Surface Resistivity and the Chemical Composition of Fly Ash

Abstract

Resistivity was determined for a group of well characterized ashes representing both eastern and western coals. Data were taken between 60 and 250°C in an environment of air containing approximately 9 volume percent water. Chemical transference experiments were conducted for two ashes having substantially different chemical compositions. Chemical analyses of the transference specimens revealed a pronounced migration of alkali metal ions toward the negative electrode. It was observed that the surface resistivity was inversely proportional to the concentration of these ions and that the iron concentration influenced particularly the participation of potassium. Surface resistivity is sensitive to the chemical composition of fly ash because the alkali metals serve as charge carriers. The conduction mechanism is probably analogous to that of glass. This viewpoint is compatible with the usual empirical observations regarding the effect of certain parameters on resistivity; for example, the interaction between ash and the environment.