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Study of plasmachemical reduction of corrosive layers on bronze
Zemánek, Nikola ; Selucká, Alena (referee) ; Krčma, František (advisor)
The application of low-pressure low-temperature hydrogen plasma on artificial corrosion layers on bronze has been studied. For this purpose, three sets of bronze corroded samples were prepared. The first step of the model sample preparation was grinding of the bronze surface by using emery with 60, then 280 and finally by 600 grains density, in order to achieve the defined surface roughness. The next step of the work were optical and scanning electron microscopy observations with energy dispersive X-ray micro analysis (SEM-EDX) of the prepared bronze sample for purpose of surface structure characterization and element composition determination. Bronze samples with defined surface structure were corroded in different corrosion atmospheres. Three different model corrosion layers were formed by acidic atmospheres of hydrochloric acid, nitric acid and sulphuric acid. The element composition and structure of corrosion layer was determined by SEM-EDX again. The different amounts of oxygen, nitrogen, chlorine, sulfur, copper, tin and lead in the corrosion layer according to different types of corrosion atmospheres were determined. The next and also main part of the work was a plasma chemical reduction of corroded samples. The plasma reactor used the RF discharge (13.56 MHz) created in quartz tube with outer electrodes. The generation of capacitively coupled plasma in continuous or pulse mode by different supplied power was carried out. The plasma radiation emitted from the RF discharge during the sample treatment was measured by optical emission spectroscopy. The quantity of OH radical created in an active discharge by reactions of atomic hydrogen with the corrosion layer is a significant indicator of a reduction process. Therefore the OH radical band integral intensities observed as a function of the treatment time were used as a monitor for plasma chemical reduction process. The OH emission showed different behavior depending on corrosion layer composition during the plasma treatment. The transformations of the corrosion layer due to the plasma effect were investigated by means of SEM-EDX once again. Changes in the element composition of corrosion (or surface) layers in consequence of plasma chemical treatment are given. Generally, the element composition after the plasma chemical treatment showed explicitly that oxygen and chlorine content in the corrosion layer decreased, nitrogen was removed totally. Metal deposition on the reactor wall was observed occasionally. The SEM-EDX analyzes also showed that in some cases the tin content in sample surface layers was significantly decreased. For that reason, in case of bronze sample (artifacts) treatment, the sample and plasma temperature seem to be very important parameters for the process optimization. The acceptable conditions for plasma chemical treatment has been found in case of corrosion layer formed by nitric acid, only. The other corrosions will be a subject of further studies.
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Study of plasmachemical reduction of corrosive layers on copper
Šimšová, Tereza ; Selucká, Alena (referee) ; Krčma, František (advisor)
The present diploma thesis concerns the research of plasmachemical reduction of copper corrosion layers. The process was based on using low pressure hydrogen RF plasma in which copper samples are treated for several hours. Four series of copper corrosion layers were prepared in four different corrosion atmospheres. The first two were prepared using saturated vapors of HCl and ammonium acetate that affected copper samples for one week. The second two sets were prepared by samples dipping in HNO3 and H2SO4. EDX analysis confirms visual composition of corrosion layers – chlorides, nitrides and sulphate, respectively. The ammonium acetate produced no corrosion layers and thus this set of samples was omitted. The optical emission spectroscopy was used to find out reactions in a hydrogen RF discharge. At the first, a character of plasma without samples was taken by measuring in continuous and pulsed regime. The integral spectrum intensity (300-700 nm) and intensities of hydrogen atomic lines were observed in the dependences on hydrogen flow, power and duty cycle. After that copper samples were treaded under various conditions in continual and pulse regime, typically at pressure of 170 Pa, 200 W power and hydrogen flow rate of 10.2 ml/min. The integral OH radical spectral intensity in the range of 305 – 330 nm was used as a monitor of plasma treatment process. The experimental results showed that intensities of OH radical depended strongly on the corrosion layer kind as well as on the RF discharge mode. Reduction of corrosion layers treated in the pulsed regime was not so satisfactory then in the continuous regime probably due to lower temperature of sample during the treatment. The total supplied energy into the system was also lower in this case. The sample sputtering was observed during the reduction in continuous regime. It means the corrosion was successfully removed but the process was not stopped at that moment, so it is necessary to propose another additional monitoring process besides observing OH radicals. Our experimental results are the first step in the spread research of plasmachemical treatment of copper made archaeological artifacts.
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Study of plasmachemical reduction of corrosive layers on bronze
Miková, Petra ; Selucká, Alena (referee) ; Krčma, František (advisor)
One of the important stages of the human history is certainly Bronze Age, on our territory dated 1900 - 800 BC. At that times, it was produced many objects of bronze, such as swords, spears, daggers, ornaments, jewelry. These artifacts are now found by archaeologists in excavations around the whole world. During the years there was an exposure to various types of substances and the environment and result in extensive corrosion of the used materials. To better understand the culture and traditions of our ancestors, it is necessary to carefully eliminate the corrosion and thorough inspection of these subjects. In this work, we consider the model corrosion layers removal by reduction in low-temperature hydrogen plasma. Plasma chemical reduction method was developed during the eighties years of last century and currently is further rapidly improved. Unfortunately, the process mechanism is not yet precisely known. Preparation of model corrosion layers were as follows: bronze blocks (weight approximately 80 g) were sharpend by electrical grinding machine (used paper 280 and then 600). Thus treated samples were rinsed in ethanol, dryed by hot dryer and stored in plastic bags. A Petri dish was placed at the bottom of the desiccator and it was poured by 20 ml of concentrated hydrochloric acid. Above the bowl has punched ceramic grid, on which the samples were placed. Closed desiccator was placed in darkness at the ambient laboratory temperature. To accelerate the samples corrosion process in a desiccator, the samples were sprinkled with acid. Plasma chemical treatment was carried out in a cylindrical reactor of quartz glass with outer copper electrodes. The RF (13.54 MHz) capacitivelly coupled plasma was used for the samples treatment. For each sample have been selected specific conditions: power (50 - 300 W), pulse (duty cycle of 10 – 25 %) or continuous mode. The optical emission spectroscopy monitored dependence of OH- intensity during the reduction. The decrease to the 1/10 of the maximum value leads to end the experiment. Based on this criterion, the treatment time of samples was in the range of 30 - 80 minutes. Corrosion has been removed from 7 samples. All the samples were covered by corrosion deep green color with a clearly visible crystalline structure before their inserting into the reactor. After the treatment, the color was dark black, and after leaving the air began to surface green, in some samples was observed in white and yellow tint. Surface top layer was removed on samples 1 and 5, where spontaneous dropout was reached. The pulse mode with duty cycle of 10 % and the powers of 200 and 300 W were applied for these two samples. The surface layer of samples treated with pulsed mode of 25 % was easily removable by spatula. The work demonstrated the applicability of hydrogen RF plasma in pulsed mode for the corrosion removal from bronze samples. The further work will be focused on the optimal treatment conditions search.
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Study of plasmachemical reduction of corrosive layers on brass
Řádková, Lucie ; Selucká, Alena (referee) ; Krčma, František (advisor)
The main topic of this bachelor thesis is plasmachemical treatment of archeological artifacts, especially plasma chemical treatment of brass corrosion layers. Low-pressure, low-temperature hydrogen plasma is used for this process. Nowadays, the technology is used mainly for iron or silver based materials but even for them the optimal conditions for the corrosion removal are not fully known yet. The knowledge about other metallic materials is fully missing. Two sets of brass samples were prepared in different corrosion atmospheres. The first atmosphere was prepared using saturated vapors of HCl. The samples were in this atmosphere during one month, and corrosion layers were orange-brown. The second set was prepared using ammonium solution, the samples were in this atmosphere for one day, corrosion layers were blue. The generation of capacitively coupled plasma in continuous mode by different supplied power was done. The experiments were carried out at 100 Pa with hydrogen gas flow of 50 sccm. Discharge power was varied in the interval 50 – 200 W and the treatment duration was 70 – 140 min. The optical emission spectroscopy of OH radical was used to find out all changes those have been resulting from plasmachemical reactions. The OH radical integral intensities were observed, they were used to monitoring plasma chemical reduction process. Spectral intensity of spectroscope was in the range 290 – 330 nm. After the plasmachemical treatment, it was very difficult to remove corrosion layers of HCl, but removing of NH3 corrosion layers was easy. It was caused by type of corrosion process (corrosion layers were influenced by time of corrosion process). This bachelor thesis is the start to find out conduct corrosion layers of brass in plasma treatment. In future, plasma treatment could be used to treatment of real archaeological artifacts.
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