1070-4272/01/7406-1031 $25.00 C 2001 MAIK [Nauka/Interperiodica]
Russian Journal of Applied Chemistry, Vol. 74, No. 6, 2001, pp. 1031!1033. Translated from Zhurnal Prikladnoi Khimii, Vol. 74, No. 6, 2001,
Original Russian Text Copyright C 2001 by Lazareva, Shinkareva, Prodan.
AND POLYMERIC MATERIALS
Effect of Modifying Reagents on Rheological Characteristics
of Magnetite Dispersions in Transformer Oil
T. G. Lazareva, E. V. Shinkareva, and S. A. Prodan
Institute of General and Inorganic Chemistry, Belarussian National Academy of Sciences, Minsk, Belarus
Received December 18, 2000
Abstract-Rheological properties of magnetite dispersions in transformer oil were studied in relation to
the conditions of modification of the magnetite surface with water vapor and water-soluble polymers such
as polyvinyl alcohol and carboxymethyl cellulose. Various modification modes are considered.
Directed preparation of various structures with pre-
scribed mechanical properties is among the most im-
portant tasks of the modern physical chemistry of
dispersed systems . The commonly accepted ap-
proach is the optimal combination of mechanical dis-
persion with modification of the dispersed phase sur-
face by, e.g., introduction of such modifying reagents
as water-soluble polymers able to affect the strength
of interparticle interactions and to be readily cross-
linked in the presence of metal cations. The perfor-
mance characteristics of such systems are largely con-
trolled by their rheological parameters such as the
viscoelastic, strength, and hyperelastic indices of so-
lutions. In turn, these parameters are governed by
the strength of macromolecular interaction responsi-
ble for the formation of a three-dimensional network
structure. The basic factors controlling the viscosity
of a structured suspension are the concentrations of
the polymer and dispersed phase and temperature.
In this work, we studied the effect of sorption of
water vapor and water-soluble polymers by magnetite
particles on the structural and rheological character-
istics of magnetite dispersions in transformer oil.
Rheological measurements were carried out with
a Rheotest-2 rotary viscometer for determining the
dynamic viscosity of both Newtonian and non-New-
tonian fluids over a wide range of the shear rates
from 3 to 1312 s
at a temperature of 30370oC.
As the continuous phase served transformer oil,
and as the dispersed phase, magnetite Fe
grade), finely ground and dried at 105oC prior to use.
The magnetite concentration in the oil dispersions var-
ied from 5 to 25%. Sorption of water vapor on mag-
netite was studied as follows. A sample was placed
in a desiccator and allowed to stand over saturated
salt solutions at room temperature for 20 days at
a fixed relative humidity of 30, 60, 80, and 100%.
To obtain modified magnetite, it was brought in con-
tact with solutions of water-soluble polymers such
as 0.5% carboxymethyl cellulose (Na-CMC, 70/300)
or 5% polyvinyl alcohol (PVA, 16/1). The liquor ra-
tios were, respectively, Na-CMC/Fe
= 2.5 and
= 5. The resulting mixtures were then
allowed to stand at 105oC for 5 h and ground in an
The temperature and concentration dependences of
the dynamic viscosity h of magnetite in transformer
oil at 30, 40, 60, and 70oC and a shear rate of 81 s
are given in Fig. 1. With increasing temperature, h
decreases from 16 to 3, from 22 to 7, from 32 to 16,
from 50 to 30, and from 130 to 54 mPa s
in 5, 10,
15, 20, and 25% magnetite suspensions, respectively.
With increasing magnetite concentration, h grows,
which is due to the increasing number of contacting
dispersed phase particles in unit volume, leading to
intensive structurization and higher dynamic viscosity.
The fact that h strongly depends on the shear
stress or rate (Fig. 2) indicates that magnetite dis-
persions in transformer oil are non-Newtonian fluids.
In a 5% magnetite dispersion, h initially decreases
rapidly with increasing shear stress (portion I of the
curve), and then a uniform flow of a fluid anisotro-
pically oriented in the field is established (portion II).
Therefore, the system demonstrates the property of
plasticity as a result of particle structuration and for-
mation of a structure anisotropically oriented in the
mechanical field. Sorption of water on magnetite