Transformations initiated montmorillonite

In Chapter 2 the interfacial processes are discussed in a model system. A clay mineral, montmorillonite, has been chosen to illustrate important interfacial processes of geological formations. Some transformations initiated by interfacial processes are demonstrated. 

Pore ice plays a particular role for the self-preservation effect in frozen soils Initial hydrate preservation apparently is helped by frozen pore water (not transformed into hydrate). Additional ice formation in the form of a film on the surface of gas-hydrate forming due to hydrate surface dissociation is expected to take place upon gas pressure release. Thus in the sample with 7% of montmorillonite particles (Win=17%), pore hydrate showed a higher stability after pressure release as a consequence of the greater ice content due to the freezing of remaining pore water (Figure 4).Our results clearly indicate that the hydrate content decreases on the expense of an increases of ice (Figure 5). 

During the ablation experiment, temperature within the char layer exceeds 1000°C and approach 2000-2500°C at the surface. At these temperatures, any carbonaceous residue from the pol3oner will contain graphite. Additionally, mica-type layered silicates, such as montmorillonite, irreversibly transform into other aluminosilicate phases. Between 600 and 1000 C, montmorillonite dehydroxylates and has been observed to initially transform into spinel, cristobolite, mullite and/or pyroxenes (enstatite) (24). At temperatures greater than 1300 C, mullite, cristobolite and cordierite form and subsequently melt at temperatures in excess of 1500 C (mullite 1850 C, pure cristobolite 1728°C and cordierite --ISSO C) (25). The presence of an inorganic that transforms into a high viscosity melt on the surface of the char will improve ablation resistance by flowing to self-heal surface flaws. This is known to occur in silica-filled ablatives (26). 

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