Data on the formation of periodic and labyrinth structures in thin layers of a kerosene-based magnetic fluid (MF) under the action of electric and magnetic fields is given in [1,2]. In this paper, we analyze the possible reasons and mechanisms of the observed phenomenon and present new experimental results concerning the structurization processes in the MF. The total set of the existing data enables us to state that the magnetic ordering of single-domain particles in aggregates is possible. EXPERIMENTAL METHOD AND OBJECT OF RESEARCHTo study the structures formed and their transformation under the effect of various factors, we used the diffraction scattering of a He-Ne laser beam perpendicular to a thin layer of the MF. The scheme of the experimental setup is thoroughly described in [2]. The intensity of the scattered light was measured by a photoelectric detector (type FES-25) with a diaphragm or by a miniature photoresistor, depending on the actual aims of the experiment. The measuring cell consisted of two rectangular glass plates with a transparent conducting coating. A fluoroplastic film with a circular hole in the center was placed between the glass plates; this hole was filled with the MF in question. The thickness of the MF layer amounted to 20-40 µ m and was determined by the thickness of the fluoroplastic films. To generate the electric field, voltage from a stabilized d.c. source was applied to the plates. As the magnetizing system, we used Helmholtz coils generating a uniform field in a volume several times larger than that of the cuvette. The same cuvette was also used for visual optical-microscopic observation of the processes in the MF. To study one of the structure-sensitive parameters of the MF, its magnetic susceptibility, the bridge method was used.The magnetic susceptibility was calculated according to the change in the inductance of the measuring solenoid caused by the sample placed into it. The inductance was measured by an LCR-817 immittance meter at a measuring field frequency of 70 Hz; the error did not exceed 0.1%. The object of study was a kerosenebased MF with magnetite particles stabilized by oleic acid. The volume concentration of the dispersed phase was 11%; the dynamic viscosity amounted to 5 × 10 -3 Pa s. EXPERIMENTAL RESULTS AND DISCUSSIONEarlier studies [2] showed that periodic structural lattices can be formed in thin MF layers in an electric field in the near-electrode space and can be transformed following a change in the external conditions. The formation of structural lattices was observed when a certain (critical) voltage at the electrodes was reached. Its value depended on the temperature and the intensity of the applied magnetic field. It was concluded that the structural transformations can be interpreted as phase transitions in disperse systems. Such an interpretation of structural transformations in MFs was earlier proposed in many studies (e.g., see [3][4][5]).Meanwhile, our experimental investigations showed that stabilized kerosene-based MFs are sufficiently stable ...
The phase separation and structural organization of a thin layer of a magnetic fluid under the influence of a constant electric field are investigated. It is shown that the action of an electric field leads to the appearance of labyrinth structures in a thin layer of a magnetic fluid, which subsequently leads to the formation of a free charge at the boundary of this layer with the rest of the liquid volume. The results of the study of the current strength on the shear rate dependence made it possible to estimate the value of the surface charge density and the time of its formation in the near-electrode space. By artificially increasing the electrical conductivity of the initial magnetic fluid, it is shown that the formation of labyrinth structures in a magnetic fluid in an electric field occurs at a certain critical value of its electrical conductivity.
The article presents the results of an experimental study of the heat transfer process in magnetic fluid under the influence of electric and magnetic fields of various configurations. It is shown that a constant electric field leads to an increase in the heat transfer coefficient when a certain threshold value of tension in a thin layer of magnetic fluid is reached. The possibilities of controlling the heat transfer process using the additional effects of homogeneous and inhomogeneous magnetic fields are found.
In this article, the processes of structuring non-magnetic microparticles of various shapes (spherical and cylindrical) placed in magnetic liquid are investigated. It was established that the equilibrium orientation of non-magnetic microparticles and structural formations from them in magnetic and electric fields is determined by the ratio of both field strengths and magnetic and electrical parameters of the carrier medium and material of non-magnetic inclusions. Analysis of mechanisms of interaction of non-magnetic filler particles and orientation of formed structures under the influence of magnetic and electric fields was carried out. It has been found that the action of a uniform magnetic field on a magnetic liquid with a dispersed non-magnetic filler leads to a significant anisotropy of the thermal conductivity coefficient - the difference in the thermal conductivity coefficient in the direction coinciding with the field strength vector and perpendicular to it can reach 25%. The analysis of the detected effect is made on the basis of ideas about the occurrence of structural anisotropy in such a medium due to the structural organization of non-magnetic filler particles in the magnetic field.
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