Plasma-chemical Synthesis Research Articles

Analysis of the Influence of Modes of Plasmachemical Synthesis and Precursor Evaporation on Geometric Characteristics of Ceramic Powders Produced

Mathematical model of evolution of a liquid precursor droplet in the process of plasma-chemical transformations for production of micro-and nano-structured ceramic powders on the basis of metal oxides is described. A criterion of production of particles with different morphology is determined. The results of numerical analysis are given.

Application of Ellipsometry to Control the Plasmachemical Synthesis of Thin TiONx Layers

Ellipsometry is often used to determine the characteristics of films. Ellipsometric studies may turn out to be ineffective because several solutions correspond to the same polarization angles. It is demonstrated that the ambiguity is not due to the physical limitations of the method but it has a purely mathematical character. So, additional information about the film is necessary to determine the absolute values of refractive index, attenuation, and thickness.

Preparation of nanopowders of carbides and hard-alloy mixtures applying low-temperature plasma

The preparation of nanodimensional powders of tungsten carbides, as well as other transitionmetal carbides, using plasma-chemical reduction synthesis are investigated. The main regularities of preparing powders of specified dispersity and composition are revealed. Characteristic particle sizes of carbides are 40–80 nm. In order to prepare a homogeneous mixture of WC-Co nanoparticles with an exact weight content, the procedure of deposition of cobalt on the tungsten carbide powder with the simultaneous introduction of an additive of inhibitor carbides such as carbides of chromium, vanadium, and tantalum is developed. The prepared powders were investigated using modern methods, including high-resolution scanning electron microscopy and fractional gas analysis.

Obtaning of nanodispersed ferriferous pigments using contact nonequilibrium plasma

The paper shows the efficiency of using a contact nonequilibrium low-temperature plasma for producing nanodispersed pigments of different colours. The influence of the initial pH, treatment time and electrical parameters of the plasma-chemical synthesis on the main technological properties of the pigments was determined. Colour characteristics of the obtained products were studied. Their phase composition was analyzed. According to the data on the dependence of the phase composition of the products formed by the oxidation of iron hydroxide (II) on the synthesis parameters, the system diagram was created to display predominant areas of each phase formation in the pH plasma treatment time coordinates. The main trends in changing the phase composition of the solid phase from the synthesis conditions were determined during the studies. It was found that the final product of iron hydroxide (II) oxidizing depending on the synthesis parameters can be oxyhydroxide of iron (III -a) − modification, magnetite or iron hydroxide (II). A phase composition of the obtained product depends largely on the solution’s pH. With increasing the pH from 6 to 10 under the same synthesis parameters, such sequence of phase formation is indicated: Fe(OH) 2 − a − FeOOH − Fe 3 O 4 . With the further increase of the solution’s pH, Fe 3 O 4 is formed.

Gas-dynamic and thermal processes in the synthesis of trichlorosilane by hydrogen reduction of silicon tetrachloride in a high-frequency discharge

The results of numerical simulation of gas-dynamic processes in heat exchange during a plasma chemical synthesis of trichlorosilane under high frequency discharge were reported. Modeling was performed for optimal conditions of trichlorosilane synthesis with use of contemporary computational methods of hydrodynamics that allowed more exact definition of the velocity and temperature fields, gas flow in a plasma area, and also determination of temperature ranges of reaction zones and proportion in the gas mixture entering the respective zones.

Modeling the plasmachemical synthesis of nanopowdered materials using a combined plasmatron

Processes involved in the production of nanopowders using a combined plasmatron are analyzed. Results of numerical simulation of the plasmachemical synthesis are presented, including calculations of the motion and heating of a finely dispersed powder in the plasma jet at the output of the combined plasmatron. Based on analysis of the results of simulations, recommendations for the choice of optimum parameters of plasmatron operation are given.

Investigation of the propagation of a gigawatt pulsed electron beam in compositions of high-pressure gas

The paper presents the results of the experimental investigation of pulsed electron beam propagation with a varying current density (electron energy Ee = 350–400 keV; total current of a diode Ie up to 11 kA; (half-amplitude) pulse duration t = 60 ns, pulse energy We up to 120 J) in two- and three-component gas compositions used in the pulsed plasma chemical synthesis of nanosized oxides. The mean value of the specific absorbed energy within the zone of pulsed electron beam propagation with a current density of 0.05–0.06 kA/cm2 in gas compositions has been determined.

Characteristics of pulsed plasma-chemical synthesis of silicon dioxide nanoparticles

This paper investigates the effect of plasma-chemical synthesis modes of nanosized silicon dioxide initiated by a pulsed electron beam on the geometric size distribution of the product nanoparticles. Findings show that the particles are enlarged following multiple exposures to a pulsed electron beam. Meanwhile, when adding a buffer gas into the initial mixture, the size of the particles decreases.

Study of Microwave Torch Plasmachemical Synthesis of Iron Oxide Nanoparticles Focused on the Analysis of Phase Composition

This work presents the results obtained on the single-step route towards the synthesis of iron oxide nanoparticles in a microwave plasma torch. The torch is supplied by 660 sccm of Ar mixed with 1 sccm of Fe(CO)5 and a variable amount of O2. The influence of oxygen addition on the phase composition of the synthesized powder was studied. Magnetite and maghemite phases could not be distinguished using the standard X-ray diffraction (XRD) analysis. Therefore, a combined XRD and Raman spectra analysis had to be applied, which is based on fitting of selected diffraction peaks and spectral features. According to XRD and Raman spectroscopy, the powder synthesized from Ar/Fe(CO)5 consisted about 50 % of magnetite, Fe3O4, the rest being α-Fe and FeO. An increase in oxygen flow rate led to an increase in γ-Fe2O3 percentage, at the expense of α-Fe, FeO and Fe3O4. Almost pure γ-Fe2O3 was synthesized at oxygen flow rates 25–75× higher than the flow rate of Fe(CO)5. A further increase in the oxygen flow rate led to α-Fe2O3 and e-Fe2O3 production. The distributions of nanoparticles’ (NPs) diameters were obtained using transmission electron microscopy (TEM) and dynamic light scattering (DLS). The mean diameter of the NPs measured by TEM was 13 nm while the DLS measurements led to the mean diameter of 12 nm. About 90 % of all particles had the diameter in the range of 5–21 nm but a few larger particles were observed in TEM micrographs.

Evaluation of the morphology of particles produced by plasma-chemical synthesis of ceramic powders

A physicomathematical model of thermal and diffusion processes in a drop of a dilute metal salt solution during its heating in a plasma-chemical reactor for synthesizing metal oxide powders is presented. The results of numerical calculations are analyzed to assess the possible influence of the operation parameters of the reactor and the characteristics of the initial solution (precursor) on the morphology of the particles formed.

Pulse Plasma-Chemical Synthesis of Ultradispersed Powders of Titanium and Silicon Oxide

This paper is devoted to studying the plasma-chemical synthesis of nanosized SiO2 and TiO2 powders and to the analysis of their major characteristics. The nanosized powder was synthesized in the plasma-chemical reactor using a pulse electron beam to generate low-temperature plasma. The synthesized powders were studied by the transmission electron microscopy to determine the morphology and the size of the nanosized powder with respect to by-products of the reaction. The elemental composition was studied using the Oxford ED2000 X-ray fluorescent spectrometer. To determine the crystal structure of the nanosized powder, we used the standard technology of X-ray phase analysis. The reaction products were processed using Shimadzu XRD-6000/7000. The substances included in the composition of the nanosized powder were identified using Nicolet 5700 Fourier transform infrared spectrometer.

Size characteristics of copper nanopowders before and after oxidation

The size characteristics of copper nanopowders obtained by the plasma-chemical synthesis are investigated by electron microscopy and X-ray diffractometry. Metallic and oxidized samples are investigated. The average sizes of particles and coherent scattering regions are determined and histograms of size distributions for particles and coherent scattering regions are plotted. The size characteristics of nanopowders before and after oxidation are compared.

Combined barrier discharge in atmospheric-pressure air

A combined (dual) barrier electric discharge in atmospheric-pressure air is investigated. The discharge is induced in a discharge chamber with two pairs of electrodes of different configurations. The electrodes are connected to two independent high voltage power supplies. The plasma-chemical synthesis of ozone was studied in atmospheric pressure air depending on the parameters of each discharge contour. The analysis was performed in terms of efficiency and practical application of a combined barrier discharge.

Properties of nanosilicon obtained by plasma chemical decomposition of monosilane in a microwave discharge

Investigations of nanoscale silicon powders obtained by plasma chemical synthesis in various process parameters were carried out by transmission electron microscopy, X-ray photoelectron spectroscopy, and infrared (IR) spectroscopy. It was demonstrated that the powders consist of spherical particles with an average diameter from 20 to 30 nm. Each particle includes a single-crystal silicon core and amorphous shell whose chemical composition is defined by bonds of silicon with oxygen and hydrogen. The measurements of photoluminescence (FL) show the presence of dim near-infrared FL in the specimen powders, and more intensive emission around 420 nm in the suspension of the powder in ethanol. The character of this emission has not been determined yet.

Plasma-Chemical Synthesis of Nanosized Powders-Nitrides, Carbides, Oxides, Carbon Nanotubes and Fullerenes

In this article the plasma-chemical synthesis of nanosized powders (nitrides, carbides, oxides, carbon nanotubes and fullerenes) is reviewed. Nanosized powders - nitrides, carbides, oxides, carbon nanotubes and fullerenes have been successfully produced using different techniques, technological apparatuses and conditions for their plasma-chemical synthesis.

Plasmachemical synthesis of aluminum-based nitride compounds in vacuum-arc discharge plasma

A vacuum-arc plasmachemical synthesis of aluminum-based nitride compounds (AlN and Ti-Al-N) is described. The compositions and structures of the obtained coatings have been studied. It is shown that the composition and structure of a coating can be effectively controlled by varying the discharge current, ion current density distribution, and gas pressure, provided that the plasma flow is free of droplets.

Investigation of Production of Fine-grained SiAlON Ceramics from Nanopowders

Different sialons’ compositions were used to find the effect of material starting components on sintering and properties of sialon materials. The nanopowders (Si3N4, AlN, Al2O3, Y2O3 and Si3N4-27 wt.% AlN nanocomposite) were produced by the plasmachemical synthesis. The composite materials were sintered by the method of pressure-less sintering. Sintering temperature decreased significantly, if Si3N4-AlN nanocomposite was used as one of the components. The increased amount of a- sialon phase and higher hardness are characteristic for materials obtained from separate Si3N4, AlN, Al2O3, Y2O3 nanocomponents.DOI: http://dx.doi.org/10.5755/j01.ms.18.3.2439

The Synthesis, Characterization and Sintering of Nickel and Cobalt Ferrite Nanopowders

The NiFe2O4 and CoFe2O4 ferrites were synthesized by two methods – chemical sol-gel self-combustion method and the high frequency plasma chemical synthesis and magnetic properties, crystallite size, specific surface area of synthesized products are characterized. Nanopowders synthesized in the high frequency plasma are with specific surface area in the range of (28 – 30) m2/g (the average particle size (38 – 40) nm, crystallite size ~40 nm). The ferrite nanopowders obtained by sol-gel self-combustion method have the specific surface area of (37 – 43) m2/g (average particle size (26 – 31) nm, crystallite size (10 – 20) nm). All synthesized nanopowders were sintered via pressure-less sintering method and magnetic properties of compacted materials were studied, as well.DOI: http://dx.doi.org/10.5755/j01.ms.18.1.1332

Nanodisperse Nickel Ferrite: Methods of Production, Structure and Magnetic Properties

Nanodisperse Nickel Ferrite: Methods of Production, Structure and Magnetic Properties The nickel ferrite nanoparticles were prepared using combustion synthesis and plasma chemical synthesis based on evaporation of coarse-grained oxide powders in an inductively coupled air plasma, and their characteristics were compared. The crystallite size of nanoparticles produ-ced by combustion synthesis and plasma synthesis were of 29 and 45 nm respectively. The saturation magnetization of the plasma-prepared samples (43.5 emu/g) and coercivity (74 Oe) exceed values reported in literature for NiFe2O4 powders and could be explained by wide particle size distri-bution. The magnetic characteristics of the chemically prepared samples with more narrow particle size distribution were close to the respective literature data.

Hydrogenation of the nanopowders that form in a carbon-helium plasma stream during the introduction of Ni and Mg

Composite nanoparticles consisting of magnesium, nickel, and carbon atoms are studied both theoretically and experimentally. The calculations performed in terms of the density functional theory show that the jump frequency of hydrogen atoms in nickel-containing magnesium hydride increases substantially near impurity nickel atoms; as a result, the rate of hydrogen absorption by magnesium also increases. Nickel on the magnesium surface is shown to be absorbed via an island growth mechanism. Composite Mg-C, Ni-C, and Mg-Ni-C powders are produced by plasmachemical synthesis in a carbon-helium plasma stream. Hydrogen is introduced into a chamber during synthesis. It is found by X-ray photoelectron spectroscopy and thermogravimetric analysis that, among these three composites, only Mg-Ni-C contains magnesium fixed in the MgH2 compound. The process of such “ultrarapid” hydrogenation of magnesium, which occurs in the time of formation of composite nanoparticles, can be explained by the catalytic action of nickel, which is enhanced by a high temperature. Scanning electron microscopy micrographs demonstrate the dynamics of the dehydrogenation of Mg-Ni-C composite nanoparticles in heating by an electron beam.