  The effect of temperature modes and heating rates (Vh) on the shrinkage
kinetics of submicron and fine aluminum oxide powders has been studied. The
objects of research comprised (i) submicron alfa-Al2O3 powder, (ii) submicron
alfa-Al2O3 powder with an amorphous layer on particle surface, (iii) fine
alfa-Al2O3 powder. The alumina ceramic specimens were produced by Spark Plasma
Sintering (SPS). Equally fine powders (i) and (ii) were used to analyze the
effect of an amorphous layer on sintering kinetics. Powders (i) and (iii) were
used to analyze the effect of the initial particle size on shrinkage kinetics.
Shrinkage curves were analyzed using the Young-Cutler and Coble models. It has
been shown that sintering kinetics is determined by the intensity of grain
boundary diffusion for submicron powders and by simultaneous lattice and grain
boundary diffusion for fine powders. It has been determined that an amorphous
layer on the surface of submicron alfa-Al2O3 powder affects grain boundary
migration rate and the Coble equation parameters at SPS final stages. It has
been suggested that abnormal characteristics of the alumina ceramics sintered
from a submicron powder with an amorphous layer on the particle surface are
associated with an increased concentration of defects at grain boundaries that
were formed during crystallization of the amorphous layer.
