the $\cdot $OH emission spectra is not overlapped by any radiation, we use its integral intensity in the range of 300 - 330 nm as an indicator of the oxides reduction effectiveness. The OH radiation shows specific dependence on time. Initially a fast increase, later a slower non-exponential decrease. The duration of the OH integral intensity decrease to the value of 10% of its maximum can be taken as the end of the reduction. It was found out that during the first two hours the reduction is completed. Besides, during the plasmachemical treatment of artifacts in ammonia-water vapour the intensities of the spectral lines of atomic hydrogen H(alpha) and H(beta) were measured as a function of plasmachemical treatment time. But in this case the end of reduction processes was difficult to estimate. The measuring device used for our experiments could be used in practice for plasmachemical treatment monitoring.

optical spectroscopy, archaelogy, plasmachemical reduction, ancient metal conservation

RAŠKOVÁ, Z., KRČMA, F., KLÍMA, M., KOUSAL, J.

2002

1. 6. 2002

AV ČR

0011-4626

Czechoslovak Journal of Physics

52

D

Czech Republic

D927

6