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Aluminum (Al) and Al alloys exhibit unusual passivity when immersed in alkaline lithium (Li) salt solutions. This passivity is a result of precipitation of a continuous, polycrystalline talc coating. Talc coatings persist when removed from the Li salt solution and offer increased corrosion protection during exposure to aggressive environments. Efforts to develop a low-cost, low-toxicity, easily applied corrosion-resistant coating for Al are ongoing. Surface analytical and electrochemical experiments aimed at characterizing the structure, composition, and barrier properties of talc coatings were conducted. The solution chemistry involved in talc formation was studied, and the conditions under which coatings form readily were established. Results showed coatings formed by immersion in an alkaline Li salt bath followed by a low-temperature (≤ 100°C) heat treatment in air or water provided barrier properties that compared favorably with those of traditional inorganic corrosion-resistant coatings, such as those produced by chromate conversion.

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In the two cases the pO 2-remains constant, but as for c~ > 0.25 the shape of the curve in Fig. 2 shows the independence of the pO ~-with Co, the first case has to be eliminated and the pO ~-is given by pO ~-= pK2 -2 log S(NaFeO2) REFERENCES l. P. Spiteri, EDF report D 554 MAT/T 40 (June 1984 11, 44 (1976).3. A. A. E1 Hosary, A. Baraka, and A. I. Abdel Rohman, ibid., 11, 163 (1976).4. Sandia National Laboratories Report 78-8256, Albuquerque, NM (Feb. 1979). 5. Sandia National Laboratories Report 80~8062, Albuquerque, NM (March 1981). 6. Sandia National Laboratories Report 81-8210, Albuquerque, NM (Feb. 1982 132, 863 (1985).12. S. L. Marchiano and A. J. Arvia, EIectrochim. Acta, 17, 861 (1972); S. L. Marchiano and A. J. Arvia, ibid., 17, 25 (1972); S. L. Marchiano, and A. J. Arvia, J. Appl. Electrochem., 4, 191 (1974). 13. A. Conte and S. Casadio, Ricerca Sci., 36, 488 (1966). 14. A. Conte and M. D. Ingram, Electrochim. Acta., 13, 1551 (1968).15. R. B. Flinn and K. H. Stern, J. Electroanal. Chem., 63, 191 (1975 37, 1893 (1975).18. G. Tridot, G. Nowogroki, J. Nicole, M. Wozniok, and J.Canone, Compt. Rend., 270 C, 204 (1970). 19. J. Th6ry, Ann. Chim., 7, 207 (1962). 20. R. Collongues and J. Th6ry, Bull. Soc. Chim. Fr, 7, 1141 (1959. D. R. Boehme and R. W. Bradshaw, High TemperatureSci., 18, 39 (1984). ABSTRACT In this investigation, the effect of alloying on catalysis, especially with respect to oxygen and the ORR, was examined. A series of PtCr alloys allowed four major aspects of alloying to be investigated: (i) effect of decreasing lattice parameter with increasing Cr content in the Pt terminal solid solution, (it) effect of an order/disorder transition, (iii) difference between intermetallic and solid solution structures, and (iv) effect of dendritic segregation. Results indicated that contrary to the findings of previous investigators, decreased lattice spacing did not correlate with an increase in ORR activity. Atomic ordering in low Cr content specimens, however, was found to generally increase catalysis. Results also indicated that disordered structures interact more strongly with impurities than the ordered structures. ORR Tafel slopes, however, were unaffected by atomic ordering although additional chromium, up to at least 35 atom percent (a/o), caused a decrease in Tafel slope apparently due to oxide reduction effects. At higher Cr concentrations, catalysis decreased due to the passive nature of chromium oxide. The change in crystal structure which occurs for the 80 a/o Cr sample and the dendritic structure, had little effect on most of the electrochemical parameters studied relative simply to the additional Cr content. The results of this work also indicated that, in general, no alloy in the PtCr system is more catalytic than pure Pt. This result is in contrast to gas diffusion cell studies which have shown significant increases in catalysis due to PtCr alloying. The Effect of Metallurgical Variables on the Electrocatalytic Properties of PtCr AlloysOxygen electrode interactions are of impo...