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|Title: ||Electric transport in different granitic rocks|
|Authors: ||Silva, Hugo Gonçalves|
|Keywords: ||Seismic precursors|
|Issue Date: ||8-Apr-2011|
|Publisher: ||EGU General Assembly 2011|
|Citation: ||Geophysical Research Abstracts
Vol. 13, EGU2011-3097, 2011|
|Abstract: ||Many studies are being done to understand acoustic to electromagnetic conversion in rocks, , mainly because
of the so-called seismo-electromagnetic phenomena (SEMG). Nevertheless, to our knowledge, most of them
disregard a preliminary analysis of the electrical transport occurring in these rocks. These are, in fact, crucial
to understand any electromagnetic process occurring in the materials since they clarify the transport mechanism
(typically in rocks it is ionic, but it could also be tunnelling, among others), the energies involved (typically
1-100 meV), charge accumulation effects, and many other aspects. Thus, we believe that it deserves more
attention by researchers.
The objective of this work is, indeed, to initiate a detailed analysis of the electrical transport in various
rocks using our experience with other materials . As a start three different granitic samples with different
mineralogical content have been studied: the ﬁrst is a coarse grained biotitic granite, yellow coloured and
characterized by an abundance of large feldspar megacrystals usually showing poorly deﬁned shapes, the second is
a quartz diorite grey coloured and medium grained rock with homogeneous appearance, dominantly biotitic, and
the third is a medium grained homogeneous pophyroid granite, with light rosy colour determined by the tonality
of the feldspar crystals that stand out from a greyish with matrix containing dark grains. Moreover, granites are
abundant in the lithosphere and should, in principle, play a fundamental role in (SEMG).
Circular samples with approximately 24 mm diameter and 2-4 mm in thicknesses were prepared. Once cut
and carefully polished (with a 15 m polishing disc) the samples here heated from room-temperature up to 400
K and after cooled down again. Circular electrodes with a diameter of 20 mm were then established using silver
conductive paint. The samples were submitted again to a heat treatment at 400 K to evaporate the silver paint
solvent. After this preparation procedure the samples were attached to a sample holder and inserted in a bath
Moreover, the focus of this work is to elucidate the effect of conﬁned water in the electrical transport
properties for temperatures ranging from 80 K up 400 K. The presence of conﬁned water was observed through
an anomaly in the dielectric behaviour near T ~ 220K. This temperature is typical of the super-cooled phase
transition of strongly conﬁned water affecting electronic devises . Thus, in this work we explore this anomaly
in the three different natural rock samples mentioned above. Other techniques used in the literature can also be
considered like thermal stimulated depolarization current  to characterize transport mechanisms.
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387, 4940 (2008).
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Mariano, S. Cardoso, and P.P. Freitas, Magnetic and transport properties of diluted granular multilayers, J. Appl.
Phys. 106, 113910 (2009).
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by trapped supercooled water, Appl. Phys. Lett. 88, 082101 (2006).
 A.N. Papathanassiou and J. Grammatikakis, Dielectric characterization of the water-matrix interactionin porous materials by thermal depolarization spectroscopy, Phys. Rev. B 61, 16514 (2000)|
|Appears in Collections:||CGE - Comunicações - Em Congressos Científicos Internacionais|
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