4 Conclusions
The choice of milling additive was shown to have a
significant effect on the particle size distribution and
surface chemistry of NiO powders. Residues from
all milling additives were detectable by X-ray
photoelectron spectroscopy and thermogravimetric
analysis. Even though all milling additives desorbed
from the powders by 900 ℃, NiO milled with different
additives and sintered to 1100 and 1500 ℃ displayed
microstructural differences. Some of these differences
may be due to the effects of the milling additives on
the particle size distributions of the powders. However,
the presence of distinct melting transitions for NiO
milled with carbon and methanol suggests another
mechanism by which additives may steer sintered
body microstructure, even past the additive desorption
temperature. Specifically, when sintering is performed
in an oxygen free atmosphere, desorption of carboncontaining
species may drive surface reduction. This
change in surface oxidation state introduces a metallic
Ni species which facilitates rapid grain growth
and decrease in porosity. The presence of such a
mechanism suggests that the interplay between milling
additive and sintering environment cannot be
disregarded, even for high temperature sintering of
NiO.
Acknowledgements
The authors thank the N.Y.S. Graduate Research and
Teaching Initiative (GRTI) for financial support. L. J. D.
thanks the Air Force Summer Faculty Fellowship
program for fellowship support. The authors thank the
Advanced Imaging Facility of the College of Staten
Island for SEM images, and Prof. William L’Amoreaux
and Dr. Mike Bucaro for their help with SEM images.
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