Slayt 1

1


The Investigation of Dielectric Properties of
Tremolite
E. Izci, A. Izci Email erizci_at_anadolu.edu.tr
Anadolu University Physics Department 26470
Eskisehir TURKEY Eskisehir Osmangazi
University, Department of Chemical Engineering,
Meselik 26480-Eskisehir/TURKEY
Fig. 1
Results and Discussion
Tremolite Tremolite is a member of the calcic
amphibole group of minerals. The essential
feature of the structures of all amphiboles is
the presence of (Si, Al)O4 tetrahedral linked to
form chains which have double the width of those
in pyroxenes and have the composition (Si,
Al)4O11. The crystal structure of tremolite is
characterized by double silicate chains linked
together by strips of Mg2cations occupying three
octahedral sites (M1, M2, and M3) and an ideal
eightfold- coordinated polyhedral site (M4). The
M1, M2, and M3 sites are fully occupied by Mg and
the M4 site by Ca. These chains repeat along
their length at intervals of 5.275 A0 for
tremolite and this defines the c parameter of the
unit cell. Its A sites are vacant. Tremolites
chemical formula is Ca2Mg5Si8O22(OH)2. When it is
heated and decomposes, it loses water 1 10.
The variation of the permittivity, e/, with log
frequency at different firing temperatures
between 200 and 1200 0C is shown in Fig. 1. At
frequencies between 3 kHz and 40 MHz, the
permititvity, e/, is in the range of 3.48 6.18
at different firing temperatures between 200 and
1200 0C. The permittivity of tremolite at 20 0C
is 7.03 17. It is known to be a member of low
permitivity dielectrics because its permittivity
values are lower than 15 and because of these
properties. It is widely used for straightforward
insulation 18 It can be seen that the
permittivity decreases gradually with an increase
in firing temperatures up to 400 0C. It is seen
that permittivity, e/, decreases with an increase
in log frequency at all the firing temperatures.
This is a normal behavior of dielectric
materials.
Conclusion
The applied frequency and firing temperature
affect the conductivity and dielectric
properties. In this work, we have studied the
effects of the firing temperature and frequency
on the dielectric properties of tremolite at room
temperature. The permittivity values of tremolite
range from 3.90 to 6.18 depending on the firing
temperatures at 1 kHz frequency. Tremolite is a
dielectric material and it is a member of low
permittivity dielectrics (e/ lt 15). It can widely
used for straightforward insulation and it can
find some applications as capacitor dielectrics
where very small capacitances are required for
use at higher frequencies.
Fig. 1. Frequency dependence of the permittivity
of tremolite that was fired different firing
temperatures at room temperature.
Fig. 2
Fig. 2 shows the variation of the loss tangent,
tand, with log frequency at different firing
temperatures between 200 and 1200 0C for
tremolite at room temperature. This variation is
similar to the variation of permittivity with log
frequency. It is observed that both permittivity
and loss tangent decrease with frequency, which
is one of the features of polar dielectrics 19,
20. The loss tangent, tand, decreases from 0.046
to 0.004 when log frequency is increased from
5.00 to 7.00, at different firing temperatures.
Especially at low frequencies, the dielectric
losses are due to ionic conduction, and at higher
frequencies, rotation of permanent dipoles. The
ionic conduction losses are due to ohmic losses.
Ohmic losses occur when ions move through the
material. Ionic conduction losses decreases with
increasing frequency the time allowed for
transport in the direction of the field decreases
with increasing frequency. Both processes
contribute to the losses 21. At 6.6 MHz
frequency, loss tangent of firing tremolite at
1200 0C sharply increases because of tremolite
property.
Dielectric Properties 11 14. C0 The
geometrical capacitance in vacuum A Area of the
large plate capacitor d Thickness of the large
plate capacitor e0 Dielectric constant of a
vacuum ( 8,85.10-12 F/m). er The relative
permittivity of the material e/ The permittivity
e// The dielectric loss ( loss factor) G
Conductance B Susceptance tand Loss
tangent sac AC Conductivity
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Fig.2. Dependence of the loss tangent (tand) on
frequency of tremolite that was fired different
firing temperatures at room temperature.
Fig. 3


Aim The aim of the present study was to
investigate dielectric properties of tremolite
that was fired at different temperatures.
The variation in the AC conductivity with log
frequency at different firing temperatures for
tremolite sample is shown in Fig. 3, it is
observed that the rate of increase of AC
conductivity with log frequency is found to be
highest for sample which was fired at 400 0C.
Experimental
Material The natural tremolite mineral used in
this study was supplied from Mihalliccik,
Eskisehir in Turkey. Tremolite used in this study
contains mainly 54.4 SiO2, 22.82 MgO, 15.04
CaO, and 1.45 Al2O3.
Fig. 4
Fig. 3. Variation of conductivity with log
frequency at different firing temperatures at
room temperature.
Fig. 5 shows the variation of the permittivity,
e/, with firing temperatures between 200 and 1200
0C at 0.1 MHz, 1 MHz and 10 MHz frequencies. From
the graph, it can be seen that the permittivity
increases gradually in firing temperatures below
to 400 0C. The value of permittivity is constant
during firing at 400 to 1000 0C and it decreases
at firing temperature between 1000 and 1200 0C.
When tremolite is fired at temperatures gt 1000
0C, it transforms into Mg - silicate 21. As a
result, the permittivity value decreases sharply
at 1200 0C, its value is minimum for 1, 5 and 10
MHz frequencies. Decomposition temperature is
between 950 and 1040 0C and the fusion
temperature for tremoite exceeds 1224 0C 21,
22.
Characterization The x- ray powder diffraction
(XRD) measurements were taken on a Rigaku
RINT2000 difractometer using run at 40kV and 30
mA by using the CuKa radiation.
Tremolite Hastingsite
Fig. 5
Fig.4. Dependence of permittivity on firing
temperature of tremolite at room temperature, for
constant frequencies (0.1 MHz, 1 MHz and 10 MHz).
Acknowledgements I
Experimental Procedure The partical size of
the tremolite which was milled was in the range
of 60 90 µm. The samples used in this study
were compacted to pellets with a diameter of 6.5
mm and thickness of 0.693 / -0.082 mm, under a
pressure of 3 ton. They were placed on a ceramic
plate and fired at different temperatures for 1 h
and afterwards, they cooled to room temperature
15, 16. Electric contacts are deposited by
sputtering a platinum film on the surface of
them. The conductance (G) and susceptance (B) of
these pellets were measured in the frequency
range 103 Hz to 40x106 Hz at room temperature by
using HP 4194A LF Impedance Analyzer. The
permittivity (e/), loss tangent (tand) and ac
conductivity (sac) of them were calculated at
these measuring results. e/, tand and sac versus
frequencies between 103 Hz and 106 Hz for
different firing temperatures were plotted and
commented them.
We thank Prof. Dr. H. Mandal and Prof. Dr. Aydin
Dogan and other members of this department
allowing and helping us to take our measurements
in investigation laboratories of Department of
Material Science and Engineering at Anadolu
University in Turkey.
The loss tangent of each sample fired at
temperatures from 200 up to 1200 0C is
graphically plotted as a function of firing
temperature in Fig. 5. It can be seen that the
loss tangent values for these samples increase
with firing temperatures between 200 and 400 0C
and at 0.1 MHz frequency the loss tangent of
tremolite sample has maximum value at firing
temperature 400 0C at room temperature. Because
of decomposition and fusion temperature of
tremolite samples, the loss tangent values of
samples decrease in the firing temperature
between 400 and 1000 0C at room temperature.
Then, stable loss tangent values are observed
with increasing temperature at room temperature.
Decomposition temperature of tremolite is between
950 and 1040 0C and fusion temperature of it is
1224 0C 21, 22.
Fig. 5. Dependence of loss tangent on firing
temperature of tremolite at room temperature, for
constant frequencies (0.1 MHz, 1 MHz and 10 MHz).
10th International Conference of the European
Ceramic Society Poster No C - 436