Determination of the infrared-optical properties of absorbing and scattering pigments at elevated temperatures
Marco H. Keller, Mariacarla Arduini-Schuster and Jochen Manara
In this work, a new measurement setup is presented, which allows the determination of the directional-hemispherical reflectance and transmittance of powders at temperatures up to 350ºC with a Fourier Transform – IR spectrometer. From these measurements, the specific effective extinction coefficient can be calculated via the three-flux-method, which is a solution of the equation of radiative heat transfer in absorbing and scattering media. Furthermore, these values are compared with data obtained from theoretical calculations according to the Mie-Theory, which describes a plane electromagnetic wave that is scattered or absorbed at a spherical particle. The investigations cover mainly absorbing materials like carbon black and mainly scattering materials like aluminum. Different mixtures of carbon black and precipitated silica powder were also analyzed in order to vary the absorption properties of the mixture.
Keywords: Thermal insulation; opacifier; extinction; scattering; absorbing; infrared; three-flux approximation.