Polymer Characterization - ACS Publications - American Chemical

19 Organic Coatings Analysis by Scanning Electron Microscopy and Energy Dispersive x-Ray Analysis

Downloaded by UNIV OF CALIFORNIA SAN DIEGO on April 2, 2016 | http://pubs.acs.org Publication Date: June 1, 1983 | doi: 10.1021/ba-1983-0203.ch019

RICHARD M. H O L S W O R T H Glidden Coatings and Resins, Strongsville, OH 44136

The use of the scanning energy dispersive ings/substrate Examples

defects

discussed

mental analysis chemical

problems

microscope

and problems

include

the

is

such as mildew

sure panel, interior

growth

can corrosion,

coatings on metal substrates are

the

demonstrated.

morphology and

and exposed to various

tests. Miscellaneous

and

in the study of coat-

of metal pretreatments

both unexposed and

electron

x-ray analyzer

and elesubstrates,

environments

coatings/substrate on an exterior

expo-

and defects in clear shown.

S C A N N I N G E L E C T R O N M I C R O S C O P Y ( S E M ) w a s f i r s t u s e d b y u s to s t u d y the surface of p a i n t f i l m s a n d substrates i n 1962. T h i s w o r k w a s p e r f o r m e d at t h e P u l p a n d P a p e r R e s e a r c h I n s t i t u t e o f C a n a d a , at t h a t time, one of the few locations w h e r e S E M e q u i p m e n t was available. Pigment volume concentration ladders and pigmentation were studied. Later, untreated a n d b o n d e r i z e d steel panels a n d electrocoated panels w e r e s t u d i e d . O n e of the first p u b l i c a t i o n s c o n c e r n i n g S E M i n v e s t i g a t i o n o f coatings a p p e a r e d i n 1967 (I). T h i s e x c e l l e n t w o r k

demon-

strated the usefulness of S E M i n coatings analysis a n d characterization. A symposium on " S c a n n i n g E l e c t r o n Microscopy of Polymers a n d C o a t i n g s " (2) w a s h e l d i n T o r o n t o , O n t a r i o , i n 1 9 7 0 u n d e r s p o n s o r s h i p of the C h e m i c a l Institute of C a n a d a a n d the A m e r i c a n C h e m i c a l Society. S i n c e that t i m e , m a n y articles have b e e n p u b l i s h e d c o n c e r n i n g either i n w h o l e o r i n p a r t S E M a n a l y s i s o f c o a t i n g s (3,4). T h e c o a t i n g s s e c t i o n o f Analytical

Chemistry's

" A p p l i c a t i o n R e v i e w s 1 9 7 9 " (5) l i s t e d 4 3

r e f e r e n c e s to t h e u s e o f m i c r o s c o p y , 2 7 r e f e r e n c e s t o t h e u s e o f s u r f a c e a n a l y s i s , a n d 18 r e f e r e n c e s to t h e u s e o f x - r a y s i n t h e a n a l y s i s a n d characterization of coatings. T h e r e have, of course, b e e n m a n y a d d i tional publications i n this area i n recent years. 0065-2393/83/0203-0363$06.00/0 © 1983 A m e r i c a n C h e m i c a l Society

Craver; Polymer Characterization Advances in Chemistry; American Chemical Society: Washington, DC, 1983.

364

POLYMER CHARACTERIZATION


T h e use of S E M has i n c r e a s e d d r a m a t i c a l l y i n the past several years, not only i n the coatings industry, but other surface-oriented d i s c i p l i n e s as w e l l . P r o b a b l y t h e m o s t s i g n i f i c a n t r e a s o n for t h i s i s t h e r e l a t i v e l y l o w p r i c e o f S E M t o d a y , c o m p a r e d to t h e c o s t s e v e r a l y e a r s a g o . S p e c i a l t y S E M s t h a t g i v e g o o d r e s o l u t i o n at l o w a n d i n t e r m e d i a t e magnification ranges have b e e n c o m m e r c i a l i z e d a n d , thereby, put S E M w i t h i n the r e a c h of m a n y i n d u s t r i a l labs. S u c h a specialty S E M is t h e M I N I - S E M - I I (6); i t has m a d e t h e S E M n o t o n l y a r e s e a r c h t o o l at t h e D w i g h t P . J o y c e R e s e a r c h C e n t e r , b u t a t o o l for r o u t i n e a n a l y s i s and problem solving.

Experimental T h e S E M used i n our lab is a M I N I - S E M M o d e l II (International S c i e n tific Instruments, Inc.) w i t h a 16-step magnification range of 3 0 x - 4 0 , 0 0 0 x and resolution of 250 A . T h e accelerating voltage is fixed at 15 k V . T h e samples are coated i n an A k a s h i v a c u u m evaporator w i t h p a l l a d i u m - g o l d (40—60) or carbon. A K E V E X 5100 x-ray energy spectrometer is used for the analysis of heavy elements found on surfaces, substrates, a n d i n organic coatings.

Results and

Discussion

P i g m e n t V o l u m e Concentration ( P V C ) Ladders. O n e of the e a r l y s t u d i e s u t i l i z i n g S E M w a s to o b s e r v e t h e m o r p h o l o g i c a l c h a n g e s t h a t o c c u r i n a p a i n t f i l m as t h e p i g m e n t v o l u m e c o n c e n t r a t i o n ( P V C ) is i n c r e a s e d t h r o u g h t h e c r i t i c a l p i g m e n t v o l u m e concentration ( C P V C ) . M a n y of the physical and mechanical properties of paint f i l m s s u c h as t e n s i l e s t r e n g t h , e l o n g a t i o n , a n d m o i s t u r e p e r m e a b i l i t y c h a n g e d r a m a t i c a l l y at t h e C P V C . T h e C P V C w a s d e f i n e d (7) as t h e P V C at w h i c h t h e b i n d e r o r r e s i n j u s t f i l l s t h e v o i d s b e t w e e n t h e p a c k e d p i g m e n t particles. W h e n the P V C lies b e l o w the C P V C , the f i l m is c o m p o s e d o f p i g m e n t d i s p e r s e d i n a c o n t i n u o u s r e s i n phase. A b o v e the C P V C there is i n s u f f i c i e n t b i n d e r to f i l l the spaces b e t w e e n the p a c k e d p i g m e n t p a r t i c l e s . T h e r e s u l t is a v o i d - f i l l e d f i l m . It w a s anticipated that this p h e n o m e n o n c o u l d be s t u d i e d b y S E M . S o m e r e s u l t s o f t h i s s t u d y are s h o w n i n F i g u r e s 1 - 4 . F i g u r e 1 at 7 7 0 x m a g n i f i c a t i o n s h o w s the surface of a 30 P V C latex paint. T h e surface a p p e a r s to b e b i n d e r r i c h i n t h i s c a s e . F i g u r e 2 at 7 5 0 x m a g n i f i c a t i o n s h o w s t h e s u r f a c e o f a 6 0 P V C l a t e x p a i n t . T h e s u r f a c e a p p e a r s to b e v e r y porous a n d b i n d e r d e f i c i e n t i n this case. T h e latex p a i n t is m o s t l i k e l y a b o v e t h e C P V C o r t h e p o i n t o f o p t i m u m p i g m e n t l o a d i n g to m a i n t a i n an o p t i m u m balance of properties. F i g u r e 3 shows the surf a c e o f a 5 0 P V C l a t e x p a i n t at 5 0 0 x m a g n i f i c a t i o n . T h e s u r f a c e l o o k s v e r y s i m i l a r to t h a t o f F i g u r e 2. F i g u r e 4 s h o w s t h i s p a i n t s u r f a c e at 25,000x magnification. T h e smooth b i n d e r matrix can be seen along w i t h s e v e r a l v o i d s . T h e p i g m e n t p a r t i c l e s t h a t are s e e n r e a d i l y are most likely single a n d agglomerated particles of T i 0 . 2



19.

HOLSWORTH

Organic

Figure

Coating

365

Analysis

1. 30 PVC Latex paint (770 x).

Figure 2. 60 PVC Latex paint

(750x).



366


Figure 3. 50 PVC Latex paint (500 x).

Figure 4. 50 PVC Latex paint (25,000 x).



19.

HOLSWORTH

Organic

Coating

367

Analysis

M i l d e w Defacement. D u r i n g a routine evaluation of exposure p a n e l s , a p a n e l f r o m t h e e x p o s u r e f e n c e a p p e a r e d to h a v e a v e r y h e a v y d i r t p i c k u p . T h e r e w e r e t i n y b l a c k spots o n t h e s u r f a c e t h a t a p p a r e n t l y d i d n o t w a s h off. T h e b l a c k spots d i d a n d d i d n o t b e h a v e l i k e d i r t , a n d u p o n visual observation, they d i d not look like m i l d e w . T h e S E M p h o t o m i c r o g r a p h at 4 0 0 X m a g n i f i c a t i o n , F i g u r e 5, s h o w s t h e s u r f a c e o f t h e f i l m to b e b r o k e n , a n d m i l d e w g r o w i n g out onto t h e surface o f t h e c o a t i n g . F i g u r e 6, at 7 0 0 X m a g n i f i c a t i o n , s h o w s t h i s e v e n b e t t e r . T h e c o a t i n g is b e i n g p u s h e d o f f o r b r o k e n b y t h e e r u p t i o n a n d g r o w t h of the m i l d e w f r o m b e n e a t h the top coat. F i g u r e 7 is a 1300 X m a g n i f i c a t i o n o f t h e s a m e p a n e l . T h e c o a t i n g c a n b e s e e n to b e f r a c t u r e d b y t h e e r u p t i o n o f t h e m i l d e w g r o w t h . F i g u r e 8, at 7 0 0 X m a g n i f i c a t i o n , i s o f a s i m i l a r s p o t t h a t has b e e n w a s h e d f r e e o f t h e m i l d e w . F i g u r e 9 at 3000X magnification, shows residual m i l d e w w i t h i n the defect i n the p a i n t film. W h e t h e r t h e s p o r e g o t i n t o t h e p r i m e r b y w a y o f s m a l l f o a m or a i r v o i d s t h r o u g h the top coat to the substrate, or w a s o n the p l y w o o d substrate before it w a s p a i n t e d is not k n o w n . T h e m i l d e w does not s e e m to b e starting its g r o w t h o n the surface b u t r a t h e r f r o m u n d e r neath the top coat of latex paint. A l u m i n u m S i d i n g C o m p l a i n t . F i g u r e 10 i s a m i c r o g r a p h at a m a g n i f i c a t i o n o f 1 0 0 x o f a l u m i n u m s i d i n g t h a t w a s i n v e s t i g a t e d as t h e result of a complaint. T h e siding had become very dirty. H e a v y dirt

Figure 5. Mildew

growth on panel surface

(400x).



POLYMER

Figure 6. Mildew

Figure

7. Mildew

growth on panel surface

CHARACTERIZATION

(700x).

growth on panel surface (1300 x).



HOLSWORTH

Organic

Coating

Figure 8. Scrubbed

Figure 9. Scrubbed

mildew

mildew

Analysis

covered panel

(700x).

covered panel (3000 x).



370


Figure

10. Aluminum

siding complaint

(lOOx).

p i c k u p a n d s m a l l p i m p l e s or b u m p s h a d d e v e l o p e d across the surface of the panel. T h i s micrograph shows several of these little b u m p s . A r o u n d the b u m p s c a n b e s e e n a p p a r e n t b o u n d a r y l i n e s that are r e a l l y d e f e c t s i n t h e film r e s u l t i n g f r o m s o l v e n t e v a p o r a t i o n a n d t h e f o r m a tion of B e n a r d cells. T h i s leaves a fairly regular pattern of resin-rich areas o n t h e s u r f a c e t h a t d e g r a d e at a r a p i d r a t e . I t i s a s s u m e d t h a t t h e b o u n d a r y l i n e s t h a t c a n b e s e e n a r e , i n s o m e a r e a s , o p e n t h r o u g h to t h e m e t a l o r are v e r y t h i n s p o t s i n t h e c o a t i n g t h a t a l l o w e a s i e r p e n e t r a t i o n o f m o i s t u r e o r o t h e r c o n t a m i n a n t s t h a t c a n l e a d to c o r r o s i o n o f t h e a l u m i n u m s u b s t r a t e . F i g u r e 11 i s a c l o s e - u p o f a c r o s s - s e c t i o n o f t h e b u m p s o n t h e p a n e l at 3 5 0 x m a g n i f i c a t i o n . It s h o w s t h a t u n d e r n e a t h the r a i s e d p o r t i o n o f the coating, a crystal or salt g r o w t h f o r m a t i o n has d e v e l o p e d b e t w e e n t h e a l u m i n u m s u b s t r a t e a n d t h e c o a t i n g . T h i s area was s t u d i e d b y e n e r g y d i s p e r s i v e x-ray analysis ( E D X R A ) , a n d t h e c r y s t a l s p r o v e d to b e a l u m i n u m salts i n c l u d i n g s u l f u r a n d chlorine. C l e a r Coatings o n Reflective M e t a l Substrates. T h e inspection o f c l e a r coatings o n h i g h l y r e f l e c t i v e m e t a l substrates is a n a n n o y i n g p r o b l e m i n optical microscopy. T h e reflection of the incident light from the m e t a l o b s c u r e s the fine d e t a i l o f the surface m o r p h o l o g y that n e e d s to b e s e e n . A s t y r e n e - a c r y l i c b a s e c o a t for a q u a l i t y as r e c e i v e d p l a t e w a s o b s e r v e d u n d e r t h e o p t i c a l l i g h t m i c r o s c o p e f r o m 10 x t o 200 X magnification. T h e o n l y defects that c o u l d be s e e n w e r e occas i o n a l gas b u b b l e s t h a t h a d b e e n t r a p p e d i n t h e f i l m . T h e r e w a s n o v i s i b l e s i g n o f t h e 2 % w a x t h a t h a d b e e n a d d e d t o t h e c o a t i n g as a l u b r i cant u n d e r the optical m i c r o s c o p e . A l t h o u g h the coating passed v i s u a l i n s p e c t i o n , w h e n the m a t e r i a l w a s p l a c e d i n a c o p p e r sulfate b a t h , m e t a l l i c c o p p e r w a s f o r m e d o n the i r o n substrate b y a d i s p l a c e m e n t r e a c t i o n , i n d i c a t i n g t h a t t h e d e f e c t s i n t h e c o a t i n g are o p e n to t h e i r o n substrate. F l o w e r - l i k e c o p p e r deposits c o u l d be seen o v e r a w i d e area o f t h e p a n e l . F i g u r e 12 s h o w s o n e o f t h e c o p p e r d e p o s i t s o n t h e p a n e l s u r f a c e at 5 0 X m a g n i f i c a t i o n . M a n y o t h e r d e f e c t s o n t h e s u r f a c e o f t h e



19.

HOLSWORTH

Figure

Organic

Coating

11. Cross-section

371

Analysis

of aluminum

siding defect (350 x).

p a n e l c a n b e s e e n i n t h e m i c r o g r a p h . A r e a A o f F i g u r e 12 i s s h o w n at 6 0 0 X m a g n i f i c a t i o n i n F i g u r e 13. T h r e e t y p e s o f d e f e c t s c a n b e s e e n i n F i g u r e 1 3 ; o p e n b u b b l e s f r o m e n t r a p p e d gas b u b b l e s ( B ) , craters p r o b a b l y r e s u l t i n g from the w a x l u b r i c a n t o n the surface (C), a n d craters from insufficient flow of a b r o k e n b u b b l e (F). T h e large crater i n the c e n t e r o f F i g u r e 13 i s s h o w n at 3 0 0 0 X m a g n i f i c a t i o n i n F i g u r e 14. T h e d e f e c t s are l a b e l e d t h e s a m e as i n F i g u r e 13. T h e m a t e r i a l i n t h e b o t t o m of the large crater is p r o b a b l y r e s i d u a l w a x or other r e s i d u e from the bath. A n a l y s i s of a similar type of structure b y E D X R A s h o w e d the m a t e r i a l t o b e i r o n salts. A v e r y s m a l l c o p p e r c r y s t a l f o r m a t i o n i s s e e n i n F i g u r e 15 at 3 0 0 0 x m a g n i f i c a t i o n . T o d e t e r m i n e w h i c h t y p e o f d e f e c t w a s o p e n to t h e s u b s t r a t e a n d a l l o w e d the c o p p e r crystals to g r o w , the c o p p e r d e p o s i t w a s d i s s o l v e d w i t h nitric a c i d a n d the resulting clear area studied i n the S E M . F i g u r e 16 at 5 6 0 X m a g n i f i c a t i o n s h o w s t h e d a r k i r r e g u l a r a r e a t h a t w a s

Figure

12. Metallic

copper deposit on panel surface (50 x).



372

POLYMER

Figure

CHARACTERIZATION

13. Surface defects in clear coating (600 x).

Figure 14. Surface defects in clear coating

(3000x).



19.

HOLSWORTH

Organic

Coating

373

Analysis

Figure 15. Copper deposit on panel surface

(3000x).

Figure 16. Area of copper deposit after acid treatment (560 x).



374


Figure 17. Area of copper deposit after acid treatment (2400 x). covered by the copper, residue from the a c i d dissolution of the copp e r , a n d a gas b u b b l e d e f e c t i n t h e c e n t e r o f w h a t w a s t h e c o p p e r . F i g u r e 17 at 2 4 0 0 x m a g n i f i c a t i o n s h o w s t h e gas b u b b l e d e f e c t a n d w h a t looks l i k e a crack or split i n the bottom of the crater. T h i s c o u l d b e t h e o p e n i n g to t h e s u b s t r a t e . M e t a l Substrate Pretreatment. W h e n r u n n i n g accelerated or natu r a l i n - u s e tests o n a c o a t i n g , i t is i m p o r t a n t to k n o w t h e s u b s t r a t e b e i n g u s e d . T h e f o l l o w i n g are s e v e r a l e x a m p l e s w h e r e c o n f u s i o n d e v e l o p e d somewhere between the initial pretreatment of the panels a n d t h e a n a l y s i s o f t h e s u r f a c e . F i g u r e s 18 a n d 19 s h o w t h e t w o

Figure 18. Zinc phosphate

with calcium

rinse pretreatment

(700 x).



19.

HOLSWORTH

Organic

Coating

Analysis

375

Figure 19. Zinc phosphate without calcium rinse pretreatment

(700 x).

phosphate-treated panels i n question. Physically they appear similar. T h e z i n c p h o s p h a t e a p p e a r s as s m a l l a l m o s t m i c r o c r y s t a l s a n d as l a r g e plate-like crystals, mostly w i t h a vertical orientation. T h e sample i n F i g u r e 18 w a s t o h a v e r e c e i v e d a c a l c i u m r i n s e , w h i l e t h e s a m p l e i n F i g u r e 19 d i d n o t . T h e E D X R A s p e c t r a i n F i g u r e s 2 0 a n d 2 1 s h o w t h e p a n e l s to b e s i m i l a r i n s u r f a c e t r e a t m e n t . I n fact, b o t h s a m p l e s s h o w t h e p r e s e n c e o f c a l c i u m . I n F i g u r e s 2 2 a n d 2 3 are t h e f a m i l i a r c r y s t a l s o f z i n c p h o s p h a t e p r e t r e a t m e n t . T h e s a m p l e i n F i g u r e 2 2 w a s to h a v e received a chrome rinse, w h i l e the sample i n F i g u r e 23 r e c e i v e d no rinse. T h e spectra of these t w o samples, s h o w n i n F i g u r e s 24 a n d 25, exhibit no c h r o m i u m . O n l y zinc, phosphorus, iron, and nickel from a n i c k e l f l u o r i d e r i n s e are p r e s e n t .

Figure 20. EDXRA

spectrum

of Figure

18.



376


Figure 21. EDXRA



spectrum

pretreatment

pretreatment

of Figure

19.

with chrome rinse (700 x).

without chrome rinse

(700x).



19.

HOLSWORTH

Organic

Coating

Figure 24. EDXRA

377

Analysis

spectrum

of Figure

22.

F i g u r e s 26 a n d 27 s h o w the surface of t w o samples w i t h a c a l c i u m z i n c phosphate surface treatment. T h e E D X R A spectra i n F i g u r e s 28 a n d 2 9 s h o w t h e o v e r a l l s u r f a c e s to b e c h e m i c a l l y s i m i l a r . H o w e v e r , w h e n the surfaces o f t h e t w o s a m p l e s are c o m p a r e d , t h e test p a n e l i n F i g u r e 26 shows s m a l l crystals tightly p a c k e d o n the surface, w h i l e the plant m e t a l substrate i n F i g u r e 27 shows crystals larger t h a n i n F i g u r e 26, plus some plate-like crystals w i t h mostly vertical orientation. O f m o r e i m p o r t a n c e i s t h e o b v i o u s fact t h a t t h e c r y s t a l s a r e so l o o s e l y p a c k e d o n the surface that the m e t a l substrate is e x p o s e d . T h i s is c o n f i r m e d b y E D X R A w h i c h s h o w s o n l y i r o n to b e p r e s e n t i n t h e e x p o s e d areas ( F i g u r e s 2 8 a n d 29).

Figure 25. EDXRA

spectrum

of Figure

23.



378


Figure 26. Calcium

Figure 27. Calcium

zinc phosphate

zinc phosphate

Figure 28. EDXRA

spectrum

pretreatment

pretreatment

of Figure

(700x).

(700x).

26.



19.

HOLSWORTH

Organic

Coating

Figure 29. EDXRA

379

Analysis

spectrum

of Figure

27,

C a n C o a t i n g Substrate C o r r o s i o n . T h e u s e o f w a t e r b o r n e c o a t i n g s f o r m e t a l s u b s t r a t e s , s u c h as c a n c o a t i n g s , h a s i n c r e a s e d t h e o c c u r r e n c e o f a p r o b l e m , n o t u n i q u e to w a t e r b o r n e systems. T h i s p r o b l e m o c c u r s as a r e s u l t o f e n t r a p p e d f o a m o r p o o r f l o w o u t o f f o a m o r b u b b l e i n d u c e d defects a n d is characterized b y b l i s t e r i n g a n d corros i o n . A film d e f e c t s u c h as s e e n p r e v i o u s l y i n F i g u r e 1 7 c a n , u p o n a c c e l e r a t e d l a b t e s t i n g , p r o d u c e a n a r e a s u c h as t h a t s e e n i n F i g u r e 3 0 . T h i s S E M p h o t o m i c r o g r a p h at 2 0 0 x m a g n i f i c a t i o n s h o w s a s m a l l crater-like defect i n t h e center o f w h a t appears to b e a b l i s t e r . U n d e r t h e o p t i c a l m i c r o s c o p e t h e b l i s t e r a p p e a r e d t o b e filled, i n p a r t , w i t h a

Figure 30. Coating

defect and blister

over tin-plated

steel (200 x).



380


Figure 31. Corroded

area under blister

in Figure 30 (400 x).

rust b r o w n l i q u i d over the still s h i n y t i n plate surface. After b e i n g e x p o s e d to r o o m c o n d i t i o n s for s e v e r a l d a y s , t h e b l i s t e r w a s t a p e d off, i . e . , r e m o v e d b y a d h e s i v e t a p e . T h e r e s u l t s are s h o w n i n F i g u r e s 3 1 a n d 3 2 at 4 0 0 X m a g n i f i c a t i o n . F i g u r e 3 1 i s t h e a r e a i m m e d i a t e l y u n d e r l y i n g the b l i s t e r . T h e m e t a l substrate is c o r r o d e d t h r o u g h a l m o s t completely. E D X R A indicates iron throughout the corroded area a n d h i g h l e v e l s of p h o s p h o r u s a n d c h l o r i n e . F i g u r e 32 is the t a p e d off material that consists o f the i r o n corrosion products, the t i n plate, a n d t h e organic top coat. A m e c h a n i s m for c o r r o s i o n o f t h i s t y p e has b e e n d e s c r i b e d e l s e w h e r e (8). F i g u r e 33 shows a l i n e of e n t r a p p e d blisters or b u b b l e s i n a clear coating on t i n p l a t e d steel substrate. T h e closed a n d partially o p e n blisters s h o w e d no corrosion w i t h i n the blister, although moisture h a d p e r m e a t e d t h e film a n d w a s t r a p p e d i n s i d e t h e b u b b l e s . T h e e x p o s e d area i n the center was f i l l e d w i t h a rusty l i q u i d . T h e top was carefully r e m o v e d , i n c l u d i n g corrosion products from the center, exposing the p i t a n d a c o v e r i n g of the clear coating over most of the surface. F i g u r e 34 shows a s i m i l a r b u b b l e w i t h the top r e m o v e d , e x p o s i n g the corrosion p l u g i n the center of the b u b b l e , plus corrosion products o n the interior w a l l . A p p a r e n t l y , a defect l i k e that i n F i g u r e 30 was present i n s i d e t h e b u b b l e a n d c o r r o s i o n started after p e r m e a t i o n o f l i q u i d t h r o u g h the b u b b l e w a l l .



HOLSWORTH

Organic

Figure 32. Backside

Figure 33. Corrosion

Coating

of taped off blister

area within

381

Analysis

blister,

in Figure 30 (400 x).

corrosion

removed (50 x).



382


Figure

34. Corrosion

area within

blister

(200x).

Conclusions S E M a n d S E M / E D X R A have b e e n demonstrated to b e extremely u s e f u l tools for c h a r a c t e r i z i n g coatings, substrates, a n d interfaces a n d for o r g a n i c coatings f a i l u r e a n a l y s i s . S a m p l e p r e p a r a t i o n i s m i n i m a l c o m p a r e d w i t h t h e w e a l t h o f i n f o r m a t i o n that c a n b e o b t a i n e d b y these methods. T h e S E M is a logical extension o f the l o w p o w e r stereomicroscope available

f o r coatings a n a l y s i s , a n d t h e great d e p t h o f f i e l d

is i n v a l u a b l e for coatings

problem

analysis. T h e S E M /

E D X R A s y s t e m i s a fast, e a s y m e t h o d f o r r a p i d i d e n t i f i c a t i o n o f s m a l l inclusions o r defects, a n d for the q u i c k c o m p a r i s o n o f coatings f o r m u lations. Literature 1. 2. 3. 4. 5. 6. 7. 8.

Cited

Brooks, L . E.; Sennett, P.; Morris, H . H. J. Paint Technol. 1967, 39, 472. Princen, L . H. Appl. Polym. Symp. 1971, 16. Princen, L. H.; Baker, F. L. Paint Varn. Prod. 1971, 16, 21. Princen, L . H. Appl. Polym. Symp. 1974, 23. Anderson, D. G.; Vandeberg, T. Anal. Chem. 1979, 31, 80R. Evins, D. J.; Engle, R. J. Am. Lab. (Fairfield, Conn.) 1974, 6, 51. Asbeck, W. K.; Van Loo, M. Ind. Eng. Chem. 1949, 41, 1470. Funke, W. Prog. Org. Coat. 1981, 9, 29.

RECEIVED for review October 14, 1981. ACCEPTED March 12, 1982.


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