Nano-indentation on nickel aluminate spinel and the influence of acid and alkaline attacks on the spinel surface

Nickel aluminate spinel phase was successfully sintered from the thermal reactions between nickel oxide and kaolinite or gamma-alumina precursor, to simulate the stabilization mechanism of hazardous metal-bearing waste by ceramic matrix. The product phases were then tested using nano-indentation to obtain their nanohardness and Young's modulus, as a means to evaluate the properties of the product after incorporating the waste material. The results indicate the beneficial effect of forming aluminate spinel phase in the system due to its superior mechanical properties. A higher sintering temperature was found to enhance crystal growth in the spinel phase, together with its nanohardness and modulus. The minimum temperature for fabricating nickel aluminate spinel with a surface property comparable to ceramic materials was found to be 1200 degrees C, although the initiation of the spinel phase can be achieved at a lower temperature. Nano-indentation experiments performed on the spinel-containing samples leached by strong acid and alkaline solutions reveal the superiority of nickel aluminate spinel in resisting acid and alkaline attack and also suggest a reliable mechanism for hosting hazardous nickel in the crystal structure. (C) 2011 Elsevier Ltd and Techna Group S.r.l. All rights reserved.