Anticorrosive and physicochemical properties of modified phosphate pigments

Many studies have been carried out in the direction of improvement of the effectiveness of commonly utilized phosphate corrosion inhibitors. For this purpose various types of modifications are realized, e.g. introduction of different cations to the pigment composition or replacement of phosphate anions with others. In the presented work, anticorrosive pigments containing calcium hydrogen phosphate, and/or calcium hydroxyphosphate, and calcium molybdate were obtained. The phase and chemical composition and the oil absorption number of those materials were determined. The anticorrosive properties were investigated by an electrochemical noise method. The obtained results were compared with previously published studies concerning pigments containing (NH₄)₃Al₂(PO₄)₃ and/or AlPO₄, and CaMoO₄. It was found that the pigment containing only calcium molybdate(VI) is not an effective corrosion inhibitor. However, the pigments comprising a mixture of CaHPO₄ and CaMoO4 exhibited good anticorrosive properties and they were characterized by higher effectiveness in the corrosion protection than compared materials.