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be present also in alloy systems such as Cr-Ni. With this assumption the authors investigated the Cr-Ni, Cr-Fe, Cr-Co, and Cr-Ni-Fe systems by duplicating the experimental methods employed by Kimoto and Nishida. Kimoto and Nishida found that the fine chromium particles obtained by vaporization in a mixture of 6 torr of argon and 0.I torr of air were a-Cr (bcc; ao = 2.88A). On the other hand those metal particles produced in pure argon were found to possess a new crystal structure. The structure of the new modification of chromium, designated 5 phase, was determined to be of a simple cubic lattice with a = 4.588A. This structure has the disordered atomic arrangement derivable from the A-15 type (or W30 type) structure, Fig. i. Table I shows the X-ray diffraction results for the 5-Cr phase which were reported by Kimoto and Nishida. The reflections designated by (s) in the table are those caused by the A-15 type structure while other reflections are those produced by the aforementioned disordered structure. These investigators reported also that the new modification transformed to the ordinary bcc form (a-Cr phase) above 400~ Although the data obtained in the Cr-Ni, 14'15 Cr-Fe, 15 and Cr-Co 15 binary systems were published previously in Japan, it was considered pertinent to redescribe the results in this paper along with the data on the Cr-NiFe system.

EXPERIMENTAL Starting Materials

and Alloy Ingots

High-purity chromium (99.999 pct, supplied by Johnson Matthey and Co.), nickel (99.98 pct purity), cobalt (99.8 pct purity), and electrolytic iron which was annealed in dry hydrogen were used in the study. Alloy additions to chromium were made at 5 to I0 wt pct or at. pct increments. Button ingots ranging from 5 to 20 VOLUME 3, APRIL 1972-887

x/

~,

~

~/Mercury High.Purity Ar e"

~VaporizationChamber ~SheeM t esh Holder

~W-conic~l

Heater

|

(

I .cl Source O- 50v

z Fig. 1--A-15

VacuumPump

type structure.

Fig. 2--Schematic particles.

Table I. Diffraction Lines of $-Cr (Kimoto et al.)

N (h 2 + k 2 + 12)

hkI

1 2 3 4 5 6 8 9 10 11 12 13 14 16 17

I0O 110 111 200~) 210~) 211~) 220 300 310 311 222~) 320~) 321~) 400~) 410

dob s , A (Mo-K~) -

-

2.300 2.049 1.873 1.611 1.441 1.387 1.327 1.274 1.226 1.145 -

dcaI , A 4.588 3.244 2.649 2.294 2.052 1.873 1.622 1.451 1.383 1.324 1.272 1.226 1.147 1.113

g in s i z e w e r e p r e p a r e d by e i t h e r a r c m e l t i n g o r p l a s m a j e t in h i g h - p u r i t y a r g o n (99.9 pct p u r i t y ) a t m o s p h e r e . P r e p a r a t i o n of F i n e A l l o y P a r t i c l e s T h e a p p a r a t u s c o n s t r u c t e d f o r p r e p a r a t i o n of a l l o y p a r t i c l e s c o n s i s t e d of a p y r e x b e l l j a r , a t u n g s t e n - w i r e h e a t e r (in c o n i c a l b a s k e t s h a p e ) , a c o p p e r m e s h b a c k e d b y c a r b o n f i l m ( c o m m o n l y u s e d in e l e c t r o n m i c r o s c o p y ) and the n e c e s s a r y v a c u u m s y s t e m and e l e c t r i c p o w e r s o u r c e a s shown in F i g . 2. E a c h