Vaporization of Lead Zirconate-Lead Titanate Materials

A thermogravimetric investigation of the vaporization of cold-pressed Pb(Zr_0.65Ti_0.35)O₃ in vacuum from 690° to 1130°C shows that the vaporization occurs in two steps. An initial loss of 1 to 7 wt% proceeds by a mechanism with a logarithmic time dependence and represents the vaporization of the unreacted PbO that remains after the initial calcining. The second step proceeds by a slower, diffusion-controlled mechanism with a parabolic time dependence. It is shown that this rate-determining step is bulk diffusion across a thickening lead-depleted layer in the cold-pressed pellet, despite pore volumes of 24 to 42%. The rate constant, g/cm² sec½, for the parabolic weight loss process is expressed by: log K = (3.37 ± 0.14) - (8.46 ± 0.16) (10³/ T _K). The activation energy is 38.7 ± 2.0 kcal/mole.