MOLYBDENUM PERMALLOY FOR INDUCTANCE COILS 



387 



alloy is manufactured commercially by the Western Electric Company 

 for use in loading coils and filter coils. 



Physical and Magnetic Characteristics 



The raw materials and necessary embrittling agents " are melted 

 together and cast into ingots which are rolled to develop the desired 

 grain structure. The density of this alloy is 8.65 gm/cm^ The brittle 

 material is pulverized to the desired fineness and finally annealed to 

 soften the alloy particles before insulation and pressing into core form. 



The distribution by weight of the particle sizes of a sample of 120- 

 mesh powder is given in Fig. 1, showing a root mean square size of 50 



200 



i2 100 



-^ 60 

 2 50 



<: 20 



0.2 12 5 10 20 30 40 50 60 70 80 90 95 98 99 



PER CENT SMALLER THAN SIZE INDICATED 



Fig. 1 — Distribution of particle size of 120-mesh powder, by weight. 



99.8 99.9 



microns.'" Since the effective resistance of a coil due to eddy-current 

 losses in its core is proportional to the mean square particle diameter," 

 it can be decreased when desired by the use of more finely pulverized 

 material. 



The problem of insulating 2-81 molybdenum-permalloy powder is to 

 coat the particles with a minimum thickness of a material which will 

 not break away during the pressing operation, which will not fuse and 

 flux the magnetic particles together during the core heat treatment, 

 which will prevent the flow of eddy currents between metallic particles, 

 and which will be chemically inert throughout the lifetime of the 

 magnetic core. The difficulty of the problem will be appreciated from 

 the fact that the separation between adjacent particles of a core of 

 125 permeability is approximately equal to the wave-length of visible 



