A pin-on-disk tribometer was used to study the coefficient of fiictio~z (1s (L filnction of temperature for tricresylphosphate (TCP) on C V M M -5 0 tool steel under the following conditions: T C P was present i n (L liquid reservoir (bulk lubrication), and T C P was applied cw. a liquid layer directly to the disk (limited lubrication). Under limited lubrication conditions, experiments were performed i n dry ( < 100 ppm H20) air, dry ( C 20 ppm H20) nitrogen, clry nitrogela zoith tlre disks heated to 700°C, then cooled to room temperu1~1,rc before the T C P was applied and the measurements made (/)reheated disks), and moist nitrogen using preheated disks. The coefficient of friction decreased at a characleristic temperature, T,.'I',. values obse~ved were: 265OC for bulk lubrication conditions i n dly air, 225OC for limited lubrication conditions i n dry air, and 215°C for limited lzibrication conditions i n dry nitrogen. The w e of preheated disks produced a sharp failure temperature at 2 1 8°C rohich was taken as the temperature about which the behavior of T C P should be judged. X-ray photoelectron spectroscopy confirmed tlre presence of phosphate on the surface of TCP-lubricated iron pins. Depth profile studies support the suggestion that a chemical reaction occurs between the T C P and the metal surjkce at T,.

N a t i o n a l A e r o n a u t i c s and Space A d m i n i s t r a t i o nLewis Research Center C l e v e l a n d , O h i o 44135 SUMMARYThe r e a c t i o n s o f l i n e a r p e r f l u o r o p o l y a l k y l e t h e r (PFAE) l u b r i c a n t s w i t h a-FezO3 and Fe203-based s o l i d s u p e r a c i d s were s t u d i e d . a-Fe2O3 proceeds i n two s t a g e s . The first s t a g e i s an i n i t i a l slow c a t a l y t i c d e c o m p o s i t i o n o f t h e f l u i d . T h i s r e a c t i o n r e l e a s e s r e a c t i v e gaseous p r o d u c t s which a t t a c k t h e m e t a l o x i d e and c o n v e r t i t t o FeF3. more r a p i d d e c o m p o s i t i o n o f t h e f l u i d , e f f e c t e d b y t h e s u r f a c e FeF3. A s t u d y of t h e i n i t i a l breakdown s t e p was p e r f o r m e d u s i n g a-Fe203, a-FezO3 p r e c o n v e r t e dt h e breakdown r e a c t i o n i n v o l v e s a c i d i c a t t a c k a t f l u o r i n e atoms on a c e t a l carbons i n t h e l i n e a r PFAE. P o s s i b l e approaches t o combat t h e p r o b l e m a r e o u t 1 i ned .The r e a c t i o n w i t hThe second s t a g e i s a

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Thiourea Complexes of Cobalt(II) 17 ions. Mo* 11 and Re111, which are the species formally present in the two cases, are isoelectronic (d4). However, if each were to adopt the other's structure, we should have [Mo3C112]6~a nd [Re6Cls]ll,+. The charges in both cases are quite high, and, in the former case, there is the added consideration that even the [Mo3-Cle]8core would have a substantial negative charge, so that it would be unlikely to combine with 3C1~to give [Mo3C1i2]6-.In summary, the combined requirements of filling only the bonding molecular orbitals and satisfying electrostatic requirements may place very severe restrictions on how many metal atom clusters are capable of existence. Nonetheless, chemical studies of the lower oxidation states of the heavier transition metals should be carried out with at least some alertness to the possibility of encountering further metal atom cluster compounds.

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