Rock sample models Sample Clauses

Rock sample models. Quartz crystal The single crystal model of quartz is derived from experimental data by Xxxxxx et al. (1980). The lattice parameters are a = b = 4.916 Å, c= 5.405 Å, α=β= 90° and γ=120°. Unlike clay and C-S-H structures, the quartz crystals do not have obvious cleavage planes that can be used to create slit-like nanopores. In fact, a typical quartz crystal habit exposes surfaces oriented along numerous directions (Figure 4), of which the crystallographic planes (101) and (100) are the most abundant (Xxxxxxxx and Xxxxxxx, 2005; Xxxxxxx et al., 2015). These two planes are marked as surfaces r and m in Fig. 4. Consequently, a quartz supercell of 6 x 6 x 6 was created and then cleaved along the (101) and (100) surfaces. All the surface oxygen atoms were protonated to create a surface as illustrated in Figure 5 (right). 1-nm pores were then created to investigate CO2/H2O adsorption and transport properties. GCMC simulations of CO2/H2O intercalation into a 1-nm pore of quartz indicate that the mole fraction of CO2 is 0.0366 (Table 1). This value is higher than that found within the C-S-H models, indicating that CO2 intercalates more easily into quartz rock pores than in cement. Figure 4: Common habit of a natural quartz crystal (after Xxxxxxxx and Xxxxxxx, 2005). The MD-simulated atomic density profiles of CO2 and H2O within a quartz nanopore formed by (101) surfaces are shown in Figure 5. They indicate that CO2 molecules also occupy the surface region, similarly to what was observed within pores representative of low-C/S C-S-H cement phases (Figure 6). The less sharp peak of the water molecules is an indication of weaker structuring of H2O molecules in the vicinity of the quartz surface. Further analysis of the CO2 and H2O orientation and adsorption sites on the quartz crystal is currently underway. Figure 5: (Left) A snapshot of CO2/H2O mixture confined within quartz along the (101) surface. (Right) Zoomed image showing the (101) quartz surface hydroxylation details.