Analysis of (Zn+Mg) Pigment Mixtures In Metal - Rich Corrosion Protective Primers For Steel Available to Purchase

There is evidence that mixing/alloying Mg with Zn in a galvanizing layer greatly increases (up to 40%) the corrosion protective life time of such a galvanizing layer.1 By analogy, one would expect that one could possibly improve standard Zn-rich paints by adding Mg particles to a Zn rich primer2 to increase the overall protective life time of the system. We have done this in “some initial proof-of-concept experiments, and indeed the primer coatings that contain Mg particles added with Zn particles to form an improved metal rich coating for steel did indeed give longer corrosion protective lifetimes over steel than equivalent coatings made with Zn alone. A two-segment study was conducted to observe the corrosion-resistant effects on 3” x 6” steel panel substrates by blending magnesium pigment into zinc pigment in epoxy-based primer. In the first segment our study, 100% zinc formulation (F 100) was compared to the 95% Zn to 5% Mg (F 95/5) and 90% Zn to 10% Mg (F 90/10). F 100, F 95/5 and F 90/10 were examined as primer only and primer + topcoated samples. The results suggested that that protective properties increase with increasing levels of magnesium in the formula. The second segment of our study was a primer only study that compared F 90/10 to 85% Zn to 15% Mg (F 85/15), 80% Zn to 20% Mg (F 80/20), 75% Zn to 25% Mg (F 75/25), 70% Zn to 30% Mg (F 70/30). The results of the second segment of our study again, suggested that protective properties increase with increasing levels of magnesium in the formula. The accelerated weathering exposure chosen for this study was the Prohesion ASTM 85-A5 method which is cyclic, temperature variable and mimics the effects of acid rain.