Optimization of the Measurement Method for Zinc Content in Zinc-Rich Epoxy Coatings Using Differential Scanning Calorimetry

Abstract

The performance of zinc-rich coatings, widely used as primers for cathodic protection of steel structures against corrosion, depends on their zinc content in the dry film. This study aimed to optimize the method for measuring zinc content in zinc-rich epoxy-polyamide coatings using Differential Scanning Calorimetry (DSC) in accordance with ASTM D6580. Two coatings with zinc contents of 80% and 85% by weight were prepared, and sampling methods from the dry coating film (scraping-grinding from glass vs. free-film detached from polypropylene surface) were investigated as key factors. The measured zinc contents for the 85 % coating were 85.01 and 78.78 % for the free-film and ground powder methods, respectively, while for the 80% coating, the values were 80.19 and 73.70 %, respectively. Results from free-film samples showed lower standard deviation and were closer to the actual formulation values. This discrepancy was mainly attributed to the settling of zinc particles, oxidation probability, and the inhomogeneity of the samples selected for DSC testing. Therefore, using free films is recommended for measuring zinc content via DSC analysis.