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Titanium dioxide blocking layers fabricated by material printing
Lásko, Ondřej ; Pospíšil, Jan (referee) ; Dzik, Petr (advisor)
In this theses TiO2 blocking layers were fabricated using material inkjet printing and spincoating methods. These layers were then analyzed using cyclic voltammetry to find any defects and to determine the type of those defects. We found that layers of over 120 nm made using ITO glass and spincoating method had the best blocking capabilities. Blocking layers prepared using FTO glass were underperforming greatly throughout the whole experiment. We also achieved good results with material ink jet printing. The best results out of all printed samples were achieved with DPI of 635, although these layers also had problem with the electrolyte rising through microscopic pores in the layer thus changing the results.
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Preparation and characterization of thin barrier layers
Blahová, Lucie ; Mráček, Aleš (referee) ; Buršíková, Vilma (referee) ; Krčma, František (advisor)
Combinations of different acrylic resins and microcrystalline waxes are most often used for the conservation and preservation of metallic archaeological artefacts these days. However, their properties are not sufficient and satisfactory in many ways. Therefore, the aim of this doctoral thesis is to develop a conservation system which will draw on the new knowledge gained in the field of advanced materials and technologies during last years. A conservation coating based on a thin barrier film appears the most promising. The conservation coating must fulfil particularly following rather contradictory requirements: good barrier function against oxygen, humidity and other corrosive agents; transparency because of colour appearance preservation; long term stability and easy removability; possibility to apply to more objects at the same time and reasonable financial requirements of a deposition process. Parylene C polymer was chosen as suitable material for this purpose. It was prepared via modified chemical vapour deposition. Parylene removability was ensured through the soluble interlayer made of Laksil silicone-acrylic lacquer which was applied between the protected metallic object and the parylene thin film. Initially, the deposition process of Laksil/parylene bilayer was optimized, then its physical and chemical characteristics were determined and eventually, they were compared with the conventional conservation coating composed of Paraloid B72 acrylic resin and Revax microcrystalline wax. Regarding to the demands of the conservation coating, we were interested especially in barrier properties, optical properties, surface morphology and removability of Laksil/parylene bilayer. The most useful method for description of coating barrier properties was corrosion testing in which coated metallic samples were exposed to highly corrosive environment of salt spray (made of 50 g•l–1 brine), 100% humidity and temperature of 35 °C (ISO 9227). The Laksil/parylene bilayer showed excellent barrier properties; samples treated this way sustained unchanged in the corrosion chamber for almost three months. The surface roughness measured by profilometry and surface morphology scanned by SEM illustrated the synergy between Laksil and parylene layer which leads to the exceptional barrier and anticorrosion function of bilayer. The Laksil layer is able to flatten out rough surface of a substrate. Furthermore, it can toughen the item surface which is, in case of a number of archaeological findings, created by corrosion product layers with variable mechanical strength. Thereon deposited parylene film becomes smooth and defect free and can act as a good diffusion barrier. The colouristic measurements confirmed that the Laksil/parylene bilayer does not almost change the appearance of protected item, in terms of colour. The caused colour difference (ISO 11664-4) ranged around 1 which value is defined as “perceivable only for experienced observers”. The Laksil/parylene bilayer is removable thanks to the Laksil solubility in xylene. It is necessary to carefully scratch the outer parylene film to enable access of xylene solvent to the lacquer. The successful removal of Laksil/parylene bilayer was first confirmed by the EDX on metallic iron samples. Afterwards, the possibility of bilayer complete removal even from a corroded surface of the original artefact was proved by TGA. Thus the conservation treatment can be considered fully reversible.
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Barriere layers for culture herritage objects preservation
Procházka, Michal ; Lehocký, Marián (referee) ; Zahoranová, Anna (referee) ; Krčma, František (advisor)
Every year, many archeological findings are discovered. It is necessary to document and conserve these items dug up from the ground. However, archeologists and conservators cannot handle such a big amount of newly found items. This work offers an alternative approach to standard conservation techniques, increasing the processing capacity and lowering the cost on items’ conservation. Studied alternative, mainly for protection of metallic artefacts, includes thin films based on parylene and organosilicons. Thin films were prepared on two experimental apparatuses. Parylene films were deposited by chemical vapour deposition (CVD). Final product was a thin film of parylene C. Organosilicon thin films were deposited via plasma enhanced chemical vapour deposition (PECVD). PECVD apparatus operates with capacitively coupled radiofrequently initiated plasma. Using hexamethyldisiloxane, thin films very similar to silicon dioxide were produced, thus called SiOx. Thin films were characterized by several methods and compared to standard treatment used by conservators – tannate layer, acrylic furnish Paraloid B72 and microcrystalline wax Revax 30. Parylene films showed excellent conformity and resistance to corrosion on iron substrate. First signs of corrosion were observed on layer of 5 µm thickness after 24 hours in salt fog. On samples coated by SiOx films, corrosion was spreading wide even during 1st hour of the corrosion test. Most probable cause was that SiOx film has thermal expansion coefficient different from iron substrate and due to this fact cracking occurs during cooling down of the treated substrate. On samples coated by standard treatment, corrosion occurred after 1-3 hours of the test. Oxygen transmission rate (OTR) measurements (performed on polypropylene substrate) confirmed good barrier properties of parylene C. Best parylene thin films had OTR approximately 170 cm3•m-2•atm-1•day-1. SiOx films reached good results with OTR 300 cm3•m-2•atm-1•day-1, compared to clean polypropylene substrate with OTR 1700 cm3•m-2•atm-1•day-1. Standard conservation layers could not be applied on polypropylene substrate, thus their OTR was not measured. We did not succeed in finding a substrate which is compatible for all types of treatments. Next, the study focused on combinations of thin films forming sandwich structures. All types let the corrosion attack the substrate during the 1st hour of the test. The cause was insufficient film thickness as well as crack ing of SiOx films due to different thermal expansion properties from the iron substrate. Although SiOx thin films were not deposited on substrate directly, they have excellent adhesion to parylenu and thus they could tear parylenu films due to thermal expansion. However, OTR measurements showed improvement in barrier properties. Multilayer parylene C–SiOx–parylene C–SiOx had OTR 5 cm3•m-2•atm-1•day-1. Final result is that parylene C thin films have better barrier properties than standard coatings and are suitable for conservation of metallic archaeological artefacts. SiOx films and multilayers showed poor anticorrosion protection of metallic substrates but they have good barrier and chemical properties in combination with other types of substrates. Mainly deposited on polymers, there is great potential for their application in many fields. Further research would be focused on new substrates for SiOx thin films and on the improvement of UV stability of parylene films.
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Titanium dioxide blocking layers fabricated by material printing
Lásko, Ondřej ; Pospíšil, Jan (referee) ; Dzik, Petr (advisor)
In this theses TiO2 blocking layers were fabricated using material inkjet printing and spincoating methods. These layers were then analyzed using cyclic voltammetry to find any defects and to determine the type of those defects. We found that layers of over 120 nm made using ITO glass and spincoating method had the best blocking capabilities. Blocking layers prepared using FTO glass were underperforming greatly throughout the whole experiment. We also achieved good results with material ink jet printing. The best results out of all printed samples were achieved with DPI of 635, although these layers also had problem with the electrolyte rising through microscopic pores in the layer thus changing the results.
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Preparation and characterization of thin barrier layers
Blahová, Lucie ; Mráček, Aleš (referee) ; Buršíková, Vilma (referee) ; Krčma, František (advisor)
Combinations of different acrylic resins and microcrystalline waxes are most often used for the conservation and preservation of metallic archaeological artefacts these days. However, their properties are not sufficient and satisfactory in many ways. Therefore, the aim of this doctoral thesis is to develop a conservation system which will draw on the new knowledge gained in the field of advanced materials and technologies during last years. A conservation coating based on a thin barrier film appears the most promising. The conservation coating must fulfil particularly following rather contradictory requirements: good barrier function against oxygen, humidity and other corrosive agents; transparency because of colour appearance preservation; long term stability and easy removability; possibility to apply to more objects at the same time and reasonable financial requirements of a deposition process. Parylene C polymer was chosen as suitable material for this purpose. It was prepared via modified chemical vapour deposition. Parylene removability was ensured through the soluble interlayer made of Laksil silicone-acrylic lacquer which was applied between the protected metallic object and the parylene thin film. Initially, the deposition process of Laksil/parylene bilayer was optimized, then its physical and chemical characteristics were determined and eventually, they were compared with the conventional conservation coating composed of Paraloid B72 acrylic resin and Revax microcrystalline wax. Regarding to the demands of the conservation coating, we were interested especially in barrier properties, optical properties, surface morphology and removability of Laksil/parylene bilayer. The most useful method for description of coating barrier properties was corrosion testing in which coated metallic samples were exposed to highly corrosive environment of salt spray (made of 50 g•l–1 brine), 100% humidity and temperature of 35 °C (ISO 9227). The Laksil/parylene bilayer showed excellent barrier properties; samples treated this way sustained unchanged in the corrosion chamber for almost three months. The surface roughness measured by profilometry and surface morphology scanned by SEM illustrated the synergy between Laksil and parylene layer which leads to the exceptional barrier and anticorrosion function of bilayer. The Laksil layer is able to flatten out rough surface of a substrate. Furthermore, it can toughen the item surface which is, in case of a number of archaeological findings, created by corrosion product layers with variable mechanical strength. Thereon deposited parylene film becomes smooth and defect free and can act as a good diffusion barrier. The colouristic measurements confirmed that the Laksil/parylene bilayer does not almost change the appearance of protected item, in terms of colour. The caused colour difference (ISO 11664-4) ranged around 1 which value is defined as “perceivable only for experienced observers”. The Laksil/parylene bilayer is removable thanks to the Laksil solubility in xylene. It is necessary to carefully scratch the outer parylene film to enable access of xylene solvent to the lacquer. The successful removal of Laksil/parylene bilayer was first confirmed by the EDX on metallic iron samples. Afterwards, the possibility of bilayer complete removal even from a corroded surface of the original artefact was proved by TGA. Thus the conservation treatment can be considered fully reversible.
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|
|
Barriere layers for culture herritage objects preservation
Procházka, Michal ; Lehocký, Marián (referee) ; Zahoranová, Anna (referee) ; Krčma, František (advisor)
Every year, many archeological findings are discovered. It is necessary to document and conserve these items dug up from the ground. However, archeologists and conservators cannot handle such a big amount of newly found items. This work offers an alternative approach to standard conservation techniques, increasing the processing capacity and lowering the cost on items’ conservation. Studied alternative, mainly for protection of metallic artefacts, includes thin films based on parylene and organosilicons. Thin films were prepared on two experimental apparatuses. Parylene films were deposited by chemical vapour deposition (CVD). Final product was a thin film of parylene C. Organosilicon thin films were deposited via plasma enhanced chemical vapour deposition (PECVD). PECVD apparatus operates with capacitively coupled radiofrequently initiated plasma. Using hexamethyldisiloxane, thin films very similar to silicon dioxide were produced, thus called SiOx. Thin films were characterized by several methods and compared to standard treatment used by conservators – tannate layer, acrylic furnish Paraloid B72 and microcrystalline wax Revax 30. Parylene films showed excellent conformity and resistance to corrosion on iron substrate. First signs of corrosion were observed on layer of 5 µm thickness after 24 hours in salt fog. On samples coated by SiOx films, corrosion was spreading wide even during 1st hour of the corrosion test. Most probable cause was that SiOx film has thermal expansion coefficient different from iron substrate and due to this fact cracking occurs during cooling down of the treated substrate. On samples coated by standard treatment, corrosion occurred after 1-3 hours of the test. Oxygen transmission rate (OTR) measurements (performed on polypropylene substrate) confirmed good barrier properties of parylene C. Best parylene thin films had OTR approximately 170 cm3•m-2•atm-1•day-1. SiOx films reached good results with OTR 300 cm3•m-2•atm-1•day-1, compared to clean polypropylene substrate with OTR 1700 cm3•m-2•atm-1•day-1. Standard conservation layers could not be applied on polypropylene substrate, thus their OTR was not measured. We did not succeed in finding a substrate which is compatible for all types of treatments. Next, the study focused on combinations of thin films forming sandwich structures. All types let the corrosion attack the substrate during the 1st hour of the test. The cause was insufficient film thickness as well as crack ing of SiOx films due to different thermal expansion properties from the iron substrate. Although SiOx thin films were not deposited on substrate directly, they have excellent adhesion to parylenu and thus they could tear parylenu films due to thermal expansion. However, OTR measurements showed improvement in barrier properties. Multilayer parylene C–SiOx–parylene C–SiOx had OTR 5 cm3•m-2•atm-1•day-1. Final result is that parylene C thin films have better barrier properties than standard coatings and are suitable for conservation of metallic archaeological artefacts. SiOx films and multilayers showed poor anticorrosion protection of metallic substrates but they have good barrier and chemical properties in combination with other types of substrates. Mainly deposited on polymers, there is great potential for their application in many fields. Further research would be focused on new substrates for SiOx thin films and on the improvement of UV stability of parylene films.
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