Hydrothermal synthesis of dittmarite-group NH 4 (Co 1- x Mn x )PO 4 ·H 2 O particles as inorganic violet pigments.

Dittmarite-group NH 4 (Co 1- x Mn x )PO 4 ·H 2 O particles were prepared via a hydrothermal route. Single-phase platelike NH 4 (Co 1- x Mn x )PO 4 ·H 2 O particles were obtained from aqueous solutions containing MnCl 2 ·4H 2 O, CoCl 2 ·6H 2 O, and (NH 4 ) 2 HPO 4 , where the [Mn 2+ ]/([Co 2+ ] + [Mn 2+ ]) mole ratios in the products were controlled by changing the MnCl 2 and CoCl 2 concentrations of the precursor solutions. The vivid violet colour of the ammonium cobalt phosphate (NH 4 CoPO 4 ·H 2 O) particles was maintained upon substitution of Co 2+ with Mn 2+ ions up to x = 0.8, thus achieving an 80% saving of cobalt in the preparation of violet pigments.