Reaction mechanisms,resultant microstructures and tensile properties of Al-based composites fabricated in situ from Al-SiO2-Mg system

Reaction mechanisms, microstructures and tensile properties of the aluminum matrix composites made from Al-SiO₂-Mg system were investigated. When the temperature increased from room temperature to around 761 K, Mg dissolved into Al to form Mg-Al alloy. As the temperature increased to about 850 K, the remaining Mg reacted with SiO₂ to form MgO, Mg₂Si and Si as expressed in step reaction I: 6Mg + 2SiO₂ → 4MgO + Mg₂Si + Si. Finally, with a further increase in temperature, the remaining SiO₂ reacted with Al to produce Al₂O₃ and Si, while MgO reacted with Al₂O₃ to form MgAl₂O₄ as expressed in step reaction II: 4Al + 3SiO₂ + 2MgO → 2MgAl₂O₄ + 3Si. The Si also dissolved into matrix Al to form Al-Si alloy. Accordingly, its reaction process consisted of two steps and their apparent activation energies were 218 kJ/mol and 192 kJ/mol, respectively. As compared to the composites prepared by Al-SiO₂ system, its density increased from 2.4 to 2.6 g/cm³, and its tensile strength and elongation increased from 165 MPa and 3.95% to 187 MPa and 7.18%, respectively.     

Magnetic separation and adsorptive performance for methylene blue of mesoporous NiFe2O4/SBA-15 nanocomposites

Magnetic NiFe₂O₄/SBA-15 nanocomposites were synthesized by a facile impregnation method, and NiFe₂O₄ nanoparticles presented spinel phase structure and existed in the mesopores of SBA-15. Partial mesopores were blocked by NiFe₂O₄ nanoparticles and micropores formed, which the capillarity of micropores played a decisive role for methylene blue (MB) adsorption. The saturation magnetization increased from 2.34 emu g^?1 to 10.03 emu g^?1 with the NiFe₂O₄ content, while the specific surface area decreased from 552.18 m² g^?1 to 260.40 m² g^?1 and pore volume decreased from 1.13 cm³ g^?1 to 0.49 cm³ g^?1. MB adsorption could be improved by optimizing the NiFe₂O₄ content of the nanocomposites. MB could be adsorbed completely in 60 min with the optimum nanocomposites and could be separated easily from water by magnetic separation technique.     

High efficiency visible-light-driven Fe2O3-xSx/S-doped g-C3N4 heterojunction photocatalysts: Direct Z-scheme mechanism

Several nanoporous Fe_2 O_3-xSx/S-doped g-C_3 N_4(CNS) Z-scheme hybrid heterojuctions have been successfully synthesized by one-pot in situ growth of the Fe_2O_3-xSx particles on the surface of CNS. The characterization results show that S-doping in the g-C3 N4 backbone can greatly enhance the charge mobility and visible light harvesting capability. In addition, porous morphology of hybrid composite provides available open pores for guest molecules and also improves light absorbing property due to existence of multiple scattering effects. More importantly, the Fe_2 O_3-xSx nanoparticles formed intimate heterojunction with CNS and developed the efficient charge transfer by extending interfacial interactions occurred at the interfaces of both components. It has been found that the Fe_2 O_3-xSx/CNS composites have an enhanced photocatalytic activity under visible light irradiation compared with isolated Fe_2 O_3 and CNS components toward the photocatalytic degradation of methylene blue(MB). The optimal loaded Fe_2 O_3-xSx value obtained is equal to 6.6 wt% that provided 82% MB photodegradation after 150 min with a reaction rate constant of 0.0092 min~(-1) which was faster than those of the pure Fe_2 O_3(0.0016 min~(-1))and CNS(0.0044 min~(-1)) under the optimized operating variables acquired by the response surface methodology. The specific surface area and the pore volume of Fe_2 O_3(6.6)/CNS hybrid are 33.5 m~2/g and0.195 cm~3/g, which are nearly 3.8 and 7.5 times greater compared with those of the CNS, respectively. The TEM image of Fe_2 O_3(6.6)/CNS nanocomposite exhibits a nanoporous morphology with abundant uniform pore sizes of around 25 nm. Using the Mott-Schottky plot, the conduction and valence bands of the CNS are measured(at pH = 7) equal to-1.07 and 1.48 V versus normal hydrogen electrode(NHE), respectively.Trapping tests prove that ·OH-and ·O_2-radicals are major active species in the photocatalytic reaction.It has been established that formation of the Z-scheme Fe_2 O_3(6.6)/CNS heterojunction between CNS and Fe_2 O_3 directly produces ·OH as well as ·O_2-radicals which is consistent with the results obtained from trapping experiments.     

Stabilization of SnO2 nanoparticles into the nanopores of modified Montmorillonite and their antibacterial activity

Metals and metal oxide nanoparticles clay supported composites arouse much interest in recent time. In this communication, we report the insitu synthesis of SnO₂ nanoparticles by impregnation of SnCl₂.2H₂O into the nanopores of modified Montmorillonite followed by polyol reduction and aerial oxidation. The modified Montmorillonite having nanopores act as a ‘Host’ for the SnO₂ nanoparticles. The TEM study reveals that SnO₂ nanoparticles having size <10 nm are evenly distributed on the support. The XPS results show that the binding energy peaks at 490 and 498.2 eV are due to Sn3d_5/2 and Sn3d_3/2 respectively indicating the presence of Sn⁴⁺ in the SnO₂ nanoparticles. Elemental dot mapping indicate the presence of Al, Si, O and Sn on the surface of AT-Mont. supported SnO₂ nanoparticle. The synthesized SnO₂ nanoparticles show antibacterial activity against gram +ve and gram ?ve bacterial strains.     

High performance magnetically recoverable g-C3N4/Fe3O4/Ag/Ag2SO3 plasmonic photocatalyst for enhanced photocatalytic degradation of water pollutants

The g-C₃N₄/Fe₃O₄/Ag/Ag₂SO₃ nanocomposites have been successfully fabricated by facile refluxing method. The as-obtained products were characterized by XRD, EDX, SEM, TEM, UV–vis DRS, FT–IR, TGA, PL, and VSM techniques. The results suggest that the Ag/Ag₂SO₃ nanoparticles have anchored on the surface of g-C₃N₄/Fe₃O₄ nanocomposite, showing strong absorption in the visible region. The evaluation of photocatalytic activity indicates that for the g-C₃N₄/Fe₃O₄/Ag/Ag₂SO₃ (40%) nanocomposite, the degradation rate constant was 188 × 10^?4 min^?1 for rhodamine B, exceeding those of the g-C₃N₄ (16.0 × 10^?4 min^?1) and g-C₃N₄/Fe₃O₄ (20.2 × 10^?4 min^?1) by factors of 11.7 and 9.3, respectively. The results showed that the nanocomposite prepared by refluxing for 120 min has the superior photocatalytic activity and its activity decreased with rising the calcination temperature. The trapping experiments confirmed that superoxide ion radical was the main active species in the photocatalytic degradation process. Also, it was demonstrated that the magnetic photocatalyst has considerable activity in degradation of one more dye pollutant. Finally, the reusability of the photocatalyst was evaluated by five consecutive catalytic runs. This work may open up new insights into the utilization of magnetically separable nanocomposites and provide new opportunities for facile fabrication of g-C₃N₄-based plasmonic photocatalysts.     

Co2(OH)3Cl nanoparticles as new-type electrode material with high electrochemical performance for application in supercapacitor

In this work, we report the preparation of Co₂(OH)₃Cl nanoparticles with average size of ～20 nm and well-defined cubic shape at room temperature by an epoxide precipitation route. It was found that the as-prepared Co₂(OH)₃Cl nanoparticles could be used as a promising new electrode material for application in redox supercapacitors due to its high electrochemical performance. It presented superior specific capacitance of 783 F g^?1 at low current density of 2.8 A g^?1, while it had a high value of 604 F g^?1 at high current density of 56.6 A g^?1, proving its excellent high rate performance. Its 75% capacitance retention after 10,000 cycles of charge–discharge demonstrated its long-life span. According to characterization results, the possible mechanism for the electrochemical process that Co₂(OH)₃Cl nanoparticles underwent was proposed as a process of Co₂(OH)₃Cl → β-Co(OH)₂ → CoOOH ? Co₃O₄.     

Synthesis and characterization of novel magnetically separable NiFe2O4@AlMCM-41-Cu2O core-shell and its performance in removal of dye

The synthesis of magnetic NiFe₂O₄@AlMCM-41-Cu₂O core-shell as a new class of visible light driven photocatalyst was suggested. The magnetic NiFe₂O₄ core was prepared by solvothermal method. The intermediate AlMCM-41 shell was prepared by the method of liquid crystal templating mechanism and subsequently cuprous oxide (Cu₂O) nanoparticles (NPs) were synthesized in NiFe₂O₄@AlMCM-41core-shell via colloidal chemistry approach. The properties of prepared magnetic core-shell were characterized by scanning electron microscope (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), nitrogen adsorption–desorption measurement and vibration sample magnetometer (VSM). Based on EDX results, the weight percentage (wt%) of NiFe₂O₄ core, MCM-41 shell and Cu₂O NPs were calculated to be 68.89, 30.55 and 0.56%, respectively. It consisted of mesoporous structure with a surface area of 687.00 m² g^?1, an average pore size of 2.95 nm and possessed excellent magnetic properties of 4.74 emu g^?1. The TEM results indicated that the NiFe₂O₄ as core were regular spheres with diameter of 68 nm, and the average thickness of AlMCM-41 shells was ～35 nm. The particles size of Cu₂O incorporated in core-shell was less than 5 nm. The photocatalytic activity was evaluated under visible light irradiation using the removal of methylene blue (MB) dye as a model reaction. The removal rate of MB achieved up to 90% after 60 min under visible light irradiation, and the NiFe₂O₄@AlMCM-41-Cu₂O can be recycled and reused.     

Synthesis of titanium carbide and TiC–SiO2 nanocomposite powder using rutile and Si by mechanically activated sintering

High-energy ball milling was applied with subsequent heat treatment for synthesizing nanoparticles of TiC powders by the carbothermic and carbosilisisothermic reduction of titanium oxide (rutile type). The milling procedure involved milling of TiO₂/C and TiO₂/Si/C powders at room temperature in an argon atmosphere. The progress of the mechanically induced solid state reaction was monitored using X-ray diffraction (XRD) and scanning electron microscopy (SEM). The XRD results showed that TiC nanoparticles were duly synthesized in the TiO₂/C system at 1700 °C in 60-h milled samples. In the non-milled samples, although heated at the same temperature, only a minor amount of a lower degree of titanium oxide (Ti₃O₅) was observed to form. Further, in other non-milled samples, but with Si initially present, despite heating to 1550 °C no TiC phase was detected. However, using Si as a reducing agent accompanied by graphite, after 60 h ball milling, only Si remained as a distinguishable crystalline phase. Further, heat treatment of activated powders by forming the interphase compounds (such as Ti₃Si₅ and Ti₅Si₃) remarkably decreased the synthesis temperature to 900 °C for the 60 h milled samples.     

Magnetic 99mTc- core-shell of polyethylene glycol/polyhydroxyethyl methacrylate based on Fe3O4 nanoparticles: Radiation synthesis,characterization and biodistribution study in tumor bearing mice

Magnetic nanoparticles (Fe₃O₄) coated with polyethylene glycol (PEG), (Fe₃O₄/PEG), were synthesized by chemical co-precipitation of Fe²⁺/Fe³⁺ salts by aqueous ammonia in PEG solution. Radiation polymerization of 2-hydroxyethyl methacrylate (HEMA) monomer solution onto Fe₃O₄/PEG was performed at different doses to synthesize (Fe₃O₄/PEG)-pHEMA, namely FPH, nanocomposites. Properties of FPH nanocomposites were characterized by FT-IR, XRD, SEM, TEM, DLS, ESR and TGA techniques. The XRD of FPH nanocomposites showed all the peaks of Fe₃O₄ nanoparticles. SEM was used to assess the surface morphology of FPH. TEM showed that the average diameter of FPH nanocomposites was in the range of 9–40 nm. The thermal stability of FPH nanocomposites was higher than that of Fe₃O₄ and Fe₃O₄/PEG. Radio-labeling of (Fe₃O₄/PEG)-pHEMA nanocomposite irradiated at 10 kGy (FPH10) with ^99mTc was performed using stannous chloride as reducing agent. Factors affecting the labeling yield (%) such as the substrate amount, the amount of reducing agent, the pH of reaction medium, the reaction time and the reaction temperature were investigated. The maximum labeling yield was 93% using 0.25 mg of FPH10 at pH 6 and 20 min reaction time. The biodistribution study of ^99mTc-FPH10 was examined on two groups of ascites and solid tumor bearing mice. The biodistribution results referred that ^99mTc-FPH10 was rapidly uptake in tumor sites ascites or solid tumors. The results indicated that FPH nanocomposites could be potentially used for tumor imaging and therapy.     

Exploration of structural,thermal, vibrational and spectroscopic properties of new noncentrosymmetric double borate Rb3NdB6O12

New noncentrosymmetric rare earth borate Rb₃NdB₆O₁₂ is found in the ternary system Rb₂O–Nd₂O₃–B₂O₃. The Rb₃NdB₆O₁₂ powder was fabricated by solid state synthesis at 1050 K for 72 h and the crystal structure was obtained by the Rietveld method. Rb₃NdB₆O₁₂ crystallized in space group R32 with unit cell parameters a = 13.5236(4), c = 31.162(1) Å, Z = 3. From DSC measurements, the reversible phase transition (I type) in Rb₃NdB₆O₁₂ is observed at 852–936 K. The 200 μm thick tablet is transparent over the spectral range of 0.3–6.5 μm and the band gap is found as E_g ～ 6.29 eV. Nonlinear optical response of Rb₃NdB₆O₁₂ tested via SHG is estimated to be higher than that of K₃YB₆O₁₂. Blue shift of Nd luminescent lines is found in comparison with other borates. The vibrational parameters of Rb₃NdB₆O₁₂ are evaluated by experimental methods.     

A novel protocol to design TiO2-Fe2O3 hybrids with effective charge separation efficiency for improved photocatalysis

TiO₂-based heterogeneous photocatalysis has been widely considered as a promising technique for decontamination of water. Herein the hybrid of TiO₂ nanocrystals decorated Fe₂O₃ nanoparticles was successfully synthesized via a mild hydrothermal method, derived from favorable titanium glycolate and water-soluble Fe^II salt precursors. The composition and structure of the as-synthesized TiO₂-Fe₂O₃ hybrids were characterized by Powder X-ray diffraction (XRD), EDX mapping, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and selected area electron diffraction (SAED). The photocatalytic activity was evaluated by the decomposition of Rhodamine B in an aqueous solution under visible-light (λ > 420 nm). The results show that the TiO₂-Fe₂O₃ nanocomposite exhibits superior photocatalytic capability to the bare ones upon Rhodamine B degradation, owing to promoted photo-induced electrons and holes separation and migration on the basis of photoluminescence spectra, photocurrent measurements, and electrochemical impedance (EIS) spectroscopy.     

Solvothermal synthesis of Ag/ZnO micro/nanostructures with different precursors for advanced photocatalytic applications

Micro/nanostructured systems based on metallic oxide (ZnO) with noble metal (Ag) on the surface (Ag/ZnO) are synthesized by solvothermal method from zinc nitrate hexahydrate (Zn(NO₃)₂·6H₂O), zinc acetate dehydrate (Zn(CH₃COO)₂·2H₂O), zinc acetylacetonate hydrate (Zn(C₅H₇O₂)₂·xH₂O) and silver nitrate (Ag(NO₃)) as precursors. In these systems, polyvinylpyrrolidone (PVP) is used as surfactant for controlling particle morphology, size and dispersion. The obtained materials are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HR-TEM), UV–vis diffuse reflectance spectroscopy (DRS), N₂ gas adsorption–desorption (BET) and Raman spectroscopy (RS). By XRD results, all major peaks are indexed to the hexagonal wurtzite-type structure of the ZnO and samples with noble metal, extra diffraction peaks are detected which correspond to the face-centered-cubic (fcc) structure of the metallic Ag. Depending on used precursor, different morphologies have been obtained. Mainly, ZnO prims-like rods – NRs (with 0.8 ? aspect ratio ? 3.4) – have been observed. Quasi-spherical particles of metallic Ag (with diameters between 558 ± 111 μm and 22 ± 1 nm) have been detected on the ZnO surface. Photocatalytic results (all samples studied >30% MB degradation) verify the important effect of surfactant and the viability of synthesized Ag/ZnO micro/nanocomposites for environmental applications.     

Extending LaMer's mechanism using open system for increasing forced and controlled growth of Au nano particles: Desired decreasing Fe3O4 nano particles size during simultaneous synthesis in optimized conditions

The most effective parameters were found to obtain Au/Fe₃O₄ nano particles (NPs)-oleylamine composite. Having Au NPs with the controlled maximum mean size under the forced conditions was the main aim of this study. We used the continuous flow rates of oleylamine 75% to produce Au NPs under an open system by extended LaMer mechanisms. This process decreased the mean size of Fe₃O₄ NPs synthesized simultaneously, by classic LaMer mechanism. The Fe₃O₄ NPs production was carried out without continuous adding of any iron reactant, viz. as a closed system. In the absence of gold ions, the mean size of the synthesized Fe₃O₄ NPs using 2.5 ml/min oleylamine was about 35.0 nm at 2.0 ± 0.5 °C after 120 min. This mean size was decreased to 27.2, 21.4, 16.8 and 8.7 nm, when Au NPs were simultaneous prepared using 0.5, 0.75, 1.5 and 2.5 ml/min of oleylamine, respectively, at the same conditions. Surface Plasmon Resonance (SPR) adsorption was used to evaluate Au NPs production at first 30 min, while Small Angle X-ray Scattering (SAXS) method was used to monitor the reaction progression for near-real time analysis of increasing the growth of Au NPs up to 280 min, at the optimum conditions. Changing the properties of Fe₃O₄ NPs during processes was determined by studying Magnetization, Potentiometric titration, Inductive heating and Zeta potential.     

Investigations on the MnO2-Fe2O3 system roasted in air atmosphere

Solid-state reaction method is a common and effective technique to synthesize ferrites. This work investigated the phase transformation of MnO₂ and Fe₂O₃ system roasted at 500–1400 °C in air atmosphere to understand the formation process of manganese ferrite. The results showed that the formation of manganese ferrite (Mn_xFe_3?xO₄) was derived from the reaction between Fe₂O₃ and Mn₃O₄ (the decomposition product of MnO₂). Below 900 °C, MnO₂ firstly decomposed to Mn₂O₃ and then to Mn₃O₄, and Fe₂O₃ was seldom reacted with Mn₂O₃ and Mn₃O₄. When the temperature went up to 1000 °C, Fe₂O₃ easily reacted with Mn₃O₄ to generate manganese ferrite. The reaction degree was enhanced dramatically with the rising of temperature. Moreover, the x value in the Mn_xFe_3?xO₄ increased from 0 to 1 from 900 °C to 1400 °C. In other words, the higher the temperature was, the closer the Mn_xFe_3?xO₄ was to MnFe₂O₄. Thermodynamic analysis of MnO₂-Fe₂O₃ system under different O₂ partial pressures was carried out to further explain the formation mechanism.     

Stable controlled growth of 3D CuO/Cu nanoflowers by surfactant-free method for non-enzymatic hydrogen peroxide detection

Sensitive, convenient and rapid detection of hydrogen peroxide(H_2 O_2) is highly desirable in fields like fundamental biological research, food industries, and clinical environmental analysis. Herein, a hierarchical porous CuO/Cu flower-like active electrode material for non-enzymatic H_2 O_2 sensor was synthesized via a low-cost and one-step chemical oxidation of Cu powder in water bath without surfactants. In order to discuss the growth mechanism of the product, products with different growth time length were fabricated. The electro-catalysis of all products were first exhibited by cyclic-voltammetry,and the product under 6 h reaction shows the best result. The detailed electro-catalytic behaviors of the best product(under 6 h reaction) are characterized by cyclic-voltammetry and amperometry under alkaline conditions. The materials have high sensitivity of 103 μA mM~(-1) cm~(-2)(R~2= 0.9979), low detection limit of 2 μmol/L and wide concentration range(from 2 μmol/L to 19.4 mmol/L). Large specific surface area and stabled nanostructure enabled good features, such as stability and sensitivity for the H_2 O_2 determination.     

Influence of different parameters and their coupled effects on the stability of alumina nanofluids by a fractional factorial design approach

Nanofluids have been introduced as new-generation fluids able to improve energy efficiency in heat exchangers. However, stability problems related to both agglomeration and sedimentation of nanoparticles have limited industrial-level scaling. A fractional factorial experimental 2^k?1 design was applied in order to evaluate the effects of nanoparticle concentration, surfactant type and concentration, ultrasonic amplitude as well as ultrasonic time on the stability of alumina (Al₂O₃) nanofluids. Commercial alumina nanoparticles (particle diameter <50 nm) were dispersed in deionized water using ultrasonic probe dispersion equipment. Sodium dodecylbenzenesulfonate (SDBS) and cetyltrimethylammonium bromide (CTAB) were used as surfactants. The stability of the nanofluids in static mode was monitored by visual inspection and UV visible spectroscopy. The results of the experimental design showed that the coupled effects between surfactant type and surfactant concentration and between ultrasonication tip amplitude and ultrasonication time had the most pronounced effects on nanofluid stability. The experimental conditions providing the best stability were 0.5 wt% of Al₂O₃, CTAB, critical micelle surfactant concentration, 30% ultrasonic amplitude and 30 min of ultrasonication.     

Improved hydrogen storage properties of Mg-Li-Al-H composite system by milling with Fe2O3 powder

A sample of Fe₂O₃-doped 4MgH₂-Li₃AlH₆ composite was prepared by the ball milling technique, and the hydrogen storage properties were investigated for the first time. Results showed that the addition of Fe₂O₃ powder reduced the decomposition temperature and improved de/hydrogenation kinetics compared with undoped 4MgH₂-Li₃AlH₆. The onset decomposition temperature for the Fe₂O₃-doped 4MgH₂-Li₃AlH₆ composite decreased by 75 °C compared with that of the undoped composite. For the sorption kinetics, a hydrogen absorption capacity of 2.4 wt% was reached after 60 min in the 10 wt% Fe₂O₃-doped 4MgH₂-Li₃AlH₆ composite, whereas the neat composite absorbed 2.3 wt% hydrogen under the same conditions. For desorption kinetics, the Fe₂O₃-doped 4MgH₂-Li₃AlH₆ sample released 2.5 wt% hydrogen under 10 min of dehydrogenation, but the neat 4MgH₂-Li₃AlH₆ composite only desorbed 2.0 wt% hydrogen within the same period. The apparent activation energy calculated by Kissinger analysis for hydrogen desorption decreased to 112.9 kJ/mol after Fe₂O₃ was added compared with the undoped composite, which was 145.4 kJ/mol. The X-ray diffraction analysis shows the formation new phase of Li₂Fe₃O₄ in the doped sample after ball milling processes that could act as the real catalyst in the Fe₂O₃-doped 4MgH₂-Li₃AlH₆ composite.     

Synthesis and characterization of sulfur/carbon/porous nanostructured V2O5 composite cathodes for lithium sulfur batteries

Porous nanostructured V₂O₅ (PN-V₂O₅) was prepared by a facile spray pyrolysis and used as additive to synthesize sulfur/carbon/PN-V₂O₅ (S/C/PN-V₂O₅) composite by a combination of wet-ball-milling and heat treatment. The meso- and macropores in PN-V₂O₅ were confirmed by pore size distribution, which provided the favorable space to accommodate sulfur. The X-ray diffraction analysis showed that the crystal structures of S and V₂O₅ could be preserved below the heating temperature of 160 °C and that high heating temperature (200 °C) will result in reaction between S and V₂O₅. The pore size distribution curves of S/C/PN-V₂O₅ composites revealed that the penetrated S in PN-V₂O₅ pores mainly occupied the mesopores and macropores, which was further confirmed by a typical cross-sectional PN-V₂O₅ with Auger analysis. The S/C/PN-V₂O₅ composite cathode exhibited a discharge capacity of 632 mAh g^?1 after 60 cycles at the current density of 100 mA g^?1 and the capacity retention of S/C/PN-V₂O₅ electrode was 27.3% higher than that of S/C electrode, demonstrating a better cycling performance.     

Preparation of w–cu nano-composite powders with high copper content using a chemical co-deposition technique

A novel chemical co-precipitation was used to produce W-70%Cu nanocomposite powders with coating structure. The precursors consisting of CuC₂O₄·xH₂O and WO₃·2H₂O were first synthesized using copper nitrate, ammonium metatungstate(AMT) and oxalic acid as the raw materials at 80?°C for 1.5?h when the concentrations of the reactants were 0.8?mol/L and the hydrogen ion concentration was 1.2?mol/L. The precursors were calcined to produce the powders with different phase components and microstructure at various temperatures. The CuWO₄ and CuO nano-powders were obtained at 300?°C, which is colder than the traditional reaction temperature (1000?°C) of CuO?+?WO₃ = CuWO₄. However, the cubic Cu₂O and Cu₂WO₄ could be formed when the calcining temperature was 600?°C. The hydrogen reduction results show that the calcined powder is reduced to obtain W-Cu composite powder at 750?°C and 800?°C. In reduction process, volatile WO₂(OH)₂ through chemical vapor transport(CVT) continuously spreads to the copper surface and is reduced to form W and the coated particle is eventually formed. This particle is Cu particle coated by W phase and the interface between W and Cu phases is semi-coherent. It is found that the average particle size of the reduced powder is 30–50?nm observed by TEM images.     

Microstructure and morphology of Mo-based Tm2O3 composites synthesized by ball milling and sintering

Mo-based Tm₂O₃ composites used as neutron absorbers were synthesized by ball milling, cold isostatic pressing and sintering. The size of Mo grain was decreased rapidly in the initial stage and then kept a constant in the later stage. After ball milling for 96 h, the size of Mo grain was up to approximately 8 nm. Ball milling induced Tm₂O₃ to be first fined, nano-crystallized, then transformed to amorphization, and finally dissolved into Mo crystal. The supersaturated nanocrystalline solid solution of Mo (Tm, O) was formed after 96 h of ball milling. Sintering caused Tm and O atoms precipitated from Mo crystal and then formed Tm₂O₃ precipitates that uniformly distributed in the Mo matrix. After sintered for 12–24 h at 1400–1600 °C, only diffraction peaks of Tm₂O₃ and Mo could be observed in the XRD spectrums, which indicated that there was not a chemical reaction between Tm₂O₃ and Mo. The microhardness of sintered bulks increased with increasing ball-milling time, sintering temperature and time, and the chemical content of Tm₂O₃ in the powder mixtures. The evolutionary mechanism of the microstructural characteristics during ball milling and subsequent sintering was discussed.