Alumina trihydrate color study

Reflectance is a production specification for Raiser alumina trihydrate. Currently, the product reflectance averages about 81% reflectance, with a goal of 85%. This study was undertaken to better understand the relationship between color and reflectance and the effects of particle size distribution, trace metals, acid insolubles and caustic sediments on color, for the purpose of improving product reflectance. This study used the Photovolt 577 Reflectance Meter, the HunterLab D25 DP9000 Colorimeter and Raiser alumina trihydrate composite samples. Several trends were observed during this investigation: 1. As reflectance increases,the Hunter Lightness value increases. 2. As reflectance decreases, the Hunter Red and Yellow values increase. 3. Acid insolubles and caustic sediments appear to have no impact on color. 4. Increased titanium and manganese content improved hydrate color. All other trace metals were detrimental. Alumina trihydrate samples were screened and evaluated for the effect of particle size on color and reflectance. The results suggest that: 1. Increasing the 45-75 micron particle size fraction and decreasing the > 75 micron fraction would improve the hydrate color; 2. There is a stronger correlation between metal impurities and color than between particle size and color.