Search

In this work, synthesis of WO 3 nanoparticles is reported using a novel, yet simplified microwave-metal discharge approach. The discharge was triggered from the pointed tip of a tungsten electrode, which eventually got vaporized and deposited on the collector substrates surrounding the metallic electrode. The buildup of high electric field at the tip of the tungsten electrode ionized the surrounding air molecules that lead to the discharge formation. X-Ray diffraction revealed monoclinic phase of the synthesized WO 3 nanoparticles. The morphological analysis executed using transmission electron microscopy showed the presence of single crystalline nanoparticles in spherical, rhombic, and rectangular shapes. X-ray photoelectron spectroscopy confirmed the elemental composition and showed formation of stoichiometric WO 3. Thermal stability analysis showed high stability of the nanoparticles below 1200 °C. The nitrogen absorption-desorption studies suggested that the nanoparticles exhibited a mesoporous structure. The antimicrobial susceptibility tests indicated an increased resistance towards Gram-negative bacteria (E. coli) compared to Gram-positive bacteria (S. aureus). [Display omitted] [ABSTRACT FROM AUTHOR]

The steadily high interest in metal oxides, including in the form of fine powders, has led to a rapid increase in their production, the search for new synthetic methods and the expansion of possible applications. CO 2 has proven itself as a cheap and abundant source of mild oxidant, which can potentially be used for oxidation reactions. However, the key problem of CO 2 application is the necessity to break the bonds of the CO 2 molecule that requires a large amount of energy. This work presents a fundamentally new approach for metal oxide synthesis, when applying CO 2 as a gaseous precursor and oxidant, based on application of a pulsed arc discharge plasma of the electroerosion type. The implementation of the proposed method called plasma dynamic synthesis results in obtaining dispersed metal oxides that is demonstrated by the examples of Cu–O, Fe–O, Ti–O and Al–O systems. The influence of the metal-containing plasma type and operation modes on the formation of metal-oxide dispersed materials is studied. The multi-pulse operation mode in the considered system with titanium and aluminum electrodes provides obtaining almost completely oxidized products that is found to depend on the electronegativity of the initial metals. When applying aluminum electrodes, the process not only provides a high productivity of obtaining dispersed materials (up to 15 g per cycle), but also allows the CO 2 conversion rate of up to 14.5%. Moreover, the electroerosion plasma demonstrates the energy efficiency of CO 2 decomposition exceeding other plasma-based methods due to ongoing exothermic reactions of metal oxide formation. The as-synthesized products can be used to obtain bulk ceramic materials that is shown by the example of aluminum oxide powders. The hardness of the obtained ceramic specimens produced by SPS method is found to be ∼22 GPa and correlates with the best samples for aluminum oxides. • Plasma sputtering in CO 2 medium results in forming dispersed metal oxides. • CO 2 conversion rate in multi-pulse operation mode of system with Al electrodes is 14.5%. • Electronegativity of electrode metal affects the oxide formation process and CO 2 conversion rate. • Electroerosive plasma application provides higher energy efficiency of CO 2 conversion. • Obtained Al–O-based dispersed materials can serve as a charge for hard ceramics (22 GPa). [ABSTRACT FROM AUTHOR]

Titanium dioxide is currently one of the most known promising photocatalysts. However, its use in the visible light range is limited due to its high energy gap. In this work, to solve the mentioned problem, it is proposed to obtain highly defect structures of titanium dioxide by means of a high-energy plasma dynamic synthesis method. It possible to synthesize TiO 2 Titanium dioxide powders with a tunable ratio of rutile and anatase modifications, as well as a particle size distribution were synthesized, by optimizing the synthesis conditions, including the process energy and parameters of the gaseous medium. The formation of shock-wave structures in the pulsed synthesis process results in obtaining fine particles of rutile and anatase with a highly defective crystal structure. The final product was revealed to have an extended working absorption spectrum region and a reduced band gap (2.74 eV). A possibility of photocatalytic applications for the synthesized TiO 2 powder was demonstrated in measurements of photocurrent density with time (j - t) under intermittent visible light irradiation. • TiO 2 with rutile and anatase structures can be synthesized in arc discharge plasma. • The phase composition can be tuned by changing the process energy and oxygen concentration. • The formed shock-wave plasma jet makes it possible to obtain defective TiO 2 structures. • The synthesized defect fine titanium dioxide has a smaller band gap of 2.74 eV. [ABSTRACT FROM AUTHOR]

Selective N moieties in N-doped carbon catalysts were successfully controlled by a room temperature plasma process, where its ORR catalytic activity was found to be related to Lewis Basicity of catalysts. • Tailored 4 types of nitrogen bonding states in N-doped carbon by plasma synthesis. • Correlated the Lewis basicity of N-doped carbon catatlysts to their ORR activities. • Amino-N showed the superior Lewis basicity and ORR activity. The ORR electrocatalytic activity of nitrogen-doped carbon (N-doped carbon) is highly related to the type of nitrogen bondings, which is originated to the charge transfer between carbon and nitrogen. Based on Lewis theory of acid-base reactions, N-doped carbon can be defined as a Lewis base catalyst. The lone pair of electrons on the nitrogen atom mainly contributed to its reactivity, or in other terms, Lewis basicity. Herein, we fabricated selective amino-N, pyrrolic-N, nitrile-N, and oxide-N in N-doped carbon systematically, as well as compared their electrocatalytic activities and Lewis basicities for the first time. Based on the molecular structure of four starting precursors, aniline (C 6 H 5 NH 2), pyrrole (C 4 H 5 N), benzonitrile (C 5 H 7 N), and nitrobenzene (C 6 H 5 NO 2) were successfully formed as selective amino-N, pyrrolic-N, nitrile-N and oxide-N, respectively, via a room temperature plasma synthesis process. From the electrochemical performance, N-doped carbon catalyst with highly selective amino-N demonstrated comparatively higher ORR activity in terms of ORR onset potential and current density. Also, we confirmed the correlation between the ORR activity and Lewis basicity of various N moieties. Based on the electronic structural properties, amino-N with the most superior ORR activity also exhibited the highest basic strength among the studied C N bonding structure. This study provided the relationship among the structural properties, Lewis basicity, and electrocatalytic activity of selective N-doped carbon. [ABSTRACT FROM AUTHOR]

Abstract Thermally conductive composites aimed for dielectric application were achieved by embedding spherical MgSiO 3 -SiO 2 -hBN powders into cyanate ester resin as functional fillers. The MgSiO 3 -SiO 2 -hBN particles were prepared by plasma sythesized process employing talc and hexagonal boron nitride (hBN) as sources. The morphology, phase structure of the MgSiO 3 -SiO 2 -hBN powders were characterized by changing the content of BN. Meanwhile, the thermal and dielectric properties of the composites with different filler loading were investigated. Results show that phase transformation from talc to protoenstatite and critobalite occurred. The thermal conductivity shows a drastic enhancement with the increase of the filler loading. Further contrast analyzed by Bruggeman model shows that the tested values agree well with estimated ones when fillers fraction are less than 15 vol%. However, an obvious deviation for the values of thermal conductivities is thought to arise from the randomly oriented hBN and the formation of the thermal conductive networks in composites. Relatively low dielectric constants and dielectric losses (tanδ) are obtained for all the composites. [ABSTRACT FROM AUTHOR]

Various silicon carbide nanostructures are attracting close attention due to their excellent performance and great potential, including utilization in a variety of catalytic applications. Approaches, utilizing different industrial wastes as a starting material for the synthesis of SiC nanoparticles, are especially distinguished due to their environmental friendliness. This paper demonstrates a new two-stage technique of the preparation of dispersed SiC/C nanocomposite. A highly mineralized carbonaceous residue obtained by thermal processing of agricultural waste was used as a precursor for the synthesis in a pulsed arc discharge plasma. Rice husks, oat husks and oat straw were chosen as agricultural wastes with a high content of silicon in the mineral component. Carbonaceous residues (biochars) were obtained from the selected wastes by oxidative carbonization in a reactor with a fluidized bed of a deep oxidation catalyst at 460 °C. High-energy (up to 20 kJ) treatment of the obtained biochars in a pulsed (up to 1 ms) arc discharge plasma jet resulted in synthesizing a nanodispersed material (particle size <50 nm) containing hexagonal silicon carbide α-SiC. The principal possibility of using the synthesized SiC-based composite as a catalyst and cocatalyst of platinum in the hydrogen evolution reaction (HER) of water splitting is shown. The most impressive results (η 10 = 18–28 mV, η 100 = 84–98 mV, b = 32–64 mV) comparable with standard commercial Pt/C samples were obtained by modifying the synthesized SiC-based composite with 5 % platinum. Thus, the developed approach allows us to convert the agricultural waste into useful high-tech products in the form of an electrocatalytically active material. [Display omitted] • A new two-stage approach provides SiC/C nanocomposite from Si-containing biomass. • The proposed approach is almost CO 2 -neutral when utilizing plant agricultural waste. • Pt-modified SiC/C composites has a high activity in HER reaction of water splitting. • Catalytic performance and stability of Pt/SiC/C is almost equal to commercial Pt/C. [ABSTRACT FROM AUTHOR]

Substrate and catalyst free gas-phase plasma synthesis of freestanding few-layer graphene (FLG) flakes leads to crumpled FLG structures. In this paper, we elucidate a folding-based mechanism and structure-formation process in accordance with literature on the stability of graphene sheets. Transmission electron microscopy is applied to thermophoretically-sampled FLG at various distances from the plasma zone. Single-layer and few-layer graphene were observed, and a morphology pattern evolution could be discerned. A conceptual model of graphene formation and growth is derived, starting from initial rounded single-layer graphene of a few hundred nanometer in diameter to, eventually, self-folded and strongly crumpled FLG. [Display omitted] • Plasma synthesis and TEM images to study growth of free-standing few-layer graphene. • Experimentally demonstrated how outer shape of graphene flakes form and evolve. • First single-layer free-standing graphene sheets have a rounded shape. • Single-layer graphene sheets crumple/self-fold to form larger crumpled structures. • It seems to exist a maximum diameter for a single unfolded graphene layer (≤370 nm). [ABSTRACT FROM AUTHOR]

This article reports the synthesis of tungsten nanoparticles predominantly in α-W phase by a single step plasma expansion technique. The oxidation of the metal and contribution from the β-W phase in the nanomaterial samples was observed to decrease with the increase of both the pressure in the sample collection chamber and the plasma power. We had observed production of faceted, lightly sintered particles with up to 300 nm individual sizes during high plasma current/high pressure synthesis conditions, which were measured to have the highest specific surface area of 35 m 2 /g. Condensation of this high temperature material at low saturation ratio and the high collisional regime had led to the synthesis of relatively bigger particle sizes in this experiment. Cauliflower like particle morphologies was observed during low pressure synthesis conditions, which is considered to have formed through spherulitic growth processes. Transmission Electron Microscopy (TEM) micrographs show very small crystallites remaining dispersed in an amorphous moss like the background, which was confirmed to be a mixture of tungsten and its oxides. [ABSTRACT FROM AUTHOR]

The evolution of magnetic phases in multi-phase iron oxide nanoparticles, synthesized via the transferred arc plasma induced gas phase condensation method, was investigated by X-ray diffraction, vibrating sample magnetometry and 57 Fe Mössbauer spectroscopy. The particles are proposed to be consisting of three different iron oxide phases: α-Fe 2 O 3 , γ-Fe 2 O 3 and Fe 3 O 4 . These nanoparticles were exposed to high temperature (∼935 K) under vacuum (10 −3 mbar He pressure), and the thermally induced phase transformations were investigated. The Rietveld refinement of the X-ray diffraction data corroborates the least-squares fitting of the transmission Mössbauer spectra in confirming the presence of Fe 3 O 4 , γ-Fe 2 O 3 and α-Fe 2 O 3 phases before the thermal treatment, while only Fe 3 O 4 and α-Fe 2 O 3 phases exist after thermal treatment. On thermal annealing in vacuum, conversion from γ-Fe 2 O 3 to Fe 3 O 4 and α-Fe 2 O 3 was observed. Interestingly, we have observed a phase transformation occurring in the temperature range ∼498 K–538 K, which is strikingly lower than the phase transformation temperature of γ-Fe 2 O 3 to α-Fe 2 O 3 (573–623 K) in air. Combining the results of Rietveld refinement of X-ray diffraction patterns and Mössbauer spectroscopy, we have attributed this phase transformation to the phase conversion of a metastable “defected and strained” d- Fe 3 O 4 phase, present in the as-prepared sample, to the α-Fe 2 O 3 phase. Stabilization of the phases by controlling the phase transformations during the use of different iron-oxide nanoparticles is the key factor to select them for a particular application. Our investigation provides insight into the effect of temperature and chemical nature of the environment, which are the primary factors governing the phase stability, suitability and longevity of the iron oxide nanomaterials prepared by the gas-phase condensation method for various applications. [ABSTRACT FROM AUTHOR]

We have used high heat flux plasma synthesis process to grow Co those for the morphology, stoichiometry and the local structure as a function of plasma current. We find that the nanoparticles produced by the thermal plasma method have different shapes and size distribution with the plasma current being a key parameter in controlling the formation of composition, morphology and crystalline structure. X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) measurements at Co K-edge have revealed formation of metal and metal oxide nanoparticles with the composition mainly depending on the arc current. While low plasma current appears to produce nanoparticles solely of CoO with a small amount of Co metal, the high plasma current tends to produce nanoparticles of CoO and Co 3 O 4 oxides with increased amount of Co metal. The results are consistent with the morphological and structural analysis, showing nanoparticles of different shapes and size depending on the arc current. [ABSTRACT FROM AUTHOR]

We report a versatile route for the preparation of metal phosphides using PH 3 plasma for supercapacitor applications. The high reactivity of plasma allows rapid and low temperature conversion of hydroxides into monometallic, bimetallic, or even more complex nanostructured phosphides. These same phosphides are much more difficult to synthesize by conventional methods. Further, we present a general strategy for significantly enhancing the electrochemical performance of monometallic phosphides by substituting extrinsic metal atoms. Using NiCoP as a demonstration, we show that the Co substitution into Ni 2 P not only effectively alters the electronic structure and improves the intrinsic reactivity and electrical conductivity, but also stabilizes Ni species when used as supercapacitor electrode materials. As a result, the NiCoP nanosheet electrodes achieve high electrochemical activity and good stability in 1 M KOH electrolyte. More importantly, our assembled NiCoP nanoplates//graphene films asymmetric supercapacitor devices can deliver a high energy density of 32.9 Wh kg −1 at a power density of 1301 W kg −1 , along with outstanding cycling performance (83% capacity retention after 5000 cycles at 20 A g −1 ). This activity outperforms most of the NiCo-based materials and renders the NiCoP nanoplates a promising candidate for capacitive storage devices. [ABSTRACT FROM AUTHOR]

Amorphous carbon nitride (ACN) is a promising semiconductor photocatalyst for photocatalytic H 2 O 2 production. However, its actual activity is hindered by a high recombination rate of photoexcited charge carriers. Herein we report a K-doped ACN (K-ACN) photocatalyst synthesized via Ar plasma treatment to the modified melamine and KCl powder mixture at a moderate temperature. The as-synthesized K-ACN exhibits significantly enhanced photocatalytic properties for H 2 O 2 production with a yield of 6.21 mM h−1, which is 6 times higher than that of bulk CN. Moreover, the H 2 O 2 yield can be further increased to 13.95 mM h−1 by adjusting the pH value. The significantly enhanced photocatalytic property is mainly attributed to the introduction of K+, which is conducive to tuning the electronic structure, extending π conjugated system, passivating trap states and enhancing photocatalytic activity. The result has provided a facile and effective strategy for the modification of ACN to significantly boost its photocatalytic activity. [Display omitted] • K-ACN photocatalyst was synthesized via Ar plasma treatment to the modified melamine and KCl powder mixture. • The as-synthesized K-ACN exhibits 6-fold photocatalytic H 2 O 2 production relative to pristine carbon nitride. • The passivated trap states were observed in K-ACN and result in faster transport of light-induced active electrons. • K doping is conducive to tuning the electronic structure and enhanceing photocatalytic activity of ACN. [ABSTRACT FROM AUTHOR]

With the emerging climate and environmental problems, it is necessary to develop renewable energy technologies to alleviate the energy crisis. As one of the most promising technologies for hydrogen production, electrocatalytic water splitting has received extensive research attention in recent years, with efficient electrocatalysts as the key to realizing large-scale hydrogen production. After decades of development, non-noble metal-based materials have been widely studied in the fabrication of water splitting catalysts, while these materials still need to be improved compared to commercial noble metal catalysts. Among the many existing electrocatalyst modification strategies, low temperature plasma technology stands out due to the low energy consumption, high efficiency, and low chemical waste generation. Recent advances in the development and application of low temperature plasma technology in the synthesis and modification of electrocatalytic materials for water electrolysis is highlighted. It is expected to provide reference for the design and research of electrode materials in electrocatalytic water splitting with plasma-assisted technologies. [Display omitted] [ABSTRACT FROM AUTHOR]

Owing to the direct activation of reactant species, plasma has been playing an important role in surface engineering in recently years, especially for production of nano-materials. Herein, molybdenum derived nano-fiber films have been synthesized via thermal plasma method under the irradiation of dense helium plasma. Surface composition of the nano-fiber films can be controlled by following plasma treatment or chemical reaction to produce molybdenum nitrides or molybdenum oxides while the nanofiber structure is retained. When applied as substrates for the Raman detection of Rhodamine 6G molecule (R6G), the Mo nano-fiber film with amorphous MoO x layer on surface showed strong SERS effect, by pushing the detection limit of R6G from 10−4 M to 10−7 M, while those with MoO 3 and Mo 2 N surface compositions only displayed very weak or none SERS effect. These results indicated that the surface composition of the nano-fiber molybdenum films rather than surface structure plays an important role regarding to their SERS performance. Thermal plasma synthesized molybdenum-derived nano-fiber films and the influence of surface composition regulation on their SERS performance. [Display omitted] • In-situ growth of nano-fiber structures on molybdenum surface using thermal plasma method. • Surface composition regulation to obtain molybdenum oxide (MoO x , MoO 3) or molybdenum nitride (Mo 2 N). • Different surface compositions show different SERS performances towards the Raman detection of Rhodamine 6G molecules. • Amorphous MoO x coated molybdenum nano-fiber substrate showed strong SERS effect. [ABSTRACT FROM AUTHOR]

The β-cyclodextrin/Al(OH) 3 composites (β-CD/Al(OH) 3 ) were synthesized using the plasma-induced grafting technique and were employed to remove UO 2 2 + from aqueous solutions under ambient conditions. Based on the characteristic results of SEM, FT-IR, XRD, and TGA techniques, β-CD was satisfactorily grafted onto the Al(OH) 3 surface. The maximum adsorption capacity of β-CD/Al(OH) 3 composites calculated from Langmuir model at pH 6.0 and 303 K was 63.29 mg/g, which was significantly higher than Al(OH) 3 (23.31 mg/g). The high adsorption capacity of β-CD@Al(OH) 3 composites was due to the inner cores of the hydrophobic cavity of CD incorporated with UO 2 2 + ions. The calculated thermodynamic parameters showed that the adsorption of UO 2 2 + on Al(OH) 3 and β-CD@Al(OH) 3 composites was an endothermic and spontaneous process. The batch desorption indicated that the adsorption of UO 2 2 + on β-CD@Al(OH) 3 composites was an irreversible process. Based on the surface complexation modeling, the adsorption mechanism of UO 2 2 + on Al(OH) 3 and β-CD@Al(OH) 3 composites was outer-sphere surface complexation at pH < 5.0, whereas inner-sphere surface complexation dominated the UO 2 2 + adsorption on Al(OH) 3 and β-CD@Al(OH) 3 composites at pH > 6.0. These observation showed that β-CD/Al(OH) 3 composite can be used as a promising adsorbent for the preconcentration and immobilization of UO 2 2 + ions in environmental pollution cleanup. [ABSTRACT FROM AUTHOR]

Abstract: Quantum confined silicon nanoparticles (SiNPs) may allow for the fabrication of an all silicon multiple junction photovoltaic cell, or novel photovoltaic cells that surpasses the single junction limitations. One method of growing SiNPs is by PECVD where the plasma is confined to a quartz tube. To further understand this technique, computational fluid dynamic calculation were coupled with experimental growths, which allows for the development of a phase diagram based around the reactor pressure, and gas flow. SiNP size and crystallinity were evaluated using a combination of Raman scattering, X-ray diffraction, and transmission electron microscopy (TEM), these results were used to further the develop the phase diagram. For residence times less than 1ms, SiNPs were produced a band gap of >1.6eV, but very low crystallinity. By maintaining a constant low gas flow (100sccm) and increasing reactor pressure, crystallinity and size of the SiNPs were improved and increased, respectively. For SiNPs grown with a constant residence time (~2ms), we observe a reduction in the crystallinity with increased gas flow. Closer inspection by TEM showed a significant amount of a-Si with the SiNPs. Using this growth technique we can reliably grow SiNPs with diameters from 3nm to 8nm, relating to a photoluminescence peak position from 1.6eV to 1.3eV. This range is ideal for the development of an all silicon tandem photovoltaic cell. [Copyright &y& Elsevier]

Highlights: [•] Nonagglomerated TiO2 and SiO2 nanoparticles are generated in a plasma reactor. [•] Electrostatic deposition enables fast fabrication of films with highly uniform pore structures. [•] Particle agglomeration strongly affect the pore structure of film. [•] Pore sizes of films can be tuned by only changing the diameter of nanoparticles. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, the effect of ambient gas species on the characteristics of the produced nanoparticles in wire explosion process is reported. Cu wires with a diameter of 125 μm and length of 6.1 cm were exploded in different ambiances of Ar and admixtures of Ar and N2 at 500 mbar pressure. Immediate formation of arc plasma is observed for Ar ambiance. On the other hand, considerable delay in formation of arc plasma is observed for the admixtures of Ar and N2. The arc plasma formation time is found to increase with increasing N2 concentration in the admixture. Transmission electron microscope and X-ray diffraction were used to characterize the produced nanoparticles. Among the nanoparticles produced in different ambient gas species, the nanoparticles produced in Ar ambiance have higher particle size compared to admixtures of Ar and N2. The particle size is found to reduce with increasing N2 concentration in the ambiance. Difference in arc plasma formation time is probably the factor that gives rise to the difference in the particle sizes. [Copyright &y& Elsevier]

Abstract: Nanoparticles of crystalline, phase-pure γ-alumina is synthesized in a supersonically expanded thermal plasma jet assisted experimental chemical reactor, with good control over the average particle sizes independently with respect to plasma current, oxygen flow rate and the ambient pressure in the sample collection chamber. Most of the synthesized particle samples were seen to be transparent, which gets more transparent with decrease in the particle sizes. The lowest achievable pressure in the chamber had produced particles with average 10 nm sizes, which was best also in terms of narrow size distribution. Another important observation was the absence of serious inter-particle agglomeration, producing free-flowing particles. Optical emission spectroscopic technique was used to study the plasma chemistry of the reaction zone as well as the plasma jet. [Copyright &y& Elsevier]

Abstract: Nanoparticles of copper and copper oxide were synthesized by wire explosion technique in the environment of different ambient air pressure. Copper wire with a diameter of 125 μm and 6.1 cm in length has been exploded in air at 1 bar, 500 mbar, 100 mbar and 50 mbar. Current density in the order of 106 A cm−2 has been applied to disintegrate the wire by discharging a 1.85 μF capacitor at 10 kV. It is found that the particle size distribution for nano-sized particles follows the log-normal distribution and the median diameter is found to decrease from 31.3 nm to 23.6 nm as the pressure is decreased from 1 bar to 50 mbar. [Copyright &y& Elsevier]

Abstract: A study was carried out into the processing of Mg-10 vol.% Ti powder mixture for hydrogen storage purposes. Two processing routes were evaluated; mechanical milling and plasma synthesis. Mechanical milling, carried out with a high speed planetary mill, yielded a particulate structure made up of large Mg agglomerates, 90–100 μm, with embedded Ti fragments of approx. 1 μm in size with a uniform distribution. Mg agglomerates were made up of coherently diffracting volumes that were less than 50 nm in size. Plasma processing was carried out with an RF plasma torch of 25–27 kW applied power, the powder mixtures fed with 1–3 g/min axially into the torch. The mixture Mg-10 vol.% Ti after plasma processing comprised Mg powders which were extremely fine, <100 nm. Ti occurred as separate particles mixed with Mg nanopowders. The powders had a coherently diffracting volumes that were comparable to the size of the particles themselves indicating that the plasma processing yields relatively defect free crystals. The formation of the nano-size particulate structures is evaluated with regard to their possible implications on the hydrogenation of Mg–Ti alloys. [ABSTRACT FROM AUTHOR]

Abstract: Magnetic nanoparticles of iron oxide were synthesized by transferred arc plasma induced gas phase condensation method. Structural, morphological and magnetic studies of the as synthesized powder were carried out using X-ray diffraction, transmission electron microscopy and Mössbauer spectroscopy. These studies have revealed the simultaneous nucleation and condensation of different magnetic phases with a broad size distribution of the nanoparticles which is peaked at 30–50 nm and ranges from 10 nm to 80 nm. 57Fe Mössbauer spectra recorded at various temperatures (5 K–300 K) in presence of external magnetic field (at 5 K) have suggested the presence of different phases of iron oxide with sizable amounts of γ-Fe2O3 and α-Fe2O3 in addition to Fe3O4. The relative concentrations of these phases have been obtained by a self consistent spectral area analysis and were found to be 44:22:34 (%). [Copyright &y& Elsevier]

Si–Ti–N coatings with various compositions were deposited on molybdenum substrates using hypersonic plasma particle deposition (HPPD). In this method, vapor phase precursors (TiCl4, SiCl4 and NH3) are dissociated in a DC plasma arc and the hot gas is quenched in a rapid nozzle expansion to nucleate nanoparticles. These nanoparticles are then accelerated in hypersonic flow, causing them to deposit by ballistic impaction on a substrate placed downstream of the nozzle. Films of 10–25 μm thickness were deposited at rates of 2–10 μm/min, depending on reactant flow rates, at substrate temperatures ranging from 200 to 850 °C. When the reactant gases were premixed the coatings consisted of nc-TiN, nc-TiSi2, nc-Ti5Si3 and amorphous Si3N4. For the unpremixed reactants case, the coatings consisted of free Si, nc-TiN and amorphous Si3N4. Hardness of as-deposited films was evaluated by nanoindentation of polished film cross-sections. Measured hardness values, averaged over 10–15 locations for each film, ranged from 16–24 GPa.In separate experiments with the same conditions, particle size distributions were measured by placing a sampling probe at the same location as the film substrate. The sampled aerosol was rapidly diluted and delivered to a scanning mobility particle sizer (SMPS). In-situ particle size distribution measurements confirmed that the coatings were formed by impaction of nanoparticles in the 5–15 nm range, with higher reactant flow rates producing larger particles.Focused ion beam (FIB) milling was used to observe film cross-section and porosity. For as-deposited films containing pores, in-situ plasma sintering was used to densify the film without grain growth. [Copyright &y& Elsevier]

Hydroxyapatite (HA)/nano-zirconia composite coatings were successfully produced through high velocity oxy-fuel (HVOF) spraying of radio frequency (RF) plasma synthesized powders. Microstructure characterization and morphology analysis on the nano-structured coatings were conducted using scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffractometry (XRD), and differential scanning calorimetry (DSC). Elastic modulus of the coatings was determined using nano-indentation on polished cross-sections, which revealed Young''s modulus value of ∼130 GPa. Results also showed that the nano-sized zirconia particles (<90 nm) did not coarsen drastically after HVOF deposition, and were uniformly distributed throughout the coating. The crystallite size of tetragonal zirconia in the coating was found to be less than 13 nm. Furthermore, HA phase decomposition and chemical reaction between HA and zirconia was virtually undetected, which is beneficial towards the biological performance of the coatings. XRD analysis together with Rietveld refinement quantitatively revealed the content of the phases present in the coatings, including ∼1.2 wt.% CaZrO3. The conversion temperature of amorphous calcium phosphate to HA was found to be ∼750 °C and the ancillary influence of the heat treatment on coating structure and properties were revealed. [Copyright &y& Elsevier]

Abstract: A method for synthesis of large quantities of iron oxide nanowires using low purity substrates is presented. One cm thick commercially available iron plates of purity 98 at.% were supplied from a steel company. The plates prepared by hot rolling contained several μm thick surface oxide films formed during industrial processing. Plates were cut to small samples and exposed to highly dissociated oxygen plasma and heated to elevated temperatures. The evolution of surface morphology on plasma treated samples was monitored by scanning electron microscopy. Nanowires of typical diameter about 20 nm and length of several μm grew on the substrate surface in a narrow temperature range and best results were obtained at about 1200 K. Higher temperature caused shortening and widening the nanowires. The results clearly show possibility for cheap manufacturing of iron oxide nanowires suitable for application in photovoltaics. [Copyright &y& Elsevier]

• A two-step plasma method has been proposed for nanomaterial synthesis; • Nano-fuzz tungsten nitride (W 2 N) layer has been prepared from tungsten sample; • The thickness of the nano-fuzz W 2 N layer is about 700 nm; • The core-shell W 2 N/W nano fibers are around 40 nm in diameter. Owing to the direct activation of reactant species, plasma has been playing a role in material synthesis and surface modification since the mid-1970s, especially for the production of nanomaterials. Tungsten nitride with nanostructures has attracted much attention for applications in catalysis and electrocatalysis, due to their noble metal-like properties. In this work, we propose a two-step strategy to prepare tungsten nitride (W 2 N) layer simply from tungsten sample by means of dense helium and nitrogen plasma treatment. Various surface characterization and cross-section analysis methods have confirmed the formation of W 2 N nano fuzz structure. After a sequential exposure to helium plasma for 20 minutes and nitrogen plasma for 30 minutes, corresponding to the ion fluence of 8.4 × 1025 m−2 and 2.3 × 1026 m−2 respectively, a nano-fuzzy layer with thickness of ~700 nm has been formed on tungsten surface and the core-shell structured W 2 N/W nano fibers are around 40 nm in diameter. The synthesis of nanostructured W 2 N via plasma environment has not only broadened the application of plasma methods, but also offers a facile and universal way for the design of materials with different morphologies and properties. [ABSTRACT FROM AUTHOR]

Nanocrystals sintering is a critical way to achieve full-densified compact with fine grain size, which is highly desired to improve its mechanical properties by grain boundaries strengthening. In this work, a one-step plasma synthesis strategy was developed to synthesize Mo nanopowder using ammonium molybdate as precursor, and the reaction could be completed by an ultrafast way in several seconds. As obtained products exhibit single-crystalline structure and quasi-spherical shape with size of about 30 nm. The sintering behavior of Mo nanoparticles was further investigated by isothermal and nonisothermal processes, and the results reveal that Mo compact experiences different grain growth and microstructure evolution at different sintering stages. Fully densified Mo compact (99.13%) with well suppressed grain growth of about 7 μm was obtained at a rather low temperature of 1500 °C, and kinetics analysis illustrates that the surface diffusion with low activation energy is responsible for the high sintering activity of nanosized powder at low temperature. • Mo nanoparticles were synthesized by a one-step and ultrafast way. • Fully densified Mo compact with well suppressed grain growth was obtained. • Surface diffusion mechanism is responsible for the high sintering activity. [ABSTRACT FROM AUTHOR]