Determination of the thermal stability of CoAl2O4, ZnAl2O4 and NiAl2O4 single nanocrystals

Abstract

The synthesis of spinel type mixed oxides (CoAl2O4, ZnAl2O4, and NiAl2O4) by solvothermal method was studied using toluene as a solvent at various reaction temperatures for 2h. The molar ratio of Co/Al, Zn/Al, and Ni/Al was 0.5. The powder obtained from air dried was characterized by X-ray diffraction (XRD), Transmission Electron Microscopy (TEM) and BET surface area measurement. The thermal stability was defined by the ratio of BET surface area of product after calcined (m2/g) to BET surface area of as-synthesized product (m2/g), and the ratio of the crystallite size of calcined product (nm) to the crystallite size of as-synthesized product (nm). Each particle of spinel products was single crystal and was formed without any contaminated phase. The crystallite size and surface area properties depended on the calcination temperature and the reaction temperature in the synthesis. It was found that the reaction temperature in the synthesis and the calcination temperature affected the thermal stability of each metal aluminate spinels that result in the change of crystallite size and BET surface area. The varying of divalent ions (Co2+, Zn2+ and Ni2+) in tetrahedral sites of metal aluminate spinels affected the thermal stability. The thermal stability of the metal aluminate spinel revealed in the order of, NiAl2O4 > CoAl2O4 > ZnAl2O4. That is the result of the difference in bond dissociation energy of metal oxides and cation distribution over sites with tetrahedral coordination in the spinel-type structure