ABSTRACT
The red phosphate pigments without harmful metals were prepared by heating a mixture of iron oxalate and sodium dihydrogen phosphate or potassium dihydrogen phosphate or ammonium dihydrogen phosphate in P/Fe = 1/1 at 300–700°C. In the samples, iron was oxidised to trivalent, causing the red colour. The red colour of the samples was affected by the different cations and heating temperatures. Samples prepared using NaH2PO4 and KH2PO4 exhibited a relatively strong red colour when heated to 600°C and 700°C, with a* values above 30. The samples were red after treatment with acid and base solvents, among which the samples prepared with NaH2PO4 showed high acid and base resistance.
Disclosure statement
No potential conflict of interest was reported by the authors.