Study On Silver-Ytterbia Contact Material Prepared By Electroless Plating

In order to improve the performance of AgYb₂O₃ electrical contact materials, it needs to control the morphology and size of Yb₂O₃ particle in electrical contact materials and improve the wettability and interface behavior of Ag-Yb₂O₃. AgYb₂O₃ composite powder was prepared by electroless plating instead of coprecipitation, accordingly.Effects of the morphology and size of the precursors and calcination methods on the morphology and size of Yb₂O₃ powder were studied. The Yb₂O₃ precursors with different morphology and size can be made by precipitation in solution. Strip precursor Yb₂(C₂O₄)₃·4H₂O which is well dispersed in micron dimension was got using oxalic acid as precipitating agent. And amorphous precursor Yb(OH)₃·2H₂O and Yb₂(CO₃)₃·2.5H₂O in nano dimension when using ammonia and ammonium bicarbonate as precipitating agent. Single-dispersed spherical amorphous precursor Yb(OH)CO₃·H₂O can be got using urea as precipitation. Uniform ytterbium oxalate particle with the average diameter between 1-3μm can be prepared by controlling reactant concentration, react temperature, aging temperature and aging time. According to thermogravimetry and differential scanning calorimetry curves of precursor, a non-linear calcination method was established which can alleviate reunite phenomenon in calcination. The higer the calcination temperature is,the larger size Yb₂O₃ particle got.Varied size ytterbia powder coated with Ag by electroless plating, AgYb₂O₃ composite powder with core/shell microstructure can be attained. The influence of powder pretreatment technics, reductant, PH values, formaldehyde concentration and react temperature was studied on plating Ag effect and the ratio of reduced Ag. It was found that Ag can be easily reduced on the surface of Yb₂O₃ powder after sensitization and activation treatment avoiding the appearnce of silver glass at the same time. Chosing right reductant can get compact and fine silver layer by controlling reducing speed. Increasing PH value and react temperature can enhance reducing ability of formaldehyde, but if they were too high, the solution will be self-reduced. When the formaldehyde concentration is more than 60ml/L, formaldehyde begins to react with ammonia. As the result, the ratio of reduced Ag rises at first ,then falls down.AgYb₂O₃ wire was perared by AgYb₂O₃ composite powder via billet molding, sintering, extrusion and wire drawing. The result shows that the wire prepared by electroless plating behave better than the wire by coprecipitation on mechanical performance. The performance of former was that tensile strength was 217-230MPa, and hardness was 804-844 N·mm²,and elongation was 17-19%; specific resistance was 2.05-2.11μΩ·cm.