Controlled Synthesis of Core-Shell Nickel Microspheres with Solid Core and Porous Shell by Precipitation and Thermal Decomposition Method

Nickel oxalate micro-spheres with core-shell structure of solid core and radiate shell were synthesized by precipitation method in a mixed water solution, with oxalic acid and nickel acetate as raw materials, through dropping ammonium hydroxide to adjust the solution pH value to about 8.0. Nickel microspheres with core-shell structure of solid core and porous shell were prepared by decomposing of nickel oxalate microspheres precursor at about 340 ℃ in argon atmosphere. The analyses of infrared spectroscopy(IR)indicates that the composition of the powders is nickel oxalate. The analyses of atomic absorption spectrometry(AAS) and organic elemental analysis(OEA) indicate that the molar ratio of(C2O4)^2-/Ni^2+ is about 1.02, close to the theoretical value of 1.0. The results of the thermo-gravimetric and differential thermal gravity analyses(TG-DTG) indicate that the molar ratio of(C2O4)^2-/Ni^2+ is about 1.06, also close to the theoretical value of 1.0.The analysis of X-ray diffraction(XRD) indicates that the composition of black powders as-prepared is nickel,which has a face-centered cubic crystal structure with average crystal grain size about 16.87 nm. The images of scanning electron microscopy(SEM) indicate that the morphology of nickel oxalate microspheres is a coreshell structure with solid core and radiate shell. The diameter of nickel oxalate microspheres is about 3 μm, and the shell consists of a large number of thin nanorods. The images of SEM also indicate that the morphology of nickel microspheres is a core-shell structure with solid core and porous shell. The diameter of nickel microspheres is about 2 μm, and the shell consists of a large number of nickel grains, surface holes and through holes. The diameter of nickel grains is about 50-100 nm, and the diameter of holes is about 50-200 nm.