Electrochemical properties and thermal stability of epoxy coatings electrodeposited on aluminium and modified aluminium surfaces

Abstract

The corrosion behavior of epoxy coatings electrodeposited on aluminum, as well as on electrochemically and chemically modified aluminum were investigated during exposure to 3 % NaCl. Electrochemical impedance spectroscopy (EIS) and thermogravimetric analysis (TGA) were used for the determination of the protective properties of epoxy coatings on aluminum, anodized aluminum, phosphatized and chromatized-phosphatized aluminum. The protective properties of epoxy coatings on anodized and chromatized-phosphatized aluminum are significantly improved with respect to the same epoxy coatings on aluminum and phosphatized aluminum: higher values of the pore resistance and charge-transfer resistance, lower values of the coating capacitance, double-layer capacitance and relative permittivity (from EIS) smaller amount of absorbed water inside the coating (From TGA). On the other hand, the lower values of the ipdt temperature indicate a lower thermal stability of the epoxy coatings on anodized and chromatized-phosphatized aluminum.

Proučavano je koroziono ponašanje epoksidnih prevlaka dobijenih kataforetskim taloženjem na aluminijumu i elektrohemijski i hemijski modifikovanom aluminijumu tokom delovanja 3 % rastvora NaCl. Za određivanje zaštitnih osobina epoksidnih prevlaka na aluminijumu, anodiziranom aluminijumu, fosfatiranom i hromatno-fosfatiranom aluminijumu korišćene su metode spektroskopije elektrohemijske impedancije i termogravimetrijske analize. Zaštitne osobine epoksidnih prevlaka na anodiziranom i hromatno-fosfatiranom aluminijumu su značajno poboljšane u odnosu na iste epoksidne prevlake na aluminijumu i fosfatiranom aluminijumu: veće vrednosti otpornosti u porama prevlake i otpornosti prenosa naelektrisanja na graničnoj površini metal-elektrolit i manje vrednosti kapacitivnost prevlake, kapacitivnosti električnog dvojnog sloja i relativne permitivnosti prevlake (impedansna merenja) i manja količina absorbovane vode u prevlaci (termogravimetrijska analiza). S druge strane, manje vrednosti ipdt temperature ukazuju na manju termičku stabilnost epoksidnih prevlaka na anodiziranom i hromatno-fosfatiranom aluminijumu.