Pyrolysis profile of a rectangular kiln – natural scientific investigation of a traditional charcoal production process

Abstract

Rectangular kilns are a traditional technique in charcoal production in the second half of Modern Period in Middle Europe. Only in Austria there is still an active tradition that is of broader interest in an archaeological context. One of these kilns in Rohr im Gebirge, Lower Austria, was equipped with thermocouples to record pyrolysis temperature during the whole process. The removal of ready charcoal was paralleled by sampling, in total 103 charcoal samples were collected. Based on the infrared (FTIR) spectral pattern the pyrolysis temperature was predicted. It is the first reconstruction of the temperature profile of the whole kiln. Elemental analyses were performed and prediction models for carbon (R² = 0.93), hydrogen (R² = 0.96) and oxygen (R² = 0.98.) content based on FTIR spectra established. Therefore, FTIR spectroscopy rolls the degree of pyrolysis and elemental analyses into one single analytics. Further analyses by means of NMR spectroscopy, X-ray diffraction and He-pycnometry complete the picture.