The apparatus used for the testing is a custom built arrangement utilizing a high temperature oven, a controlled temperature water bath for gas humidity adjustment, a DC power source, and an electrometer for current flow measurement. Resistivity values are calculated from
= (V/I) . (A/L)
= resistivity, OHM-CM
V = applied voltage, Volts
I = measured current, Amperes
L = Ash thickness, cm
A = current measuring electrode face area, cm²
The resistivity testing was conducted in ascending temperature order.