The relationship between relative oxide ion content of Na 2 SO 4 , the presence of liquid metal oxides and sulfidation a
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turbine fuels, can, a s the pentoxtde, i n c r e a s e the r a t e of oxidation of many a l l o y s . Bornstein, et al. *~ r e p o r t that vanadium p r e s e n t in the fuel should be p r e s e n t in the hot section of the gas turbine engine in the gaseous state. However, due to nonequilibrium burning conditions which can exist in a gas turbine engine, it is p o s sible for condensed V=O5 to impinge upon or f o r m irasit** on turbine components. It has been r e p o r t e d that s a l t s containing Na=SO4 and V=Os a r e e x t r e m e l y c o r r o sive and m a r k e d l y a c c e l e r a t e the r a t e of oxidation of gas turbine alloys.** The purpose of this study is to investigate the r e l a tionship between vanadium oxide and NaaSO4 a c c e l e r ated oxidation.
EXPERIMENTAL PROCEDURES The n i c k e l - b a s e s u p e r a l l o y B-1900 and seven b i n a r y n i c k e l - b a s e a l l o y s were chosen for this study. The nominal compositions a r e p r e s e n t e d in Table I. Test s p e c i m e n s a p p r o x i m a t e l y 1 by 1 by 0.090 in. in the " a s c a s t " condition were polished with 600 g r i t e m e r y , washed and r i n s e d with acetone i m m e d i a t e l y p r i o r to all e x p e r i m e n t s . The method of inducing s u l fidation attack, i . e . , application of Na2SO4 and s u b s e quent exposure in pure (3= (1000 cu cm p e r min) at e l e -
Table I. Nominal Composition of Alloys
Alloy
Ni
Cr
Co
Ti
B-1900 Ni-lv Ni-5V Ni-I 0V Ni-4Mo NiAI Ni-2Al Ni-6A1
Bal 99 94.5 89 96 67 98 94.3
8
10
1
Al 6
Me
Ta
C
6
4
0.1
V 1 5.5 I1
4 33
2 5.7
V O L U M E 4, A U G U S T 1 9 7 3 - 1 7 9 9
v a t e d t e m p e r a t u r e s , h a s b e e n d e s c r i b e d in d e t a i l in p r e v i o u s p u b l i c a t i o n s . 8 Continuous o x i d a t i o n s t u d i e s w e r e p e r f o r m e d using an A l n s w o r t h t h e r m o b a l a n c e and a t h r e e zone M a r s h a l l f u r n a c e a l l of which h a s also been described elsewhere. 8 The NiAl s p e c i m e n s w e r e p r e p a r e d b y hot p r e s s i n g f i n e l y d i v i d e d ( - 325 m e s h ) Ni-33 Al p o w d e r s . C o n s o l i dation was a c h i e v e d in a r g o n b y p r e s s i n g at 1250~ f o r one hour a t an a p p l i e d p r e s s u r e of 5000 p s i . NiAl a l l o y e d with e i t h e r C r , Mo, o r V was o b t a i n e d b y m i x i n g the r e s p e c t i v e m e t a l p o w d e r s with the NiAl p o w d e r p r i o r to c o n s o l i d a t i o n . A high t e m p e r a t u r e e l e c t r o c h e m i c a l c e l l was e m p l o y e d to m e a s u r e the r e l a t i v e oxide ion content of f u s e d Na2SO4. The e x p e r i m e n t a l c e l l c o n s i s t s of a s i l v e r - s i l v e r ion r e f e r e n c e e l e c t r o d e (as d e s c r i b e d b y D a n n e r and Rey 12 and Liu is) and a p l a t i n u m w i r e e l e c t r o d e i m m e r s e d in m o l t e n Na~SO4. The o p e r a t i o n of, i n s t r u m e n t a t i o n , and r e p r o d u c i b i l i t y of the c e l l is d e s c r i
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