Microstucture and Heat Resistance of Coated Yellow Iron Oxide Pigment

Poor heat resistance of iron oxide yellow pigment limits its application in plastics processing and coil coatings. Yellow iron oxide pigments coating with aluminum hydroxide were synthesized by a precipitation method using yellow iron oxide as precursor. Structure of the composite pigment is characterized using XRD, FT-IR, TG-DTA, SEM-EDS, and TEM. The effect of pH on structure and heat resistance of the pigments was investigated. All results show that iron oxide yellow coating layer is amorphous aluminum hydroxide when pH is 4. When pH increases to 6, 8 and 10, the surface coating layer is boehmite phase. The heat resistance of coated yellow iron oxide pigments is greatly improved, and the color difference value of pigments after treatment at 240 [degrees]C for 30 min is low, owing to the surface coating layer of boehmite structure. After coating, the iron oxides yellow maintains the original acicular structure, and pigment does not aggregate. When pH is 10, the coated iron oxides yellow composed both large stick and needle like structure, possibly because of the nucleation formation of Al OOH in the reaction process. This result may explain the special endothermic peaks of 246 [degrees]C appeared on the DTA curves. This research might provide theoretical and practical guidance for developing heat resistant yellow iron oxide pigments.