Determination of Porosity and Moisture Content of Granular Activated Carbon Using Sub-Thz Ellipsometry

The paper is devoted to studying the possibilities of sub-terahertz ellipsometry to determine the technological characteristics (porosity and moisture content) of activated carbon granules as a working medium for air filters, including ventilation systems of nuclear power plants. Samples with a flat surface of sufficient size for ellipsometric measurements were formed from vertically located close-packed granules. Two types of industrial granules of different sizes were investigated. The applicability of various surface models and effective media for processing experimental ellipsometric data is considered. For the first time, it was proposed to use a model of an effective medium with a screening factor depending on the angle of incidence to analyze ellipsometric data. An algorithm to simultaneously determine the porosity and moisture content of activated carbon granules was developed and tested. The moisture range was determined, within which sub-terahertz ellipsometry allows one to unambiguously determine both required parameters and in which—only porosity. The obtained results are corroborated by independent experimental and theoretical methods and consistent with the data provided by the manufacturers of the materials under study. In general, the effectiveness of sub-terahertz ellipsometry has been demonstrated for rapid assessment of the characteristics of activated carbon granules to determine the condition and predict the service life of carbon air filters. The proposed model of the effective medium with a variable screening factor can be used to study other objects with a similar structure.