Emission characteristics of some dilute tungsten alloys
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M E T A L S which exhibit high b a r e w o r k functions have b e e n t h e s u b j e c t of e x t e n s i v e r e s e a r c h in r e c e n t y e a r s . R e f r a c t o r y m e t a l s have r e c e i v e d s p e c i a l a t t e n t i o n f o r such a p p l i c a t i o n s a s high t e m p e r a t u r e t h e r m i o n i c e m i t t e r s f o r d i r e c t e n e r g y c o n v e r s i o n . Tungsten h a s r e c e i v e d m o r e e x t e n s i v e i n v e s t i g a t i o n s than the o t h e r r e f r a c t o r y m e t a l s b e c a u s e of i t s u s e in e l e c t r o n t u b e s and l a t e l y , b e c a u s e of i t s c o m p a t i b i l i t y in t h e r m i o n i c n u c l e a r r e a c t o r s . In the q u e s t to obtain r e f r a c t o r y m e t a l s with high w o r k f u n c t i o n s , s o m e s i n g l e c r y s t a l i n v e s t i g a t i o n s h a v e b e e n conducted. Cost and g e o m e t r y a r e two f a c t o r s which l i m i t the u t i l i t y of s i n g l e c r y s t a l s . The o b j e c t of t h i s w o r k w a s to i n v e s t i g a t e s o m e t u n g s t e n a l l o y s which, b a s e d upon the r e p o r t e d w o r k functions of the a l l o y i n g m a t e r i a l s , would a p p e a r to p r o v i d e e n h a n c e d b a r e w o r k f u n c t i o n s . In o r d e r to d e t e r m i n e the a l l o y i n g effect, Re, Os, I r , and T a w e r e a d d e d to t u n g s t e n . F r o m s o u r c e s such a s M i c h a e l s o n , 1 one can s e e that t h e f i r s t t h r e e e l e m e n t s have a h i g h e r w o r k function than t u n g s t e n , w h i l e that of t a n t a l u m i s l o w e r . Nine tungsten a l l o y e l e c t r o d e s a c q u i r e d f r o m the B a t t e l l e M e m o r i a l I n s t i t u t e w e r e e x a m i n e d in two different emission measuring devices, a vacuum emiss i o n v e h i c l e and a t h e r m i o n i c e m i s s i o n m i c r o s c o p e . EXPERIMENTAL APPARATUS A) V a c u u m E m i s s i o n V e h i c l e D e t a i l e d r e v i e w s of the c o n s t r u c t i o n and o p e r a t i o n p a r a m e t e r s of the v a c u u m e m i s s i o n v e h i c l e h a s been p r e s e n t e d in two e a r l i e r p a p e r s . 2'3 F i g . 1 shows the g e o m e t r y of the v a c u u m e m i s s i o n v e h i c l e which c o n s i s t s of f o u r m a j o r c o m p o n e n t s : e m i t t e r s a m p l e , e l e c tron bombardment heater assembly, collector, and g u a r d r i n g . In the e l e c t r i c a l t e s t s e t u p , a K e i t h l e y 610R m i c r o - m i c r o a m m e t e r and a C a r y 31 w e r e u s e d i n t e r c h a n g e a b l y to m e a s u r e c o l l e c t o r c u r r e n t . The K e i t h l e y h a s an a c c u r a c y of 3 p c t f r o m 3 to 10 -l~ a m p and 4 p e t f o r 10 -~~ to 1 0 -13 a m p , and the C a r y 31 i s g u a r a n t e e d to b e within 1 p c t a c c u r a c y . A Boonton 95A m i c r o - m i c r o a m m e t e r with an a c c u r a c y of 4 p c t to 10 -13 a m p w a s u s e d to null the c u r r e n t flow b e t w e e
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