Sintering behavior of aluminum nitride powder prepared by self-propagating high-temperature synthesis method

Fully dense aluminum nitride(AIN) ceramics were synthesized by self-propagating high-temperature synthesis(SHS) method using AIN powder as raw material with Y_2 O_3 additive. The sintering behavior was studied at different sintering temperatures and additive contents. The change of phase compositions, secondary phase distributions and grain morphologies during sintering process were investigated. It is shown that fully dense ceramics using AIN powder prepared by SHS method can be obtained when the sintering temperature is above 1830 ℃. Both Y_2 O_3 content and sintering temperature have an important influence on the formation of Y-Al-O phase and grain shape. When Y_2 O_3 content is identified, the grain morphology converts from polyhedron into sphere-like shape with the rise of sintering temperature. At a certain sintering temperature,the grain size decreases with the increase in Y_2 O_3 content. The influencing mechanisms of different YAl-O secondary phases and sintering temperatures on the grain size and morphology were also discussed based on the experimental results.     

Preparation of silver tin oxide powders by hydrothermal reduction and crystallization

Silver tin oxide composite powders were synthesized by the hydrothermal method with a silver ammine solution and a Na2SnO3 solution as raw materials. H2C2O4 was used as the co-precipitator of silver ions and tin ions. The co-precipitation conditions were investigated. The results show that the co-precipitate of Ag2C2O4 and Sn（OH）4 is available when the pH value of the solution is 4.27-8.36. Using the obtained precipitate as precursor,the reduction of Ag＋ and the crystallization of tin oxide were carried out simultaneously by the hydrothermal method and silver tin oxide composite powders were obtained. The composite powders were characterized by X-ray diffraction （XRD） analysis,scanning electron microscope （SEM）,and energy spectrum analysis. The results show that the silver tin oxide composite powders are small with a diameter of about 2 μm and with homogeneous distribution of tin.     

Synthesis and electrochemical behavior of LiCoO2 recycled from incisors bound of Li-ion batteries

LiCoO2 was separated from AI foil with dimethyl acetamide（DMAC）, and then polyvinylidene fluoride（PVDF） and carbon powders in active material were eliminated by high temperature calcining. The content of the elements in the recovered powders were analyzed. Then the Li2CO3 was added in recycled powders to adjust molar ratio of Li to Co to 1.00, 1.03 and 1.05, respectively. The new LiCoO2 was obtained by calcining the mixture at 850 ℃ for 12 h in air. Structure and morphology of the recycled powders and resulted sample were observed by XRD and SEM technique, respectively. The layered structure of the LiCoO2 is improved with the decrease of molar ratio of Li to Co. The charge/discharge performance, and cyclic voltammograms performance were studied. The recycle-synthesized LiCoO2 powders, whose molar ratio of Li to Co is 1.0, is found to have the best characteristics as cathode material in terms of charge--discharge capacity and cycling performance. And the cyclic voltammograms（CV） curve shows the lithium extraction/insertion characteristics of the LiCoO2 well.     

Anode material NbO for Li-ion battery and its electrochemical properties

The NbO electrode materials were successfully synthesized by high-temperature solid-phase method using Nb powders and Nb_2O_5 powders as raw materials. The crystalline structure, morphology, and electrochemical properties of the obtained materials were characterized by X-ray diffraction(XRD),scanning electron microscopy(SEM), dynamic light scattering instrument(DLSA), halfcell charge-discharge tests, and cyclic voltammetry(CV).The reaction mechanism of lithium with NbO was investigated by ex-situ XRD studies. The results show that material average Li storage voltage is nearly located at 1.6 V, and the lithium intercalation into NbO remains a single-phase process. For the first discharge, a capacity of 355 mAh·g^-1 is obtained at a current rate of 0.1 C,and 293 mAh·g^-1 is maintained after 50 cycles, whereas a capacity of 416 mAh·g^-1 is obtained at a current rate of 0.1 C after ball milling. And 380 mAh·g^-1 reversible capacity remains for the ball milling sample.     

Low temperature solid-state synthesis and characterization of uniform YF3 submicroparticles

In this paper, submicro-scaled YF3 particles with uniform rice-like morphologies were facilely synthesized by reacting yttrium nitrate with tetrabutylammonium fluoride via a solid-state reaction process at 50 °C for 12 h.The phase confirmation and morphology of the as-prepared YF3 particles were investigated by X-ray powder diffraction（XRD） and scanning electron microscopy（SEM）.SEM results reveal that the YF3 submicroparticles are about 700 nm in length and 260 nm in width. Eu^3＋ and Tb^3＋ doped YF3 submicroparticles were also prepared with similar process and their photoluminescence properties were studied. Results demonstrate that the doping of Eu^3＋ and Tb^3＋ has slight effect on the morphologies of the product. Owing to the small average crystallite size or the low crystallinity of the product, the photoluminescence intensity of the Eu^3＋ and Tb^3＋ doped YF3 submicroparticles is very weak. Some characteristic peaks even cannot be observed in the emission spectrum.     

Preparation for intermetallic powders of Cu-Sn and Cu-Ni-Sn systems via solid-liquid reaction milling technique

The Cu-Sn binary intermetallic powders were obtained via a patented reaction ball milling technique. The Sn melt reacted with the solid-state Cu during the milling process at different temperatures for different intervals. Two kinds of binary intermetallics were obtained. For 12 h, Cu6Sn5 was prepared by milling Sn melt at 573 K while Cu3Sn by milling Sn melt at 773 K. And a mixture of Cu6Sn5 and Cu3Sn was fabricated at 673 K. All these intermetallic powders had mean grain sizes of less than 100 nm. A finer microstructure was obtained by milling Sn melt blended with 20%（mass fraction） Ni powders at 573 K for 12 h. The reaction mechanism and advantages were discussed in comparison with that of high-energy ball milling. The results show the solutionizing of Ni powders in the Cu6Sn5 intermetallic.     

Synthesis of spherical COA12O4 pigment particles with high reflectivity by polymeric-aerosol pyrolysis

Spherical cobalt blue particles with good reflectivity characteristics were synthesized by spray pyrolysis. Two different spray solutions were prepared to investigate the differences in the morphology and the reflectivity properties of cobalt blue particles. One was an aqueous solution, and the other was a polycation solution that was obtained by chemically modifying the aqueous solution with NH4OH. The cobalt blue particles prepared with the aqueous solution had an irregular morphology after heat treatment at 1000℃ for 2 h. On the contrary, spherical and dense particles were obtained from the polycation solution. The spherical and dense cobalt blue particles showed remarkable improvement in reflectivity compared with that of irregular morphology particles as well as the commercial.     

Rapid electroplating of Cu coatings by mechanical attrition method

The compact Cu coating with smooth surface and refined grain was prepared at high current density by mechanical attrition enhanced eleetroplating（MAEE） process. The mechanical attrition（MA） action was supplied by the vertical movement of glass balls on the sample surface with a special vibrating frequency. The plating bath was CuSO4 and H2SO4. It is demonstrated from field emission scanning electron microscopy（FESEM） results that the new coating shows smooth and refined surface morphology in high speed MAEE process. The further studies show that the spherical grain or pillar-shape grain can be obtained by traditional eleetroplating process at the current density of 200-600 mA/cm^2. And the coatings are loosen, porous and easy to brush off. The pyramid-shape grain with diameter of less than 1 μm was obtained by MAEE process under the same condition. And the coatings are compact and pore-free. The rapid electroplating process can be obtained by MA action.     

Synthesis of spherical CoAl_2O_4 pigment particles with high reflectivity by polymeric-aerosol pyrolysis

Spherical cobalt blue particles with good reflectivity characteristics were synthesized by spray pyrolysis. Two different spray solutions were prepared to investigate the differences in the morphology and the reflectivity properties of cobalt blue particles. One was an aqueous solution, and the other was a polycation solution that was obtained by chemically modifying the aqueous solution with NH4OH. The cobalt blue particles prepared with the aqueous solution had an irregular morphology after heat treatment at 1000°C for 2 h. On the contrary, spherical and dense particles were obtained from the polycation solution. The spherical and dense cobalt blue particles showed remarkable improvement in reflectivity compared with that of irregular morphology particles as well as the commercial.     

Photoelectrochemical characteristics of AB5-type hydrogen storage alloy modified with SrTiO3 photocatalyst

Perovskite-type SrTiO3 powders were prepared by using strontium acetate, tetrabutyl titanate and sodium hydroxide via direct hydrolysis-precipitatlon process. AB5-type hydrogen storage alloy（HSA） electrodes modified with SrTiO3 powders were prepared and the photoelectrochemical characteristics of the as-prepared electrodes were investigated. The results of cyclic voltammograph show that the current of reduction peak increases remarkably under the light irradiation. The obvious photochargeable properties are obtained for the hydrogen storage alloys modified with Perovskite-type SrTiO3 powders. During photocharging process, the potential of the electrode shifts quickly to negative direction and a potential plateau occurs. HSA electrode modified with SrTiO3 powders prepared by direct hydrolysis-precipitation process gives the higher potential of about -0.90 V（vs Hg/HgO） under the light irradiation. SEM observation discloses that a large amount of microcracks occur on the surface of the electrode after photocharging process, which is caused by the formation of hydride in the bulk of electrode.     

Influence of high intensity ultrasonic vibration on microstructure of in-situ synthesized Mg2Si/Mg composites

Coarse and agglomerated primary Mg2Si phase in in-situ synthesized Mg2Si/Mg composite with 4%Si was treated in remelting process by means of high intensity ultrasonic vibration. The effects of ultrasonic vibration duration and temperature on size, morphology and distribution of the primary Mg2Si were studied. The evolution mechanism was discussed. The microstructures of the composites were investigated by means of optical microscopy （OM） and scanning electronic, microscopy （SEM）. The components were inspected with energy dispersion spectrum （EDS） and X-ray diffraction （XRD）. The results indicate that ultrasonic vibration does not alter two constituents of the composites, but changes the size and distribution of aggregated primary Mg2Si particles. The size of primary Mg2Si particles decreases with the increase of vibration duration and vibrating temperature. High intensity ultrasonic has little effects on the primary Mg2Si morphology. The high intensity ultrasonic vibration is an effective means to prepare well-proportioned in-situ synthesized magnesium matrix composites.     

Fluorescence and preparation of Sr2（P2O7）：Ce,Tb phosphate by co-precipitation method

The micron-sized Sr2（P2OT）：Ce,Tb green phosphors were prepared by being annealed at different temperatures with its precursors synthesized by co-pre-cipitates of （NH4）2HPO4 at ambient temperature. The phase structure, grain size, surface morphology, and luminescent properties of phosphors were investigated by X-ray diffraction, scanning electron microscope, trans-mission electron microscope, and fluorescence spectrum. The results show that the product of precursor annealed at 1,100 ℃ is Sr2（P2O7）：Ce,Tb, which belongs to ortho-rhombic phase. The powder is spherical and the size dis-tribution is in micron grade. The sample with the molar ratio of Sr/Tb/Ce of 100.0：0.4：0.6 shows the best fluores-cence effect annealed at 1,100 ℃ for 3 h. The phosphors produce green fluorescence by being excitated with ultra-violet radiation of 254 nm wavelength, and the main emission peak is at 547 nm. The Sr2（P2O7）：Ce,Tb phos-phors synthesized by co-precipitation method of precursors at ambient temperature is a kind of efficient green-emitting phosphors.     

Preparation and characterization of （metal, nitrogen）-codoped TiO2 by TiCl4 sol-gel auto-igniting synthesis

The nitrogen-doped and （metal, nitrogen）-codoped TiO2 photocatalysts （metal = Ag, Ce, Fe, La） were synthesized by sol-gel auto-igniting synthesis （SAS） with the complex compound sol of TiCl4-NH4NO3-citri acid-metal nitrate- NH3.H20 as a precursor. The products were characterized by means of XRD, XPS, and UV-Vis diffuse reflectance spectra, and their photocatalytic activity was investigated under visible light. It was found that all the synthesized powders showed good absorption for visible light, and that the radius and alterable valence states of doping metallic cations played important roles on their photocatalytic activity. These results were discussed in detail.     

Synthesis of Mg＇Cu-Gd amorphous alloy by mechanical alloying and its thermal stability

Mg65Cu25Gd10 amorphous alloy powders were synthesized by mechanical alloying （MA）. The most suitable process is that the milling velocity is 600 r/min and the mass ratio of ball to powder is 20：1, so the shortest forming time of the amorphous is about 40 h. The thermal stability of the powders was analyzed by differential scanning calorimetry （DSC）. The glass transition temperature, （Tg）, onset temperature of crystallization（Tx）, width of supercooled liquid region, were determined to be 444.8, 531. 1 and 86.3 K, respectively. Contrasting them with the parameters of samples produced by traditional copper-mold casting, it is found that the thermal stability of the former is better than .that of the latter. At the same time, the crystallization kinetics of those amorphous powders was researched by Kissinger equation and the apparent activation energy at Tg and Tx was calculated.     

Growth Morphologies of a Binary Alloy with Low Anisotropy in Directional Solidification

Two new classes of growth morphologies, called doublons and seaweed, were simulated using a phase-field method. The evolution of doublon and seaweed morphologies was obtained in directional solidification. The influence of orientation and velocity on the growth morphology was investigated. It was indicated that doublons preferred growing with its crystallographic axis aligned with the heat flow direction. Seaweed, on the other hand, could be obtained by tilting the crystalline axis to 45°. Stable doublons could only exist in a range of velocity regime. Beyond this regime the patterns formed would be unstable. The simulation results agreed with the reported experimental results qualitatively.     

Electrochemical performance of C-La~(3+) codoped LiFePO_4 synthesized by microwave heating

La3+ was selected to elevate the lattice electronic conductivity of LiFePO4,and LiFePO4/(C+La3+) cathode powders were synthesized by microwave heating using a domestic microwave oven for 35 min. The microstructures and morphologies of the synthesized materials were investigated by XRD and SEM. The electrochemical performances were evaluated by galvanostatic charge-discharge. The electrochemical performance of LiFePO4 with different La3+ contents was studied. Results indicated that the initial specific disch...     

Nanosized GdVO_4 powders synthesized by sol-gel method using different carboxylic acids

Nanosized GdVO_4 powders were synthesized via a sol-gel method using different carboxylic acids as chelating agent, followed by calcination at 600 ℃ for 3 h.The effect of different carboxylic acids such as citric acid,malic acid, and tartaric acid on the characteristics of the nanosized GdVO_4 powders was investigated. The GdVO_4 powder was also synthesized without carboxylic acid for comparison. The thermal decomposition process of the carboxylate precursors was investigated by thermogravimetric differential thermal analysis(TG-DTA). X-ray diffraction(XRD), Fourier transform infrared spectroscopy(FTIR),field emission scanning electron microscope(FESEM),transmission electron microscope(TEM), and surface area measurement data were used to confirm the formation of nanocrystalline GdV04 powders. It is found that the synthesis using the carboxylic acid with higher heat of combustion results in the powder with larger crystallite size. The difference in the steric effect of the acids used,which was evaluated by a computational method, also affects the degree of agglomeration of the synthesized powders.     

Synthesis of TiAl-Al2O3 composites by high energy milling and hot-press sintering

A sub-microstructure titanium aluminide alloy/Al2O3 （3A） composite was obtained by crystallization of the amorphous powders, which were prepared by mechanical alloying （MA） in a planetary ball milling system using Ti-AI-TiO2 as raw materials. The experimental results show that, when the milling time increases up to 30 h, the hep Ti（Al） supersaturated solid solution disappears, only amorphous phase is left. The compact samples were synthesized by hot-press to 1 200 ℃ with the amorphous as a precursor; the final phases of the matrix and strengthened phase are y-TiAl and Al2O3. The phases come from in situ crystallization and transformation. The samples, fabricated from the amorphous phase by hot press sintering, have high bending strength and fracture toughness.     

Nanoparticles α-Al2O3 prepared by combustion synthesis method

Nanometer α-Al2O3 powders were synthesized by the method of low-temperature combustion synthesis （LCS） with aluminum nitrate nonahydrate and urea as raw materials. The prepared powders were studied by XRD, TG-DTA, FT-IR and TEM. It is found that the average size of particles is 60 -80 nm. The optimal synthetic conditions are obtained, i.e. , the suitable fuel is urea; the molar ratio of oxidizer to fuel is 1 ： 2 and the igniting temperature is 700℃. The results show that the size of particles is governed by synthesizing temperature, the fuel and the molar ratio of oxidizer to fuel. TEM image of the particles collected shows that the crystal habits of particles have a spheric structure and particles are polycrystal.     

Microwave absorbing properties of La0.8Ba0.2MnO3 nano-particles

La0.8Ba0.2MnO3 nano-particles were synthesized by sol-gel process, and the crystal structure and morphology＇ were characterized by XRD and SEM, respectively. The complex permittivity and permeability were determined by microwave vector network analyzer in the frequency range of 2-18 GHz. The relationship between reflection coefficient and microwave frequency of La0.8Ba0.2 MnO3 was calculated based on measured data. The results show that the average diameter of La0.8Ba0.2MnO3 crystal powders is about 80 nm and the crystal structure is perovskite when being calcined at 800 ℃ for 2 h. The microwave absorbing peak is 13 dB at 6.7 GHz and the effective absorbing bandwidth above 10 dB reaches 1.8 GHz for the sample with the thickness of 2.6 mm. The microwave absorption can be attributed to both the dielectric loss and the magnetic loss from the loss tangents of the sample, but the former is greater than the latter.