twice as large as the 529.5 peak. Since the BET data
indicate that the extent of comminution of NiO in
methanol is not that high, it seems likely that for NiO
milled in methanol, the 531.2 eV peak is not solely
composed of contributions from defect sites. The
presence of C–H stretching peaks in diffuse reflectance
infrared spectroscopy of the methanol milled NiO (data
not shown) provides support for the hypothesis that
alcohol and/or alkoxide moieties are present on the
surface of NiO milled with methanol.
3. 2 Scanning electron microscopy and thermal
analyses of sintering
SEM images of sintered pellets from milled and
unmilled NiO show significant differences in
microstructure as a function of milling additives
(Fig. 4). For intermediate temperature sintering
(1100 ℃) (Fig. 4(a)), the unmilled NiO sample shows
notable but inhomogeneous particle size growth with
some sub-micron particles remaining, but significant
fusion of particles into grains greater than two microns.
The porosity of the unmilled NiO sample sintered to
1100 ℃ is 1.6%. The sample milled with carbon
undergoes an accelerated grain growth, maintaining
almost no sub-micron particles and achieving a
porosity of 1.7%, nearly the same as that of the
unmilled NiO sample. In contrast, both of the slurry
milled samples (NiO/Vertrel and NiO/methanol)
display a hindered particle size growth maintaining
smaller, more homogeneous particle sizes, and higher
porosities of 2.3%. The combination of hindered
particle size growth and higher porosity suggests that,
after sintering to intermediate temperatures, the slurry
milled samples bear a closer resemblance to unsintered
pressed powder compact as compared to the dry milled
or unmilled samples. Notably, for NiO milled in
methanol, sintering to 1100 ℃ results in minimal
particle size growth with almost all particles
maintaining sizes below 500 nm. Despite this hindered
particle size growth, for both NiO/methanol and
NiO/Vertrel, there are regions where the small particles
have fused together resulting in amorphous regions
with indistinct grain boundaries. Finally, we note that
preliminary investigations of NiO milled with no
additive produce a structure with inhomogeneous pores
and large irregular grains. Because of the non-optimal
characteristics of this microstructure, we elected not to
carry it forward in the future studies.
Differences in porosity and grain growth persist
twice as large as the 529.5 peak. Since the BET dataindicate that the extent of comminution of NiO inmethanol is not that high, it seems likely that for NiOmilled in methanol, the 531.2 eV peak is not solelycomposed of contributions from defect sites. Thepresence of C–H stretching peaks in diffuse reflectanceinfrared spectroscopy of the methanol milled NiO (datanot shown) provides support for the hypothesis thatalcohol and/or alkoxide moieties are present on thesurface of NiO milled with methanol.3. 2 Scanning electron microscopy and thermalanalyses of sinteringSEM images of sintered pellets from milled andunmilled NiO show significant differences inmicrostructure as a function of milling additives(Fig. 4). For intermediate temperature sintering(1100 ℃) (Fig. 4(a)), the unmilled NiO sample showsnotable but inhomogeneous particle size growth withsome sub-micron particles remaining, but significantfusion of particles into grains greater than two microns.The porosity of the unmilled NiO sample sintered to1100 ℃ is 1.6%. The sample milled with carbonundergoes an accelerated grain growth, maintainingalmost no sub-micron particles and achieving aporosity of 1.7%, nearly the same as that of theunmilled NiO sample. In contrast, both of the slurrymilled samples (NiO/Vertrel and NiO/methanol)display a hindered particle size growth maintainingsmaller, more homogeneous particle sizes, and higherporosities of 2.3%. The combination of hinderedparticle size growth and higher porosity suggests that,after sintering to intermediate temperatures, the slurrymilled samples bear a closer resemblance to unsinteredpressed powder compact as compared to the dry milledor unmilled samples. Notably, for NiO milled inmethanol, sintering to 1100 ℃ results in minimalparticle size growth with almost all particlesmaintaining sizes below 500 nm. Despite this hinderedparticle size growth, for both NiO/methanol andNiO/Vertrel, there are regions where the small particleshave fused together resulting in amorphous regionswith indistinct grain boundaries. Finally, we note thatpreliminary investigations of NiO milled with noadditive produce a structure with inhomogeneous poresand large irregular grains. Because of the non-optimalcharacteristics of this microstructure, we elected not tocarry it forward in the future studies.Differences in porosity and grain growth persist
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