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- Bispo-Santos, Franklin, et al.
(författare)
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Columbia revisited : paleomagnetic results from the 1790 Ma colider volcanics (SW Amazonian Craton, Brazil)
- 2008
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Ingår i: Precambrian Research. - : Elsevier BV. - 0301-9268 .- 1872-7433. ; 164:1-2, s. 40-49
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Tidskriftsartikel (refereegranskat)abstract
- In an attempt to improve our understanding of the Paleoproterozoic geodynamic evolution, a paleomagnetic study was performed on 10 sites of acid volcanic rocks of the Colider Suite, southwestern Amazonian Craton. These rocks have a well-dated zircon U-Pb mean age of 1789 +/- 7 Ma. Alternating field and thermal demagnetization revealed northern (southern) directions with moderate to high upward (downward) inclinations. Rock magnetism experiments and magnetic mineralogy show that this characteristic magnetization is carried by Ti-poor magnetite or by hematite that replaces magnetite by late-magmatic cleuteric alteration. Both magnetite and hematite carry the same characteristic component. The mean direction (Dm = 183.0 degrees, Im = 53.5 degrees, N = 10, alpha(95) = 9.8 degrees, K = 25.2) yielded a paleomagnetic pole located at 298.8 degrees E, 63.3 degrees S (alpha(95) = 10.2 degrees, K = 23.6), which is classified with a quality factor Q = 5. Paleogeographic reconstructions using this pole and other reliable Paleoproterozoic poles suggest that Laurentia, Baltica, North China Craton and Amazonian Craton were located in laterally contiguous positions forming a large continental mass at 1790 Ma ago. This is reinforced by geological evidence which support the existence of the supercontinent Columbia in Paleoproterozoic times.
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- Nunes, S. C., et al.
(författare)
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Diurea cross-linked poly(oxyethylene)/siloxane ormolytes for lithium batteries
- 2005
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Ingår i: Journal of the Electrochemical Society. - : The Electrochemical Society. - 1945-7111 .- 0013-4651. ; 152:2
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Tidskriftsartikel (refereegranskat)abstract
- Poly(oxyethylene) (POE)/siloxane hybrids (di-ureasils) doped with a wide concentration range of lithium triflate (LiCF3SO3) were investigated. The host matrix of these materials [d-U(2000)] is a sol-gel-derived siliceous framework to which POE chains with about 40.3 repeat units are bonded through urea linkages. Xerogels with ∞ ≥ n ≥ 5 (n is the molar ratio OCH2CH2/Li+) were obtained as amorphous monoliths thermally stable up to at least 340°C. A crystalline POE/LiCF3SO3 complex was detected spectroscopically in samples with n ≤ 10. Below 90°C the ormolyte with n = 20 exhibits the highest conductivity (5.8 × 10-6 n-l cm-1 at 26°C). The redox stability domain of this material spans 4.1 V. Although Fourier transform infrared spectroscopy data suggest that the Li+ ions are complexed by the POE ether oxygen atoms at n ≤10, this threshold composition is probably located at slightly lower salt content "Free" triflate ions and weakly coordinated anions, present in all the samples examined, must be the main charge carriers of the d-U(2000) 20LiCF3SO3 xerogel. Ion pairs (Li +CF3SO3-) or negatively charged triplets ([Li(CF3SO3)2]-) are formed at n ≤ 40. At n ≤ 5 positively charged triplets [Li2(CF 3SO3)]+ also appear. Divalent positively charged multiplets [Li3(CF3SO3)]2+ occur at n = 1.
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