Fabrication of Ni_3Al by hot pressing from element powders

Ni3Al intermetallic was synthesized by hot pressing from element powders of nickel, aluminum, and boron. The influences of parameters on the properties of Ni3Al were investigated. The parameters include the particle size of nickel powder, adding or without boron powder, hot pressing temperature, etc. The properties include the density of hot-pressed samples, resultant ratio of Ni3Al phase, and bending strength. The microstructures of hot-pressed samples were investigated by X-ray diffraction and scan electronic microscopy, and the properties, such as density and bending strength, were also measured. The results show that a higher bending strength was obtained under the same hot pressing conditions by the fine nickel powder than the coarse one, and there is little difference about density. Boron powder added in this process acceler- ates the formation of Ni3Al and markedly increases the hot pressed density. In the temperature range of this study, the den- sity increases along with the hot pressing temperature. Full dense Ni3Al samples were obtained under the condition of 860°C, 10 min, 45 MPa from Ni-22.89Al-0.5B powder.     

Fabrication of Ni3AI by hot pressing from element powders

Ni3Al intermetaUic was synthesized by hot pressing from element powders of nickel, aluminum, and boron. The influences of parameters on the properties of Ni3Al were investigated. The parameters include the particle size of nickel powder, adding or without boron powder, hot pressing temperature, etc. The properties include the density of hot-pressed samples, resultant redo of Ni3A1 phase, and bending strength. The microstructures of hot-pressed samples were investigated by X-ray diffraction and scan electronic microscopy, and the properties, such as density and bending strength, were also measured. The results show that a higher bending strength was obtained under the same hot pressing conditions by the fine nickel powder than the coarse one, and there is little difference about density. Boron powder added in this process accelerates the formation of Ni3Al and markedly increases the hot pressed density. In the temperature range of this study, the density increases along with the hot pressing temperature. Full dense Ni3Al samples were obtained under the condition of 860℃, 10 min, 45 MPa from Ni-22.89A1-0.5B powder.     

Fabrication and mechanical properties of MWCNTs-reinforced aluminum composites by hot extrusion

Over the past decade,the interest in aluminum composites reinforced with carbon nanotubes has grown significantly.Studies have been carried out to overcome problems with uniform dispersion,interfacial bonding,void formation and carbide formation of the composites.In the present work,multi-wall carbon nanotubes(MWCNTs)aluminum composites were produced.High-energy ball milling with the aim at developing well-dispersed MWCNTs Al composites was followed by cold compaction,sintering,and hot extrusion at 500 ℃.Different amounts of stearic acid as processing control agent(PCA)is used in order to minimize cold welding of the Al particles,and to produce finer particles.Differential scanning calorimetry(DSC),scanning electron microscopy(SEM),transmission electron microscopy(TEM),and X-ray diffraction(XRD)were employed to analyze the MWCNTs,the aluminum powder,and the composites' microstructural behavior.The hardness and tensile properties of the composites are also evaluated.The results showed 500％ increase in yield stress after the addition of 1 wt％ MWCNTs in Al-MWCNTs based composite.The ball-milling time of 4 h is found to be sufficient as excessive milling time destroys a vast number of MWCNTs.     

Fabrication of micro-fine high Nb-containing TiAl alloyed powders by fluidized bed jet milling

A fluidized bed jet milling process was used to make micro-fine high Nb-containing TiAl alloyed powders from the chippings obtained by crushing the Ti-45Al-8.5Nb-(W,B,Y) ingot.The influences of classifier frequency on powder characteristics were investigated.The results show that the powders with controlled average particle size can be prepared on a large scale.The powders with different sizes are all dominated by γ with a minor amount of α2-Ti3Al.The particle size significantly decreases with the classifier frequency increasing.At a classifier frequency higher than 38 Hz,the average particle size of the ground powders is lower than 25 μm.The powders are composed of two different sizes of particles:shaped particles and some clastic particles,and both particle sizes meet the log-normal distribution.With the classifier frequency increasing,the both sizes decrease; meanwhile,the proportion of the clastic particles gradually increases,and the size distribution span value of the ground powders increases correspondingly.     

Preparation and magnetic properties of nickel nanorods by thermal decomposition reducing methods

The single-crystalline nickel nanorods with narrow size distribution and better magnetic properties were synthesized by thermal decomposition of nickel hydroxide nanorods precursor powders, which were produced by soft template method using nickel oxalic acid as raw material. The influences of hydrothermal reaction temperature and time on morphology of the products were investigated. The structure, morphology and magnetic properties of the products were characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), thermogravimetric differential scanning calorimetry (TGA-DSC) and vibrating sample magnetometer (VSM). The as-prepared nickel nanorods are uniform with a diameter of 10–15 nm and length 70–120 nm. The results of magnetic measurements show that the specific saturation magnetization(σ_s) and coercivity values(H_c) of the nickel nanorods are 50.649 A·m²/kg and 190.0×(10³/4 π)A/m, respectively. Finally, a possible mechanism for the formation of nickel nanorods was discussed briefly.     

Preparation and characterization of fibrous NiO particles by thermal decomposition of nickelous complex precursors

The influences of pyrolytic conditions, including temperature, time, the flow rate of air, and the heating rate, on the morphology, average size and specific surface area of the NiO particles were investigated, and the composition and morphologies of the products were characterized by using of XRD, SEM and BET. It is found that fibrous NiO particles were produced under the optimal conditions. A suitable range of pH for preparing dispersive precursors was chosen according to analysis of zeta potential. Based on the observations of NiO precursors growth and SEM morphology of the precursor, the oriented attachment was proposed for the well-aligned growth of the NiO precursor fibres. The final product NiO inherits the morphology of the precursor.     

Fabrication of TiB2 composite powders coated with BN by high speed airflow impact

TiB2 powders coated with BN were prepared by Hybridization System making use of dry impact blending method to achieve powder surface modification. Parameters of coating were analyzed and the most appropriate condition was summarized. Scan electron microscope of JSM-5610LV and transmission electron microscope of H600STEM/EDS were used to observe the microstructure of coated powders. Results show that treatment time, rotation speed, granularity ratio of TiB2 to BN, pretreatment of materials etc influence the coating results evidently.Mixing raw materials and coating with BN under the appropriate condition can get round TiB2/BN composite powder with smooth surface and compact coating layer.     

Particular properties of Ti_2O and TiN_x nanoparticles prepared by thermal decomposition

Particular properties of Ti2O and TiNx prepared by thermal decomposition were introduced. A precursor prepared by titanium powder react- ing with oxalate acid was thermally decomposed in nitrogen atmosphere at 840°C for 15 min, and relatively pure Ti2O was then obtained. Conductive TiNx was also prepared after altering reaction conditions. Samples were characterized by resistivity, X-ray powder diffraction, transmission electron microscope, Ultraviolet-Visible diffuse reflection, and electromagnetic shielding efficiency. The results indicate that both Ti2O and TiNx have good conductivity. Moreover, Ti2O shows a better solar photocatalytic activity and TiNx does well in the electro- magnetic shield.     

Electrochemical performance of multi-element doped α-nickel hydroxide prepared by supersonic co-precipitation method

The multi-element doped α-nickel hydroxides have been prepared by supersonic co-precipitation method. Three kinds of samples A, B, C were prepared by chemically coprecipitating Ni, Al, Co, Y, Zn. It was found that sample C produced better performance than the others. The cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) measurements indicated that sample C has better electrochemical performance, such as better reaction reversibility, higher proton diffusion coefficient and lower charge-transfer resistance, than those of samples A and B. The charge-discharge tests showed that the discharge capacity (346 mA h/g) of sample C is even larger at 0.5 C rate than that (337mAh/g) at 0.1 C rate, while the discharge capacity at 0.5 C rate is much lower than that at 0.1 C rate for samples A and B. It indicates that all doped elements can produce the synergic effect and further improve the electrochemical properties of the active materials.     

Synthesis of Ti3SiC2 by spark plasma sintering(SPS)of elemental powders

Ti3SiC2 materials have been fabricated by spark plasma sintering of the elemental powders with the addition of Al.At the heating rate of 80℃/min and under the pressure of 30MPa,the ideal synthesis temperature of Ti3SiC2 is in the range of 1150-1250℃.The addition of Al is in favor of the formation of Ti3SiC2.The synthesized compound has the molecular of Ti3Si0.8Al0.2C2 and lattice parameters of α=0.3069nm,c=1.7670nm.Its grain is plane-shape with a size of about 50μm in the elongated dimension.The prepared material has Vickers hardness of 3.5-5.5GPa(at 1N and 15s) and is as readily machinable as graphite‘s.     

Enhanced Cu(Ⅱ) adsorption by orange peel modified with sodium hydroxide

Copper adsorption by orange peel, which was chemically modified with sodium hydroxide, was investigated. The adsorbent was characterized using surface area analyzer, infrared spectroscopy and scanning electron microscopy. Total negative charge and zeta potentials on the adsorbent surface were determined. Equilibrium isotherms and kinetics were obtained and the effects of solution pH value, adsorbent concentration and temperature were studied in batch experiments. Column experiments were performed to study practical applicability, and breakthrough curves were obtained. Equilibrium is well described by Langmuir and Freundlich isotherms, and kinetics is found to fit pseudo-second order type adsorption kinetics. According to Langmuir equation, the maximum adsorption capacity for Cu(II) is 50.25 mg/g at pH value of 5.3. The results show additional chemical modification of the adsorbent by NaOH and the increased adsorption capacity.     

Synthesis of Mo-Si-B intermetallic compounds with continuous α-Mo matrix by pulverization of ingot and hydrogen reduction of MoO3 powders

The fabrication of the intermetallic phase T2-Mo₃Si with continuous matrix of α-Mo was attempted with the combination process of high energy ball milling, pulverization of arc-melted ingot, addition of Mo by hydrogen reduction of MoO₃ and spark plasma sintering processes. High energy ball milling or arc melting of Mo-16.7Si-16.7B (at %) powders were performed to obtain to intermetallic phase T2 and Mo₃Si. The Mo phase of 57 vol% distributed intermetallic compound powders were prepared by hydrogen reduction of MoO₃ and further mixing of elemental Mo powders. X-ray diffractometry analysis revealed that the intermetallic phase T2-Mo₃Si can be produced by the pulverization process of arc-melted ingot. Hydrogen reduction of 1 vol% MoO₃ mixed intermetallic powder followed by further addition of Mo powders was a more adequate method enabling the homogeneous distribution of the Mo phase than that of added MoO₃ powders with total amount. The powder mixture was successfully consolidated by spark plasma sintering yielding a sound microstructure comprising the intermetallic phase T2-Mo₃Si uniformly distributed in a continuous matrix of α-Mo.     

Wetting of (0001) α-Al2O3 single crystals by molten Al

The wetting behavior of (0 0 0 1) α-Al₂O₃ by molten Al was studied over a wide temperature range between 700 and 1500 °C. The increase in the contact angle with time at temperatures lower than 1200 °C is attributed to the surface structural reconstruction of the (0 0 0 1) α-Al₂O₃. High-temperature annealing of the substrate does not have a significant influence on the wettability.     

Preparation of Mo(Si, Al)2–ZrO2 nanocomposite powders by mechanical alloying

Phase transformations and the final formation of Mo(Si, Al)₂–ZrO₂ nanocomposite during high-energy ball milling of a series of Mo–Si–Al–ZrO₂ powders were investigated. Mechanical alloying led to phase transformations from the initial Mo–Si–Al powders mixture to Mo_ss (2 h) → C40 Mo(Si, Al)₂ (4, 8 h) → Mo_ss (12 h) phases. The phase transformations studied by XRD are discussed considering the alloying and second phase effects. Finally, the Mo_ss matrix reinforced with ZrO₂ particles nanocomposite structure was studied by means of TEM. The Mo_ss matrix phase formed was revealed to be strongly inhomogeneous even after 12 h of mechanical alloying and Mo-, Si- and Al-enriched regions were observed. The ZrO₂ nanostructured phase, evenly distributed in the Mo_ss matrix, had grain size of about 5–20 nm.     

Fabrication of hexagonal gallium nitride films on silicon (111) substrates

Hexagonal gallium nitride films were successfully fabricated through ammoniating Ga2O3 films deposited on silicon (111) substrates by electrophoresis. The structure, composition, and surface morphology of the formed films were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The measurement results reveal that the polycrystalline GaN films with hexagonal wurtzite structure were successfully grown on the silicon (111) substrates. Preliminary results suggest that varying the ammoniating temperature has obvious effect on the quality of the GaN films formed with this method.     

Non-isothermal decomposition kinetics and lifetime of Tb2(0-MBA)6(PHEN)2

The thermal decomposition of Tb2(O-MBA)6(PHEN)2 (O-MBA: o-methylbenzoate; PHEN: 1,10-phenanthroline) and its kinetics were studied under the non-isothermal condition by thermogravimetry-derivative thermogravimetry (TG-DTG) techniques. Kinetic parameters were obtained from analysis of TG-DTG curves by the Achar method and the Madhusudanan-Krishnan-Ninan (MKN) method. The most probable mechanism function was suggested by comparing the kinetic parameters. The kinetic equation for the first stage can be expressed as dcddt = Aexp(-E/RT) 3(1 - α)2/3 The lifetime equation at mass loss of 10% was deduced as lnr= -28.7429 + 19797.795/Tby isothermal thermogravimetric analysis.     

Effect of ultra-fine powders on the microstructure of Ti(CN)–xWC–Ni cermets

Microstructural and compositional analyses of Ti(CN)–xWC–20Ni cermets were done in order to better understand the dissolution behavior of ultra-fine sized Ti(CN) and WC in comparison with a micro-sized system. The WC content was varied from 5 to 75 wt%. A discrete composition (∼50 wt%WC addition) at which WC does not dissolve any longer in the ultra-fine system was found. At this composition, the W concentrations, not only in the rim, (Ti,W)(CN), but in the binder as well were at a maximum. Depending on the powder size and morphology, these values are strongly affected due to the surface areas of Ti(CN) and WC for dissolution and precipitation sites. Furthermore, a significant improvement in the mechanical properties of simple ultra-fine systems was found, compared to that of corresponding micron-sized systems (Hv 14–15 GPa, K_IC 8–10 MPa m^1/2), which are comparable to commercial cermets. The refined microstructure and high fraction of rim phase in the ultra fine systems are likely responsible for this difference.     

Electrochemical properties of aluminum-substituted α-Ni(OH)_2

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