• Journal of Powder Materials
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• v.26 no.3
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• pp.231-236
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• 2019

Ni hydroxides ($Ni(OH)_2$) are synthesized on Ni foam by varying the hexamethylenetetramine (HMT) concentration using an electrodeposition process for pseudocapacitor (PC) applications. In addition, the effects of HMT concentration on the $Ni(OH)_2$ structure and the electrochemical properties of the PCs are investigated. HMT is the source of amine-based $OH^-$ in the solution; thus, the growth rate and morphological structure of $Ni(OH)_2$ are influenced by HMT concentration. When $Ni(OH)_2$ is electrodeposited at a constant voltage mode of -0.85 V vs. Ag/AgCl, the cathodic current and the number of nucleations are significantly reduced with increasing concentration of HMT from 0 to 10 mM. Therefore, $Ni(OH)_2$ is sparsely formed on the Ni foam with increasing HMT concentration, showing a layered double-hydroxide structure. However, loosely packed $Ni(OH)_2$ grains that are spread on Ni foam maintain a much greater surface area for reaction and result in the effective utilization of the electrode material due to the steric hindrance effect. It is suggested that the $Ni(OH)_2$ electrodes with HMT concentration of 7.5 mM have the maximum specific capacitance (1023 F/g), which is attributed to the facile electrolyte penetration and fast proton exchange via optimized surface areas.

• Journal of Powder Materials
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• v.26 no.3
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• pp.237-242
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• 2019

In this study, ultrasonic spray pyrolysis combined with salt-assisted decomposition, a process that adds sodium nitrate ($NaNO_3$) into a titanium precursor solution, is used to synthesize nanosized titanium dioxide ($TiO_2$) particles. The added $NaNO_3$ prevents the agglomeration of the primary nanoparticles in the pyrolysis process. The nanoparticles are obtained after a washing process, removing $NaNO_3$ and NaF from the secondary particles, which consist of the salts and $TiO_2$ nanoparticles. The effects of pyrolysis temperature on the size, crystallographic characteristics, and bandgap energy of the synthesized nanoparticles are systematically investigated. The synthesized $TiO_2$ nanoparticles have a size of approximately 2-10 nm a bandgap energy of 3.1-3.25 eV, depending on the synthetic temperature. These differences in properties affect the photocatalytic activities of the synthesized $TiO_2$ nanoparticles.

• Journal of Powder Materials
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• v.26 no.2
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• pp.132-137
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• 2019

Tungsten carbide (WC) hard materials are used in various industries and possess a superior hardness compared to other hard materials. They have particularly high melting points, high strength, and abrasion resistance. Accordingly, tungsten carbide hard materials are used for wear-resistant tools, cutting tools, machining tools, and other tooling materials. In this study, the WC-5wt.%Co, Fe, Ni hard materials are densified using the horizontal ball milled WC-Co, WC-Fe, and WC-Ni powders by a spark plasma sintering process. The WC-5Co, WC-5Fe, and WC-5Ni hard materials are almost completely densified with a relative density of up to 99.6% after simultaneous application of a pressure of 60 MPa and an electric current for about 15 min without any significant change in the grain size. The average grain size of WC-5Co, WC-5Fe, and WC-5Ni that was produced through SPS was about 0.421, 0.779, and $0.429{\mu}m$, respectively. The hardness and fracture toughness of the dense WC-5Co, WC-5Fe, WC-5Ni hard materials were also investigated.

• Journal of Powder Materials
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• v.26 no.2
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• pp.138-145
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• 2019

In this study, Al-Si-Mg alloys are additively manufactured using a selective laser melting (SLM) process from AlSi10Mg powders prepared from a gas-atomization process. The processing parameters such as laser scan speed and laser power are investigated for 3D printing of Al-Si-Mg alloys. The laser scan speeds vary from 100 to 2000 mm/s at the laser power of 180 and 270 W, respectively, to achieve optimized densification of the Al-Si-Mg alloy. It is observed that the relative density of the Al-Si-Mg alloy reaches a peak value of 99% at 1600 mm/s for 180 W and at 2000 mm/s for 270W. The surface morphologies of the both Al-Si-Mg alloy samples at these conditions show significantly reduced porosities compared to those of other samples. The increase in hardness of as-built Al-Si-Mg alloy with increasing scan speed and laser power is analyzed due to high relative density. Furthermore, it was found that cooling conditions after the heat-treatment for homogenization results in the change of dispersion status of Si phases in the Al-Si matrix but also affects tensile behaviors of Al-Si-Mg alloys. These results indicate that combination between SLM processing parameters and post-heat treatment should be considered a key factor to achieve optimized Al-Si alloy performance.

• Journal of Powder Materials
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• v.26 no.1
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• pp.49-57
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• 2019

Layered $LiNi_{0.83}Co_{0.11}Mn_{0.06}O_2$ cathode materials single- and dual-doped by the rare-earth elements Ce and Nd are successfully fabricated by using a coprecipitation-assisted solid-phase method. For comparison purposes, non-doping pristine $LiNi_{0.83}Co_{0.11}Mn_{0.06}O_2$ cathode material is also prepared using the same method. The crystal structure, morphology, and electrochemical performances are characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectrometer (EDS) mapping, and electrochemical techniques. The XRD data demonstrates that all prepared samples maintain a typical ${\alpha}-NaFeO_2$-layered structure with the R-3m space group, and that the doped samples with Ce and/or Nd have lower cation mixing than that of pristine samples without doping. The results of SEM and EDS show that doped elements are uniformly distributed in all samples. The electrochemical performances of all doped samples are better than those of pristine samples without doping. In addition, the Ce/Nd dual-doped cathode material shows the best cycling performance and the least capacity loss. At a 10 C-rate, the electrodes of Ce/Nd dual-doped cathode material exhibit good capacity retention of 72.7, 58.5, and 45.2% after 100, 200, and 300 cycles, respectively, compared to those of pristine samples without doping (24.4, 11.1, and 8.0%).

• Journal of Powder Materials
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• v.26 no.1
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• pp.6-10
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• 2019

In this study, freeze drying of a porous Ni with unidirectionally aligned pore channels is accomplished by using a NiO powder and camphene. Camphene slurries with NiO content of 5 and 10 vol% are prepared by mixing them with a small amount of dispersant at $50^{\circ}C$. Freezing of a slurry is performed at $-25^{\circ}C$ while the growth direction of the camphene is unidirectionally controlled. Pores are generated subsequently by sublimation of the camphene during drying in air for 48 h. The green bodies are hydrogen-reduced at $400^{\circ}C$ and then sintered at $800^{\circ}C$ and $900^{\circ}C$ for 1 h. X-ray diffraction analysis reveals that the NiO powder is completely converted to the Ni phase without any reaction phases. The sintered samples show large pores that align parallel pores in the camphene growth direction as well as small pores in the internal walls of large pores. The size of large and small pores decreases with increasing powder content from 5 to 10 vol%. The influence of powder content on the pore structure is explained by the degree of powder rearrangement in slurry and the accumulation behavior of powders in the interdendritic spaces of solidified camphene.

• Journal of Powder Materials
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• v.26 no.1
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• pp.34-39
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• 2019

Current synthesis processes for titanium dioxide ($TiO_2$) nanoparticles require expensive precursors or templates as well as complex steps and long reaction times. In addition, these processes produce highly agglomerated nanoparticles. In this study, we demonstrate a simple and continuous approach to synthesize $TiO_2$ nanoparticles by a salt-assisted ultrasonic spray pyrolysis method. We also investigate the effect of salt content in a precursor solution on the morphology and size of synthesized products. The synthesized $TiO_2$ nanoparticles are systematically characterized by X-ray diffraction, transmission electron micrograph, and UV-Vis spectroscopy. These nanoparticles appear to have a single anatase phase and a uniform particle-size distribution with an average particle size of approximately 10 nm. By extrapolating the plots of the transformed Kubelka-Munk function versus the absorbed light energy, we determine that the energy band gap of the synthesized $TiO_2$ nanoparticles is 3.25 eV.

• Journal of Powder Materials
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• v.26 no.1
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• pp.40-44
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• 2019

Tungsten trioxide ($WO_3$) is a promising candidate as a photocatalyst because of its outstanding electrical and optical properties. In this study, we prepare $WO_3$ thin films by electrodeposition and characterize the photocatalytic degradation of methylene blue using these films. Depending on the voltage conditions (static and pulse), compact and porous $WO_3$ films are fabricated on a transparent ITO/glass substrate. The morphology and crystal structure of electrodeposited $WO_3$ thin films are investigated by scanning electron microscopy, atomic force microscopy, and X-ray diffraction. An application of static voltage during electrodeposition yields a compact layer of $WO_3$, whereas a highly porous morphology with nanoflakes is produced by a pulse voltage process. Compared to the compact film, the porous $WO_3$ thin film shows better photocatalytic activities. Furthermore, a much higher reaction rate of degradation of methylene blue can be achieved after post-annealing of $WO_3$ thin films.

• Journal of Powder Materials
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• v.25 no.6
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• pp.494-500
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• 2018

In this study, the effect of the content of $MgO-CaO-Al_2O_3-SiO_2$ (MCAS) glass additives on the properties of AlN ceramics is investigated. Dilatometric analysis and isothermal sintering for AlN compacts with MCAS contents varying between 5 and 20 wt% are carried out at temperatures ranging up to $1600^{\circ}C$. The results showed that the shrinkage of the AlN specimens increases with increasing MCAS content, and that full densification can be obtained irrespective of the MCAS content. Moreover, properties of the AlN-MCAS specimens such as microhardness, thermal conductivity, dielectric constant, and dielectric loss are analyzed. Microhardness and thermal conductivity decrease with increasing MCAS content. An acceptable candidate for AlN application is obtained: an AlN-MCAS composite with a thermal conductivity over $70W/m{\cdot}K$ and a dielectric loss tangent (tan ${\delta}$) below $0.6{\times}10^{-3}$, with up to 10 wt% MCAS content.

• Journal of Powder Materials
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• v.26 no.3
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• pp.201-207
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• 2019

Tungsten heavy alloys (W-Ni-Fe) play an important role in various industries because of their excellent mechanical properties, such as the excellent hardness of tungsten, low thermal expansion, corrosion resistance of nickel, and ductility of iron. In tungsten heavy alloys, tungsten nanoparticles allow the relatively low-temperature molding of high-melting-point tungsten and can improve densification. In this study, to improve the densification of tungsten heavy alloy, nanoparticles are manufactured by ultrasonic milling of metal oxide. The physical properties of the metal oxide and the solvent viscosity are selected as the main parameters. When the density is low and the Mohs hardness is high, the particle size distribution is relatively high. When the density is high and the Mohs hardness is low, the particle size distribution is relatively low. Additionally, the average particle size tends to decrease with increasing viscosity. Metal oxides prepared by ultrasonic milling in high-viscosity solvent show an average particle size of less than 300 nm based on the dynamic light scattering and scanning electron microscopy analysis. The effects of the physical properties of the metal oxide and the solvent viscosity on the pulverization are analyzed experimentally.