Preparation Of Cu-wrapped Al₂O₃ Nano Powders By Electroless Plating Method

The Cu-wrapped Al2O3 nanocomposite powders were prepared by the electroless plating method, which was an aim of this text. Dispersive effect and adsorptive quantity of citric sodium on nano-Al2O3 were studied. Influence of dispersant, sensitization, activation, components of plating solution and antioxidant to pretreating, velocity, stability and plating cell were discussed. Pretreating of plating copper, phase composition of composite powders, plating cell, surface morphology and grain size of nanocomposite powders were analyzed or indicated by UV spectrometer, Fourier transform infrared spectrometer, X-ray diffraction (XRD), transmission electron microscopy (TEM), EDS energy spectrum and multiangle ultra-fine grain analyzer and so on. It is great significant for expending the application of the nanoceramic powders.Because the nano-Al2O3 powders have an extreme ratio surface area, they are easy to aggregate. Whether aggregations have been dispersed evenly and plated successfully or not would directly affect the uniformity of nanocomposition powders. It is necessary to be dispersed before electroless plating copper. In this experiment, physical (ultrasonic wave) and chemical (dispersant) methods were both used to disperse nano-Al2O3 powders. The dispersed powders appeared to be single particle or smaller aggregations. Plating solution with fixed volume was used as a reference bath. The concentration of only one species would be changed in the reference both for each experiment, in order to investigate influences of velocity and stability. The optimum concentration of plating solution was selected according to results investigated. Meanwhile, the mechanism of sensitization and the reutilization of activation were explored relatively. When the wavelength was 198nm and pH value was 10, The results showed that adsorption behaviors of citric sodium on nano-Al2O3 accorded with langmuir monolayer adsorption. The maximum of adsorption was 1.583mg.mL-1. At the same time, the amount of sodium citrate related to nano-alumina was 2.5 percent, the viscosity and the sedimentation velocity could get the lowest value. That is to say, stability and adsorptive capability achieved optimum states together. Under the condition of optimum plating solution containing 25～30g.L-1 of CuSO4.5H2O, 10.125～12.027ml.L-1 of HCHO 68～90g.L-1 of KNaC4H4O6 6～9ml.L-1 of CH3OH 11～12 of pH and 25～30℃of temperature, electroless plating copper was proceeding with stable velocity. The copper ions were reduced to metallic copper, which deposited on the nano-Al2O3 powders surface. The deposited coppers have autocatalytic character, which makes reaction keep on proceeding. Formaldehyde can effectively suppress formation of Cu2O in the reaction. After plating copper, the composite powders were immersed into antioxidant to decrease Cu2O formation during drying. Cu/Al2O3 nanocomposite powders were obtained. Their mean diameter was about 80nm. Compared with raw nano-Al2O3 powders, the mean diameter extended approximately by 30nm.