Controlled synthesis of hexagonal α-Fe2O3 crystals for ceramic colors by hydrothermal reaction of FeCl3 and NaOH solutions

Abstract The effect of mixing process of FeCl 3 and NaOH solution on the formation of platy (hexagonal) α-Fe 2 O 3 was investigated at 160 and 180 °C by the hydrothermal process. The crystal growth of platy α-Fe 2 O 3 was promoted at higher hydrothermal temperature, higher concentration of NaOH solution and by the addition of FeCl 3 solution to NaOH solution instead of the reverse addition. Platy crystals of α-Fe 2 O 3 showed dark red wine color while nanophase equiaxed crystals showed yellowish red color. The platy crystals of 3–6 µm in average diameter kept their platy structure after heating at 900 and 1100 °C in air due to their higher thermal stability towards sintering.