Carbonization of iron-treated Loy Yang coal

Carbonization of untreated and iron-treated Loy Yang coal was carried out a t selected temperatures in the range of 200 degrees C-700 degrees C. The el ectrical conductivity was higher in all the iron-treated samples, except fo r the sample prepared at 700 degrees C, which was identical. Arrhenius plot s of the conductivity of carbons treated above 500 degrees C exhibited cons iderable non-linearity but showed that the conductivity increase was caused by a change in the pre-exponential factor rather than in the activation en ergy. Mossbauer measurements revealed that the three, initially dispersed, paramagnetic iron species were transformed into magnetite and then principa lly, alpha- and gamma-iron between 400 degrees C and 600 degrees C. The ele ctrical conductivity depended strongly on the concentration of carboxyl gro ups and suggested a model in which conduction between the pi-electron reser voirs was via an electron hopping mechanism along hydrogen-bonded cross-lin ks. The enhanced removal of the carboxyl groups by the presence of iron aid s the destruction of these poorly conducting links during carbonization. (C ) 1999 Elsevier Science Ltd. All rights reserved.