ABSORPTION INDEX AND COLOR OF COLLOIDAL HEMATITE

A light scattering method is described which permits determination of the absorption index of colloidal particles. This technique requires transmission and scattering measurements but not particle size information provided that the particles are small compared to the wavelength (Rayleigh scatterers). It has been applied to hematite (α - Fe2O3) pigment particles over the visible wavelengths. The results were checked by comparing measured values of the Rayleigh ratio for a dispersion of larger particles of known particle size distribution with calculations based upon the newly determined absorption index. The agreement was within the experimental error. When literature values of the absorption index were used in such calculations, there were significant differences from the measured values. Color calculations based upon tristimulus color theory which utilized the new values of the absorption index agreed with qualitative observation of color, both in dilute sols where single scattering predominates and in multiply scattering concentrated sols. © 1979.