Title of Invention

"A PROCESS FOR THE PREPARATION OF PZT-POLYMER COMPOSITE

Abstract This invention relates to a process for the preparation of PZT-po1ymeric composite with 1- 3 connectivity pattern with high figure of merit for advanced hydrophone applications. The process comprises in preparing an aqueous nitrate solution of Pb, Zr, Ti. and dopants in stoichionietric proportions. The solution is crystallised by spray drying using a centrifugal disk-atomiser to obtain fine and homogenous PZT powder. Heating said powder for decomposition of the dried nitrate particles into homogenous oxide mixture and solid state reaction of the said mixture and then cold compacting the same. Low temperature is employed for sintering cycle followed by lapping, electroding and poling for consolidation of the reacted powders to obtain square plates of the required size, shape, density and microstructure.
Full Text This invention relates to a process for preparation of PZT-polymer composite particularly used advanced hydrophones having receiving voltage sensitivity (RVS) in the range of -195dB to -205 dB re 1 V/uPa.
Lead Zirconate Titanate (PZT) materials are used in hydrophones because of their high piezoelectric coefficients. These materials are prepared by solid state reaction between the oxides of lead, zirconium and titanium alongwith certain dopants added in small quantities to modify the desired properties making it suitable for hydrophone application. Intimate, fine, pure and stoichiometric mixture of constituent oxides is prepared by various chemical methods.
PZT materials being prepared by the existing processes have several disadvantages. These have small hydrostatic strain coefficient (dh). The high permittivity of PZT lowers the hydrostatic voltage coefficient (gh) to a very low values. In addition, the high density of PZT makes it difficult to obtain good impedance matching with water. Furthermore, PZT being a brittle ceramic, does not provide the desirable shock resistance. Investigations on other monolithic materials have indicated that none of them are ideal for hydrophones.
PZT-polymer composite on the other hand, have a high figure of merit for hydrophone applications. In such a composite, PZT ceramic produces the desired piezoelectric effect while the polymer phase lowers the density and dielectric constant and increases the elastic compliance. The performance of these composites depends upon the composition of the PZT powder, thickness of the composite, uniformity of the dimensions of the PZT rods, the uniformity of spacing between them and volume % of PZT. The values of dj3 decrease
with volume % of PZT while the values of g33 and gh of the composite increase with the decrease in volume % of PZT thereby increasing the figure of merit for the hydrophone applications.
The primary object of the present invention is to propose a process for the preparation of 1-3 PZT-polymer composites with high figure of merit for hydrophone applications.
Another object of the present invention is to propose a process for preparation of 1-3 PZT-polymer composite which uses partial dicing technique to produce highly and uniformly dense PZT bar having uniform dimensions, uniform spacing between them and vertical alignment throughout the polymer matrix which result in composites having desirable characteristics for development of • advanced sensitive hydrophones.
Still another object of the present invention is to provide a process for preparation of 1-3 PZT-polymer composite which uses spray drying technique using a centrifugal disk atomiser to prepare pure and homogenous PZT powder which on compaction and sintering lead to ceramics with high density and improved piezoelectric properties, for use in the composite.
Further object of the present invention is to propose process for the preparation of PZT-polymer composite with high hydrostatic strain coefficient (dh) and high hydrostatic voltage coefficient (gn)•
Yet further object of the present invention is to provide a process which yields PZT-polymer composites which have higher receiving sensitivities, in the order of magnitude, higher than the standard PZT hydrophones and sensitivity response is flat in the frequency range from 0.1 to 100KHz.
Still further object of the present invention is to propose a process for the preparation of PZT-polymer composites with reproducible properties from batch to batch.
Yet further object of the present invention is to provide a process which provides PZT-polymer composites which have low density and low acoustic impedance which give better acoustic coupling with water.
Still further object of the present invention is to propose a process which provides PZT-polymer composites with uniform properties throughout the composite.
According to this invention there is provided a process for the preparation of PZT polymer composite particularly used in advanced hydrophones having higher receiving voltage sensitivity in the range of-195 dB to -205 dB re 1 V/µPa wherein PZT has general formula of Pbi-3x Lax (Zry Ti].y) Os with x varying from 0.03 to 0.05, y varies from 0.50 to 0.54 and polymer is conventional epoxy and wherein volume percent of PZT in the composite is in the range of 20 to 30% and wherein the process comprises steps of :-
(a) mixing aqueous nitrate solutions of lead (Pb), Zirconium (Zr), Titanium
(Ti) and a conventional dopant in stoichiometric proportions wherein
mole ratio of Zr to Ti is in the range of 50:50 to 54:46;
(b) spray drying the nitrate solution obtained by step (a) using a centrifugal
disk atomiser to obtain fine and homogenous nitrate powder wherein
spray drying is carried out at solution feed ratio of 2-3 litres/hour, inlet temperature of 300 to 350°C, outlet temperature of 90-100°C and at speed of centrifugal atomizer at 20,000-30,000rpm;
(c) decomposing and calcining the composite nitrate powder obtained by
step (b) at 400-550°C for 1-2 hours to obtain homogenous mixture of
their oxides;
(d) mixing 2% PVA binder to the oxide mixture obtained by step (c) and
subjecting to cold hydraulic compacting at 175-200MPa followed by
sintering at 1150 to 1220°C for 1-3 hours obtaining PZT blocks;
(e) mounting the PZT blocks obtained by step (d) on high speed saw
making grooves of desired thickness in one direction, subjecting them
to ultrasonic cleaning and back filling with a polymer, curing for 24
hours followed by polishing, remounting to make cuts in a direction
orthogonal to the direction of first cuts, ultrasonic cleaning and back
filling with polymer, obtaining PZT-polymer composite, wherein
polymer taken is commercially available epoxy;
(f) electroding PZT-polymer composite obtained by step (e) using
conventional air-drying silver paste, followed by conventional poling
by application of high dc voltage in the range of 15-12kv/cm at a
temperature between 60-80°C for a duration of 15-45 min in a silicone
oil bath, obtaining the desired PZT-polymer composite;





I CLAIM:
I. A process for the preparation of PZT-polymer composite particularly used in
advanced hydrophones having higher receiving voltage sensitivity in the range of -195 dB to -205 dB re I V/uPa wherein PZT has general formula of Pb1-3x Lax (Zry Tii-y) 63 with x varying from 0.03 to 0.05, y varies from 0.50 to 0.54 and polymer is conventional epoxy and wherein volume percent of PZT in the composite is in the range of 20 to 30% and wherein the process comprises steps of:-
(a) mixing aqueous nitrate solutions of lead (Pb), Zirconium (Zr), Titanium
(Ti) and a conventional dopant in stoichiometric proportions wherein mole
ratio of Zr to Ti is in the range of 50:50 to 54:46;
(b) spray drying the nitrate solution obtained by step (a) using a centrifugal
disk atomiser to obtain fine and homogenous nitrate powder wherein spray
drying is carried out at solution feed ratio of 2-3 litres/hour, inlet
temperature of 300 to 350°C, outlet temperature of 90-100°C and at speed
of centrifugal atomizer at 20,000-30,000rpm;
(c) decomposing and calcining the composite nitrate powder obtained by step
(b) at 400-5 50°C for 1-2 hours to obtain homogenous mixture of their
oxides;
(d) mixing 2% PVA binder to the oxide mixture obtained by step (c) and
subjecting to cold hydraulic compacting at 175-200MPa followed by
sintering at 1150 to 1220°for l-3hours obtaining PZT blocks;
(e) mounting the PZT blocks obtained by step (d) on high speed saw making
grooves of desired thickness in one direction, subjecting them to ultrasonic
cleaning and back filling with a polymer, curing for 24 hours followed by
polishing, remounting to make cuts in a direction orthogonal to the
direction of first cuts, ultrasonic cleaning and back filling with polymer,
obtaining PZT-polymer composite, wherein polymer taken is
commercially available epoxy;
(f) electroding PZT-polymer composite obtained by step (e) using
conventional air-drying silver paste, followed by conventional poling by
application of high dc voltage in the range of 15-12kv/cm at a temperature
between 60-80°C for a duration of 15-45 min in a silicone oil bath,
obtaining the desired PZT-polymer composite;
A process for the preparation of PZT-polymer composite for use in hydrophones as substantially herein described and illustrated.


Documents:

527-del-1996-abstract.pdf

527-del-1996-claims.pdf

527-del-1996-complete specification (granted).pdf

527-del-1996-correspondence-others.pdf

527-del-1996-correspondence-po.pdf

527-del-1996-description (complete).pdf

527-del-1996-form-1.pdf

527-del-1996-form-2.pdf

527-del-1996-form-3.pdf

527-del-1996-form-4.pdf

527-del-1996-gpa.pdf


Patent Number 193975
Indian Patent Application Number 527/DEL/1996
PG Journal Number 36/2004
Publication Date 04-Sep-2004
Grant Date 03-Feb-2006
Date of Filing 12-Mar-1996
Name of Patentee CHIEF CONTROLLER, RESEARCH & DEVELOPMENT
Applicant Address B-341, SENA BHAWAN, DHQ P.O., NEW DELHI -110 011, INDIA,
Inventors:
# Inventor's Name Inventor's Address
1 LAXMAN ANANTA GAVANE TECHNICAL OFFICER-'A' NAVAL MATERIALS RESEARCH LABORATORY, BOMBAY, INDIA
2 CHADALAPAKA DURGA PRASAD SCIENTIST 'C' NAVAL MATERIALS RESEARCH LABORATORY, BOMBAY, INDIA
3 RAMJI LALL SCIENTIST 'F'NAVAL MATERIALS RESEARCH LABORATORY, BOMBAY, INDIA
4 SURESH CHANDRA SHARMA SCIENTIST 'E'NAVAL MATERIALS RESEARCH LABORATORY, BOMBAY, INDIA
PCT International Classification Number C01G 21/00
PCT International Application Number N/A
PCT International Filing date
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 NA