  In-situ powder diffraction was used to study the annealing of dislocations in
the archetypal hydrogen absorbers Pd and LaNi5. The relationship between
dislocations and trapped hydrogen was explored using thermally induced
desorption. It was found that the dislocations in Pd caused by hydrogen
absorption anneal over a wide range of temperatures and that although they
start to anneal below 250 $^\circ$C, temperatures well above 750 $^\circ$C are
required to fully anneal the metal. It was shown that allowing further time at
lower temperatures does not further anneal the metal. It is suggested that this
is due to dislocation tangling and pinning, causing different temperatures to
be required for different pinning defects. It was found that hydrogen trapped
in LaNi5 is released in a wide range of temperatures and it was therefore
concluded that hydrogen is trapped in the dislocation strain field and
dislocation core as well as vacancies. The direct comparison of deuterium
release and dislocation density showed no correlation, in agreement with
previous indirect comparisons. Dislocations in LaNi5 were shown to anneal at
temperatures as low as 150 $^\circ$C, in contrast to previous reports which
suggested more than 500 $^\circ$C was required. This lower annealing
temperature for dislocations at least partly explains why low temperature
ageing increases the pressure hysteresis in hydrogen cycled LaNi5.
