The synthetic process of some copper (II) phosphate compounds by the liquid method of CuSO4 -Na2HPO4-H2O system at 96°C were investigated. The composition of the precipitate changed with varying initial concentration ratio and stirring time.
The initial precipitate obtained by this method was Cu4 (HPO4) (PO4) 2·3H2O including sodium phosphate, however Cu3 (PO4) 2·3H2O reported by Hanawalt et al. did not produce from the above system. Further stirring of the precipitate in suspension at 96°C, the composition of the precipitate changed to Cu2 (PO4) OH in case of initial concentration ratio R (Na2HPO4/CuSO4 : molar ratio) =0.5-2.0, to 5NaCuPO4·2Na2HPO4 (Pe : 18.0%, Y : 78.0%, λd : 488.9nm, pale greenish blue) in case of more than R=3.0, respectively. 5NaCuPO4·2Na2HPO4 decomposed to α-NaCuPO4 and Na4P2O7 on heating at ca.500°C. Their morphologies of Cu2 (PO4) OH obtained by controlling synthetic conditions were spherical, pine needle-like, chestnut-like, rod-like and octahedral crystal. Cu4 (PO4) 2O obtained by heating Cu2 (PO4) OH is sufficiently applicable as inorganic pigment because of its vivid color (Pe : 33.8%, Y : 32.4%, λd : 554.9nm, brilliant yellow green).
