Retained metal concentration and thermal degradation pathways in inorganic salt-treated oak

This study examines how the amount of retained metal influences the thermal degradation behaviour of oak wood treated with inorganic salts. After controlled impregnation and removal of loosely bound fractions, metal uptake was quantified by atomic absorption spectroscopy and related to changes in degradation behaviour observed by evolved gas analysis–mass spectrometry and pyrolysis–gas chromatography/mass spectrometry. Clear differences were observed between the various salt treatments. Calcium-based systems showed the highest metal retention and were associated with increased thermal stability, whereas alkali metals promoted more pronounced fragmentation of degradation products. Transition metals exhibited intermediate behaviour, reflecting the combined influence of metal-specific interactions and treatment conditions. The pH of the treatment solutions decreased after contact with wood, indicating that chemical changes during impregnation contribute to the observed behaviour. In addition, thermo-hygrometric ageing led to a general increase in degradation temperatures for all samples, while differences between treatments remained evident. These results highlight the combined role of metal retention, cation chemistry, and environmental exposure in controlling the thermal behaviour of salt-treated oak.