Industrial Applications of Surface Analysis - American Chemical Society

15 Applications of Surface Analysis in the Nuclear Industry N. S. McINTYRE

Downloaded by FUDAN UNIV on January 22, 2017 | http://pubs.acs.org Publication Date: September 22, 1982 | doi: 10.1021/bk-1982-0199.ch015

University of Western Ontario, Center for Interdisciplinary Studies in Chemical Physics, London, Ontario N6A 3K7, Canada

In the past ten years the number of chemistry-related research problems in the nuclear industry has increased dramatically. Many of these are related to surface or interfacial chemistry. Some applications are reviewed in the areas of waste management, activity transport in coolants, fuel fabrication, component development, reactor safety studies, and fuel reprocessing. Three recent studies in surface analysis are discussed in further detail in this paper. The f i r s t concerns the i n i t i a l corrosion mechanisms of borosilicate glass used in high level waste encapsulation. The second deals with the effects of residual chloride contamination on nuclear reactor contaminants. Finally, some surface studies of the high temperature oxidation of Alloys 600 and 800 are outlined; such characterizations are part of the effort to develop more protective surface films for nuclear reactor applications. In the past ten years, the nature of the research and development tasks facing the nuclear power industry has changed markedly. Many of these tasks represent the finishing stages of developments which began two decades before with the f i r s t commerialization of nuclear energy. In contrast to early research and development, many of the new tasks have been chemistry-related, rather than more directly associated with physics or engineering topics, as in the past. Much nuclear r e actor related chemistry of interest in the past 10-15 years has involved reactions at interfaces; thus the introduction of surface analysis techniques, around 1970, has coincided with the undertaking of a number of research projects in the nuclear industry where surface analysis has been of much value. In Table 1, some examples of actual surface analysis studies are given, along with the particular area of nuclear energy 0097-615 6 / 8 2 / 0 1 9 9 - 0 3 4 5 $ 0 6 . 0 0 / 0 © 1982 American Chemical Society

Casper and Powell; Industrial Applications of Surface Analysis ACS Symposium Series; American Chemical Society: Washington, DC, 1982.

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Table 1 Some A p p l i c a t i o n s of Surface A n a l y s i s i n the N u c l e a r Industry 1. R a d i o n u c l i d e W a s t e Management

- Waste f o r m l e a c h i n g - Ion absorption on minerals and backfill - Container corrosion

2. T r a n s p o r t o f R a d i o a c t i v i t y in Reactor Coolants

- Chemical decontamination of reactor circuits - Corrosion of heat-transport tubing

3. R e a c t o r C o m p o n e n t Development

- G r o w t h of passive oxides - Hydrogen embrittlement - Surface chloride contamination

4. F u e l a n d C l a d d i n g Fabrication

- U r a n i u m precipitation i n m i x e d fuels - Acid cleaning of fuel c l a d d i n g

5. R e a c t o r S a f e t y

6. F u e l R e p r o c e s s i n g

• Iodine surface reactions • H i g h temperature cladding reactions - Fuel dissolution mechanisms - C o r r o s i o n o f vessels


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r e s e a r c h t o w h i c h t h e y were r e l e v a n t . A number o f a s p e c t s o f h i g h l e v e l r a d i o a c t i v e w a s t e management i n v o l v e t h e s t u d y o f i n t e r f a c e s and m a t e r i a l t r a n s f e r a c r o s s them: l e a c h i n g s t u d i e s of the g l a s s o r c e r a m i c waste form r e q u i r e a d e t a i l e d c h a r a c t e r i z a t i o n o f t h e s u r f a c e f i l m f o r m e d , i n o r d e r t o d e t e r m i n e t h e me\ c h a n i s m s o f r a d i o n u c l i d e movement. X P S d > 2 ) A E S , (3) and SIMS( s t u d i e s o f waste g l a s s have a l r e a d y been r e p o r t e d . Typical nuc l e a r w a s t e r e p o s i t o r y m i n e r a l s u r f a c e s have b e e n r e a c t e d w i t h w a t e r and t h e i r t r a n s f o r m a t i o n s s t u d i e d by X P S . T h e adsorpt i o n o f some f i s s i o n p r o d u c t i o d i d e s on c o p p e r h a s b e e n i n v e s t i g a t e d by X P S ' i n a p r e l i m i n a r y s t u d y o f w a s t e c o n t a i n e r c o r r o s ion. Radioactivity transport in reactor b o t h s u r f a c e c o r r o s i o n and d e p o s i t i o n .

coolant Several

circuits involves XPS s t u d i e s

(8,9) o f r e a c t o r b o i l e r a l l o y s h a v e b e e n r e p o r t e d w h i c h show t h e v e r y s t r o n g e f f e c t o f c o o l a n t c h e m i s t r y on t h e f i l m s d e p o s i t e d . The c h e m i s t r y o f c o r r o s i o n p r o d u c t s p r e c i p i t a t e d on ZrO and A l O s u r f a c e s has b e e n s t u d i e d u s i n g X P S . ( More r e c e n t l y , c h e m i c a l d e c o n t a m i n a t i o n o f r a d i o a c t i v e b o i l e r c i r c u i t s has b e e n a s s i s t e d by XPS a n a l y s i s o f t h e s u r f a c e - a c t i v e d e c o n t a m i n a t i n g a g e n t . ( 1 ) S u r f a c e o x i d a t i o n i n g a s - c o o l e d r e a c t o r c i r c u i t s has a l s o been investigated. AES has b e e n u s e d t o f o l l o w t h e CC o x i d a t i o n o f a chromium s t e e l and some p u r e m e t a l s . (12) The d e v e l o p m e n t o f i m p r o v e d s t r u c t u r a l m a t e r i a l s f o r r e a c t o r components has sometimes r e l i e d on t h e g r o w t h o f t h i n o x i d e f i l m s to p a s s i v a t e t h e s u r f a c e and t h e s e c a n be m o n i t o r e d by s e v e r a l surface techniques. The n a t u r e o f p r o t e c t i v e f i l m s grown on n u c l e a r b o i l e r a l l o y d u r i n g gas p h a s e o x i d a t i o n has b e e n s t u d i e d u s i n g SIMS.(13) Hydrogen e m b r i t t l e m e n t , p a r t i c u l a r l y of z i r c o n ium a l l o y s , i s a m a j o r c o n c e r n b e c a u s e o f t h e i n c r e a s e d s u s c e p t i b i l i t y to d e l a y e d f a i l u r e o f t h e h y d r i d e s . Surface a n a l y s i s of z i r c o n i u m h y d r i d e s u s i n g SIMS has b e e n shown t o be r e l a t i v e l y q u a n t i t a t i v e and has a l l o w e d t h e d i s t r i b u t i o n o f h y d r o g e n t o be m o n i t o r e d on a +5 4m s c a l e , ( l ) AES h a s b e e n u s e d t o r e l a t e g r a i n b o u n d a r y c h e m i s t r y t o f r a c t u r e b e h a v i o r o f i r o n and n i c k e l alloys. ( R e s e a r c h d i r e c t e d t o new methods o f u r a n i u m / p l u t o n i u m / t h o r i u m f u e l p r o d u c t i o n has b e n e f i t t e d from s u r f a c e a n a l y s i s . The a i r o x i d a t i o n o f p l u t o n i u m m e t a l has b e e n s t u d i e d by X P S . ( * ' Res e a r c h i n t o s o l - g e l p r o d u c t i o n o f UCL-ThC f u e l p e l l e t s has used XPS t o i d e n t i f y UO c o m p l e x e s o f d i f f e r i n g s t i o c h i o m e t r i e s w h i c h are recovered d u r i n g c e n t r i f u g a t i o n . ' The c h e m i c a l p r o c e s s e s i n v o l v e d i n c l e a n i n g of z i r c o n i u m - n i o b i u m f u e l c l a d d i n g has been investigated using X P S . ( ) D i s c o l o r a t i o n o f t h e s u r f a c e was a s s o c i a t e d w i t h N b O p r o d u c t which r e s u l t e d from the h y d r o l y s i s of a n i o b i u m f l u o r i d e . A E S ( 1 9 ) and SIMS(20) f o r s u r f a c e analysis of h i g h l y r a d i o a c t i v e f u e l have been d e s c r i b e d r e c e n t l y . Irradia t e d High Temperature R a c t o r f u e l p a r t i c l e s have been a n a l y z e d by X P S , w i t h o u t r e c o u r s e t o a h i g h l y - s h i e l d e d f a c i l i t y . R e c e n t l y begun r e a c t o r s a f e t y s t u d i e s w i l l r e q u i r e s u r f a c e s t u d i e s to d e t e r m i n e the n a t u r e of the r e a c t i o n p r o d u c t s fission 1 5 )


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g a s e s , s u c h as i o d i d e s , w i t h c o n t a i n m e n t s u r f a c e s . Also, during p o s s i b l e thermal excursions i n a r e a c t o r , chemical reactions w i t h i n the f u e l elements themselves a r e of g r e a t i m p o r t a n c e — p a r t i c u l a r l y those i n v o l v i n g interphase r e l a t i o n s h i p s . Within z i r c o n ium a l l o y c l a d d i n g , t h e l o c a l o x y g e n c o n c e n t r a t i o n s h a v e b e e n i n v e s t i g a t e d by A E S , ( ' f o l l o w i n g thermal c y c l i n g of the c l a d d i n g t o r e p r e s e n t a c c i d e n t c o n d i t i o n s . T h i s work h a s shown t h a t and p h a s e s o f z i r c o n i u m c a n be d i s t i n g u i s h e d on a m i c r o n l a t e r a l s c a l e , b a s e d on t h e m e a s u r e o f l o c a l o x y g e n c o n c e n t r a t i o n . In t h e c h e m i c a l r e p r o c e s s i n g o f s p e n t r e a c t o r f u e l , t h e r e a r e a number o f p o s s i b l e a p p l i c a t i o n s o f s u r f a c e a n a l y s i s techniques. Q u i t e r e c e n t l y - XPS s t u d i e s o f d i s s o l u t i o n mechanisms o f UC fuel have begun. Studies i n support of s u r f a c e p r o t e c t i o n of d i s s o l u t i o n v e s s e l and o f f - g a s h a n d l i n g s y s t e m s h a v e r e q u i r e d e x t e n s i v e work u s i n g A E S .


2

T h i s p r e s e n t p a p e r d i s c u s s e s i n more d e t a i l t h r e e separate n u c l e a r - r e l a t e d s t u d i e s where s u r f a c e a n a l y s i s has b e e n u s e d e x tensively: b o r o s i l i c a t e glass leaching, surface chloride conta m i n a t i o n , and gas p h a s e o x i d a t i o n o f some n i c k e l a l l o y s . A n a l y s i s of B o r o s i l i c a t e G l a s s L e a c h i n g U s i n g Secondary Ion Mass S p e c t r o m e t r y (SIMS) T h i s s t u d y has i n v o l v e d the r e a c t i o n of a s i m p l e sodium b o r o s i l i c a t e ' g l a s s w i t h w a t e r a t room t e m p e r a t u r e . This followed p r e v i o u s SIMS i n v e s t i g a t i o n s o f a much more c o m p l e x g l a s s c o n t a i n i n g elements s i m u l a t i n g the composition of a h i g h l e v e l n u c l e a r waste. (A) Some t y p i c a l SIMS d e p t h p r o f i l e s f o r some e l e m e n t s i n t h i s s i m u l a t e d w a s t e g l a s s a r e shown i n F i g u r e 1. P r o f i l e s shown f o l l o w e d a q u e o u s l e a c h i n g a t 2 5 ° C f o r p e r i o d s o f 2d and 5 0 d . An important b e n e f i t of such p r o f i l e s i s the c a p a b i l i t y f o r f o l l o w i n g c o n c e n t r a t i o n changes o f m i n o r , but i m p o r t a n t elements such as c e s i u m and s t r o n t i u m ( t y p i c a l l y 1 0 0 - 5 0 0 i t g / g i n t h e b u l k p h a s e ) . The shape o f t h e v e r y r e p r o d u c i b l e b o r o n e l e m e n t a l profiles s u g g e s t e d a d i f f u s i o n - r e l a t e d phenomenon m i g h t be r e s p o n s i b l e f o r the c o n c e n t r a t i o n change. This present paper r e p o r t s f u r t h e r i n v e s t i g a t i o n of the b o r o n c o n c e n t r a t i o n p r o f i l e s at a v e r y e a r l y stage i n the w a t e r - g l a s s r e a c t i o n . F o r t h i s p u r p o s e , a much s i m p l e r g l a s s f o r m u l a t i o n was u s e d : 1:1:4 :Na 0jSi0 , contain 2

ing trace concentrations ( 1000 as an i n t e n s i t y r e f e r e n c e s i n c e leaching.

2

g/g of V O . The ν i o n was u s e d it was n o t n o t i c e a b l y a f f e c t e d by

F r e s h g l a s s sample s u r f a c e s were p r o d u c e d i m m e d i a t e l y p r i o r t o l e a c h i n g by f r a c t u r e . T h e s e were e x p o s e d t o s t a t i c aqueous l e a c h i n g at 2 5 ° C i n a T e f l o n v e s s e l f o r p e r i o d s of 1 minute to 3 days. A t s e v e r a l r e a c t i o n t i m e s , s a m p l e s were a l s o l e a c h e d i n an i c e - w a t e r m i x t u r e ( 0 ° C ) . B l a n k s p e c i m e n s were f r a c t u r e d a t t h e same t i m e and l e f t i n c o n t a c t w i t h t h e a m b i e n t a t m o s p h e r e . A l l s a m p l e s were a n a l y z e d w i t h a P h y s i c a l E l e c t r o n i c s I n d u s t r i e s S I M S - 3 5 0 0 s p e c t r o m e t e r u s i n g a 5 KeV A r + p r i m a r y i o n beam and a 5 KeV r a s t e r e d e l e c t r o n beam t o r e d u c e c h a r g i n g o f t h e i n s u l a t i n g glass surface.



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SPUTTER TIME (min)

Figure 1. SIMS depth profiles in a simulated nuclear waste glass. Major and minor elemental profiles are shown for fractured surfaces exposed to 25 °C aqueous leaching for 2 d (a) and 50 d (b). (Reproduced, with permission, from Ref. 4. Copyright 1980, North-Holland Publishing Co.)


349

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SURFACE ANALYSIS

In F i g u r e 2 t h e p o s i t i v e i o n i n t e n s i t i e s a r e p l o t t e d as a f u n c t i o n of time f o r s e v e r a l major elements i n the g l a s s . These d e p t h - c o m p o s i t i o n p r o f i l e s a r e c o m p a r e d f o r u n l e a c h e d and 30 m i n u t e aqueous l e a c h i n g c o n d i t i o n s . F o r each c a s e , the r e s u l t s of p r o f i l e s on two s e p a r a t e s a m p l e s have b e e n shown ( s o l i d and d a s h e d l i n e s ) , so t h a t t h e r e p r o d u c i b i l i t y o f t h e method c a n be judged. The p r o f i l e s o f t h e u n l e a c h e d g l a s s s u r f a c e showed e s s e n t i a l l y no c h a n g e i n i n t e n s i t y o f t h e s o d i u m and p o t a s s i u m i o n s as a f u n c t i o n of depth. H o w e v e r , S i and Β ion i n t e n s i t i e s were f o u n d t o be c o n s i s t e n t l y l o w e r a t t h e o u t e r s u r f a c e t h a n w i t h i n the b u l k of the g l a s s . D e p t h p r o f i l e s f o r b o t h i o n s have a s i m i l a r shape. T h i s e f f e c t i s b e l i e v e d to r e s u l t from s u r f a c e h y d r a t i o n which a l t e r s the y i e l d of i o n s from the b o r o s i l i c a t e network. Unhydrated g l a s s s u r f a c e s , i n t r o d u c e d i n t o the s p e c t r o m e t e r i m m e d i a t e l y a f t e r f r a c t u r i n g , showed l i t t l e o r no d e p r e s s i o n of e i t h e r S i o r Β s i g n a l s , and h y d r a t e c l u s t e r s , s u c h as S i ( 0 H ) + were much r e d u c e d i n i n t e n s i t y .


+

F o l l o w i n g a t h i r t y minute l e a c h i n g r e a c t i o n , the i n t e n s i t y of Na i o n s a t t h e o u t e r s u r f a c e was r e d u c e d by a f a c t o r o f t e n ; t h e s u r f a c e r e g i o n so a f f e c t e d was f o u n d t o be a l t e r e d t o a minimum d e p t h o f 2 . 0 nm ( b a s e d on a s p u t t e r i n g r a t e o f O.5 n m / m i n f o r SiO). U n l i k e t h e b o r o n and s i l i c o n b e h a v i o r , t h e d e p r e s s i o n o f s o d i u m a t t h i s p a r t i c u l a r s u r f a c e i s b e l i e v e d t o r e s u l t f r o m an a c t u a l m i g r a t i o n o f Na ions i n t o the l e a c h s o l u t i o n . A certain q u a n t i t y o f b o r o n may be l e a c h i n g c o n c u r r e n t l y , s i n c e t h e d e p t h p r o f i l e o f b o r o n no l o n g e r i s p a r a l l e l t o t h a t o f t h e S i , b u t i s r e d u c e d i n i n t e n s i t y r e l a t i v e to t h a t o b s e r v e d f o r a n o n leached sample. +

Temperature changes a r e e x p e c t e d to a f f e c t b o t h s o l i d d i s s o l u t i o n r a t e s and d i f f u s i o n c o e f f i c i e n t s d u r i n g t h e i n i t i a l s t a g e s of l e a c h i n g . In F i g u r e 3 ( a ) , t h e d e p t h p r o f i l e s o f s u r f a c e s l e a c h e d f o r 30 m i n u t e s a t 2 4 ° C and 0 ° C a r e c o m p a r e d . From a c o m p a r i s o n o f t h e a t t e n u a t i o n o f t h e b o r o n and s i l i c o n intensities at each t e m p e r a t u r e , the depth o f p e n e t r a t i o n o f s u r f a c e h y d r a t i o n was j u d g e d t o be t w i c e as g r e a t f o r a 2 5 ° C l e a c h s o l u t i o n than a 0 ° C s o l u t i o n . In a d d i t i o n , t h e s u r f a c e r e g i o n d e p l e t i o n of s o d i u m was i n t e r p r e t e d t o be s u b s t a n t i a l l y g r e a t e r i n d e p t h and m a g n i t u d e f o r t h e s a m p l e l e a c h e d a t 2 4 ° C t h a n f o r 0 ° C . In F i g u r e 3 ( b ) an a t t e m p t i s made t o d e t e r m i n e how w e l l t h e s h a p e s of t h e b o r o n d e p t h p r o f i l e s c o n f o r m t o s i m p l e F i c k i a n d i f f u s i o n model. The e r r o r f u n c t i o n p l o t s o b t a i n e d s u g g e s t t h a t a s i n g l e d i f f u s i o n - c o n t r o l l e d mechanism i s more a p p r o p r i a t e f o r t h e r e actions at 0°C than at 2 4 ° C The d i f f u s i o n - c o n t r o l l e d l i m i t i n g r e a c t i o n i s l i k e l y t h e i n w a r d movement o f h y d r o g e n o r h y d r o n i u m ion to r e a c t w i t h the b o r o s i l i c a t e n e t w o r k , p r o d u c i n g the h y d r a t i o n s p e c i e s w h i c h a r e d e t e c t e d by S I M S . ( 2 5 ) In F i g u r e r e a c t i o n times

4 , t h e c h a n g e s i n i o n i n t e n s i t y f o r two d i f f e r e n t a r e p l o t t e d f o r 0 ° C aqueous l e a c h i n g . The i o n



Figure 2. SIMS depth profiles for a sodium borosilicate glass blank sample, airexposed only (a), and sample exposed to aqueous leaching at 25°C for 30 min (b).


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Figure 3. Comparison of SIMS depth profiles of aqueous leaching of a sodium borosilicate glass, for 30 min (a). Key: , 0°C.; and , 25°C. Error function plot for boron ion intensities in a (b). Key: —. —, 0°C.; and 25°C.


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Figure 4.

SIMS depth profiles for a borosilicate glass exposed to 0°C aqueous leaching for periods of 5 ( ) and 30 ( ) min.


353

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SURFACE ANALYSIS


i n t e n s i t i e s m e a s u r e d a f t e r s p u t t e r i n g 15-20 nm i n t o t h e l e a c h e d g l a s s s u r f a c e s agree very w e l l w i t h the r e l a t i v e i o n i n t e n s i t i e s for unleached glass surface. The m a j o r c h a n g e s o b s e r v e d as t h e l e a c h i n g p e r i o d i n c r e a s e s f r o m 5 t o 30 nm i s an i n c r e a s e d d e p t h to which the apparent h y d r a t i o n o c c u r s . In a d d i t i o n , t h e r e is some e v i d e n c e t h a t , w i t h i n c r e a s e d l e a c h i n g , s o d i u m a c c u m u l a t e s w i t h i n t h e zone d i r e c t l y b e l o w t h e s o d i u m d e p l e t e d r e g i o n . I n summary, t h e s e SIMS s t u d i e s h a v e shown t h a t r e p r o d u c i b l e m e a s u r e m e n t s o f some s u r f a c e c h e m i s t r y c h a n g e s a r e p o s s i b l e f o l l o w i n g v e r y e a r l y a t t a c k of g l a s s s u r f a c e s by w a t e r . Early d e p l e t i o n s o f s o d i u m and more s u r p r i s i n g l y , b o r o n , a r e i n d i c a t e d e v e n a f t e r a few m i n u t e s o f l e a c h i n g t i m e . The a p p a r e n t e f f e c t s o f s u r f a c e h y d r a t i o n on t h e SIMS r e l a t i v e i o n y i e l d s a l s o w a r r a n t s further investigation. Reaction of

Chlorinated

H y d r o c a r b o n s w i t h N u c l e a r Component

Surfaces I t i s w e l l known t h a t c h l o r i d e i o n s i n a q u e o u s o r humid systems promote p i t t i n g c o r r o s i o n of s t a i n l e s s s t e e l surfaces. T h i s i s g e n e r a l l y b e l i e v e d to r e s u l t from the s u b s t i t u t i o n o f c h l o r i d e ions i n t o the s u r f a c e o x i d e l a t t i c e w i t h subsequent breakdown o f the p a s s i f i c a t i o n o f the u n d e r l y i n g a l l o y . The e l i m i n a t i o n o f i n o r g a n i c c h l o r i d e c o n t a m i n a t i o n from s t a i n l e s s s t e e l components u s e d i n n u c l e a r a p p l i c a t i o n s h a s b e e n a g o a l o f d e s i g n e r s f o r many y e a r s . T h e e f f e c t o f o r g a n i c - c h l o r i d e compounds o n t h e s e a l l o y s u r f a c e s i s much l e s s u n d e r s t o o d , a l t h o u g h many c h l o r i n a t e d h y d r o carbons are used i n t h e i r manufacture. F o r example, drawing f l u i d s o f t e n c o n t a i n c h l o r o c a r b o n s , as do i n s p e c t i o n c h e m i c a l s w h i c h a r e s p r a y e d o r b r u s h e d on s u r f a c e s i n a s e a r c h f o r i n c i p i ent c r a c k s . F o r a l o n g t i m e , it h a s b e e n a r g u e d b y u s e r s t h a t v o l a t i l e c h l o r o c a r b o n s would not remain l o n g i n c o n t a c t w i t h the e x p o s e d s u r f a c e , and t h a t any r e s i d u e c o u l d be removed b y r i n s i n g with another s o l v e n t . However, entrapment of c h l o r i n a t e d h y d r o carbons i n m i c r o s c o p i c f i s s u r e s or s u r f a c e features could lead to t h e i r r e t e n t i o n as a h y d r o l y z e d p r o d u c t . T h i s p r e s e n t study has u s e d s u r f a c e a n a l y s i s t o d e t e c t any c h e m i c a l c h a n g e s w h i c h o c c u r when s t a i n l e s s s t e e l s u r f a c e s a r e c o n t a c t e d w i t h a c h l o r i n a t e d hydrocarbon, trichloroethane. Coupons o f T y p e 304 s t a i n l e s s s t e e l w e r e p r e p a r e d by m e c h a n i c a l a b r a s i o n and r i n s e d w i t h m e t h a n o l . E a c h sample was a n a l y z e d by XPS p r i o r t o t r e a t m e n t t o e n s u r e t h a t no d e t e c t a b l e c a s u a l l y i n t r o d u c e d c h l o r i n e was p r e s e n t . Two s e p a r a t e s e r i e s o f l a b o r a t o r y e x p e r i m e n t s were d o n e : one s e r i e s (a) f o l l o w e d t h e e f f e c t s o f s h o r t - t e r m c o n t a c t b e t w e e n c h l o r o c a r b o n and t h e a l l o y s u r f a c e , a s e c o n d s e r i e s (b) i n v e s t i g a t e d t h e e f f e c t s o f p r o l o n g e d v a p o r and l i q u i d c o n t a c t w i t h t h e a l l o y i n a g l a s s r e f l u x e r . In s e r i e s (a) t h e c l e a n a l l o y s u r f a c e was swabbed u s i n g t r i c h l o r o e t h a n e s o a k e d t i s s u e and i m m e d i a t e l y i n s e r t e d i n t o t h e vacuum chamber o f an XPS s p e c t r o m e t e r f o r a n a l y s i s . A f t e r a n a l y s i s , t h e same c o u p o n was e x p o s e d t o t h e a t m o s p h e r e f o r p e r i o d s o f 72 and 336 h o u r s


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(14 d a y s ) . A f t e r e a c h e x p o s u r e , an i d e n t i c a l s u r f a c e r e g i o n o f t h e c o u p o n was a n a l y z e d by X P S . I n s e r i e s (b) i n d i v i d u a l c o u p o n s were s u s p e n d e d i n t r i c h l o r e t h a n e l i q u i d a t 2 5 ° C and 6 5 ° C f o r p e r i o d s up t o 60 h o u r s . T h e c h l o r o c a r b o n l i q u i d was c o n t a i n e d i n a r e f l u x i n g c o l u m n and a d d i t i o n a l c o u p o n s w e r e s u s p e n d e d i n t h e v a p o r i n a manner e n s u r i n g good d e g r e a s i n g a c t i o n . Following e x p o s u r e , a l l samples were l e f t i n the l a b o r a t o r y atmosphere f o r a p p r o x i m a t e l y 1500 h o u r s (2 m o n t h s ) . The s a m p l e s were t h e n a n a l y zed b y XPS a n d / o r by S c a n n i n g A u g e r M i c r o s c o p y (SAM). S t a i n l e s s s t e e l s u r f a c e s swabbed w i t h t r i c h l o e t h a n e immedia t e l y b e f o r e i n s e r t i o n i n t h e XPS s p e c t r o m e t e r , consistently showed e v i d e n c e o f c h l o r i d e r e t e n t i o n i n t h e i r C l ( 2 n ) s p e c t r a , e v e n a f t e r e x p o s u r e t o a s p e c t r o m e t e r vacuum o f 10 ' P a f o r 24 hours at 3 4 - 4 0 ° C . F i g u r e 5 ( a ) shows s u c h a s p e c t r u m . From t h e C l ( 2 p ) s p e c t r a l e n v e l o p e , two s e t s o f CI (2p 3 / 2 - 1 / 2 ) d o u b l e t s were d e r i v e d by d e c o n v o l u t i o n . The more i n t e n s e d o u b l e t "1" i s a s s i g n e d to o r g a n i c a l l y - b o u n d c h l o r i n e , b e i n g c l o s e i n e n e r g y t o c h l o r i n e bound i n some a l i p h a t i c h y d r o c a r b o n s . The C l ( 2 p 3 / 2 ) l i n e l a b e l l e d "2" c o r r e s p o n d s c l o s e l y t o t h e b i n d i n g e n e r g i e s o b s e r v e d f o r i o n i c m e t a l c h l o r i d e s s u c h as i n F e C l ~ and F e C l ~ . E x p o s u r e o f t h e same a r e a o f t h e a l l o y s u r f a c e t o t h e a t m o s p h e r e f o r 72 h o u r s r e s u l t e d i n a l a r g e r e l a t i v e i n c r e a s e i n t h e amount of i o n i c c h l o r i d e i n t h e s p e c t r u m ( F i g u r e 5 ( b ) ) , a l t h o u g h t h e t o t a l q u a n t i t y of c h l o r i n e r e l a t i v e to i r o n decreased somewhat (Cl/Fe = O.04). T h u s , c h e m i c a l a l t e r a t i o n of the s u r f a c e c h l o r i d e i s e v i d e n t d u r i n g ambient e x p o s u r e . L o n g e r - t e r m exposures of the a l l o y to t r i c h l o e t h a n e v a p o r and l i q u i d were made i n a g l a s s r e f l u x i n g c o l u m n . Some s p e c i m e n s e x p o s e d f o r 50 h o u r s a t 2 5 ° C were a n a l y z e d by XPS i m m e d i a t e l y a f t e r w a r d s , and some were l e f t i n t h e l a b o r a t o r y f o r a f u r t h e r 1500 h o u r s (2 months) b e f o r e a n a l y s i s . In b o t h cases the s u r f a c e C / / F e r a t i o was O.08-O.10, i . e . , about t w i c e the c o n c e n t r a t i o n of c h l o r i n e i n the p r e c e d i n g s h o r t - t e r m exposure. These s u r f a c e s had v i s i b l y d a r k e n e d , i n d i c a t i n g t h e g r o w t h o f a f i l m o f significant thickness, i . e . , 1 0 - 1 0 0 nm. The CI (2p) s p e c t r u m showed t h a t a s u b s t a n t i a l p o r t i o n was b o u n d as i o n i c c h l o r i d e (Figure 5 ( c ) ) . S i g n i f i c a n t l y , the s u r f a c e oxide c o m p o s i t i o n d i f f e r e d c o n s i d e r a b l y from t h a t of specimens a n a l y z e d i m m e d i a t e l y a f t e r exposure to v a p o r . Chromium ( I I I ) o x i d e , C r O - , r a t h e r t h a n f O , was t h e d o m i n a n t o x i d e , (see F i g u r e 6 ( b ) ; . Figure 6(a) i s , f o r c o m p a r i s o n , the spectrum o f the n e a r normal s u r f a c e , t h a t o f t h e s p e c i m e n e x p o s e d b r i e f l y by s w a b b i n g w i t h t r i c h l o r ethane j u s t before a n a l y s i s . On t h e c h r o m i u m - r i c h s u r f a c e ( F i g u r e 6 ( b ) ) p r o d u c e d by c h l o r i d e c o n t a m i n a t i o n , t h e i r o n i s n o t e n t i r e l y bonded as o x i d e . The F e ( 2 p ) s p e c t r u m i n F i g u r e 7(a) d i f f e r s from t h a t f o r ~ 2°3 ê ?(b), normal surface i r o n o x i d e on t h e a l l o y . The s a t e l l i t e l i n e on t h e h i g h b i n d i n g e n e r g y s i d e o f t h e l i n e (see a r r o w ) o c c u r s a t t h e same e n e r g y as the prominent s a t e l l i t e i n the spectrum of F e C . The s u r f a c e s o f s t a i n l e s s s t e e l c o u p o n s were a l s o e x p o s e d F e

F

u

r

e

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n

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Figure 5. Three CI 2p photoelectron spectra for a 304 stainless steel surface immediately after rinsing with trichloroethane (a), the same surface after atmospheric exposure for 50 h (b), and the surface of 304 stainless steel exposed to trichloroethane vapor for 50 h and to atmosphere for 3000 h (c).


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15.

ι 725.

1 720.

1 1 1 715. 710. 705. B I N D I N G ENERGY ( EV)

1

706.

Figure 6. Two x-ray photoelectron spectra of the Fe 2p photoelectron line for a 304 stainless steel surface exposed to trichlorethane vapor for 50 h and atmosphere for 1500 h (a) and a 304 stainless steel surface as received (b).



Figure 7. Two total energy range x-ray photoelectron spectra for a 304 stainless steel surface exposed to trichlorethane vapor for 50 h and atmosphere for 1500 h (a), and a 304 stainless steel surface as received (b).


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i n a c o m m e r c i a l c h l o r o c a r b o n v a p o r d e g r e a s e r . T h e s e were a n a l y z e d s u b s e q u e n t l y b y XPSand SAM, a l o n g w i t h a p p r o p r i a t e " b l a n k " s p e c i mens, w h i c h had n o t b e e n e x p o s e d t o t h e s o l v e n t . B o t h s u r f a c e t e c h n i q u e s d e t e c t e d s m a l l c h l o r i d e c o n c e n t r a t i o n s on t h e " b l a n k " s p e c i m e n s , as s o d i u m c h l o r i d e ( C l / F e = O.02). H o w e v e r , t h e r e was a s i g n i f i c a n t l y h i g h e r c h l o r i d e l e v e l on t h e c o m m e r c i a l l y - d e greased surfaces (Cl/Fe = O.04). No s o d i u m a c c o m p a n i e d t h e c h l o r i d e on t h e s e s a m p l e s . The A u g e r d e p t h - c o m p o s i t i o n p r o f i l e s v a p o r - d e g r e a s e d s u r f a c e s and a " b l a n k " s u r f a c e a r e compared i n F i g u r e s 8 ( a ) and ( b ) . F i g u r e 8 ( b ) shows t h a t t h e s m a l l amount o f c h l o r i d e on t h e " b l a n k " s u r f a c e i s a maximum a t t h e o u t e r s u r f a c e and d r o p s t o u n d e t e c t a b l e as t h e f i l m i s p e n e t r a t e d 2 nm. By c o n t r a s t , on t h e s p e c i mens e x p o s e d t o v a p o r d e g r e a s i n g , t h e c h l o r i d e c o n c e n t r a t i o n c o n s i s t e n t l y r e a c h e d a maximum 2 t o 4 nm w i t h i n t h e f i l m . This i n c r e a s e d l e v e l o f c h l o r i n e i n t h e f i l m a p p e a r e d t o be r e l a t e d t o a d e c r e a s e i n t h e r a t i o o f i r o n t o chromium o x i d e s , p a r t i c u l a r l y a t t h e d e p t h where t h e c h l o r i n e c o n c e n t r a t i o n was a maximum. The s h o r t e r - t e r m e x p o s u r e e x p e r i m e n t s show t h a t some p o r t i o n o f t h e o r g a n i c a l l y - b o u n d c h l o r i n e , s u c h as t r i c h l o r e t h a n e o r i t s d e c o m p o s i t i o n p r o d u c t s , r e m a i n s a b s o r b e d on a 304 s t a i n l e s s s t e e l s u r f a c e , even a f t e r h e a t i n g at 3 5 - 4 0 ° C i n a h i g h vacuum. Conv e r s i o n t o an i o n i c s p e c i e s b e g i n s a f t e r a s h o r t c o n t a c t p e r i o d and c a n be d e t e c t e d u s i n g X P S . F o r m a t i o n o f t h e i o n i c c h l o r i d e i s l i k e l y t h e r e s u l t o f h y d r o l y s i s b y w a t e r a l s o a b s o r b e d on t h e s u r f a c e , and i s p e r h a p s c a t a l y z e d by t h e s u r f a c e m e t a l o x i d e s . F u r t h e r a t m o s p h e r i c e x p o s u r e up t o a few months i n c r e a s e s t h e r e l a t i v e amount o f t h e i o n i c form o f c h l o r i n e . The c o m p o s i t i o n o f t h e s u r f a c e o x i d e l a y e r was a l t e r e d , w i t h chromium o x i d e r e p l a c i n g i r o n o x i d e as t h e m a j o r s p e c i e s . T h e r e was f u r t h e r e v i d e n c e t h a t c h l o r i n e was p r e s e n t as i r o n c h l o r i d e , p e r h a p s up t o 5% o f the s u r f a c e f i l m . The c o n d i t i o n s under w h i c h o x i d a t i o n o f such surfaces o c c u r r e d are q u i t e comparable to those which c o u l d occur on s t e e l s u r f a c e s i n i n d u s t r i a l u s a g e . Surface Studies of B o i l e r Tubing O x i d a t i o n The i n i t i a l s u r f a c e c o m p o s i t i o n o f b o i l e r t u b i n g , p r i o r t o i t s i n s t a l l a t i o n w i l l h a v e a n i m p o r t a n t i m p a c t on t h e amount and t y p e o f a c t i v a t e d c o r r o s i o n p r o d u c t s i n a n aqueous r e a c t o r c o o l ant. C o n s e q u e n t l y , the type of t h e r m a l p r e - t r e a t m e n t the t u b i n g undergoes, f o r example, f o r mechanical s t r e s s r e l e a s e , w i l l affect t h e s u r f a c e o x i d e f i l m , and u l t i m a t e l y , t h e c o r r o s i o n b e h a v i o r . T h i s p a r t i c u l a r work has b e e n d i r e c t e d t o w a r d c h a r a c t e r i z a t i o n o f s u r f a c e o x i d e f i l m s w h i c h f o r m on I n c o n e l 600 ( n o m i n a l c o m p o s i t i o n : 77% N i , 16% C r , 7% F e , — a t r a d e n a m e o f I n c o M e t a l s L t d . , T o r o n t o , C a n a d a ) and I n c o l o y 800 ( n o m i n a l c o m p o s i t i o n : 31% N i , 19% C r , 48% Fe 2% o t h e r , — a tradename o f Inco M e t a l s L t d . , T o r o n t o , Canada) h e a t e d t o t e m p e r a t u r e s o f 5 0 0 - 6 0 0 ° C f o r p e r i o d s o f up t o 1 m i n u t e in flowing argon. These a r e c o n d i t i o n s e q u i v a l e n t to t h o s e e x p e r i e n c e d by CANDU(CANadian D e u t e r i u m U r a n i u m ) r a c t o r b o i l e r h a i r p i n s d u r i n g in s i t u s t r e s s r e l i e f .



360

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S P U T T E R TIME (min)

Figure 8. Two depth composition profiles obtained by AES: a 304 stainless steel surface exposed to commercial vapor degreasing, then exposed to atmosphere for 1500 h (a), and a stainless steel surface as received (b). Key: Ο (Xl); - -Μ- - , Cr (X2); - Ο - Cl (χ10); and -Χ-, Fe (χΐ).


15.


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361

S a m p l e s o f I n c o n e l 600 and I n c o l o y 800 c o u p o n s were e x p o s e d h e a t i n g i n a f l o w c e l l f o r p e r i o d s up t o 60 s e c o n d s a t 5 5 0 - 5 5 0 ° The r e a c t i v e gas u s e d was a r g o n c o n t a i n i n g O.01% o x y g e n .

XPS d e p t h p r o f i l e s a r e p a r t i c u l a r l y u s e f u l f o r f o l l o w i n g t h e e v o l u t i o n o f f i l m c o m p o s i t i o n , s i n c e d i f f e r e n t o x i d e and m e t a l p h a s e s c a n o f t e n be d i s t i n g u i s h e d . ( 7 ) ' I n F i g u r e 9 ( a ) - ( d ) , XPS d e p t h p r o f i l e s a r e shown f o r f i l m s grown on an a b r a d e d I n c o n e l 600 s u r f a c e f o l l o w i n g e x p o s u r e s o f 1 m i n u t e ; 2 m i n u t e s , 5 m i n u t e s , and 60 m i n u t e s a t 5 0 0 ° C . The c o n c e n t r a t i o n and c o m p o s i t i o n o f the main a l l o y c o n s t i t u e n t s : c h r o m i u m , n i c k e l and i r o n a r e p l o t t e d c u m u l a t i v e l y s h o w i n g b o t h m e t a l l i c and o x i d e c o n c e n t r a t i o n s as a f u n c t i o n o f d e p t h i n t o t h e o x i d e f i l m . Thus, the r e l a t i v e o x i d e phase a r e a s s h o u l d c o r r e s p o n d r o u g h l y t o the t o t a l amounts o f t h e s e o x i d e s p r e s e n t . T h r o u g h o u t t h e f i r s t 60 m i n u t e s , t h e o x i d a t i o n p r o c e s s i s d o m i n a t e d b y t h e o u t w a r d movement o f c h r o m i u m and i t s p r e f e r e n t i a l o x i d a t i o n . I n i t i a l l y , this process v i r t u a l l y prevents s i g n i f i c a n t oxidation of n i c k e l ; e v e n t u a l l y t h e r a t e o f r e p l e n i s h m e n t o f c h r o m i u m i o n i s s l o w e d by the growing c o m p l e x i t y o f the f i l m and the n i c k e l phase n e a r the s u r f a c e becomes o x i d i z e d . Iron also exhibits strong tendencies to m i g r a t e to the o u t e r s u r f a c e , which i s s u b s e q u e n t l y restricted by t h e t h i c k e n i n g o x i d e f i l m . A f t e r 1 minute of o x i d a t i o n the s u r f a c e f i l m c o m p o s i t i o n c h r o m i u m and i r o n o x i d e s , i s significantl y l e s s complex t h a n at l o n g e r o x i d a t i o n t i m e s . In t h e c a s e o f I n c o l o y 800 o x i d a t i o n , c h r o m i u m a n d i r o n s u r f a c e — e n r i c h e d o x i d e s were f o u n d i n e q u i v a l e n t X P S d e p t h p r o f i l e s ' s u r p r i s i n g l y l a r g e c o n c e n t r a t i o n s o f t h e m i n o r 01%) m a t r i x e l e m e n t s , t i t a n i u m a n d manganese w e r e however a l s o d e t e c t e d . Figure 10 shows t h e e n r i c h m e n t o f t i t a n i u m e l e m e n t s a t t h e o u t e r - s u r f a c e o f t h e 5 5 0 ° C o x i d i z e d a l l o y , as w e l l as p r o f i l e s o f t h e m a j o r matrix elements. The m o b i l i t y o f b o t h t i t a n i u m and manganese at t h i s temperature i s c o n s i d e r a b l y h i g h e r than f o r the major elements. O x i d a t i o n a t 4 5 0 ° C a l s o r e s u l t e d i n manganese e n r i c h ment i n t h e s u r f a c e o x i d e l a y e r , b u t , i n t h i s c a s e , no t i t a n i u m was d e t e c t e d . In the s t u d y of complex o x i d e f i l m s , the d e t e r m i n a t i o n o f p h a s e d i s t r i b u t i o n becomes o f p r i m e i m p o r t a n c e . In these c a s e s , e l e m e n t d i s t r i b u t i o n s a l o n g one d i r e c t i o n on t h e s u r f a c e a r e particularly useful. F i g u r e 11 shows c h r o m i u m , manganese and titanium distributions. Manganese and t i t a n i u m d i s t r i b u t i o n s a r e h i g h l y l o c a l i z e d and p r o b a b l y a f f e c t e d by t h e g r a i n b o u n d a r y i n t e r s e c t i o n s w i t h the s u r f a c e . The d i s t r i b u t i o n o f t i t a n i u m i s , moreover, a s t r o n g f u n c t i o n of the temperature which is a l t e r e d w i t h d i s t a n c e a l o n g t h e s u r f a c e b e c a u s e o f t h e f l o w o f gas i n one direction. The s t r o n g t e m p e r a t u r e d e p e n d e n c e o f t i t a n i u m may, i n f a c t , be u s e f u l as a n i n d i c a t o r o f t h e t e m p e r a t u r e h i s t o r y o f the s u r f a c e . Conclusions The e x a m p l e s d e s c r i b e d a r e t h o s e o f work p r e s e n t l y i n p r o g r e s s w h i c h w i l l be r e p o r t e d i n more d e t a i l a t a l a t e r d a t e .


362


SURFACE ANALYSIS

Figure 9.

XPS depth composition of an Inconel 600 alloy surface exposed to 550°C air oxidation-



Figure 10.

A ES depth composition profile of an Incoloy 800 alloy surface oxidized at 550°C for 1 min. Air heated to 800°C for 10 s.


CO

3-

Ci «—ι

s

S'

f

CO

M

*J

Kj

Η

3

ο

I—*


Figure 11.

A ES line scan of element distributions on an Incoloy 550 surface oxidized at 600 °C for 1 min. Key: , Cr;..., Mn (X3); and , Ti (χ3).


>

>

w

Ο

>

d

OS

15.

McINTYRE

Surface Analysis

in the Nuclear

Industry

365

B e c a u s e o f t h e a p p l i e d n a t u r e o f much o f t h e w o r k i n t h e n u c l e a r power i n d u s t r y , t h e r e a r e many good e x a m p l e s o f s u r f a c e a n a l y s i s w h i c h w i l l u n f o r t u n a t e l y , n e v e r a p p e a r i n t h e open l i t e r a t u r e . I t i s e n t i r e l y l i k e l y t h a t many s t u d i e s s i m i l a r t o t h o s e r e p o r t e d h e r e have been u n d e r t a k e n i n l a b o r a t o r i e s o t h e r t h a n t h o s e f a m i l iar to the a u t h o r . I n any c a s e , t h e r e a r e s t i l l many c h a l l e n g i n g research p r o j e c t s w i t h i n the i n d u s t r y for a surface s c i e n t i s t with a f e r t i l e imagination.


A c k n o w l e d gement The a u t h o r a c k n o w l e d g e s t h e e x p e r i m e n t a l a s s i s t a n c e o f F . W . S t a n c h e l l and t h e a d v i c e and e n c o u r a g e m e n t o f R . B . S t e w a r t , both of W h i t e s h e l l N u c l e a r Research E s t a b l i s h m e n t , Pinawa, Canada.

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B.W. Veal, D.J. Lam, A.P. Paulikas, and D. P. Karim, Nucl. Technol., (1980) 51, 136. L.R. Pederson, M.T. Thomas, and G. L. McVay, J. Vac. S c i . Technol. (1981) 18, 732. D.E. Clark and Ε. Lue Yen-Bower, Surface Science (1980) 100, 71. N. S. McIntyre, B.F. P h i l l i p s , and G. G. Strathdee, Surface Science (1980), 100, 71. P.C. Fung, G.W. Bird, N.S. McIntyre, G.G. Sanipelli, and V. J . Lopata Nucl. Technol. (1980), 51. 188. Z. Haq., G.M. Bancroft, W.S. Fyfe, G. Bird, and V. J . Lopata Environmental Sc. Technol. (1980) 14, 1106. N.S. McIntyre, D. G. Zetaruk, and D. Owen, J. Electrochem.Soc (1979) 126, 750. N.S. McIntyre, D.G. Zetaruk, and E.V. Murphy, (1979) 2. 151 P.H. Tewari and N.S. McIntyre, Prog. Chem. Eng.(1975) 71,134 D.W. Shoesmith and N.S. McIntyre, WNRE, unpublished results. G.C. Allen, I.T. Brown, and R.K. Wild, J. Nucl. Mater.(1977) 68, 179. G.C. Allen, I.T. Brown, and R.K. Wild, Oxid. Met.(1978)12,83. H.F. Bittner, J.T. B e l l , J.D. Redman,W.H. Christie and R.E. Eby, Met. Trans.(AIME)(1980) 11Α, 783. C.D. Cann, K. Nuttal, V.R. Deline, and N.S. McIntyre, abstract, Microscopal Society of Canada, Montreal(1981). S.M. Bruemmer, R.H. Jones, M.T. Thomas, and D.R. Baer, Scripta Met. (1980) 14, 137. G.F. Larson, J. Vac. Sci. Technol.(1979) 17, 000. N.S. McIntyre and P.H. Tewari, WNRE, unpublished results. N.S. McIntyre, WNRE, unpublished results. M.W. Urie, N.F. Panayotou, and J.E. Robinson, Hanford Engineering Development Laboratory Report, (1980)HEDL-SA-2027 G. Bart, T. Aerne, U. Flukiger, and Ε. Sprunger, EIR (Switzerland) Report No. 390 (1980) G.C. Allen, P.M. Tucker, and R.K. Wild, J. Nucl. Mater.(1978) 71, 345


366

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H. Schneider, Mikrochimica Acta, (1979) Suppl. 8, 149. N.S. McIntyre, S. Sunder, D.W. Shoesmith, and F.W. Stanchell, J. Vac. Sci. Technol. (1981) 18, 714. S.P. Clough and T.R. Pinchback, J. Materials for Eng.Systs. (1979) 1, 55 E.H. Doremus in Treatise on Materials Science and Technology, (Academic Press, N.Y, 1979) Vol 17, M. Tornozawa and R.H. Doremus, Eds. C.D. Wagner, W.M. Riggs, L.E. Davis, J.F. Moulder, and G.E. Muilenburg, Handbook of X-Ray Photoelectron Spectroscopy, (1979) Perkin-Elmer Corporation, Eden Prairie, MN G.A. Vernon, G. Stuckey, and T.A. Carlson, Inorganic Chemistry (1976), 15, 278.

24. 25.

26.


27.

RECEIVED A p r i l 5,

1982


Industrial Applications of Surface Analysis - American Chemical Society

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