Tuning the microwave electromagnetic properties of biochar-based composites by annealing
Daniele Torsello,
Gianluca Ghigo,
Mauro Giorcelli,
Mattia Bartoli,
Massimo Rovere,
Alberto Tagliaferro
Affiliations
Daniele Torsello
Department of Applied Science and Technology, Politecnico di Torino, C.so Duca degli Abruzzi 24, 10129 Turin, Italy; Istituto Nazionale di Fisica Nucleare, Sez. Torino, Via P. Giuria 1, 10125 Torino, Italy
Gianluca Ghigo
Department of Applied Science and Technology, Politecnico di Torino, C.so Duca degli Abruzzi 24, 10129 Turin, Italy; Istituto Nazionale di Fisica Nucleare, Sez. Torino, Via P. Giuria 1, 10125 Torino, Italy; Corresponding authors.
Mauro Giorcelli
Consorzio Interuniversitario Nazionale per la Scienza e Tecnologia dei Materiali (INSTM), Via G. Giusti 9, 50121 Florence, Italy; Italian Institute of Technology, Via Livorno 60, 10144 Torino, Italy
Mattia Bartoli
Department of Applied Science and Technology, Politecnico di Torino, C.so Duca degli Abruzzi 24, 10129 Turin, Italy; Consorzio Interuniversitario Nazionale per la Scienza e Tecnologia dei Materiali (INSTM), Via G. Giusti 9, 50121 Florence, Italy
Massimo Rovere
Department of Applied Science and Technology, Politecnico di Torino, C.so Duca degli Abruzzi 24, 10129 Turin, Italy; Consorzio Interuniversitario Nazionale per la Scienza e Tecnologia dei Materiali (INSTM), Via G. Giusti 9, 50121 Florence, Italy
Alberto Tagliaferro
Department of Applied Science and Technology, Politecnico di Torino, C.so Duca degli Abruzzi 24, 10129 Turin, Italy; Consorzio Interuniversitario Nazionale per la Scienza e Tecnologia dei Materiali (INSTM), Via G. Giusti 9, 50121 Florence, Italy; Faculty of Science, Ontario Tech University, 2000 Simcoe Street North, Oshawa, Ontario, Canada; Corresponding authors.
We report on the effects of thermal treatment of biochar embedded in epoxy-based composites on their microwave electrical properties, linking such properties to the material structure investigated by Raman, X-ray photoelectron spectroscopy, and X-ray diffraction. Annealing temperatures in the range 900–1500 °C and biochar concentrations in the epoxy matrix in the range from 5 to 25 wt.% were investigated. The microwave analysis, in the range from 250 MHz to 6 GHz, allowed us to determine the complex permittivity of composites and, through a proper deconvolution technique, to determine the contribution of biochar inclusions alone. High values of real permittivity (up to 220) and conductivity (up to 17 S/m) were evaluated for the biochar particles at 5 GHz, after the 1500 °C thermal treatment. A clear correlation between electrical properties and the biochar microstructure emerged from the dataset, with real permittivity and conductivity increasing as carbon inclusions transform from amorphous to nanocrystalline graphite. Conversely, the percentage of aromatic carbon has a weaker influence on the microwave properties. This study opens to the possibility of tailoring the high-frequency properties of biochar and biochar composites through proper thermal treatments.
