Powder metallurgy preparation of new silver-tin oxide electrical contacts from electrolessly plated composite powders

A novel method of coating tin oxide particles with silver by an electroless plating process has been developed to produce silver-tin oxide electrical contact alloys. This has been done by introducing silver nitrate and formaldehyde solution into a dilute solution of the colloidal tin oxide aquasol. Optimal conditions have been suggested for making fine and uniform powders without agglomeration, i.e., bath temperature at 50{dollar}spcirc{dollar}C; 0.69 M of sliver nitrate solution; 1.5 M of formaldehyde solution; 20.7 mmmole/min. of silver ion feed rate; pH of 9.5. Electrochemical measurement of mixed potential and plating rate has indicated that the electroless silver plating process has an activation energy of 22-24 KCal and is activation controlled. It has also shown that the microstructures of the silver-tin oxide composite powders are controlled by the plating rate.; The electrolessly plated silver-tin oxide composite powders have been consolidated to a fully dense compact by an optimal powder metallurgy condition, i.e., compaction at 108 Ksi; sintering at 850{dollar}spcirc{dollar}C for 3 hours with heating rate of 8{dollar}spcirc{dollar}C/min. in an air atmosphere. Silver with 15 volume percent tin oxide prepared in this manner has had good enough ductility to be formed into shapes which can be used as electrical contacts. This composite has sufficient hardness to ensure good resistance for contact points and also has high electrical conductivity to minimize the heat generated during passage of current.