Synthesis and characterization of nanocrystalline NiAl2O4 spinel powder by low temperature combustion

Interest in the synthesis of nanoparticles has increased due to their different properties when compared to the corresponding bulk material. Nickel aluminate (NiAl2O4) is a mixed cation. oxide with normal spinel structure, where Al occupies the octahedral sites and Ni occupies the tetrahedral sites. Industrial application of this material is mainly based on its stable structure at high temperature and catalytic features combined with high surface area. NiAl2O4 acts as a catalytic support which can provide a stabilizing effect while maintaining a high degree of chemical inertia. A much greater stability for nickel is observed if it is supported on nickel aluminate than on other supports [1].Several preparation methods have been studied to obtain nanocrystalline nickel aluminate with small particle size, such as ultrasound irradiation [2], and microwave heating [3]. The sol–gel method [4] provides powder with small particle size and high surface area; however, this method releases dangerous gases which require great care during sintering. The solid solution reaction needs high temperature for sintering and large power time consumption; also, the powder produced has low surface area which is undesirable, for instance, in catalyst materials. The advantage of the solution techniques is the quasi-atomic dispersion of the component cations in liquid precursors, which facilitates synthesis of the crystallized powder with nanosize and high purity at low temperatures.The properties of the powder may vary as different preparation methods are used. The selection of the preparation method is usually based upon the desired properties of the final material. The polymeric precursor method, in which a solution of ethylene glycol, citric acid and metal ions is polymerized to form a polyester-type resin, has recently received considerable attention because of its simplicity.Thus, this method has a distinct advantage over most other methods, in that very pure mixed oxides can be prepared[5]. Furthermore, powders with nanosizes make the ceramic system very attractive for designing new functional materials, where the properties depend on the particle size. For these reasons, knowledge of the nucleation and growth is very important in order to control the particle size.