As-produced Powders Research Articles

Temperature Dependence on Opto-structural Parameters of Sol-gel Derived Tin Doped Zirconia Nanoparticles

Recently, nanocrystalline zirconia was widely employed in photocatalytic applications .Tin doped zirconia nanoparticles were prepared by sol-gel process followed by spin coating technique. The as-produced powders and thin films were heat treated in air at 500, 650 and 800 0C for 2h. Structural parameters of annealed samples were characterized by X-ray diffraction and Fourier transformed infrared studies. XRD spectra revealed the mixed phases such as t-ZrO2, m-ZrO2 and o-ZrSnO4. Structural parameters viz. crystallite size, lattice constants, dislocation density, microstrain, orientation parameter and activation energy were evaluated. XRD data depicted that crystallite size increased, while lattice parameters slightly decreased with increase in annealing temperature. Expected functional groups were established by FTIR spectra. Optical parameters of nanopowders/thin films such as PL emission wavelength and optical band gap were determined by photoluminescence and UV-visible absorption. The energy band gaps of thin films were increased with increase in temperature. The emission peak exhibited a blue shift with increase in temperature. In addition, thermogravimetric-differential thermal analysis of as prepared sample was investigated.

Structural, Magnetic and Dielectric Properties of Nanocrystalline (M = Li and Mg) Ferrites Synthesized via EDTA/EG Assisted Sol-Gel Method

ABSTRACTIn this study, lithium and magnesium ferrites have been synthesized using EDTA/EG assisted sol-gel method. Based on X-ray diffraction data, it is identified that a spinel-type structure of Li ferrite with space group of P4332 and Mg ferrite with space group of Fd3m has been successfully formed. The estimated value of crystallite size falls within 33-42 nm range. The microstructure of the as-produced powders examined by a field emission scanning electron microscope shows that secondary particles with the mean particle size of 30-170 nm tend to agglomerate severely. Regarding the magnetic properties measured by a vibrating sample magnetometer, Li ferrite, due to higher saturation magnetization than that of Mg ferrite (53.54 versus 23.27 emu.g–1) exhibits superior magnetic properties. In contrast, dielectric properties shows that Mg ferrite gives a much greater dielectric constant at all the measured frequency range.

Low Temperature Synthesis and Properties of Gadolinium-Doped Cerium Oxide Nanoparticles

Gadolinium-doped cerium oxide (GDC) is an attractive ceramic material for solid oxide fuel cells (SOFCs) both as the electrolyte or in composite electrodes. The Ni/GDC cermet can be tuned as a catalytic layer, added to the conventional Ni/yttria-stabilized zirconia (YSZ), for the internal steam reforming of different fuels. Such an anode allows the SOFC to operate with hydrocarbon fuels by internal reforming. GDC exhibits high oxygen ion conductivity at a wide range of temperatures and displays a high resistance to carbon deposition. However, an inconvenience of ceria-based oxides is the high sintering temperature needed to obtain a fully dense ceramic body, which can result in undesired reactions with YSZ. In this study, a green chemistry route for the synthesis of 10 mol% GDC nanoparticles is proposed. Such a low temperature synthesis provides control over particle size and sinterability of the material. The aqueous precipitation method starts from the nitrates of both cerium and gadolinium and uses excess hexamethylenetetramine (HMT) to produce crystalline GDC at 80 ºC. As-produced powders were found to be GDC crystalline fluorite-type structure, with crystallite size ≤ 10 nm. Thermalgravimetric analysis show a small mass loss and dilatometry profiles show a total retraction of ˃ 20% up to 1400 °C. The electrical properties of the material were studied by impedance spectroscopy measurements of sintered samples in a controlled atmosphere. The samples sintered for 2 hours at 1400 °C exhibited electrical conductivity comparable to previously reported data for GDC.

Particle size distribution of tin powder produced by centrifugal atomisation using rotating cups

Centrifugal atomisation is a low-cost technology for producing metal powders, but its wide applications are hampered by its limited capability of producing fine powders and there is insufficient research on the particle size distributions of centrifugally produced powders. This paper studies the effects of the atomiser geometry and the key process parameters on the particle size distribution of tin powders produced by centrifugal atomisation. The results showed that the particle sizes of the as-produced powders follow lognormal distribution. The median particle size for all atomisers decreases with increasing atomiser rotation speed and with decreasing melt flow rate, due to reduced film thickness of the melt before disintegration. The cup atomiser with a wall angle of 67.5° produced the finest powders, because of a significant improvement of dynamic wetting between the melt and the atomiser. The particle size distributions of all the powder samples have a similar lognormal bell shape with the geometric standard deviations between 1.6 and 2.5. Narrow particle size distributions can be achieved by reducing the variability of any of the processing parameters affecting the particle size.

Influence of synthesis conditions on microstructure and phase transformations of annealed Sr2FeMoO6-x nanopowders formed by the citrate-gel method.

The sequence of phase transformations during Sr2FeMoO6−x crystallization by the citrate–gel method was studied for powders synthesized with initial reagent solutions with pH values of 4, 6 and 9. Scanning electron microscopy revealed that the as-produced and annealed powders had the largest Sr2FeMoO6−x agglomerates with diameters in the range of 0.7–1.2 µm. The average grain size of the powders in the dispersion grows from 250 to 550 nm with increasing pH value. The X-ray diffraction analysis of the powders annealed at different temperatures between 770 and 1270 K showed that the composition of the initially formed Sr2FeMoO6−x changes and the molybdenum content increases with further heating. This leads to a change in the Sr2FeMoO6−x crystal lattice parameters and a contraction of the cell volume. An optimized synthesis procedure based on an initial solution of pH 4 allowed a single-phase Sr2FeMoO6−x compound to be obtained with a grain size in the range of 50–120 nm and a superstructural ordering of iron and molybdenum cations of 88%.

Characterization of Ni ferrites powders prepared by plasma arc discharge process

The aim of this work was to synthesize a single-phase spinel structure from a mixture of zinc, iron and nickel powders by plasma arc discharge method. A mixture of zinc, iron and nickel powders with the appropriate molar ratio was prepared and formed into a cylindrical shape. The synthesis process was performed in air, oxygen and argon atmospheres with the applied arc current of 400A and pressure of 1atm. After establishing an arc between the electrodes, the produced powders were collected and their structure and magnetic properties were examined by XRD and VSM, respectively.ZnO as an impurity was appeared in the as-produced powders owing to the high reactivity of zinc atoms, preventing the formation of Ni–Zn ferrite. A pure spinel structure with the highest saturation magnetization (43.8emu/g) was observed as zinc powders removed completely from the initial mixture. Morphological evaluations using field emission scanning electron microscopy showed that the mean size of fabricated nanoparticles was in the range 100–200nm and was dependent on the production conditions.

Synthesis of CdS Sensitized TiO2Photocatalysts: Methylene Blue Adsorption and Enhanced Photocatalytic Activities

A series of CdS/TiO2nanocomposites with different Cd to Ti molar ratio were synthesized from P25-TiO2nanopowder using microwave-assisted hydrothermal method. The as-produced powders were characterized by XRD, electron microscopy, EDX, and UV-Vis diffuse reflectance spectroscopy. The adsorption capacity and photocatalytic activity of the samples were investigated using methylene blue as a model pollutant. Sorption tests revealed that the adsorption of MB onto the samples obeys the Freundlich-Langmuir isotherm model. The sorption capacity decreased as follows:TiO2>TCd2>TCd1>TCd3>TCd4. The results of the photocatalytic tests under high-intensity discharge (HID) lamp revealed that CdS/TiO2powders with low Cd to Ti molar ratios exhibited much higher activities than P25-TiO2. The CdS/TiO2sample with 20% CdS/(TCd2) showed the most activity among all these samples. The results also show that the Cd to Ti molar ratio of the nanocomposite has a significant effect on the photodegradation of MB and the enhanced activities exhibited by the nanocomposites are because of the low rate of electron-hole recombination.

Uniformly dispersion of carbon nanotube in aluminum powders by wet shake-mixing approach

Since its discovery, carbon nanotube (CNT) was proposed as an ideal reinforcement material for metal matrix composite for its high strength, excellent electrical and thermal conductivity. CNT reinforced aluminum matrix composite has attracted most attention at the beginning of 21st century due to the need for advanced lightweight alloys for aerospace, automotive and defense industries. However, few researchers have successfully incorporated pristine and undamaged CNT into matrix to enhance the properties of the composite. Both traditional and novel powder metallurgical routes have been explored, nevertheless, challenges like the poor distribution of CNT in Al matrix, the agglomeration of CNTs and the damage of essential CNT tubular structure impeded the full translation of CNT potential into various matrix. To achieve a uniform dispersion of CNT without damaging the CNT structure, the authors have applied a novel wet shake-mixing method which combined the advantages of ultrasonication, turbular mixing and ball milling to fabricate an homogenous Al–0.5wt.% multi-walled carbon nanotube (MWNT) composite. The original structure and morphology of MWNTs and aluminum powders were well preserved even after all the processing procedures in the as-produced powders. This is confirmed by scanning electron microscopy and X-ray diffraction analysis, particle size distribution and the Raman spectra of the as-produced composite powders.

Polyol-made stoichiometric Co<SUB align="right">0.2Ni<SUB align="right">0.3Zn<SUB align="right">0.5Fe<SUB align="right">2O<SUB align="right">4 nanoparticles: synthetic optimisation, structural, and microstructural studies

Crystalline and stoichiometric Co0.2Ni0.3Zn0.5Fe2O4 ferrite nanoparticles were successfully synthesised in polyol medium starting from the low-cost iron (III) chloride and acetates as precursors by the optimisation a number of synthetic parameters. The crystalline structure, the chemical composition, the microstructure, and the thermal stability of the as-produced powders were investigated by X-ray diffraction, infrared spectroscopy, energy dispersive X-ray, X-ray fluorescence spectroscopy, and transmission electron microscopy. We demonstrated that in contrast to the stoichiometric ferrite, which showed excellent thermal stability, the non-stoichiometric ferrites thermally decompose resulting in a stoichiometric ferrite as a major phase and hematite. The degree of deviation from the stoichiometry was calculated on the basis of a proposed decompositional thermal scheme and a quantitative analysis using Rietveld refinement.

Synthesis and characterisation of potassium polytitanate for photocatalytic degradation of crystal violet

Potassium titanate nanostructures were synthesised by hydrothermal treatment of TiO2 (P25) in KOH and H2O2. As-produced powders were characterised by scanning electron microscopy, energy-dispersive X-ray spectroscopy, transmission electron microscopy, X-ray diffraction, and nitrogen adsorption–desorption methods. Longitudinally-oriented-wire-like structures with a length up to several micrometres and diameters ranging from 10 to 30nm were obtained. Larger size fibrous nanowires resulting from the hydrothermal treatment showed high affinity in adsorbing crystal violet (CV), which was mainly due to their high surface area. The photocatalytic bleaching of CV solution revealed that the wires are photoactive under ultraviolet light irradiation. Macroporous nanowires are considered as effective adsorbents of CV, capable of photocatalytic degradation, and they can be easily separated from the solution by settling.

Fe3O4 nanoparticles and nanocomposites with potential application in biomedicine and in communication technologies: Nanoparticle aggregation, interaction, and effective magnetic anisotropy

Magnetite nanoparticles with a size of 5–6 nm with potential impact on biomedicine and information/communication technologies were synthesized by thermal decomposition of Fe(acac)3 and subsequently coated with a silica shell exploiting a water-in-oil synthetic procedure. The as-produced powders (comprised of either Fe3O4 or Fe3O4@silica nanoparticles) were mixed with a photocurable resin obtaining two magnetic nanocomposites with the same nominal amount of magnetic material. The static magnetic properties of the two nanopowders and the corresponding nanocomposites were measured in the 10 K–300 K temperature range. Magnetic measurements are shown here to be able to give unambiguous information on single-particle properties such as particle size and magnetic anisotropy as well as on nanoparticle aggregation and interparticle interaction. A comparison between the size distribution functions obtained from magnetic measurements and from TEM images shows that figures estimated from properly analyzed magnetic measurements are very close to the actual values. In addition, the present analysis allows us to determine the value of the effective magnetic anisotropy and to estimate the anisotropy contribution from the surface. The Field-cooled/zero field cooled curves reveal a high degree of particle aggregation in the Fe3O4 nanopowder, which is partially reduced by silica coating and strongly decreased by dissolution in the host polymer. In all considered materials, the nanoparticles are magnetically interacting, the interaction strength being a function of nanoparticle environment and being the lowest in the nanocomposite containing bare, well-separate Fe3O4 particles. All samples behave as interacting superparamagnetic materials instead of ideal superparamagnets and follow the corresponding scaling law.

Microwave-activated formation of lattice defects in alumina polycrystals consolidated by spark plasma sintering

A wet-chemical synthesis and microwave calcination approach was found to be efficient for synthesizing α-alumina powders and polycrystals with high levels of lattice defects. The defects of the as-produced powders were determined from the optical transmittance of spark-plasma-sintered compacts with an identical microstructure using a conventional calcination method. The existence of a high lattice defect concentration was verified by positron annihilation lifetime analysis and X-ray diffraction. The microwave-activated lattice defect phenomenon has potential applications in the production of semiconductor materials or films with high chemical activity or crystal doping.

Synthesis of nanodiamond-reinforced aluminum metal composite powders and coatings using high-energy ball milling and cold spray

Nanodiamond-reinforced aluminum metal matrix composites (ND–Al MMC) powders were synthesized by means of high energy ball milling. We present a systematic study of the effect of various milling conditions on the structure and properties of the resulting MMC powders. The described method can be used to control important powder characteristics, including particle size and shape, Al crystal size and residual strain, and structural integrity and dispersion of the nanoparticle inclusions, a crucial requirement for subsequent powder consolidation. Raman spectroscopy was utilized for the first time to directly verify the structural integrity and the dispersion of ND in the Al matrix. For low ball-to-powder ratios (BPR), average particle size and size range of the ND–Al composite powders were found to decrease during milling, while the hardness increases. A BPR of 10:1, a milling time of 10h, and a ND content of 10wt.% were most effective in obtaining small powder particle sizes, small Al crystal sizes, and improved mechanical properties reaching a hardness of 3.46GPa, a 210% increase over the pristine, untreated Al powder (1.10GPa). Finally, we demonstrate that the as-produced composite powders are well-suited for low-temperature consolidation processing by fabricating the first cold-sprayed ND–Al MMC coating.

Superparamagnetic CoFe2O4 prepared via a modified oxalate method

Abstract The modified oxalate precursor method was used for the preparation of nanocrystalline CoFe2O4. Structural investigations of as-produced powders performed by means of high-resolution transmission electron microscopy and X-ray diffraction revealed an average particle size of 8 nm. The nanocrystallites are pure CoFe2O4 and present a well crystallized spinel structure with lattice constant of 8.3583 Å. The particles are superparamagnetic exhibiting a blocking temperature around room temperature. The magnetization and the coercive field values obtained at 9 T are 56.8 emu · g−1 and 17.0 kOe (at 4.2 K), respectively. The crystalline anisotropy determined from the coercive field as a function of temperature is 8.0 × 105 J · m−3, which is much higher than that of bulk materials.

Rapid synthesis and morphology control of nickel powders via a microwave-assisted chemical reduction method

Nickel powders with different morphologies, such as sphere, chain, and thorn-like nickel wire have been successfully synthesized by hydrazine reduction of NiCl2 in the presence of polyvinyl pyrrolidone (PVP) by using microwave-assisted chemical reduction method. The obtained products were characterized by XRD, SEM, TEM, and SAED techniques. Characterization by TEM and SAED showed that as-produced nickel powders were formed by self-assembly and aggregation of nanometer-sized nickel crystallites. PVP served as the structure directing agents and plays a key role for the morphology transformation of the nickel powders. In addition, compared with conventional heating method, microwave irradiation heating was in favor of the formation of nickel wires. The resultant nickel wires showed excellent electrical properties in the nickel wires/epoxy composite.

A dense oxygen separation membrane deriving from nanosized mixed conducting oxide

In this paper, nanosized SrCo 0.4Fe 0.5Zr 0.1O 3− δ (SCFZ) powders, which were synthesized via a flame aerosol synthesis (FAS) method, were successfully used to fabricate oxygen separation membranes with densified structure. XRD, TEM (HRTEM), O 2-TPD and TG were used to characterize the crystal structure, morphology, oxygen desorption property and oxygen non-stoichiometry of SCFZ-FAS powders. The densification process and the oxygen permeability of the SCFZ-FAS membranes were examined by SEM and the high temperature oxygen permeation measurements. The as-produced SCFZ-FAS powders were of the typical perovskite structure with high degree of crystallinity. Hard agglomerations, which were induced from the high temperature of the flame, were found among the nanosized rod-like SCFZ-FAS particles. Compared with SCFZ synthesized by the traditional solid-state reaction (SSR) method, the densification temperature of SCFZ membranes was reduced and the oxygen permeation flux was increased by 40% at the elevated temperatures (1073–1223 K) when SCFZ-FAS powders were used as the starting material. Long-term oxygen permeation measurement (1123 K, 180 h) showed that SCFZ-FAS possessed stable structure under low oxygen partial pressure (about 10 −3 atm) environment.

高周波熱プラズマによる球状銅系サブミクロン粒子の作製

Spherical submicron copper particles were synthesized through evaporation and subsequent condensation of copper powders in Ar-H2 thermal plasma. Copper powders of ∼40μm in size injected into the plasma, evaporated instantly and fine particles were formed through homogeneous nucleation and subsequent heterogeneous condensation. Particle size and the distribution in the synthesized powders were changed depending on the powder feed rate. Formation of submicron size spherical powders attributed to a significantly high degree of supersaturation in a vapor phase. Particle sizes of the as-produced powders range from submicron to several tens of micrometers. A simple sedimentation treatment was successfully applied to separate the as-formed powders with alcohol solvent to give uniform spherical submicron-size particles with monomodal size distributions. Cu-W composite powders were synthesized through the Ar-H2 plasma treatment of Cu-WO3 composite powders. The starting temperature of shrinkage was made significantly higher than pure Cu powders by mixing with several wt% of W.

Sensor performance of nanostructured TiO 2 thin films derived from particulate sol–gel route and polymeric fugitive agents

High specific surface area (SSA) nanocrystalline powders and dip-coated TiO 2 thin films have been prepared by a particulate sol–gel route with added polymeric fugitive agents (PFAs), namely trehalose dihydrate (THD), polyethylene glycol (PEG6000) and hydroxypropyl cellulose (HPC). One of the highest SSA reported in the literature, obtained without PFA, was achieved (i.e., 181 m 2/g), a value that could be increased up to 304 m 2/g, 274 m 2/g and 200 m 2/g for PEG/TiO 2, HPC/TiO 2 and THD/TiO 2 powders, respectively. Furthermore, the crystallite size varied from 1 nm for as-produced powders up to 4 nm for powders heat-treated at 600 °C. Thin films produced under optimised conditions showed excellent microstructural properties for gas sensing applications. They exhibited a stable and reproducible response towards CO and NO 2 at a low operating temperature of 200 °C. Calibration curves revealed that all sensors followed the power law ( S = A[gas] B ) (where S is sensor response, and coefficients A and B are constants) for the two kinds of gases and they have good capability for the detection of low gas concentrations (25 ppm CO and 0.5 ppm NO 2). Amongst all sensors, HPC/TiO 2 sensor showed the highest response towards CO ≤ 100 ppm and NO 2 ≤ 2 ppm, whereas PEG/TiO 2 sensor had the highest response towards CO > 100 ppm and NO 2 > 2 ppm operated at 200 °C. The response of the sensors to both CO and NO 2 changed with operating temperature reaching a maximum at a specific temperature. Moreover, the sensor response decreased by increasing the film annealing temperature. The response magnitude and response time of the sensors obtained in this work are superior to those reported in previous studies. Furthermore, their low power consumption as a result of their low operating temperature manifests their good potential for industrial application.

Preparation of tantalum nanopowders through hydrogen reduction of TaCl 5 vapor

Tantalum powders, ranging from 14 to 56 nm in primary particle size, were produced through hydrogen reduction of TaCl 5 vapor in a furnace aerosol reactor. The mass of the precursor, solid TaCl 5, was instantaneously measured during vaporization with a load cell to determine and control the precursor concentration at the reactor inlet. Tantalum pentachloride to tantalum conversion was 35% and 98% at 1000 and 1400 °C, respectively. The primary particle size increased with increasing the evaporator temperature and the hydrogen flow rate. The tantalum powder produced was amorphous at 1000 °C and crystalline at 1400 °C. The XRD peaks of the as-produced powders shifted towards lower angles due to the partial dissolution of hydrogen in the tantalum. Upon removal of the hydrogen through heat treatment in a vacuum, the shift disappeared. The oxygen content of the powder was 6.0 to 6.9 wt.%, with an oxide layer about 3 nm thick formed on individual particles. Through thermogravimetric analysis in air, the powders were found to be resistant to further oxidation at up to 200 °C, but to have been completely oxidized at 400 °C.

Preparation of high surface area titania (TiO 2) films and powders using particulate sol–gel route aided by polymeric fugitive agents

High specific surface area (SSA) nanocrystalline powders and dip-coated TiO 2 films have been prepared by particulate sol–gel route aided with polymeric fugitive agents (PFA), namely trehalose dihydrate (THD), polyethylene glycol (PEG6000) and hydroxypropyl cellulose (HPC). Powders obtained without PFA, heat-treated at 160 °C show a SSA of 181 m 2/g, a value that could be increased up to 271 and 223 m 2/g for samples heat-treated at 300 °C when PEG6000 and HPC were used, respectively, whereas SSA of 201 m 2/g were achieved by using THD and subsequence heat-treating at 500 °C. Such surface area is one of the highest reported in the literature under these conditions. Crystallite sizes vary from 1 nm for as-produced powders up to 4 nm for powders heat-treated at 600 °C. It was found that crystallite size, microstructure, specific surface area and phase transformation are strongly dependent upon the PFA/TiO 2 ratio and annealing temperature. Films produced under optimised conditions showed excellent microstructural properties for gas sensing applications.