Protection of Archaeological Artefacts by Deposition of Parylene and SiOx Thin Films

abstract

English

The treatment process of archaeological artefacts is usually divided into two main steps. A surface corrosion removal is the first step that is performed by low pressure hydrogen plasma. Its chemically reducing atmosphere allows a careful removal of corrosion without damaging the artefact surface details. After the procedure, the surface is highly reactive and inclines to oxidation. To prevent this process, it is necessary to protect the surface with a barrier film preventing the penetration of oxygen (as well as the other corrosion agents) to the surface. This study focuses on possibilities of the archaeological artefacts (copper, iron, brass and bronze) protection by a thin film deposition of SiOx and Parylene thin films. Parylene (poly-para-xylylene) is used in a wide range of applications, particularly as a coating for biomedical implants and microelectronics. Parylene coatings are chemically inert, conformal and transparent with excellent barrier properties [1] but relatively small adhesion. These all properties determine parylene to be a perfect material for protection of archaeological artefacts. Parylene coatings are prepared by the standard chemical vapor deposition (CVD) method [2]. SiO2-like high density films are widely used in contemporary industrial technologies because they have very good barrier properties and excellent adhesion improving also the mechanical properties of the substrate [3]. Plasma enhanced chemical vapor deposition (PECVD) enables the preparation of SiOx based thin films with higher flexibility due to incorporated organics groups. SiOx layers were deposited by PECVD in a low pressure reactor with capacitively coupled plasma discharge (13.56 MHz). Mixture of Hexamethyldisiloxane with oxygen was used as a precursor of plasmachemical reactions. The coatings were characterized by various methods in order to obtain information about their thickness (ellipsometry), chemical structure (FTIR) and elemental composition (XPS), surface morphology (LCSM, SEM) and barrier properties (OTR). Standard corrosion tests were performed to determine the effectiveness of corrosion protection. The results were compared with those on samples treated by conventional conservation procedures.

SiOx plasma deposition, parylene films, barriere properties

BALAŠTÍKOVÁ, R.; PROCHÁZKA, M.; MENČÍK, P.; HORÁK, J.; PŘIKRYL, R.; KRČMA, F.

10. 9. 2012

Istanbul

629

629

1