THE INFLUENCE OF MORPHOLOGY, CONDITIONS OF PRODUCTION AND EXTERNAL EFFECTS ON NANOPARTICLES’ (IN TERMS OF IRON) DIELECTRIC PROPERTIES

It was shown that the complex research of iron nanoparticles properties by different methods, supplemented each other, permit to receive the data about the interior sizes of nanoparticles, a number of physical properties of particles, their dependence on frequency and changes produced by various influences. It was found that the conductivity of nanoparticles changed under the square dependence σ = σoω2.


Introduction
In recent years research of different production methods of nanomaterials and investigation of their properties causes a great interest [1,2]. Thanks to specifi c properties of superdispersed powders such as signifi cant contribution of surface properties, internal stress, peculiar magnetic characteristics, appearing due to similar structure; size factor, defi ning a higher level of extra energy; high catalyst properties -those materials can fi nd a great amount of potential application in metal manufacture, electronics, biological, chemical and pharmaceutical industries [3][4][5][6][7][8][9][10][11][12].
The gap between the opportunities of creating objects and the abilities of getting knowledge about their properties and data of nanoparticles is widening. This gap is becoming an inhibitive factor in nanostructure research and more over in their practical application. To our opinion we should mention some specifi c applications that characterize the breadth and range of this problem.
To reach electromagnetic compatibility in aircraft special materials absorbing electromagnetic radiation are used; and one of extenders used in absorbers is superdisperced and powder carbonyl iron [3]. Magnetopolymer composition of micro-or/ and nanosize, distributed in highly elastic polymeric matrix, having the ability to deform to hundreds percent under the action of external magnetic fi eld are widely used [4].
Wide-range research showed high effi ciency of iron nanopowders application in plant cultivation, animal husbandry, poultry farming, fi shery and in feeding stuff [5]. It is stated that application of aqueous suspension on the basis of nano crystal iron promotes the immunological index adjustment of animals infected with a virus just a like the man's T-cell leukemia. Stimulating effect is obvious in seeds germinability [6,7]. Great interest is arising out of developing and perfecting the © Биленко Д. И., Терин Д. В., Тозкопаран О., Йлдырым О., Галушка В. В., Динкер И., Добринский Э. K. , Элерман Я., Вениг С. Б., 2015 Научный отдел 22 methods of magnetic nanoparticles (in the terms of iron) production. They might serve as target drug carrier in chemotherapy [8]. Not less important seems the problem of predicting and evaluating of the future probable infl uence of new materials on a man's health and the environment, so the task is to develop new appropriate security standards. Nanoparticles can penetrate unchangeable through blood-brain barrier and cumulate in organs and tissues, toxicity of nanoparticles is defi ned by their shape and size [9].
The problem of nanoparticles' diagnosis is in their instability, high reactivity and internal inhomogeneity. Nowadays there is no common method or complex of methods in scientifi c literature for multiparametric investigation, calibration and classifi cation of nanoparicles.
The problem of identifi cation the form, structure, size and the character of size distribution, structure and inner properties of nanoparticles and also their static and dynamic, electric and magnetic properties is thought to be fundamental. The solution of those tasks is determined by the fi eld of superdispersed powders application.
One of the informative ways getting these data is the research of frequency dependences of complex dielectric and magnetic permeability, which are the basis to multivariate multiparametric investigation of nanoparticles. Those investigations are necessary to establish the correlation between their properties and the effectiveness of application in different fi elds. The aim of this work is a complex research of iron nanoparticles properties.

Samples and production methods
Some dozens methods of NP production are known nowadays. There are three kinds of methods that are of great interest from technological point of view. They are mechanical method, chemical and plasma ones. To get the investigated materials we used the reactor 25 kW. Plasma reactor is the electroarc evaporator-condenser with stabilized plasma fl ow. Gas system permitted to delete moisture and oxygen, imported with the stuff and when the apparatus was opened, from technological gas. The system was hermetically assembled and vacuumized up to residual pressure 0.05 kg/сm 2 and fi lled in with inert gas-argon up to pressure 1.2 kg/sm 2 . Electric arc was burned up between the electrodes of reactor and under the infl uence of stabilizing (vortical) technological stream it localized in the centre of the reactor. The stuff of the powder had physicochemical composition: carbon 0.6−0.8; nitrogen 0.5−0.8; oxygen 0.8−1.2; iron 98.10−97.20 (fraction of total mass, %).
The average diameter of spherical stuff particles was 2.2 μm. The delivery of raw material was performed with pneumotransport method. The produced aerosol proceeded into the electric arc zone and the particles are exposured by 5000−6000 K plasma discharge. Gas-vapor stream with evaporated material were mixed with hardening and stabilizing gas on the output from the reactionary zone and was cooled up to temperature 50−60 o C. Then separation of large-scale fraction from nanopowder was done. The nanopowder collected on the fi lter was put into the storage fi lled in with inert gas. This method permits to produce powders of narrow fractional composition. Large surface of material contact with plasma increases the effectiveness and rises the process effi ciency. Specifi c surface area of producted iron nanopowder was determined by the method of nitrogen thermal desorption.

Scanning electron microscopy (SEM)
To investigate the morphology characteristics with the help of scanning electron microscopy the samples were subjected to preliminary preparation. SEM images were got just by simply pilling the powder or by monitoring the pressed pills. Material consumption for one pill 3 mm diameter was from 40 to 200 μgm. The pressure of forming pills variated from 500 to 600 MPa but it didn't exceed 700 MPa. After that the pill was kept in the press for 30−50 min. We have got series of typical SEM images containing somewhere about 500−1200 spherical particles, represented on Fig. 1. Analyzing SEM images we have got differential distribution curves of nanoparticle sizes. Apart from distribution diagrams polydispersion systems could be described with the following parameters: number-average diameter  where n i -the number of globule fractions with average diameter. The results are represented in Table 1.

Elemental composition-based method (ECM) of determining core-shell parameters
Nanoparticles (NP) can be indicated by a great number of different parameters and the most signifi cant among them is their core-shell structure. Recently, a considerable interest has been drawn to the creation of methods that could provide the ability of reliable and nondestructive detection of the topology of NP [13]. Particularly, the identifi cation of the shell thickness l and core diameter d are of interest. However, they are diffi culty determined by the fact that the models of NP are a priori unknown and, moreover, their properties can differ from the properties of a solid material. That is why it seems reasonable to use several independent methods which will permit to confi rm the applicability of the proposed model, to check if the fi ndings are reliable and to obtain more specifi c data in case of need. So this study presents a determination of the oxide layer thickness and the diameter of the core in core-shell iron NP using three independent methods. The fi rst of them is based on elemental composition of NP, the second one relies on NP density and the last is grounded on frequency impedometry.
In the majority of possible cases when the shell is generated due to the oxidation process the usage of EDX analysis data (Fig. 2) permit to fi nd a concentration ratio N Fe /N O (for instance, for the iron NP):

Particle density-based method (pdm) of determining core-shell parameters
A single particle density is connected with the values of its sizes by means of the following correlation: where ρ 1 and ρ 2 are the core and the shell densities, respectively. Connecting experimental density ρ e with referred ρ, we have got the expression for the core diameter d: then thickness of the shell is l = (D -d) / 2. Iron powder samples were investigated using scanning electron microscope (SEM). After respective calculations it was found that the shell thickness l founded with ECM virtually coincide with PDM thickness (Table 1). Calculating error amounts to 1.25 nm, which confi rms the validity of the proposed methods.

Frequency impedometry method
For the realization of this method the formula for the effective permittivity obtained in [14] was applied: , ε 1 is the effective permittivity of metallic core, ε 2 is the effective permittivity of the shell, ε eff is the permittivity of composite medium, p is the volume fraction of metal in the effective medium, ε g is the permittivity of paraffi n. In our experiment the iron spherical core-shell particles were randomly distributed in a dielectric matrixparaffi n. Firstly, 10% and then 20% of composite was located between two glass slices covered with the conductive layer of InxSnyOz. This set up was fulfi lles the role of the capacitor.
We investigated frequency dependence of dielectric loss tangent and capacity of composite medium on the precision analyzer components WK 6440B (frequency range 20 Hz − 3 MHz). Special shielded container was used to reduce electromagnetic distortions. Dielectric loss tangent and capacity error was not less than 0.2%. We determined fre- , quency dependences of real and imaginary dielectric permittivity and conductivity on the base of С(ω) and tgδ(ω) frequency dependences of investigated , where  is a real part complex dielectric permittivity of nanocomposite; ε 0 -permittivity of vacuum, S is sample's area, h is the thickness of nanocomposite layer,    is an imaginary part complex dielectric permittivity of nanocomposite). A special computer program was designed for solving the direct problem -to permit modeling of ε' and ε" frequency dependences subjected to the quantity of frequency dependences of NP conductivity, core-shell parameters, their volume fraction in composite and the properties of matrix material. As a result of modeling it was determined that real and imaginary parts of the complex permittivity of composite media depend on the shell thickness. For instance, the variation of the thickness within 0,5 and 4 nm produces changes of the real part from 100 to 20 (Fig. 3). The dependences of ε' and ε" on z and on l are essentially different over a various range of values z. Such relations make it possible to determine the parameters of NP as their thickness l, conductivity σ and its frequency dependence (Fig. 4). and z (z =σ/ω) Experimentally obtained frequency dependences of complex dielectric permeability components were the basis for solving the inverse problemdefi nition of NP properties. The parameters of NP were processed with a specially created computer program. NP frequency dependence conductivity was assigned as . Sought quantities σ o , n и l were varied up to the best coincidence between rated and experimental dependences ε(ω).

Научный отдел 26
The approximating line was drawn and the slope of this line n was determined (Table 2) to on the base plot of the conductivity-frequency of NP. We investigated composites with various volume fraction of nanoparticles -q. The coincidence of values σ 0 and n of samples with various volume fraction q confirme the correctness of simulated results. The same value of n was predicted by [15]. It was found that the conductivity of NP changed under the following law σ = σ o ω 2 .
The methods suggested in the work supplement each other. The most informative is the method which permits to receive the data not only about the interior sizes of NP, but also about a number of physical properties of particles, their dependence on frequency and changes produced by various influences. Such the results can be obtained only by using the measurements of the impedance frequency dependences. More simple methods based on the elemental structure of NP and their density can serve for the data acquisition. These data facilitate appreciably the inverse solution of the multiparameter analysis based on the frequency dependence of complex permittivity.

Conclusion
The complex research of iron nanoparticles properties by ECM, SEM and PDM methods, supplemented each other, permit to receive the data about the interior sizes of NP, a number of physical properties of particles, their dependence on frequency and changes produced by various influences. It was found that the conductivity of NP changed under the square dependence ~ ω 2 .
This work was performed as part of the state task of the Ministry of Education and Science of the Russian Federation. Project №3468: Phase and structural modifi cation of micro-and nanostructures by electromagnetic radiation of a wide range of energies. The registration number 114121550163.