Electromagnetic shielding efficiency of the electric field of charcoal from six wood species

Six wood species were carbonized under various carbonization temperatures and nonoxygen conditions to obtained charcoal. The effects of wood species, rate of temperature rise, and carbonization temperature on the electromagnetic shielding efficiency (ESE) of the electric field were investigated. The wood species used in this study were Japanese cedar, China fir, western hemlock, red oak, fortune paulownia, and Taiwan acacia. Tested materials were carbonized in a high-temperature oven under the following conditions: rate of temperature rise 1 degrees5 degreesC/min; carbonization temperature 500 degrees-1100 degreesC, with temperature intervals of 100 degreesC; maximum temperature maintained for I h; and flow rate of nitrogen 300 ml/min. The electromagnetic insulation strength system was used to detect the ESE of the electric field of charcoal. It was found that western hemlock and fortune paulownia charcoal showed maximum ESE values of of 36 and 61 dB generated at a carbonization temperature of 1000 degreesC. The charcoals derived from four other wood species showed maximum ESE values of 28 dB for Japanese cedar, 23 dB for China fir, 32 dB for red oak, and 38 dB for Taiwan acacia, respectively, at a carbonization temperature of 1100 degreesC. The ESE value for fortune paulownia charcoal was similar to those of metal nets. The relations between ESE and logarithmic values of resistivity (log rho) could be represented by a negatively exponential formula.