Grain boundary plane populations in minerals: the example of wet NaCl after low strain deformation

Abstract

Many physical properties of rocks are sensitive to grain size and hence to the structure of grain boundaries. Depending on their properties, such as deformation and transport behaviour, boundaries may be divided into two broad types, namely special and general grain boundaries. Electron backscattered diffraction (EBSD) is used to investigate the misorientation distributions of grain boundaries and, more recently, to determine the population of grain boundary planes. Studies on metals and ceramics suggest that the grain boundary plane, rather than the misorientation, is the key parameter when defining special and general grain boundaries. In this study, the distribution of grain boundary plane orientations has been successfully determined using EBSD for a slightly deformed, synthetic NaCl material containing 22 ppm water. Boundaries showed a preference for {100} planes, which occurred with twice the frequency of a random distribution. The grain boundary plane distributions found in NaCl were largely in agreement with studies on MgO. Grain boundaries, with a coincident site lattice (CSL) misorientation, also showed a preference for {100} planes, rather than the planes of high coincident density associated with the CSL. Three main types of boundary were identified, namely {100} twist boundaries, boundaries with {100}{hkl} planes and general {hkl}{hkl} boundaries. As the properties of these three types of boundary differ, then the transport and creep properties in wet NaCl will depend on the fraction of the different boundary types found in the grain boundary population.

Full‐Field Numerical Simulation of Halite Dynamic Recrystallization From Subgrain Rotation to Grain Boundary Migration

“…Analysis of the grain boundary orientation distribution of slightly deformed polycrystalline aggregates of synthetic rock salt using EBSD reveals that grain boundaries show a preference for {110} planes, which may be related to the anisotropy of the grain boundary energy (Pennock et al., 2009). Our study assumes that all planes per unit length have the same grain boundary energy (i.e., isotropic) and, therefore, we refer to GBM driven by isotropic grain boundary energy (and dislocation energy) as isotropic GBM to distinguish it from natural and synthetic rock experiments.…”

“…Large free grains are visible in the reflected light micrograph of the experimental microstructure corresponding to the grain growth CPO of Armann (2008) (see Figure 6a of Armann, 2008), which means that discontinuous grain growth took place at high temperature. Therefore, the formation of such CPOs may be influenced by the discontinuous grain growth with anisotropic grain boundary energy (Piazolo et al, 2006) or by the preferred elimination of high-energy grain boundaries during grain growth (Dillon & Rohrer, 2009;Pennock et al, 2009).…”

Full-Field Numerical Simulation of Halite Dynamic Recrystallization From Subgrain Rotation to Grain Boundary Migration

“…Analysis of the grain boundary orientation distribution of slightly deformed polycrystalline aggregates of synthetic rock salt using EBSD reveals that grain boundaries show a preference for {110} planes, which may be related to the anisotropy of the grain boundary energy (Pennock et al, 2009). Our study assumes that all planes per unit length have the same grain boundary energy (i.e., isotropic) and, therefore, we refer to GBM driven by isotropic grain boundary energy (and dislocation energy) as isotropic GBM to distinguish it from natural and synthetic rock experiments.…”

Application of Electron Backscatter Diffraction to Grain Boundaries

“…These include a range of ceramics, e.g. MgO, NaCl, SrTiO 3 , TiO 2 , WC, MgAl 2 O 4 [10][11][12][13][14][15] and metals, e.g. Al, Cu, Ni, brass, austentitic steels and Ti [16][17][18][19][20].…”

“…The five-parameter methodology has been used to measure the distribution of grain boundary planes in lightly deformed, wet rocksalt [13]. This topic is of interest because in rocksalt (a rock containing predominantly halite) understanding the distribution of intergranular fluids is important for predicting the location of impermeable cap rocks that trap mobile fossil fuels, and also in determining the long term stability of caverns and back-fill used for storage of oil, gas and nuclear waste [13]. Figure 4 shows examples of the measured distributions of boundary planes taken from the subset of boundaries misoriented on the [100] axis.…”