Impact of carbonization on oak wood δ$^1$$^8$O: A preliminary study

Diane Du Boisgueheneuc (1, 2) , Frédéric Delarue (3) , Valérie Daux (1) , Thanh Thuy Nguyen Tu (3) , François Baudin (4) , Alexa Dufraisse (2)

1 GEOTRAC - Géochrononologie Traceurs Archéométrie
2 AASPE - Archéozoologie, archéobotanique : sociétés, pratiques et environnements
3 METIS - Milieux Environnementaux, Transferts et Interactions dans les hydrosystèmes et les Sols
4 iSTeP - Institut des Sciences de la Terre de Paris

The carbonization process induces significant physical, elemental, and structural transformations of wood. In this study, the modification of δ$^1$$^8$O in wood during the carbonization process was investigated in conjunction with elemental analysis, infrared spectroscopy (FTIR), and Rock-Eval thermal analysis, to explore the connection between the chemical composition of the materials and the alterations in δ$^1$$^8$O. Quercus petraea wood samples were experimentally burned at temperatures ranging from 200°C to 1000°C under inert (pyrolysis) and oxidative atmospheres. The results reveal that the modification of δ$^1$$^8$O values in charred wood can be described as a sequential two-step process. The initial step, occurring below 300°C, involves the volatilization and preferential degradation of thermolabile compounds, leading to an increase of +1.6‰ in δ$^1$$^8$O. The subsequent step, below 700 °C, results in a decrease in δ$^1$$^8$O values of –21.6‰, primarily driven by the thermal degradation of cellulose and lignin, as well as the increase of aromaticity and reorganization. The components and the δ$^1$$^8$O of wood undergo distinct changes in combustion mode, due to different carbonization kinetics as evidenced by FTIR and elemental analysis. To assess the intensity of the carbonization process, influenced by temperature, oxygen availability, and wood characteristics, the H/C atomic ratio, a good indicator of aromaticity, is used. A non-linear regression model was established, relating δ$^1$$^8$O to the H/C atomic ratio, thereby demonstrating that δ$^1$$^8$O values undergo changes as wood aromatization progresses, independent of the carbonization conditions. The second order model has a mean confidence interval of 1.9‰ and a prediction interval of 8.1‰. This work provides a fundamental understanding of the connection between the chemical composition of woody materials, alterations in δ$^1$$^8$O, and the carbonization process, offering valuable insights for further studies and applications related to oxygen-related information that may be preserved in charcoals.

Mots clés: Oak; Charcoal; δ18O; Pyrolysis; Combustion; FTIR; Panoply

Domaines: Matériaux

Diane Du Boisgueheneuc, Frédéric Delarue, Valérie Daux, Thanh Thuy Nguyen Tu, François Baudin, et al.. Impact of carbonization on oak wood δ$^1$$^8$O: A preliminary study. Journal of Analytical and Applied Pyrolysis, 2023, 175, pp.106198. ⟨10.1016/j.jaap.2023.106198⟩. ⟨hal-04234813⟩