Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02480285 2004-09-22
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LEAD IRON TUNGSTATE CAPACITIVE TRANSDUCER, RELAXOR MATERIAL
THEREFOR, METHOD OF MANUFACTURE OF RELAXOR MATERIAL
Field of the invention
This invention relates to a lead iron tungstate capacitive transducer. More
particularly,
the invention relates to a lead iron tungstate capacitive pressure transducer
with low
temperature coefficient, high pressure coefficient and low hysteresis.
Background of the invention
Measurement of pressure is very vital in industrial manufacturing and
processing.
Particularly measurement of pressure with accuracy over a wide range is needed
in such
industries as automobiles, aerospace, steel and for synthesis of high strength
materials. In all
these industrial sectors, the accuracy in measurement is of paramount
importance not only
due to quality considerations but also to safety requirements. No single
gadget can measure
the entire pressure range with the same accuracy and reproducibility. The
gadgets may also
not be sensitive enough to small changes in pressure and be stable over a wide
working
temperature (in the range of 10-50 C). A system is therefore required which
will have the
necessary characteristics of large pressure coefficient to detect small
changes even in a large
absolute value and have a minimum drift over a large temperature range i.e.
have a low
temperature coefficient. Pressure measurements have traditionally been made
using a liquid
column manometer. While this serves as an absolute instrument, its use is
limited to lower
ranges for pressure of 0.1Pa to 200 kPa. Another disadvantage of this device
is that it cannot
be transported easily from one place to another. P. L. M. Heydemann and B. E.
Welch, et al
in `Experimental Thermodynamics', (Vol. II, B. LeNiendre and B. Vodar (eds),
Butterworths
(1975)), R. S. Dadson, et al in `The Pressure Balance: Theory and Practice',
National
Physical Laboratory, Teddington, England and J. K. N. Sharma and Kamlesh K.
Jain,
Pramana, JPhys Vo127 pp 417 (1986) disclose that pressures up to 300MPa can be
measured
easily by piston gauges and that these piston gauges can be transported after
taking certain
precautions. However, these piston gauges cannot be used for pressures beyond
300MPa
without increasing the size of the entire assembly thereby making it
cumbersome to use even
with trained manpower. As a result this device is useless for fieldwork.
G. F. Molinar and L. Bianchi and J. K. N. Sharma, et al disclose use of
manganin
resistance wires to sense pressures over a wide range. The main drawback of
manganin
resistance wires is low accuracy of just 0.1 % when the requirement normally
is of at least
0.05% or better. Further this sensor has an undesirable property of zero shift
with time
leading to erroneous measurements and needs stringent temperature control
during
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measurement. While this device may be useful for high-pressure work, use for
low pressure
ranges like 58 Mpa is limited. In order to cover lower ranges one necessarily
has to use
another device. Another pressure measuring device is disclosed by A. W. Birks
(Report No.
1566 of Queen's University of Belfast). This disclosure describes the device
as a Strain
Gauge. However, this device also suffers from the same drawbacks as for
manganin wire and
accuracy in pressure measurement of this device is low due to large hysteresis
and zero shift.
Yet another type of a pressure measuring device based on resistance
measurement has
been disclosed in a US Patent No. 5,578,765. The said patent disclosure
teaches that the
pressure due to an applied force on a transducer array, essentially consisting
of resistive
elements leads to a change in the resistance value when the applied force is
changed. The
dependence of pressure is related to gradual touching of the two arrays
thereby decreasing the
resistance of the system. The inventors have disclosed curvilinear relation
between the
measured resistance and the applied pressure. At high pressures, the
resistance drops to fairly
low values. This low resistance values may not be measurable so accurately
thereby leading
to possible errors in pressure measurement. Another drawback is that the
device of this patent
needs a threshold pressure for it to act as a pressure sensor. As a result,
the use of this device
is limited in respect of pressures lower than the required threshold value. G.
F. Molinar, et al
in 1998 attempted to use a ceramic rod to improve upon the existing pressure
sensor
(Measurement, Vol. 24, pp 161 (1998)). While this pressure transducer had
improved
resolution and sensitivity, it lacked repeatability and had marked hysteresis.
The presence of
last property is undesirable as this leads to increased error in the measured
pressure.
PCT Application PCT/WO US9405313 discloses a capacitive transducer that can
measure pressure from as low as 100PSI to 22,000 PSI. However, the structure
used is rather
complicated - a metal diaphragm is separated from a dielectric alumina by as
small a distance
as 0.00005 inch and 0.020 inch. This small distance between the metal
diaphragm and the
insulator disc is difficult to maintain. Further the transducer when needed
for a field
experiment, does not possess the ruggedness to withstand transit movements.
The device of
this disclosure also has high hysteresis due to its very structure. Andeen, et
al, in Rev. of Sci.
Instruments, Vol. 42, PP 495, (1971), disclose the use of ionic crystals as
pressure sensing
elements when formed as capacitor in sandwich structure. The pressure
measurement is
based on the principle of change in capacitance with applied pressure, of the
capacitor
structure with the material as dielectric medium between two electrodes.
However the
materials reported showed a larger change in capacitance by a change in
temperature (temp.
coefficient = 250ppm/ C) and low pressure coefficient (-38 ppm/MPa). As a
result, the
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materials disclosed serve more as temperature sensors rather than pressure
sensors.
Kamlesh K. Jain and Subhash C. Kashyap in `High Temperature and High
Pressures'
Vol. 27/28 pp 371 (1995), disclose the use of bismuth germanium oxide. It is
disclosed that
pressure coefficient and temperature coefficient of capacitance are 100
ppm/MPa and
60ppm/ C respectively. This is an indication 6f the utility of variation of
capacitance with
pressure as a means to measure pressure. The reliability is guaranteed to a
certain extent due
to low temperature coefficient but not to a level of being used as a pressure
gauge. Yet
another material is disclosed by M. V. Radhika Rao, et al in J Material
Science Letter Vol.
12, pp 122 (1997). The material disclosed is a relaxor material of following
composition:
44% Lead Iron Niobate, 44% Lead Zirconium Niobate and 12 % Barium Titanate.
Pressure
coefficient of this complex was observed to increase but without any
significant decrease in
temperature coefficient thereby again rendering material not worthy of being
used as pressure
transducer with capacitance parameter. Typical sintering process parameter as
temperature:
900 C.The pressure coefficient was 430ppm/MPa while temperature coefficient
was
+0.002/ C. Thus, the said relaxor material does not have much use as a
pressure transducer.
The general draw back in all the prior art disclosure, is, therefore, low
accuracy,
limited usable pressure range, dependence on the need to maintain precise
temperature of the
transducer, and hysteresis.
Objects of the invention
The main object of the present invention is to provide a lead iron tungstate
capacitive
transducer.
Another object of the invention is to provide a process of preparation of lead
iron
tungstate material with low thermal coefficient, high-pressure coefficient and
low hysteresis.
A fiu-ther object of the invention is to provide a solid state calcination
method for
preparation of doped lead iron tungstate relaxor material.
A still further object of the present invention is to provide a two step
calcination
process for the preparation of lead iron tungstate relaxor material not
requiring any doping.
Another object of the invention is to provide a capacitance pressure
transducer for
wide pressure range measurement from a low value of 0.5MPa to a high value of
415MPa.
Summary of the invention
Accordingly the present invention provides lead iron tungstate capacitive
pressure
transducer which comprises: a disc having a polished smooth first flat
surface, a polished
smooth second flat surface, the said polished smooth first flat surface being
completely
coaxed with metal electrode, the polished smooth second flat surface also
being coated with
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metal electrode, the said metal electrode on polished smooth second flat
surface comprising
formed coated circular portions comprising a central portion and a coated
annular concent: ==- ,
portion separated from the central portion by an annular concentric clear
region, conducting
metal wires being fixed to the metal electrode on polished smooth first flat
surface, metal
electrode on coated central portion of polished smooth second flat. surface
and metai
electrode on coated annular eoncentric portion of polished smooth second flat
surface.
In an embodiment of the present invention, the metal electrode is selected
from the
group consisting of silver, aluminum and gold.
In another embodiment of the present invention, the thickness of metal
electrode is in
the range of 1000-2000 A.
In another embodiment of the present invention, the width of annular
concentric
region is in the range of 10-50 A
In another embodiment of the invention, metal wires are gold or silver.
In another embodiment of present invention, purity of metal wire is at least
99.99%.
In a further exnbodiment of the present invention, the metal electrode is
deposited by a
known vacuum evaporation method such as thermal evaporatioii.
In a further embodiment of the present invention, the capacitive pressure
transducer is
useful for pressure measurement in a range of 0.5 Wa - 415MPa.
In another embodiment of the present invention, the accuracy of pressure
transducer is
0.05% over the entire range of 0.5 MPa - 4l 5Mpa.
In yet another embodiment of the present invention, the absolute value of
pressure
coefficient of the transducer is in the range of 497ppm/MPa to 622ppm/MPa.
In another embodiment of the present invention, the temperature coefficient of
the
transducer is in the range of -0.006/ C to 0.008/ C.
In another embodiment of the invention, the transducer has negligible
hysteresis.
The invention also relates to lead iron tungstate relaxor material used for
manufacture
of capacitive transducers comprising in undoped form stoichiometric Pb(Fev3
W113)03.
In one embodiment of the invention, the relaxor material is doped with lead in
an
amount of 1% by wt or 5% by weight.
The invention also relates to a process for the preparation of relaxor
material useful in
the manufacture. of lead iron tungstate capacitive transducer by siibjecting
appropriate
mixture of weighed amount of the wet ground iron oxide and tungsten oxide and
lead oxide
taken in such quantities so as to yield the final material as an undoped
stoichiometric Pb(Fev3
W I/3)U 3 to solid state sintering.
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In one einbodiment of the process, purity of the starting materials is at
least 99.9%.
In another embodiment of the invention, excess PbO is used to obtain a self-
doped
stoichiometric relaxor material the level of doping being to the extent of 1%
5% by weight.
In another embodiment of the process, doping is done by adding excess amount
of
PbO salt in the initial mixture and wet grinding the mixture so obtained.
In another embodiment of the invention, the wet ground material is calcined at
a
temperature of at least 800 C for a period of 2 hours.
In another embodiment of the invention, the calcined material is further
ground for
about ten hours to ensure complete homogenization of the mixed and reacted
constituents.
In another embodiment of the invention, a binder, preferably polyvinyl alcohol
is
added to the homogenized powder.
The invention also relates to a two-step calcination process for the
preparation of lead
iron tungstate relaxor niaterial by subjecting appropriate mixture of weighed
amount of the
wet ground iron oxide and tungsten oxide to calcination at a temperature of
about 1000 C for
I5 a period of 2 hours, subjecting the calcined material to further grinding
for about ten hours
a Ler ri,ixin -t ;e lead-o~citl~'tt~yr '
g etd-a7finai pradnCt 5WrChibmetric Pb(Fev3-Wiii)03: --- -
Brief description of the accompanying drawings
Figure 1 represents variation of relative dielectric constant with pressure.
Plot (A) is
for pure lead iron tungstate matetia1, (B) is for lwt % lead doped material
and (C) is for
5wt o lead doped material.
Figure 2 represents variation of relative dielectric constant with temperature
of the
sample. Plot (A) is for pure lead iron tungstate rnaterial, (B) is for Iwt %
Pb doped material
and (C) is for 5 wt% o lead doped material.
Figure 3 represents variation of relative dielectric constant with pressure.
Curve (A) is
for the second calcination teinperature of 750 C. Curve (B) is for the second
calcination
teniperature of 810 C and curve (C) is for the second calcination temperature
of 830 C. The
sample temperature during capacitance measurement is 30 C.
Figure 4 represents variation of relative dielectric constant with temperature
of the
sample. Curve (A) is for the second calcination temperature of 750 C. Curve
(B) is for the
second calcination temperature of 810 C and curve (C) is for second
calcination temperature
of 830 C. The, applied pressure during all' measurements was 0.1 MPa.
Figure 5 is a cross-sectional view of the lead iron tungstate capacitive
pressure
transducer of the present invention.
5
,,..~....w. ~.,.~ ~~w , .
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Figure. 6 is top-plan view of the lead iron tungstate capacitor transducer of
Figure. 5.
DETAILED DESCRIPTION OF THE INVENTION
As shown in Figure. 5, lead iron tungstate capacitive pressure transducer 1
includes a lead
iron tungstate disc 2 having a polished smooth first flat surface 3, a
polished smooth
second flat surface 4, the polished smooth first flat surface 3 being
completely coated
with metal electrode 5, the polished smooth second flat surface 4 also being
coated with
metal electrode, the metal electrode on polished smooth second flat surface 4
including
formed coated circular portions comprising a central portion 6 and a coated
annular
concentric portion 7 separated from the central portion by an annular
concentric clear
region 8, conducting metal wire 9 being fixed to metal electrode 5 on polished
smooth
first flat surface 3, conducting metal wire 10 being fixed to metal electrode
6 on coated
central portion of polished smooth second flat surface 4 and conducting metal
wire 11
being fixed to metal electrode 7 on coated annular concentric portion of the
polished
smooth second flat surface 4.
Figure. 6 shows a top-plan view of the lead iron tungstate capacitive pressure
transducer
1, incTuding metal electrode 6 on coated central portion of polished smooth
second flat
surface 4, metal electrode 1 1 on coated annular concentric portion of
polished smooth
second flat surface 4, and annular concentric clear region 8.
The relaxor material of the present invention is prepared by solid state
sintering. All
the starting materials are pure and preferably have a purity of at least
99.9%. The materials
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are weighed in such quantities so as to yield the final material as an undoped
stoichiometric
Pb(Fe2/3 Wli3)03, (PFW). The same material can also be prepared by using
excess PbO such
that a self-doped stoichiometric PFW is obtained. Doping is done by putting
excess amount
of PbO salt in the initial mixture for wet grinding, for homogenization of the
material. Excess
amount of lead oxide is added to compensate for any loss of the lead component
due to high
vapour pressure during high temperature treatment. The other advantage of
adding excess
lead oxide is to get self-doping of lead in the final material to see the
effect on the
characteristics. Weighed and wet ground material is then calcined to effect
the complete
reaction of oxides to form the PFW. Calcination is generally done at a
temperature of at least
800 C for a period of 2 hours. Calcined material is further ground for about
ten hours. This
long duration grinding is necessary to ensure complete homogenization of the
mixed and
reacted constituents. A binder, preferably polyvinyl alcohol was added to this
powder. This
mixture is then put in a pelletising machine for making samples.
In a preferred embodiment, two-step calcination process for the preparation of
lead
iron tungstate relaxor material is used. In this method, referred to as
Columbite method, all
the starting materials are pure and preferably have a purity of at least
99.9%. The materials
are weighed in such quantities so as to yield the final material as a
stoichiometric Pb(Fe2/3
W1i3)03 herein after referred to as PFW. The appropriate weighed amount of the
wet ground
iron oxide and tungsten oxide is mixed and then calcined at a temperature of
preferably at
1000 C for a period of 2 hours. The calcined material is further ground for
about ten hours
after mixing the lead oxide. This long duration grinding is necessary to
ensure complete
homogenization of the mixed and reacted constituents. The mixed calcined
powder is again
calcined at a temperature in a range of 750 to 830 C and preferably at a
temperature of 810 C.
A binder, preferably polyvinyl alcohol is added to this powder. This mixture
is then put in a
pelletising machine for making disc shaped samples.
Typical size of the samples in both the preferred embodiments of preparation
of
relaxor material was, but not limited to, 18 mm in diameter and 1.5 mm
thickness. The PFW
samples prepared were then used to determine the parameters for pressure
measurement.
These samples were coated with a silver film on both sides by vacuum
evaporation to
complete the capacitive structure. The electrode structure was such that one
flat surface of the
disc was coated completely by a thin film of, preferably, silver. The other
flat surface
opposite to the first surface of the pellet was also coated with the silver
film through a thin
wire ring mask such that a central circular portion of the coated film was
formed along with a
peripheral annular concentric film at the rim.
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All the depositions were done by standard vacuuni thermal evaporation systems.
The
two portions were separated by a narrow clear annular concentric space. Width
of this clear
annular space was typically 50A.. The annular concentric ring was used to
eliminate errors
due to straY capacitance during ac measurement.s. Thin silver wires of purity
99.99% wee
attached to the metal electrodes. The so fonned capacitive structure was then
used to measure
the thermal coefficient and the pressure coefficient of the doped and undoped
PFW material
prepared by the two preferred embodiments of this invention for the
preparation of relaxor
material. For temperature and pressure measurement, the capacitive structure
was placed in a
standard speciunen holder. This holder was placed in a conventional high
pressure vessel.
Temperature of the vessel was maintained to within =0.05 C using temperature
bath (Model
No. RTE 8DD, NESLAB, USA). Pressure was transmitted through diethyl hexyl
sebacate
fluid.
At a preset constant temperature, pressure was varied gradually from
atmospheric
pressure (4.1 MPa to 415 Mpa) and the variation in the capacitance of the
specimen was
measured at fixed frequency of 1kHz by ft autpmatic capacitance. bridge
(Andeen
Hagerling, model 2500 A, USA). During measurement of pressure characteristics
of relaxor
rnaterial, the data were taken of variation of capacitance witli pressure
increasing in
magnitude as well as with decreasing pressure from the maximum pressure
applied. This was
done to deterniinne hysteresis in material.
Figure 1 shows the variation of the ratio KJICo with applied pressure at a
sample
temperature of 30 C. The ratio K/Ko is determined by calculating the
dielectric constants K
and Ka from the measured capacitance using the formula as given below:
Thickness of pellet x Capacitance
Dielectric constant =
Electrical permitivity of vacuum x Area of parallel plate
K and KQ are dielectric constant with pressure applied and without any applied
pressure
respectively.
In Figure 1, plot (A) is the variation of K/Ko with pressure for undoped
relaxor
material and shows a near straight line without any hysteresis. Plot (B) in
the same figure is
for doped material with I wt % Pb. The slope of this line is seen to be more
than that of (A)
indicating the -;ole of doping in improving pressure characteristics. This is
due to the fact that
a small change in pressure results in a large change in dielectric constant.
Curve (C) is for a 5
wt% doped lead material which further gives an enhanced slope of the curve
between
and pressure. Thus, increased doping leads to better characteristics of the
material. The
pressure coefficient being calculated by using the following expression:
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Change in dielectric constant
Pressure coefficient =
Initial Dielectric Constant x change in pressure
Next keeping a fixed pressure say of 0.1 MPa, temperature was varied from 10 C
to
50 C to measure the temperature coefficient of capacitance. During the
measurement of
temperature characteristics of the relaxor material, data was taken of
variation of capacitance
with temperature increasing in magnitude as well as with decreasing
temperature from the
maximum temperature reached in order to determine the hysteresis in the
material.
From the capacitance data and the dielectric constant, temperature coefficient
and the
pressure coefficient of the specimen were calculated using following formulas
Change in the dielectric constant
Temperature coefficient =
Initial Dielectric Constant x change in temperature
The dielectric constant was determined using the capacitance value and other
material
parameters and constants from the expressions given earlier in the
description.
Figure 2 shows the variation of K/Ko as a function of temperature at a given
fixed
pressure, say 0.1 MPa. Curve (A) is for undoped material while (B) and (C) are
for I wt /a
and 5wt % doped materials respectively. Plot (A) in the figure gives the slope
of the variation
as higher than that for plot (B) and (C). This clearly indicates that doping
by lead improves
the temperature behavior of the lead iron tungstate and that the material can
be easily put to
use as a pressure transducer having the desired property of high pressure
coefficient, and low
temperature coefficient.
Figure 3 shows the variation of the ratio K/Ko for the lead iron tungstate
relaxor
material samples prepared with the two-step calcination (Columbite process),
with applied
pressure at a sample temperature of 30 C, maintained to within 0.05 C. The
ratio K/K-0 is
determined by calculating the dielectric constants K and Ko from the measured
capacitance
using the following formula:
Thickness of pellet x Capacitance
Dielectric constant =
Electrical permitivity of vacuum x Area of parallel plate
K is the dielectric constant with pressure applied and Ko is the dielectric
constant
without any applied pressure.
In Figure 3 plot (A) is the variation of K/Ko with pressure for the relaxor
material and
shows a near straight line without any hysteresis. The plot is for a sample
which was calcined
. for a second time at 750 C after mixing required quantity of lead oxide for
a stoichiometric
material. Plot (B) in the same figure is for material with second calcination
temperature of
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810 C. The slope of this line is seen to be a bit less than that of (A)
indicating the role of
increase in sintering temperature on the pressure characteristics. Curve (C)
is for a sample
with second calcination temperature of 830 C, which shows some anomalous
behaviour but
has a tendency to give enhanced slope of the curve between K/Ko and pressure.
This points to
the fact that increase in cacination temperature may affect the pressure
characteristics. The
pressure coefficient being calculated by using the following expression:
Change in dielectric constant
Pressure coefficient =
Initial Dielectric Constant. x change in pressure
Next keeping a fixed pressure say of 0.1MPa, temperature of the sample was
varied
from 10 C to 50 C to measure the temperature coefficient of capacitance.
During the
measurement of temperature characteristics of the relaxor material, the data
were taken of
variation of capacitance with temperature increasing in magnitude as well as
with decreasing
temperature from the maximum temperature reached. This was done to determine
the
hysteresis in the material. From the capacitance data the dielectric constant,
temperature
coefficient of the specimen were calculated using following formula
Change in the dielectric constant
Temperature coeffcient =
Initial Dielectric Constant x change in temperature
The dielectric constant was determined using the capacitance value and other
material
parameters and constants from the expressions given earlier in the
description.
Figure 4 shows the variation of K/Ko, as a function of temperature at a given
fixed
pressure, say 0.1 MPa. Here Ko is the dielectric constant at 10 C. Plot (A) is
the variation of
K/Ko with temperature for the relaxor material and does not show any
hysteresis. The plot is
for a sample, which was calcined for a second time at 750 C after mixing the
required
quantity of lead oxide for a stoichiometric material. The curve shows a
negative slope and
decreasing with increasing teinperature. This means that the material has a
better temperature
characteristic when worked at slightly higher temperature. Plot (B) in the
same figure is for a
material with second calcination temperature of 810 C. (B) in the figure gives
the slope of the
variation as higher than that for plot (A) though still being negative in the
temperature range
studied. Curve (C) is for a sample with second calcination temperature of 830
C. This curve
shows an anomalous behavior compared to (A) and (B) but is still capable of
being used as a
pressure transducer.
This is clearly indicative of the fact that the present process which does not
use any
doping material can be easily put to use as a pressure transducer having the
desired property
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of high pressure coefficient and low temperature coefficient. The above
mentioned behavior
in pressure and temperature characteristics may well be attributed to increase
in grain size of
the polycrystalline material which is formed as perovskite phase. The
scientific principle
underlying the use of lead iron tungstate relaxor material for pressure
measurement lies in the
fact that these materials show a large change in capacitance per unit change
in applied
pressure. In other words these materials have a large pressure coefficient of
capacitance.
Another characteristic of the material is that it has a low value for
temperature coefficient.
This property is very desirable and essential for the material to act as a
pressure sensor usable
in an environment where temperature fluctuations are inevitable. Also the
material to be
useful as a pressure sensor should not have a memory effect i.e. should not
have a hysteresis.
Novelty of relaxor material of the invention lies in its having low
temperature
coefficient, high pressure coefficient and low hysteresis due to the inventive
step of doping
by lead in excess of 1% of lead to the parent lead iron tungstate material.
For preparing Lead
Iron Tungstate [Pb(Fe2/3 Wli3)03-specimens abbreviated - PFW], starting oxides
were PbO,
Fe203 and W03. Specimens were prepared using following formula:
PbO + 1/3 Fe203 + 1/3 W03 + X
where X is the excess (0%, 1%, 5%) wt. % of PbO. PFW was prepared as 7 gm
sample by
taking 4.4171 gm of PbO, 1.0535 gm of FeZO3 and 1.5294 gm of W03.
In the two-step Coulumbite process X was zero.
The following examples are given by way of illustration only and should not be
construed to limit the scope of the invention.
Egample-1
Weighed quantities of lead oxide, tungsten trioxide and ferric oxide were
taken and
mixed and wet ground in acetone for 10 hours. This mixture was then calcined
at 810 C for
2h. The calcined powder was further ground for 10 hours. To this ground
calcined powder,
polyvinyl alcohol was added as binder, for making circular pellets of diameter
18 nun and
thickness 1.5 mm. The pellet was later sintered at a temperature of 870 C for
2 hours. After
sintering the specimen was cooled and after polishing of the surfaces, silver
electrodes were
formed on the flat surfaces by vacuum evaporation.
Example 2
The material of Examplel was used to measure the pressure characteristics. The
temperature of the material was kept constant at 30 C to within 0.05 C by
keeping the
inaterial in a constant temperature bath. The capacitance of the capacitor
structure
incorporating the lead iron tungstate material; was measured as a function of
pressure applied
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from 0.1 MPa to 415 MPa. The dielectric constant of the material was then
calculated and
plotted as a function of pressure. Pressure coefficient calculated from slope
of variation of
dielectric constant with pressure was found to be -500ppm/MPa
Example 3
The material of Example 1 was used to measure temperature characteristics.
Pressure
applied on the material was kept constant at 100 Mpa. Capacitance of the
capacitor structure
incorporating the lead iron tungstate material was measured as a function of
temperature of
the material (varying from 10 - 50 C) keeping the temperature constant to
within f0.05 C by
keeping the material in a constant temperature bath. Dielectric constant of
the material was
then calculated and plotted as a function of temperature. Temperature
coefficient calculated
from slope of variation of dielectric constant with temperature was found to
be -0.0066/ C
Example 4
Weighed quantities of lead oxide, tungsten trioxide and ferric oxide were
taken and
mixed with additional amount of 1 wt % PbO and wet ground in acetone for 10
hours. This
mixture was then calcined at 810 C for 2h. The calcined powder was further
ground for 10
hours. To this ground calcined powder, polyvinyl alcohol was added as binder
for making
circular pellets of diameter 18 mm and thickness 1.5 mm. The pellet was then
sintered at a
temperature of 870 C for 2 hours. After sintering, the specimen was cooled and
the surfaces
polished and silver electrodes were formed by vacuum evaporation.
Example 5
Material of Example 4 was used to measure pressure characteristics.
Temperature of
material was kept constant at 30 C to within f0.05 C by keeping material in
constant
teinperature bath. Capacitance of capacitor structure incorporating lead iron
tungstate
material was measured as function of pressure applied from 0.1MPa to 415 MPa.
Dielectric
constant of material was then calculated and plotted as function of pressure.
Pressure
coefficient calculated from slope of variation of dielectric constant with
pressure was found
to be 515ppm/Mpa.
Example 6
Material of Example 4 was used to measure temperature characteristics.
Pressure
applied on material was kept constant at 100 MPa Capacitance of capacitor
structure
incorporating lead iron tungstate material was measured as function of
temperature of
material (varying from 10-50 C) keeping temperature constant to within 0.05 C
by keeping
the material in a constant temperature bath. Dielectric constant of the
material was then
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calculated and plotted as a function of temperature. Temperature coefficient
calculated from
slope of variation of dielectric constant with temperature was found to be -
0.0069/ C.
Example 7
Weighed quantities of lead oxide, tungsten trioxide and ferric oxide were
taken and
mixed with additional amount of 5 wt% PbO and wet ground in acetone for 10
hours. The
mixture was then calcined at 810 C for 2h. Calcined powder was further ground
for 10 hours.
To this ground calcined powder, polyvinyl alcohol was added as binder for
making circular
pellets of diameter 18 mm and thickness 1.5 mm. The pellet was then sintered
at a
temperature of 870 C for 2 hours. After sintering, specimen was cooled and
surfaces polished
and silver electrodes formed by vacuum evaporation.
Example 8
Material of Example 7 was used to measure pressure characteristics.
Temperature of
material was kept constant at 30 C (f0.05 C) by keeping material in constant
temperature
bath. Capacitance of capacitor structure incorporating lead iron tungstate
material was
measured as function of pressure applied from 0.1MPa to 415 MPa. Dielectric
constant of
material was then calculated and plotted as function of pressure. Pressure
coefficient
calculated from slope of variation of dielectric constant with pressure was
found to be
556ppm/Mpa.
Example 9
The material of Example 7 was used to measure temperature characteristics.
Pressure
applied on the material was kept constant at 0.1 Mpa. Capacitance of the
capacitor structure
incorporating the lead iron tungstate material was measured as a function of
temperature of
the material (varying from 10 - 50 C) keeping the temperature constant to
within t0.05 C by
keeping the material in a constant temperature bath. Dielectric constant of
the material was
then calculated and plotted as a function of temperature. Temperature
coefficient calculated
from slope of variation of dielectric constant with temperature was found to
be -0.007 C.
Example 10
Weighed quantity of wet ground iron oxide and tungsten oxide was calcined at a
temperature of 1000 C for a period of 2 hours. The calcined material was
further ground for
about ten hours after mixing the lead oxide. This mixture was then calcined at
750 C for 2h.
The calcined powder was further ground for 10 hours. To this ground calcined
powder
polyvinyl alcohol was added as binder for making cylindrical shaped specimen
which was
then sintered at a temperature of 870 C for 2 hours. After sintering, the
specimen was cooled
and after polishing of the surfaces, silver electrodes were formed by vacuum
evaporation.
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Example 11
The material of Example 10 was used to measure pressure characteristics.
Temperature of the material was kept constant at 30 C to within 0.05 C by
keeping material
in a constant temperature bath. Capacitance of the capacitor structure
incorporating the lead
iron tungstate material was measured as a function of pressure applied from
0.5MPa to 415
MPa. Dielectric constant of the material was then calculated and plotted as a
function of
pressure. Pressure coefficient calculated from slope of variation of
dielectric constant with
pressure was found to be -497 ppm/Mpa.
Example 12
The material of Example 11 was used to measure temperature characteristics.
Pressure
applied on the material was kept constant at 0.1 Mpa. Capacitance of the
capacitor structure
incorporating the lead iron tungstate material was measured as a function of
temperature of
the material (varying from 10 - 50 C) keeping the temperature constant to
within 0.05 C by
keeping the material in a constant temperature bath. Dielectric constant of
the material was
then calculated and plotted as a function of temperature. Temperature
coefficient calculated
from slope of variation of dielectric constant with temperature was found to
be -0.0033 C.
Example 13
Weighed quantity of the wet ground iron oxide and tungsten oxide was calcined
at a
temperature of 1000 C for a period of 2 hours. The calcined material was
further ground for
about ten hours after mixing the lead oxide. This mixture was then calcined at
810 C for 2h.
The calcined powder was further ground for 10 hours. To this ground calcined
powder
polyvinyl alcohol was added as binder for making cylindrical shaped specimen
which was
then sintered at a temperature of 870 C for 2 hours. After sintering, the
specimen was cooled
and after polishing of the surfaces, silver electrodes were formed by vacuum
evaporation.
Example 14
Material of Example 13 was used to measure pressure characteristics.
Temperature of
material was kept constant at 30 C (t0.05 C) by keeping the material in
constant temperature
bath. Capacitance of capacitor structure incorporating lead iron tungstate
material was
measured as function of pressure applied from 0.5MPa to 415MPa. Dielectric
constant of
material was then calculated and plotted as function of pressure. Pressure
coefficient
calculated from slope of variation of dielectric constant with pressure was
found to be -534
ppm/Mpa.
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Example 15
The material of Example 13 was used to measure temperature characteristics.
Pressure
applied on the material was kept constant at 0.1 Mpa. Capacitance of the
capacitor structure
incorporating the lead iron tungstate material was measured as a function of
temperature of
the material (varying from 10 - 50 C) keeping the temperature constant to
within f0.05 C by
keeping the material in a constant temperature bath. Dielectric constant of
the material was
then calculated and plotted as a function of temperature. Temperature
coefficient calculated
from slope of variation of dielectric constant with temperature was found to
be -0.008 C.
Example 16
Weighed quantity of the wet ground iron oxide and tungsten oxide was calcined
at a
temperature of at 1000 C for a period of 2 hours. The calcined material was
further ground
for about ten hours after mixing the lead oxide. This mixture was then
calcined at 830 C for
2h. The calcined powder was fiuther ground for 10 hours. To this ground
calcined powder
polyvinyl alcohol was added as binder for making cylindrical shaped specimen
which was
then sintered at a temperature of 870 C for 2 hours, After sintering, the
specimen was cooled
and after polishing of the surfaces, silver electrodes were formed by vacuum
evaporation.
Example 17
Material of Example 16 was used to measurdpressure characteristics.
Temperature of
the material was kept constant at 30 C to within t0.05 C by keeping the
material in a
constant temperature bath. Capacitance of the capacitor structure
incorporating the lead iron
tungstate material was measured as a function of pressure applied from 0:1MPa
to 415 MPa.
Dielectric constant of the material was then calculated and plotted as a
function of pressure.
The pressure coefficient calculated from slope of variation of dielectric
constant with
pressure was found to be -622 ppm/Mpa.
Example 18
The material of Example 16 was used to measure temperature characteristics.
Pressure
applied on the material was kept constant at 0.1 Mpa. Capacitance of the
capacitor structure
incorporating 'the lead iron tungstate material was measured as a function of
temperature of
the material (varying from 10 - 50 C) keeping the temperature constant to.
within 0.05 C by
keeping the material in a constant temperature bath. Dielectric constant of
the material was
then calculated and plotted as a function of temperature. Temperature
coefficient calculated
from slope of variation of dielectric constant with temperature was found to
be 0.007 C.
The main advantages of the present invention are
1. The relaxor material can be used over a wide pressure range.
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2. The relaxor material can be used under varying temperature ambiences
thereby
avoiding the use of additional means for temperature control.
3. The material can be used over a wide temperature range of 10-50 C.
4. The capacitive transducer can be used to measure pressure over a wide range
from
0.5MPa to4l5Mpa with an accuracy of 0.05% over the entire range.
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