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Electrochemical synthesis of Cr(II) at carbon electrodes in acidic aqueous solutions (2000)

Yin, Q. ; Brandon, N.P. ; Kelsall, G.H.

Springer

Journal of applied electrochemistry 30 (2000), S. 1109-1117

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ISSN: 1572-8838

Keywords: carbon electrode ; chromium (III)/(II) ; electrochemical synthesis ; electrochemistry

Source: Springer Online Journal Archives 1860-2000

Topics: Chemistry and Pharmacology , Electrical Engineering, Measurement and Control Technology

Notes: Abstract The electrochemical synthesis of Cr(II) has been investigated on a vitreous carbon rotating disc electrode and a graphite felt electrode using cyclic voltammetry, impedance spectroscopy and chronoamperometry. The results show that in 0.1 M Cr(III) + 0.5 M sulphuric acid and in 0.1 M Cr(III) + 1 M hydrochloric acid over an electrode potential range of −0.8 to 0.8 V vs SCE, the electrochemical reaction at carbon electrodes is essentially a surface process of proton adsorption and desorption, without significant hydrogen evolution and chromium(II) formation. At electrode potentials more negative than −0.8 V vs SCE, both hydrogen evolution and chromium(II) formation occurred simultaneously. At electrode potentials −0.8 to −1.2 V vs SCE, the electrochemical reduction of Cr(III) on carbon electrodes is controlled mainly by charge transfer rather than mass transport. Measurements on vitreous carbon and graphite felt electrodes in 1 M HCl, with and without 0.1 M CrCl3, allowed the exchange current density and Tafel slope for hydrogen evolution, and for the reduction of Cr(III) to Cr(II), to be determined. The chromium(III) reduction on vitreous carbon and graphite electrodes can be predicted by the extended high field approximation of the Butler–Volmer equation, with a term reflecting the conversion rate of Cr(III) to Cr(II).

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1023/A:1004052419708

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Micromagnetic coercivity distributions and interactions in chondrules with implications for paleointensities of the early solar system (2007)

Acton, G. ; Yin, Q.-Z. ; Verosuv, K. L. ; [et al.]

American Geophysical Union

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Publication Date: 2017-04-04

Description: Chondrules in chondritic meteorites record the earliest stages of formation of the solar system, potentially providing information about the magnitude of early magnetic fields and early physical and chemical conditions. Using first-order reversal curves (FORCs), we map the coercivity distributions and interactions of 32 chondrules from the Allende, Karoonda, and Bjurbole meteorites. Distinctly different distributions and interactions exist for the three meteorites. The coercivity distributions are lognormal shaped, with Bjurbole distributions being bimodal or trimodal. The highest-coercivity mode in the Bjurbole chondrules is derived from tetrataenite, which interacts strongly with the lower-coercivity grains in a manner unlike that seen in terrestrial rocks. Such strong interactions have the potential to bias paleointensity estimates. Moreover, because a significant portion of the coercivity distributions for most of the chondrules is 〈10 mT, low-coercivity magnetic overprints are common. Therefore paleointensities based on the REM method, which rely on ratios of the natural remanent magnetization (NRM) to the saturation isothermal remanent magnetization (IRM) without magnetic cleaning, will probably be biased. The paleointensity bias is found to be about an order of magnitude for most chondrules with low-coercivity overprints. Paleointensity estimates based on a method we call REMc, which uses NRM/IRM ratios after magnetic cleaning, avoid this overprinting bias. Allende chondrules, which are the most pristine and possibly record the paleofield of the early solar system, have a mean REMc paleointensity of 10.4 μT. Karoonda and Bjurbole chondrules, which have experienced some thermal alteration, have REMc paleointensities of 4.6 and 3.2 μT, respectively.

Description: NSF and INGV

Description: Published

Description: B03S90

Description: 2.2. Laboratorio di paleomagnetismo

Description: JCR Journal

Description: reserved

Keywords: paleomagnetism coercivity ; paleointensity ; magnetic interactions ; meteorite ; Chondrules ; FORC diagrams ; 01. Atmosphere::01.03. Magnetosphere::01.03.01. Interplanetary physics

Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)

Type: article

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