Abstract
Topography observation of the nanoscale passivation film on tinplate using a scanning electron microscope and an electro-optical surface profilometer showed that it was difficult to observe the true topography because of the high surface roughness of the tinplate. Topography observation using a profilometer on bright tin plating with low surface roughness and work function measurement on tinplate surface using a Scanning Kelvin Probe Microscope (SKPM) were then carried out to solve the problem. The results indicated that there was a thin chemical passivation film distributed uniformly in different areas of microscopic bulges and valleys on the tinplate surface, and the film became more uniform with longer passivation time. In comparison, the electrolytic passivation film was thick, and the distribution uniformity was poorer. Specifically, the film was thicker on microscopic bulges and thinner in microscopic valleys, and this was worse with longer passivation time. Thus, the difference in performances of the corrosion and paint adhesion of the tinplate treated with different passivation processes can be explained in terms of the topography and distribution state of the passivation film.
Highlights
The passivation film that forms on the surface of tinplate via chemical or electrochemical reaction plays a vital role during tinplate storage, transportation, and use [1,2,3]
The results indicated that the elements chromium, oxygen, and tin were detected on the tinplate surface
We observed the topography of the nanoscale passivation film on tinplate samples with high surface roughness, and found the difference in the distribution state of the films prepared with different passivated processes using a profilometer and Scanning Kelvin Probe Microscope (SKPM)
Summary
The passivation film that forms on the surface of tinplate via chemical or electrochemical reaction plays a vital role during tinplate storage, transportation, and use [1,2,3]. A thicker film results in better corrosion resistance, it is believed that a film that is too thick results in poor paint adhesion [1,10]. It is essential for a passivation film to be uniformly thick because in a corrosive environment, if the thickness is not uniform, it is likely that corrosion microcells will develop between the local regions without film (or with a thinner film covering) and the regions covered with thicker film because of the different surface potential between the regions; this causes pitting corrosion [11,12]
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