Preparation And Study Of Electroless Alloys Coating Of Fly-ash Cenosphere Particles

Fly-ash cenospheres are primarily a by product in thermal power plant, which are characterized by their fine, lightweight, smooth surface and inner hollow. The main composition of fly ash cenospheres is quartz and mullite. Fly-ash cenospheres that are coated with metal or metal alloys can replace metal powder to be used as Rader Absorbing Material (RAM) or EMI—shielding materials for their lower density than that of pure metal powder. The most important problem in this application is how to make metal or metal alloys uniformly deposited on the surface of the fine particles and finally clad the particle.Electroless NiCoP alloys coating of cenosphere particles were demonstrated in the present investigation. As providing non-catalytic surface for electroless, cenosphere particles were experiencing a two-step process involving sensitization and activation to produce some catalytic clusters on the surface so as to make them suitable for subsequent deposition. In our ameliorative procedure, replacing the conventional PdCl2 activator with AgNO3 activator and replacing Sn2+ with H2PO2- as the reducing agent decreased the overall cost of the coating process and simplified the whole process.SEM and EDX characterized the cenosphere particles after the coating process. It showed that NiCoP alloys uniformly covered the surface of the cenospheres under the given coating conditions. The XRD analysis indicated that the coating alloys were amorphous,therefore,having no ferromagnetism while they changed to be crystal and had somewhat ferromagnetism after the coating being heat-treated. Next, the possible mechanism of electroless NiCoP alloys coating of cenosphere particles was suggested. The ions' adsorption process at the solid-solution interface was the key step in this improved procedure and the ultrasonic vibration was necessary to the electroless reaction.Finally, how the concentration of all constitutes,pH,the temperature of the electroless solution ,the loading and some other factors affected the incubation period of the electroless was discussed, in the end, some questions worth further studying were given out.