Effect of synthesis parameters on a hematite–silica red pigment obtained using a coprecipitation route

The morphology and the dimensions of the hematite particle influenced the shade of the red pigments obtained; both fine (<30 nm in length) spherical and long (>250 nm in length) acicular shapes gave poor red shades. The morphology of the hematite particles depends on the precipitant used; ammonia provided spherical, whereas NaOH produced acicular hematite particles. The dimensions of the hematite particles depended on the mineralisers used; while the silica structure did not influence pigment shade, the use of mineralisers promotes tridymite structure crystallization.