Particle size comparison of hydrothermally synthesized cobalt and zinc aluminate spinels

Nanosized CoAl2O4 and ZnAl2O4 powders with particle sizes of 67 and 6.5 nm are synthesized under hydrothermal conditions at 245degreesC for 20 h. The precursors are reacted at different temperatures to provide intermediate phase transformations using X-ray diffraction (XRD), infrared (IR) spectra, and thermal gravity and differential thermal analysis (TG-DTA). XRD patterns and IR spectra demonstrate that the CoAl layered double hydroxide structure (CoAl-LDHs) is more stable than ZnAl layered double hydroxide structure (ZnAl-LDHs) when they are hydrothermally treated. The different thermal stability of the CoAl- and ZnAl-LDHs results in the different aluminum source, e.g., beta-Al(OH)(3) for ZnAl2O4 vs gamma-AlO(OH) for CoAl2O4, when the aluminate spinels are formed. The different aluminum sources lead to the particle size difference. The phenomenon is reasonably expounded based on the nucleation theory from the microscopic scale.