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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 181 records · Page 10
All sourcesNASA NTRSDOE OSTI
DOE OSTI2013

Size and structure of Chlorella zofingiensis /FeCl 3 flocs in a shear flow: Algae Floc Structure

Flocculation is a promising method to overcome the economic hurdle to separation of algae from its growth medium in large scale operations. But, understanding of the floc structure and the effects of shear on the floc structure are crucial to the large scale implementation of this technique. The floc structure is important because it determines, in large part, the density and settling behavior of the algae. Freshwater algae floc size distributions and fractal dimensions are presented as a function of applied shear rate in a Couette cell using ferric chloride as a flocculant. Comparisons are made with measurements made for a polystyrene microparticle model system taken here as well as reported literature results. The algae floc size distributions are found to be self-preserving with respect to shear rate, consistent with literature data for polystyrene. Moreover, three fractal dimensions are calculated which quantitatively characterize the complexity of the floc structure. Low shear rates result in large, relatively dense packed flocs which elongate and fracture as the shear rate is increased. Our results presented here provide crucial information for economically implementing flocculation as a large scale algae harvesting strategy.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2011

Structure Stability of Methane Hydrate at High Pressures

The structural stability of methane hydrate under pressure at room temperature was examined by both in-situ single-crystal and powder X-ray diffraction techniques on samples with structure types I, II, and H in diamond-anvil cells. The diffraction data for types II (sII) and H (sH) were refined to the known structures with space groups Fd3m and P6{sub 3}/mmc, respectively. Upon compression, sI methanehydrate transforms to the sII phase at 120 MPa, and then to the sH phase at 600 MPa. The sII methanehydrate was found to coexist locally with sI phase up to 500 MPa and with sH phase up to 600 MPa. The pure sH structure was found to be stable between 600 and 900 MPa. Methanehydrate decomposes at pressures above 3 GPa to form methane with the orientationally disordered Fm3mstructure and ice VII (Pn3m). The results highlight the role of guest (CH{sub 4})-host (H{sub 2}O) interactions in the stabilization of the hydratestructures under pressure.

03 NATURAL GAS↗
DOE OSTI2011

Phase stability of some actinides with brannerite structure at high pressures

Structure behavior of actinide brannerites ThTi{sub 2}O{sub 6}, Y{sub 0.5}U{sub 0.5}Ti{sub 1.5}Nb{sub 0.5}O{sub 6} and their analog oxide CeTi{sub 2}O{sub 6} was studied at high pressure by using in situ x-ray diffraction, Raman scattering and infra-red absorption techniques, respectively. Brannerite structure was found to be not stable and started to become amorphous at pressures above 20 GPa. Some minor crystalline phase(s) due to phase decomposition was observed in all the three samples during pressurization. In addition, the observed bulk modulus indicated that the actinide-bearing brannerites are more compressible than their analog compound CeTi{sub 2}O{sub 6}, which may be related to the asymmetric 5f electron orbits of actinide elements. - Graphical abstract: Actinide-bearing compounds with brannerite structure and their analog CeTi{sub 2}O{sub 6} are not stable at high pressure. They were amorphized after {approx}20 GPa and a minor pressure-induced phase transition or decomposition process was always observed before amorphization. Highlights: > Phase stability of three brannerites CeTi{sub 2}O{sub 6}, ThTi{sub 2}O{sub 6}, and (U,Y)(Ti,Nb){sub 2}O{sub 6} at high pressures. > Brannerite structure was not stable and became amorphous after {approx}20 GPa. > Actinide-bearing brannerites are easier compressed than their analog compound CeTi{sub 2}O{sub 6}.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗