J. Kuhn et al., INFRARED-OPTICAL TRANSMISSION AND REFLECTION MEASUREMENTS ON LOOSE POWDERS, Review of scientific instruments, 64(9), 1993, pp. 2523-2530
A method is described to determine quantitatively the infrared-optical
properties of loose powder beds via directional-hemispherical transmi
ssion and reflection measurements. Instead of the integration of the p
owders into a potassium bromide (KBr) or a paraffin oil matrix, which
would drastically alter the scattering behavior, the powders are place
d onto supporting layers of polyethylene (PE) and KBr. A commercial sp
ectrometer is supplemented by an external optics, which enables measur
ements on horizontally arranged samples. For data evaluation we use a
solution of the equation of radiative transfer in the 3-flux approxima
tion under boundary conditions adapted to the PE or KBr/powder system.
A comparison with Kubelka-Munk's theory and Schuster's 2-flux approxi
mation is performed, which shows that 3-flux approximation yields resu
lts closest to the exact solution. Equations are developed, which corr
ect transmission and reflection of the samples for the influence of th
e supporting layer and calculate the specific extinction and the albed
o of the powder and thus enables us to separate scattering and absorpt
ion part of the extinction spectrum. Measurements on TiO2 powder are p
resented, which show the influence of preparation techniques and data
evaluation with different methods to obtain the albedo. The specific e
xtinction of various TiO2 powders is presented.