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BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a
method of manufacturing porous PZT ceramics used for high sensitivity hydrophones for
underwater acoustic sensors.
2. Description of the Related Art Conventionally, as materials for hydrophones for underwater
acoustic sensors, lead zirconate titanate ceramics (referred to as PZT ceramics), composites of
PZT ceramics and plastics such as epoxy resin, etc. Piezoelectric materials such as body or
composites of PZT ceramics and air (ie, porous PZT ceramics) have been used. The
manufacturing method of the hydrophone processed these porous PZT ceramics to a designated
shape, formed the electrode by silver baking etc. on the surface, and made it the water-resistant
structure by resin sealing etc.
Among these piezoelectric materials, the porous PZT ceramic material contains a pore forming
agent such as carbon or plastic, and the method of manufacturing the porous PZT ceramic is to
make the pore forming agent uniform with the ceramic material. The mixture was molded, dried,
and fired to eliminate the pore-forming agent to obtain porous PZT ceramics. And as the porosity
is larger, the hydrophone having better sensitivity is obtained.
As a specific forming method of this porous PZT ceramic, a slurry comprising PZT calcined
powder, carbon particles, a dispersant, a binder, and water is prepared, and this slurry is used as
the bottom of a water-permeable sheet such as filter paper. There is a method of pouring into a
mold placed on top of the mold and sucking and dewatering from the bottom of the mold with a
vacuum suction device such as an aspirator to obtain a molded body. There is also a method of
pouring the above slurry into a gypsum mold and dewatering it by the water absorption action of
the gypsum to form a molded body. These forming methods are referred to as slip casting
However, the molded article produced by the above-mentioned slip casting method is a watercontaining molded article containing water. If the water content in the compact is not sufficiently
removed by drying before firing the water-containing compact, cracks or deformation occur in
the binder removal step and the firing step, and good porous PZT ceramics are obtained. I can
not get it. However, in drying by hot air in a normal high temperature tank, drying occurs from
the surface of the molded product, so that a large difference occurs in the drying state between
the surface and the inside of the molded product. The amount of contraction with the inside will
be different. For this reason, if the shape of the shaped body is large or complicated, there is a
problem that a crack is generated on the surface of the shaped body or an internal stress is
generated in the shaped body to appear as a crack at the time of firing.
Therefore, the present invention provides a method for producing porous PZT ceramics in which
a uniform drying can be performed on the inside and the surface of a slip cast molding, no cracks
are generated during drying, and no internal stress is generated. It is to provide.
SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present
invention forms a water-containing molding by a slip casting method using a PZT calcined
powder containing a pore-forming agent, In the method of drying, debinding, and firing to
produce porous PZT ceramics, high frequency heating is used to dry the water-containing
As described above, according to the method for producing porous PZT ceramics of the present
invention, since high frequency heating is used to dry the water-containing compact, heating
does not differ between the inside and the outside of the compact and uniformity is uniform.
There is no difference in the dry state.
In this water-containing molded body, if the binder is not completely removed before baking, the
water volatilizes during heating in the binder-removing step, so that a large volume expansion
occurs rapidly and a large pressure is generated inside the molded body. This may cause cracks
or deformation in the molded body.
EXAMPLE First, a calcined powder of PZT is prepared as follows.
Predetermined amounts of high purity lead monoxide (PbO, 99.9% purity), titanium dioxide
(TiO2, 99.9% purity), zirconium oxide (ZrO2, 99.9% purity) and other additives are weighed. The
mixture was mixed with pure water for about 20 hours using a pot mill. The mixture was
dehydrated and dried, and calcined at 900 ° C. for 5 hours to obtain a calcined PZT. Pure water
was added to the calcined product, and the mixture was pulverized and mixed in a pot mill, and
then dehydrated and dried to obtain a calcined powder of PZT.
Next, 13 parts by weight of carbon particles having a particle diameter of about 0.3 mm (having
a porosity of 40% after firing), 10 parts by weight of water, with respect to 100 parts by weight
of the obtained calcined PZT powder. 5 parts by weight of a dispersant D-134 (trade name,
manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) was added, and mixed for 5 hours with a pot
mill to uniformly disperse PZT and carbon particles. To this dispersion, 2 parts by weight of a
binder TB-13 (trade name, manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.) and 0.5 parts by
weight of an antifoaming agent were added and mixed for 20 hours to disperse PZT and carbon
particles uniformly. A slurry was produced.
Next, a filter paper for suction filtration is placed on a cylindrical molding die with a diameter of
45 mm having a built-in ultrasonic oscillation unit and many small holes at the bottom, and the
slurry is poured into the molding die Then, the ultrasonic wave was oscillated and the slurry in
the mold was vibrated, and it was sucked and dewatered by the aspirator from the lower part of
the mold. Due to the ultrasonic vibration, the slurry in the mold increased its fluidity by
thixotropy, and flowed into the details of the mold, and when it was poured into the mold, the
bubbles were lifted by the vibration and defoamed on the slurry. In this way, a disc-shaped
compact having a uniform thickness and a thickness of about 10 mm without bubble entrapment
was obtained.
The following molded product was manufactured as another manufacturing example of the
molded product. The slurry from which carbon particles are removed and the slurry containing
carbon particles are alternately poured into the mold and dewatered in the same manner as
described above, and a layer in which carbon particles are uniformly distributed and a layer in
which carbon particles are not present are alternately A laminated, anisotropic molded article
was obtained. The moldings obtained by these slip casting methods are water-containing
moldings containing water. The water-containing compact was dried by a high frequency heating
apparatus capable of widely changing the high frequency output. The high-frequency heating can
perform uniform heating both internally and externally, and can also uniformly dry. First, the
output of the high frequency was weakly controlled and the molded product was irradiated, and
dried while preventing the water contained in the molded product from boiling. Thus, when the
water content in the compact was almost evaporated, the output of the high frequency was
increased to irradiate the compact with the residual moisture completely removed and dried. By
drying the molded product in this manner, the dried state of the surface of the molded product
was good, and a micro-crack-free molded product without deformation was obtained.
Next, the dried molded product is put in a magnesia crucible, debinded by holding at a
temperature rising rate of 30 ° C./h for 5 hours at 600 ° C., and carbon particles are burned
off. Then, by firing at a temperature rising rate of 100 ° C./h and holding conditions of 1300 °
C. for 2 hours, a porous PZT ceramic fired body having pores after disappearance of carbon
particles was obtained.
As described above in detail, according to the present invention, since the dried state of the
surface and the inside of the molded body can be made constant, the density of the molded body
is uniform, and the internal stress can not be obtained. A small, dry molded body free of cracks
on the surface was obtained.
Further, the dried compact was debindered and fired, and no cracking occurred. Therefore, a
porous PZT ceramic produced by removing the binder from the dried compact and firing it can
be obtained uniformly without cracking and deformation. Therefore, the porous PZT obtained by
the method of the present invention can be obtained. Ceramics have the effect that they can be
used for highly sensitive and stable hydrophones.
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