Non-destructive evaluation of ceramic porosity using terahertz time-domain spectroscopy

Dielectric constants of Al2O3 (alumina) ceramic samples have been measured with non-destructive terahertz time-domain spectroscopy. Using an effective medium approximation, we demonstrated that the relative permittivity can be used to evaluate porous alumina samples, porosity fractions ranging from 0% 20% per volume. This result makes it possible control sample porosity, a key material parameter related mechanical strength under compression load, hardness and wear resistance, or thermal stability. We also employed spectroscopy differentiate fabricated different grain sizes, reveal small fraction impurities, such as 5%vol ZrO2, embedded in non-porous alumina. These results potential radiation for characterization low loss high dielectric constant ceramics.