Structural and optical characterization of mechanochemically synthesized copper doped CdS nanopowders

Incorporation of copper into CdS crystals has been successfully prepared by mechanical alloying using a planetary ball mill. The powders are prepared with different milling times at 300 rpm with various Cu/Cd ratios from 0.1 to 25 at%. X-ray diffraction (XRD) analysis of milled powders showed peaks corresponding to hexagonal structure with a detection of phase transition to a cubic structure with increasing milling time. Grain sizes varied from 21 to 30 nm corresponding to different Cu/Cd ratios. Field emission scanning electron microscopy (FESEM) images reveal agglomerated materials with particle size of approximately 28 nm (5 Cu at%) and layered structures caused due to the milling process. Powder composition by energy dispersive analysis of X-rays (EDAX) reveals the incorporation of copper into the CdS. Micro Raman spectroscopy showed peaks approximately at 301 and 585 cm⁻¹ corresponding to first and second order scatterings of longitudinal optical phonon mode. The LO mode at 301 cm⁻¹ shifted towards lower wave number due to decrease of grain size by increase in milling time. From high resolution transmission electron microscope (HRTEM), the dominant phase of individual CdS nanocrystals was found to be hexagonal structure along with cubic structure.     

Two new kinds of nanodiamonds with the structure of controlled sp3/sp2 carbon ratio and carbon atom dimer by the cleavage plane mechanical stripping crush separation preparation technology

Two new diamond nanostructures of nanoparticles and multilayer nanosheets were prepared through cleavage plane crush separation preparation technology by synthetic diamond as starting material. All samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), Raman spectroscopy (Raman), and ¹³C Solid-state Magic Angle Spinning Nuclear Magnetic Resonance (MASNMR). The influence of precipitation time on the particle size, crystalline, morphology, structure of the nanostructures was investigated. The crystalline phase of the final products was determined as diamond phase. More importantly, the morphology of nanodiamond was closely related to the structure. Nanoparticles consisted of carbon atom dimer structure on the surface, while the multilayer nanosheets contained unsaturated sp² hybridization carbon, and the unsaturated sp² hybridization carbon contents increased with increasing particle size. Possible formation mechanisms of diamond nanostructures with various structures and morphologies were proposed in detail.     

Effect of milling time,MWCNT content,and annealing temperature on microstructure and hardness of Fe/MWCNT nanocomposites synthesized by high-energy ball milling

Nanocrystalline pure Fe and Fe/MWCNT nanocomposites powders with 0.25, 0.5, 1, and 10 wt% MWCNT contents were synthesized by high-energy ball milling (HEBM). The as-milled powders were cold-compacted and annealed at 400 °C and 600 °C for 1 h in Ar atmosphere. The effect of ball milling on pristine MWCNT and Fe/MWCNT composite powders was also investigated as a function of milling time up to 20 h. The physical properties of MWCNT were imaged by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) before and after HEBM. The structural damage of MWCNT as a function of milling time and MWCNT content was studied using Raman spectroscopy. The structural characterization of MWCNT and Fe/MWCNT composites was conducted by X-ray diffraction (XRD) as a function of milling time, MWCNT content, and annealing temperature. The chemical properties of the synthesized composite powders were investigated using X-ray photoelectron spectroscopy (XPS). The microhardness test was performed to assess the effect of milling time, annealing temperature, and MWCNT content on the mechanical properties. The results indicated that after the ball milling process, the structure of MWCNT was destroyed, and the formation of the amorphous carbon phase was observed, which was confirmed by XRD and TEM analyses. In addition, decreased defect and carbon intensity ratios (I_D/I_G) were calculated from the Raman results with longer ball milling processes, which is attributed to the destruction of carbon bonds. The XPS results confirmed the presence of FeC bonds as a result of the formation of carbide phases. A fine dispersion of precipitated carbides determined by TEM is found to promote the grain size stability below 100 nm in the nanocrystalline Fe matrix. The results from the micro-hardness tests showed that Orowan particle strengthening resulting from the carbide formation, as well as grain size hardening, is an important contributor to strengthening in Fe/MWCNT composites.     

The Effect of Silver Inclusion on Superconducting Properties of YBa2Cu3O y Prepared Using Planetary Ball Milling

The effect of Ag inclusion on the structure microstructure and the critical current density of the YBa₂Cu₃O_7?δ sample prepared using the planetary ball milling process has been investigated. YBa₂Cu₃O_7?δ ceramics have been synthesized in air by a solid state reaction method from an oxide precursor powder, which was prepared from the starting powders of Y₂O₃, Ba₂CO₃, and CuO via a one-step annealing process in air at 950 ^°C. After planetary ball milling for 4 h of the oxide precursor powders, it was mixed with an AgNO₃ solution, and then was dried and uniaxially pressed, and subsequently annealed at 950 ^°C in air. Phase analysis by X-ray diffraction (XRD), granular structure examination by scanning electron microscopy (SEM), microstructure investigation by transmission electron microscopy (TEM) coupled with energy dispersive X-ray spectroscopy (EDXS) were carried out. To understand the effects of the ball milling on the pinning behavior, magnetic field and temperature dependences on a critical current density have been studied. Analyses show that Ag-milled YBCO samples exhibit higher values of critical current density in applied magnetic field compared to Ag-unmilled one. The better pinning properties of the Ag-milled samples are believed to be due to the microstructure of more fine and uniform distribution of silver and Y-deficient nanosized generated by ball milling.     

Electrochemical investigation of silicon/carbon composite as anode material for lithium ion batteries

Silicon-graphite composites were prepared by mechanical ball milling for 20 h under argon protection. The microstructure and electrochemical performance of the composites were characterized by X-ray diffraction (XRD), scanning electron microscopy, and electrochemical experiments. XRD showed that the materials prepared by ball milling were composites consisting of Si and graphite powders. The composite electrode showed the best performance, especially when annealed at 200 °C for 2 h, which had a reversible capacity of 595 mAh g⁻¹ and an initial coulombic efficiency of 66%, and still retained 469 mAh g⁻¹ after 40 cycles with about 0.6% capacity loss per cycle.     

Effect of dispersion method on the deterioration,interfacial interactions and re-agglomeration of carbon nanotubes in titanium metal matrix composites

The influence of various synthesis techniques on the dispersion and evolution of multi-walled carbon nanotubes (MWCNTs) in titanium (Ti) metal matrix composites (TMCs) prepared via powder metallurgy routes has been investigated. The synthesis techniques included sonication, high energy ball milling (HEBM), cold compaction, high temperature vacuum sintering and spark plasma sintering (SPS). Powder mixtures of Ti and MWCNTs (0.5 wt.%) were processed by HEBM in two batches: (i) ball milling of the mixtures (Batch 1) and (ii) ball milling of Ti powder alone, followed by a further ball milling with sonicated MWCNTs (Batch 2). Both batches of the powder mixtures were pressed at 40 MPa into green compacts and then sintered in vacuum. Batch 2 powder mixtures were also consolidated using SPS. The crystallinity and sp² carbon network of the MWCNTs were characterized through analyzing the characteristic Raman peak ratio (I_D/I_G) of each processed sample. X-ray diffraction (XRD) was used for phase identification. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to study the morphology of the MWCNTs in the powder mixtures. The evolution of MWCNTs during the fabrication process and mechanical properties of the sintered compacts were discussed in conjunction with the formation of nano-crystalline TiC.     

Thermally activated crystalline phase restoration in disordered barium ferrite powder prepared by ball milling

Depending on milling conditions (air or vacuum) for the same milling time, a different level of decomposition and structure disorder in BaFe₁₂O₁₉ ferrite powders can be obtained by ball milling. Air-milled material has a tendency to form a gas-saturated disordered structure (superoxide) and to transform into simple oxides (reduction process through oxygen-saturated disordered phase) as opposed to the vacuum-milled powder where a highly disordered phase occurs. Both powders have a different morphology (particle size and distribution). Annealing processes produce crystalline barium ferrite phase with interesting magnetic properties, but in the present paper only structural transformations are analysed. Scanning electron microscopy, X-ray diffraction and thermal analysis techniques were applied to study the effects of heat treatment (10 h at 773 or 1273 K) in disordered BaFe₁₂O₁₉ ferrite powders prepared by 1000 h ball milling in air and vacuum.     

Can the degree of crystallinity of ball-milled Mg2Ni intermetallic compound decide its electrochemical characteristics?

ABSTRACT

Nanostructured Mg₂Ni intermetallic compounds were synthesized by high-energy ball milling. Effect of milling time on structure and surface morphology of milled powders were studied using x-ray diffraction and scanning electron microscopy. Crystallite size and degree of crystallinity were confirmed by using transmission electron microscopy and selected area electron diffraction analysis. The particle size of 20 h milled electrode material is 230 nm and it reduced to 40 nm when the milling time is increased to 30 h. Further increase in the milling time reduces the particles size drastically and starts agglomerating. In order to understand the effect of milling time on reaction rates, differential thermal analysis was performed. Activation energy of the milled powders was calculated using Kissinger analysis. 30 h milled powder exhibits lower activation energy than others. Cyclic voltammetry, electrochemical impedance spectroscopy, and charge–discharge studies were done on the prepared electrode materials. 30 h milled electrode material delivers maximum discharge capacity with a superior capacity retention after 20 cycles at 20 mAg^?1.     

Formation of novel assembled silver nanostructures from polyglycol solution

This paper described a simple and mild chemical reduction approach to prepare novel silver nanostructures with different morphologies. Dendritic silver nanostructure was obtained by a fast reduction reaction using hydrazine as a reducing agent in aqueous solution of polyglycol, while both the zigzag and linear Ag nanostructures were slowly assembled using polyglycol as a reducing agent. Powder X-ray diffraction (XRD), transmission electron microscopy (TEM), high-resolution TEM (HRTEM) and field emission scanning electron microscopy (FE-SEM) were used to characterize the obtained silver nanostructures. Fourier transform infrared absorption (FT-IR) spectra were recorded to show that there exists a certain coordination of the oxygen atoms in the polyglycol with Ag⁺ ions in aqueous solution of the AgNO₃/polyglycol. Furthermore, the examination of the morphologies of the products obtained at different stages of the reaction of Ag⁺ ions with polyglycol revealed that such a coordination is of utmost importance for the formation of the silver nanostructures, namely polyglycol provided lots of active sites for the coordination, nucleation, growth and serves as backbones for directing the assembly of the metal particles formed. The formation mechanism of the dendritic silver nanostructure was called a coordination–reduction–nucleation–growth–fractal growth process. The strong surface plasmon absorption bands at 470 nm for the zigzag silver and at 405 nm for the dendritic silver were found.     

Synthesis and Characterization of CuNi Magnetic Nanoparticles by Mechano-Thermal Route

In the present investigation, Cu_0.5Ni_0.5 nanoparticles were synthesized using high energy ball milling of a mixture of Cu₂O, NiO, and graphite powders. The mixture of powders was milled up to 50 h. The 30 h milled sample was heat treated at various temperatures for 1 h in a vacuum tube furnace. The effects of milling time and heat treatment temperature on the powder particle characteristics were studied employing X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), differential thermal analysis (DTA), and vibrating sample magnetometer (VSM) techniques. XRD results indicated incomplete formation of Cu_0.5Ni_0.5 after 30 h of milling. Further heat treatment at 500 ^°C led to the formation of a single phase Cu_0.5Ni_0.5 powder. FESEM and TEM images of the heat treated sample showed spherical Cu_0.5Ni_0.5 nanoparticles with a mean particle size of 15 nm. Magnetic properties data measured by VSM of the above sample are correlated well with the XRD results. Coercivity and saturation magnetization have been approximately achieved at 25 Oe and 18 emu/g, respectively.     

Low temperature synthesis and photoluminescent properties of CaMoO4:Eu red phosphor with uniform micro-assemblies

Scheelite-type Eu³⁺-doped CaMoO₄ red phosphor with uniform micro-assemblies has been successfully synthesized via a facile hydrothermal method at 120 °C for 10 h. The Eu³⁺-doped CaMoO₄ microstructures were assembled by small nanostructures and the morphology of materials was found to be manipulated by dropping different alkalis into the stock solution for the first time. The structure, morphology, and luminescent property were characterized and investigated by techniques of X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), and photoluminescence (PL). The luminescent investigations confirmed that the Eu³⁺ ions have been effectively doped into CaMoO₄ nanostructures. The successfully achieved Eu³⁺-doped CaMoO₄ nanostructures will be potential in technological applications on near UV chip-based white light emitting diode (WLED).     

A simple route to synthesis of BaCO3 nanostructures in water/ethylene glycol mixed solvents

Barium carbonate (BaCO₃) nanostructures with different morphologies were synthesized using Ba(NO₃)₂ and (NH₄)₂CO₃ in the water/ethylene glycol (EG) mixed solvents by oil bath heating at 80 °C for 30 min. The molar ratio of water to EG had an effect on the morphology of BaCO₃. The products were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and high-resolution transmission electron microscopy (HRTEM).     

Production of Fe3Al–TiC nanocomposite by mechanical alloying of FeTi2–Al–C powders

Abstract

The aim of the present work was to produce Fe₃Al/TiC nanocomposite by mechanical alloying of the FeTi₂30Al10C60 (in at-%) powder mixture. The morphology and the phase transformations in the powder during milling were examined as a function of milling time. The phase constituents of the product were evaluated by X-ray diffraction (XRD). The morphological evolution during mechanical alloying was analysed using scanning electron microscopy (SEM). The results obtained show that high energy ball milling, as performed in the present work, leads to the formation of a bcc phase identified as Fe(Al) solid solution and an fcc phase identified as TiC and that both phases are nanocrystalline. Subsequently, the milled powders were sintered at 873 K. The XRD investigations of the powders revealed that after sintering, the material remained nanocrystalline and that there were no phase changes, except for the ordering of Fe(Al), i.e. formation of Fe₃Al intermetallic compound, during the sintering process.     

Growth mechanisms of SnO(2)/Sn nanocables

SnO(2)/Sn nanocables have been grown on single-crystal Si substrates by metal catalyst assisted thermal evaporation of SnO powders. The morphologies and structures of the prepared nanocables were determined on the basis of field emission scanning electron microscopy (FESEM), high-resolution transmission electron microscopy (HRTEM), x-ray diffraction (XRD), Raman and photoluminescence (PL) spectra analyses. The microstructures and compositions of the top and bottom regions of the SnO(2)/Sn nanocables were identified by HRTEM in detail, which revealed some basic physical and chemical processes involved in the formation of the nanocables. A growth model was proposed to address the formation of SnO(2)/Sn nanocables on the basis of the vapour-liquid-solid (VLS) process.     

Synthesis of CeB6 thin films by physical vapor deposition and their field emission investigations

High quality CeB₆ thin films have been obtained through direct evaporation of raw micron-sized CeB₆ powders at a pressure of 70 Pa. The X-ray diffraction (XRD), Raman spectrum, scanning electron microscope (SEM), transmission electron microscopy (TEM), selected-area electron diffraction (SAED) and the field-emission equipment were used to characterize the morphology, structure, composition and FE properties of the samples. The XRD and Raman spectrum analysis results show the as-prepared product is cubic phase CeB₆. The TEM, SAED and HRTEM analysis reveal that the samples are mixtures of thin films (polycrystalline) and small crystals (single crystallines aligned preferentially in the [1 1 0] direction). Compared to oxide nanostructures, field-emission measurements show that the CeB₆ films have better FE performance with turn-on field and threshold field of 12.93 V/μm and 14.86 V/μm, respectively.     

Low-temperature hydrothermal synthesis of α-MnO2 three-dimensional nanostructures

Single-crystalline α-MnO₂ three-dimensional nanostructures were synthesized via a novel redox reaction of KMnO₄ and Cr(NO₃)₃ under hydrothermal conditions. The products were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), energy-dispersive spectroscopy (EDS), and high-resolution transmission electron microscopy (HRTEM). The addition of HNO₃ into the reaction has a significant effect on the morphologies of the final products. The α-MnO₂ three-dimensional nanostructures were obtained under the acidic condition, while α-MnO₂ nanowires were obtained without the addition of HNO₃. A mechanism for the growth of α-MnO₂ three-dimensional nanostructures was proposed.     

Effect of milling time in characteristics of the powder Cu-5wt.%Graphite

Composites of Cu-5wt.%Graphite were prepared by high-energy milling, under argon atmosphere for milling time of up to 50 h, to investigate the influence of the milling time on the size and dispersion of the copper and carbon phases. The formation of a monophasic carbon-copper solid solution was also investigated. The powder samples were collected at different times and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM and FESEM), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDS) and Raman spectroscopy. Composite particles were formed by fragments of graphite embedded in the soft Cu matrix. After 50 h of milling, the Cu phase had a crystallite size of 24 nm and micro-strain of 0.26 %. The lattice parameter showed a reduction of 0.001545 nm and reached a value of 0.360152 nm. Furthermore, no carbon diffraction peak was observed in the milled powders, due to the small graphite crystallites. Meanwhile, the Raman spectra showed that the carbon phase remains crystalline, even after 50 h of milling. When the composite was annealed at 600 °C, for 1 h and under argon atmosphere, no carbon precipitate was observed. These results suggest the absence of the formation of a solid solution of carbon in copper.     

Probing the structure of nanograined CuO powders

The microstructural properties of polycrystalline CuO powders and their evolution during controlled high energetic ball milling (HEBM) were studied using conventional X-ray diffraction (XRD) techniques and in situ temperature-dependent small and wide angle scattering (SAXS–WAXS) synchrotron radiation experiments. Volume weighted average grain size, unit cell expansion, oxygen deficiency, and microstrain values as a function of milling time were obtained from XRD. SAXS data revealed different nanostructures for samples synthesized by one-step solid-state reaction (SSR) or HEBM-treated powders. The latter presented the characteristics of a multilayered nanoscale solid system with surface fractal behavior. Correlation of the XRD microstructural parameters and the power law exponent of the SAXS curves as a function of temperature and milling time provided a coherent picture of the structure of HEBM-treated powders. The overall structural information presented in this article may shed some light on the macroscopic physical properties of CuO nanostructures.     

Mechanochemical synthesis and characterization of nanocrystalline 0.4Bi(Zn1/2Ti1/2)O3-0.6PbTiO3 powders

Perovskite 0.4Bi(Zn_1/2Ti_1/2)O₃-0.6PbTiO₃ (BZT-PT) powders were successfully synthesized from precursor oxides using a high-energy planetary ball milling. The phase development of the powders during milling was studied by means of X-ray diffraction and Raman scattering techniques. The microstructure of the powders was characterized using transmission electron microscopy, and the thermal behavior was studied as well. The results reveal that after 15 h of milling the formation of BZT-PT phase can be completed and submicron agglomerates of small crystallite sized ~ 12 nm are present in the powders. However, further prolonging the milling time to 25 h leads to the amorphization of the BZT-PT phase.     

Mechanochemical assisted synthesis of B4C nanoparticles

The present work reports on the preparation of boron carbide nanoparticles by the reduction of boron oxide with magnesium in the presence of carbon using the mechanochemical processing. The phase transformation and microstructure of powders during ball milling were investigated by X-ray diffractometry (XRD) and scanning electron microscopy (SEM). The results showed that during ball milling the B₂O₃–Mg–C reacted with a self-propagating combustion mode producing MgO and B₄C compounds. To separate B₄C from the milled powder mixture, an appropriate leaching process was used. After leaching, the purified powder mixture was characterized using XRD and transmission electron microscope (TEM). XRD studies indicated that the prepared particles were single phase crystalline B₄C. Moreover, TEM studies showed the size of B₄C particles were ranging from 10 to 80 nm.