Polymer grafting onto magnetite nanoparticles by “click” reaction

In this article, we described click chemistry methodology for the incorporation of biocompatible polymer chains to Magnetite nanoparticles (NPs). We used a reduction co-precipitation method to obtain Fe₃O₄ particles in aqueous solution. As a next step, magnetic NPs surface were modified by a silanization reaction with (3-bromopropyl)trimethoxysilane in order to introduce bromine groups on the particles surface which were converted to azide groups by the reaction with sodium azide. Acetylene functionalized poly(ethylene glycol) (a-PEG) and poly(ε-caprolactone) (a-PCL) were synthesized and grafted onto the surface of azide functionalized NPs via “click” reaction to obtain magnetic NPs. Success of the different functionalization processes at different stages was studied using Fourier Transform infrared spectroscopy (FTIR). The morphologies of magnetic NPs were further investigated by transmission electron microscopy (TEM). The magnetization and superparamagnetic behavior of naked Fe₃O₄ NPs and coated NPs at room temperature was investigated by the measurement of hysteresis curves using a Vibrating Sample Magnetometer (VSM).     

Nature of the anomalous dispersion of particles in fullerite-alkali-metal-halide composites

The occurrence of a solid-phase reaction between powders of the fullerite C₆₀ and potassium halides under the conditions of mechanical grinding is established. The electrostatic potential and surface-active properties of C₆₀ molecules are considered as causes of the anomalously high degree of dispersion of the particles within a composite. Pis’ma Zh. Tekh. Fiz. 25, 45–49 (April 26, 1999)     

Global stochastic particles in a field-reversed configuration

This paper discusses the dynamics of the fusion products of the D-He³ reaction in a field-reversed configuration, with application to a reactor regime with a large value of the plasma β. It shows that, under the conditions in the Artemis-L design [H. Momota and Y. Tomita, J. Plasma Fusion Res. 69, 801 (1993)], the motion of protons with an initial energy of 14.1 MeV is strongly stochasticized. The confinement time of these particles and the energy transfer from the fusion products to the plasma are very small. Pis’ma Zh. Tekh. Fiz. 23, 37–39 (November 12, 1997)     

Multiple strengthening mechanisms in nanoparticle-reinforced copper matrix composites

The multiple hardening mechanisms of a copper matrix have been presented and discussed. The pre-alloyed ball milled Cu–3 wt.%Al and the atomized Cu–0·6 wt.%Ti–2·5 wt.%TiB ₂ powders have been used as starting materials. Dispersoid particles Al ₂ O ₃ and TiB _2\thinspace _{{\bf 2}\thinspace }were formed in situ. The powders have been hot consolidated. Optical microscopy, SEM, TEM, and X-ray diffraction analysis were performed for microstructural characterization. Increase in microhardness of Cu–3 wt.%Al compacts is a consequence of the crystallite size refinement and the presence of Al ₂ O ₃ particles. High hardening of Cu–0·6 wt.%Ti–2·5 wt.%TiB ₂ is a consequence of the presence of modular structure, Cu ₄ Ti_(m), and TiB ₂ particles.     

Theory of the Lesage-Jeans instability in a linear chain of dust particles in plasma

The dynamics of the Lesage-Jeans instability in a linear infinite periodic chain of dust particles in plasma is studied theoretically by deriving and numerically solving the nonlinear wave equation. Pis’ma Zh. Tekh. Fiz. 25, 84–89 (September 12, 1999)     

Influence of thermomechanical aging on fatigue behaviour of 2014 Al-alloy

The fatigue behaviour of 2014 Al-alloy has been studied in various thermomechanically aged conditions. It is observed that fatigue properties can be improved by a thermomechanical treatment, which would reduce the concentrations of dispersoids, provide a relatively uniform deformation structure and produce fine distribution of θ’ precipitates. Fine θ’ particles inhibit dynamic recovery and produce uniform deformation structure, which improves fatigue behaviour. Presence of dispersoids and coarse precipitate particles leads to the formation of persistent slip bands (PSBs) and a highly heterogeneous deformation structure, which cause damage to fatigue properties.     

Theory of multiple scattering in a fractal medium

An analysis is made of multiple scattering of particles whose ranges have a power-law distribution corresponding to a fractal medium. The small-angle approximation is used to derive an expression for the angular distribution of particles which have traversed a specific path. The results of numerical calculations are presented. Pis’ma Zh. Tekh. Fiz. 25, 34–40 (June 12, 1999)     

Effect of particle mass on the behavior of stochastic ratchets

Nonlinear Brownian motion in stochastic rachets is investigated by electronic simulation methods. It is shown experimentally that it is possible to sort particles by mass using a discrete random process, binary noise, as the source of the nonequilibrium stochastic ratchets. Pis’ma Zh. Tekh. Fiz. 24, 47–53 (January 26, 1998)     

Effect of zirconium addition on the recrystallization behaviour of a commercial Al-Cu-Mg alloy

It is well known that the second phase particles have an effect on recrystallization and grain growth behaviour of an alloy. Particularly the bimodal distribution of second phase particles has an effect which is opposite in sense where coarse second phase particles (> 1 μm) stimulate nucleation while fine particles exhibit Zener drag. In the literature, the effect of zirconium addition to aluminium alloys has been well documented in order to produce superplasticity by giving ultra fine grain size to the alloy. Addition of zirconium produces Al ₃ Zr particles which pin the grain boundaries during recrystallization and grain growth. In the present work, zirconium was added to a commercial Al-Cu-Mg alloy and by heat treatment Al ₃ Zr particles were precipitated and after forging, the grain size was an order of magnitude lower than the alloy without zirconium. Transmission electron microscopy was employed to characterize the second phase particles, i.e. Al ₃ Zr particles and found to be rod shaped and identified to be cubic ordered L 1 ₂ phase with a lattice parameter of 0.408 nm. Further, it was observed that fine (100 nm) Al ₃ Zr particles promote only continuous recrystallization which is polygonization of subgrains and subgrain growth. It was found that the fine dispersion of Al ₃ Zr particles inhibits both recrystallization and grain growth in the commercial Al-Cu-Mg alloy.     

Variation in magnetic properties during chemical reactions producing Fe1-xS and FeCl2

 By use of a Hall measurement gaussmeter, the magnetic properties of chemically-reacting iron-sulfur powder mixtures and of iron powder plus hydrochloric acid have been extensively studied. In the case of iron sulfide (non-stoichiometric Fe_1-xS) the measured value of the magnetic (B) field first increased continuously and significantly as the chemical reaction proceeded, then decreased sharply as the reaction neared completion. This behavior was stronger in the presence of an externally applied static magnetic field but was also clearly observed in the absence of an external field. The recovered product of the reaction was bronze-colored pyrrhotite which was in the form of a thin magnetic coating on Fe particles with a narrow conical morphology aligned with the external B field. The magnetic behavior during the Fe+HCl reaction was similar but far less pronounced. The general magnetic field behavior in both systems parallels the character of an activated state energy behavior. Received: 21 July 1998 / Accepted: 28 August 1998     

Self-similarity and branching of wavelet transforms of microwave signals generated by a vircator

The turbulence regimes of an electron flow with a virtual cathode are studied. The microwave signals generated by a vircator are calculated by the method of large particles. The wavelet transforms of these signals are constructed, and it is shown that they have a complicated self-similar and branching structure. It is concluded that the turbulence of an electron flow is caused by macroscopic instabilities. Pis’ma Zh. Tekh. Fiz. 22, 92–96 (December 26, 1996)     

Preparation of SiC hollow particles by gas-phase reaction in the SiH4-CH4-H2 system

The formation of SiC hollow particles by gas-phase reaction in the silane-methane-hydrogen system was studied at temperatures from 1200 to 1400° C. Synthesized powders were analysed by means of the thermogravimetry, X-ray diffraction, transmission electron microscopy, infrared irradiation, etc. The powders synthesized at 1200 to 1300° C consisted ofβ-SiC and silicon phases, but they became almost hollowβ-SiC particles at 1400° C. The composition, particle size, and shell thickness of the synthesized particles were dependent on the reaction conditions. From lattice parameter measurements, a certain amount of excess silicon was verified to be incorporated into theβ-SiC lattice. On the other hand, excess carbon existed, for the most part, as an amorphous phase not forming solid solutions withβ-SiC. Transmission electron microscopy observations and infrared absorption measurements have shown that excess carbon is contained within the shells of hollow particles, while unreacted excess silicon exists as a crystalline phase mostly in the cores of the particles.     

Uncatalyzed synthesis of polypyrrole with viologen side groups and its chemical properties

A substituted polypyrrole (PPr) with viologen side groups (polymer-1) was obtained from the reaction of N-aminopyrrole with 1-hexyl-1′-(2,4-dinitrophenyl)-4,4′-bipyridinium dihalide (salt-1). A model compound (model-1) was synthesized by the reaction of N-aminopyrrole with N-(2,4-dinitrophenyl)-4-(4-pyridyl)pyridinium chloride (salt-2). UV–vis spectra revealed that polymer-1 had an expanded π-conjugation system along the polymer chain: the polymer showed an onset position of absorption at a wavelength approximately 200 nm longer than the corresponding wavelength of model-1. Polymer-1 received an electrochemical oxidation of the pyrrole ring and reduction of the viologen group within the polymer.     

Electroconductivity of sintered bodies of α-Al2O3-TiN composite prepared by CVD reaction in a fluidized bed

α-Al₂O₃ particles whose primary size is ca. 450 nm are smoothly fluidized by forming agglomerates of ca. 200 μm and are coated with TiN crystallites generated by a chemical vapour deposition (CVD) reaction of TiCl₄ and NH₃ at 973 K. The α-Al₂O₃-TiN composite particles and those obtained by mechanically mixing constituent particles are sintered at 1873 K in a nitrogen atmosphere, and the electroconductivity of sintered bodies is measured at 298 K. The electroconductivity of the CVD-hybridized composites is higher than that of mechanically mixed ones. This shows the effectiveness of fluidized-bed CVD processing in the preparation of composite ceramic particles.     

Interaction between relativistic charged particles and an extended strong rf field

An investigation is made of the interaction between relativistic charged particles and a high-intensity microwave electric field over long interaction lengths. The microwave field has no magnetic component over the entire interaction length. It is shown that the interaction of the relativistic particles has features which depend on the relation between the incoming particle energy and the field strength. In particular, part of a monoenergetic particle beam may be accelerated by the beam’s own energy with some of the energy being transferred from the beam to the field. Pis’ma Zh. Tekh. Fiz. 24, 80–86 (May 26, 1998)     

Synthesis of spherical Al2O3 and AlN powder from C@Al2O3 composite powder

A novel approach has been taken to produce (1) spherical Al₂O₃ particles by decarbonisation and (2) spherical AlN particles by nitridation and subsequent decarbonisation of C@Al₂O₃ composite particles. C@Al₂O₃ composite particles have been prepared by heterogeneous nucleation and crystallisation of Al(NO₃)₃ on surfactant encapsulated carbon nano particles followed by evaporative decomposition of the nitrate. Overpressure (0.4 MPa) of nitrogen and a temperature range (1723–1873 K) have been used for nitridation. Whiskers as well as spherical particles of AlN have been observed in the final product. The final product has been characterised by X-Ray Diffraction, Scanning Electron Microscope and Carbon–Hydrogen–Nitrogen content analysis by Elemental Analyser and the mechanism of the nitridation reaction has been analysed. The average size of the spherical AlN particles consisting of crystallites in nano-dimensions (30–50 nm) could be varied from 100 nm to 8 μm by changing the composition of the sol.     

Formation of macroparticle structures in an rf induction discharge plasma

It was demonstrated experimentally that macroparticles may undergo levitation and form ordered structures in an rf induction discharge plasma. The experiments were carried out using 1.87 μm melamine formaldehyde particles in neon at a pressure of 25–500 Pa. The generator frequency was 100 MHz. Pis’ma Zh. Tekh. Fiz. 24, 62–68 (October 12, 1998)     

Motion of a “drift island” in a toroidal magnetic confinement device with Coulomb scattering of the particles

A resonant drift trajectory of a charged-particle in a magnetic field (a “drift island”) can be used to remove high-energy impurities from a thermonuclear plasma and to introduce (inject) high-energy particles into the plasma. As a rule, these effects are studied neglecting the Coulomb scattering, i.e., in the collisionless approximation. In the present letter, the effect of Coulomb scattering of a particle with a resonant trajectory by plasma particles is studied. The conditions under which the drift resonance is maintained are found, i.e., the plasma densities and plasma density profiles for which the “drift island” can still move over the transverse section of the plasma are determined. Pis’ma Zh. Tekh. Fiz. 25, 19–27 (September 26, 1999)     

Superdeep penetration efficiency

The efficiency of an explosive accelerator is analyzed. The efficiency of the stream of particles in penetrating into a target to ultralarge depths is determined. Pis’ma Zh. Tekh. Fiz. 24, 81–84 (September 12, 1998)     

Behavior of magnesium and silicon in the formation of MgO/AlN composite

MgO/AlN composites have been fabricated by directed metal nitridation of Al–Si alloy in flowing N₂ at 1473 K. A mixture of magnesia particles and chemically pure magnesium powder was placed on the surface of Al–Si alloy block as reinforcement materials. Mg powder initiates the infiltration and nitridation of Al alloy melt by eliminating protective Al₂O₃ film at the reaction frontier. New Mg vapor from the interface reaction between Al and MgO particles, keeps as continuous deoxidization agent as the added Mg powder. The spinel layer thickness due to the reaction of Al melt with MgO particles is controlled by Mg content. Si not only reduces the surface tension and viscosity of Al alloy melt, but also leads to increase in N₂ content.