The Effect of Nonstoichiometry on the Initial Sintering Kinetics of MnO₁₊ᵪ

Abstract

<p>A study has been made of the initial stage sintering kinetics of nonstoichiometric MnO as a function of the oxygen partial pressure. The shrinkage and neck growth were measured for pairs of oxide spheres in the temperature range 900-1100°C and pressure range 10ˉ¹⁴</p> <p>The shrinkage was analyzed using both the classical single mechanism control approach and the more recent simultaneous mechanism approach. It was found that the sintering behavior as a function of oxygen pressure, hence the concentration of Mn vacancies, does not follow a simple relationship has been suggested. The kinetics indicate grain boundary diffusIon control at oxygen pressures less than 10ˉ¹² atm. and greater than 10ˉ⁹ atm. and volume diffusion control at pressures in between.</p> <p>Using the simultaneous mechanism approach, the predominance of grain boundary control at low and high oxygen pressures was verified; however, a substantial contribution from volume diffusion was present. The volume diffusion contribution reached a maximum at 1 x 10ˉ¹⁰ atm., the same pressure at which the maximum shrinkage and shrinkage rate was found.</p> <p>Diffusion coefficients calculated from both methods of analysis agree well with published values and with the published defect structure for MnO.</p> <p>The surface topography of the spheres was studied. It was found to influence the sintering behavior substantially and to be dependent on the atmosphere composition. A qualitative model for the effect of surface topography is presented.</p>