Surface charge properties of zirconium dioxide

Zirconium dioxide, commonly known as zirconia, is an interesting material and is receiving growing attention due to its excellent mechanical properties. The solid was characterized for surface area measurements, scanning electron microscopy (SEM), Energy dispersive X-ray diffractometry (EDX) and potentiometric titrations. Surface titrations were carried out at the temperature range 303 to 323K in the presence of different concentrations (0.1, 0.01 and 0.001mol/dm3) of NaNO3 as a background electrolyte. Surface charge density and point of zero charge (PZC) of ZrO2 were determined from the titration data. Salt addition method was also applied to measure the PZC of the solid. The surface charge densities of ZrO2 were observed to increase with increase in temperature but decrease while increasing the concentration of electrolyte. Further, the PZC was found to decrease with the rise in temperature. However, it was found to increase with increase in concentration of the background electrolyte. The thermodynamic parameters such as ?H and ?S were also determined from the slope and intercept of the linear plot of (pHpzc - ½ pKw) versus reciprocal temperature (1/T). The values of both the ?H and ?S were found to be negative, while that of ?G were positive. From these thermodynamic parameters, it was suggested that the protonation / de-protonation process of ZrO2 is non-spontaneous.