Synthesis of CoxMg1−xAl2O4 nanospinel pigments by microwave combustion method

Abstract The aim of the work is optimizing the calcined temperature for CoxMg1−xAl2O4 nanospinel pigment formation after microwave treatment. The powders were prepared by the microwave combustion method (MCM), using Magnesium chloride hexahydrate (Mg(Cl)2·6H2O), cobalt nitrate hexahydrate (Co(NO3)2·6H2O) and Aluminum chloride hexahydrate (Al(Cl)3·6H2O), as starting materials and starch as a fuel. The powder precursors were calcined at different temperatures; 400 °C, 550 °C and 800 °C to optimize the nanospinel formation. The properties of products were characterized using differential thermal analysis and thermogravimetric analysis (DTA/TGA), X-ray diffraction (XRD), scanning electron microscope (SEM), infrared spectra (IR) and transition electron microscope (TEM). Finally, determination of the magnetic properties of nanocrystalline CoxMg1−xAl2O4 spinel powders was performed by means of Mossbauer spectroscopy, using a vibrating sample magnetometer (VSM). The results revealed that CoxMg1−xAl2O4 compositions exhibited crystal size below 35 nm except for the powders containing high level of the cobalt content. The particle size was below 100 nm except for the MgAl2O4. The diffuse reflectance spectra of the CoxMg1−xAl2O4 pigments confirmed the presence of tetrahedrally coordinated Co2+. Magnetic measurements revealed that the nanocrystalline CoxMg1−xAl2O4 have ferromagnetic behavior. Therefore, the present experiment succeeds in synthesis of nanospinel blue compositions in short time based on microwave combustion method to be applied in various applications such as in the fields of pigment, ceramic and magnetic applications.