The report gives results of research to improve and extend the capabilities of a technique for predicting fly ash resistivity from the ultimate coal analysis and the coal ash composition. Emphasis was on determining the quantitative effect of adsorbed sulfuric acid vapor on resistivity. Ten fly ash samples were used in order to have a reasonable spectrum of ash composition. Resistivity was determined as a function of temperature in air environments containing 5 and 10% water. Isothermal resistivity was measured for each ash at three temperature levels using three concentrations of sulfur trioxide (SO3). With respect to resistivity predictions for conditions not including SO3, the present data did not suggest modifying Model I of the resistivity prediction. However, the much larger and improved data base recently acquired with respect to environments containing SO3 has required a new approach for predicting the effect. The report presents these data and illustrates Model II of the resistivity prediction.

Caption title. "Mar. 1986." "EPA/600/7-86/010." Microfiche.