| The objective of this paper is to obtain metal-ceramic composite materials with better complex properties by the way of preparing nano-composite powders of metal and ceramic. In our thought, firstly we should prepare nano-ceramic powders coated with metal, and then during the period of sintering, the film of metal could prevent the nano ceramics powder from dumpling and keep the powders to be nano-sized. It's well known that nano-materials have good ductility, and the composite powders have the better consistency properties . On the other hand, because the metal phase was evenly distributed, the ductility of the ceramic composites could be promoted further. In this paper, we tried to get nano-composite powders of metal-coated ceramic by electroless cobalt plating of nano-Al2O3 powder.The nano-Al2O3 powder used in experiments were about 10 to 20 nanometer, and they were pretreated to produce catalytic activity before the electroless copper plating. The solution was alkaline, and formaldehyde (HCHO) was used as a reducing agent. Plating was carried out at middle temperature/low temperature and ultrasonic radiation. Plating rate was determined by measuring the weight gain of powder after plating, and the ingredients of solution were determined by chemical analysis. The morphology of powders was observed using high-resolution transmission electron microscopy (HRTEM); X-ray diffraction (XRD) pattern was used to analyze the phases of the powders;At first, the feasibility of electroless copper plating of nano-Al2O3 powder with ultrasonic radiation was studied. Ultrasonic radiation made the reaction happen at room temperature, furthermore, the reaction was accelerated, and more importantly, the powders were dispersed evenly so that makes as more particles as possible coated. The observation by HRTEM indicated that the size of particles coated with ultrasonic radiation at room temperature in alkaline formaldehyde bath was about 50~60nm. The originally granular form of the nano-Al2O3 particles has changed into spheral-like shape. The X-ray analysis showed that the plate was the alloy of Co-P.In this paper, a number of deposition parameters, such as the pH, the temperature and the concentration of the bath, were studied.It was found that before the plating ,there is section time to gestating, that we call the "gestating time" and the plating was ended spontaneously after some time, named "plating time". The analysis of the solution after plating indicated that the too much decrease of pH value results in the reaction to be stopped. The plating time was shortened when the pH and the temperature of the bath were increased. It was also shortened by increasing the concentration of copper sulfate and by decreasing the concentration of EDTA. When the bath load was increased, the plating time was shortened, because the surface to be plated was increased.All the factors studied had an effect on plating rate, i.e., weight gain per unit of time. The results showed that the factors that could shorten the plating time increasedthe plating rate. The plating rate was increased when the pH and the temperature of the bath were increased. It was also increased by increasing the concentration of copper sulfate and by decreasing the concentration of EDTA. When the bath load was increased, the plating rate was shortened.The effects of bath composition and plating conditions on the composition were also investigated. The X-ray analysis showed that EDTA and the stabilization agent can effectively increase the content of the copper oxidation in the composite powders. That is important factor to get better composite material.The factors which affected composition affected the thickness and the uniformity of the plate too. It was concluded that the pH value, plating temperature and the concentration of every component of the plating solution can affect the plating layer. It is better way to control the plate thickness by controlling the concentration of copper sulfate and the bath load, of course ,.when changing the c... |
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