Sonochemical coating of nanosized nickel on alumina submicrospheres and the interaction between the nickel and nickel oxide with the substrate

The preparation and coating of nickel on amorphous and crystallized alumina were carried out by employing a sonochemical method. The interaction betwe en the nickel as well as its oxide and the alumina core was then studied by TEM, XRD, DSC, DRS, FTIR, and magnetization measurements. The following we re found: (1) Amorphous alumina can provide a great number of active sites for reaction with nickel and can yield a good coating effect in which most of nickel is adhered to the alumina surface tightly, while in the case of t he crystallized alumina as substrate, most of nickel particles is distribut ed in the free space among the alumina submicrospheres; (2) As compared to the unadhered nickel, the adhered nickel has a strong interaction with the alumina core, which can retard the crystallization of elemental nickel and, conversely, promote the formation of the spinel phase NiAl2O4. (3) The fir st stage of the interaction between the nickel and the alumina may be throu gh the isolated hydroxyl groups to form a kind of interface Ni-O-Al bond. T he connection positions further become nucleation centers far elemental nic kel. After the sample is heated to high temperatures, DRS and IR results sh owed the diffusion of nickel ions into the vacant tetrahedral sites in alum ina. At higher temperature, an inversion process-the substitution of Ni2+ i ons for part of Al3+ at octahedral sites has taken place, and it results in the final formation of the disordered spinel phase. (4) Magnetization meas urements show that the as-prepared sonication products are superparamagneti c due to the ultrafine nature of nickel particles.