Synthesis Of Ultrafine Particles Research Articles

Ultrafine Metal Powders Used as Gas to Liquids Catalysts

The paper deals with the effect of synthesis parameters on the reactivity of Fischer– Tropsch iron-based catalyst resulting from electrical wire explosion in a carbon monoxide medium. The technology provides the synthesis of ultrafine particles with a large specific surface area and a given phase composition. A mixture resulting from the synthesis of liquid hydrocarbons contains hydrocarbons of a paraffinic and aromatic structure, and its further use requires additional refinement.

Selection of injection conditions for aluminum particles as a raw material by numerical analysis in the synthesis of ultrafine particles with transferred type arc plasma

AbstractWe investigated by numerical analysis the dependence of vaporization behavior of aluminum particles injected into transferred type arc plasma on injection conditions in synthesis of aluminum nitride ultra fine particles. On the basis of calculation results, we chose one proper injection condition where aluminum particles vaporized more. © 2009 Wiley Periodicals, Inc. Electr Eng Jpn, 170(2): 46–52, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20852

Synthesis of Ultrafine Particles of Iron and Iron Nitride by Evaporation of Iron in Gas Mixtures of Argon and Ammonia or Argon and Nitrogen

As a series of fundamental study on the gas evaporation method, a levitation-melted iron was evaporated in the gas mixtures of argon + ammonia, argon + nitrogen to synthesize ultrafine particles of iron nitride that got attention as one of the magnetic materials. The particles that were obtained in the gas mixture of argon and nitrogen were α-Fe. But nitrogen was chemisorbed on the surface of the particle, because nitrogen content in the particles was larger than the solubility of nitrogen in iron. The particles that formed in the mixed gas of argon and ammonia were Fe4N. The mean size of the particles of iron nitride was approximately 60 nm. The formation ratio of iron nitride was about 86 %.

Selection of Injection Conditions for Aluminum Particle as a Raw Material by Numerical Analysis in Synthesis of Ultra-fine Particles with Transferred Type Arc Plasma

We investigated by numerical analysis the dependence of vaporization behavior of aluminum particle injected into transferred type arc plasma on injection conditions in synthesis of aluminum nitride ultra fine particle. On the basis of calculation results, we chose one proper injection condition where aluminum particle vaporized more.

Synthesis of ultra fine particles by plasma transferred arc: Influence of anode material on particle properties

There is a great deal of interest today in the special properties of nanoparticles and their potential applications. Gas-phase process, although having some drawbacks, has the largest control possibilities and is therefore the method chosen here. The size of the primary particles depends on the temperature/time history and material properties. Further growth of the particles strongly depends on the properties of the flow into which they are imbedded. In the current work, a transferred arc is used to produce nanometric particles from the condensation of metallic vapours obtained by controlled evaporation of the anode material, which becomes the solid precursor of the synthesis. As all types of anode materials would be used, depending of the nature of the desired particles, this technique requires a good control of the heat transfer and its application time to a given anode location, as well as the separation of evaporation/ nucleation-growth steps. That is why a new and original experimental set-up was built in order to control vapour production and its thermal history. Experiments showed that the heat transfer at the anode precursor strongly depends on the cold boundary layer (CBL) properties close to the anode. For adequate parameters, it becomes possible to generate either diffuse or constricted stable arc root, and so to control vapour production. Orientation and so dissociation of evaporation and nucleation events is also achieved by tilting the angle between the jet issued from the cathode and the anode. The vapours produced are then naturally entrained towards a temperature controlled zone, where they are collected onto a water cooled substrate. It thus becomes possible to control the residence time and the thermal vapour history of the particles. Whereas aluminium oxide particles synthesized are clearly nanoparticle chain aggregates, iron oxides particles are spherical, in the micrometric range and no aggregates or agglomerates are visible. These experiments show that particle morphology, size and shape, for given working parameters, strongly depend on the properties of the material to be vaporized.

Discussion of “synthesis of ultrafine particles of intermetallic compounds by the vapor-phase magnesium reduction of chloride mixtures: Part I. Titanium aluminides”

A new chemical synthesis process for the preparation of intermetallic compounds has been developed. It involves the vapor-phase reduction of mixtures of constituent metal chlorides by magnesium vapor to produce intermetallic compounds in the form of fine powder. The advantages of the process include (a) the use of inexpensive raw materials, (b) low reaction temperatures, and (c) products in the form of fine particles. Part I describes the synthesis of titanium aluminide particles by this method, whereas Part II presents the synthesis of nickel aluminides particles. Although nickel aluminides can also be prepared by the hydrogen reduction of nickel chloride and aluminum chloride vapor mixtures, titanium aluminides cannot be produced by hydrogen reduction because of unfavorable thermodynamics. The effect of AlCl3/TiCl3 partial pressure ratio on the formation of different titanium aluminides was studied. A two-phase mixture containing 80 mol pct of TiAl+20 mol pct of TiAl3 formed at an AlCl3/TiCl3 ratio of 10. The amount of TiAl3 was maximized to 72 mol pct at an AlCl3/TiCl3 ratio of 16. The maximum conversion of the limiting chloride TiCl3 was 94 pct. The product particles were very fine in the size range of 0.2 to 0.3 µm.

Computational fluid-particle dynamics for the flame synthesis of alumina particles

A mathematical model for the dynamics of particle growth during synthesis of ultra fine particles in diffusion flames is presented. The model includes the kinetics of particle coalescence and coagulation, and when combined with a calculation of the temperature, velocity and gas composition distribution in the flame, the effluent aerosol characteristics are calculated. The model is validated by comparison with an experimental study of the synthesis of alumina particles by combustion of Al-tri-sec-butoxide. Two parameters of the coalescence kinetics are estimated by regression of the model predictions to the measured specific surface area of the product particles. The estimated kinetics can be used to predict the surface area and shape of the particles for a wide range of synthesis conditions.

Synthesis of ultrafine particles and thin films of Ni 4Mo by the vapor-phase hydrogen coreduction of the constituent metal chlorides

Ultrafine particles of Ni 4Mo were synthesized by reducing mixtures of NiCl 2+MoCl 5 vapors by hydrogen. Effects of the MoCl 5/NiCl 2 and H 2/NiCl 2 partial pressure ratios and temperature on the content of the intermetallic phase were investigated. The maximum content of Ni 4Mo obtained was 93 mol.%. Product particles were in the size ranges of 100–200 nm. A coating of Ni 4Mo+Ni of 0.7 μm thickness on a Ni substrate was also prepared.

Synthesis of ultrafine particles of intermetallic compounds by the vapor-phase magnesium reduction of chloride mixtures: Part II. Nickel aluminides

Synthesis of ultrafine particles of intermetallic compounds by the vapor-phase magnesium reduction of chloride mixtures: Part II. Nickel aluminides

Synthesis of ultrafine particles of intermetallic compounds by the vapor-phase magnesium reduction of chloride mixtures: Part I. Titanium aluminides

Synthesis of ultrafine particles of intermetallic compounds by the vapor-phase magnesium reduction of chloride mixtures: Part I. Titanium aluminides

SYNTHESIS OF ULTRAFINE PARTICLES OF MATERIALS IN EROSIVE LASER PLASMA IN A HIGH-PRESSURE GAS ATMOSPHERE

Synthesis of ultrafine particles as a result of condensation in an erosive jet at laser vaporization of materials (metals, metal oxides, carbon) in gases (hydrogen, oxygen, helium, argon, xenon and air) at high pressures is investigated. The granulometric, phase, and chemical composition of the condensate particles is analyzed in relation to the elaboration conditions. It is found that the mean dimensions of the condensate particles increase with an increase of the ambient gas pressure. A particle nucleation and growth theory is used to describe the formation of the dispersed condensate in the erosive plasma. It is shown that the resulting particle size distribution is determined by the dependence of the cooling rate of the vapor-gas mixture on the pressure of the surrounding gas.

Synthesis of ultrafine particles of barium ferrite by chemical coprecipitation

A new method to synthesize barium hexaferrite by chemical coprecipitation is described. A mixed precursor was precipitated by addition of a barium salt to a strongly alkaline ferrate (VI) solution. The precursor yielded barium hexaferrite on heating for 6 h at 800 °C; partial transformation was evident even at lower temperatures, from X-ray patterns and Mossbauer spectra. Scanning electron microscopy of the powders fired at 800 °C, showed that the particles were less than 0.5 μm in diameter.

ＲＦ熱プラズマ蒸発法によるＹ‐Ｆｅ‐Ｏ系新相超微粒子の合成

ＲＦ熱プラズマ蒸発法によるＹ‐Ｆｅ‐Ｏ系新相超微粒子の合成

Particles synthesis in erosive laser plasma in a high pressure atmosphere

Synthesis of ultrafine particles as a result of condensation in an erosive jet at laser vaporization of materials (metals, metal oxides, carbon) in gases (hydrogen, oxygen, helium, argon, xenon and air) at high pressures is investigated. The granulometric, phase, and chemical composition of the condensate particles is analyzed in relation to the elaboration conditions. It is found that the mean dimensions of the condensate particles increase with increasing the ambient gas pressure. A particle nucleation and growth theory is used to describe the formation of the dispersed condensate in the erosive plasma. It is shown that the resulting particle size distribution is determined by the cooling rate dependence of the vapor-gas mixture on the pressure of the surrounding gas.

Synthesis of Ultrafine Particles by Thermal Plasmas

Synthesis of Ultrafine Particles by Thermal Plasmas

Synthesis of ultrafine particles and thin films of BaFe 12O 19 by the spray-ICP technique

Ultrafine particles and thin films of BaFe 12O 19 were synthesized by introducing aqueous nitrate solutions of barium and iron into a high temperature argon inductively coupled plasma (ICP) generated under ambient pressure (the spray-ICP technique). As-deposited powders revealed hexagonal particle images of 10–50 nm in size, and their crystalline phase was BaFe 12O 19. Thin films of single phase BaFe 12O 19 were successfully synthesized on a (001) surface of single crystal sapphire by controlling the metal ratio of the mother solutions, the temperature of the sapphire substrates and their position from the ICP. They exhibited a (001) orientation and were composed of crystallites of 100–300 nm in size. They were also oriented along the sapphire surface, and the a-axes of the BaFe 12O 19 and the sapphire crossed each other at 30°.

Synthesis of ultrafine particles by surface discharge-induced plasma chemical process (SPCP) and its application

A comparison was made between the present surface discharged-induced plasma chemical process (SPCP) approach to chemical vapor deposition (CVD) and another type of cold plasma CVD using a silent glow discharge (GPCP). In the GPCP CVD system, two coaxial cylindrical electrodes are used in combination with two coaxial quartz tubes spaced at a small gap to generate silent discharge in the gap. In the SPCP CVD system, a ceramic-made electrode assembly is used, and a high frequency and a high voltage are applied to form an energetic and stable surface discharge. Both of the methods can produce ultrafine particles of silicone dioxide and titanium dioxide under room temperature and atmospheric pressure. However, SPCP CVD has a great advantage over GPCP CVD in that it permits further electrostatic processing in the same reaction region. For example, a very peculiar ceramic membrane could be produced with SPCP CVD by depositing electrostatically the ultrafine particles on a ceramic substrate and sintering the deposited layer.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>