doktorska disertacija
Saša Skale (Author), Valter Doleček (Mentor), Mojca Slemnik (Co-mentor)

Abstract

Elektrokemijsko impedančno spektroskopijo (EIS) smo uporabili za preučevanje zaščitnih lastnosti različnih sistemov protikorozijske zaščite z epoksi premazi. Pripravili smo dve seriji vzorcev z epoksi sisitemi zaščite v intervalu med približno 150µm in 250µm. Pri prvi seriji vzorcev smo na površine peskane do stopnje Sa 21/2 po ISO 8501-1 nanesli epoksi cink fosfatni temelj, epoksi vmesni premaz z železovim luskavcem (MIOX) in običajni epoksi pokrivni premaz. Druga serija je imela navaden barierni epoksi temelj. Vmesni in pokrivni premaz pa sta ostala ista kot pri prvi seriji vzorcev. Prvi trije vzorci druge serije, so bili nanešeni na površine peskane do stopnje Sa 21/2 po ISO 8501-1. Preostanek druge serije pa je bil nanešen na ročno očiščene površine do stopnje St 2 po ISO 8501-1. Pripravljene vzorce smo izpostavili v vlažni komori (ISO 6270-1) in jih preučili z elektrokemijsko impedančno sprektroskopijo. Vrednotenje začetnih EIS meritev vzorcev je pokazalo pomembna odstopanja od običajnih modelov nadomestnih vezij. Na kompeksni ranini smo ugotovili, pred razvojem prevodnih por v premaznem sistemu, precejšen obseg realne komponente impedance, kasneje pa širjenje oziroma sploščitev polkroga. Preučitev začetnih meritev je pokazala, da njihovo slabo ujemanje s nadomestnimi vezji ne more biti posledica hrapavosti kovinske podlage ali pa nehomogenosti premaznega filma. Predlagali smo izboljšan model nadomestnega vezja, ki dodatno upšteva neposreden prenos — difuzijo ionov skozi premazni film. Izboljšan model uveljavi dodatni neskončni Warburgov element, ki premošča dosedanja elementa za kapacitvnost premaza in upornost por. Neskončni Warburgov element je rezultat rešitve drugega Fick-ovega zakona v primeru difuzije ionov skozi premazni film. Izboljšan model bolje razlaga EIS meritve, tudi v primerjavi s nadomestnim vezjem, ko namesto kapacitivnosti premaza uporabimo empirični konstantni fazni element (CPE). Vrednosti elementov nadomestnega vezja, ki jih določimo s primerjavo z EIS meritvami odražajo mehanizme transporta ionov skozi premazni film. Predlagali smo, da se vrednosti elementov nadomestnega vezja uporabijo za razvrščanje oziroma kvalitativno vrednotenje površinske zaščite s premazi. Rezultati razvrščanja se v veliki meri ujemajo z rezultati konvencionalnega ocenjevanja sistemov zaščite v vlažni komori. Primerjava aktivne inhibicije korozije zaradi cink fosfatnega temelja z bariranimi lastnostmi premaznega filma pokaže, da so slednje prevladujoče pri opredelitvi kvalitete sistema zaščite. Izkaže se tudi, da uporaba cink fosfatnega temelja pri debelinah sisteme zaščite nad 200µm ni potrebna. Obseg prenosa naboja skozi premazni sistem je pri prvi seriji vzorcev bistveno večji kot pri drugi seriji. To posredno potrjujejo rezultati konvencionalnega staranja premazov v vlažni komori. Ocenjevanje vzorcev druge serije pokaže bistveno slabše zaščitne lastnosti sistemov nanešenih na ročno očiščeno podlago (St 2 po ISO 8501-1). Ti kažejo večje obsege difuzije in prenosa ionov skozi pore v primerjavi z vzorci s sistemom zaščite na peskani podlagi. Rezultate ocenjevanja s pomočjo elementov nadomestnih vezij potrjujejejo tudi rezultati staranja v vlažni komori. Ob koncu staranja v vlažni komori so imeli vzorci druge serije, s sistemom zaščite na ročno očiščeni podlagi, poslabšano adhezijo,. Vzorci s sistemi na peskani podlagi pa so ohranili začetno popolno adhezijo. To je v skladu z uveljavljenimi konvencijami za pripravo površin v industriji protikorozijske zaščite s premazi.

Keywords

elektrokemijska impedančna spektroskopija;EIS;protikorozijska zaščita;epoksi premazi;

Data

Language: Slovenian
Year of publishing:
Typology: 2.08 - Doctoral Dissertation
Organization: UM FKKT - Faculty of Chemistry and Chemical Engineering
Publisher: S. Skale]
UDC: 620.193(043.3)
COBISS: 13712150 Link will open in a new window
Views: 4139
Downloads: 490
Average score: 0 (0 votes)
Metadata: JSON JSON-RDF JSON-LD TURTLE N-TRIPLES XML RDFA MICRODATA DC-XML DC-RDF RDF

Other data

Secondary language: English
Secondary title: EVALUATION OF EPOXY COATINGS SURFACE PROTECTION WITH ELECTROCHEMICAL IMPEDANCE SPECTROSCOPY
Secondary abstract: Electrochemical Impedance Spectroscopy (EIS) was used for study of corrosion protection properties of various configurations of epoxy protective systems. Two series of samples were prepared in dry thickness ranges approximately between 150 and 250 micrometers. First series were prepared with epoxy zinc phosphate primer, epoxy micaceous iron intermediate coat and ordinary epoxy top coat on surfaces grit-blasted to Sa 21/2 (ISO 8501-1). Second series used ordinary barrier epoxy primer in place of zinc phosphate primer. Other qualities of coatings remained the same, as in the first series. First three samples of 2nd series were applied on Sa 21/2 (ISO 8501-1) grit-blasted surfaces and second three samples of 2nd series were applied on hand-tool cleaned surfaces – St 2 (ISO 8501-1). Samples were exposed for various periods in wet chamber (ISO 6270-1) and analyzed with EIS. Preliminary EIS measurements show significant departure from usual equivalent circuit models. At start, EIS data showed a significant amount of real impedance component in the complex plane. Later after development of conductive pores through coatings system we detected broadening of the semicircle in complex plain. Since, lack of good correlations can not be attributed to roughness of the surface or non-homogeneities of coatings, we proposed an improved equivalent circuit model for description of protective coatings, prior development of measurable corrosion cells. Solution of the Fick’s second law gives us the infinite Warburg impedance element. This usually bridges circuit elements for coating capacity and pore resistance. The proposed model showed a better quality of fittings for our EIS data in comparison to the usual model, moreover even in case of substitution of coating capacity with the empiric constant phase element (CPE).On the basis of EIS circuit elements; we proposed the ranking system for qualitative evaluation of protective coatings. This showed good agreement with results of conventional accelerated aging in the wet chamber. Comparison of 1st series data showed that barrier properties of coatings are more important than corrosion inhibition with the zinc phosphate anti-corrosive pigment. Results also showed that at protective systems, over dry film thickness 200 μm, use of active anti-corrosive pigment is obsolete. Extend of ion transport through coatings (ion diffusion and ion conduction) is in case of 1st series much greater then in 2nd series. This results in lower protective quality of 1st series in comparison to 2nd series. These were also confirmed by results of conventional aging in the wet chamber. Comparison of 2nd series EIS circuit elements showed worse performance of coating systems, which were applied on hand-tool cleaned surfaces. Protective systems on hand tool cleaned surface (St 2 under ISO 8501-1) showed higher amounts of ion diffusion and ion conduction in comparison with grit-blasted samples. EIS results of surface preparation influence on anti-corrosion protective properties were also confirmed by conventional aging in the wet chamber, where adhesion (ASTM D 3359) of hand tool cleaned samples after exposures decreased. This is in agreement with industry established conventions in the design of surface protection with protective coatings.
Secondary keywords: electrochemical impedance spectroscopy;EIS;corrosion protection properties;epoxy protective systems;Materiali;Disertacije;Korozija;Zaščita;
URN: URN:SI:UM:
Type (COBISS): Dissertation
Thesis comment: Univ. Maribor, Fak. za kemijo in kemijsko tehnologijo
Pages: XV, 92 str.
ID: 8715829