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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 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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