Magnetorheological suspension based on mineral oil, iron and graphite micro-particles

Article abstract of DOI:10.1016/j.jmmm.2004.05.036

The paper presents the process of obtaining magnetorheological suspensions based on mineral oil, iron and graphite micro-particles and thermal decomposition of Fe₂(CO)₉. The suspension is characterized by its magnetic and magnetorheo

Full text of DOI:10.1016/j.jmmm.2004.05.036

ARTICLE IN PRESS
Journal of Magnetism and Magnetic Materials 283 (2004) 335–343
www.elsevier.com/locate/jmmm
Magnetorheological suspension based on mineral oil, iron
and graphite micro-particles
Ioan Bica
Department of Physics, Faculty of Physics, West University of Timisoara, Bd. V. Parvan, no. 4, 1900 Timisoara, Romania
Received 24 March 2004; received in revised form 9 April 2004
Available online 26 June 2004
Abstract
The paper presents the process of obtaining magnetorheological suspensions based on mineral oil, iron and graphite
micro-particles and thermal decomposition of Fe2(CO)9. The suspension is characterized by its magnetic and
magnetorheological properties. The device presented in the paper is used to determine the electrical conductivity of the
suspension under the influence of the magnetic field and to interpret the results obtained in this manner.
r 2004 Elsevier B.V. All rights reserved.
PACS: 75.50.T
Keywords: Magnetorheological suspensions; Graphite; Iron micro-particles; Magnetic field; Electrical conductivity
1. Introduction
Sensible manifestations of the viscosity of the
suspension in magnetic field. For suitable values of
the intensity of the magnetic field, the suspension
Bingham plastic [11–15]. These properties of MRS
are successfully used in the following areas:
Magnetorheological suspensions (MRS) are
polyphase fluids. They comprise a liquid (silicon
oil, mineral oil, etc), the stearic acid and magnetic
micro-particles [1–3]. The orientation of the latter
ones follows the lines of the external magnetic
field. The strength of the particle chains depends
on the intensity of the magnetic field, the dimen-
sion of the particles, the concentration of the
suspensions, and on the magnetic properties of the
micro-particles [4–12].
ꢀ dampers for the attenuation of vibrations
[16–20] and absorption of seismic shocks
[20–22];
ꢀ under the influence of brakes and clutches with
pre-established coupling coefficients an external
magnetic field [16,23,24];
ꢀ manufacturing of orthopedic protheses [24,25]
and, last but not least, in bio-medical studies
[26].
E-mail address: ibica2@yahoo.com (I. Bica).
0304-8853/$ - see front matter r 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.jmmm.2004.05.036

ARTICLE IN PRESS
336
I. Bica / Journal of Magnetism and Magnetic Materials 283 (2004) 335–343
The manufacturing of sensors or/and magnetic
Table 1
The structure of the liquid matrix
field transductors, as well as resistors with
resistance values controlled by an external mag-
netic field, is based on the production of MRS
electroconductors [27].
103 ꢁ m1 (kg)
103 ꢁ m2 (kg)
103 ꢁ m3 (kg)
Obs.
—
25
82
1.5
Note: m1: the mineral oil mass (ANERON-Merck type), m2: the
Fe2(CO)9 mass (powder of granulation ranging between 4.5 and
5.2 mm, with a minimum of 97% Fe), m3: the stearic acid mass.
2. Experimental device for the production of MRS
The illustrative scheme of the device for the
production of MRS is shown in Fig. 1. In this
figure, the description and main technical char-
acteristics of the installation comes from Ref. [3].
The liquid matrix (location 8 in Fig. 1) has the
structure presented in Table 1. The thermal
treatment of the matrix is achieved according to
the temperature–time diagram displayed in Fig. 2.
During thermal treatment, the oil in the liquid
matrix was supplemented with mineral oil, origi-
nating from the basin F, in quantities with up to
18.5 ꢁ 10ꢂ3 kg.
Fig. 2. Temperature–time diagram.
One-chamber (60 ꢁ 10ꢂ6 m3), 2-pipe for argon
dispersion, 3-palette, 4-oil supplying, 5-thermocou-
ple iron-constantan, 6-autotransformer (0–220Vac/
8Aac), 7-heater (500W), 8-liquid matrix, ‘‘a’’and
‘‘b’’-electric outlets (220 Vac).The water input and
the water output are displayed by the arrow
sequence ‘‘—— -’’and ‘‘- -’’, respectively.
The argon flow, injected from the cylinder C
through the tube 2 (Fig. 1) into the liquid matrix,
is of 5 l minꢂ1 (83.33 ꢁ 10ꢂ6 m3 sꢂ1). The pressure
in the enclosure 1 is maintained at –220 mm.col.
H2O710% (ꢂ2.0594 Pa710%). Fe2(CO)9 is
heated up to T ¼ ð573 Æ 10%Þ K (Fig. 2) during
30 min (1.800 s) and it decomposes thermically.
Starting from 573 K, the liquid matrix 8 (Fig. 1)
is cooled at the velocity of 0.074 K sꢂ1, to
(314710%) K. Whenever the stearic acid mass is
larger than 1.5 ꢁ 10ꢂ3 kg, the liquid matrix gets
transformed into a plastic body.
The shape and the dimensions of the particles in
the suspension are shown in Fig. 3a, while the
dimensional distribution of the particles is dis-
played in Fig. 3b.
The mean diameter of the iron particles is
0.595 mm, with a standard deviation of 0.337 mm.
The iron particles are not oxidated and do not
get oxidated during time. This is due to the
underlying production procedure as well as the
fact that an oil layer with stearic acid as well is
adsorbed on the surface of the particles [28].
At the temperature of (314710%) K of matrix 8
in room 1 (Fig. 1), one introduces graphite in
Fig. 1. The illustrative scheme of the experimental device
designed to produce magnetorheological suspensions: (A)
chemical reactor; (B) water ejector vacuum pump; (C) the gas
container, (D) electric motor (24 Vdc=3Adc; 0–50 rev sꢂ1), (E)
indicator millivoltmeter, (F) mineral oil supplier.

ARTICLE IN PRESS
I. Bica / Journal of Magnetism and Magnetic Materials 283 (2004) 335–343
337
Table 2
The compositions of EMRS
103 ꢁ m1
103 ꢁ m2
103 ꢁ m3
103 ꢁ m4
Obs.
—
(kg)
(kg)
(kg)
(kg)
25
25.23
1.5
6.21
Note: m1: the mineral oil mass (ANERON-Merck type), m2: the
mass of the iron particles (of mean diameter 0.595 mm at a
standard deviation of 0.337 mm), m3: is the stearic acid mass,
and m4: the mass of the graphite powder.
powder form (its granulation ranging between 2
and 32 mm) whereas the mechanical mixing is
performed with the palette 3 (10 rev./s710%).
Proceeding in this manner, a magnetorheologi-
cal suspension based on mineral oil, iron micro-
particles and mineral oil (EMRS) is formed. The
composition of EMRS is presented in Table 2.
The EMRS in a 1:1000 dilution with mineral oil
visualized by the optic microscope is presented in
Fig. 4.
The MRS magnetization curve and the EMRS
magnetization curve are presented in Fig. 5. For
this purpose a magnetometer with a vibratory
specimen (VSM 880 type) has been used.
It can be seen from Fig. 5 that the saturation
magnetization of EMRS is about 7% lower than
the saturation magnetization curve of MRS. This
difference is due to the influence of graphite in the
EMRS composition (Table 2).
The magnetorheological characterization of the
suspensions is presented in Fig. 6 for values of H,
at which the magnetization of the suspensions
exhibits the same values.
For these measurements, a magneto-rheological
device (type Physica MRC 300), has been used.
The increased values for the dynamic viscosity Z
and the shear stress t of EMRS as compared to the
ones of MRS, are due to the form of the graphite
micro-particles [29].
3. Electrical conductivity
3.1. Experimental device
Fig. 3. The iron micro-particles: (a) shapes and dimensions, (b)
dimensional distribution (nc is the cumulated frequency, d is the
particle diameter, d denotes the mean particle diameter and s is
the standard deviation), and (c) roentgenogram.
The experimental device used for the determina-
tion of the electrical conductivity of the
ꢀ

ARTICLE IN PRESS
338
I. Bica / Journal of Magnetism and Magnetic Materials 283 (2004) 335–343
Fig. 5. The magnetization M of the MRS and the magnetiza-
tion M of the EMRS versus the intensity H of the magnetic
field.
Fig. 6. Magnetorheological data. (a) the variation of the
dynamic viscosity Z as a function of the intensity H of the
magnetic field and (b) the variation of the shear stress as a
function of the intensity H of the magnetic field. In both cases,
Fig. 4. The MRS graphite mixture: (a) in the absence of the
external magnetic field and (b) in the presence of the external
magnetic field.
_
the g’s stand for parameters.
suspensions is shown in Fig. 7. It consists of an
electromagnet (1), the measure cell (2), the
ohmeter (3), (Voltcraft VC 332 type), the tesla-
meter (4), (GM04, Hirst type) with the Hall sonde
(5) and the steady current source S with the
ampermeter A (Voltcraft M-3650B type).

ARTICLE IN PRESS
I. Bica / Journal of Magnetism and Magnetic Materials 283 (2004) 335–343
339
The detailed design of the electromagnet from
position 1 in Fig. 7 is presented in Fig. 8. The
electromagnet has attached screws (position 3 in
Fig. 8). They serve for fixing of the polar parts of
measuring cells on the electromagnet.
The detailed configurations of the measure cells
are presented in Figs. 9 and 10. The dependence of
the intensity H of the magnetic field such as
measured at point O (Figs. 9 and 10), on the
intensity I of the current through the coil of the
electromagnet is displayed in Fig. 11a. The values
of the magnetic field intensity gradient in the
space between the polar parts as a function of
the intensity of the current through the coil of the
electromagnet are presented in Fig. 11b.
The modulus dH=dx of the gradient of the
magnetic field as a function of the intensity I of the
current. (A) longitudinal magnetic field. (B) trans-
versal magnetic field.
Fig. 7. Experimental device for determining the electrical
conductivity s of the magnetorheological suspensions (block
scheme): 1—electromagnet, 2—measuring cell, 3—ohmmeter,
4—teslameter, 5—Hall probe, A—ampermeter, S—current
supply.
Fig. 9. Overall configuration of the measuring cell for the case
in which the applied magnetic field is parallel to the specimen.
1—magnetic pole, 2—specimen (suspension), 3—electrode
(non-magnetic), 4—glass cylinder, 5—nut, 6—rubber fitting.
Fig. 8. Electromagnet (overall configuration): 1—coil, 2—core,
3—screws.

ARTICLE IN PRESS
340
I. Bica / Journal of Magnetism and Magnetic Materials 283 (2004) 335–343
Fig. 11. The intensity H of the magnetic field as a function of
the intensity I of current (a) dH=dx as a function of the
intensity I of the current (b). (A) longitudinal magnetic field, (B)
transversal magnetic field.
determined via
Fig. 10. Measuring cell for the case in which the magnetic field
is applied perpendicularly to the specimen. 1—magnetic pole,
2—specimen (suspension), 3—fixing element (non-magnetic),
4—nut, 5—glass cylinder, 6—electrode (non-magnetic), 7—
rubber fitting.
250
A
s ð Þ ¼
:
ð1Þ
RðMOÞ
The temperature of the suspension is
(29775%) K. The MRS exhibiting the composi-
tion shown in Table 1 is a magneto-dielectric one.
On the other hand, the suspension having the
composition shown in Table 2 concern a conduct-
ing phase. Values of the electrical conductivity s of
EMRS are shown in Fig. 12. The magnetic
pressure generated in the suspension by the
magnetic field is [15]:
3.2. Experimental results and discussion
The length of the suspensions (position 2 in
Figs. 9 and 10) is equal to their diameter, that is
5 ꢁ 10ꢂ3 m. The measurement of the resistance R
of the suspension specimen is achieved by means
of the experimental device presented in Fig. 7. The
resistance R of the suspension is the one measured
at the moment of the application of the magnetic
field. Other values of R are recorded at interval
of 15 s.
Dpmagn ¼ m0MsHh=2r;
ð2Þ
in which m0 is the magnetic permeability of the
vacuum, Ms is the saturation magnetization of the
suspension, whereas h and 2r are the length and
the diameter of the specimen, respectively.
From values and dimensions of the specimen,
the electrical conductivity of the suspension is

ARTICLE IN PRESS
I. Bica / Journal of Magnetism and Magnetic Materials 283 (2004) 335–343
341
equation [29]
d2x
dt2
dx
dt
M
þ x
þ m0mrmd ¼ 0;
ð3Þ
where M is the mass of the magnetic micro-
particle, x is the micro-particle friction coefficient,
mr is the relative magnetic permeability of the
suspension, m is the magnetic moment and d ¼
dH=dx is the value of the gradient of the magnetic
field intensity.
Considering that at the initial moment (t ¼ 0)
the distance between particles is xð0Þ ¼ D such that
x0ð0Þ ¼ 0, one obtains [29]
ꢂ
ꢀ
ꢁ
ꢃ
m0mrmdM
x
M
x
M
xðtÞ ¼ D þ
1 ꢂ exp ꢂ
t
ꢂ
t
x2
ð4Þ
has
If
tꢃðM=xÞ ꢄ 1028ꢂ
s
[29],
one
À
Á
exp ꢂðx=MÞt !0, so that Eq. (4) becomes
ꢀ
ꢁ
m0mrmdM
x
M
xðtÞ ¼ D þ
1 ꢂ
t
ð5Þ
x2
At this point we shall consider that particles
meet together at the migration time, which
Fig. 12. The variation of the conductivity s of EMRS during
the application of the magnetic field, for: H ¼ 43:780 kA=m (a)
and H ¼ 78:008 kA=m (b). (A) longitudinal magnetic field, (B)
transversal magnetic field.
amounts to saying that x ¼ 0 when t ¼ tmig:
.
Accordingly, one obtained
D ꢅ x
3p ꢅ Z ꢅ d
D
tmig:
ffi
¼
ð6Þ
m0mrm ꢅ d m0mrm ꢅ d
The magnetic particles follow, of course, the
magnetic field lines. When the magnetic field is
applied parallel to the suspension specimen, the
contact resistance between the electrodes of the
device in Fig. 7 is much smaller as compared to
that when the magnetic field is perpendicular to
the specimen, due to Dpmagn. Fig. 12 shows that,
for a given t, the high values of s obtained under
conditions of which the magnetic field is parallel
to the suspensions, are much larger than the ones
corresponding to a transversal field. We have
to account for magnetic field gradients, under the
conditions for which the magnetic field is not
uniform, as indicated in Fig. 11b. Then, graphite
particles, driven by the magnetic ones, migrate
in the direction of the magnetic field gradient [29].
Let us consider an easy configuration in which
the field is applied along the ‘‘x’’-axis. Then
the motion of the particles is governed by the
by virtue of Eq. (5) where d ¼ 0:595 mm is
the diameter of the magnetic particles in EMRS,
x ¼ 108ꢂ kg=s and m ꢄ 1014ꢂ A m2.
It is seen from Fig. 5 that mMRS ꢄ mEMRS ¼ 3 for
Ho100 kA=m. From the viscosity measurements
presented in Fig. 6, one obtains Z ¼ 24 and
50 kPa s for H ¼ 43:780 and H ¼ 78:008 kA=m,
respectively.
So, the magnetic field gradients concerning
Fig. 11b are given by d ¼ 66 kA=m2 (H ¼ 43:780
kA=m) and d ¼ 98 kA=m2 (H ¼ 78:008 kA=m) for
a transversal magnetic field, while d ¼ 24 kA=m2
(H ¼ 43:780 kA=m) and d ¼ 30 kA=m2 (H ¼
78:008 kA=m) for a longitudinal one.
Eq. (6) also furnished the D-dependence of the
migration time, as shown in Fig. 13.
It follows from Fig. 13 that the distance D
between the graphite particles is located between
0.01 and 0.1 nm. Under the action of the magnetic

ARTICLE IN PRESS
342
I. Bica / Journal of Magnetism and Magnetic Materials 283 (2004) 335–343
field pressure Dpmagn, at t ¼ tmig: the inter-particle
,
distance gets diminished, as indicated in Fig. 13.
Accordingly, the contact resistance between the
graphite particles and the electrodes (position 3 in
Fig. 9 and position 6 in Fig. 10) diminishes itself
and the conductivity s increases with time as
shown in Fig. 12. The same method was used to
determine the field dependence of the conductivity
as shown in Fig. 14. The value of s was determined
15 s after the application of the magnetic field’s
intensity. The measurements were performed at
intervals of 45 s.
One sees from Fig. 14 that s depends on the
value of the intensity of the magnetic field and it is
considerably influenced by the direction of the field
with respect to the specimen.
Fig. 14. The conductivity s versus the intensity H of the
magnetic field. (A) longitudinal magnetic field, (B) transversal
magnetic field.
4. Conclusions
ꢀ Magnetorheological suspensions based on
mineral oil, iron and graphite micro-particles
have been obtained by means of the device
presented in Fig. 1 through thermal decomposi-
tion of Fe2(CO)9:
ꢀ For T ¼ ð573 Æ 10%Þ K The mean dimension of
magnetic particles is 0.595 mm for T ¼ ð573 Æ
10%Þ K at a standard deviation of 0.375 mm
(Fig. 3b).
ꢀ The magnetic particles obtained in mineral oil
and in inert gas atmosphere (Ar) are not
oxidated (Fig. 3c). They do not get oxidated
with time because the oil and stearic acid layer
get adsorbed on the surface of the iron micro-
particles.
ꢀ The magnetization curve of MRS is of the same
shape as the one of the EMRS magnetization.
But, because of the graphite, the saturation level
of EMRS is 7%—smaller as compared with the
saturation magnetization of EMRS (Fig. 5).
ꢀ Both MRS and EMRS are non-Newtonian
fluids. Their dynamic viscosity and shear stress
are considerably modified under the influence of
the magnetic field (Fig. 6).
ꢀ The device in Fig. 7 helps to determine the
conductivity s of the suspensions in parallel and
longitudinal magnetic fields.
Fig. 13. The migration time tmig. of the suspension micro-
particles as a function of the distance D between the micro-
particles, for H ¼ 43:780kA=m (a) and H ¼ 78:008kA=m (b).
(A) longitudinal magnetic field, (B) transversal magnetic field.
ꢀ MRS is not conductive. On the contrary,
EMRS, due to its graphite content is conductive

ARTICLE IN PRESS
I. Bica / Journal of Magnetism and Magnetic Materials 283 (2004) 335–343
343
owing to the pressure of the magnetic field
strength.
[9] S. Melle, M.A. Rubio, G.G. Fuler, in: Proceedings of the
seventh International Conference ERF and MRS, 1999,
pp. 205–223.
ꢀ The electrical conductivity of EMRS, deter-
mined by means of the device in Fig. 7, comes
up during time (Fig. 12), and depends on the
intensity of the magnetic field as well as the field
direction.
[10] G.L. Gulley, R. Tao, in: Proceedings of the seventh
International Conference ERF and MRS, 1999, pp. 331–338.
[11] K. Minagawa, T. Watanabe, M. Munakata, K. Koyama,
J. Non-Newtonian Fluid Mech. 52 (1994) 59.
[12] X. Wang, F. Gordaninejad, in: Proceedings of the seventh
International Conference ERF and MRS, 1999, pp.
568–578.
[13] D.-Y. Lee, N.M. Wereley, in: Proceedings of the seventh
International Conference ERF and MRS, 1999, pp. 579–586.
[14] W. Kordonski, S. Gorodkin, N. Zhuravski, in: Proceed-
ings of the seventh International Conference ERF and
MRS, 1999, pp. 661–620.
Acknowledgements
Iam thankful to. E. Papp, A. Ercuta and C.T.
Cheveresan from the West University of Timi-
soara for interesting discussions. Ialso like to
thank O. Marinica from the Romanian Academy-
Timisoara, for help in perfuming magnetorheolo-
gical measurements.
[15] W.I. Kordonsky, J. Magn. Magn. Mater. 122 (1993) 395.
[16] K. Worden, W.A. Bullough, J. Haywood, Smart Technol-
ogies, World Scientific, Singapore, 2003 pp. 193–220.
[17] Y. Lee, D. Leon, in: Proceedings of the eighth Interna-
tional Conference ERF and MRS, 2001, pp. 70–76.
[18] M. H. Nam, Y. M. Han, S. S. Han, H. G. Lee, S. B. Choi.
C. C. Cheong, in: Proceedings of the eighth International
Conference ERF and MRS, 2001, pp. 302–308.
[19] H. Gavin, J. Hohagg, M. Dobossy, in: Proceedings of US-
Japan Workshop on Smart Structures for Improved
Seismic performance in Urban Regions, 2001, pp. 225–236.
[20] I. Bica, J. Magn. Magn. Mater. 241 (2002) 107.
References
[1] Cl. Korman, H.M. Leun, H.J. Richter, Int. J. Mod. Phys.
B 10 (23–24) (1996) 3167.
[21] B. Erkus, M. Abe, Y. Fujino, Eng. Struct. 24 (2002) 281.
´
[2] A.J. Margida, K.D. Weiss, J.D. Carlson, Int. J. Mod.
Phys. B 10 (23–24) (1996) 3335.
[22] A. Milechi, Int. J. Machine Tools Manuf. 41 (2001) 379.
[23] J. David Carlson, M.R. Jolly, Mechatronics 10 (2000) 555.
[24] D.G. Breese, F. Gordaninejad, Int. J. Vehicle Design 33
(2003) 128.
[3] I. Bica, Mater. Sci. Eng. B 98 (2) (2003) 89.
[4] K. Koyama, Int. J. Mod. Phys B 10 (23–24) (1996) 3067.
[5] G.A. Flores, M.L. Ivey, J. Liu, M. Mohebi, N. Jamashi,
Int. J. Mod. Phys. B 10 (23–24) (1996) 3283.
[25] I. Bica, J. Magn. Magn. Mater. 270 (2004) 321.
[26] G.A. Flores, J. Liu, in: Proceedings of the eighth Interna-
tional Conference ERF and MRS, 2001, pp. 146–152.
[27] St. Bednarek, J. Magn. Magn. Mater. 202 (1999) 574.
[28] J. Florea, T. Petrovici, D. Robescu, D. Stamatoiu,
Poliphasic Fluids Dinamic and Their Technical Applica-
tions, Technical Press, Bucharest, 1987 (in Romanian).
[29] S. Melle, Doctoral Thesis, Ciudad Universitaria, Madrid,
2002, p. 29.
[6] P. Carletto, G. Bossis, A. Cebers, in: Proceedings of the eighth
International Conference ERF and MRS, 2001, pp. 331–337.
[7] E.M. Furst, A.P. Gast, Physical Review E 61 (6) (2000)
6732.
[8] W.A. Bullough, R.J. Atkin, S. Urang, T.G. Kum, C.
Mush, T. Rober, in: Proceedings of the seventh Interna-
tional Conference ERF and MRS, 1999, pp. 202–214.