778 



THE BELL SYSTEM TECHNICAL JOURNAL, MAY 1957 



Reference 8, Fig. 1). The minimum arc current is much lower for active 

 contacts than for inactive or clean contacts, and one can perhaps think 

 of the decrease of the minimum aic current for noble metal contacts 

 from a vahic of the order of 1 ampere for clean surfaces to 0.1 ampere 

 or less for active surfaces as the chief characteristic of activation. 



1.4 Erosion 



Active contacts of palladium and of silver transfer metal in cjuite 

 different ways. The transfer at active silver contacts is the more complex, 

 and for this reason the transfer that occurs at acti\'e palladium contacts 



-1.5 



15 



U 

 O 



-4.0 



(a) LIMONENE AT 1 MM PRESSURE 



ANODE 



-T- 



CATHODE 



••o- 



0.07 0.2 



(b) NAPTHALENE AT ROOM TEMP 



J L 



.-O- 







0.51 1,03 0.07 0.2 0.51 



ARC TIME IN MICROSECONDS 



1.03 



Fig. 6 — Results of measurement l)y weighing of the erosion of palladium elec- 

 trodes produced by active arcs in limonene vapor (a) and in napthalene vapor 

 (b). 



will be taken up first. The behavior of platinum is in general like that 

 of palladium, and gold is like silver. 



1.4 (a) Palladium andPlatimim. It is found that arcing on closure at ac- 

 tive contacts of palladium or platinum causes loss of metal at the cathode 

 of the order of 4 X 10~^^ cc/erg. The anode often loses metal also, but the 

 loss at the anode is considerably less and may be zero in some cases. The 

 results of two sets of measurements upon active palladium contacts are 

 plotted in Fig. 6. These data represent changes in volume (calculated 

 from weighings) per unit of arc energy after repeated arcs in limonerie 

 vapor at a vapor pressure of 1 mm Hg, Fig. 6(a), and in the vapor of 

 napthalene saturated at room temperature. Fig. 6(b). Tests were made 

 by closing electrodes to discharge on each closure a properly terminated 

 fixed length of cable charged always to 200 \'olts, to gi\-e in each case a 

 constant arc current of 4 amperes, with the arc lasting for the time de- 

 termined by the cable length. For the shortest arc time, the energy of 



