Corrosion of enamelled steel by domestic cleaning fluids

Abstract

The damage promoted on two different kinds of enamelled specimens was evaluated. One was coated with a single layer of pyrolytic electrostatic powder enamel (referred to as black enamel), and the other was coated with ground coat wet enamel (white enamel). Specimens were cyclically subjected to the action of an oven cleaner and temperatures of about 250°C. After a few cycles the surfaces lost their smooth, shiny appearance, revealing that some damage was induced during the treatment. Roughness measurements and electrochemical tests showed that the degradation of the coating was rather superficial and that the metal substrate was still very well protected. Further tests showed different performances depending on the type of coating. While the black enamel revealed some pits with brown corrosion products across the surface, indicating the onset of attack of the base metal, the white enamel displayed a surface that was highly porous compared with the untreated specimens. Potentiodynamic polarisation curves showed the presence of a pitting potential together with a hysteresis loop for the black enamel, indicating the presence of small pores providing access for electrolyte (chloride) to corrode the metal base. Conversely, polarisation curves for the white enamel only displayed higher values of passive current density, suggesting a difference in the dielectric properties of the enamels.