1110 THE BELL SYSTEM TECHNICAL JOURNAL, SEPTEMBER 1954 



at no stress is given^ as 38 kilocalories per mole which is 4 kilocalories 

 higher than that for aluminum and 3 kilocalories under that for tin. 

 The activation energy of silver and cadmium into copper also have 

 low values. Hence, if the effect of stress parallels that for tinned copper, 

 zinc and cadmium should diffuse into copper and nickel silver faster than 

 tin. Furthermore, the limiting shearing 5000 pounds per square inch. 

 Zinc, silver and cadmium are readily plated on the terminals or the wire. 



Zinc plating has been tested experimentally bj- constructing a solder- 

 less wrapped connection of bare copper wire on zinc plated nickel silver 

 or brass terminals. The stripping force for a bare copper wire wrapped on 

 a terminal plated with 0.001 inch thickness of zinc has been measured at 

 175°C and at 100°C as a function of time with the results shown by Fig. 

 15. The strength increases to 60 per cent over that found initially in a 

 time of less than two hours at 175°C. At 100°C, the time required is a little 

 over a day. If we subtract the relaxed force from the stripping force 

 and divide by the area of the connection, the shear strength of the con- 

 nection is as shown by Fig. 15, lower cur^'es, for the two temperatures. 

 From these two curves, an activation energy versus hoop stress can be 

 obtained with the results shown by Fig. 16. These values allow one to 

 extend the time variation of the shear stress down to room temperature 

 with the result shown by Fig. 15. Adding these values multiplied by the 

 area of the connection to the relaxed hoop stress, the indicated stripping 

 force at room temperature is shown by Fig. 15, room temperature curve. 

 This force increases at such a fast rate that the strength can be observed 

 to increase at room temperature and corresponding measurements are 

 shown by the circles. Since corrosion cannot occur in a region of fusion, 

 a criterion for the corrodability of a connection is the time required to 

 complete half of the total fusion at room temperature. On this basis, 

 the zinc plated connection has the lowest half fusion time of any of the 

 materials tested. 



Although zinc diffuses more readily than other materials examined, it 

 tends to form more brittle alloys and hence its use has not been seriously 

 considered for solderless wTapped connections. 



8 R. M. Barrer, Diffusion In and Through Solids, Cambridge University 

 Press, 1941, Table 67, p. 275. 



I 



