D. Janová

Application of low temperature plasmas for restoration/conservation of archaeological objects

The low-temperature low-pressure hydrogen based plasmas were used to study the influence of processes and discharge conditions on corrosion removal. The capacitive coupled RF discharge in the continuous or pulsed regime was used at operating pressure of 100-200 Pa. Plasma treatment was monitored by optical emission spectroscopy. To be able to study influence of various process parameters, the model corroded samples with and without sandy incrustation were prepared. The SEM-EDX analyzes were carried out to verify corrosion removal efficiency. Experimental conditions were optimized for the selected most frequent materials of original metallic archaeological objects (iron, bronze, copper, and brass). Chlorides removal is based on hydrogen ion reactions while oxides are removed mainly by neutral species interactions. A special focus was kept for the samples temperature because it was necessary to avoid any metallographic changes in the material structure. The application of higher power pulsed regime with low duty cycle seems be the best treatment regime. The low pressure hydrogen plasma is not applicable for objects with a very broken structure or for nonmetallic objects due to the non-uniform heat stress. Due to this fact, the new developed plasmas generated in liquids were applied on selected original archaeological glass materials.

Reliable surface reconstruction from stereo pairs of images provided by scanning electron microscope

A method is described providing quantitative surface description of samples on the basis of stereoscopic couples of microscopic images. The main problem which is the reliable identification of corresponding pixels in both differing images has been solved using a suitable criterium of similarity. An approximate solution to the other problem of identifying the geometry of the sample stand in the range of micrometers is shown too. The whole procedure is rather demanding as to computational complexity concerns but provides more detailed and substantially more reliable data than the professional software of the used scanning microscope.

Robust Surface Reconstruction from Stereo SEM Images

The contribution describes a robust method providing quantitative surface description of microscopic samples from scanning electron microscope based on disparity analysis in stereoscopic couples of microscopic images. The three basic steps forming the surface calculation are described: disparity analysis using vector grey level registration based on vector angle minimisation (rather than on correlation or distance minimisation) in comparison with a feature matching approach, the disparity based identification of measuring geometry and the calculation of surface matrix. The presented approach is distinguished from most current stereo works by not imposing any constraints concerning the computed surface while still keeping the computational demands at a reasonable level for the application. It also provides a simple geometrical model of measurement (partly different from the standard epipolar geometry) that allows identification of the measurement parameters based on statistical processing of the disparity matrices.

Application of low-temperature low-pressure hydrogen plasma: treatment of artificially prepared corrosion layers

Abstract The aim of this work is the application of low-temperature low-pressure hydrogen plasma on artificially prepared corrosion layers, so called plasma chemical reduction. It is necessary to use samples with artificially prepared corrosion layers because it is impossible to use the real artifacts for fundamental research. The bronze was chosen as a sample material. Formation of corrosion layers on the bronze samples was carried out in concentrated hydrochloric acid vapors with the addition of sand. The radio-frequency hydrogen plasma was generated in the flowing regime at a pressure of 160 Pa. Different values of supplied power were chosen as well as different discharge modes: continuous or pulsed mode with varied duty cycles. By the combination of supplied power and mode factors, we selected two values of effective power. The process of plasma chemical reduction was monitored by optical emission spectroscopy (OES) and simultaneously, the sample temperature was measured. Rotational temperatures were calculated from OH radicals spectra. Changes in the structure and elemental composition were determined using scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDX). Graphical Abstract