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International Journal of Plasma Environmental Science & Technology, Vol.5, No.1, MARCH 2011
Geomagnetism due to a Piezo Electrical Activity of D” Layer
A. Toureille1, G. Touchard2, and A. Mizuno3
1
IES, Montpellier 2 University, France
2
LEA, University of Poitiers, France
3
Department of Environmental and Life Sciences, Toyohashi University of Technology, Japan
Abstract—The origin of geomagnetism is problematic: the latest theory made by geologists tries to explain
geomagnetism by MHD complex phenomena in the liquid core, with the help of an original magnetic field. The latter came
from the sun in the past to give the quick initial impulsion to start the geodynamo which is now auto-excited. But the MHD
simulations fail to explain geomagnetism, even during the reverse periods. The very center of the Earth is made of hard
iron too hot to be ferromagnetic. So, first, we’ll discuss about the failure of this theory. Then, concerning certitudes, the
relative movement of the liquid core is the main mechanical cause of the geomagnetism origin: this liquid core contains
essentially iron, nickel, sulphur, and oxygen and is submitted to important axial convection vortexes. So, in D”-CMB area,
the liquid part of the core penetrates periodically in the particular clusters of solid mantle at very high pressure and high
temperature. Recent discovery shows that these materials are perovskytes and post-perovskytes which are piezo and
pyroelectric. Therefore, it appears that there must be a phenomenon of electrical activity due to the dynamic interface
mantle-liquid core. So, then referring to that effect, never considered in the past, we give a new theory, supported by
experiments, explaining the origin of geomagnetism by involving a particular “flow electrification” associated with high
piezo and pyroelectrical materials. To finish, we discuss about the plausibility of this new theory.
Keywords—Geomagnetism, D” layer, flow-electrification, piezo and pyroelectricity, perovskites, post-perovskytes
I. INTRODUCTION
So far we have not got any confirmed theory of
geomagnetism: most specialists think that the
phenomenon « would come from convective movements
of the liquid core which would be a good electric
conductor revolving in a magnetic field » [1]. This MHD
theory starts from the existence of an original magnetic
field created by a current from the sun in the past. Then,
it appeared, by reaction, a complex moving distribution
of curls of current in the liquid core volume which would
have maintained geomagnetism, like an auto-excited
dynamo after energization. Experiments made with
sodium revolving at high speed in copper gave positive
results which seemed encouraging, but the experimental
conditions have been questioned [2].
But at present no simulation based on this MHD
theory, referring to plausible physical parameters, seems
satisfying and theoreticians need enormous computers
and informatic means which could be reached in a few
years from now [3, 4].
The long standing evocation (and in nearly most
publications) of this auto-excited geodynamo is very
surprising for us. As a matter of fact, the current given by
an outside excitation in a circuit tends to create an
opposition to this excitation but it disappears once this
excitation is finished (Lenz’s law). Moreover in the case
of the Earth, the active revolving conductor submitted to
the perpendicular magnetic field can give a radial current
in the direction of its electromotive force and therefore
this system is unable to create an axial current likely to
engender the principal geomagnetism.
Corresponding author: Alain Toureille
e-mail address: [email protected]
Received; April 15, 2010
Then, according to MHD theory, the principal
geomagnetism is created by curls of currents that exist in
the liquid core volume. We cannot agree with this
assumption: we think that those curls of currents are
submitted to Laplace force which extends them towards
the interface mantle-core area where they are blocked.
So, taking into account these fundamental features,
we think interesting to analyze the phenomenon
differently. Here, we give a different interpretation of the
principal geomagnetism field. Our theory explains that
the geomagnetism is due to the presence of an axial
spheric current in D” layer which is a transition area
between the liquid core and the mantle of the Earth.
The flow electrification, the pyro and piezo
electricity, are natural phenomena which can induce
important voltage by streaming an insulating liquid on
conductor solid [5, 6]. But, also, a strong current can be
obtained by short-circuiting this device or using a metal
liquid streaming on glass as shown by us in an
experimental part and other publications: using these
assumptions, we have shown in a previous paper the
possibilities of explanation of geomagnetism by this way
[7].
In the present paper, we add and study the properties
of piezoelectricity of D” recently discovered by
geologists [8-10] in 2004.
We call this model “D” model” by opposition to
MHD model which is a bulk model in the liquid core.
First, here, we recall the geologic situation and we
fix the electrical parameters in the D” model to create the
principal geomagnetism (current and current density).
Then, we have made experiments with powders of
BaTiO3 to evaluate the contribution of piezo materials
(characteristics of BaTiO3 is similar to Mg-FeSiO3
perovskytes discovered in D”), and we’ll transfer these
results to the Earth to obtain conform numerical values of
Toureille et al.
81
the source of the current. To finish we will discuss the
results and their consequences.
Upper mantle
II. GEOLOGIC SITUATION
Today, geologists seem to agree with the following
composition of our spherical planet as shown in Fig. 1:
-the mantle (silicate, olivine) a bad electric conductor,
goes from the surface (with a radius of 6470 km) to the
Core Mantle Boundary (CMB with a radius r0 = 3480
km). There the temperature goes up to 2250oC. The
origin of the inner thermal sources of our planet is
essentially nuclear (40 Tw are produced in the mantle as
thermal power)
-the core contains principally liquid iron (85%), Ni
(7.5%), sulphur and oxygen and goes from this interface
(Core Mantle Boundary or CMB) with a radius of r0 =
3480 km to a radius of r1 = 1221 km where it becomes
solid (the grain). The temperature there goes from 4000
to 5000oC. The conductibility of the liquid would be
about 0.1 MS/m
-the D” transition layer between the core and the
mantle: it is about 200 km thick. There, the temperature
evolves very quickly from 2250 to about 4000oC;
therefore we have a strong thermal gradient and a high
pressure (130 GPa). But the featured property is that it is
a very particular matter: there exist a great number of
solid clusters of pallasites and siderites (iron and olivine)
in this liquid magma. These materials have strong
permittivities. Moreover recent discoveries show that
with the particular conditions existing in D”, the silicate
MgSiO3 is transformed into perovskyte then postperovskyte which is an orthorhombic crystal group
Cmcm: this crystal is oriented by the pressure and
temperature gradient and the diagram stability is about 6
MPa/deg [8-10]
So, these last crystals are ordered anisotrops and
have a strong permittivity: they are piezo and pyro
electric.
In fact, geologists think that the whole liquid core is
submitted to important convection movements (2 Tw are
needed as mechanical power): apparently they have the
shape of gigantic vortexes revolving on an axis almost
parallel to that of the Earth with a maximum velocity of
about some mm/s relative to the mantle [3].
III. THEORY OF D” MODEL
First we evaluate the current and its density to create
geomagnetism from D” layer.
We use a very simple macroscopic model to evaluate
the order of magnitude concerning the different
parameters.
With a piezoelectric material submitted to the
pressure we can obtain several components of current.
Here we have the principal pressure P (135 GPa)
oriented to the center of the Earth. The variation dP of
this component creates currents whose sum is zero
Lower mantle
D''
CMB
r0
Liquid
core
Grain
r1
Fig. 1. Cross section of the Earth.
(spherical geometry). Moreover if this effect can bring
charges locally on the surfaces limiting D”, these charges
can be removed only by the conductive vortex at the
basis of D”, giving one axial current.
By the same result, the variation of pressure due to
the vortexes on the faces of the clusters are also axial [4]
and give an axial current component.
Consequently, we think the axial component is
majority in a spherical layer (part or all D” area).
We suppose that the vortex speed is maximum at the
equator level and nil at the pole level.
Fig. 2 shows a cross section of the Earth at D”-CMB
area, the current I, the direction of the geomagnetism B,
the clusters, the vortexes from the core penetrating in D”,
the pressure.
Following this model, we consider in D” area the
component J0 of the current density inside the D” zone at
the equator level. To simplify e is the active thickness of
D” (e << r0, radius of CMB sphere).
The magnetic momentum of the Earth is about M =
8×1022 Am².
Taking into account that the convection is function
of the latitude we write:
J = J0 cos
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International Journal of Plasma Environmental Science & Technology, Vol.5, No.1, MARCH 2011
contacts. Therefore, the solid wall given by the end of the
mantle is submitted to the total Laplace force.
In MHD theory, where the current buckles are in the
bulk of the liquid core, this effect is not compensated: it
is an important aspect in favor of D” model.
After calculating D” model parameter, we must link
these values with the experimental values and physical
causes.
CMB
Active layer
thickness e
D”
Current
B
CORE
IV. EXPERIMENTS AND LINK WITH THE EARTH
Pressure
Vortexes
Clusters
Fig. 2. The D” model.
 being the latitude, J0 is the current density, mean
value of all the concerned systems: it can go in one way
or in the opposite one (reversal of geomagnetism).
Elementary current is dI = J dS, with elementary of
surface dS = r0e d, then the elementary magnetic
momentum is given by:
dM = dI r2, with r = r0cos
therefore:
dM = J0 d er0cos3
By integrating from -/2 to /2, we find:
M = 4J0r03e/3
Our experiments have been made on BaTiO3
powder to measure the longitudinal current component
given by pressure on this piezoelectric material. The
results have shown current density of 0.8 A/m2 with a
pressure variation of 4000 Pa, during several ten seconds.
This law was checked linear to 40000 Pa at least. With a
linear extrapolation of some 1.5 GPa of variation (1% of
150 GPa existing in D”), we can reach 200 mA/m²
without considering the temperature effect!. That is
largely sufficient to create the some mA/m2 asked. But
the pressure moves of vortex are periodic and the
pressure effects are in two opposite ways creating a
positive current (pressure) then a negative current
(depressure). If the two effects do not have exactly the
same dynamic (shocks between the clusters, geometry
and particular positions of clusters, then an effect is
stronger (positive or negative) corresponding to positive
or negative geomagnetism.
Piezoelectric and pyro-electric material have high
permittivity, therefore, in electric field, those clusters
orient the direction towards the e-field. This could cause
a positive feedback of the charge generation in the D”
zone. With time, the high permittivity clusters gradually
orient their direction towards the external e-field, and
with the nature of their piezo and pyro-electricity,
direction of the generated current by pressures and
collisions tends to align to form a current to form B.
(1)
And the total current is:
I = 2Jr0e
Using that e (D” zone) is about 200 km [1] we find:
J0 = 2.25×10-3 A/m2, I = 3.15×109 A (3.15 GigaA)
These values seem realistic, but the density J0 is a
minimum: in fact the active thickness e is smaller and J0
taller.
In D”, the current I which creates B, is submitted to
the electromagnetic (Laplace) force which extends to the
mantle, but here the clusters constitute a resistant
material which limits the displacement. Even if this light
displacement exists, it can contribute to shocks and
V. CONCLUDING REMARKS
In using all D” zone, the value of some mA/m²
necessary to explain the principal geomagnetism is
therefore well inferior to piezo capacities. But in fact, the
active area e can be less than 200 km and would concern
the interface zone with CMB (called ULVZ zone of some
km thick at the basis of D”). With this assumption the
reverse of geomagnetism can be explained by a change
of the vortex dynamic.
Certainly all those given values can be slightly
modified, but, our aim is to attract geologists’ attention
about these important electric phenomena often ignored
by non-electrical specialists. Electrically speaking, the
materials in D” area are very sensitive: during volcano
eruptions, flashes of lightning among the plumes of
smoke have often been observed.
Toureille et al.
83
ACKNOWLEDGMENT
The authors are grateful to late Prof. Emeritus J. S.
Chang of McMaster University for pertinent discussions
given to this work. We want to thank gratefully Philippe
Cardin from Université Joseph Fourier (Grenoble France)
who is studying successfully the convection movements
of the core: He has informed us about the principal
parameters of the Earth and also about the problem of the
origin of geomagnetism [4].
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