Corrosion aggressiveness of oxalic acid solutions simulating canned vegetables

When choosing metal packaging for canned vegetables, it is advisable to take into account the corrosion aggressiveness, because corrosion of the inner surface is one of the factors affecting the products quality during storage. The main corrosion-aggressive substances in canned vegetables are organic acids and their salts. To rationalize the corrosion tests of metal-packaging materials, it is advisable to replace food with model media - solutions of organic acids. The objective of this work was to study the kinetics of corrosion of electrolytic tinplate in model media - aqueous solutions of oxalic acid with the concentration of 0.25-1.00 %. The rate of uniform corrosion was measured by the linear polarization resistance method, and of pitting corrosion - by zero resistance amperometry method. The experiments were carried out using Ekspert-004 corrosion-meter, according to a two-electrode scheme. For oxalic acid solutions with the concentration of 0.25 and 0.50 %, at the beginning of the experiment the maximum values of the uniform and pitting corrosion rates are observed, which drop to a steady value within 4-16 hours. The process is characterized as uniform corrosion, because the stationary pitting rate is 7-8 times less than the uniform corrosion rate (2.54-3.53 and 19.87-23.83 µm / year, respectively). For solutions with the concentration of 0.75 and 1.00% for 4-12 hours from the beginning of the experiment, the uniform corrosion and pitting rates values are set at 48-51 and 5-7 µm / year, respectively. Then, after 48-72 hours, the uniform corrosion rate reaches a minimum value of 1.04-2.95 μm / year, and then increases to a steady value (10.71-12.56 μm/year). The pitting rate after 96-104 hours increases to a steady value (21.26-32.8 µm/year). According to the results of research, it was found that oxalic acid solutions with the concentration of 0.25 and 0.50 % are the most corrosion-aggressive against tinplate - they should be used as components of model media for corrosion tests.