Impact of carbonization on oak wood δ18O: A preliminary study

The carbonization process induces significant physical, elemental, and structural transformations of wood. In this study, the modification of delta O-18 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 delta O-18. Quercus petraea wood samples were experimentally burned at temperatures ranging from 200 degrees C to 1000 degrees C under inert (pyrolysis) and oxidative atmospheres. The results reveal that the modification of delta O-18 values in charred wood can be described as a sequential two-step process. The initial step, occurring below 300 degrees C, involves the volatilization and preferential degradation of thermolabile compounds, leading to an increase of +1.6 parts per thousand in delta O-18. The subsequent step, below 700 degrees C, results in a decrease in delta O-18 values of -21.6 parts per thousand, primarily driven by the thermal degradation of cellulose and lignin, as well as the increase of aromaticity and reorganization. The components and the delta O-18 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 delta O-18 to the H/C atomic ratio, thereby demonstrating that delta O-18 values undergo changes as wood aromatization progresses, independent of the carbonization conditions. The second order model has a mean confidence interval of 1.9 parts per thousand and a prediction interval of 8.1 parts per thousand. This work provides a fundamental understanding of the connection between the chemical composition of woody materials, alterations in delta O-18, and the carbonization process, offering valuable insights for further studies and applications related to oxygen-related information that may be preserved in charcoals.