Amorphous Nanopowders Research Articles

Synthesis of ultra-high-temperature nitride amorphous bulk by reaction of halide precursors with sodium in liquid ammonia

Amorphous Si-B-N nanoparticles of uniform composition tunable over the entire range spanning pure Si3N4 to pure BN was synthesized through a simple homogeneous chemical reaction of the mixture of SiCl4 and BBr3 with Na in liquid ammonia. With these amorphous nanopowders, dense amorphous bulk material was obtained with SPS sintering at the temperature before the crystallization. The dense amorphous bulk of Si3B3N7 exhibited the highest value of hardness (8.8 GPa), flexural strength s (545 MPa), and fracture toughness KIC (10.6 MPa m1/2). These are significantly higher than those reported for other crystalline ceramics of the same composition and surpass those of the completely dense crystalline ceramics. The fully-dense amorphous bulk material exhibited excellent resistance to oxidation up to 1550 °C.

Characterization of nimodipine amorphous nanopowder prepared by quenching cooling combined with wet milling and spray drying

Currently, reducing particle size or preparing drugs into amorphous forms are widely used methods to improve the solubility and dissolution rate of insoluble drugs. The purpose of this study was to prepare nimodipine amorphous nanopowder (NMD-NAP) using nimodipine (NMD) as a model drug to increase the solubility and dissolution rate of insoluble drugs by the combined effect of reducing the particle size and preparing the drug into an amorphous form. The NMD-NAP was successfully prepared by quenching cooling combined with wet milling and spray drying. The prepared NMD-NAP was shown to have good redispersibility by particle size analysis. The shapeof NMD-NAP was characterized by SEM and AFM, showing a spherical or spheroidal structure. The results of PLM, DSC, XRD, and FT-IR indicated that the drug existed in an amorphous form. The dissolution study showed that the dissolution rate of NMD in NMD-NAP was improved about 5 times that of pure NMD and 3 times that of nimodipine nanocrystalline (NMD-NC), indicating the combination of nano size and amorphous form produced a synergistic effect that could significantly increase the dissolution rate of NMD. Due to the significantly improved solubility and good industrial feasibility of the prepared NMD-NAP, the preparation of insoluble drugs into amorphous nanopowders is an effective method to improve the solubility of insoluble drugs and has good application prospects.

Preparation of iron oxide nanopowders by the radiation-chemical method

Various magnetic nanopowders of iron oxide were obtained using the radiation-chemical method when irradiated with a nanosecond electron beam. The main physical and chemical characteristics of the prepared nanopowders were studied, such as structure, porosity, thermal resistance and magnetic properties. It was found that, by selecting precursors and the composition of the solution, it is possible to control not only the textural properties and yield of the obtained nanopowders (by changing the dose and dose rate intensity of the electron beam), but also to obtain crystalline or amorphous nanopowders, on which their magnetic properties depend.

Etoposide Amorphous Nanopowder for Improved Oral Bioavailability: Formulation Development, Optimization, in vitro and in vivo Evaluation.

IntroductionEtoposide refers to a derivative of podophyllotoxin, which plays an important role in the treatment of cancer due to its prominent anti-tumor effect. As a BCS IV drug, etoposide exhibits insufficient aqueous solubility and permeability, thereby limiting its oral absorption. To enhance the oral bioavailability of etoposide, this study developed an amorphous nanopowder.MethodsBased on preliminary screening and experimental design, the stabilizer and preparation process of etoposide nanosuspension were explored. Subsequently, using a Box–Behnken design, the effects of independent factors (ultrasonication time, ratio of two phases and stabilizer concentration) on response variables (particle size and polydispersity index) were studied, and then the formulation was optimized. Finally, nanosuspension was further freeze dried with 1% of mannitol resulting in the formation of etoposide amorphous nanopowder.ResultsThe optimized etoposide nanopowder showed as spherical particles with an average particle size and polydispersity index of 211.7 ± 10.4 nm and 0.125 ± 0.028. X-ray powder diffraction and differential scanning calorimetry confirmed the ETO in the nanopowder was amorphous. Compared with coarse powder and physical mixture, etoposide nanopowder achieved significantly enhanced saturated solubility and dissolution in various pH environments. The Cmax and AUC0–t of etoposide nanopowder after oral administration in rats were respectively 2.21 and 2.13 times higher than the crude etoposide suspension. Additionally, the Tmax value of nanopowder was 0.25 h, compared with 0.5 h of reference group.DiscussionIn the present study, the optimized amorphous nanopowder could significantly facilitate the dissolution and oral absorption of etoposide and might act as an effective delivery method to enhance its oral bioavailability.

Characterization of Freeze-Dried Boron Nanopowders and Parameter Optimization in Ex Situ MgB2 Wire Production

This article reports a study to identify optimal synthesis parameters for a pure boron precursor prepared following a patented process developed at CNR-SPIN laboratories, performed in the framework of a collaboration between CNR-SPIN and CERN. Boron is a precursor that plays a crucial role in the MgB2 wire manufacturing, as a consequence, the synthesis parameters of the superconducting phase have been investigated. In this article, we report results for MgB2 samples synthesized at 870 °C for 17nbsp;h under Ar/5% H2 flow and 760 °C for 0.2 h. Magnesiothermic amorphous nanoboron (MANB) and commercial boron nanopowders (purchased from Pavezyum) have been compared in terms of morphological features. MgB2 derived from both sources has been characterized and the superconductive properties in the wire form have been compared. Results demonstrate that the MANB performance is comparable with the nanoboron obtained via gas synthesis.

Plasma Synthesis of Spherical Crystalline and Amorphous Electrolyte Nanopowders for Solid-State Batteries

Here we demonstrate the theory-guided plasma synthesis of high purity nanocrystalline Li3.5Si0.5P0.5O4 and fully amorphous Li2.7Si0.7P0.3O3.17N0.22. The synthesis involves the injection of single or mixed phase precursors directly into a plasma torch. As the material exits the plasma torch, it is quenched into spherical nanocrystalline or amorphous nanopowders. This process has virtually zero Li loss and allows for the inclusion of N, which is not accessible with traditional synthesis methods. We further demonstrate the ability to sinter the crystalline nanopowder into a dense electrolyte membrane at 800 °C, well below the traditional 1000 °C required for a conventional Li3.5Si0.5P0.5O4 powder.

Earthquake lubrication and healing explained by amorphous nanosilica

During earthquake propagation, geologic faults lose their strength, then strengthen as slip slows and stops. Many slip-weakening mechanisms are active in the upper-mid crust, but healing is not always well-explained. Here we show that the distinct structure and rate-dependent properties of amorphous nanopowder (not silica gel) formed by grinding of quartz can cause extreme strength loss at high slip rates. We propose a weakening and related strengthening mechanism that may act throughout the quartz-bearing continental crust. The action of two slip rate-dependent mechanisms offers a plausible explanation for the observed weakening: thermally-enhanced plasticity, and particulate flow aided by hydrodynamic lubrication. Rapid cooling of the particles causes rapid strengthening, and inter-particle bonds form at longer timescales. The timescales of these two processes correspond to the timescales of post-seismic healing observed in earthquakes. In natural faults, this nanopowder crystallizes to quartz over 10s–100s years, leaving veins which may be indistinguishable from common quartz veins.

New amorphous nanophosphors obtained by evaporation of silicates and germanates REE

Abstract Amorphous nanophosphors have been produced by pulsed electron beam evaporation of bulk phosphors of rare earth elements (REE) silicates and germanates with oxyapatite structure activated with europium. The processes of crystallization of amorphous nanopowders (NP) have been studied by differential scanning calorimetry and thermogravimetry (40–1400°C) methods. A modification of the Raman and IR spectra of the samples was found when the particle size decreased from bulk to nanostate due to insignificant polymerization of Si(Ge)O4 tetrahedra. The spectral and luminescence characteristics of the bulk samples as well as nanoamorphous samples have been examined. It was established that Eu3+ forms two types of optical centers. Upon the transition of Sr2Gd8(SiO4)6O2:Eu3+ phosphor from bulk state to nanostate during laser excitation, the luminescence intensity of Eu3+ ions increases 10 times. Blue and white amorphous nanophosphors have been obtained for the first time by evaporation of Ca2M8(SiO4)6O2:Eu (M=Y, Gd) and Ca2La8(GeO4)O2:Eu phosphors. Radiation reduction of ions Eu3+→Eu2+ in electron beam has been presumably found.

The spectral characteristics of blue nanophosphors obtained by evaporation of Ca2M8(SiO4)6O2:Eu (M=Y, Gd) polycrystals

Amorphous blue nanophosphors have been produced for the first time by pulsed electron beam evaporation of polycrystalline phosphor targets of the composition Ca2M8(SiO4)6O2:Eu (M=Y, Gd) with oxyapatite structure. Radiation reduction of Eu3+→Eu2+ ions in the electron beam has been detected. The crystallization of amorphous nanopowders has been studied by differential scanning calorimetry and thermogravimetry (40–1400°C). A modification of the Raman spectra of the samples has been found when the particle size decreases from the bulk to the nanodimensional state. The variation in the forbidden band Eg width of the samples during transition from bulk powder to NP has been considered. The spectral luminescent characteristics of the samples in polycrystalline and nanoamorphous states have been examined. It was shown that the ligand field around Eu2+ changes during the bulk→nano transition. This can be due to the violation of translational symmetry in NP. The bonding of the 4f and 5d electrons weakens. The 2eg level degenerates.

Obtention of Li3xLa2/3−xTiO3 ceramics from amorphous nanopowders by spark plasma sintering

ABSTRACTIn this work, Li3xLa2/3−xTiO3 powder with nominal lithium content (x = 0.08) was synthesized by mechano synthesis method. Spark plasma sintering (SPS) was employed to prepare lithium lanthanum titanium oxide solid-state ceramic. The techniques of X-ray diffraction, high resolution scanning electron microscopy, and Raman spectroscopy were used to characterize the composition and microstructure of samples. The results showed that fine-grained ceramics with relative density of 95.5% were obtained by sintering the oxide powders at 1100°C for only 5 min.

Enhanced mechanical properties in ZrO2 multi-walled carbon nanotube nanocomposites produced by sol–gel and high-pressure

Sol–gel processing and heat-treatment were used to obtain nanopowders with tetragonal phase of undoped zirconia reinforced with well-dispersed multi-walled carbon nanotube (MWCNTs), having contents between 1 and 5 wt.%. Amorphous nanopowders treated at 500 °C crystallized in the tetragonal phase of zirconia with an average crystallite size of 25 nm. The nanocomposites containing 3 wt.% of MWCNTs reached 98% of the theoretical density, with an increase in hardness of about 15%, and a fracture toughness about 110% higher compared to the values obtained for pure zirconia compacted at the same conditions. The novelty in our study is the production of zirconia/MWCNTs nanocomposites with enhanced mechanical properties by compaction of nanopowders under high-pressure at moderate temperature.

Nanopowder processing of ultrafine Si3N4 with improved wear resistance

The processing, microstructure, and material properties of monolithic Si3N4 were investigated by using two amorphous Si3N4 nanopowders doped with (1) 6 wt% Y2O3 and (2) 6 wt% Y2O3 + 8 wt% Al2O3. The orthorhombic Si2N2O-based phase was found in the two as-sintered bulks. Carbothermal reduction treatment (CRT) was thus applied at 1400 °C for 10 h with 3 wt% and 6 wt% carbon black added to the precursor powders of the Si–Y–O–N and Si–Y–Al–O–N systems, respectively, resulting in an increased nitrogen-to-oxygen (N:O) ratio and elimination of Si2N2O within the sintered bulks. The possible mechanisms of nucleation and grain growth of Si3N4 are discussed during CRT and the sintering process. The best wear resistance was achieved in ultrafine Si3N4 doped with Y2O3, which has good hardness, indentation toughness and a protective tribo-film.

Properties of Silicon Dioxide Amorphous Nanopowder Produced by Pulsed Electron Beam Evaporation

SiO2amorphous nanopowder (NP) is produced with the specific surface area of 154 m2/g by means of evaporation by a pulsed electron beam aimed at Aerosil 90 pyrogenic amorphous NP (90 m2/g) as a target. SiO2NP nanoparticles showed improved magnetic, thermal, and optical properties in comparison to Aerosil 90 NP. Possible reasons of emergence of d0ferromagnetism at the room temperature in SiO2amorphous NP are discussed. Photoluminescent and cathode luminescent properties of the SiO2NP were investigated.

Separation of medical nanopowder from the natural minerals by supercritical CO2

Nano-sized medical raw material has been derived from the medical quality natural spar (CaCO3) without the use of chemical salt. The theoretical base of the method consists in the transferring and keeping CO2 to a supercritical state during thermo-chemical processing of the spar at 900-950°C. The supercritical CO2 has a form of solid solution that holds the properties of both gas and solid. Afterwards, with dissolving it in the animal milk, the solution is equalized by the sovent’s expansion with the decrease of temperature and creates amorphous crystal nanopowder. The size of the resultant product was determined both by XRD and TEM analysis as to be 13.51 nm (Lu »13.09 nm). DOI: http://dx.doi.org/10.5564/mjc.v14i0.202 Mongolian Journal of Chemistry 14 (40), 2013, p66-70

The investigation of the structure control possibility of nanocrystalline yttrium orthoferrite in its synthesis from amorphous powders

Mechanism by which nanocrystalline yttrium orthoferrite is formed in thermal treatment of amorphous nanopowders produced by the glycine-nitrate combustion method was studied. It was shown that orthorhombic YFeO3 is formed from the amorphous phase via intermediate formation of a metastable nanocrystalline hexagonal phase of yttrium orthoferrite. The main parameter controlling the process in which the orthorhombic form of YFeO3 is determined. It was demonstrated that YFeO3 crystallizes from an amorphous powder in the hexagonal modification up to nanocrystal sizes of approximately 33 nm and transforms to the orthorhombic phase at larger sizes.

Synthesis, Characterization, and Bioactivity Evaluation of Amorphous and Crystallized 58S Bioglass Nanopowders

The aim of this work was synthesis and characterization of amorphous and crystallized 58S nanopowders produced via sol‐gel method. According to the thermal analysis, the nanopowders were heat‐treated at 600°C and 1100°C. X‐ray diffraction results revealed that the phases of Wollastonite and tricalcium phosphate were formed at 1100°C. The in vitro tests showed that hydroxyl carbonate apatite was precipitated on both crystallized and amorphous nanopowders, while amorphous nanopowder showed a higher bioactivity than that of crystallized nanopowder. In contrast, mechanical properties of crystallized specimen were higher than those of amorphous specimen.

Spectral characteristics of nanoamorphous phosphors obtained by evaporation of Sr2Gd8(SiO4)6O2: Eu polycrystals

Amorphous nanophosphors have been obtained for the first time by pulsed electron beam evaporation of targets from bulk polycrystalline phosphors of the composition Sr2Gd8(SiO4)6O2: Eu with oxyapatite structure. The processes of crystallization of amorphous nanopowder were studied using differential scanning calorimetry and termogravimetry (40−1400°C). It was found that the Raman spectra of the samples are modified when the particles decrease from bulk to nanodimensional state. The spectral and luminescent characteristics of the phosphors in polycrystalline and nanoamorphous states have been examined. It was established that Eu3+ forms two types of optical centers. Unlike bulk phosphors, in the nanophosphors no Eu2+ ions are formed. The ratio of red to orange luminescence intensity for nanophosphors was found to increase as compared with bulk phosphors. This effect is due to disordering of nanoparticles. A resonant transfer of excitation energy from Gd3+ to Eu3+ ions was found in bulk and nanophosphors. Upon transition from polycrystalline to nanoamorphous state and laser excitation of phosphors, the luminescence intensity of Eu3+ ions increases approximately 10 times. This effect is explained in the framework of the configuration coordinates model.

Characterization of Silicon Nanoparticles Formed from a Fluidized Bed Reactor and Their Incorporation onto Metal-Coated Carbon Fibers

Enhancing the light trapping using nonwoven arrays of fibers has the potential to improve the photocurrent of silicon solar cells. In this work, amorphous and crystalline Si nanopowders (30–300 nm) were embedded in carbon fibers and fixed in place with electrodeposited nickel. Scanning and transmission electron microscopy techniques have been used to study the morphology of the Si particles and their interactions with the coatings. Two types of nanoparticles are identified, homogeneous nucleated particles (amorphous particles with some crystalline regions) and attrition particles (mostly crystalline products formed from fracture of particles as they grow in a fluidized bed reactor). Using the Brunauer–Emmett–Teller (BET) technique, the surface area and the pore diameter of these agglomerated Si nanoparticles were calculated to be 6.4 m2/g and 9.8 nm, respectively. After embedding the Si particles into the carbon matrix with the metal coatings, the electrical resistivity decreases, suggesting it is possible to enhance the light extraction of silicon solar cells using Si nanoparticles.

Dielectric behavior, conduction and EPR active centres in BiVO4 nanoparticles

Bismuth vanadate (BiVO4) nanomaterials were synthesized by mechano-chemical ball milling method and complementary investigations were devoted to their structures, nanoparticle morphologies and electronic active centres. The dielectric and conductivity behaviour were analysed systematically in wide temperature and frequency ranges to correlate such physical responses with the peculiarities of the samples. Large interfacial polarisations favoured by high specific surfaces of nanoparticles account for a drastic enhancement of the dielectric function in the quasi-static regime. Exhaustive analyses of the dielectric experiments were achieved and account for the main features of dielectric functions and their related relaxation mechanisms. The electrical conductivity is thermally activated with energies in the range 0.1–0.6eV depending on the sample features. DC conductivity up to 10–3S/cm was obtained in well crystallized nanoparticles. Vanadium ions reduction was revealed by EPR spectroscopy with higher concentrations of the active centres (V4+) in more agglomerated and amorphous nanopowders. The EPR spectral parameters of V4+ were determined and correlated with the local environments of reduced vanadium ions and the characteristics of their electronic configurations. An insight is also made on the role of active electronic centres (V4+) on the conduction mechanism in nanostructured BiVO4.

Polyacrylamide gel synthesis and sintering of Mg 2 SiO 4 :Eu 3+ nanopowder

A Mg2SiO4:Eu3+ nanopowder was synthesized by a polyacrylamide gel method. In this route, the gelation of the solution is achieved by the formation of a polymer network which provides a structural framework for the growth of particles. The densification of the powders was also studied. An amorphous nanopowder was synthesized and crystallized to Mg2SiO4 after heat-treatment via a solid-state reaction at a relatively low temperature of about 700 °C. The powders prepared by the polyacrylamide gel method showed better sinterability than the powders synthesized by the conventional sol–gel method. The relative density of the sample was 97% at 1500 °C.