C3N4 as a precursor for the synthesis of NbC, TaC and WC nanoparticles

While there already exit some routes to prepare carbides, highly efficient and facile routes are still desired to meet the increasing demand on carbides. By a facile solid-state reaction process using graphite-like phase of C₃N₄ (g-C₃N₄) as the carbonizing reagent, we synthesized three technologically important carbides including cubic NbC and TaC, and hexagonal WC nanoparticles at relatively low temperature (1150 °C). The products were characterized by power X-ray diffraction (XRD), field-emission scanning electron microscope (FE-SEM), energy-dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM) and high-resolution TEM (HRTEM). The results show that g-C₃N₄ is a highly efficient carbonizing reagent and the oxides Nb₂O₅, Ta₂O₅ and WO₃ are completely converted into the corresponding carbides at 1150 °C, which is significantly lower than that reported for the commercial preparation of the carbides, typically >1600 °C. The NbC, TaC and WC nanoparticles are found to have an average particle size of 4, 35 and 60 nm, respectively. An important feature of this solid-state reaction process is that g-C₃N₄ plays double roles as both efficiently reducing and carbonizing reagent.     

pH值对CeO2/SiO2纳米复合磨粒分散性的影响

以胶体SiO₂溶液作硅源,采用均相沉淀工艺制备壳-核结构完整的CeO₂/SiO₂纳米复合磨粒。采用X射线衍射仪和透射电子显微镜对复合磨粒样品进行物相组成分析和微观形貌观察;通过粒径分布、Zeta电位分析,研究水相分散系中pH值对CeO₂/SiO₂复合磨粒分散性的影响。结果表明:所制备的CeO₂/SiO₂复合磨粒为壳-核包覆结构完整的纳米微球,粒径约110 nm,内核为无定形SiO₂,壳层为立方萤石型CeO₂;CeO₂/SiO₂复合磨粒的等电位点pH值约为5,其值由SiO₂等电位点向CeO₂等电位点明显偏移。CeO₂/SiO₂复合磨粒在酸性水相介质中分散性差,容易出现严重的团聚现象;而在碱性环境下,CeO₂/SiO₂复合磨粒分散性良好。      

Direct synthesis of A2(Ti(1 − y)Zry)2O7 (A = Gd, Y) solid solutions by ball milling constituent oxides

Different compositions in two solid solutions, A₂(Ti_(1 − y)Zr_y)₂O₇ (A = Gd³⁺, Y³⁺), with high oxygen ion conductivity, have been successfully prepared at room temperature via mechano-chemical synthesis. Stoichiometric mixtures of the constituent oxides were milled in a planetary ball mill by using zirconia vials and balls. Chemical changes in the powder mixtures as a function of composition and milling time were followed by using X-ray diffraction showing that in all cases and after milling for 19 h, the powders consisted of a single phase. Powders were also examined by scanning electron microscopy (SEM) finding out that they basically consist of sub-micron size agglomerates and aggregates of nanoparticles.     

Highly enhanced degradation of dye with well-dispersed TiO2 nanoparticles under visible irradiation

TiO₂ nanoparticles were prepared through a facile flame method. The samples were characterized by means of X-ray diffraction, transmission electron microscopy, zeta potential measurement and transmittance spectrum. Compared with TiO₂ P-25, smaller particle size, less agglomeration and well dispersion are shown for the prepared TiO₂ particles. The photosensitized catalytic activity of as-prepared TiO₂ was investigated upon its degradation of Rhodamine B under visible light irradiation. It is found that the optical characteristics of TiO₂ have great influence on the photosensitized catalytic activity due to its crystalline forms, smaller size, higher surface area and well dispersion.     

Structural and electrical properties of SrBi2(Ta0.5Nb0.5)2O9 thin films

SrBi₂(Ta_0.5Nb_0.5)₂O₉ (SBTN) thin films were obtained by polymeric precursor method on Pt/Ti/SiO₂/Si(1 0 0) substrates. The film is dense and crack-free after annealing at 700 °C for 2 h in static air. Crystallinity and morphological characteristic were examined by X-ray diffraction (XRD), field emission scanning electron microscopy (FEG-SEM) and atomic force microscopy (AFM). The films displayed rounded grains with a superficial roughness of 3.5 nm. The dielectric permittivity was 122 with loss tangent of 0.040. The remanent polarization (P_r) and coercive field (E_c) were 5.1 μC/cm² and 96 kV/cm, respectively.     

WC-Co based cemented carbides with large Cr3C2 additions

Five model alloys based on WC-16.6 vol% Co with different amounts of Cr₃C₂ (0–12 vol%) substituting WC were studied. Their microstructures were characterised with X-ray diffraction, scanning electron microscopy and transmission electron microscopy in combination with energy dispersive X-ray analysis. Thermodynamic calculations on the C-Co-Cr-W system were carried out using the Thermo-Calc software. The microstructures were related to previously published results on properties (magnetic coercivity, hardness, transverse rupture strength and indentation fracture toughness) of these materials. The aim of this work was to investigate whether the positive effect of small Cr₃C₂ additions on grain refinement and various properties remains also for large Cr₃C₂ additions. For Cr₃C₂ additions larger than 2 vol%, the most obvious effect on the microstructure was the formation of a chromium- and cobalt-rich M₇C₃ carbide. The Cr/Co ratio of this phase depends on the amount of Cr₃C₂ substituting WC. Some large WC grains were present in the WC-Co material, but not in the materials with Cr₃C₂ additions. Apart from this, no major changes of the WC grain size with Cr₃C₂ content were observed. The partial replacement of tough binder by presumably brittle M₇C₃ carbide might explain the lower toughness of these materials.     

Characterization and sintering of BaZrO3 nanoparticles synthesized through a single-step combustion process

Barium zirconate (BaZrO₃) nanoparticles synthesized by a self-sustained single-step combustion process is reported in this paper. In this process, a phase pure nanopowder of BaZrO₃ has been obtained by the combustion of an aqueous solution containing Ba and Zr ions by using citric acid as complexing agent and liquor ammonia as fuel, thus giving rise to phase pure BaZrO₃ nanopowder in a single-step combustion without any further calcination. The X-ray diffraction studies have shown that the as-prepared powder was single phase, crystalline, and has a cubic perovskite structure (ABO₃) with a lattice constant a = 4.19 Å. The average particle size calculated from FWHM is 30 nm. The phase purity of BaZrO₃ nanopowder has been examined using differential thermal analysis (DTA), thermo gravimetric analysis (TGA) and Fourier transform of infrared spectroscopy (FTIR). The transmission electron microscopic investigation has shown that the particle size of the as-prepared powder was in the range 30–50 nm with a mean size of 40 nm. The nano BaZrO₃ has been sintered to a density of 99% of the theoretical density at 1650 °C in 2 h without the use of any sintering aids. The morphology of the sintered pellets has been studied with scanning electron microscopy (SEM). The dielectric constant (_r) and loss factor (tan δ) values obtained at 10 MHz for a well-sintered barium zirconate pellet has been found to be 32.2 and 1 × 10⁻⁴, respectively, at room temperature.     

A facile route to VN and V2O3 nanocrystals from single precursor NH4VO3

V₂O₃ and VN nanocrystals have been synthesized by the decomposition of the precursor NH₄VO₃ and following nitridation in an autoclave with metallic Na flux at 450–600 °C. X-ray powder diffraction (XRD) recorded the evolution process of the reaction from precursor NH₄VO₃ to hexagonal V₂O₃ and then to NaCl-type VN. In addition, the products were characterized by X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM).     

Microstructure and composition analysis in plasma sprayed coatings of Al2O3/ZrSiO4 mixtures

Plasma spraying of Al₂O₃/ZrSiO₄ was performed using spray dried and plasma spheroidised powder feedstock. The mixtures were sprayed using different spray stand-off distances and plasma power levels. X-Ray diffraction (XRD) was used to characterise the phase composition and scanning electron microscopy (SEM) examined the morphology of the sprayed surface and polished cross-sections. The results showed that the plasma spray process parameters played an important role in the final outcome of microstructures of the coatings. The coatings produced with spheroidised powders displayed a much denser structure than those produced with the spray-dried powders. The phase composition analysis showed the presence of amorphous phases in addition to crystalline alumina, zircon and tetragonal (t) zirconia (ZrO₂). Transmission electron microscopy (TEM) showed that amorphous phases and t-ZrO₂ crystals with particle size 100–200 nm could coexist within a single splat due to the relatively low local cooling rate.     

Pulsed laser deposited Sb2Se3 anode for lithium-ion batteries

Sb₂Se₃ thin film has been successfully fabricated by reactive pulsed laser deposition and was investigated for its electrochemistry with lithium for the first time. The reversible discharge capacities of Sb₂Se₃/Li cells cycled between 0.3 and 2.5 V were found in the range of 530.5–660.7 mAh g⁻¹ during the first 100 cycles. By using ex situ X-ray diffraction, transmission electron microscopy, and selected-area electron diffraction measurements, both classical alloying process and the selenylation/reduction of nanosized metallic antimony were proposed in the lithium electrochemical reaction of Sb₂Se₃. Sb₂Se₃ has high reversible capacity and good cycle performance, which makes it potential anode material for future lithium-ion batteries.     

Synthesis and characterization of proton conducting Sr(Ce1−xZrx)0.95Yb0.05O3−δ by the citrate method

The citrate method was used to synthesize Sr(Ce_1−xZr_x)_0.95Yb_0.05O_3−δ (x = 0.1, 0.2, 0.3, 0.4) and to avoid the drawbacks of the conventional solid state reaction method. The products were characterized by thermal analysis (TG-DTA), X-ray diffraction (XRD), scanning electron microscopy (SEM) and electron probe X-ray microanalyzer (EPMA). The results indicate that the citrate method is an advantageous route in producing Sr(Ce_1−xZr_x)_0.95Yb_0.05O_3−δ materials. Sr(Ce_0.9Zr_0.1)_0.95Yb_0.05O_3−δ powders are composed of nanoscaled crystallites with the average grain size in the range of 60–70 nm. Single phase is confirmed over the whole x range. In addition, chemical stability against CO₂ and electrical conduction behavior of the sintered Sr(Ce_1−xZr_x)_0.95Yb_0.05O_3−δ ceramics were investigated. The chemical stability of the ceramics against CO₂ is certified to increase with the increase in zirconium content. Impedance spectroscopy was used to study the electrical conduction behavior of Sr(Ce_0.9Zr_0.1)_0.95Yb_0.05O_3−δ ceramic.     

Coercivity enhancement in melt-spun SmCo5 by Sn addition

Additions of Sn to SmCo_4.7 alloy were found to increase the coercivity of melt-spun ribbons by forming an Sn-rich non-magnetic grain boundary phase. The highest coercivity of 2.56 MA/m (32 kOe) was obtained for the composition SmCo_4.7Sn_0.08. Microstructures of the melt-spun alloys SmCo_4.7Sn_x (x = 0–0.35), SmCo₇Sn_0.08 and Sm_1.25Co_4.7Sn_0.25 were analyzed by transmission electron microscopy, energy filtered electron microscopy and X-ray diffraction in order to discuss the increase in coercivity.     

Microstructure and mechanical properties of mechanically alloyed and spark plasma sintered amorphous–nanocrystalline Al65Cu20Ti15 intermetallic matrix composite reinforced with TiO2 nanoparticles

Multiphase Al₆₅Cu₂₀Ti₁₅ intermetallic alloy matrix composite, dispersed with 10 wt.% of TiO₂ nanoparticles, has been processed by mechanical alloying, followed by spark plasma sintering under pressure in the temperature range of 623–873 K. Differential scanning calorimetry and X-ray diffraction suggest that equilibrium crystalline phases evolve from the amorphous or intermediate crystalline phases. Transmission electron microscopy shows that the composite sintered at 873 K has partially amorphous microstructure, with dispersion of equilibrium, crystalline, intermetallic precipitates of Al₅CuTi₂, Al₃Ti, and Al₂Cu of 25–50 nm size, besides the TiO₂. The composite sintered at 873 K exhibits little porosity, hardness of 5.6 GPa, indentation fracture toughness in the range of 3.1–4.2 MPa√m, and compressive strength of 1.1 GPa. Indentation crack deflection by TiO₂ particle aggregates causes increase in fracture resistance with crack length, and suggests R-curve type behaviour. The study provides guidelines for processing high strength amorphous–nanocrystalline intermetallic composites based on the Al–Cu–Ti ternary system.     

Fabrication and wear characteristics of MoSi2 matrix composite reinforced by WSi2 and La2O3

MoSi₂ matrix composites (RWM) reinforced by the addition of both WSi₂ and La₂O₃ were fabricated by mechanical alloying and self-propagating high-temperature synthesis (SHS) technique. This composite was analysed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). It is difficult to synthesize RWM composite by mechanical alloying with Mo–W–Si–La₂O₃ powder mixture, and suitable by self-propagating high-temperature synthesis. The hardness and toughness of MoSi₂ was improved significantly by the addition of both, WSi₂ and La₂O₃ more than by only WSi₂. By adding 0.8 wt.% La₂O₃ and 50 mol.% WSi₂ into the MoSi₂ matrix, this composite has the highest hardness and toughness and exhibits more wear resistance than monolithic MoSi₂ during the sliding wear test under oil lubrication, in this case, the material removal mechanism has been observed to be micro-cutting and micro-fracture.     

Crystallisation of oxygen-stabilised amorphous phase in a Zr50Cu50 alloy

The crystallisation of the oxygen-stabilised amorphous phase in a Zr₅₀Cu₅₀ alloy has been investigated by means of neutron diffraction and electron microscopy. The crystallisation microstructure consists of ZrO₂, Zr₂Cu and Zr₇Cu₁₀. A two-stage crystallisation mechanism is suggested: (i) primary crystallisation of Zr₂Cu and (ii) formation of nanocrystals ZrO₂ and Zr₇Cu₁₀. In (i), it is proposed, Zr₂Cu crystallises from the oxygen-stabilised amorphous phase, leaving an oxygen- and copper-enriched matrix ; Zr₂Cu rapidly grows and eventually attains a grain size of about 100 nm. In (ii), it is suggested, the residual amorphous matrix crystallises into nanocrystals ZrO₂ and Zr₇Cu₁₀ due to the sluggish growth of ZrO₂ and to the already formed ZrO₂ which acts as a growth barrier to Zr₇Cu₁₀. In this case there is no particular orientation relationship between Zr₂Cu and Zr₇Cu₁₀.     

电弧喷涂制备Fe65Cr20Mo7B3.5SiMn1.5W3涂层

在Q235低碳钢板上利用电弧喷涂工艺进行喷涂,以制得Fe65Cr20Mo7B3.5SiMn1.5W3涂层。喷涂材料为自行配制的丝材,按照35%的填充率将配好的粉填充到U型不锈钢外皮中,经过多道拉拔、挤压工艺制成Φ2mm的粉芯丝材。采用X射线衍射仪、扫描电镜、能谱分析仪、透射电镜对涂层的物相和组织形貌及成分进行了表征;采用差示扫描量热仪、显微硬度仪等设备对涂层的热稳定性及显微硬度进行了检测和分析。试验结果表明:涂层组织形貌呈典型的层状组织结构,由变形良好的带状粒子相互搭接堆积而成。涂层含有50.63%的非晶相,同时含有纳米级的晶相。涂层组织均匀、结构致密、孔隙率低,并且涂层硬度高达1040.5HV0.3,属硬质涂层,具有良好的热稳定性。     

Vanadium-Doped Magnesium Oxide Nanoparticles Formation in Presence of Ionic Liquids and Their Use in Photocatalytic Degradation of Methylene Blue

Magnesium oxide(MgO) is one of the metal oxides having unique properties with numerous potential industrial applications.In this study,MgO and vanadium-doped MgO nanoparticles were synthesized by sol–gel method in 1-butyl-3-methylimidazolium tetrafluoroborate [BMIM][BF_4] and 1-octyl-3-methylimidazolium tetrafluoroborate [OMIM][BF_4] ionic liquids.Vanadium-doped MgO nanoparticles exhibited nanosphere and nanorod morphologies with 40–80 nm in particle size,primarily due to the influence of ionic liquids as demonstrated by high-resolution scanning electron microscopy and transmission electron microscopy.Characteristics of nanoparticles were also studied by thermal gravimetric analysis,X-ray diffraction and energy-dispersive X-ray spectroscopy.Photodegradation ability of synthesized nanoparticles was evaluated for methylene blue(MB) in specially designed UV reactor.Photodegradation is found to be dependent on doping,and particle characteristics change due to the influence of ionic liquid.The ionic liquid-assisted vanadium-doped MgO nanoparticles showed good reusability under UV irradiation and MB degradation ability under visible light.     

Microstructural characterization and abrasive wear performance of HVOF sprayed Cr3C2–NiCr coating

Cr₃C₂–NiCr coatings were deposited by high velocity oxy-fuel (HVOF) process with different spray parameters to examine dominant microstructural factors in abrasive wear of the coatings. The microstructure of the HVOF sprayed Cr₃C₂–NiCr coatings was characterized by scanning electron microscopy and transmission electron microscopy (TEM). The apparent average size and volume fraction of carbide particles in the coatings were estimated through a quantitative imaging analysis. The formation of carbide phases in the coating was discussed based on the TEM observation results. The abrasive wear behavior of the coating was evaluated by the dry rubber wheel abrasive wear test and the wear mechanisms were elucidated. Influences of apparent size and volume fraction of carbide particles on the abrasive wear weight loss were examined through correlating the proposed relation with the experimental results. Results showed that Cr₃C₂ particle size was significantly reduced after the spraying and Cr₇C₃ carbide was present around Cr₃C₂ particles, and Cr₂₃C₆ carbide was dispersed in NiCr alloy matrix with a nano-crystalline structure. The three carbides were formed in the coating through different mechanisms. The removal of carbide particles in the coating was mainly responsible for the abrasive wear of the coating. The content and particle size of the Cr₃C₂ carbides were the two key factors controlling the abrasive wear of the HVOF sprayed Cr₃C₂–NiCr coatings.     

Preparation and electrochemical performance of nanosized Co3O4 via hydrothermal method

The hydrotalcite-type cobalt compounds were prepared through oxidation of Co（OH）2 gel using NH4OH as precipitating agent and H2O2 as oxidant. These hydrotalcite-type cobalt compounds were transformed into Co3O4 through hydrothermal decomposition with nanostructural deformation. The precursor and product were characterized by Fourier-transform infrared（FT-IR） spectrum, X-ray diffractometry（XRD） and transmission electron microscopy（TEM）. The electrochemical performances of as-prepared nanosized Co3O4 as anode materials in lithium-ion batteries were tested by charge-discharge test in the voltage range of 0-3.0 V. The influence of morphology of Co3O4 particle on the capacity and cycling performance was studied. The results show that the shape and size of the final product can be controlled by altering cobalt sources. The irregular cubic Co3O4 with the average particle size of about 10 nm shows the best electrochemical performance. After 10 charge-discharge cycles, the specific charge capacity retains 555 mA.h/g.     

SEM and TEM characterization of magnesium hydride catalyzed with Ni nano-particle or Nb2O5

The microstructures of MgH₂ catalyzed with Ni nano-particle or Nb₂O₅ mesoporous powders are examined by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) observations. For MgH₂ catalyzed with Ni, the Ni particles with the diameter smaller than 1 μm were detected on the MgH₂ particles with the diameter smaller than 5 μm by the back scattering electron (BSE) microscopy. In details, the TEM micrograph indicates that the Ni particles distribute 20 nm in diameter on MgH₂ uniformly, which was the same size as the additive doped in MgH₂ before milling. On the other hand, for MgH₂ catalyzed with Nb₂O₅, the additive particles could not be found anywhere in the BSE image. Even in the TEM micrograph by much larger magnification than the SEM micrograph, the particles corresponding to the additive cannot be observed at all. Furthermore, an energy dispersive X-ray (EDX) analysis in spots with a diameter of 20 nm indicated that the existing ratio of Mg to Nb was evaluated to 98:2, being the same as the starting ratio before milling. Therefore, the metal oxide Nb₂O₅ becomes extremely small particle that could not be observed by the present work after milling compared to metal Ni^nano.