Transcript Processing Electroceramics - School of Materials and Mineral

Processing & Testing
Electroceramics
EBB 443-Technical Ceramics
Dr. Sabar D. Hutagalung
School of Materials and Mineral Resources Engineering
Universiti Sains Malaysia
Processing of Electroceramics
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The properties of electroceramic components greatly
depend upon the processing conditions of the ceramic.
The raw materials are first weighed according to the
stoichiometric formula.
The raw materials should be of high purity.
The particle size of the powders must be in the
submicron range for the solid phase reactions to occur
by atomic diffusion.
The powders are then mixed either mechanically or
chemically.
Mechanical mixing is usually done by either ball milling
or attrition milling for a short time.
Processing of Electroceramics
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During the calcination step the solid phase
reaction takes place between the constituents
giving the electroceramic phase.
The calcining temperature is important as it
influences the density and hence the
electromechanical properties of the final
product.
The higher the calcining temperature, the
higher the homogeneity and density of the
final ceramic product.
Processing of Electroceramics
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After calcining, the lumps are ground by milling.
The green bodies should have a certain minimum
density before they can be sintered.
The desired shape and a minimum green density can be
provided by various techniques including powder
compaction, slip-casting, and extrusion.
The choice of the method depends on the type of
powder used, particle size distribution, state of
agglomeration, desired shape, and thickness of the part.
After shaping, the green bodies are heated very slowly in
order to remove any binder present.
Processing of Electroceramics
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The binder burnout rate should be  1-2 ° C/min in
order to allow the gases to come out slowly without
forming cracks and blisters in the ceramic part.
After the binder burnout is over, the samples are
taken to a higher temperature for sintering to take
place.
The sintering temperature and time should be
optimum for proper densification to occur without
abnormal grain growth.
The sintering of oxide ceramics must be carried out
in an oxidizing atmosphere or in air.
Solid State Reaction
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The above technique is refer as a solid state
reaction or conventional method.
In briefly, the steps including:
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Mixing or milling (dry or wet milling)
Calcination
Compaction (for pellet formation)
Sintering
Example: Solid State
Reaction of CCTO
Ball milling 1 hour of a
stoichiometric ratio of raw
materials (CaCO3, CuO & TiO2)
XRD Analysis
(calcined powders)
Calcination 900 oC/12 hrs.
Compaction with pressure 300
MPa (thickness ~0.5-1.0 mm)
Dielectric measurement
by using LCR meter
Sintered sample with
silver electrodes
Sintering at 1050 oC
for 12 hrs.
XRD Analysis (sintered pellets)
Processesing of Magnetic Ceramics
Production scheme of ‘Nd2Fe14B-type’ magnets (REM XIII,
1994 p 303)
Processing of ferroelectric ceramics
Flowchart for the processing of ferroelectric ceramics
Processing of ferroelectric ceramics
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The dipoles within a single domain have the
same orientation.
In ferroelectric ceramics with fine grain sizes
(< 1 mm) each grain is a single domain with
the domain wall at the grain boundary.
If the grain size is larger (> 1 mm) then there
could be multiple domains in a single grain.
Processing of ferroelectric ceramics
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Piezoelectric behavior can be induced in a
ferroelectric ceramic by a process called "poling".
In this process a direct current (dc) electric field with
a strength larger than the coercive field strength is
applied to the ferroelectric ceramic at a high
temperature, but below the Curie point.
On the application of the external dc field the
spontaneous polarization within each grain gets
orientated towards the direction of the applied field.
Processing of ferroelectric ceramics
Schematic of the poling process in piezoelectric ceramics: (a) In the
absence of electric field the domains have random orientation of
polarization; (b) the polarization within the domains aligns in the
direction of the applied field.
Slip Casting Method
In a typical experiment, a solid
mixture containing requisite
quantities of aluminum nitrate,
magnesium nitrate, and urea was
taken in a Pyrex glass dish and
was irradiated with microwaves in
a modified domestic microwave
oven (Microwave 700W, input
range 210–230 V-ac 50 Hz,
microwave frequency 2.45 GHz) to
produce MgAl2O4 spinel material.
Modified domestic microwave oven used
for the powder synthesis.
MW Irradiation?
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In conventional or surface heating, the heat
flow rate into the body from the surface
determined by its specific heat, thermal
conductivity, density and viscosity.
Surface heating is not only slow, but also
non-uniform with the surfaces being much
hotter than the inside of the material.
Consequently, the quality of conventionally
heated materials is variable and frequently
inferior to the desired result.
1050 oC/4 h
1050 oC/24 h
MW Irradiation?
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Conversely, with microwaves, it is possible to
heat the volume of a material at the same rate.
Energy is transferred through the material
electro-magnetically, not as a thermal heat flux.
Therefore, the rate of heating is not limited and
the uniformity of heat distribution is greatly
improved.
Heating times can be reduced to a very short
time.
Methodology
Ball milling 5 h of stoichiometric ratio
of CaCO3, CuO, TiO2.
MW kitchen oven
(2.45 GHz, 1.1 kW).
XRD analysis
(calcined powder)
MW irradiation 30-90 min
Compaction , 520 MPa
(d ~1.2-1.5 mm, Ø 5 & 12 mm)
MW sintering 60 min
Dielectric
measurement
Samples with
silver electrodes
Post-MW sintered
SEM analysis
(surface & fracture)
30-150 min
Sintering at
1000oC/10h
Domestic MW oven (2.45 GHz, 1.1 kW)
Susceptor/Crucible
Alumina
SiC/graphite
Sol-Gel Processing
Sol-Gel Processing: Basic Reactions
Sol-Gel: Steps of film formation
Sol-Gel: Stability of sols
Unique structures by sol-gel
Sol-Gel: Multilayer
Ceramic sol-gel films
Testing
Ball milling 5 h of stoichiometric ratio
of CaCO3, CuO, TiO2.
XRD analysis
(calcined powder)
MW irradiation 30-90 min
Compaction , 520 MPa
(d ~1.2-1.5 mm, Ø 5 & 12 mm)
MW sintering 60 min
Dielectric
measurement
Samples with
silver electrodes
XRD analysis
SEM analysis
(surface & fracture) (sintered sample)
Sintered pellet
Dielectric Testing
Dielectric Testing
Piezoelectric Measurement
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PIEZO software takes input on the Multichannel from
displacement or force sensors to collect piezoelectric
properties simultaneously with electric properties.