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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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Low pressure plasma application for the surface cleaning of archaeological objects
Bubnová, Kateřina ; Grossmannová, Hana (referee) ; Krčma, František (advisor)
This diploma thesis builds on my bachelor thesis, which was focused on the application of low-pressure hydrogen plasma and argon-hydrogen plasma on layers of corrosion products. According to results of the experiments, an appropriate temperature for plasma chemical treatment of lead samples was detected. However, the process of corrosion removal through plasma chemical treatment needs to be further optimized to prevent potential damage to the original historical artefacts. Optimization of the treatment process is therefore the main subject of this work’s research. The model samples with artificial corrosion layers with dual composition were prepared. These samples were put to desiccator with sand and organic acid. The samples corroded in environment of acetic acid or formic acid with the aim of creating the corrosion, which would be at least partially simulated with corrosion on the original artefacts. The process of corrosion lasted for eleven months. After that, the samples were dried out under reduced pressure, put to the protecting foil with humid and oxygen absorbers. In contrast with my bachelor thesis where the continuous regime was chosen for the treatment, the pulse regime with three different condition settings is used. Process of experiment was monitored by OES, surface of samples was analyzed by SEM, EDX, XRD methods. Results from experiments with model samples were used for treatment of original artefacts with missing documentation, so their eventual damaging was acceptable.
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Plasma cleaning of corroded plumb objects
Bubnová, Kateřina ; Grossmannová, Hana (referee) ; Krčma, František (advisor)
This bachelor thesis deals with the application of low-pressure hydrogen plasma to lead corrosion products. There are many historical objects and these objects require careful removal of corrosion layers. Therefore, it is necessary to optimize the treatment process in order not to destroy real historical artefacts in the future. This work is focused on lead, which has not been explored by this method yet. Model samples with corrosion were prepared for comparison and these samples corrode in vapors of concentrated acetic acid and formic acid. There were three working temperatures for plasma chemical treatment because of the low lead melting point and the atomic heating. Argon-hydrogen plasma and hydrogen plasma was applied to 12 corroded samples during the experiment. Process progress was monitored by optical emission spectrometry and surface analysis was performed by SEM, XRD and EDX analysis. The results of these analyzes showed that the most appropriate temperature for plasma chemical treatment was 130 ° C. Based on the obtained results many suggesstions and ideas were obtained for the future research like using of pulse mode and gas composition.
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Preparation and Plasmachemical Reduction of Model Corrosion Layers on Iron.
Sázavská, Věra ; Novák, Stanislav (referee) ; Zahoranová, Anna (referee) ; Krčma, František (advisor)
The plasmachemical removal process of corrosion layers is based on a reduction effect of RF hydrogen low-pressure plasma, and it is used for archaeological objects. Incrustation layers on artifact surface become brittle and porous due to plasma processing. The structure and composition of corrosion layers is changed. Therefore, it is much easier to recover the original surface of the plasma treated artifacts in contrary to those treated by conventional ways. Moreover, we can save time on invasive and thus dangerous mechanical removal of corrosion layers as for example sanding is. After plasma treatment, we can observe fine details of the original surface and memory of tools used during its manufacturing. These details are important information on the origin and manufacturing methods of the artifacts. The plasma reduction process leads to the removal of impurities from cavities as well, and a function of mechanical components of archaeological object can be restored. Moreover, chlorides can be easily removed from the corrosion layers and thus any significant post-corrosion is protected. Each archaeological object is original and it has its own “corrosion history”. First, the object had been exposed to the atmosphere for a long time. Then, it had been often placed in a tomb or grave or it otherwise got into the soil or sea. Thus, each archaeological object was exposed to different corrosion stress (humidity, composition of corrosive environment, etc.). Due to these facts, any universal way of a corroded object treatment is very difficult or even impossible to propose. In this work, the problem was solved using model samples of common metals which were treated at various plasma treatment conditions. Archaeological objects made of iron are the most common artifacts, and the typical corrosion products on iron are akaganeite, rokuhnite, and szomolnokite. These three corrosion products were created on the model samples in laboratory and then, the plasmachemical reduction was applied for their removal. The experiment was done in a Quartz cylindrical reactor with capacitive coupled RF plasma created using outer electrodes. We used discharge power from 100 W to 400 W in a continuous or pulsed regime (duty cycle of 75 %, 50 % and 25 %). Flowing plasma was created in pure hydrogen at pressure of 150200 Pa. Sample temperature was monitored by a thermocouple, and it did not exceed 200C during all these experiments. This temperature is regarded as a limit temperature for metallographic changes of archaeological iron. Higher temperature can cause destruction of archaeological iron objects. The optical emission spectroscopy of OH radical was used for the process monitoring. We focused on the monitoring of OH-radicals generated in the plasma, which are characteristic species formed by this process. Each corrosion product has a different time evaluation of generated OH-radicals, which is closely related to the degradation of a given corrosion product. Corrosion layers were analyzed before and after the plasmachemical reduction by SEM-EDX. We have found that the plasmachemical reduction is not very suitable for the szomolnokite corrosion product, which is degraded with difficulty and at high applied powers, only. However, very good removal efficiency was obtained for the rokuhnite and akaganeite corrosion.
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Low pressure plasma application for the surface cleaning of archaeological objects
Bubnová, Kateřina ; Grossmannová, Hana (referee) ; Krčma, František (advisor)
This diploma thesis builds on my bachelor thesis, which was focused on the application of low-pressure hydrogen plasma and argon-hydrogen plasma on layers of corrosion products. According to results of the experiments, an appropriate temperature for plasma chemical treatment of lead samples was detected. However, the process of corrosion removal through plasma chemical treatment needs to be further optimized to prevent potential damage to the original historical artefacts. Optimization of the treatment process is therefore the main subject of this work’s research. The model samples with artificial corrosion layers with dual composition were prepared. These samples were put to desiccator with sand and organic acid. The samples corroded in environment of acetic acid or formic acid with the aim of creating the corrosion, which would be at least partially simulated with corrosion on the original artefacts. The process of corrosion lasted for eleven months. After that, the samples were dried out under reduced pressure, put to the protecting foil with humid and oxygen absorbers. In contrast with my bachelor thesis where the continuous regime was chosen for the treatment, the pulse regime with three different condition settings is used. Process of experiment was monitored by OES, surface of samples was analyzed by SEM, EDX, XRD methods. Results from experiments with model samples were used for treatment of original artefacts with missing documentation, so their eventual damaging was acceptable.
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|
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Plasma cleaning of corroded plumb objects
Bubnová, Kateřina ; Grossmannová, Hana (referee) ; Krčma, František (advisor)
This bachelor thesis deals with the application of low-pressure hydrogen plasma to lead corrosion products. There are many historical objects and these objects require careful removal of corrosion layers. Therefore, it is necessary to optimize the treatment process in order not to destroy real historical artefacts in the future. This work is focused on lead, which has not been explored by this method yet. Model samples with corrosion were prepared for comparison and these samples corrode in vapors of concentrated acetic acid and formic acid. There were three working temperatures for plasma chemical treatment because of the low lead melting point and the atomic heating. Argon-hydrogen plasma and hydrogen plasma was applied to 12 corroded samples during the experiment. Process progress was monitored by optical emission spectrometry and surface analysis was performed by SEM, XRD and EDX analysis. The results of these analyzes showed that the most appropriate temperature for plasma chemical treatment was 130 ° C. Based on the obtained results many suggesstions and ideas were obtained for the future research like using of pulse mode and gas composition.
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|
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Preparation and Plasmachemical Reduction of Model Corrosion Layers on Iron.
Sázavská, Věra ; Novák, Stanislav (referee) ; Zahoranová, Anna (referee) ; Krčma, František (advisor)
The plasmachemical removal process of corrosion layers is based on a reduction effect of RF hydrogen low-pressure plasma, and it is used for archaeological objects. Incrustation layers on artifact surface become brittle and porous due to plasma processing. The structure and composition of corrosion layers is changed. Therefore, it is much easier to recover the original surface of the plasma treated artifacts in contrary to those treated by conventional ways. Moreover, we can save time on invasive and thus dangerous mechanical removal of corrosion layers as for example sanding is. After plasma treatment, we can observe fine details of the original surface and memory of tools used during its manufacturing. These details are important information on the origin and manufacturing methods of the artifacts. The plasma reduction process leads to the removal of impurities from cavities as well, and a function of mechanical components of archaeological object can be restored. Moreover, chlorides can be easily removed from the corrosion layers and thus any significant post-corrosion is protected. Each archaeological object is original and it has its own “corrosion history”. First, the object had been exposed to the atmosphere for a long time. Then, it had been often placed in a tomb or grave or it otherwise got into the soil or sea. Thus, each archaeological object was exposed to different corrosion stress (humidity, composition of corrosive environment, etc.). Due to these facts, any universal way of a corroded object treatment is very difficult or even impossible to propose. In this work, the problem was solved using model samples of common metals which were treated at various plasma treatment conditions. Archaeological objects made of iron are the most common artifacts, and the typical corrosion products on iron are akaganeite, rokuhnite, and szomolnokite. These three corrosion products were created on the model samples in laboratory and then, the plasmachemical reduction was applied for their removal. The experiment was done in a Quartz cylindrical reactor with capacitive coupled RF plasma created using outer electrodes. We used discharge power from 100 W to 400 W in a continuous or pulsed regime (duty cycle of 75 %, 50 % and 25 %). Flowing plasma was created in pure hydrogen at pressure of 150200 Pa. Sample temperature was monitored by a thermocouple, and it did not exceed 200C during all these experiments. This temperature is regarded as a limit temperature for metallographic changes of archaeological iron. Higher temperature can cause destruction of archaeological iron objects. The optical emission spectroscopy of OH radical was used for the process monitoring. We focused on the monitoring of OH-radicals generated in the plasma, which are characteristic species formed by this process. Each corrosion product has a different time evaluation of generated OH-radicals, which is closely related to the degradation of a given corrosion product. Corrosion layers were analyzed before and after the plasmachemical reduction by SEM-EDX. We have found that the plasmachemical reduction is not very suitable for the szomolnokite corrosion product, which is degraded with difficulty and at high applied powers, only. However, very good removal efficiency was obtained for the rokuhnite and akaganeite corrosion.
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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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