Abstract
The formation and sintering of PbTiO3 containing a small amount of PbO-TiO2-Al2O3-SiO2 glass were investigated by means of X-ray diffraction, thermal analysis, electron microscopy, dilatometry and the measurement of isothermal shrinkage.
The rate of formation of PbTiO3 from PbO and TiO2 containing 0.01 wt % glass was determined. Reaction isotherms were best described by the Jander's equation. The apparent activation energy of the reaction was about 50 kcal/mol.
The PbTiO3 powder was mixed with 0.005 or 0.01 wt % glass powder, pressed into pellets at 1 ton/ cm2, and heated at 1100-1200°C for 1-2 hr in various atmospheres. All the sintered specimens had grain size of 0.5-2μ and a bulk density of 7.23-7.63g/cm3. The density of 7.63 g/cm3 was obtained by heating at 1120°C for 1 hr in the oxygen atmosphere. The order of the sinterability in various atmospheres of PbTiO3 contained the glass was O2>PbO>air>N2. This fact suggests that the sintering of PbTiO3 is affected by partial pressure of oxygen.
The mechanism of initial sintering in PbTiO3 contained 0.01 wt % the glass was studied by isothermal shrinkage at temperatures ranging from 900°to 1050°C in air and oxygen. Time dependence of the shrinkage was consistent with the mechanism based on grain boundary diffusion in air and volume diffusion in oxygen, and the activation energies for sintering processes were about 46 kcal/mol and 76 kcal/ mol, respectively. Comparison our data with others suggests that the diffusion of Pb2+ in air and Ti4+ in oxygen control the initial sintering.
