Synthesis Of Nanopowders Research Articles

The role of phase transition by inception and surface reactions for the synthesis of silicon nanoparticles in a hot-wall reactor – Simulation and experiment

A novel Eulerian particle model tailored for the application in computational fluid dynamics (CFD) is presented. The model is based on a bivariate moment method and features a full coupling with the gas-phase by kinetic formulations for inception, and activated and non-activated surface reactions. A new formulation for the particle composition accounts for the volatile content and its emission. The model is applied in the context of silicon nanopowder synthesis from monosilane, where a validation is performed with a well-established hot-wall reactor experiment from the literature. It is characterized by high precursor concentrations at moderate heating temperature of 853 K. Further, a new experiment was conducted for the comparison with the new model approach in a three-dimensional, transient simulation. The semi-industrial hot wall reactor features an unsteady complex flow field with buoyancy driven recirculation. The simulations enable new insights into the unsteady flow, mixing and nanoparticle formation process and contribute to their understanding. For the validation, residence-time dependent data for the precursor concentration, the primary particle size, and the particle number concentration are compared with results of the simulation at different stages. A comparison with the results of stochastic methods serves as further benchmark for the presented model. An excellent agreement with the experimental data is obtained, if essential growth mechanisms are considered. For the semi-industrial hot-wall reactor experiment, the BET surface and particle diameter, as well and the precursor consumption, are compared to the results of the new model and to a description with inception, coagulation, and sintering only. Due to the absence of crucial activated and non-activated surface reactions, the latter model predicts values that deviate more than one order of magnitude from the experimental data, while the new model shows an overall good agreement.

Facile synthesis of high-entropy zirconate nanopowders and their sintering behaviors

The challenge in synthesizing high-entropy ceramic (HEC) nanopowders is to suppress severe grain coarsening and particle agglomeration, which occur at elevated temperatures. This challenge could be addressed by the polyacrylamide gel method. In this work, single-phase high-entropy (La_0.2Nd_0.2Sm_0.2Gd_0.2Yb_0.2)₂Zr₂O₇ and (La_0.2Nd_0.2Y_0.2Eu_0.2Gd_0.2)₂Zr₂O₇ nanopowders without agglomeration were successfully synthesized using the polyacrylamide gel method for the first time. The results showed that phase composition, particle size, and agglomeration degree of the nanopowders were greatly influenced by the molar ratio of acrylamide (AM)/Zr and calcination temperature. These as-synthesized high-entropy zirconate (HEZ) nanopowders could be sintered into fully dense ceramics at 1500 ℃ for 2 h. These HEZ nanopowders showed a phase transformation from a defect-fluorite phase to a pyrochlore phase with the increase of sintering temperature. Additionally, two-step sintering of these nanopowders was conducted, and the HEZ ceramics with fine grains were prepared. The polyacrylamide gel method is simple and easily operated, which is a facile approach of producing the HEC nanopowders with excellent sinterability.

A Novel Approach to the Rapid in situ Synthesis of Tungsten Carbide Nanopowder by Plasma Milling and Carbothermal Reduction

Plasma milling results in more reactive sites and a larger contact area between WO3 nanoparticles and C atoms, and simultaneously generats more oxygen vacancies and defects on the surfaces of WO3 and C respectively via plasma discharge as describe in the article, number 2200175 by Zhongchen Lu and co-workers. Thus, the reaction temperature for the carbothermal reduction reaction reduces significantly by plasma milling.

Synthesis of Cu-doped ZnS nano-powder by chemical co-precipitation process

Copper doped zinc sulphide nanopowders (ZnS: Cu NPs) were synthesized using chemical co-precipitation technique. The Cu-doping content in the NPs was varied in the range, 0–4 wt%. The undoped and Cu-doped ZnS nanoparticles were prepared at 70 °C and dried at low temperatures. The prepared powders were investigated to understand the structure, surface topography, optical and photoluminescence (PL) properties using appropriate techniques. The X-ray diffraction (XRD) studies of prepared NPs revealed the (111) plane as the dominant orientation related to the cubic structure of ZnS. Also, XRD spectra exhibited broadening of the crystal planes on increasing Cu-content in the starting solution. The topography studied revealed a change from granular shaped crystals to flower shaped surface morphology upon Cu-doping. From the optical absorption studies, it was noted that increase ofCu-doping in the starting solution, shifted the absorption edge toward the smaller wavelength. The band gap energy of the NPs was evaluated by using Tauc plots, which varied from 3.7 eV to 4.1 eV with increase of Cu-doping. The PL studies indicated a small peak at 440 nm in pure ZnS and large peak at 522 nm that are related to the characteristic bands of ZnS. The properties of ZnS: Cu NPs were analysed for their suitability for mono-grain solar cell application.

Ultrafast microwave-assisted solvothermal synthesis and characterization of near-spherical CoSb3 nanopowders

Ultrafast microwave-assisted solvothermal synthesis and characterization of near-spherical CoSb3 nanopowders

Recent Research Trend in Powder Process Technology for High-Performance Rare-Earth Permanent Magnets

Higher performance is constantly required in rare earth permanent magnets, which are an indispensable component of the motors of electric vehicles. When producing sintered magnets, advanced structural control is necessary in the powder metallurgy process in order to achieve high performance. Especially in recent years, it has become important to develop processes for Sm-Fe-N magnets and metastable phase magnets as next-generation magnets to replace the Nd-Fe-B magnets. Because the crystal grain refinement of sintered magnets is most effective for improving coercivity, production methods for raw powders have evolved from the traditional pulverization to chemical synthesis approaches, and as a result, a submicron-sized Sm-Fe-N powder with huge coercivity has been developed. State-of-the-art physical synthesis methods have also been applied successfully to the synthesis of nanopowders. Since control of the grain boundary is very effective in Nd-Fe-B magnets, this approach has also been evolved to Sm-Fe-N magnets by nano coating. On the other hand, since technologies for crystalline orientation control and high-density sintering are indispensable for improvement of remanence, new low-thermal load consolidation techniques such as spark plasma sintering are being developed for Sm-Fe-N magnets and metastable phase magnets in order to overcome the inherent low thermal stability of these materials.

Oxygen-deficient low band gap black zirconia nanoparticle synthesis and tailoring its band gap/photoluminescence via silver doping

This study focuses on the non-aqueous sol-gel synthesis of zirconia nanopowder and explores the tunability of its band gap, absorption, and photoluminescence. Multiple characterization techniques were used to examine the impact of oxygen vacancies (color centers) and silver doping on changes in the structural and optical properties of zirconia. XRD results confirmed the rare black-colored pure tetragonal zirconia and monoclinic-tetragonal mixed zirconia products. The UV–Vis analysis provided insights about the absorbance and confirmed the extraordinarily high absorbance over the entire visible spectrum of electromagnetic radiation and also ascertained the defect level that governed the low band gap of the synthesized black zirconia powders. With increasing the doping concentration, the photoluminescence emission spectroscopy stimulated at an excitation wavelength of 250 nm revealed a rising luminescence peak at 422 nm (2.94eV). The distinctive stretching modes of zirconia powder samples were validated by FTIR investigations. The FESEM was used to study the microstructure's morphology, and the EDX spectrum was used to analyze the samples' elemental composition. The high-bandgap white samples with strong PL emission (blue) can be used to create high-quality wLEDs, whereas the low-bandgap black zirconia may prove to be an outstanding solar light absorption material.

A method of real-time monitoring beam output stability of intense pulsed ion beam

Intense pulsed ion beam (IPIB) technology has made remarkable progress in surface modification, mixing, polishing, film deposition, and nano powder synthesis in recent years. However, the surface properties of materials under IPIB irradiation are highly sensitive to beam intensity variations. Deviations from acceptable parameter range can change the surface characteristics and increase prevalence of defects. Consequently, the real-time online monitoring of beam stability during irradiation experiments and promptly identifying of pulses exhibiting significant parameter jitter are of significance in accurately analyzing results and optimizing surface modification. This study presents a fast-response pulse X-ray diagnostic system by employing EJ-200 plastic scintillator, 9266FLB photomultiplier tube, and Tektronic TDS 2024 four-channel oscilloscope. Single particle test demonstrates that the system achieves a time resolution of 6 ns, meeting the requirements for temporal response to detecting pulse X-ray signals with a half-width of ~80 ns. By adjusting the insulation magnetic field strength of the ion diode, the IPIB output level is regulated. The diagnostic system successfully captures X-rays emitted by the external magnetic insulated ion diode operating at different output levels. Simultaneously, the ion beam energy density is measured by using an infrared camera. To mitigate diagnostic errors stemming from target ablation, the maximum energy density is controlled to be below 1.32 J/cm<sup>2</sup>. Analysis results establish a positive correlation between X-ray intensity and ion beam energy density. This relationship arises from the influence of the insulating magnetic field adjustment on the diode's operating voltage, which subsequently affects the bremsstrahlung radiant intensity and ion beam emission intensity. This correlation offers the potential for the real-time monitoring of IPIB beam output stability by utilizing X-ray signals. To further corroborate the synchronized changes in pulse X-ray intensity and ion beam intensity, Faraday cup is employed as an alternative to infrared imaging method for measuring ion current density. Results demonstrate that the amplitude of the X-ray signal changes synchronously with fluctuations of ion current density. It is worth noting that when the output intensity of ion beam deviates significantly (more than 10% of the preset value), the diagnostic system will respond quickly. These findings validate the efficacy of the proposed non-interceptive diagnostic method of real-time monitoring the intense pulsed ion beam output stability.

Molten salt synthesis of CrMnFeNi alloy nanopowder passivated by TiO x -ZrO y shell used as a superior catalyst support in liquid-phase hydrogenation.

A molten salt method was used to prepare CrMnFeNi alloy nanopowder passivated by TiO x -ZrO y surface shell with a high specific surface area (23 m2 g-1) from the oxide precursors. Analyses by scanning electron microscopy/transmission electron microscopy with energy-dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy revealed the formation of an alloyed Cr-Mn-Fe-Ni-rich core surrounded by an oxide surface shell with a Ti/Zr-rich composition, confirming the formation of TiO x -ZrO y /CrMnFeNi nanopowder. It was speculated that the CrMnFeNi alloy nanoparticles were preferentially formed from the constituent metals by a faster reduction of any oxides of Cr, Mn, Fe, and Ni and a subsequent alloying with Ti and Zr could hardly occur due to the high thermodynamic stability of CrMnFeNi alloy. A Ni-loaded TiO x -ZrO y /CrMnFeNi catalyst exhibited superior catalytic performance to common Ni-loaded TiO2 and ZrO2 in the liquid-phase hydrogenation of p-nitrophenol at room temperature. The enhancement could have originated from an excellent electrical property of CrMnFeNi alloy, promoting the formation of active metallic nickel on the surface during the reaction. Leaching amounts of the constituent elements of Ti-Zr-Cr-Mn-Fe-Ni and loaded Ni was very little in the reaction solution after the reaction; the results confirmed that the prepared CrMnFeNi alloy nanopowder was very stable due to the protection of the Ti/Zr-rich oxide shell. Thus, the potential application of the alloyed powder used as catalyst support was demonstrated.

Сфероидизация нанопорошковых микрогранул вольфрама в термической плазме электродугового разряда

A method for producing tungsten powder consisting of spherical microparticles with dimensions of 20 – 50 µm is considered when processing a granular tungsten nanopowder in a flow of argon electric arc thermal plasma. Experimental studies of plasma chemical synthesis of tungsten nanopowder in a plasma reactor with a limited jet flow during the interaction of tungsten trioxide with a flow of hydrogen-containing plasma generated in an electric arc plasma torch have been carried out. The conditions of spray drying and the properties of a suspension consisting of tungsten nanoparticles have been experimentally determined, ensuring the production of mechanically strong nanopowder microgranules of rounded shape with a homogeneous internal nanostructure that does not contain cavities, with the yield of microgranules with a size of less than 60 µm at the level of 65 %. The influence of the parameters of the plasma processing of nanopowder microgranules in the thermal plasma flow on the degree of spheroidization and the microstructure of the resulting particles has been established.

A new electrolytic process for the synthesis of tungsten oxide nanopowder from WC-6Co scrap

An improved process was developed for the synthesis of hydrated tungsten oxide nanopowder from WC-6Co scrap at room temperature. This process is relatively less expensive and energy efficient. The conventional processes used for synthesizing tungsten oxide nanopowder are performed at high temperatures. In this study, tungsten oxide nanopowders are produced via electrolysis of WC-6Co pellet using sulfuric acid as an electrolyte; followed by dehydration at 150 °C. The dehydration treatment resulted in phase transformation. High purity nanorods and nanoplates of hydrated tungsten oxide were produced. The crystal size in the range of 9.6–13.8 nm was produced. The effect of process parameters on phase, crystal size, lattice strain, and morphology of tungsten oxide nanopowder is discussed.

Исследование фазового состава и микроструктуры сложного карбида (Ti, W)C, полученного электроимпульсным плазменным спеканием порошков WC и TiC

The possibility of low-temperature in-situ synthesis of (Ti, W)C ceramics from plasma-chemical nanopowders of tungsten carbide and commercial micron-sized titanium carbide powders has been demonstrated. Sintering/synthesis of WC – (25, 50, 75) wt. % TiC ceramics was carried out by spark plasma sintering (SPS) by heating powders at a rate of 50 °C/min in vacuum under conditions of application of a voltage of 70 MPa, to a temperature of more than 1200 °C. It has been established that the synthesis proceeds most efficiently in nanopowders with the addition of 50 and 75 wt. % TiC. It is shown that the joint application of plasma-chemical synthesis of nanopowders and the SPS method makes it possible to obtain fine-grained ceramics with increased density and satisfactory mechanical properties (Vickers hardness 17 – 18 GPa, minimum crack resistance coefficient according to Palmquist ~ 3 MPa·m1/2).

The Synthesis of Carbon Nanoparticles in a Compression Reactor in the Atmosphere of Buffer Gases

We investigated the physicochemical aspects of the gas-phase nanopowder synthesis using a cyclic compression reactor. Compression of precursors (methane, ethylene, acetylene) under conditions close to the adiabatic ones in the atmosphere of buffer monatomic gases (argon, helium, neon) was used. The influence of pressure in the reactor and volumetric ratio of precursor/buffer gas mixture on the composition, morphology, and structure of carbon-containing particles representing the pyrolysis product was studied. Complete pyrolysis was observed for all studied precursors, but under different conditions. Thermal decomposition of methane, having the minimum enthalpy of formation, was observed in an atmosphere with argon content 97.5 % at a peak pressure more than 10 MPa. Helium showed limited possibilities for thermal relaxation under the conditions of fast reactions (< 50 ms). Only acetylene with the maximum enthalpy of formation was decomposed in the atmosphere of helium. The solid reaction products represented black colored powders with a bulk density of 20–30 mg/cm3. The powders were examined by transmission electron microscopy and scanning electron microscopy, Raman scattering and X-ray diffraction analysis. The particles represent globular bulbous structures up to 100 nm in size, either hollow or filled inside. X-ray diffraction analysis showed the presence of a graphite-like structure with crystallite sizes less than 10 nm in all samples. Raman analysis showed mainly sp2 hybridization of carbon. The cyclic compression method demonstrates wide range of opportunities for the pyrolysis of hydrocarbons aiming at the production of a variety of carbon structures, which enables for the fine tuning in terms of the yield of products of the required morphology for practical use.

Laser Synthesis of Nanopowders Based on Zinc Selenide for Production of Highly Transparent Ceramics

Laser Synthesis of Nanopowders Based on Zinc Selenide for Production of Highly Transparent Ceramics

Molten Salt Synthesis of Intermetallic Compound TiNi Nanopowder Passivated by TiOx Shell Prepared from NiTiO3 for Catalytic Hydrogenation.

Titanium-nickel alloy is an attractive material due to its unique properties of shape memory effect, superior elasticity, and biocompatibility. Generally, Ti-Ni alloy powders are prepared from pure elemental powders of Ti and Ni as starting materials, but it is an energy-intensive process to obtain pure titanium. In this study, intermetallic compound TiNi powder passivated by TiOx shell was prepared by directly reducing a commercial NiTiO3 using CaH2 reducing agent in a molten LiCl at 650 °C. Analyses by X-ray diffraction, scanning electron microscopy/transmission electron microscopy with energy-dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy revealed that the powder had a core-shell structure, with the core of TiNi and the shell of TiOx-rich composition with scarce metallic Ni nicely catalyzing hydrogenation reactions with good recyclability and stability.

Microwave-assisted synthesis of boron monophosphide nanopowder

Boron monoposphide (BP) has exclusive physical and chemical characteristics allowing it to be used in a variety of practical aspects. However, the usage of BP is limited as the single phase of boron monophosphide is notorious for its difficult synthesis. Moreover, the known methods of synthesis of BP with nanoscale sizes are challenging due to the usually required high temperatures and long synthesis durations. This paper reports the development of a simple, energy-efficient, straightforward Microwave activation synthesis method. Affordable raw materials were used to obtain pure single-phase BP nanopowder with narrow size distribution (70–90 nm) in a short time of synthesis (synthesis duration is 10 min).

Synthesis of N-doped SiC nano-powders with effective microwave absorption and enhanced photoluminescence

Although their preparation remains challenging, N-doped SiC nanostructures have received much attention due to their high performance characteristics compared to pure Si3N4 and SiC phases. In this study, N-doped SiC nano-powders were synthesized in one step through hexamethyldisilane pyrolysis in Ar/N2 plasma atmosphere. The results show that the undoped products included β-SiC nanoparticles sized in the range of 5–20 nm and carbon layers with 1–10 layers, while N-doped SiC nano-powders were mainly amorphous Si3N4/SiCN aggregates sized in the range of 30–200 nm with some β-SiC nanoparticles attached. The increased N2 flow rate and arc currents favored nitrogen doping and carbon removal. In addition, according to the X-ray photoelectron spectroscopy, the highest N-doping level approached 20% (atomic ratio). Nitrogen doping can effectively adjust the dielectric properties and affect the microwave absorption ability. The optimal reflection loss reached −56.2 dB at 8.9 GHz under an absorber thickness of 3.1 mm when the N-doping level was 12.1%. Moreover, due to the defect states, the N-doped SiC nano-powders exhibited good photoluminescence performance in the blue-green emission region. Therefore, the synthesized N-doped SiC nano-powders developed herein present potential applicability as microwave absorbers and light-emitting sources.

Optical and structural properties of cost-effective nanostructured calcium titanate blue phosphor

The current study reports nanostructured CaTiO3 powder produced by two different novel modified sol-gel methods. The chemical reaction between the calcium oxide (CaO) extracted from chicken eggshell (ES) and titanium (IV) isopropoxide (TTIP) leads to the synthesis of calcium titanate nanopowder. Further leaf extract has also been added in one method which shows the significant effect to reduce particle size up to a certain extent. X-ray diffraction (XRD) and field-emission scanning electron microscopy (FE-SEM) were examined to confirm the nanometric particle size. Further, the crystalline structure and phase involvement were also investigated by Rietveld refinement. Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), ultraviolet–visible (UV–Vis), and photoluminescence spectra (PL) characterization were used to study the functional groups, elemental composition, and optical properties of the material. The photoluminescence emission that occurred in the sample was due to the distortion between [TiO6] – [TiO6] complex clusters causing a difference in the charge density, which can promote a charge transfer between these clusters. The CIE chromaticity coordinates were determined and it shows that the synthesized sample is a promising candidate for the blue color phosphor application. The present phosphors were highly useful for UV chip excited white LED applications.

Synthesis of MgO Coating Gd2O3 Nanopowders for Consolidating Gd2O3-MgO Nanocomposite with Homogenous Phase Domain Distribution and High Mid-Infrared Transparency

Improved optical and mechanical properties are required for future infrared windows working in harsher mechanical and thermal environments than today. Ameliorating the homogeneity of the phase domain and reducing the size of the phase domain are effective approaches for enhancing the optical transmittance and mechanical hardness of a nanocomposite. In this work, we reported that the Gd2O3-MgO nanopowders were prepared by two different processes. The core–shell nanopowders synthesized by urea precipitation have a much lower agglomeration than the nanopowders prepared by sol–gel. Excellent transmittance (70.0%–84.1%) at 3–6 μm mid-infrared wave range and a high Vickers hardness value (10.3 ± 0.6 GPa) were maintained using the nanopowders synthesized by urea precipitation mainly due to its homogenous phase domain distribution.

Silicic Acid Polymerization and SiO2 Nanoparticle Growth in Hydrothermal Solution.

The approach of numerical simulation of orthosilicic acid OSA polymerization and SiO2 nanoparticle formation in hydrothermal solution have been developed based on the model of the homogeneous stage of nucleation and the subsequent growth of particles. The influence of surface tension on the interface of SiO2–water, the rate of molecular deposition, and Zeldovich factor Z were evaluated. Temperature dependence on time, pH, initial OSA concentration, and ionic strength are the main parameters that determine the kinetics of colloid phase formation, the final average size of SiO2 nanoparticles, and the particle size distribution and its polydispersity index. The results of the numerical simulation were verified with experimental data on OSA polymerization and measurement of nanoparticles sizes using the method of dynamic light scattering in a wide range of temperatures of 20–180 °C, pH = 3–9, SiO2 content Ct of 300–1400 mg/kg, and ionic strength Is of 0.0001–0.42 mol/kg. The results obtained can be used in the technology of hydrothermal synthesis of sols, gels, and nanopowders to regulate the kinetics of OSA polymerization and SiO2 nanoparticle growth, particle size distribution, morphology, and structure of products.