Distribution of brine in grain boundaries during static recrystallization in wet, synthetic halite: insight from broad ion beam sectioning and SEM observation at cryogenic temperature |
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Authors: | Guillaume Desbois Janos L Urai Peter A Kukla Uwe Wollenberg Fabián Pérez-Willard Zsolt Radí Sandor Riholm |
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Institution: | (1) Structural Geology, Tectonics and Geomechanics, RWTH Aachen University, Lochnerstrasse 4-20, 52056 Aachen, Germany;(2) Geological Institute, RWTH Aachen University, W?llnerstr. 2, 52062 Aachen, Germany;(3) Carl Zeiss NTS GmbH, Carl-Zeiss Str. 56, 73447 Oberkochen, Germany;(4) Technoorg–Linda Ltd.Co, R?zsa Utca 24, 1077 Budapest, Hungary |
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Abstract: | We report observations from room temperature static recrystallization experiments (annealing times from minutes to year) of
cold-pressed, synthetic, coarse-grained, wet sodium chloride, prepared by broad ion beam polishing and SEM observations at
cryogenic temperature to observe directly the brine in grain boundaries. At all stages of annealing, the majority of the brine
in the samples is connected in 2D sections along grain boundaries. Another part of the brine is in isolated brine inclusion
arrays along grain boundaries and in brine inclusions left behind by migrating brine-filled grain boundaries. Most of these
boundaries are mobile because the aggregate is coarsening. We interpret that the boundaries without observable brine films
(<15 nm) and brine inclusion arrays are healed and immobile. Evolution of grain boundary structure involves three major processes.
First, dissolution on one side of the grain boundary and precipitation on the other side, resulting in grain boundary migration.
Second, the development of facets formed by low-index crystallographic planes of the grains bounding the grain boundary brine.
When both sides of a grain boundary are able to develop low-index facets in a thick brine film, the resulting impingement
boundary is interpreted to be immobile and may prevent the new grain from migrating into a deformed neighbor. When one side
of a faceted boundary consists of low-index crystallographic planes and the other side passively follows this faceted shape
along irrational surfaces, the boundary is mobile. Third, the healing of grain boundary brine films, producing solid–solid
grain boundaries without resolvable brine films. |
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