SOME ASPECTS OF POWDER METALLURGY 449 



By the use of a finely divided magnetic powder, the particles of which are 

 insulated from one another, the eddy current losses in the cores can be 

 reduced to a level low enough for satisfactory use. 



The tirst metal powder used for cores in the telephone industry w'as 

 electrolytic iron. This was later superseded by more suitable magnetic 

 materials such as the permalloys. 



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Fig. 4 — Brittle molybdenum-permalloy, as rolled to produce fine, equiaxed grain. 

 .Magnified 130 diameters." 



The procedure utihzed to obtain the permalloy powder is worthy of note. 

 Ingots of the desired composition are prepared by melting and casting in 

 the normal manner with, however, the addition to the melt of a small 

 amount of sulphur which acts as an embrittling agent to facilitate pulver- 

 ization. The sulphur exists as microscopic films of complex sulphides 

 at the crystallite boundaries. At normal temperatures these films are 

 brittle, but at elevated temperatures are either malleable or dissolve in 



