Nanometric Powders Research Articles

Characterization of Aluminum Powders: III. Non‐Isothermal Oxidation and Combustion of Modern Aluminized Solid Propellants with Nanometals and Nanooxides

AbstractAluminum powders were comprehensively described as the prospective ingredients of the modern propellants. The paper also studied the influence of micro‐ and nanopowders of metals (μ‐Me and n‐Me) and metal oxides (μ‐MeO and n‐MeO) on the burning process of modern aluminized propellant with HMX, CL‐20, AP, and active binder. The following metal additives were used: Al, B, Zn, Ni, Co, and Mo. The effect of the following oxides CoO, V2O5, MnO2, and Fe2O3 was studied together with LiF. The combustion tests of modified propellant compositions were carried out in the Vielle bomb in a pressure range 2–10 MPa. n‐Me addition resulted in an increase in the burning rate by 10 % for n‐B, by 30–40 % for n‐Ni and n‐Mo in the studied pressure range. The introduction of n‐Cu caused a burning rate to increase fivefold. n‐Zn additive resulted in increasing of the propellant burning rate by 130 % and 260 % at 4 and 10 MPa, respectively. It was probably caused by the catalytic activity of those metals in the gaseous phase. The effect of complex additive was observed to be insignificant for additives with μ‐Co3O4, μ‐V2O5, μ‐Fe2O3 and n‐Fe2O3. The burning rate of propellant with n‐CuO additive value was higher by a factor of 4 in comparison with the basic formulation in the studied pressure range.

SnO2–polyaniline composites for the desensitization of Al/SnO2 thermite composites

ABSTRACTNanothermites consisting of a reducing metal and a metal oxide nanopowder represent a new generation of energetic materials in pyrotechnics due to their impressive reactive properties. However, their extreme sensitivity regarding electrostatic discharge appears to be detrimental to their future practical applications. Herein, the mitigation of the sensitivity thresholds of the aluminium/tin (IV) oxide energetic nanocomposite is successfully achieved by using a conducting polymer, polyaniline (PAni). PAni was introduced within the thermite by the chemical polymerization of an oxidizer/PAni hybrid matrix. The SnO2–PAni composites were characterized by X‐ray diffraction, Fourier transform infrared spectroscopy, thermogravimetric analysis, electrical conductivity measurements, and transmission electron microscopy. The derived Al/SnO2–PAni thermites were investigated in terms of sensitivities and reactivity. Results revealed gradual desensitization of the Al/SnO2 thermite as a function of the concentration of PAni for both the electrostatic discharge (0.14–1212 mJ) and friction (216–360 N) tests while maintaining reactive energetic composites. This work presents a way for the preparation of insensitive and reactive energetic formulations. © 2020 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020, 137, 48947.

Interface excess on Li2O-doped γ-Al2O3 nanoparticles

One of the attempts to improve γ-alumina catalytic performance lies in the use of additives that prone to segregate on its interfaces. The catalytic activity depends on the acidity or basicity of the doping oxides. Li2O is one of these oxides that when is loaded on γ-alumina surface decreases the number of Lewis acid sites. However, little is known about the Li2O distribution in the γ-alumina structure and interfaces. Thus, a detailed study of the lithium oxide distribution in the nanostructure of γ-alumina is the aim of this study. Nanometric powders were synthesized by the polymeric precursor method. The nanopowders were doped with Li+ ions (0.1, 0.5, 1, 3, 5, and 10 mol%) followed by calcination at 650 °C and 750 °C for 15 h. The powders were characterized by XRD, XRF, FTIR-DRIFT, BET specific surface area (SSA) and helium pycnometry. The surface excess due to the lithium oxide segregation was determined by the selective lixiviation method which has proved to be effective in quantifying surface excess of segregated ions at oxide interfaces. The crystallite sizes of the nanopowders varied from 3.3 nm to 9.2 nm, while their SSA were between 82.0 m2/g to 119.9 m2/g. The chemical analyses suggest that the lithium segregates in the γ-alumina interfaces at 650 °C, but it volatilizes from the surface after calcination at 750 °C.

Assessing the efficiency of using the mineral complex based on Nanopowders of metals in Experimental Post haemorrhagic Anemia in White Rats

Assessing the efficiency of using the mineral complex based on Nanopowders of metals in Experimental Post haemorrhagic Anemia in White Rats

Morpho-physiological and productive indicators of oat under the influence of nanopowders of cobalt and copper trace elements

Metal nanoparticles are used in agriculture as trace elements for agricultural plants, as growth stimulants, and pesticides. Nanodisperse metals are known to have biological, antioxidant, and enzymatic activity. The article presents the results of research on oat of the “Skakun” variety, conducted in 2014-2017 in the conditions of the Agricultural technology station of RSATU (Ryazan region). The experiment was carried out on gray forest heavy loam soil, in 3 times repetition. Its predecessor is winter wheat. In the experiment, cobalt nanopowder (NP Co) and copper nanopowder (NP Cu) were used with a purity of 99, 98%, the size of metal particles was 20-40 nm. The effect of nanopowders of cobalt and copper metals and their combinations on the productive, physiological and biochemical parameters of oat plants in production conditions is shown. The best result was observed when using the preparation with a mixture of cobalt and copper nanoparticles at a concentration of 0.5 g per average seed rate per hectare - field germination increased by 5.0%, grain yield increased by 15.3%, grain protein content - by 2.0%, fat content - by 0.5% relative to the control.

Lanthanum titanate nanometric powder: An investigation on synthesis by solid state route

La2Ti2O7 nano metric powder was prepared using solid state route and evaluated in the present study. Precursors of lanthanum oxide and titanium dioxide were blended, synthesized at 850 °C for 8 h. The phase analysis of the synthesized powder was carried out using XRD diffraction analysis to check the purity of the perovskite La2Ti2O7 compound formed. The crystalline size measurement was carried out using Debye–Scherrer formula which reveals that the synthesized powder at 850 °C for 8 h is in the range of 49.54 nm. The powder morphology was studied using the SEM and EDS result confirms the presence of La, Ti and O elements. The SEM results reveal irregular morphology of the powders and few clusters which may be attributed to the presence of the moisture in them.

Mathematical modeling of an effect of refractory metal nanopowders on the strength of concrete

The quality of concrete and the reliability of its exploitation in structures and structures are largely determined by such characteristic as strength. Additives increasing the strength can significantly improve the quality of concrete. The aim of this work is mathematical modeling of the effect of refractory metal nanopowders on the strength of concrete. Regression equations of the first and second orders are constructed, which adequately find the dependence of the compressive strength of concrete on the input parameters. For presented model the optimal values of the concentrations of refractory metal nanopowders have been calculated.

La2Ti2O7 As Nanometric Electrode Material: An Emerging Candidate For Supercapacitor Performance

AbstractIn this study, first time the nanometric powder of La2Ti2O7 (abbreviated as LTO) is taken as the electrode material for supercapacitor. The prepared material is characterized by various characterization techniques to know its structural and textural properties. The specific capacitance of the La2Ti2O7 is calculated from charge discharge curve. The Nyquist plot, bode plot and the plot of real capacitance vs. imaginary capacitance is well in support of supercapacitive activity of La2Ti2O7. The La2Ti2O7 exhibits 71 F/g of specific capacitance in 2 M KOH with 95.7% retention after 5000 cycles is due to the effective access of electrolyte to the redox sites owing to its layered structure. As these finding are new to the scientific community and demonstrate the great potential of La2Ti2O7 as electrode material for supercapacitor, the current findings may give a new pave in the area of supercapacitor research.

Electrochemical Preparation of CuZn Metallic Foams for Removing Water Contaminants.

This study is focused on the preparation of metal (Cu, Zn) nanopowders by an electrochemical reduction/precipitation procedure, which provides the primary components for the development of CuZn alloy metallic foams. This well-controlledmethod allows straight forward control of the reaction parameters and the restriction of oxidation effects, while resulting in stable and small grain size metal nanopowders. Whether precipitation of Cu and Zn is held separately or in alternating deposition mode, the characteristics of synthesized nanopowders assist easier mixing, alloying and realization of metallic foams suitable for water treatment applications. CuZn alloy foams developed with this technique presented equivalent efficiency and lower corrosion and leaching rates compared to those prepared with commercial powder methods.

Electrospark method for obtaining nanopowders

In the paper, a metallic FexOy nanopowder was obtained by the electrospark method. The used electrospark installation consists of the electrode system, mobility system, system for measuring processing parameters (oscilloscope and current sensor, HV voltage divider, manovacuum meter), source of current pulses, vacuum system (vacuum pump, gas cylinders with working gas, gas routes, gas taps). The specific feature of the installation is the use of a power supply circuit of two generators with different voltage levels operating for one interelectrode gap. This generator circuit makes it possible to change the treatment parameters in wide ranges (pulse duration 10–100 μs, pulse energy 0.1–0.6 J, pulse repetition rate 0.1–5 kHz). It will enable to choose the optimal ratio between the energy expended and the maximum yield of the product, as well as to study the influence of treatment parameters on the composition and properties of the resulting powder. The morphology and phase composition of the FexOy synthesized metal powder was studied.

Influence of parameters of high-voltage electrospark dispersion of materials on granulometric composition of nanopowders

The influence of parameters of high-voltage electric spark dispersion of materials on the granulometric composition of nanopowders of metals and alloys is considered. The most interesting feature of the developed experimental setup is the presence of an air discharge gap (FV1), which creates an overvoltage on the working discharge gap (FV2). The discharge gaps form a voltage divider when the capacitor (C) is discharged. It was assumed that the voltage divider should have a significant impact on the operation of the experimental setup. Studies have shown that when the air gap (FV1) is much larger than the working gap (FV2), their exact ratios do not affect the size of the resulting nanoparticles. At such ratios of discharge gaps, the voltage divider allows to regulate only the performance of the process of obtaining nanopowders. The resulting silver nanopowders had a spherical shape and a rather narrow size distribution. It is necessary to further study the process of high-voltage spark dispersion of materials with a significant overvoltage of the discharge gap.

Solubility of metal oxide nanomaterials: cautionary notes on sample preparation

Eight metal oxides were obtained to investigate the dissolution behaviour of engineered nanomaterials (ENMs) dispersed in biologically relevant media. Identities of the metal oxide compounds, and their crystal form and size were checked using powder X-ray diffraction (XRD). Methods for sonication of metal oxide nanoparticles were optimized to achieve stable stock dispersions, and methods for separation of dissolved metal ions from dispersed nanoparticles were evaluated. The results of the optimization experiments showed that each metal oxide ENM required a different combination of sonication time and power (% amplitude). Optimized values for delivered sonication energy (J/mL) ranged from 24 for CuO to 833 for ɣ-Al2O3. Centrifugation at 20000G was found to be more effective and less prone to artefacts than using commercially available ultrafiltration devices for separation of dissolved metal fraction, under these experimental conditions. XRD results indicated that the composition of two metal oxide nanopowders (Mn2O3 and Fe2O3) did not meet the manufacturers’ claims, underscoring the importance of double-checking physical-chemical properties of commercial ENMs purchased for research.

Transient heating and evaporation of metallic particles under plasma conditions

The synthesis of metallic nanopowders through the vaporization and condensation of metallic precursors under plasma condition is increasingly accepted for a wide range of applications in the electronic and electrical industry. The present study aims at the computer simulation of the basic processes involved. Specific attention is given to the particle evaporation rate and the associated energy balance. Computation carried out for the vaporization of 50 µm iron and copper particles in an atmospheric pressure argon plasma at 9000 K provide means of quantifying the different energy requirements of the process including;• energy needed for the initial heating of the particle to its vaporization temperature,• energy required for particle vaporization,• energy lost by surface radiation from the particle during the evaporation process, and• energy radiated from the plasma/metal vapor cloud.The results show that energy lost by volume radiation for the plasma/metal vapor cloud is by far the most important energy requirement of the process that deserves special attention in terms of reactor engineering design in order to reduce its value and consequently increase process productivity. As expected, the results are to a large extent material dependent, varying widely with the radiative properties of the metal involved.

Plastic deformation at dynamic compaction of aluminum nanopowder: Molecular dynamics simulations and mechanical model

A mechanical model of a metal nanopowder compaction is proposed. It takes into account the change in the shape of nanoparticles during mutual indentation, the action of surface tension, elastic stresses and plastic deformation of particles. The plastic deformation is the key point of compaction; the dislocation approach is used to incorporate the plasticity into the model. The model considers the stage of free relaxation, when the nanoparticles are mutually attracted due to the surface tension and mutually repulsed due to the elastic stresses, and the stage of compaction, when the interplay between elastic deformation and plasticity defines the mechanical response of the powder. The model provides a kinetic form of the constitutive equations for nanopowder and is intended for use in macroscopic modeling of the shock-wave processes in the calculation of installations for dynamic compaction of nanopowders to describe the local mechanical reaction and estimate the degree of compaction in each finite element. Molecular dynamics (MD) simulations of the dynamic compaction of Al nanopowders with particle diameters in the range of 6–30 nm are carried out. Comparison with the results of MD shows that the proposed model adequately describes both the relaxation stage and the powder compression stage. The effects of temperature, strain rate and nanoparticles piling are considered.

Investigation of YAP/YAG powder sintering behavior using advanced thermal techniques

The fabrication process of transparent YAG (Y3Al5O12) ceramics with an emphasis on examination of the sintering process and microstructural analysis is reported herein. Nanometric powder with an equivalent spherical diameter dBET = 60 nm consists mainly of hexagonal YAP phase (YAlO3). According to sintering analysis carried out using a dilatometer and high-temperature XRD analysis, the phase composition and phase transformation taking place at elevated temperatures accompany the sintering process and the fastest sintering rate was observed at temperatures of YAG formation. Based on the dilatometric and XRD analyses vs temperature, three temperatures were selected for pressureless sintering. Presintered samples were subjected to sintering under isostatic pressure using a hot isostatic pressing, after which transparent YAG was obtained. The best results were obtained for samples presintered at a relatively low temperature of 1600 °C, and for thus obtained sample, the in-line transmittance was 64% at λ = 808 nm.

Removal of Copper(II) Ions from Aqueous Solutions by Hydroxyapatite-Based Materials Prepared from Eggshells

The experimental study aimed to establish the potential applications of the nano- and micrometric powders of hydroxyapatite in the removal processes of Cu(II) ions from synthetic aqueous solutions. For this purpose, hydroxyapatite (HAP) was used in the form of: 1) nanometric powder (labeled nano-HAP), and 2) calcium alginate hydroxyapatite composite microparticles (nicro-HAP-CaAlg). Eggshells have been used as a raw material to obtain HAP. The contact time, pH and Cu(II) concentration in the initial solution have been the main process variables with influence on the Cu(II) ions removal by HAP samples. For both HAP based materials, an optimal pH value of 5 has been established. The nano-HAP powder has a higher Cu(II) adsorption capacity than micro-HAP-CaAlg based on the specific surface area values of nano- and micrometric powders. The adsorption isotherm experiments showed that this process can be described using Langmuir model according to which the adsorption takes place as a monolayer process on an homogeneous surface. The kinetic study revealed that the sorption process of Cu(II) from synthetic aqueous solutions can be described using the pseudo-second order kinetics model according to which the rate-determining step is chemisorption. The values of the retention capacity recommends both powders tested (nano-HAP and micro-HAP-CaAlg) to be used in the Cu(II) loaded water treatment process.

Templated synthesis of Cr2O3 material for energetic composites with high performance

A facile templated approach has been developed for the synthesis of Cr2O3 chromium (III) oxide material with low particle size and tunable textural properties. While chromium nitrate nonahydrate was used as chromium source, fumed silica was selected as template. The Cr2O3 powders were characterized by X-ray Diffraction, High Resolution Transmission Electron Microcopy and nitrogen physisorption. Results showed that the particles size and the textural properties of the as-synthesized Cr2O3 materials depend on the fumed silica/Cr-precursor weight ratio. Used in energetic composites, like nanothermites implementing metal and oxide nanopowders, the silica-templated Cr2O3 material leads both to make easier the ignition and to increase the combustion velocity of the mixture.

Synthesis of Ti3SiC2 MAX phase powder by a molten salt shielded synthesis (MS3) method in air

Titanium silicon carbide (Ti3SiC2) powder was synthesized by molten salt shielded synthesis route of elemental reactants. Potassium bromide (KBr) was used for gas-tight encapsulation of the consolidated reaction mixture for further high temperature processing. The synthesis of Ti3SiC2 powder was carried out in air, the salt cladding and molten salt pool provided for the protection of the material against oxidation both at low and high temperature. The process yielded free flowing Ti3SiC2 powders without the need of a milling step. Al addition to the reaction mixture resulted in a high purity (96 wt. %) of Ti3SiC2 at a synthesis temperature of 1250 °C. The synthesized micro-metric Ti3SiC2 can be milled to nano-metric powders.

Spinning Disk Reactor Technique for the Synthesis of Nanometric Sulfur TiO2Core–Shell Powder for Lithium Batteries

Sulfur/lithium battery performances are strictly related to the morphology and nanostructure of sulfur particles. In this work, a comparison of the morphological characteristics and electrochemical properties of electrodes based on colloidal sulfur (CS) obtained by means of traditional chemical precipitation from aqueous solution and via spinning disk reactor (SDR) has been performed. In particular, through the SDR technique and by using different fluid dynamic conditions, it was possible to obtain monodisperse and nanometricsulfurparticles with higher electrochemical performances when used as the cathodic active material in lithium batteries. Moreover, a method to produce core–shell nanoparticles with sulfur and titanium dioxide, starting from a colloidal sulfur (S8) solution and produced by SDR, has been performed, obtaining good electrochemical results. In particular, the nanometric sulfur powder produced by the SDR technique showed a capacity higher than CS after 100 cycles, even if the capacity decreased rapidly in both cases. Instead, considering the core–shell S–TiO2 material, the nanostructured electrode allowed a wide use of active material and a reduced capacity decay during cycling. Specifically, the material showed an initial capacity of 1395 mAh/g, i.e., representing 83% of the theoretical value, which decreased during operation up to 450 mAh/g after about 30 cycles. Then, the material capacity remained unchanged and no substantial loss of capacity was recorded up to 100th cycle.

Hierarchically structured, highly porous nickel synthesized in sintering–evaporation process from a metal nanopowder and a space holder

This paper reports on the creation of a highly porous material with a hierarchical structure using powder metallurgy methods based on nickel nanopowder and ammonium bicarbonate NH4HCO3 as a space holder.