Recovery of deformed and hydrogen-charge palladium Page: 1 of 3
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BNL 31349
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RECOVERY OF DEFOPMED AND HYDROGEN-CHARGED PALLADIUM,C. L. Snead, Jr., K. G. Lynn, and J. F. Lynch-
BNL--313 49
DEO2 016750Brookhaven National Laboratory
Upton, New York 11973, U.S.A.Positron lifetime and Doppler-broadening studies made at 300 K have been used to
investigate the interaction between interstitial hydrogen and lattice defects in
deformed Pd. Specimens were charged with hydrogen at 300 K to levels up to 0.1%.
The presence of hydrogen was found to have no effect on the recovery curves of Pd
upon annealing to 4000C. By 4000C the values for both lifetime and Doppler-broad-
ening for both cold worked and cold worked plus hydrogen were below the values
obtained for annealed pure Pd. This can be interpreted as gaseous-impurity-trapped
vacancies being present after the 12000C anneal, but being swept away by the dis-
location microstructure recovery between 200-4000C. Although the specimens hydrided
to the S phase and outgassed back to the a phase showed continual recovery up to
4000C, complete recovery was not achieved as with the deformed specimens. The life-
time results indicate the presence of defects more open than single vacancies. One
possibility would be the formation of cavities, possibly hydrogen filled, during the
hydriding that are stable at 4000C.The defect concentration and type in the host
lattice can be a major determining factor in
both the solubility of hydrogen in metals and
the diffusion rate of hydrogen in the metals.
Flanagan et al. [L,2] demonstrated that in the
low-H-content a phase of Pd the solubility of
H as determined by absorption isotherms in-
creased with increasing prior cold work. They
attributed this increased solubility to trapp-
ing of H in the strain fields of the disloca-
tions present. The role of vacancy agglomer-
aces in the trapping process is not clear, but
is not believed to play a major role. Cold
work does decrease the diffusivity of hydrogen
In Pd [2-41. The decreased diffusivity of
hydrogen in Pd after cold work is associated
with the H trapping at the dislocation strain
fields. For Pd hydrided to the S phase and
degassed to the a phase at low temperatures,
an enhanced hydrogen absorption is observed
upon further low-concentration H charging.
Trapping at dislocations generated during the
phase charge is the currently favored explana-
tion [21.
We have used positron techniques to get infor-
mation on (1) role of vacancy-type defects on
hydrogen trapping, (2) effect of H on the dis-
location recovery upon annealing, and (3) the
defects produced by hydriding Pd. Samples
were studied in the following states: (L) cold
worked, (2) cold worked + H charged, and (3)
cold worked + annealed to 12000C and were made
from a Pd (99.99+%) sheet cold-rolled to 95%
reduction. Identical pairs sandwiched -10 uCi
of 22NaC1 deposited directly on one face for
measurement of lifetime and Doppler broaden-
ing. Standard techniques were employed. The
hydrogen charging was done at room temperature
under pressure to a hydrogen level of H/Pd
-0.006 for the cold work + H specimens. For
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the specimens hydrided and degassed to the m
phase the charging was done at room temperat-
ure to a level of H/i. -0.7 and then
held under vacuum for 12 h.
In Fig. 1 the results are presented for a
single-variable-lifetime ('1) fit for cold
worked + H charged specimens. Isochronal an-
neals were made at 100, 200, 300. and 4000C
for 2 h. A second lifetime component was fix-
ed (570 psec at 0.78%) to account for source
and surface annihilations. This component was
determined from fits to the "well-annealed"
and high-temperature-annealed cold-worked
specimens. Single-lifetime fits such as this
do not yield quantitative results as a rule
but are useful as qualitative indications of
defect changes. .
From this Fig. some small amount of recovery
is indicated from the annealing to 2000C with
a large change between 200 and 3000C. The
curve is drawn as a guide for the eye. The
lifetime data show no difference between the
recovery of the cold-worked specimens and the
cold-worked + H specimen. The values of the
room temperature 1'Y, for both treatments were
essentially the same (166 vs 168 psec).
The surprising result from the recovery de-
picted in Fig. I is that the value of t.'I after
300 or 4000C annealing (96 and 98 psec, re-
spectively, at 4000C) is below that obtained
for the "well annealed" (120 psee). The lat-
ter is represented by the horizontal dashed
curve. The interesting implication here is
that the "well annealed" specimen has a defect
population greater than that of the two treat-
ments shown after they are annealed ac 30000
or above. This suggests that the 12000C an-
neal and subsequent cooling introduces some
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Snead, C. L. Jr.; Lynn, K. G. & Lynch, J. F. Recovery of deformed and hydrogen-charge palladium, article, January 1, 1982; Upton, New York. (https://digital.library.unt.edu/ark:/67531/metadc1055732/m1/1/: accessed May 30, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.