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In-situ XRD measurements of interlayer swelling of clays

Abstract:

The swelling phenomenon of clays is one of the most important topics in the engineering and environmental work. Swelling is a time dependent volume increase involving physicochemical reactions with water. There are two categories of swelling. The inner and intracrystalline swelling is a process whereby the exchangeable cations in the interlayer and at the surface of clay minerals build one to four discrete hydration shells. At higher water content, the formation of non solvated (non bound) water is observed. The osmotic (intracrystalline) swelling results from the difference in the ion concentrations close to the clay mineral surfaces and in the pore water. The ionic composition influences the extent of swelling, due to the different hydration energies of the cations, which depends from ionic size and valence. Furthermore the swelling behaviour of clayey soils and rocks depends strongly on the mineralogical composition, i.e. on the type and quantity of clay minerals encountered and on the content of further minerals which show swelling behaviour caused by recrystallisation processes. The fabric and density of clays determines the time dependent swelling behaviour. Understanding the effects of cation valence, cation hydration energy and clay layer charge provides a model to calculate the swelling pressure. Combined experimental studies were carried out on bentonite (MX80 Wyoming and Montigel Sudchemie) as a model clay: isothermic water adsorption measurements in a gravimetric apparatus of McBain type, swelling pressure measurements in an adapted oedometer apparatus, and interlayer swelling studies with XRD at various relative humidity. Results of in-situ XRD studies of interlayer swelling d(001) will be presented for homoionic montmorillonite. The montmorillonite were exchanged with Cs+, Na+, Sr2+, Ca2+, Al3+ (related enthalpy of hydration from 276 to 4665 kJ/mol). The measurements were performed in a sample chamber (Anton Paar TTK450) mounted on a Bruker AXS D8. The relative humidity (RH) was achieved by mixing wet and dry pressure air at 26C (Sycos H). The sample temperature (26.0 0.2C) was controlled by circulating water in the double chamber wall and the sample stage. Firstly the oriented samples were dried in vacuum oven (12h at 65C). After that the XRD measurements were carried out in programmed cycles in the RH range 1-80 0.2% (stabilization and equilibration time of RH within 60 min).

Authors:

Plötze, Michael and Kahr, Günter

Further Information:

Date published: 2004