Study of preparation conditions of NiO–MgO systems to control the morphology and particle size of the NiO phase

Several NiO–MgO samples were prepared from nickel nitrate hexahydrate and different sources of magnesia by using a NiO/MgO weight ratio of 1:1 and 4:1 and two different preparative paths. All the samples were structurally characterized using BET, XRD, SEM and TPR techniques. The results showed that the sequence of decomposition of the Ni(NO3)2·6H2O–MgO systems is similar to the sequence reported for the nickel nitrate hexahydrate without magnesia. XRD identified complete solid solutions for all the NiO–MgO systems prepared. Their BET areas were similar but their different morphologies and particle sizes mainly depended on the preparative path. Independently of the magnesia used, the NiO–MgO systems prepared by controlled decomposition of the nickel nitrate hexahydrate until Ni3(NO3)2(OH)4 was formed and which were subsequently calcined to form NiO (path B) led to very homogeneous particles of sizes around 100 nm. Path B also gave the highest degrees of NiO reduction.