Synthesis of novel green phosphate pigments with phosphophyllite composition

A new green pigment with the composition of phosphophyllite was synthesized using zinc oxide, iron oxalate, and phosphoric acid in a hydrothermal process. The effects of hydrothermal treatment temperature and time were investigated. In order to obtain pigments with a variety of colors, compounds with related compositions were also prepared. Further, samples were prepared with nitrogen bubbling to suppress the oxidation of iron. The composition of the fabricated samples was evaluated by X-ray diffraction and infrared spectra. The color of the samples was evaluated by ultraviolet-visible reflectance spectra and L*a*b* color space. The samples prepared in this study were a mixture of Zn₂Fe(PO₄)₂•2H₂O, the target compound, and iron oxalate, the raw material. The obtained samples were yellow to green in color. The condition that yielded the best green pigment was hydrothermal treatment at 180°C for 20 h with nitrogen bubbling.