compaction. The resulting green pellet height was
1.61 mm. The pellets were then subjected to sintering
in N2 using a reducing furnace. The heating ramp was
1 ℃/min to the maximum dwell temperature of either
1100 or 1500 ℃. The samples were held for 4 h at the
maximum dwell temperature, then cooled at a rate of
5 ℃/min. After sintering, the pellets were cleaved and
analyzed in cross section with SEM (JSM 6060, Joel).
Sample porosities were determined from the cross
sectional images using the SEM software.
Simultaneous differential scanning calorimetry/
thermogravimetric analysis (DSC/TGA) measurements
were performed with a TA Instruments SDT Q600
instrument. The measurements were performed by
loading 20–45 mg of the NiO powders into an alumina
sample pan. All measurements were performed under
flowing nitrogen (Airgas, High Purity, 4.8 grade). The
rate of flow was 100 mL/min. The temperature was
stabilized at 40 ℃ for 10 min before ramping at a rate
of 10 ℃/min to a maximum temperature of 1500 ℃.
The samples were held at the maximum temperature
for 30 min. Weight change and heat flow were
measured during the temperature ramp and during the
dwell time at the maximum temperature. In order to
establish the reversibility of heat flow events for
the NiO/C and NiO/methanol samples, additional
experiments were performed in which the temperature
was stabilized at 40 ℃ for 10 mim before ramping at
a rate of 10 ℃/min to a maximum temperature of
1500 ℃. The samples were then cooled at a rate of
10 ℃/min down to a final temperature of 300 ℃. For
all experiments, the heat flow was normalized by the
real time sample weight and was presented as a weight
corrected heat flow.
3 Results and discussion
3. 1 Powder characterizations
The BET surface areas and corresponding average
particle diameters are shown in Table 2 for all milling
procedures. The average particle diameters were
estimated from the BET surface areas using Eq. (1)
[29]:
DBET 6 / ( SBET ) (1)
where BET D is the particle diameter estimated from
BET; is the powder density; and BET S is the BET
surface area. As seen in Table 2, the BET surface area