The Research Of Preparation Process On Nickel/silicon Nitride Coated Powder

The objective of the paper is to get Ni-Si3N4 coated Powder of high quality byelectroless plating .The rules were researched that preparation technology of Ni/Si3N4coated powder. The best composites were gained. The mostly result as follows:The effects of the styles of adding materials, pH, temperature, content of materials,pro-preparation of Si3N4 powder and the magnetic field were investigated.The morphologies of powder were observed by using scanning electron microscopeSEM, X-ray diffraction pattern(XRD) was used to analyze the Phases of the Powder,EDS was used to analyze the component of composite powder, the TEM and HREMwere used to affirm the coating layer of powder.The phases of powder can be affected by the styles of adding materials. It wasfound that the Ni(OH)2 would be preparated if the NaOH was added into the solutionfirstly, and the wrong style could make some unpulties in the reaction.It was realized that pH was a important factor to the electroless plating. If the pHwas too low, the electroless plating reaction was very difficult. The Ni(OH)2 wasattended if the pH was too high. The result showed that the pH of 10~11 was aadvisable choice.The temperature had a lesser effection on electroless plating than others, betweenthe 70℃and 90℃, the composites of Ni and Si3N4 could be gained, but theimprovement of temperature could bring down the quality of coating layer.The content of NiCl2 is a very important factor to the coating reaction, if absent ofthe sensitizing and activating of powder. Until the NiCl2 above 28g/L, the reactioncould not be carried out. And the thickness of layer was affected by the content ofNiCl2. The content of N2H4?H2O must be kept in a suitable scope, it was showed thatthe ratio of N2H4?H2O to NiCl2 was 7:1 would be proper to the electroless plating.The magnetic field could affect the distribution of Ni/Si3N4 powder. It wasfounded that the Ni-coated powders prepared using the electromagnetic stirrer were arried as lines of balls, while the powders using the mechanical stirrer present auniform distribution. The magnetism of coated powder was affected by the magneticfield.Electroless plating of Ni on Si3N4 was affected very much by the sensitizing andactivating of Si3N4 powder. The thickness of the layer could not enough thin, unlessusing of the sensitizing and activating of Si3N4. After sensitizing and activating ofSi3N4 powder, the quality of coating layer was very good, and Ni coating layer couldbe preparated with thickness of 5nm, and the thinkness is very uniformity.Taken the analysis and experiment into a word, preparation of all-coated,same-thinkness Ni/Si3N4 coated powder would be achieved by the optimized process,and could control the characters of coated powder at the same time.