Nanopowder Agglomerates Research Articles

Synthesis of nano-silicon carbide by SiO–C reaction

Carbon black has been successfully converted into silicon carbide by reacting it with SiO vapor at 1500 °C under Ar gas environment. The influence of reaction temperature, duration and Ar gas flow rate on the final product was examined. The structural and microstructural property of synthesized SiC was characterized using X-ray diffraction (XRD), Raman spectroscopy and scanning electron microscopy (SEM). Micrographs of synthesized SiC showed that the final product was an agglomeration of SiC nano-powder of 50–500 nm size and nano-whiskers/fibres having a diameter of 50–500 nm and lengths in 0.1–10 μm depending on Ar gas flow rate. The higher conversion of C into SiC was observed at 1500 °C with Ar gas flow rate ∼250 ml/min.

Changes in Mechanical Characteristics of HPC Samples Modified with WC and WO<sub>3</sub> Nanopowder Agglomerates

The paper presents the results of tests of HPC (high performance composites) samples consisting of aramid and glass fabrics modified by agglomerates of WC and WO3 nanopowders. According to the test results, introduction of WC and WO3 powders into the composite plate structure makes it more rigid and elastic, increasing its ability to dissipate energy.

Determination of changes in the mechanical properties of polymer composites with the addition of agglomerates of WC nanopowder

Recently, there has been a growing interest in the development of new composite materials with improved characteristics. The article presents the results of tests of composite specimens based on aramid fabrics modified with WC nanopowder agglomerates obtained from carbide manufacturing waste. The following mechanical characteristics were investigated: transverse bending resistance, fracture resistance and energy absorption during contact with a physical body at high speed. According to the results, the transverse bending resistance increased by 35% at a WC concentration of 5%. When 3% WC powder was added to the matrix composition, the total crack length after impact was almost halved. The largest increase in energy absorption of the samples was about 30% at 1% additive concentration. The significant increase in the investigated parameters can be explained by the complex morphology of the embedded particles. In further investigations it is planned to study in detail the mechanism of distribution of nanodispersed WC powder additive in the volume of the modified material.

Studying the effect of monochrome light on the photocatalytic activity of tungsten oxide

The paper presents studies of the photocatalytic activity of tungsten oxide nanopowder agglomerates under the action of monochrome light in the decomposition reactions of an organic pollutant (methylene blue). It is determined that the radiation of 470 nm (blue) provides the highest values of the rate constant of phototransformation of methylene blue

Improvement of magnetoelectric coupling effect in Ba0.8Sr0.2TiO3-Co0.5Cu0.5Fe2O4 multiferroic fluids by tuning the composition

Ba0.8Sr0.2TiO3 (BST) and Cu0.5Co0.5Fe2O4 (CCFO) nanopowders were prepared by hydrothermal method and chemical coprecipitation, respectively. Barium strontium titanate nanopowder–nano mixed oxides containing copper, cobalt, and iron (BST-CCFO) multiferroic fluids with different mass ratios (mBST/mCCFO = 1:2, 1:1, and 2:1) were prepared by using dimethyl silicone oil and silane coupling agent. Effect of mass ratio on the magnetoelectric performance was comparatively investigated. X-ray diffraction (XRD) showed that the BST and CCFO powders had no secondary phases, which are tetragonal perovskite structure and cubic spinel structure, respectively. Scanning electron microscopy (SEM) showed that the average grain size of BST and CCFO was 26.34 nm and 26.82 nm, respectively. The agglomeration of BST nanopowder was serious. Under the external magnetic field, the BST-CCFO multiferroic fluid will form a chain structure due to the directional movement of magnetic particles, thus enhancing the dielectric properties and ferroelectric properties of multiferroic fluid. The chain structure under the action of magnetic field will change the motion of ferroelectric particles, so that the magnetoelectric coupling effect of multiferroic fluid is significantly enhanced, which is much higher than that of the same type of magnetoelectric composite ceramics. This study is expected to provide a new way to improve the magnetoelectric coupling effect of multiferroic materials.

Study of the Effect of Tungsten Carbide Nanopowder Agglomerate Additives on the Strength Properties of Carbon Fiber-Reinforced Plastic

The paper presents the results of tests of carbon plastic samples consisting of carbon fabric Grafill TR30S-S (Italy) and epoxy resin binder EPR 320 modified by WC tungsten carbide nanopowders in the form of agglomerates. The positive effect of additives on the tensile strength and on the modulus of elasticity at transverse bending of the concentration of additives 1-3% is shown.

Formation of droplets in a heterophasic amorphocrystalline nanopowder Bi2O3 produced by pulsed electron beam evaporation in vacuum

In the present work, a mesoporous multiphase amorphous crystal nanopowder Bi2O3 with a specific surface area of up to 23 m2/g was produced by pulsed electron beam evaporation in vacuum. Influence of thermal annealing (200-500 °C) of powders in air is investigated. The formation of droplets with a size of 3-5 nm on the surface of all large nanoparticles constituting the framework 3D nanopowder agglomerates was found due to extrusion of liquid bismuth from the volume during cooling.

Effect of the toluene content on the preparation of Mg(Al,Y)2O4:Cr3＋ nanopowders by Pechini-type hydrothermal process

Cr3＋ doped magnesia aluminum spinel has potential applications in the fields of sensing, scintillator and laser. The structure, morphology, photoluminescence and diffuse reflection spectra of Mg(Al,Y)2O4:Cr3＋ were examined as a function of toluene content during the Pechini-type hydrothermal process. Toluene solvent changed the microstructure of Mg(Al,Y)2O4:Cr3＋ nanopowders, especially for the ratio of Al:Mg in the sample. Toluene also improved the agglomeration of nanopowders, and the luminescent intensity of the sample prepared with 60% and 75% toluene was enhanced by 16%.

Role of Nanopowder Agglomerates in Forming the Structure and Properties of Ceramic Materials

Role of Nanopowder Agglomerates in Forming the Structure and Properties of Ceramic Materials

Образование при отжиге дроплетов в нанопорошке Bi-=SUB=-2-=/SUB=-O-=SUB=-3-=/SUB=-, полученном импульсным электронным испарением в вакууме

Using a method of pulsed electron beam evaporation in vacuum was produced the mesoporous multiphase amorphous and crystal nanopowder of Bi2O3 with a specific surface area up to 23 sq.m/g. Influence of thermal annealing of powder (200-300 0C) in air is investigated. The formation of droplets with a size of 2-5 nm was found on the surface of all large nanoparticles that make up the framework 3D nanopowder agglomerates due to extrusion of liquid bismuth from the volume during cooling.

Role of nanopowder agglomerates in forming the structure and properties of ceramic materials

A comparative analysis of agglomerates obtained by spray drying and granulation methods and consolidated materials based on them was carried out. The paper provides the results obtained when studying zirconia nanopowders granulated in water medium with an agar agar additive obtained by chemical precipitation with zirconia partially stabilized by yttrium oxide (2.5 mol.%), and TZ-3Y-E powder manufactured by Tosoh Corp. (Japan) that was prepared by spray drying. Agglomerates as well as microsections and fractures of samples were studied by scanning electron, optical, atomic force microscopy, and Raman spectroscopy. The crack resistance coefficient (K1с) of samples was determined by indenting the polished surface of microsections with a Vickers pyramid. The specific surface of the powders measured by nitrogen thermal desorption during granulation remains unchanged indicating a significant open porosity of agglomerates obtained. With increasing compacting pressure under conditions of semi-dry compaction with an aqueous solution of PVA as a binder, agglomerates and even aggregates of granulated powders are destroyed, K1с increases with increasing compaction pressure and the accompanying material microstructure grinding. Powders agglomerated using spray drying break up much less intensively, K1с does not change with increasing pressure. The studies conducted allow us to agree with the authors pointing to the fractal nature of agglomerates obtained from chemically precipitated nanopowders without the use of spray drying. The use of granulated nanopowders in semi-dry compaction with the application of high pressures makes it possible to destroy not only agglomerates, but also aggregates, and to obtain nanostructured ceramics with grain sizes close to the size of initial particles.

Synthetic Method for Preparing High-Performance Europium-Doped Up-Conversion Ceramic Material Precursor

In this paper, a direct co-precipitation method was used to prepare antimony-doped calcium fluoride nanopowders (NPs). The effects of reaction concentration, reaction medium and lanthanum doping on the properties of calcium fluoride NPs were investigatedviaa control variable method and the best preparation conditions was identified. The structural analysis of the powder materials prepared in this work were carried out by XRD, SEM, ICP and other test methods. By analyzing the experimental data, we found that the best performance of Eu-doped CaF2NPs can be acquired under the reaction concentration of 1 mol/L in aqueous solution. In the same time, the NPs possess a high degree of dispersion with an average diameter of 22 nm, which is beneficial to the preparation of transparent Eu3+: CaF2ceramics with excellent up-conversion luminescence. The results show that the grain size, the crystallinity of the NPs and the amount of Eu infiltration have a decreasing tendency with the increasing reaction concentration, while the degree of agglomeration of the NPs can be enhanced by increasing the reaction concentration.

Ammonium oxalate-assisted synthesis of Gd2O3 nanopowders

The impacts of co-precipitation reaction temperature and duration, as well as calcination temperature and duration, on the particle morphology and properties of gadolinia (Gd2O3) nanopowders were investigated. Thermogravimetric curve of thermally treated gadolinium oxalate (Gd2(C2O4)3) showed that pure stable cubic phase Gd2O3 nanopowders could be obtained by calcining at 640 °C and higher. This finding was also supported by results obtained from Fourier Transform Infrared Spectrometry (FTIR) and Raman spectrometry. This study also shows that uniform spherules of Gd2O3 nanopowders could be obtained under controlled synthesis conditions. However, with an increase in both the co-precipitation reaction temperature and duration, the extent of agglomeration of Gd2O3 nanopowders increased, as observed under a Field Emission Scanning Electron Microscope (FESEM). The FESEM images and X-ray Diffraction (XRD) patterns also revealed accelerated grain growth and increased average crystallite size at high calcination temperatures and holding times. It was determined that the most favourable Gd2O3 particle morphology was achieved when Gd2(C2O4)3 was co-precipitated at 40 °C, then thermally degraded at 650 °C, for 1 h and 4 h, respectively. Estimated Scherrer's average crystallite size of the resulting Gd2O3 nanopowders was 16.54 nm, which was further affirmed with the transmission electron microscope (TEM) image, where crystallite sizes of 3–27.5 nm were observed in the Gd2O3 sample. This specimen also demonstrated a considerably large specific surface area of 9.16 m2/g, as measured using a Brunauer–Emmett–Teller (BET) analyser.

Sintering behavior of bimodal iron nanopowder agglomerates

AbstractThe most important issue in the processing of nanoscale metal powders is whether the metal nanopowder can be fully consolidated into ultra‐fine‐ or nano‐grained powder metallurgy parts by pressureless sintering. This paper focuses on the sintering behavior of bimodal iron (Fe) nanopowder agglomerates by considering their microstructure and densification kinetics. During the sintering, bimodal Fe nanopowder compacts underwent discontinuous shrinkage behavior until they neared full density. Three contributions to the sintering mechanisms, asymmetric sintering, densification enhancement, and grain growth inhibition, are presented in relation to the effect of bimodal nanopowder structure. Smaller nanoparticles in the bimodal nanopowders, which are predominantly present at the boundaries and interstitial spaces of larger nanoparticles, are responsible for the three mechanisms stated above. This result is strongly supported by the apparent activation energy values ranging from 48.2 to 90.6 kJ/mol, which correspond to the energy for grain‐boundary diffusion in Fe. The experimental results of this study show that bimodal nanopowder agglomerates can be used to produce full density nano‐grained powder metallurgical parts by pressureless sintering.

Analysis of the rheological behavior of Fe trimodal micro-nano powder feedstock in micro powder injection molding

The rheological behavior of Fe trimodal powder feedstock for μ-PIM was investigated using torque rheometer analysis. The feedstock was prepared by mixing Fe micropowder (~4μm) and nanopowder agglomerates containing discrete particles with sizes of ~300nm and ~30nm, with low viscosity wax-based binders. During the feedstock mixing, a significant increase in mixing torque was observed at powder content above 72vol% in the feedstock, indicating the critical powder loading. The results obtained from the torque rheometer experiment at selected powder loadings of 66–74vol% were used as fundamental rheological parameters including flow behavior index (n), flow activation energy (E), and general moldability index (αstv). In addition, the influence of shear rate, temperature, and powder loading on feedstock viscosity was evaluated. It was found that the feedstock with 72vol% powder loading exhibited the best rheological behavior with the highest moldability parameter and homogeneous microstructure. Due to the lack of research on the trimodal system in the field of powder metallurgy and powder technology, this paper provides the possibility of applying the trimodal powder mixture to a near net-shape production technique such as PIM.

Fabrication of Si nanopowder from Si swarf and application to high-capacity and low cost Li-ion batteries

Si nanopowder is expected as a high capacity anode active material for Li-ion batteries (LIBs) due to its superior theoretical capacity of ∼3600 mA h/g, which is approximately one order of magnitude higher than that of conventional graphitic materials. We have succeeded in fabrication of Si nanopowder from Si swarf using the cost-effective beads milling method. The Si nanopowder consists of Si nano-crystals having flake-like shape with two largely different sizes, i.e., several hundred nm sizes and sizes less than 15 nm. The mode diameter of Si crystallites fabricated from Si swarf is 6.3 nm. The performance of the nano-Si electrode for Li ion batteries is greatly improved by carbon-coating on Si nanomaterials and addition of fluoroethylene carbonate (FEC) in an electrolyte solution. By addition of 10–15 wt% FEC, a stable and thin (10–20 nm) solid-electrolyte interphase (SEI) layer is formed on the electrode, and the number of cracks on the electrode surfaces after the 100th cycle greatly decreases. Addition of FEC improves the cyclability and decreases the SEI resistance (RSEI) and the charge transfer resistance (Rct). However, excess FEC (25 wt%) suppresses free volume expansion of Si nanopowder due to formation of thick SEI, leading to smooth Si surfaces, and resulting in an increase in Rct. Carbon-coating on Si nanopowder greatly improves the cyclability even with the low C/Si ratio of 0.1. In the case of excess carbon-coating, Si nanopowder agglomerates during carbon-coating, which causes peeling-off of a part of carbon-coated Si nanopowder during lithiation, resulting in a decrease of the capacity. The delithiation capacity higher than 1600 mA h/g after the 100th cycle with the current density of 1800 mA/g is achieved by setting the C/Si ratio at 0.1 and the FEC concentration at 10 wt%.

Design of trimodal Fe micro-nanopowder feedstock for micro powder injection molding

The design of the trimodal powder feedstock and its feasibility for micro powder injection molding (μ-PIM) were investigated. The feedstock was prepared by mixing Fe micropowder (D50=4μm) and nanopowder agglomerate composed of a bimodal particle distribution (D50=330nm and D50=30nm, respectively) with low viscosity wax-based binders. The homogeneity of the feedstock was evaluated by torque rheometer, microstructure observations, binder burnout analysis, and an extrusion test. The trimodal concept in this study effectively improved the powder loading up to 72vol%, and the feedstock with 70vol% powder loading exhibited good homogeneity and flowability. By using the feedstock, the microparts were successfully replicated with sufficient shape retention to be potentially useful for a range of μ-PIM applications.

In-vitro performance of titania reinforced hydroxyapatite nanopowders-a microstudy

Bioinert cum bioactive titania reinforced hydroxyapatite (T-HAP) nanopowders (NPs) have been receiving great attention in load-bearing orthopedic and dental implant applications. This study comprehensively evaluated the in vitro performance of T-HAP NPs immersed in SBF for different durations for 7 and 30 days. Duration of immersion had little effect on phase constitution of phase pure and T-HAP NPs as suggested by XRD analysis. Rietveld refinement suggested that with the increase in duration of immersion, inter-atomic distance between atoms of HAP phase and crystallinity of NPs decreased, whereas lattice parameters, cell volume, crystal size, and microstrain in T-HAP NPs increased. FTIR supported XRD phase analysis and suggested bone-like apatitic formation in all NPs. SEM indicated the agglomeration of NPs composed of particles of irregular shapes and sizes. EDX results corroborated with XRD and FTIR results. Hydrodynamic diameter measured using DLS were compared to be significantly bigger than crystal sizes (Rietveld and Scherrer) calculated using XRD data. During in vitro study, pH measurement of SBF suggested the bioactive nature of all NPs and also revealed the higher rate of solubility of T-HAP NPs. All T-HAP NPs gained weight after respective days of immersion in SBF. Hence, this study systematically and minutely evaluated the in vitro performance of T-HAP NPs immersed for different durations in SBF.

Reaction kinetics and phase transformation during hydrogen reduction of spherical Fe2O3 nanopowder agglomerates

The reaction kinetics of spherical Fe2O3 nanopowder agglomerates were investigated as a preliminary study to fabricate structure optimized spherical Fe nanopowder agglomerates for processing PM parts. The apparent activation energy Ea for kinetic analysis was determined from nonisothermal thermogravimetric (TG) measurement using isoconversional Kissinger-Akahira-Sunose (KAS) method, and the result is discussed in terms of the phase transformation by XRD analysis and microstructural change by BET analysis. The calculated activation energy was in a reasonable range compared to the reported data for the hydrogen reduction of Fe2O3, but it showed three distinct slopes according to the conversion degree of the reaction. The phase analysis revealed that a two-step phase transformation occurred during the reduction process in the sequence of Fe2O3, Fe3O4, and Fe without an intermediate phase FeO. During the reduction process of Fe3O4 to Fe, the reduction rate was retarded by sintering of oxide particles leading to an abrupt increase of activation energy. As the volume fraction of the metallic iron increased through the reduction progress, the reaction accelerated remarkably. This is believed to be attributed to the catalytic role of the reduced Fe particles facilitating reduction of the adjacent oxide particles. These results provide the primary data for understanding the microstructural development of spherical Fe nanopowder agglomerates fabricated by the hydrogen reduction process.

Contact mechanics of highly porous oxide nanoparticle agglomerates.

Efficient nanopowder processing requires knowledge of the powder’s mechanical properties. Due to the large surface area to volume ratio, nanoparticles experience relatively strong attractive interactions, leading to the formation of micron-size porous structures called agglomerates. Significant effort has been directed towards the development of models and experimental procedures to estimate the elasticity of porous objects such as nanoparticle agglomerates; however, none of the existing models has been validated for solid fractions below 0.1. Here, we measure the elasticity of titania (TiO_2, 22 nm), alumina (Al_2O_3, 8 nm), and silica (SiO_2, 16 nm) nanopowder agglomerates by Atomic Force Microscopy, using a 3.75 upmum glass colloid for the stress–strain experiments. Three sample preparations with varying degree of powder manipulation are assessed. The measured Young’s moduli are in the same order of magnitude as those predicted by the model of Kendall et al., thus validating it for the estimation of the Young’s modulus of structures with porosity above 90 %.Electronic supplementary materialThe online version of this article (doi:10.1007/s11051-016-3500-4) contains supplementary material, which is available to authorized users.