In situ microstructural control of Ni/Al2O3 and Ni/NiAl2O4 composites from layered double hydroxides

The transformation of Ni/Al layered double hydroxides to Ni/Al2O3 and Ni/NiAl2O4 composites was studied via X-ray diffraction and electron microscopy. The Ni/Al layered double hydroxide powders, with Ni2+:Al3+ cation ratios varying from 0.5 to 3.3, were first synthesized by a coprecipitation route. The powders were then reduced ia a tube furnace under hydrogen to yield Ni/Al2O3 or under a CO/CO2 mixture to yield Ni/NiAl2O4. The reduced powders were uniaxially hot-pressed to form sintered pellets. In the case of the Ni/NiAl2O4 hot-pressed composites, the platelike morphology of the precursor was preserved in the final sintered microstructure. in contrast, due to the nucleation and growth mechanism that takes place in alpha-Al2O3, the Ni/Al2O3 hot-pressed composites exhibited no microstructural memory.