Phase Evolution in Co-Precipitated Stabilized Zirconia Powders

Zirconia stabilized by addition of bismuth oxide was prepared by co precipitation process from metal oxide chlorides using sodium hydroxide. The dried gels produced pure phase ZrO2-Bi2O3 powders on calcination at 800ºC for the co precipitated powders. The phase evolution was studied and it was found that the delay in obtaining isomorphous ZrO2-Bi2O3 in the co precipitated powders owed to the crystallization of an impure phase BiOCl. This phase was detected in all the calcined co precipitated powders. However, the existence of ZrO2 as a separate phase was noticed as a common feature. The characterization and structural evaluation of the synthesized powder were carried out by means of Differential Scanning Calorimetry (DSC), Thermogravimetric Analysis (TGA), X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM) and Energy dispersive X- ray Spectroscopy (EDS). Thermal analysis revealed that weight loss arising from evaporation of bound water occurred below 150ºC for all the samples and the sintering temperature was 700ºC. The phase transformation from amorphous ZrO2 to crystalline ZrO2 occurred above 600ºC while that from amorphous Bi2O3 to crystalline Bi2O3 occurred above 700ºC. The crystallite sizes of the synthesized powders were in the range of 8-33nm. SEM micrographs showed a uniform morphology for the calcined powders and revealed nearly spherical powder particles with sizes in the range of 63-101µm. EDS confirmed Zirconia as the major component in all calcined co precipitated powder sample except the sample containing 75.53% Bi.