Characterization of the pore structure of ceramics via propagation of light and infrared radiation

The pore size distributions of alumina and magnesia ceramics were determined by measuring the directional-hemispherical transmittance and reflectance. These values are highly sensitive to changes of the pore structure. The partially sintered alumina samples were measured at room temperature in a wavelength range from 0.5 to 6 μm. The equation of radiative transfer can be solved for absorbing and scattering media by a three-flux solution. With this three-flux solution the scattering coefficients were derived from the measured directional-hemispherical transmittance and reflectance. The scattering coefficients can also be calculated theoretically by the Mie theory, if the pore size distribution is known. Finally, the quantitative pore size distribution was determined by fitting the theoretical scattering coefficients to the experimental scattering coefficients. To check the correctness of the derived pore-size distribution, scanning electron microscopy (SEM) and atomic force microscopy (AFM) pictures of the alumina samples were taken. The pore-size distribution was then derived by counting the pores and determining the diameters D of the spherical pores. Both results agree well and show that the new procedure is a valuable tool to extract structural information during the final sintering state.