The Study Of Coating Al₂O₃ Particles With Cu By Electroless Plating

Cermaics materials have high melting point, high hardness, excellent wear resistance and anti-corrosion characteristic. However, due to the high brittleness, low electric conductivity and thermo-conductivity, the application of ceramics materials was limited. Composite material is a trend of the development of materials. The incorporation of ductile metal phase in ceramic can develop the comprehensive performance and produce synergies, mixing properties to satisfy some special requirements. Making suitable ceramic/metal composite powders is a key step to prepare composite materials with excellent properties. Metal-coated ceramics particles synthesized by using the electroless plating method can effectively improve the wettability between the metal and the ceramics, and the composite materials have the characteristics of both ceramic and metal. By introducing the principle, methods of preparing Cu coated Al2O3 powders by electroless plating, with the aim of obtaining Cu/Al2O3 composite powders with uniform coating surface and better dispersibility, this paper studied the influence of pretreatment, components proportion of the plating solution and technological parameter on the qulity of coating. The morphology of the powders were observed by using scanning electron microscope (SEM, JEM, Japan).The phase composition was analyzed by X-ray diffraction (XRD, PANalytical, Holland).The average size of particles of Al2O3 powder used in this experiment is 3.5μm.The Al2O3 particles need be preptreated before plating. In this experiment, the pretreatment of Al2O3 powder included as follows:disperse, alkalicleaning, etching, activation, peptization. The influence of physical and chemical dispersion on the dispersibility were studied. Trisodium citrate was used as the dispersant in this work. And the influence of its amount on the settling performance of Al2O3 powders was researched. The result showed that when the amount of trisodium citrate comparing with Al2O3 was 2.5 percent the longest settling time and the best dispersing effects can be obtained. Colloid-palladium was used as activator to catalyze the Al2O3 particles. The follow-up experiment showed that the Al2O3 particles could be effectively catalyzed by colloid-palladium activation solution and became the active site. The result also points that the peptization after activation is an indispensable process. The experiments researched also the influence of pH value and components proportion of the plating solution on the process of electroless plating. By analyzing the effect of pH value on the stability of the plating solution, the speed of plating and the weight increment, the optimum pH=12.0 was determined. The components proportion of the plating solution affected both the process of plating and the quality of the composite powders. The experiments researched the influences of main salt, reducing agent, complexing agent on the speed of plating and weight increment by controlling parameters. The optimum plating solution containing was found as:20 g/l of CuSO4?5H2O,20 g/1 of EDTA-2Na,8 g/1 of C4H4O6KN-4H2O,28 ml/l of HCHO,10 mg/l of K4[Fe(CN6)]?3H2O,16 g/l of NaOH,100 ml/1 of CH3OH. At last, the experiment researched the effect of the loadage of Al2O3 powders to the process of plating. The result shows that the loadage of Al2O3 powders can observably affect the speed of plating, and has a little relation with the weight increment. But the metal phase content of the composite powders can be controlled by adjusting the mass of Al2O3 powders.