Calcium Sulfate Whiskers Dual-Enhance Mechanical and Anti-Corrosion Properties of Magnesium Phosphate Coatings

Inorganic magnesium potassium phosphate (MKP) coatings offer rapid, zero-volatile organic compound (VOC) corrosion protection for steel structures. However, their application is impeded by insufficient mechanical strength and limited barrier durability. This study integrates calcium sulfate whiskers (CSWs) into a sprayable MKP matrix. Unlike conventional polymeric or metallic fibers, CSWs demonstrate excellent chemical compatibility with the MKP matrix, enabling a dual-enhancement mechanism. The optimal formulation, containing 15 wt.% CSWs, boosts the 28-day compressive strength by 35% and the bond strength by 39%. Electrochemical analysis shows a 93.6% increase in coating resistance (R_f), indicating an improved physical barrier against corrosive species, along with a 52% reduction in corrosion current density. These improvements result from fiber bridging and a dissolution-reprecipitation process that densifies the whisker-matrix interface. Nevertheless, an excessive amount of CSW (20 wt.%) disrupts the matrix continuity and reduces performance. This work presents a high-strength, zero-VOC, spray-applied coating with a novel dual-enhancement mechanism for durable steel protection in aggressive environments.