CP620, Shock Compression of Condensed Matter - 2001
edited by M. D. Furnish, N. N. Thadhani, and Y. Horie
© 2002 American Institute of Physics 0-7354-0068-7/02/$ 19.00
SYNTHESIS OF FUNCTIONAL CERAMICS LAYERS USING NOVEL
METHOD BASED ON IMPACT OF ULTRA-FINE PARTICLES.
J. Akedo1 and M. Lebedev2
Advanced Technology Process Mechanism Group and 2Digital Manufacturing Research Center, National
Institute of Advanced Industrial Science and Technology, Tsukuba East, Tsukuba, Ibaraki 305-8564 Japan
Abstract. A novel method of shock wave ceramics synthesis is reported. 0.3 jam in diameter ultrafine
ceramics particles were accelerated by gas flow up to velocity of 100 - 500 m/s. During interaction with
substrate, these particles formed dense, uniform and hard ceramics layers. Experiments were fulfilled at
room temperature. No additional procedure for synthesis was required. The results of syntheses of
piezoceramics oxide materials (Lead Zirconate Titanate) are presented. The density of material over
95% of the bulk density and hardness of as synthesized ceramics over 400 Hv were achieved. The
microstructure and elemental composition were investigated. Applications of functional ceramics
fabricated by reported method are discussed, as well.
INTRODUCTION
by Ide et al. [1], or via acceleration by mixing with
high-speed gas flow (Gas Deposition Method
(GDM) [2], which was originally developed in
ERATO UFP-Project of Japan [3]. For twodimensional pattern formation of the metal, Cold
Spray Method (CSM) [4, 5], developed by Institute
of Theoretical and Applied Mechanics in Russia
and Sandia National Laboratory for coating by
metal material, and Hypersonic Plasma Particle
Deposition (HPPD), originally developed by
Minnesota University group [6] for Si, SiC,
ceramics coating are used. Fundamentally, these
methods are based on shock loading consolidation
with or without thermal or plasma energy
assistance. EPID is appropriate only to conductive
material, for example metals or carbon, due to
necessity of charging up the particles. Thick film
formation (over 1 |um) in EPID has not been
reported. GDM is applicable to metal and ceramics
material using ultrafine particles, which has small
diameter under lOOnm and has highly activated
surface. In CSM large size particles with diameter
over 1 |im are accelerated by hot gas. This method
is very similar to GDM and conventional thermal
spray coating, but for ceramics material coating has
The synthesis of ceramics by shock compression
has a long history. The attractive point of such
synthesis is the high speed of the process. In the
"conventional" shock synthesis concept the primary
powder is compressed at one time. But,
unfortunately, unloading processes, which are
followed after compression, drastically destroy the
ceramic, i.e. some cracks were appeared.
Other concept of synthesis is to excite a shock
wave in a local area of primary powder material to
be synthesized. In this case to compress row powder,
individual particles of this powder are accelerated to
a velocity of a few meters per second and impact
onto the substrate. As a result of impaction area of
shock compression does not exceeded a few
diameters of particles and not destroyed other parts
of material.
Several deposition methods based on the
principle of particle impaction have already been
investigated. This family of methods include
depositing ultrafine particles via electrical field
acceleration
(Electrostatic
Particle-Impact
Deposition (EPID), which was originally developed
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not been success. In HPPD active ultrafme particles
are also used. These particles are produced under
the high pressure after condensation from the gas
phase in the nozzle. Deposition efficiency of EPID
seems very low. On the other hand, GDM, CSM
and HPPD have high potential in deposition rate.
In introduced Aerosol Deposition Method
(ADM), ultra fine (UFP) submicron particles were
accelerated by a gas flow in the nozzle and ejected
onto substrate. It is suggested that during interaction
of UFP with substrate and UFP with each other a
part of kinetic energy is transformed into thermal
energy in a local area to promote bonding between
particles. But real mechanism of deposition is not
clarified yet.
In this paper we report the result of deposition of
PZT (Lead Zirconate Titanate) ceramics by ADM.
FIGURE 1. Schematic diagram of Aerosol Deposition Method.
The PZT powder had the perovskite structure and a
composition of Pb(Zr0.52, Ti0.48)O3 which was close
to the morphotropic phase boundary. According to
Scanning Electron Microscopy (SEM) observations,
the particle size of the powder varied through the
0.08 - 0.5 |im range.
Velocity of particle flow was measured by timeof-flight method [9], in which some part of particle
flow was mechanically cut from the total flow and
deposited onto moving substrate, the deflection of
deposited pattern from the axis, geometrical
dimensions and speed of substrate provide data of
particle flow velocity. The values of PZT particle
flow velocity were varied from 100 up to 500 m/s in
these experiments.
EXPERIMENT
Our ADM apparatus had two vacuum chambers
connecting each other through a gas pipe. The first
was a deposition chamber for the formation of
ceramics. Deposition chamber contained the nozzle,
substrate holder with or without heating system and
window for diagnostic. This chamber was
vacuumed during the deposition by a rotary vacuum
pump and by mechanical booster pump. The second
chamber was an aerosol chamber for generation of
UFP aerosol. It had the accelerating gas introducing
system and vibration system for powder mixing
with accelerating gas. Aerosol flow from aerosol
chamber was transported to deposition chamber by
pressure difference between two chambers. The
UFP ceramics powder was continuously ejected
through the micro orifice nozzle and deposited onto
the substrate. The orifice size of nozzle had
rectangular shape. To get ceramics with uniform
thickness, the nozzle was continuously scanning
along the substrate. Schematic of ADM is presented
in Fig. 1. Gas flow, which was controlled by mass
flow controller, determined velocity of ejected
particles. Table 1 shows the typical parameters of
deposition condition for ADM. The details of
apparatus were described elsewhere [7,8]. As a PZT
powder, commercially available raw-material
powder (PZT- LQ; Sakai Chemical Ind. Japan) with
dry-milling process to improve the deposition rate
was used.
TABLE 1. Experimental parameters.
Pressure in deposition chamber
0.4 ~2 Ton-
Pressure in aerosol chamber
80 ~ 600 Torr
Size of nozzle orifice
Accelerating gas
5 x 0.3 mm2
10x0.4 mm2
He, N2 , air
Consumption of accelerating gas
l~101/min
Maintained substrate temperature
during deposition
Scanning area (area of deposition)
300 K
Scanning speed of the nozzle
motion along substrate
Distance between the nozzle and
substrate
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40 x 40 mm2
0.1251 .25 mm/sec
1 mm- 20 mm
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FIGURE 3. XRD patterns of PZT: a) - primary powder; b) - as
synthesized film (thickness 25 pm) at room temperature; (XRD:
Cu K-alpha, 40 kV/120 mA)
Figure 3 shows the results of XRD observations for
primary PZT powder and PZT deposited by ADM
without any additional external energy assistance.
The deposited films have randomly oriented
polycrystalline structures and have the spectra
phases similar to raw-powder. A rhombohedral
perovskite structure was retained before and after
deposition. Pyrochlor and amorphous phase were
not observed in the as-deposited PZT film.
However, broadening of the spectra and slight
shifting of the spectra angle in a higher degree were
observed. The reason of the changing between the
raw-powder and the deposited film spectra may be
due to reducing of the films' crystallite size or their
distortion during the deposition.
Structural characterization of the PZT films was
carried out using transmission electron microscopy
(TEM) (H-9000UHR, 300 kV). According to the
TEM image (Fig. 4), the PZT films have a dense
polycrystalline structure.
Elemental composition of PZT films was
measured by an energy-dispersive X-ray
microanalyzer (EDX). The measurement confirmed
that the PZT films after deposition had a
stoichiometric composition with a Pb/(ZrKTi) ratio
of about 1/1 and with Zr/Ti ratio of about 52/48
[10]. Elemental composition was the same as that of
the primary powder and that of the bulk PZT
material.
FIGURE!. Optical image of PZT ceramics synthesized by
ADM on Si and on Pt/Ti/SiO2/Si substrates. Substrate
temperature during experiment was maintained at 300K.
RESULTS AND DISCUSSION
The results of deposition of PZT on Si and Si
coated by Pt layer substrates are shown in Fig. 2.
Volume and weight of PZT film were measured
using a three-dimensional stylus profiler and a
precise weight balance with resolution of 0.1 j^m
and 10 ng, respectively. The bulk density of the
PZT film was estimated as 7.76 g/cm3, which is
more than 95% of the theoretical density
(8.10 g/cm3). Although, the interaction time of
particles with substrate and/or particles with each
other was a few nanoseconds, the ceramics
formation is a continuous process. It took 15 min to
fabricate a 500-|am-thick PZT with the area 5x5
mm2.
Adhesion force of the PZT deposited films on
stainless steel and Si substrates was measured by a
tensile testing machine and was higher than
50MPa.
Crystal structures of the deposited films
have been observed by X-ray diffraction (XRD).
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Results of measurements of micro Vickers
hardness (Hv) (DUH-W201, Shimazu Co) of
deposited films are presented in Fig. 5. The
hardness of the deposited film does not increase if
velocity of particle i.e. shock wave pressure, was
increased. This result indicates that synthesis of
ceramics was complete. For piezoelectronics
applications an additional heat treatment procedure
to improve ferroelectric properties is required. PZT
layers made by ADM after annealing have no
cracks and did not peel from substrate. PZT films
deposited by ADM have high potential for
producing microactuators and other applications of
piezoelectric ceramics [11,12].
CONCLUSION
1) Thick, dense ceramic layers with thickness up
to 1 mm were obtained during interaction of a
ceramics particle flow with the substrate; 2) No
external energy is required for synthesis; 3) Layers
have a poly crystalline structure with strong bonding
between the crystallites; 4) Chemical compositions
of ceramics did not change; 5) Layers demonstrated
high hardness, and good adhesion with the
substrates.
FIGURE 4. TEM images of PZT ceramics synthesized by ADM.
REFERENCES
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6. Rao, N. et al, J. Aerosol Sci., 29, 707 (1998)
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8. J. Akedo, N. Minami, K. Fukuda, M. Ichiki and R.
Maeda, Ferroelectrics 231, 285 (1999)
9. M. Lebedev, J. Akedo, K. Mori and T. Eiju, J. Vac.
Sci. & Technol. A. 18, 563 (2000).
10. J. Akedo and M. Lebedev, Jpn. J. Appl. Phys., 38,
5397(1999)
11. J. Akedo and M. Lebedev, Appl. Phys. Lett., 77 ,11,
1710(2000)
12. M. Lebedev, J. Akedo and Y. Akiyama, Jpn. J. Appl.
Phys. 39, 5600 (2000)
800
T
.600
w
«
= 400
m
200
0
200
400
600
velocity of PZT particles, mis
FIGURES. Micro Vickers Hardness of PZT for different
velocities of ultrafine particles during experiment: 1) - As
synthesized using oxygen as accelerative gas; 2) after heat
treatment at 600°C during 1 hour in air atmosphere. Indentation
force is 50 gf; Dwell time is 15 s
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