Ponderomotive Force Generated by Microwaves During Sintering

JURNAL APLIKASI FISIKA

VOLUME 11

NOMOR 2

AGUSTUS 2015

Ponderomotive Force Generated by Microwaves During Sintering
M. Zamrun Firihu dan I.N. Sudiana
Jurusan Fisika, Fakultas Matematika dan Ilmu Pengetahuan Alam, Universitas Halu Oleo,
Kendari, Sulawesi Tenggara, 93231
E-mail : muhammad.zamrun@uho.ac.id

ABSTRAK
Dalam beberapa tahun terakhir, banyak peneliti telah melaporkan pengamatan dari
"efek microwave" di berbagai proses material seperti pada sintering, annealing, sintesis,
Istilah efek microwave tidak didefinisikan secara ketat. Sering digunakan untuk
menandai perbedaan hasil ketika pemanasan microwave digunakan dibandingkan
dengan pemanasan biasa dengan pemanas listrik atau gas. Efek microwave dapat
dijelaskan dalam dua kategori yakni efek termal dan efek non termal. Banyak hasil

eksperimen menunjukkan adanya efek nonthermal dari microwave yang meningkatkan
laju difusi atom di zat padat. Dalam teori sintering, atom berpindah karna adanya gaya
pemicu (driving force) sebagai penyebabnya misalnya karna perbedaan tekanan
permukaan, suhu, gravitasi, dll. Para ahli meyakini bahwa selama pemanasan dengan
microwave ada gaya tambahan yang menyebabkan atom berdifusi lebih cepat akibat
kehadiran medan listrik yang dinamai ponderomotive force. Dalam tulisan ini dibahas
gaya ini terkait data ekperimen yang telah diperoleh beberapa tahun terakhir.
Keywords: efek mikrowave, efek nonthermal, poderomotive force, difusi atom
I.

deposition which provides, in particular,

INTRODUCTION

a

Many researchers have reported

possibility


of

faster and

more

controllable temperature ramp-up and

observations of "microwave effects" in a

its

variety of material processes [1-3].

selectivity

which

can


provide

concentration of energy deposition in

Microwave effect is sometime used to

the desired region result in precision

mark the enhancement of the processing

heating. All the listed peculiarities of

rate when microwave heating is utilized

microwave heating can be treated as the

such as enhancement of densification,

thermal action of the electromagnetic


atomic diffusion, chemical reaction rate

field on matter. All microwave effects

[3]. In principle, the potential benefits of

can be explained specifically to thermal

microwave heating, caused by the

and nonthermal effect.

volumetric nature of microwave energy

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Ponderomotive Force……………………………………………………………………………(Zamrun,dkk)

Numerous experimental results
suggest


existence

of

a

processes in ionic crystals subjected to a

specific

microwave field [4]. The basic idea was

nonthermal action of microwaves on

comparatively simple, based on the

mass transport in crystalline solids [4].

effect of rectification of the oscillatory


The characteristics of porosity under

vacancy drift near grain boundaries and

microwave heating were found to differ

interfaces. The additional driving force

considerably from those observed in a

is known as ponderomotive force.

conventional sintering process under the
same conditions. A direct influence of

II. RESULTS OF MICROWAVE
PROCESSING OF MATERIAL

the microwave field on the transport

phenomena in crystals was found in
investigations of atomic diffusion [1], as
well as in a study of the observation of a
quasi-stationary electric current induced
in a dielectric subjected to pulsed
microwave irradiation [5]. However, the
physical mechanisms of the effect are
not completely clear. Some researchers
proposed the additional driving force
exist during microwave processing.
Especially,

Rybakov

and

Semenov

proposed the first model being able to
explain quantitatively the existence of

an additional driving force for transport

Microwave enhanced sintering has been
reported by several scholars [1-3,6-7 ]. It
has received much attention because of
the observed substantial decrease in
sintering temperature and fast heating
rates. Tian, et al.[6], have performed
sintering of alumina at 1700 oC for 12
minutes. They reported that the sintered
samples achieved 99.8% of theoretically
density, with fine grain of 1.9 m. The
effect of microwave is not only in
ceramic

processing.

Microwave

enhanced drying have been also reported

[8-9]. Some microwave enhancement
results are shown in Fig 1 to 3.

Fig. 1. Drying curves of cocoa beans in a microwave and in an electric furnace [8]
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JAF Vol 11 No. 2 (2015) 48-52

Figure 2. Effect of microwave frequency and green sample in microwave sintering
alumina [10]

Fig. 3 Reduction of open and closed porosity of silica xerogel upon MMW as compared
to conventional sintering [2]

III.

free surfaces are replaced by lower

DISCUSSIONS


Because of all results are temperature

energy sites such as grain boundaries or

activation

be

crystalline regions. The formation of

associated to enhancement of diffusion.

these low-energy sites (neck region),

Sintering lowers the surface energy of

and subsequent reduction in surface

material by reducing surface area with


area. This reduction results in a decrease

concomitant formation of interparticle

in the overall surface energy and known

bonds. During sintering, high-energy

as driving force:

process,

they

can

(1)

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JAF Vol 11 No. 2 (2015) 44-48

where G is free energy, s is specific

For drnsification, by simplifying of

surface energy, and A is surface area.

diffusion process using two particle

The stress associated with the curved

model the relation of densification to

surface as

material transport parameters can be
expressed by following equation:

(2)
where R1 and R2 are principal radii of
curvature for this surface.

(3)

ziF rmscRT2πVmx2a33/2t3/2

Flux of atom, J, is product of inter

Where

atomic distance, reaction rate constant,

=

density,

L=

material

dimension, Q= activation energy, R is

and diffusing concentration.

the

universal

gas

constant,

T=temperature, Do is diffusion constant,
s is specific surface energy, zi = charge
Diffusion path of mass transport during

on the ion, F =Faraday constant = 9.65

sintering of crystalline materials can

kJ/ V, Erms = root mean square of the

occur by at least six mechanisms: vapor

electric field of microwave, A is the

transport

cross-sectional

(evaporation/condensation),

area

over

which

(volume)

diffusion occurs and Vm is the molar

diffusion, grain boundary diffusion, and

volume of the material being transferred,

plastic flow [25].

x is radius of neck, a is radius of

surface

diffusion,

lattice

particle, and t is time. Component
is microwave contribution on
atomic transport during sintering. It is
driving force generated by electric field
of microwaves. It should enhanced
atomic transport during sintering.
Application

of ponderomotive effect

was shown in experiment performed by
Rybakov [11]. It was shown that a
microwave field with the E-vector

Figure 4. Possible atomic diffusion ways
during sintering [10]
The enhancement shown in Figure 1-3

directed tangentially to a surface of a
solid can develop a deformation-type

reported by researchers is indicated that

instability. This results in the formation

microwaves enhanced diffusion rate

of a corrugated profile on that surface

(mass transport flux) during processing.

with

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JAF Vol 11 No. 2 (2015) 44-48

[3]

Zamrun, M F., I. N. Sudiana,
Microwaves Enhanced Sintering
Mechanisms in Alumina Ceramic
Sintering Experiments, Cont. Eng.
Sci, Vol. 9, 2016, 5, 237 – 247
[4] Rybakov, K.I. and V.E.Semenov,
Physical Review B , 52[ 5], 3030
(1995).
[5] S.A. Freeman, J.H. Booske, and
R.F. Cooper, Phys. Rev. Lett., 74
[11], 2042 (1995).
[6] Sudiana, I.N, Use of Microwave
Energy for Material Processing in
A Simple Laboratory, Jurnal
Aplikasi Fisika, Vol. 10 No. 2,
Oktober 2014, Hal. 77-81.
[7] Y. L. Tian, D. L. Johnson, M. E.
Brodwin,
Ultrafine
Microstructure of Al2O3 Produced
by Microwave Sintering, Cer.
Pow. Sci. II B. pp. 925932(1988).
[8] Sudiana, I.N, S. Mitsudo, L. O.
Ngkoimani, L. Aba, H. Aripin, I.
Usman, Fast Drying of Cocoa
Bean by Using Microwave,
CICES2014, November 10-11,
2014, Kendari, Indonesia.
[9] McMinn W. A. M., Khraisheh M.
A. M., Magee T., R. A., Food
Research International, 36, pp.
977-983 (2003).
[10] M.F. Ashby,First report on
Sintering Diagram, Acta. Met. 22,
pp.275-289(1974).
[11] K.I. Rybakov and V.E. Semenov,
Materials
Research
Society
Symposium Proceedings, Vol. 430,
Pittsburgh, PA, 1996), p. 435.

the spatial period on the order of 1
micrometer

controlled

adjusting

the

period

microwave

by

power.

However no direct experiment can
demonstrate a ponderomotive forcedriven mass transport up to now. One of
important tasks in this field of research
is now to demonstrate a ponderomotive
force-driven mass transport in a direct
experiment.

IV. CONCLUSION
A

nonthermal

action

of

microwaves which enhances diffusion in
solids appears to be reasonable. As
follows

from

the

theoretical

and

experimental results obtained for ionic
crystalline solids and drying it can be
viewed in terms of an additional driving
force

(ponderomotive

experimental

results

on

force).

The

microwave

sintering indicate supports the theory.
However no direct experiment can
demonstrate a ponderomotive forcedriven mass transport up to now.
REFERENSI
[1]

[2]

Janney, M.A, H. Kimrey, W. Allen, J.
Kiggans,1997. Enhanced diffusion in
sapphire during microwave heating,
J. Materials Science 32, 1347–1355.
Sudiana, I.N., S. Mitsudo, T.
Nishiwaki, P. E. Susilowati, L.
Lestari, M. Z. Firihu, H. Aripin,
Effect of Microwave Radiation on
the Properties of Sintered Oxide
Ceramics, Cont. Eng. Sci., Vol. 8
No. 34, 2015, pp. 1607-1615

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