New PhD from the BIOFMET project

Bayan Tallawi successfully defended her PhD thesis on April 28th, 2023. Her PhD was developed in the scope of BIOFMET, in a collaboration between LNE-CETIAT and Aix-Marseille Université. The thesis title is “Development of French metrology infrastructure for ensuring traceability to SI for moisture measurements in materials".

Bayan Tallawi and her thesis defense jury

Thesis summary

Moisture content measurements in solid materials, as accurate and traceable to the SI, are a technical and scientific challenge. The difficulty comes from the great diversity of measurements, resulting from extremely varied measurement techniques. This is reinforced by the variability of the physical and chemical properties of materials in the presence of the water molecule. Thus, materials can be affected by their chemical composition, structure, texture, mechanical properties and thermal properties. The duration of the analysis, the size of the sample, the complexity of the solid materials, and the requirement for laboratory conditions are occasionally limitations of traditional techniques for measuring moisture, which are classified as the primary techniques from a metrological view. Nevertheless, these methods also have the best accuracy and lowest uncertainties. To allow better dissemination of metrological traceability, and to overcome some limitations of reference methods, alternative measurement methods are needed. They aim to improve on-site moisture measurement or to allow calibration of devices already installed on industrial processes, all in a relatively short time and in a potentially restrictive environment: temperature, vibration, fouling, and electromagnetic perturbations. Among the solutions identified, there are several methods, falling into the category of secondary methods, such as electromagnetic spectroscopy, infrared measurement, electron microscopy and thermography. These methods are promising for determining the moisture content of solids, but often their measurement principles lead to measurements different from those of primary methods. Although, they allow characterizing the physical and chemical properties of the materials and can be used to determine their humidity, subject to performing a calibration against one of the primary techniques to ensure SI traceability.

The first part of the work was to validate a coaxial measuring cell, developed at LNE-CETIAT, for the measurement of dielectric permittivity. This validation was carried out by comparison with the EpsiMu® tool, the open-ended coaxial probe using reference materials identified in the literature. Furthermore, a cylindrical resonant cavity that serves as a transfer device was developed and characterized. This industrial equipment has notably been studied with reference materials and wood derivatives. The cavity allows the measurement of the dielectric properties of the materials, taking care however to proceed to the identification of certain characteristic parameters, by using the coaxial cell.

The second part focused on the investigation, improvement, and development of experimental procedures related to the implementation of reference methods. The loss on drying method and two electrolytic techniques including the coulometric Karl Fischer titration and the electrolysis of phosphoric acid produced when water vapour and phosphoric pentoxide are combined were discussed. The measurement methods as well as the uncertainty balances were validated through intra and inter-laboratory comparisons. Finally, by combining the electromagnetic characterization of the resonant cavity and one of the primary methods, calibration curves could be established between the measured dielectric quantities and the moisture content of the materials. As a result, the developed device enables quick analysis times and non-destructive measurements of the moisture in solids. The demonstration of its application could be done at an industrial site to calibrate an instrument measuring the moisture of pellets and wood chips.