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Clathrate Hydrates for Production of Potable Water
- Robert W. Bradshaw, Blake A. Simmons, Eric H Majzoub, W. Miles Clift, Daniel E. Dedrick
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- Journal:
- MRS Online Proceedings Library Archive / Volume 930 / 2006
- Published online by Cambridge University Press:
- 01 February 2011, 0930-JJ01-06
- Print publication:
- 2006
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Clathrate hydrates are crystalline inclusion compounds of water and a guest molecule (e.g., methane) that form at temperatures below ambient but above the freezing point of water. There are three known crystalline structures of hydrates (structure I, II, and H) in which cavities within the hydrogen bonded water molecule lattice trap the hydrate-forming species. The clathrate structure excludes dissolved solutes, such as sodium chloride, from the aqueous phase and thereby offers a possible means to produce potable water from seawater or brackish water. The concept of using clathrate hydrates for desalination is not new. However, before clathrate hydrate desalination becomes a viable technology, fundamental issues of controlled hydrate formation, hydrate size and morphology, agglomeration, amount of entrapped salt, and the efficient recovery of hydrates must be understood. This paper will report structural characterization of hydrates formed with several guest molecules over a wide range of conditions in an attempt to further the physicochemical insight needed to address these issues.
Clathrate hydrate formation experiments were performed using a variety of host molecules, including R141b, a commercial refrigerant, C2FCl2H3. Hydrates of R141b were formed at temperatures from 2°C to 6°C and atmospheric pressure from deionized water and 2% - 7% NaCl solutions. Samples of the hydrates were characterized by cold-stage x-ray diffraction and Raman spectroscopy and determined to be structure II. Additional experiments were conducted with a gaseous hydrate former, ethylene, which readily formed hydrates with deionized or saline water at 2°C and several atmospheres of pressure. Experiments with several other hydrate forming molecules were conducted and the results obtained from their structural characterization will be reported. We will also present proof-of-concept experiments demonstrating a novel technique of desalination using these hydrate formers.
Sandia National Laboratories is a multiprogram laboratory operated by Sandia Corporation, a Lockheed Martin company, for the United States Department of Energy under contract DE-AC04-94AL85000.
Indentation-Induced Debonding of Ductile Films
- Alex A. Volinsky, W. Miles Clift, Neville R. Moody, William W. Gerberich
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- Journal:
- MRS Online Proceedings Library Archive / Volume 586 / 1999
- Published online by Cambridge University Press:
- 10 February 2011, 255
- Print publication:
- 1999
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Thin film adhesion can be measured by means of the nanoindentation technique [1]. In the case of a ductile film (Cu, Al, Au, etc.) well adhered to a brittle substrate, plastic deformation in the film acts as an energy dissipation mechanism, preventing film debonding. Depositing a brittle layer of W (about 1 micron thick) on top of the film of interest increases the driving force for delamination, thus solving the problem [2]. Indentation produces circular delaminations (blisters), sometimes two orders of magnitude bigger than the indenter contact radius. Thin film adhesion was shown to scale with the film thickness, approaching the true work of adhesion of 0.8 J/m2 for Cu films less than 100 nm thick [3].
Conceptually it is important to know along what interface the fracture occurs during the blister formation. Auger electron spectroscopy (AES) has been used to determine where fracture occurs for different film systems. Cu films on SiO2 failed along the Cu/SiO2 interface. Fracture of Cu films with a 10 nm adhesion-promoting Ti underlayer occurred along the Ti/Cu interface. Significantly, Ti increased the thin Cu film adhesion by a factor of ten. Blisters were removed from the substrate, and the fracture surface was analyzed. In the case of thin Cu films, crack arrest (fiducial) marks were found upon blister removal, and represent the shape of the crack tip [4]. AFM has been used to determine the geometry of the marks. The main component of the arrest marks is carbon, which comes either from the diamond tip or from the hydrocarbons adsorbed on the newly formed surfaces in the indentation process.