NMR Studies of Aging Effects in Palladium Tritide

Abell, G.C.; Attalla, A.

doi:10.13182/fst88-a25207

Cited by 15 publications

(15 citation statements)

References 17 publications

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“…Abell and Attalla [5] showed that the abrupt change in He motion with change-of-state causes the NMR TI relaxation to follow the well-understood, temperature dependent BPP behavior [45] allowing the liquid He fraction to be quantitatively differentiated from the solid He. The helium atom density corresponding to this melting temperature is given by the bulk He melting curve E461 l/v(cm3/mole) = 0.0269 T M~.~~~ + 1.953~10-~ T M~.~~~ (13) Here it is assumed that all He atoms within a single bubble are in the same physical state, which was demonstrated experimentally by "hole-burning" of the resonance line [6].…”

Section: The Bubble Spacing Distributionmentioning

confidence: 99%

Helium Nano-Bubble Evolution in Aging Metal Tritides

Cowgill

2005

Fusion Science and Technology

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A continuum-scale, evolutionary model of helium (He) nano-bubble nucleation, growth and He release for aging bulk metal tritides is presented which accounts for major features of the experimental database. Bubble nucleation, modeled as self-trapping of interstitially diffusing He atoms, is found to occur during the first few days following tritium introduction into the metal and is sensitive to the He diffusivity and pairing energy. An effective helium diffusivity of 0 . 3~1 0 -l~ cm2/s at 300 K is required to generate the average bubble density of 5x 1017 bubbles/cm3 observed by transmission electron microscopy (TEM). Early bubble growth by dislocation loop punching with a l/radius bubble pressure dependence produces good agreement with He atomic volumes and bubble pressures determined from swelling data, nuclear magnetic resonance (NMR) measurements, and hydride pressure-compositiontemperature (PCT) shifts. The model predicts that later in life neighboring bubble interactions may first lower the loop punching pressure through cooperative stress effects, then raise the pressure by partial blocking of loops. It also accounts for the shape of the bubble spacing distribution obtained from NMR data. This distribution is found to remain fixed with age, justifying the separation of nucleation and growth phases, providing a sensitive test of the growth formulation, and indicating that further significant bubble nucleation does not occur throughout life. Helium generated within the escape depth of surfaces and surface-connected porosity produces the low-level early helium release. Accelerated or rapid release is modeled as inter-bubble fracture using an average ligament stress criterion. Good agreement is found between the predicted onset of fracture and the observed Hemetal ratio (HeM) for rapid He release from bulk palladium tritide. An examination of how inter-bubble fracture varies over the bubble spacing distribution shows that the critical H e m will be lower for thin films or small particle material. It is concluded that control of He retention can be accomplished through control of bubble nucleation.

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Section: The Bubble Spacing Distributionmentioning

confidence: 99%

Helium Nano-Bubble Evolution in Aging Metal Tritides

Cowgill

2005

Fusion Science and Technology

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“…Helium-3 nuclear magnetic resonance data for Pd tritide shows that early in life, a significant fraction of the He within the small bubbles is in the high-pressure solid state [7,8]. Analysis of the melting transition of He within the bubbles for samples of several ages found a distribution of He densities consistent with a constant distribution in bubble spacing during bubble growth [l].…”

Section: Introductionmentioning

confidence: 99%

Helium bubble linkage and the transition to rapid He release in aging Pd tritide.

Cowgill¹

2006

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A model is presented for the linking of helium bubbles growing in aging metal tritides. Stresses created by neighboring bubbles are found to produce bubble growth toward coalescence. This process is interrupted by the fracture of ligaments between bubble arrays. The condition for ligament fracture percolates through the material to reach external surfaces, leading to material micro-cracking and the release of helium within the linked-bubble cluster. A comparison of pure coalescence and pure fracture mechanisms shows the critical H e M concentration for bubble linkage is not strongly dependent on details of the linkage process. The combined stress-directed growth and fracture process produces predictions for the onset of rapid He release and the He emission rate. Transition to this rapid release state is determined from the physical size of the linkedbubble clusters, which is calculated from dimensional invariants in classical percolation theory. The result is a transition that depends on material dimensions. The onset of bubble linkage and rapid He release are found to be quite sensitive to the bubble spacing distribution, which is log-normal for bubbles nucleated by self-trapping.

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“…Moreover, in the case of Pd tritide, prior work complements well the present observations and conclusions. The main results in this field were obtained by NMR studies for 3 He nuclei [17][18][19][20]. They have clearly demonstrated the formation of 3 He nanobubbles in Pd samples aged from 6 months to 8 years.…”

Section: Discussionmentioning

confidence: 97%