Thermal Carbonization of Woody Biomass Under Inert Atmosphere with Temperature-Dependent Variation in the Effects of Cu and Ti Additives

Background Carbonization of woody biomass under inert atmospheres is a practical route for producing functional carbon materials. Carbonization behavior and microstructural development are influenced by processing temperature, heating rate, and the presence of metal additives. However, the temperature-dependent differences associated with such additives remain insufficiently understood. Methods The effects associated with copper and titanium additives were examined during the carbonization of Todo fir ( Abies sachalinensis ) wood flour at 500°C and 800°C under nitrogen at controlled heating rates. Wood flour and each metal additive were mixed at a mass ratio of 7: 3 as an exploratory, relatively high-additive condition. Carbonization behavior was evaluated by thermogravimetric–differential thermal analysis, and the resulting char residues were characterized by elemental analysis, scanning electron microscopy, and transmission electron microscopy. Results At 500°C, Cu-containing samples exhibited partially layered turbostratic carbon structures and relatively constrained apparent structural spacing, whereas Ti-containing samples showed more heterogeneous carbon structures with no systematic dependence on heating rate. At 800°C, the char residues had carbon contents of approximately 93 wt%, with only minor variation associated with heating rate. Transmission electron microscopy showed differences in apparent structural spacing and microstructural heterogeneity among the additive-free, Cu-containing, and Ti-containing samples; however, no consistent dependence on heating rate was observed at 800°C. Overall, the results indicate that final carbonization temperature had a greater influence on bulk elemental composition and structural development than heating rate under the conditions examined. Conclusions Cu- and Ti-containing samples exhibited different temperature-dependent carbonization and microstructural characteristics under the experimental conditions examined. These results provide a basis for further investigation of the combined effects of additive type and thermal conditions on biomass-derived carbon materials. Because the oxidation states and phases of Cu and Ti after carbonization were not directly determined, the observed differences should not be interpreted as definitive evidence of specific chemical or catalytic mechanisms.