The Mechanism of Electrolytic Rectification

Abstract

g r a p h i c p l a t e s w e r e p l a c e d w i t h i n 1-3 m m of the s p e c i m e n to r e c o r d the image. A n g l e s of incidence of 10~~ w e r e used, and these g a v e s u b s t r a t e cont r i b u t i o n s to the i m a g e of less t h a n 2%. E x p o s u r e times of 30 min w e r e used.Cliffe and F a r r (2) f o u n d m a r k e d differences in the t o p o g r a p h y of deposits f o r m e d a b o v e and b e l o w a critical e l e c t r o l y t e t e m p e r a t u r e r a n g e of 94~176In o r d e r to c o m p a r e these deposit structures, p l a ting was c a r r i e d out at 10 m a / c m e for 30 m i n ( g i v i n g a 6~ thick d e p o s i t ) at 25 ~ and at 99~ E L E C T R O L Y T I C R E C T I F I C A T I O N 379F i g u r e 2 is a B e r g -B a r r e t t i m a g e of the substrate, and the l i n e a r s t r i a t i o n s u b s t r u c t u r e is seen as light and d a r k bands. T h e c i r c u l a r a r e a c o r r e s p o n d s to a p o r o s i t y hole f o r m e d in freezing the metal. This f e a t u r e p r o v e d useful as a location m a r k .In the i m a g e f r o m the deposit f o r m e d at 25~ (Fig. 3), the hole m a y be seen, b u t t h e r e is no e v idence of the s t r i a t i o n s u b s t r u c t u r e . In contrast, the s t r i a t i o n s t r u c t u r e has c l e a r l y b e e n r e p r o d u c e d in the deposit f o r m e d at 99~ (Fig. 4).It a p p e a r s t h e r e f o r e t h a t deposits f o r m e d a b o v e 98~ are e p i t a x i a l w i t h the substrate. W h i l e L a u e spots w e r e still o b t a i n a b l e f r o m the d e p o s i t f o r m e d at 25~ the deposit no l o n g e r c o n f o r m e d so closely to the s t r u c t u r e of the s u b s t r a t e . AcknowledgmentsThe a u t h o r s t h a n k P r o f e s s o r E. C. Rollason for his i n t e r e s t and for the p r o v i s i o n of l a b o r a t o r y facilities. T h a n k s are also due to Messrs. J o s e p h L u c a s Ltd. for g e n e r o u s financial assistance.Manuscript received Oct. 21, 1963. A n y discussion of this paper will appear in a Discussion Section to be published in the December 1964 215, 483 (1959). 2. D. R. Cliffe and J. P. G. Farr, This Journal, 111, 299 (1964). 3. R. Brownsword and J. P. G. Farr, Nature, 195, 373 (1962). The Mechanism of Electrolytic RectificationA. Middelhoek N. V. Philips Gloeilampen3~abrieken, Zwolle, The NetherlandsIt has b e e n k n o w n for a long t i m e t h a t the s y s t e m m e t a l / m e t a l o x i d e / e l e c t r o l y t e , w h e r e the m e t a l is Ta, A1, etc. ( s o -c a l l e d v a l v e m e t a l s ) , e x h i b i t s r e c t ification. W h e n the m e t a l is a n o d i c a l l y polarized, t h e r e is a " s m a l l " c u r r e n t , the l e a k a g e c u r r e n t ; w h e n the m e t a l is c a t h o d i c a l l y polarized, a " h i g h " c u r r e n t flows, the f o r w a r d current.V a r i o u s theories, as m e n t i o n e d in S c h m i d t ' s a r t i c l e (1), h a v e b e e n p r o p o s e d to e x p l a i n the p h e n o m e n o n of...

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