Deuterium Interactions with Ion-Implanted Oxygen in Cu and Au
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DEUTERIUM INTERACTIONS WITH ION-IMPLANTED OXYGEN IN Cu AND Au S."*Sandia M. MYERS", W. A. SWANSIGER"*, AND D. M. FOLLSTAEDT* National Laboratories, Div. 1112, Albuquerque, NM 87185 ""Sandia National Laboratories, Div. 8343, Livermore, CA 94550 ABSTRACT The interactions of deuterium (D) with oxygen in Cu and Au were examined using ion implantation, nuclear-reaction analysis, and transmission electron microscopy. In Cu, the reduction of Cu 20 precipitates by D to produce D 20 was shown to occur readily down to room temperature, at a rate limited by the transport of D to the oxides. The reverse process of D 20 dissociation was characterized for the first time below the temperature range of steam blistering. The evolution of the Cu(D)-Cu2 O-D 2O system was shown to be predicted by a newly extended transport formalism encompassing phase changes, trapping, diffusion, and surface release. In Au, buried 0 sinks were used to measure the permeability of D at 573 and 373 K, thereby extending the range of measured permeabilities downward by about six orders or magnitude. INTRODUCTION Precipitates of low-stability oxides within metals have long been recognized to undergo a reduction reaction with hydrogen leading to the formation of H 2 0 inclusions. A widely recognized example is the reduction of Cu 20 particles in Cu [1,2]. This strongly exothermic reaction is given by
H(soln in Cu) + 1/2 Cu 20
=>
1/2 H 20
+
Cu, AH
= -
1.06 eV, AS
= -
0.19 k,
(1)
where k is the Boltzmann constant. The specified net changes in enthalpy, AH, and in the nonconfigurational entropy, AS, were obtained by combining the known heats and entropies of formation for Cu 2 O and H 20 with the published activation enthalpy and prefactor for hydrogen solution in Cu [3,4]. The process of Eq. (1) is responsible for "steam embrittlement", which affects impure coppers when they are heated in hydrogen ambients. This degradation is especially pronounced at temperatures of about 1000 K and above, where high pressures within the H 2 0 inclusions cause catastrophic rupturing of the Cu matrix. In the present investigation, the interactions of hydrogen with 0 in Cu and Au were examined mechanistically using ion implantation and nuclear-reaction analysis. The study had four motivations. First, we wished to determine the kinetics of the solid-state reduction reaction with Cu 20 precipitates in Cu, and further to do this for a range of temperatures extending down to 300 K. Although this reaction had previously been shown to occur readily at temperatures of several hundred OC and above, the rate-determining steps had not been established and quantified so as to provide a predictive capability, and observations were lacking for near-ambient temperatures. A second objective was to characterize the reverse of the reaction of Eq. (1), which had not previously been examined. This process reintroduces hydrogen into solution, thereby permitting its migration to the surface and subsequent release. Thirdly, we used the ion-implanted Cu(H)-Cu 20-H 2 O system to test a tra
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