microns. Similar to unmilled NiO, the porosity of NiO
milled with Vertrel decreases only modestly between
1100 and 1500 ℃ (two tenths of a percent), resulting
in a final porosity of 2.1%.
Simultaneous DSC/TGA confirms the presence
of milling additive residues and shows their effects
on heat flow during sintering (Fig. 5). In the
thermogravimetric analysis trace (Fig. 5(a)), NiO
milled with 1.5 wt% carbon shows the most
pronounced mass loss, 5.1%, upon heating. The
majority of mass is lost between 513 and 800 ℃ in a
distinct two-step process. This two-step pattern of mass
loss has been observed previously for NiO–YSZ, and
has been attributed to the carbothermal reduction of
NiO [46]. In this process, carbon abstracts surface
oxygen and desorbs from the surface as represented by
overall Eqs. (2) and (3):
C(ads) 2O(ads)CO2 (g) (2)