Iranian Journal of Wood and Paper Industries

Iranian Journal of Wood and Paper Industries

Investigation on the relationship between anisotropy and the electrical resistance of Spruce (Picea abies) carbonized wood

Document Type : Research Paper

10.22034/ijwp.2025.2071104.1727
Abstract
Problem definition and objectives: Today, there is an increasing effort to find and use biomass fuels as renewable energy sources with the aim of replacing conventional fossil fuels. Biochar is a porous material, very heterogeneous, and carbon rich, which is produced by biomass pyrolysis under an environment with anoxic conditions or limited oxygen. Among the recent applications for this material is its use as an electrode material in supercapacitors with the purpose of energy storage. The electrical conductivity of the electrode material is a very important factor for the efficiency of this tool. In this research, the relationship between the structural anisotropy of spruce wood and the pyrolysis temperature was investigated on the electrical resistance of carbon electrodes derived from it.
Methodology: Radial and tangential samples were prepared separately from the sections without defects and knots of the spruce wood. Radial and tangential samples of spruce wood were pyrolyzed at three different temperatures (700, 800 and 900 ﹾC to investigate the effect of pyrolysis temperature on the physical and chemical characteristics of biochar. 4-point probe technique was used to measure electrical resistance. Raman spectroscopy was used to investigate the degree of graphitization and X-ray diffraction (XRD) was used to investigate the effect of pyrolysis temperature on the crystallinity of biochar samples obtained from spruce wood. The surface chemistry and functional groups of the samples were investigated by Fourier transform infrared (FTIR) spectroscopy.
Results: The results showed that the pyrolysis temperature had a significant negative effect on the yield and porosity of the prepared biochar and a significant positive effect on its density. Also, the cutting type had no significant effect on the efficiency and density of biochar. According to the results, the shrinkage in three directions followed a similar pattern to that of wood. In all three temperatures in this study, the highest and lowest shrinkage values were belonged to the tangential and axial directions, respectively. Also, the results of SEM images of the cross-sectional surface of the produced spruce biochar samples showed that the anatomical characteristics of wood were preserved in the biochar. The results of the Raman spectroscopy test showed more graphitization with increasing pyrolysis temperature, which led to a decrease in electrical resistance, or in other words, an increase in electrical conductivity. In the case of both types of radial and tangential samples, the electrical resistance decreased significantly (p<0.05) by increasing the temperature. The highest electrical resistance values (5.46 Ω) correspond to the tangent to the wood biochar growth rings obtained from the tangential sample at 700 ⸰C and the lowest of it (0.05 Ω) correspond to the perpendicular to the wood biochar growth rings obtained from the radial sample at the temperature 900 ⸰C.
Conclusion: In general, the electrical resistance of spruce wood biochar decreased by increasing the temperature of pyrolysis and more graphitization of wood. Also, the structural anisotropy of the wood had no significant effect on the electrical resistance of its biochar at temperatures higher than 700 ⸰C.
Keywords
Biochar
Pyrolysis temperature
Radial and tangential samples
Electrical resistance
Spruce wood
Subjects
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Iranian Journal of Wood and Paper Industries
Volume 17, Issue 1
Spring 2026
Pages 53-68