Chemical and morphological characterization of commercial tinplate for food packaging

Abstract

The structure of tinplate is usually described as a sequence of layers involving an external tin layer (passivated by a chromate conversion coating), an intermediate FeSn2 layer, and the steel substrate. This structure description applies well to tinplate produced in the past by hot dipping but not necessarily to modern materials fabricated through tin electrodeposition and subsequent heat treatment. In this work, the chemical composition and the structure of 5 commercial tinplate materials have been investigated using Auger electron spectroscopy, scanning electron microscopy, 3D white light interferometry, and electrochemical chrono‐potentiometry. The study revealed that the intermediate layer consists indeed in a wide interface where tin, steel, and the FeSn2 alloy coexist. Moreover, the thickness of the Sn film varied locally significantly. A new tinplate structure was proposed in order to reliably appraise corrosion relevant features.

Identifying interlayer surface adhesion failure mechanisms in tinplate packaging steels

“…There is also evidence of the FeSn 2 intermetallic which can be observed with the reduction of the FeSn 2 peak at 38°. These findings are in line with literature who postulated structural changes at the iron/tin interface. As the tin coating weight increases, the materials tend towards {−101} orientation; however, it retains a strong {200} orientation.…”

“…The general findings in terms of dominant species and their distribution are in line with other studies, 19,36 but the depth resolution and comprehensive nature of these findings are significantly higher than the literature. 20,34 These measurements therefore provide a useful addition to the knowledge base on these substrates.…”

Sealing effect of surface porosity of Ti–P composite films on tinplates

“…Tinplates have been widely used for the packaging of foods and beverages. 1,2 There exist several layers with different compositions on the base steel of a commercially available tinplate in the ideal case. 2 The innermost layer is Fe-Sn alloy layer, which comes into being during the reowing process through the permeation of the molten tin into the iron crystal lattice on the base steel.…”

“…1,2 There exist several layers with different compositions on the base steel of a commercially available tinplate in the ideal case. 2 The innermost layer is Fe-Sn alloy layer, which comes into being during the reowing process through the permeation of the molten tin into the iron crystal lattice on the base steel. 3,4 However, due to limited time, the unalloyed tin will form a metallic tin layer on the alloy layer, and a thin oxide layer of tin is generated on the surface of the metallic tin layer.…”

Surface coverage characterization of tinplates after post‐treatment processes

“…The reflowing treatment can make the tinplate coating become compact. After the reflowing treatment, the tinplate has been passed to the passivation in sodium dichromate solution, and a thin passivation film layer of chromium oxide should be formed on the tin coating layer to control oxidation, improve the corrosion resistance of tinplate coating, suppress sulfide formation in use, and facilitate lacquer coating [23]. This process, using chromic acid or sodium dichromate solutions, sometimes with imposed current, leaves some chromium species in the surface, especially at the coating defects.…”