HYDROGEN SOLUBILITY IN PD AL2O3 COMPOSITES PREPARED BY INTERNAL OXIDATION OF PD-AL ALLOYS/

Internally oxidized Pd-Al alloys have been studied at 323 K using p(H2 )-composition isotherms. Internal oxidation of Pd0.97Al0.03 alloys res ults in alumina precipitates within an essentially Pd matrix, i.e. int ernal oxidation results in a Pd/Al2O3 composite. The dilute hydrogen s olubilities (323 K) in the composite are enhanced compared to annealed , pure Pd. Solubility enhancements have been measured after oxidations at 983 K, 1073 K, 1173 K and 1273 K for different times. Thermal resi dual stresses develop when the internally oxidized alloys are cooled f rom the high oxidation temperatures. The solubility enhancements are a ttributed to the presence of these residual stresses about the ceramic particles. The solubility enhancements for completely internally oxid ized alloys are greater after lower, rather than higher, oxidation tem peratures. Transmission electron microscopy indicates that alumina pre cipitates are nanometer-sized after oxidation al the lower temperature s and coherent with the Pd matrix. After oxidation at 1273 K, they pre cipitate as triangular prisms with their lengths being much greater th an their sides while after oxidation at 1073 K, their sizes are smalle r and their lengths are similar to their sides. Theoretical analysis o f solubility enhancements about spherical and cylindrical precipitates reveal that the thermal stresses about the former are greater. The re sults of the analysis are consistent with the thermal residual stresse s as the principal source of the experimental solubility enhancements. (C) 1997 Acta Metallurgica Inc.