Preparation And Application Of Lightweight Magnetic Microspheres

The conventional magnetic particles have a characteristic of heavy density, which limit their applications in some special fields. For example, conventional magnetic particles in magnetorheological fluids (MRF) can easily subside and make MRF unstable. Conventional magnetic particles work as microwave absorber in stealth plane may increase the weight of the plane. If the density of magnetic particles can be reduced, their applications would be widened.In this paper, two kinds of low-density magnetic microspheres were prepared by electroless plating Ni on hollow glass microspheres and polystyrene microspheres. In addition, their applications in MRF and microwave absorber were discussed.Pretreatment process is very.important in electroless plating nickelon hollow glass microspheres. And a new pretreatment process was investigated, which included coupling and activation. The optimum coupling conditions were determined by orthogonal tests. The effection of coupling process on activation effect was analyzed. The research showed that coupled microspheres had an enhanced capacity to absorb Pd, resulting in more active points on the surface of micro-spheres. In addition, influences of other parameters such as PH valve of plating bath and loadage were studied.The research of electroless plating nickel on polystyrene microspheres showed that activation process had an effect on the yield of magnetic microspheres. The apparent of the product was influenced by the activated microspheres that were introduced into the reaction system.The properties of the products, such as density, morphology and crystal texture of the coating, were analyzed. Based on the results, the conclusions could be drew as follows:The average density of Ni-coated hollow glass microspheres and Ni-coated polystyrene microspheres are 3.0 g/cm3 and 2.7g/cm3, respectively, which are lower than the density of conventional magnetic particles (7~8 g/cm3).The SEM photography shows that the coating is complete, uniform, and fine.The EDS and XRD analysis prove that the main component of the coating is Ni, which crystal texture is similar to pure nickel.Heat treatment on Ni-coated hollow glass microspheres can crystallize the Ni-coating, which is beneficial for improving the magnetism of the products.The two kinds of low-density magnetic microspheres were applied in MRF and microwave absorber. The results were obtained as follows:The sediment stability is evidently improved and the apparent viscosity of MRF under magnetic field is larger than the initial viscosity.The microwave absorber has a property of absorption by the electrical loss mechanism.In a word, complete, uniform and fine-coated low-density magnetic microspheres can be prepared by electroless plating Ni on hollow glass microspheres and polystyrene microspheres. As one of the promising materials, low-density magnetic microspheres will be wildly used in the future.