Papers by Keyword: Nanopowder

Abstract: A sol-gel method was used to synthesize a highly stable form of MgO from magnesium oxalate dihydrate. The sol-gel products were characterized using simultaneous thermogravimetric analysis (STA), X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and UV-Visible light spectroscopy (UV-Vis). From the XRD analysis, all the MgO samples showed a single face-centered cubic phase. FESEM micrographs showed a crystallite size ranging from 10 nm to 59 nm. The size of the MgO crystallites increased with increasing temperatures. The crystallite size of the MgO is still relatively small, that is, below 100 nm even when the precursor was calcined at a higher temperature of 950 °C and a longer time of 36 h. Such results indicated that the growth of the crystallites is slow for this route of synthesis. The morphologies of the MgO samples are varied from the all spherical of the lower temperature to the more cubic shape with less agglomeration of the higher calcined samples. The band gap energy of the MgO samples also increased with temperature.

Abstract: Zinc substituted cobalt ferrite nanopowders with the general formula Co(1-x)ZnxFe2O4(with x = 0, 0.3, 0.5, 0.7, and 1) were prepared via the sol-gel route using citric acid as a chelating agent. The influence of zinc concentration on the microstructure, crystal structure and antibacterial property of zinc substituted cobalt ferrite nanopowders has been systematically investigated. The microstructure and elemental composition were characterized using scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX), respectively. Phase analysis of cobalt ferrite nanopowders was performed using X-ray diffractometry (XRD). The antibacterial properties of zinc substituted cobalt ferrite nanopowders were investigated. The results indicate that the substitution of zinc influences strongly the microstructure, crystal structure and antibacterial property of the cobalt ferrite nanopowders.

Abstract: The present study describes the preparation, structural and electrical characterization of nanosized Zr-Mn cobalt-ferrites. The nominal compositions CoFe_2-2xZr_xMn_xO₄ (0.10.4) have been synthesized by the co-precipitation method. These nanopowder products were sintered in furnace at temperature of 800 °C for 8 hour with a heating rate of 10^οC/min to obtain these ferrites. The nanopowder was evaluated using XRD, FT-IR and SEM. The XRD data showed that all the samples are of single phase and the crystallite size is found in the range of 2630 nm. The lattice constant (a), X-ray density (dx), porosity (P) and bulk density (dm) are also calculated from XRD data. FT-IR study confirms the presence of ferrite functional groups. The IR spectra of Zr-Mn ferrite system have been analyzed in the frequency range 400650 cm^-1. It revealed two prominent bands υ₁ and υ₂ which are assigned to tetrahedral and octahedral metal complexes, respectively. The position of the highest frequency band is around 550 cm^-1 while the lower frequency band is around 425 cm^-1. The structural properties are also analyzed on scanning electron microscopy (SEM) at room temperature. Additionally, the dc electrical resistivity decreased with the rise in temperature for all the samples, showing a semiconductor like behavior. From the dc electrical resistivity the activation energy and drift mobility are determined. Both the drift mobility and activation energy increase with a rise in x.

Abstract: LaNi5 nano-powders with additions of Ce, Mn, Co (high and low content of cobalt) and Al were obtained by means of MBN technology, based on the high energy ball milling with different energy and protective atmosphere (Ar or H2). The microstructure and composition of all prepared nano-powders were investigated using the TEM/HRTEM, SEM/EDS, XRD and XPS techniques. Research showed that used technology allowed to produce materials distinguished by a fine and homogeneous chemical distribution of elements and an "ultrafine" (the nanometric size) crystalline structure. The results were then related to the preparation conditions.

Abstract: Alumina-aluminium titanate (A-AT) composites and laminates have been recently investigated because they can provide improved flaw tolerance and toughness associated to a microcracking mechanism. A-AT composites have been produced by slip casting and reaction sintering of submicron sized alumina and titania powders. This work deals with the preparation of thick self-sustained A-AT films from mixtures of submicron sized alumina and nanosized titania. Suspensions were prepared in water to high solids loadings ranging from 30 to 50 vol.%. The stability of diluted suspensions was studied through zeta potential measurements as a function of pH and deflocculant type and concentration. The stability of the concentrated suspensions as a function of deflocculant content, sonication time and solids loadings was studied from rheological measurements. Self-sustained films were obtained by aqueous EPD using graphite substrates under constant current density conditions. The evolution of mass per unit area with current density and deposition time was recorded. The films were characterized in the green state and after debinding and sintering by density measurements, and electron microscopy observations.

Abstract: Colloidal sol-gel is a common method used for the preparation of stable and homogeneous sols and thin films. The nanoparticulate sols can be easily deposited by EPD, which is a versatile technique for producing denser and thicker coatings than those produced by other techniques like dipping. A complete characterization of the sols, such as colloidal stability and electrophoretic mobility, which can be determined through zeta potential measurements, as well as the influence of deflocculants in the surface properties, is needed before using electrophoretic deposition. In this work, we have prepared sols of TiO₂ with an alkoxide:water molar ratio of 50:1 and Eu (III) doped-TiO₂ (2 mole % Eu (III)) using as precursors titanium (IV) isopropoxide and europium (III) acetate hydrate, respectively. The stability of the particulate sols was studied in terms of conductivity, zeta potential and viscosity evolution. Anatase stable sols, after peptization and without the use of any additive, were deposited on stainless steel substrates by electrophoretic deposition under both constant current and constant voltage conditions. Using different intensities and deposition times we have obtained thin films with different features (thicknesses and morphology) and different optical properties. The presence of europium (III) increases particle size, viscosity and peptization time and decreases the band gap of TiO₂.

Abstract: Vanadiunm carbide (V8C7) nanopowders were prepared by the solution-derived precursor method, ammonium vanadate (NH4VO3) and glucose (C6H12O6) were used as raw materials. The samples were characterized by TG-DTA, XRD and SEM. The results show that the weight of the sample reduces rapidly before 600°C (about 25 wt.%), but it changes very slowly (about 1.0 wt.%) after 600°C. The DTA curve mainly includes 5 endothermic peaks and an exothermic peak which are corresponding to the peaks of 110°C, 300°C, 348°C, 677°C, 1000°C and 509°C, respectively. When the carbon content between 24 wt.% and 30 wt.%, the samples mainly consist of V2O3 and VC1−X (1−X = 0.66–0.88). When the carbon content is 32 wt.%, the sample includes a main phase (V8C7) and a second phase (V2O3). When the carbon content reaches to 36 wt.%, the single-phase V8C7 powder can be obtained. The SEM results show that major powders exhibit good dispersion and are mainly composed of particles with a mean diameter of ~200 nm.

Abstract: There is a need in different industry sectors to improve the performance of material surface under corrosive environments, which cannot be fulfilled by conventional surface modifications and coatings. NiCrMoNb alloy is nickel alloy commonly used as coating in corrosive media at high temperatures. The aim of this work is to produce nickel alloy nanocomposite coatings on steel by laser cladding. They are obtained by laser melting blown powder on the steel surface. The powder precursor is obtained by mechanical milling of a NiCrMoNb alloy micropowder (20-63 μm) with yttria nanopowder (10-30 nm). A comparison between conventional nickel alloy laser cladded coating and nickel alloy with nanoparticles laser cladded coatings, regarding their microstructure, mechanical properties (hardness, wear resistance) and corrosion behavior, is established.

Abstract: In this study the effects of milling methods on particle size and phase transformation of strontium and nickel doped lanthanum chromite as an interconnect material for solid oxide fuel cells (SOFC) were investigated. Two compositions of La_0.9Sr_0.1Cr_0.9Ni_0.1O₃ (LS10N10) and La_0.7Sr_0.3Cr_0.9Ni_0.1O₃ (LS30N10) were synthesized by glycine nitrate process (GNP). The samples were characterized by means of X-ray diffraction, nitrogen adsorption–desorption, scanning and transmission electron microscope and laser particle size analyzer. Two different milling methods were used, namely, high-energy milling (HEM) and ball milling (BM) and the effects of these milling methods of as-synthesis powders on the particle size distribution, agglomeration behavior and phase transformation were also investigated. The results showed that BM caused reduction of particle size to submicron size with D50 value of 125 nm while HEM resulted in agglomeration. The obtained nanopowders, according to XRD results were single phase with perovskite type crystal structure and only in high content of Sr some SrCrO₄ was detected. HEM caused the dissolution of the second phase in LS30N10.

Abstract: Barium zirconium titanate, Ba (Zr_0.20Ti_0.80)O₃ (BZT) powders were prepared by sol-gel method. These powders were characterized by thermal gravimetric and differential thermal gravimetric analysis (TG-DTA), X-ray diffraction (XRD). The grain size and lattice constant were determined. The decomposition of the precursors was monitored by TG-DTA. XRD patterns reveal that BZT powders heat-treated at 800°C present single phase with perovskite type cubic structure. The average particle size of the BZT powders is about 25 nm.