Tailored properties of hematite particles with different size and shape

• Development of pigments for the mitigation of Urban Heat Island effects.
• Hematite particles of different size and shape were synthesized.
• Solar reflectance of hematite samples as a function of particle size and shape were evaluated.
• Color of pigments varies as a function of morphology.

Red cubic and spherical hematite red cool pigments of different particle size were synthesized following two different methods. Cubic and spherical particles with larger particle sizes were obtained through a gel–sol method using chloride and nitrilotriacetate ions as shape controllers, and changing the starting temperature to control the final particles size. Smaller spherical particles were synthesized more rapidly following a catalytic phase transformation method in which the size control is obtained by varying the reagent concentration. Cool properties for the obtained particles were evaluated by calculating the solar reflectance for all hematite samples. The cool properties differ depending on the particle size and shape. By controlling the final size and morphology of pigment particles it is possible to obtain pigments with the desired cool properties. Pigment color properties were also evaluated using CIE XYZ and CIE xyY color spaces.

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