| Abstract | Brončana kulturna baština izložena vanjskom okolišu podložna je degradaciji uslijed korozivnog djelovanja vlage i onečišćenja iz zraka. U praksi se primjenjuju različite metode korozijske zaštite bronce i brončane patine, no zbog specifičnih zahtjeva konzervatorske struke odabir tih metoda je limitiran, a često ih karakterizira nedovoljna trajnost postignute zaštite. Zbog toga je potrebno razviti nove poboljšane postupke njene zaštite. S tim ciljem je u ovom radu ispitana mogućnost primjene dugolančanih fosfonskih kiselina za korozijsku zaštitu čiste i patinirane površine bronce te za poboljšanje adhezije i zaštitnih svojstava transparentnih organskih premaza na navedenim supstratima. S obzirom da postupak formiranja filma može utjecati na njegovu uređenost i stabilnost, istraženo je dobivanje filmova fosfonske kiseline na čistoj površini bronce metodama kista, prskanja i uranjanja. Metodama kista i prskanja, koje su praktičnije za upotrebu na skulpturama, dobivaju se filmovi koji pokazuju nešto veću stabilnost u korozivnom mediju, no reproducibilniji i uređeniji filmovi dobivaju se metodom uranjanja stoga je ova metoda korištena za daljnja istraživanja. Istražen je i utjecaj duljine lanca i završne funkcionalne skupine na uređenost i zaštitna svojstva samoorganiziranih filmova pri čemu je utvrđeno da kiseline s duljim lancem formiraju uređene filmove dok kiselina s kraćim lancem formira film nižeg stupnja uređenosti. Unatoč slabijoj uređenosti filma, kiselina s kraćim lancem pruža visoki stupanj zaštite pri dovoljnoj debljini filma. U idućem koraku ispitan je utjecaj sastava brončane podloge na formiranje samoorganizirajućih filmova fosfonske kiseline. Istraživanje je provedeno na podlogama od cinka, kositra i bakra, kao najčešćim legirnim elementima u bronci, te na tri vrste bronci. Pokazalo se da se na svim ispitivanim podlogama mogu formirati zaštitni filmovi, ali da njihova učinkovitost i stabilnost ovise o korozijskoj stabilnosti supstrata. Podloge koje su manje otporne na koroziju zaštićene su u kraćem periodu jer otapanje podloge dovodi do otapanja zaštitnog filma. U ovom su radu fosfonske kiseline također ispitane kao molekularni promotori adhezije dvaju akrilnih i jednog poliuretanskog premaza na čistoj bronci. Bronca je prije nanošenja premaza tretirana fosfonskim kiselinama te su ispitane različite metode uklanjanja gornjih slabije vezanih slojeva filma kako bi adhezija premaza bila uspješnija. Fosfonske kiseline poboljšale su zaštitna svojstva i adheziju akrilnog premaza Paraloida B72 i poliuretanskog premaza te su inhibirale otapanje bronce. U konačnici je pokazano da samoorganizirajući filmovi fosfonske kiseline doprinose i korozijskoj zaštiti patinirane bronce izložene korozivnom mediju te da također poboljšavaju zaštitna svojstva Paraloida B72 na takvoj površini. Korozijska zaštita koju pružaju ispitivani sustavi određena je na temelju elektrokemijskih ispitivanja (polarizacijska mjerenja i elektrokemijska impedancijska spektroskopija) uzoraka izloženih korozivnom djelovanju umjetne kisele kiše. Dio uzoraka dodatno je bio izložen djelovanju vanjske urbane atmosfere, odnosno agresivnim uvjetima u vlažnoj komori s NO2. Izgled uzoraka prije i nakon izlaganja korozivnom mediju karakteriziran je elektronskom i optičkom mikroskopijom. Uređenost filmova i način vezanja na površinu utvrđeni su spektroskopskim (FTIR, XPS, SFG) tehnikama te TOF-SIMS spektrometrijom. Dodatno su modificirane brončane površine karakterizirane goniometrijom. Adhezija premaza na brončani supstrat određena je na temelju ispitivanja vlačnom (pull-off) metodom. |
| Abstract (english) | Bronze cultural heritage exposed to the outdoor environment is susceptible to degradation due to the corrosive effects of moisture and air pollution. In practice, various methods of corrosion protection of bronze and bronze patina are used, but due to the specific requirements of the conservation profession, the choice of these methods is limited, and they are often characterized by insufficient durability of the achieved protection. It is therefore necessary to develop new and improved methods of their protection. With this aim, the possibility of using long-chain phosphonic acids for corrosion protection of a bare and patinated bronze surface, as well as for improving the adhesion and protective properties of transparent organic coatings on these substrates was examined in this work. Given that the method of organic film formation can influence on its structure and stability, obtaining phosphonic acid films on a clean bronze surface by brushing, spraying and dip coating was investigated. The brushing and spraying methods, which are more practical for use on sculptures, produce films with slightly greater stability in a corrosive medium, however more reproducible and well-organized films are obtained by the dip coating method, so this method was used for further investigations. The influence of chain length and the terminal functional group of phosphonic acid on the crystallinity and protective properties of the self-assembled films was also investigated. It was found that acids with a longer chain form more ordered films, while acids with a shorter chain form film with a lower degree of order. Despite the lower crystalinity of the film, the acid with a shorter chain provides a high degree of protection when a sufficient film thickness is achieved. In the next step, the influence of the composition of the bronze substrate on the formation of self-assembled films of phosphonic acid was examined. The research was conducted on substrates made of zinc, tin and copper, the most common alloying elements in bronze, and on three types of bronze. It was found that protective films can be formed on all substrates, but their effectiveness and stability depend on the corrosion stability of the substrate. Substrates that are less corrosion resistant are protected for a shorter period of time, as the dissolution of the substrate leads to the dissolution of the protective film. In this work, selected phosphonic acids were also tested as molecular promoters of the adhesion of two acrylic and one polyurethane coating on pure bronze. Before applying the coating, the bronze was treated with phosphonic acids. Different methods were tested to remove the weakly bonded upper layers of the film in order to improve the adhesion of the coating. Phosphonic acids improved the protective properties and adhesion of the acrylic coating Paraloid B72 and the polyurethane coating, and inhibited the dissolution of the bronze. Finally, it was shown that self-assembled films of phosphonic acid contribute to the corrosion protection of patinated bronze exposed to a corrosive medium and improve the protective properties of Paraloid B72 on such surface. The corrosion protection provided by the studied systems was examined by electrochemical tests (polarization measurements and electrochemical impedance spectroscopy) on samples exposed to the corrosive effect of artificial acid rain. Some of the samples were additionally exposed to the effect of the outdoor urban atmosphere and to aggressive conditions in a humid chamber with NO2. The surface appearance of the samples before and after exposure to the corrosive medium was characterized by electron and optical microscopy. The structure of the films and their binding to the surface were examined by spectroscopic methods
(FTIR, XPS, SFG) and TOF-SIMS spectrometry. In addition, the modified bronze surfaces were characterized by goniometry. The adhesion of the coating to the bronze substrate was determined based on a pull-off test. |
