Synthesis, by alkaline fusion of zirconia from zirconite: characterization and preparation of lead zirconate-titanate

Zirconium oxide was prepared from zirconite by alkaline fusion. The purity of zirconia was determined by atomic absorption spectroscopy and was found to be 99,94 wt%. In order to prepare en unglomerated and dry hidrous zirconia powder it was used alcohol and acetone for washing and gel suspension; control of the drying rate; and control of the atmosphere and temperature of the oven. The physical characteristics of the hidrous zirconia powder were determined after calcining in several conditions. The zirconia obtained by calcining at 8000C during 5 hours (13,9m2/g) was used with titanium oxide (7,6m2/g and lead oxide (0,6m2/g) to prepare a lead zirconate-titanate (PZT) with composition Pb(Zr0,5Ti0,5O3. Two different procedures were used to obtain high densits PZT pellets: in the first procedure the misture of the oxide powder with above composition were reacted at 8500C for 4 hours. Then the powder was pressed and sintered at 12000C during 4 and 6 hours; in the second procedure the mixture of unreacted oxide were pressed in pellets and then reacted at 8500C during 4 hours and sintered at 12000C during 4 and 6 hours. The apparent density of the sintered pellets were determined By mercury displacement and ranged from 7,25 to 7,39 g/cm3 for the compacts obtained by the second procedure and from 8,08 to 8,10g/cm3 for the compacts obtained by the first procedure. The microstructure observed by scanning electron microscopy showed that sintered compact obtained by the first procedure has a more homogeneous size distribution when compared with samples obtained be the second procedure. (author)