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Published on: February 5, 2022
Aqueous Synthesis of Manganese Phosphate Hydrate Crystals for Creating Inorganic Pigment Materials
Hiroaki Uchiyama1, Itta Okumura2, Sho Inoue2
1Hiroaki Uchiyama, Department of Chemistry and Materials Engineering, Kansai University, 3-3-35 Yamate-cho, Suita 564-8680, Japan.
Abstract:
Manganese phosphate hydrate crystals were prepared from aqueous solutions containing MnCl2, (NH4)2HPO4, and citric acid. Switzerite [Mn3(PO4)2·7H2O] and niahite (NH4MnPO4·H2O) phases were produced at room temperature, and then, hureaulite [Mn5(PO3OH)2(PO4)2·4H2O] particles were obtained by aging at 80 °C or by hydrothermal treatment at 100-180 °C. The lower aging temperature (80 °C) and the chelation of Mn2+ ions by citric acid provided a slower crystal growth, resulting in large hexagonal prism blocks of ca. 500 μm in size. These were found to be single crystals of hureaulite by powder and single-crystal X-ray diffraction analysis. Diffuse reflectance spectroscopy and evaluation using L*a*b* color parameters indicated that the large single crystals present a vivid pink color and high transparency.
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