A very simple electrochemical cell for corrosion experiments has been developed using a syringe as the cell with the syringe plunger replaced by reference and counter electrodes. Because the exposed area is defined by a hanging droplet, no masking is required and thus no crevice corrosion forms. This cell therefore enables measurements of pitting potentials of metals that are susceptible to crevice corrosion. The method was validated by cyclic potentiodynamic polarization experiments on Type 304H stainless steel. Crevice or interfacial corrosion was not evident in multiple replicate specimens tested with the syringe cell method.

Tinplate cans used to contain foodstuff are fabricated from steel coated with a thin layer of tin and then overcoated with a thin polymeric layer. Previous papers in this series investigated the corrosion behavior of tinplate cans containing chopped tomatoes or one of the chemical components found in cans of chopped tomatoes. The amino acid cysteine was found to be an aggressive agent that can cause corrosion and blackening of the can headspace region. In this study, the corrosion phenomena associated with tinplate cans were investigated by studying the behavior, individually, of uncoated pure tin, iron, and tinplate in chopped tomato, NaCl, and cysteine solutions using electrochemistry, optical microscopy, X-ray diffraction, scanning electron microscopy, and Raman spectroscopy. Black corrosion products, identified as sulfides, formed when the tin, iron, and tinplate specimens were exposed to cysteine solution at three different pH values. The black corrosion products were also found on both iron and tinplate when the samples were immersed in tomato solution. These results indicate that blackening on bare iron and tinplate could form easily from the decomposition of chemical compounds in heated tomatoes.

Tinplate cans with polymeric coatings are commonly used for food storage. Due to health concerns related to bisphenol A (BPA), BPA-free coatings are currently being considered. Thus, understanding the degradation of BPA-free coatings is critical for predicting can integrity. In this study, the corrosion of tinplate cans with a BPA-free coating exposed to different solutions was studied using electrochemical impedance spectroscopy (EIS). To accelerate the corrosion process, cans were stored at 49 °C for varying times prior to testing in various solutions. EIS was performed first in the original storage environment and then in 3.5 wt% NaCl to investigate the performance of the can coatings. Separately, EIS was also used to investigate degradation of the coating in the headspace region. The EIS results provide insights into the degradation of the BPA-free coating and the corrosion of cans arising from the exposure to different food chemicals.

Corrosion phenomena associated with tinplate cans were investigated with aqueous solutions of different compounds commonly found in canned tomato products. After only a few weeks of storage at 49 °C, cans lined with a coating free of bisphenol A (BPA) displayed degradation of the coating. Storage of solutions containing chloride, nitrate, and thiosulfate ions in the BPA-NI coated cans resulted in extensive formation of blisters, which are attributed to cathodic delamination. Additionally, headspace blackening, which is sometimes found in packaged protein-containing foods, was also observed. Volatile sulfur-containing compounds produced during the sterilization process might be the origin of headspace blackening. In this study, the corrosion of tinplate cans exposed to different solutions at 49 °C for varying storage times was studied via optical microscopy, optical profilometry, X-ray diffraction, scanning electron microscopy, and Raman spectroscopy. The results showed a strong correlation between the presence of cysteine, an amino acid, and/or nitrate, and the degradation of the coating. Furthermore, cysteine was found to be a source of headspace blackening.

ASTM G180-13, Standard Test Method for Corrosion Inhibiting Admixtures for Steel in Concrete by Polarization Resistance in Cementitious Slurries (Superseded), testing was used to determine the effectiveness of corrosion inhibiting admixtures. However, inconsistent results have been reported due to the polishing process. Although not standardized, polished metal specimens have been used to remove contaminants or native oxides prior to electrochemical measurements to acquire stabilized electrochemical measurements. Furthermore, the open circuit potential (OCP) delay before electrochemical testing was found to be critical to the consistency of the subsequent experiment. The goal of this study was to investigate the influence of polishing and environmental factors on the OCP value and its variation. The OCP of carbon steel in high pH simulated pore solutions was measured as functions of polishing, time, chloride content, and nitrite concentration. By using a full-factorial experimental design and regression analysis, the effects of the factors were studied on both the mean value and on the standard deviation of corrosion potential. The standard deviation of repeated tests was quantified and ranked to provide guidance on specimen preparation. The regression result showed that polishing does not influence the mean value of the OCP but that the OCP standard deviation heavily depends on the polishing consistency. Based on the experimental data and analysis, a suggestion was provided for specimen preparation to address the observed inconsistency in specimen preparation for ASTM G180-13 testing.