Electrical conductivity study of porous carbon composite derived from rice husk

The objective of this investigation is to evaluate the electrical conductivity of activated carbon derived from rice husk (RHAC) by a two-stage process. dc conductivity measurements by two-probe method were determined for RHAC samples prepared at 700, 800 and 900 degrees C. The samples were compressed in the pressure range 75.9-578.2 kPa in a hollow glass cylinder using two metal plungers connected to a Keithley ammeter. The conductivity at room temperature was found to increase from 3.28 x 10(-4) to 2.02 x 10(-3) S cm(-1) for increase in compression pressure. Dense packing of the material, collapse of pores and decrease in air gap between the carbon particles could be the factors for the increase in conductivity with compression pressures. The temperature-dependent conductivity of RHAC samples were determined by compressing the sample within the metal plungers, followed by heating in a tubular furnace. A K-type thermocouple whose hot junction was located in close proximity to the specimen, was used to monitor the temperature accurately. The specimen inside the furnace was heated by a microprocessor-controlled programmer up to 250 degrees C. The temperature-dependent conductivity study conducted for the samples activated at 700, 800 and 900 degrees C, revealed that the energy gap value of the samples were 0.1023, 0.0745 and 0.052 eV respectively, determined from the linear plot of ln I versus I/T (K-1). The mesoporous RHAC samples were characterized using electron spin resonance, FT-IR spectroscopy and X-ray diffraction for quantitative evaluation of free electrons, functional groups and crystallites to support the mechanism of electrical conduction in mesoporous nonsinterable carbon samples. (c) 2004 Elsevier B.V. All rights reserved.