Fly ash composites with polyaniline: Synthesis, characterization and conductivity measurements

Abstract

In the past few decades, Fly Ash (FA) has rapidly emerged as one of the most costeffective and environment friendly resources rather than just being a waste material. A number of novel applications have been identified and are being exploited as well. The pozzolanic properties of FA make it a suitable candidate for cement replacement, as well as for the production of ceramics and glasses to be used as construction material. It can be utilized in the construction of embankments and structural fill; waste stabilization and solidification; mine reclamation; road sub-base; aggregate and mineral filler in asphalt concrete; soil amendment of soft soil and to increase bioavailability of nutrients in the soils, as well as adsorbent for heavy toxic metals. Other applications include production of roofing tiles, paints, metal casting, and as filler in wood and plastic products. Alkali rich FA can be used to neutralize the waste water from Acid Mine Drainage (AMD). Most of the current applications of FA, however, are primarily based on its microstructure and chemical composition only. Other physical and chemical properties of FA, and of the materials based on it, could possibly be utilized in other practical applications also. With this idea, we report in this chapter about the synthesis and characterization of a composite made of FA together with a very common conducting polymer: Polyaniline (PANI). The polyaniline/fly ash (PANI/FA) composites with various concentrations (20, 40 and 50 %wt) of fly ash were synthesized by the process of in-situ polymerization, by aging the starting materials (aniline and FA) before oxidative polymerization, and also by including poly-(styrene sulphonic acid) (PSSA). It was found that the process of aging assisted the composites to self-organize as nanotubes (crosssectional diameters of 50-110 nm), and that involving PSSA, produced nanorods and nanofibres (diameters of 100-500 nm, length up to 10 μm). Powder X-ray diffraction (XRD), scanning electron microscopy (SEM), UV-vis spectroscopy, Fourier transform infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) were used to characterize the samples. Further, electrochemical analysis was performed and the dc-conductivity of the samples was measured as a function of temperature in the range 80-290 K. An expected decrease of conductivity was observed with addition of FA into PANI. The temperature dependence of the dc-conductivity for pure PANI and FA/PANI composites has been explained on the basis of the quasi one-dimensional variable range hopping (quasi-1D VRH) model. Excellent agreement was found between the experimental data and the theory.