7 Evaluation of Coating Resins for Corrosion Protection of Steel Exposed to Dilute Sulfuric Acid 1
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Malcolm L. White and Henry Leidheiser, Jr.
2
1
Center for Surface and Coatings Research, Lehigh University, Bethlehem, PA 18015 Department of Chemistry and Center for Surface and Coatings Research, Lehigh University, Bethlehem, PA 18015
2
Three types of coatings--a vinyl ester, a polyester and four epoxies--were coated on steel and exposed to 0.1M H S O at 60°C. Measurements of corrosion potent i a l , AC conductance, tensile adhesion and weight gain were made on the coated substrates after 1000 hours of exposure, and the values were compared with the observed corrosion of the steel substrate. The best correlation of parameter values with corrosion was found with conductance. Corrosion potential did not show a consistent relationship, and weight gain and tensile adhesion showed no correlation with corrosion. It was concluded that the most important properties for coatings to be used in acid media are low permeability and resistance to degradation by acid. The vinyl ester, a bisphenol A epoxy cured with an aliphatic amine, and a novolac epoxy cured with a mixed aromatic/cycloaliphatic amine provided the best corrosion protection. The saturated polyester and a bisphenol A epoxy cured with a polyamide amine showed significant deterioration in acid and corrosion of the underlying steel. Two novolac epoxies cured with aromatic amines showed i n termediate performance. 2
4
The m e c h a n i s m f o r t h e i n i t i a l c o r r o s i o n o f s t e e l i n n e u t r a l o r a l k a l i n e s o l u t i o n s i s g e n e r a l l y a c c e p t e d as t h e o x i d a t i o n o f iron from the m e t a l l i c s t a t e to the f e r r o u s i o n : Fe -
Fe""
+
w i t h the attendant reduction r e a c t i o n d r o x i d e i o n f r o m o x y g e n and w a t e r [ 1 J : 1/20
2
+ H 0 2
+
2e"
(1)
being
2e~ -
the
formation
20H"
0097-6156/86/0322-0077S06.00/0 © 1986 American Chemical Society
In Polymeric Materials for Corrosion Control; Dickie, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1986.
of
hy-
(2)
POLYMERIC MATERIALS FOR CORROSION CONTROL
78
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A v a r i e t y o f t e c h n i q u e s has been d e v e l o p e d t o m e a s u r e t h e c o n d i t i o n o f a c o a t i n g s o t h a t some e v a l u a t i o n o f i t s p r o t e c t i v e a b i l i t y c a n be made. M a n y o f t h e s e a r e b a s e d on e l e c t r o c h e m i c a l m e a s u r e m e n t s [2]. The f o u r t e c h n i q u e s u s e d i n t h i s s t u d y a r e (1) corrosion p o t e n t i a l , ( 2 ) AC c o n d u c t a n c e , ( 3 ) t e n s i l e a d h e s i o n , and ( 4 ) w e i g h t gain. The c o r r o s i o n p o t e n t i a l i s d e t e r m i n e d by t h e p o t e n t i a l a t w h i c h t h e a n o d i c and c a t h o d i c r e a c t i o n s o c c u r a t t h e same r a t e [ 3 ] . T h e AC conductance i s a measure of the ease w i t h which charge i s t r a n s m i t ted through the coating [4]. The a d h e s i v e s t r e n g t h o f t h e c o a t i n g t o t h e s t e e l s u r f a c e i s a f f e c t e d by r e a c t i o n s o c c u r r i n g a t t h e interface. The w e i g h t g a i n o f c o a t i n g s h a s b e e n s t u d i e d by F u n k e and H a a g e n [ 5 ] who h a v e s h o w n t h a t a w e i g h t g a i n e x c e e d i n g t h a t o f a f r e e f i l m i n d i c a t e s an a c c u m u l a t i o n o f w a t e r a t t h e i n t e r f a c e
[5]. These t e c h n i q u e s are f r e q u e n t l y used to study c o r r o s i o n under c o a t i n g s i n n e u t r a l s o l u t i o n s and e n j o y s p o r a d i c s u c c e s s , d e p e n d i n g p r i m a r i l y on t h e t y p e and t h i c k n e s s o f c o a t i n g b e i n g s t u d i e d . The m e c h a n i s m o f s t e e l c o r r o s i o n i n a c i d s o l u t i o n s , h o w e v e r , is d i f f e r e n t from that in neutral s o l u t i o n s in that the reduction r e a c t i o n i s the f o r m a t i o n of hydrogen from hydrogen i o n : 2H
+
+
2e~
+
H
2
(3)
P r e v i o u s w o r k i n t h i s l a b o r a t o r y has e s t a b l i s h e d t h a t f o r e p o x y and f 1 uoropolymer c o a t i n g s exposed to d i l u t e s u l f u r i c acid, there i s movement o f a c i d t h r o u g h t h e c o a t i n g t o t h e s t e e l s u r f a c e so t h a t Equation 3 i s the predominant reduction r e a c t i o n [6]. Because of t h i s d i f f e r e n c e i n c o r r o s i o n mechanism i n a c i d s o l u t i o n , t h e u s e f u l n e s s o f t h e f o u r e v a l u a t i o n t e c h n i q u e s d i s c u s s e d above may be d i f f e r e n t t h a n i n n e u t r a l s o l u t i o n s . The p u r p o s e o f t h i s w o r k was t o e v a l u a t e t h e s e f o u r t e c h n i q u e s f o r p r e d i c t i n g t h e behavior of c o a t i n g r e s i n s in a c i d s o l u t i o n s . In a d d i t i o n , t h e a b i l i t y of several d i f f e r e n t types of c o a t i n g r e s i n s to p r o t e c t s t e e l a g a i n s t c o r r o s i o n i n a c i d s o l u t i o n was e v a l u a t e d . Experimental The f o l l o w i n g c o a t i n g r e s i n s w e r e u s e d : (1) a v i n y l e s t e r ( D e r a k a n e 4 7 0 f r o m Dow C h e m i c a l ) ; ( 2 ) a p o l y e s t e r ( A t l a c 3 8 2 - 0 5 AC f r o m ICI); and (3) f o u r e p o x y r e s i n / h a r d e n e r c o m b i n a t i o n s . The d e t a i l s o f t h e r e s i n s and h a r d e n e r s u s e d a r e s h o w n i n T a b l e I. One o f t h e e p o x y / h a r d e n e r c o m b i n a t i o n s was r e p r e s e n t e d by m a t e r i a l s f r o m t w o sources. The c o a t i n g s w e r e a p p l i e d t o o n e s i d e o f a s t e e l s u b s t r a t e by means o f a s p r a y gun f o r t h e l o w e r v i s c o s i t y c o a t i n g s , o r by d o c t o r b l a d i n g w i t h an a d j u s t a b l e G a r d n e r k n i f e f o r t h e h i g h e r viscosity materials. A c a s t i n g t e c h n i q u e was a l s o used i n w h i c h a known v o l u m e o f t h e c o a t i n g m a t e r i a l was p o u r e d i n t o a known a r e a d e f i n e d b y h e a v y t a p e a n d w a s a l l o w e d t o s p r e a d w h i l e on a l e v e l s u r f a c e .
In Polymeric Materials for Corrosion Control; Dickie, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1986.
In Polymeric Materials for Corrosion Control; Dickie, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1986.
Cobalt
Martek
Naphthanate
Ciba/Geigy
Epoxies CON/CHEM
(6%).
NOV/AR/AL
BPA/PA
NOV/AR 2
NOV/AR 1
BPA/AL
PE
Polyester ICI Americas (Atlac 382-05
AC)
VE
Designation
Vinyl Ester Dow C h e m i c a l (Derakane 470)
Supplier Resin
I.
A
Novolac
Bisphenol
A
Multifunctional Novolac
Multifunctional
Bisphenol
Bisphenol A-Fumarate P o l y e s t e r + 1% C o N a p * + DMA; 50% S t y r e n e
Cycloaliphatic/ A r o m a t i c Amine
Polyamideamine
Aromatic Amine
Aromatic Amine
Aliphatic Amine
MEKP
Cumene Hydroperoxide
Hardener
Coating Materials
Bisphenol A Vinyl E s t e r + . 1 5 % CoNap ; 36% S t y r e n e
Table
1.82:1
2.77:1
100:46
100:50
100:20
100:2
100:2
Resin: Hardener Ratio
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Cured
8-9
8 - 12
10-11
10-12
9-10
6-12
7- 9
(mils)
203-229
203-305
254-279
254-305
229-254
152-305
178-229
(my)
Thickness
80
POLYMERIC MATERIALS FOR CORROSION CONTROL
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The c o a t i n g s w e r e c u r e d i n t w o s t e p s : f i r s t , a room t e m p e r a t u r e e x p o s u r e f o r a t l e a s t f i v e h o u r s t o a l l o w any s o l v e n t p r e s e n t t o e v a p o r a t e a n d / o r t h e r e s i n t o g e l a n d , s e c o n d , an e l e v a t e d t e m p e r a t u r e c u r e . The v i n y l e s t e r , p o l y e s t e r and e p o x i e s w e r e b a k e d a t 60°C f o r 4-16 hours. The c o a t i n g t h i c k n e s s a f t e r c u r i n g was m e a sured w i t h a micrometer, s u b t r a c t i n g the substrate thickness. The t h i c k n e s s o f t h e c o a t i n g s r a n g e d f r o m 6 t o 12 m i l s ( 1 5 0 - 3 0 0 urn) and i s shown f o r each t y p e i n T a b l e I. The s u b s t r a t e s w e r e c o l d r o l l e d , l o w - c a r b o n SAE 1 0 1 0 s t e e l , 32 m i l s ( 0 . 8 mm) t h i c k (Q P a n e l s ) . T h e y w e r e s a n d b l a s t e d on b o t h s i d e s t o a 6 pm p r o f i l e w i t h s i l i c a s a n d . No f u r t h e r c l e a n i n g was d o n e . A c i r c u l a r d i s k 3 . 3 3 cm i n d i a m e t e r was p r e p a r e d f r o m a l a r g e r c o a t e d p a n e l w i t h a punch and d i e s e t . The d i s k was p l a c e d on a 1 2 5 ml widemouth screw-cap polypropylene b o t t l e , using a rubber gasket to make a t i g h t s e a l , w i t h t h e c o a t e d s i d e f a c i n g t h e i n s i d e o f t h e bottle. The d i s k and g a s k e t w e r e h e l d on t h e b o t t l e w i t h t h e c a p , f r o m w h i c h t h e c e n t r a l p o r t i o n had been r e m o v e d , so t h e back ( u n c o a t e d ) s i d e o f t h e s t e e l s u b s t r a t e was e x p o s e d . The b o t t l e was i n v e r t e d and h a l f f i l l e d w i t h 0.1 M H 0 S O 4 t h r o u g h a h o l e d r i l l e d i n the bottom of the b o t t l e in order to contact the a c i d w i t h the coating. The i n v e r t e d b o t t l e was p l a c e d i n an o v e n a t 6 0 ° C . The c o r r o s i o n p o t e n t i a l was m e a s u r e d b y p u t t i n g a s a t u r a t e d c a l o m e l e l e c t r o d e / s a l t bridge i n t o the s o l u t i o n through the hole in the b o t t o m o f t h e p l a s t i c b o t t l e and c o n t a c t i n g t h e b a c k s i d e o f t h e s u b s t r a t e t o c o m p l e t e t h e c i r c u i t as s h o w n i n F i g u r e 1. A K e i t h l e y 600A e l e c t r o m e t e r w a s u s e d f o r t h e m e a s u r e m e n t . T h e AC c o n d u c t a n c e was d e t e r m i n e d by i n s e r t i n g a c a r b o n r o d i n t o t h e s o l u t i o n and m e a s u r i n g t h e c o n d u c t a n c e a t 2 kHz f r e q u e n c y and 2 0 0 mv p o t e n t i a l w i t h an E x t e c h M o d e l 4 4 0 D i g i t a l C o n d u c t i v i t y M e t e r . The c o n d u c t a n c e v a l u e s w e r e c o n v e r t e d t o s p e c i f i c c o n d u c t i v i t y by m u l t i p l y i n g by t h e t h i c k n e s s a n d d i v i d i n g by t h e a r e a ( 5 c m ) . 2
The a d h e s i o n w a s m e a s u r e d b y f a s t e n i n g a l e a d a n c h o r o f known a r e a (2.84 cm ) t o the c o a t i n g w i t h a c y a n o a c r y l a t e adhesive (Loctite 4 1 4 ) and a f t e r c u r i n g , p u l l i n g i t o f f n o r m a l t o t h e s u r f a c e w i t h a Dillon tensile tester. The f o r c e t o r e m o v e t h e c o a t i n g was d i v i d e d by t h e a r e a o f a t t a c h m e n t t o c o n v e r t i t t o a n o r m a l i z e d t e n s i l e adhesion value. 2
The w e i g h t g a i n was m e a s u r e d by w e i g h i n g t h e c o a t e d d i s k a f t e r it was removed f r o m t h e p l a s t i c b o t t l e , f o l l o w i n g a w a t e r r i n s e and removal of surface water. The c o a t i n g and s u b s t r a t e w e r e o b s e r v e d t h r o u g h t h e h o l e i n t h e b o t t l e during the exposure to the acid. Since the coatings were transparent, i t was p o s s i b l e t o o b s e r v e any v i s i b l e corrosion o c c u r r i n g on t h e s t e e l s u b s t r a t e . The c o r r o s i o n p r o d u c t s on t h e s t e e l w e r e g r a y o r b l a c k , e x c e p t when t h e c o a t i n g b l i s t e r e d and some r u s t i n g was s e e n . As c o r r o s i o n p r o g r e s s e d d u r i n g t h e a c i d exposure, the steel surface gradually darkened from the i n i t i a l l i g h t g r a y o f t h e o r i g i n a l s a n d b l a s t e d s u r f a c e t o an a l m o s t black surface. The e x t e n t o f c o r r o s i o n was e s t i m a t e d f r o m t h e a m o u n t o f d a r k e n i n g o b s e r v e d on t h e s t e e l s u r f a c e .
In Polymeric Materials for Corrosion Control; Dickie, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1986.
Evaluation of Coating Resins
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WHITE A N D LEIDHEISER
F i g u r e 1. Technique f o r e l e c t r o c h e m i c a l measurements. Reproduced w i t h p e r m i s s i o n from R e f e r e n c e 12. Copyright 1985, National A s s o c i a t i o n of Corrosion Engineers.
In Polymeric Materials for Corrosion Control; Dickie, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1986.
82
POLYMERIC MATERIALS FOR CORROSION CONTROL
Results
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F i g u r e 2 summarizes the values o b t a i n e d f o r the f o u r measurements on t h e s e v e n c o a t i n g s a f t e r e x p o s u r e t o 0.1 M H 0 S O 4 a t 6 0 ° C f o r 1 0 0 0 hours. The o r d i n a t e s h o w s t h e v a l u e s m e a s u r e c f f o r e a c h o f t h e f o u r t e c h n i q u e s , and t h e a b c i s s a r e p r e s e n t s t h e amount o f c o r r o s i o n o b s e r v e d on t h e s t e e l u n d e r e a c h o f t h e c o a t i n g s a f t e r t h e a c i d exposure, w i t h the amount of observed c o r r o s i o n d e c r e a s i n g from l e f t to right. The c o r r o s i o n p o t e n t i a l s s h o w a g e n e r a l t r e n d o f i n c r e a s i n g v a l u e s with d e c r e a s i n g s u b s t r a t e c o r r o s i o n , with the exception of the p o l y e s t e r a n d t h e n o v o l a c e p o x y c u r e d w i t h an a r o m a t i c / c y c l o a l i p h a t i c amine. T h e s p e c i f i c AC c o n d u c t i v i t y v a l u e s s h o w a g e n e r a l l y d e c r e a s i n g v a l u e w i t h d e c r e a s i n g s u b s t r a t e c o r r o s i o n , w i t h one e x c e p t i o n : the n o v o l a c e p o x y c u r e d w i t h an a r o m a t i c / c y c l o a l i p h a t i c a m i n e . This is one o f t h e c o a t i n g s t h a t a l s o d i d not f i t i n t o t h e t r e n d f o r t h e corrosion potential values. The t e n s i l e a d h e s i o n v a l u e s show no c o r r e l a t i o n w i t h t h e e x t e n t o f c o r r o s i o n ; the b i s p h e n o l A epoxy cured w i t h a p o l y a m i d e amine showed b l i s t e r i n g , w h i c h r e p r e s e n t s a complete l o s s of adhesion. The p o l y e s t e r s h o w e d c o h e s i v e f a i l u r e a t l e s s t h a n 1000 h o u r s o f e x p o s u r e , so a t r u e a d h e s i o n v a l u e c o u l d n o t be d e t e r m i n e d . The o t h e r e p o x i e s a n d t h e v i n y l e s t e r a l l had v a l u e s i n t h e 1 5 0 - 2 0 0 p s i r a n g e , w i t h no a p p a r e n t r e l a t i o n s h i p t o t h e a m o u n t o f c o r r o s i o n . Weight change d a t a were o b t a i n e d f o r o n l y f o u r o f t h e seven c o a t i n g s , a n d t h o s e d a t a s h o w e d no c o r r e l a t i o n w i t h t h e e x t e n t o f s t e e l substrate corrosion. The p o l y e s t e r s h o w e d a w e i g h t l o s s , rather t h a n a w e i g h t g a i n , p r o b a b l y d u e t o an a t t a c k and d i s s o l u t i o n o f t h e e p o x y by t h e a c i d . I t s h o u l d be n o t e d t h a t t h e e l e c t r o c h e m i c a l m e a s u r e m e n t s ( c o r r o s i o n p o t e n t i a l and c o n d u c t i v i t y ) f o r t h e t w o n o v o l a c e p o x i e s c u r e d w i t h an a r o m a t i c a m i n e f r o m d i f f e r e n t s o u r c e s s h o w e d g o o d a g r e e m e n t , a l t h o u g h t h e t e n s i l e a d h e s i o n and w e i g h t g a i n v a l u e s w e r e n o t as reproducible. Discussion The b e s t p e r f o r m i n g c o a t i n g s w e r e t h e v i n y l e s t e r , t h e b i s p h e n o l A e p o x y c u r e d w i t h an a l i p h a t i c a m i n e , and a n o v o l a c e p o x y c u r e d w i t h a mixed a r o m a t i c / c y c l o a l i p h a t i c amine. The s a t u r a t e d p o l y e s t e r , and a b i s p h e n o l A e p o x y c u r e d w i t h a p o l y a m i d e a m i n e s h o w e d s i g n i f i c a n t d e t e r i o r a t i o n o f t h e c o a t i n g m a t e r i a l i n t h e a c i d , and c o r r o s i o n o f t h e u n d e r l y i n g s t e e l . Two t y p e s o f n o v o l a c e p o x i e s c u r e d w i t h a r o m a t i c a m i n e s showed i n t e r m e d i a t e p e r f o r m a n c e . O n l y one relation l a t i o n of the f a c t
o f t h e f o u r t e c h n i q u e s — t h e c o n d u c t i v i t y — s h o w e d any c o r w i t h t h e o b s e r v e d e x t e n t o f c o r r o s i o n . The l a c k o f c o r r e the t e n s i l e adhesion values w i t h c o r r o s i o n i s a r e s u l t of t h a t t h e method i n t e g r a t e s a d h e s i o n l o s s a t t h e s u b s t r a t e
In Polymeric Materials for Corrosion Control; Dickie, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1986.
In Polymeric Materials for Corrosion Control; Dickie, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1986. ΒΡΑ AL NOV AR/ AL
POTENTIAL
P
A
' c o J
ΡΕ I NOV AR/ AL
2
4
Figure H S0 .
. Γ
Γ
h
WEIGHT
NOV AR 2
GAIN
BPA AL
•
CORROSION
MINIMAL
BPA AL
VE
(AC)
to
DECREASING ·
0.1 M
EXTENSIVE MODERATE MINIMAL AMOUNT OF CORROSION
I
BLIS. WT ITER.LOSS!
I
OF
DECREASING
| B P A | PE PA
I
1
NOV AR 2
MODERATE
NOV AR 1
NOV AR/ AL
CONDUCTIVITY
AMOUNT
EXTENSIVE
BPA PA
SPECIFIC
2. P a r a m e t e r v a l u e s a f t e r 1000 h e x p o s u r e See T a b l e I f o r r e s i n d e s c r i p t i o n c o d e .
DECREASING ·
EXTENSIVE MODERATE MINIMAL AMOUNT OF CORROSION
ITERJHES.) .FAIL.,
«
100|- [BPAj
BPA AL
ADHESION
NOV AR 1 NOV AR 2
TENSILE
DECREASING ·
EXTENSIVE MODERATE MINIMAL AMOUNT OF CORROSION
ΒΡΑ ΡΑ
NOV NOV AR AR 2 1
CORROSION
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ί
». ο s,
r
70
m c/3 m
α se
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POLYMERIC MATERIALS FOR CORROSION CONTROL
i n t e r f a c e and t h e c o h e s i o n l o s s d u e t o d e t e r i o r a t i o n o f t h e p o l y m e r by a c i d . A l s o , t h e c o r r o s i o n o f t e n i s l o c a l i z e d and t h e a r e a a t t a c k e d i s a s m a l l f r a c t i o n of the t o t a l i n t e r f a c i a l area. The weight gain i s not a r e l i a b l e measure of c o r r o s i o n protection b e c a u s e t h e r e may be an a t t a c k a n d s o l u b i l i z a t i o n o f t h e c o a t i n g m a t e r i a l i t s e l f (as o c c u r r e d w i t h the p o l y e s t e r ) , so t h a t the o b s e r v e d c h a n g e i n w e i g h t w i l l be t h e n e t r e s u l t o f a w e i g h t l o s s f r o m s o l u b i l i z a t i o n and a w e i g h t g a i n f r o m w a t e r and a c i d e n t r y into the c o a t i n g . The o n l y way t o s e p a r a t e t h e t w o e f f e c t s i s t o measure the w e i g h t change o c c u r r i n g w i t h a f r e e f i l m o f t h e c o a t i n g and a s s u m e i t w i l l be t h e s a m e as a c o a t i n g on a s u b s t r a t e ; this was t h e t e c h n i q u e u s e d by F u n k e [ 5 ] . T h e r e i s much m o r e l i k e l i h o o d of attack of c o a t i n g m a t e r i a l s in a c i d s o l u t i o n s because of i n c r e a s e d r a t e s o f h y d r o l y s i s r e a c t i o n s a t l o w pH*s. T h e i n t e r p r e t a t i o n o f c o r r o s i o n p o t e n t i a l has a l w a y s b e e n d i f f i c u l t . W o l s t e n h o l m e [ 3 ] c o n c l u d e d t h a t t h e c o r r o s i o n p o t e n t i a l was n o t an u n a m b i g u o u s i n d i c a t o r o f t h e a m o u u n t o f c o r r o s i o n , and C e r i s o l a a n d B o n o r a [ 7 ] d e s c r i b e d t h e m e a s u r e m e n t a s o n e w i t h no q u a n t i t a t i v e r e l a t i o n s h i p to amount of c o r r o s i o n . The r e s u l t s shown i n F i g u r e 2 c o n f i r m the q u e s t i o n a b l e v a l u e of p o t e n t i a l m e a s u r e m e n t s i n c o r r e l a t i o n s w i t h t h e c o r r o s i o n o f an u n d e r l y i n g substrate. The c o a t i n g c o n d u c t a n c e , on t h e o t h e r h a n d , h a s b e e n r e p o r t e d by n u m b e r o f p e o p l e t o be r e l a t e d t o t h e e x t e n t o f c o r r o s i o n u n d e r coating [8-11]. The c o n d u c t a n c e , e i t h e r AC o r DC, i s a f u n c t i o n t h e amount o f c h a r g e t h a t can p a s s t h r o u g h t h e c o a t i n g and t h amount of charge i s a f u n c t i o n of the amount of aqueous phase the c o a t i n g t h a t p e r m i t s charge motion.
a a of is in
T h u s , i n a c i d s o l u t i o n i t a p p e a r s t h a t an i m p o r t a n t p r o p e r t y o f a coating for corrosion protection i s i t s permeability to acid. This v a r i a t i o n i n p e r m e a b i l i t y i s t h o u g h t t o be t h e r e a s o n f o r the d i f f e r e n c e in behavior of coatings observed during exposure to a c i d environments [12J. The p e r m e a b i l i t y i s a l s o a f f e c t e d by t h e d e g r a d a t i o n o f t h e c o a t i n g as c a u s e d b y r e a c t i o n w i t h t h e a c i d . Conclusions O f t h e f o u r t e c h n i q u e s s t u d i e d f o r e v a l u a t i n g c o a t i n g s on s t e e l f o r c o r r o s i o n c o n t r o l ( c o r r o s i o n p o t e n t i a l , c o n d u c t a n c e , a d h e s i o n and w e i g h t g a i n ) , t h e m o s t u s e f u l was c o n d u c t a n c e . Corrosion potential d i d n o t show a c o n s i s t e n t r e l a t i o n s h i p , and w e i g h t g a i n a n d t e n s i l e a d h e s i o n s h o w e d no c o r r e l a t i o n w i t h c o r r o s i o n . The b e s t p e r f o r m i n g c o a t i n g s s t u d i e d w e r e a v i n y l e s t e r , a b i s p h e n o l A e p o x y c u r e d w i t h an a l i p h a t i c a m i n e , a n d a n o v o l a c e p o x y cured w i t h a mixed a r o m a t i c / c y c l o a l i p h a t i c amine. A s a t u r a t e d p o l y e s t e r , and a b i s p h e n o l A e p o x y c u r e d w i t h a p o l y a m i d e a m i n e s n o w e d s i g n i f i c a n t d e t e r i o r a t i o n i n t h e a c i d and c o r r o s i o n o f t h e underlying steel. Two t y p e s o f n o v o l a c e p o x i e s c u r e d w i t h a r o m a t i c amines showed i n t e r m e d i a t e p e r f o r m a n c e .
In Polymeric Materials for Corrosion Control; Dickie, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1986.
7.
WHITE A N D LEIDHEISER
Evaluation of Coating Resins
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Acknowledgments The a u t h o r s a r e i n d e b t e d t o t h e E l e c t r i c P o w e r R e s e a r c h I n s t i t u t e , P a l o A l t o , C a l i f o r n i a , f o r s u p p o r t i n g t h i s w o r k and t o B. C. S y r e t t of t h a t o r g a n i z a t i o n f o r h e l p f u l d i s c u s s i o n s during the study.
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Literature Cited 1. Fontana, M. G.; Greene, N. D. "Corrosion Engineering"; McGraw-Hill: New York, 1978; 2nd ed. 2. Leidheiser, H. Jr. Prog. Org. Coatings 1979, 7, 79-104. 3. Wolstenholme, J . Corr. Sci. 1973, 13, 521-30. 4. Mansfeld, F.; Kendig, M. W.; Tsai, S. Corrosion 1982, 38, 478-85. 5. Funke, W.; Haagen, H. Ind. Eng. Chem. Prod. Res. Dev. 1978, 17, 50-53. 6. White, M. L.; Paper given at ACS Meeting, Philadelphia, PA, August 1984. Submitted to Ind. Eng. Prod. Res. Dev. for publication in 1986. 7. Cerisola, G.; Bonora, P. L. Mater. Chem. 1982, 7, 241-48. 8. D. J. Mills. In Coatings and Surface Treatment for Corrosion and Wear Resistance; Strafford, K. N., Ed.; Horwood: Chichester, England, 1984; pp. 315-30. 9. Rajagopalan, K. S.; Guruviah, S.; Rajagopalan, C. S. J. Oil Col. Chem. Assoc. 1980, 63, 144-48. 10. Touhsaent, R. E.; Leidheiser, H. Jr. Corrosion 1972, 28, 43540. 11. Vertere, V.; Rozados, E.; Carbonari, R. J. Oil Col. Chem. Assoc. 1978, 61, 419-26. 12. White, M. L.; Leidheiser, H. Jr., Materials Performance 1985, 24, 9-16. RECEIVED January 27, 1986
In Polymeric Materials for Corrosion Control; Dickie, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1986.