Hydrothermal synthesis of dittmarite-group NH4(Co1−xMnx)PO4·H2O particles as inorganic violet pigments

Abstract

Dittmarite-group NH₄(Co_1−xMn_x)PO₄·H₂O particles were prepared via a hydrothermal route. Single-phase platelike NH₄(Co_1−xMn_x)PO₄·H₂O particles were obtained from aqueous solutions containing MnCl₂·4H₂O, CoCl₂·6H₂O, and (NH₄)₂HPO₄, where the [Mn²⁺]/([Co²⁺] + [Mn²⁺]) mole ratios in the products were controlled by changing the MnCl₂ and CoCl₂ concentrations of the precursor solutions. The vivid violet colour of the ammonium cobalt phosphate (NH₄CoPO₄·H₂O) particles was maintained upon substitution of Co²⁺ with Mn²⁺ ions up to x = 0.8, thus achieving an 80% saving of cobalt in the preparation of violet pigments.