• Journal of Powder Materials
• /
• v.7 no.3
• /
• pp.149-153
• /
• 2000

In this study, the fabrication of $Al_2O_3$/5vol.%Cu nanocomposite and its mechanical property were discussed. The nanocomposite powders were produced by high energy ball milling of $Al_2O_3$ and Cu elemental powders. The ball-milled powders were sintered with Pulse Electric Current Sintering (PECS) facility. The relative densities of specimens sintered at $1200^{\circ}C$ and $1250^{\circ}C$ after soaking process at $900^{\circ}C$ were 96% and over 97%, respectively. The sintered microstructures were composed of $Al_2O_3$ matrix and the nano-sized Cu particles distributed on grain boundaries of $Al_2O_3$ matrix. The nanocomposite exhibited the enhanced fracture toughness compared with general monolithic $Al_2O_3$. The toughness increase was explained by the crack deflection and bridging by dispersed Cu particles.

• Journal of the Korean Ceramic Society
• /
• v.41 no.4
• /
• pp.334-339
• /
• 2004

Microstructures and mechanical properties of SPSed monolithic HAp, HAp-Ag, and HAp-ZrO$_2$sintered bodies were investigated by the XRD, SEM, and TEM techniques. The nano-sized HAp powders were successfully synthesized by precipitation of Ca(NO$_3$)$_2$4$H_2O$ and (NH$_4$)HPO$_4$solution. In the HAp-Ag composite, the shrinkage cavities were observed at the interfaces between HAp and large sized Ag particles due to the mismatch of their thermal expansion coefficients. However, no found the defect at the interfaces between HAp and fine-sized Ag particles. In the HAp-ZrO$_2$composite. nano-sized ZrO$_2$particles were almost dispersed at the grain boundaries of HAp phase. The fracture toughness of HAp-Ag and HAp-ZrO$_2$ composites were increased due to the plastic deformation and phase transformation mechanisms of the dispersed fine Ag and ZrO$_2$phase in the HAp matrix, respectively.

• Journal of the Korean Ceramic Society
• /
• v.49 no.1
• /
• pp.118-123
• /
• 2012

GDC20($Ce_{0.8}Gd_{0.2}O_{1.9}$) powder was synthesized from Ce and Gd nitrate solutions using ammonium carbonate($(NH_4)_2CO_3$) as a precipitant. Attrition-milling of the powder, which had been calcined at $700^{\circ}C$ for 4 h, decreased an average particle size of 2.2 ${\mu}m$ to 0.5 ${\mu}m$. The milled powder consisted of nano-sized spherical primary particles. Due to the excellent sinterability of the powder, sintering of the powder compacts for 4 h showed relative densities of 80% at 1000 $^{\circ}C$ and 96.5% at $1200^{\circ}C$, respectively. Densification was found to almost complete at $1300^{\circ}C$, resulting in a dense and homogeneous microstructure with a relative density of 99.5%. The grains of ~0.2 ${\mu}m$ in size at $1200^{\circ}C$ grew to ~1 ${\mu}m$ in size at $1300^{\circ}C$ as a result of a rapid grain growth.

• Journal of the Korean Ceramic Society
• /
• v.46 no.2
• /
• pp.131-136
• /
• 2009

Radio frequency (RF) plasma treatment is studied for the size reduction and the spheroidization of coarse particles to change them into nano-sized powders of spherical shape in MLCC fields. The uni-nanoadditives manufactured by RF plasma processing for high dispersion have been investigated for the effect on core-shell structure in dielectrics of MLCC. Microstructures have been characterized using scanning electron microscope (SEM), transmission electron microscope (TEM) and Electron Probe Micro Analyzer (EPMA). We compared the distribution of core-shell grains between specimens manufactured using uni-nanoadditive and using mixed additive. In addition, the uniformity of rare earth elements in the core-shell structured grains was analyzed. It was shown, from TEM observations, that the sintered specimen manufactured using uni-nanoadditives had more dense small grains with well-developed core-shell structure than the specimen using mixed additives, which had a homogeneous microstructure without abnormal grain growth and shows broad temperature coefficient of capacitance (TCC) curves in all temperature ranges because of well dispersed additives.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
• /
• v.24 no.9
• /
• pp.760-765
• /
• 2011

Znic sulfide (ZnS) thin films were deposited on glass substrates by radio frequency magnetron sputtering. The substrate temperature varied from room temperature (RT) to $500^{\circ}C$. The structural and optical properties of ZnS films were studied by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), energy dispersive analysis of X-ray (EDAX) and UV-visible transmission spectra. The XRD analyses reveal that ZnS films have cubic structures with (111) preferential orientation, whereas the diffraction patterns sharpen with the increase in substrate temperatures. The FESEM images indicate that ZnS films deposited at $400^{\circ}C$ have nano-sized grains with a grain size of ~ 67 nm. Then films exhibit relatively high transmittance of 80% in the visible region, with an energy band gap of 3.71 eV. One obvious result is that the energy band gap of the film increases with increasing the substrate temperatures.

• Journal of Powder Materials
• /
• v.11 no.3
• /
• pp.247-252
• /
• 2004

Recently, it has been found that mechanical alloying (MA) facilitates the nanocomposites formation of metal-metal oxide systems through solid-state reduction during ball milling. In this work, we studied the MA effect of Fe$_{3}$O$_{4}$-M (M = Al, Ti) systems, where pure metals are used as reducing agents. It is found that composite powders in which $Al_{2}$O$_{3}$ and TiO$_{2}$ are dispersed in $\alpha$-Fe matrix with nano-sized grains are obtained by mechanical alloying of Fe$_{3}$O$_{4}$ with Al and Ti for 25 and 75 hours, respectively. It is suggested that the large negative heat associated with the chemical reduction of magnetite by aluminum is responsible for the shorter MA time for composite powder formation in Fe$_{3}$O$_{4}$-Al system. X-ray diffraction results show that the reduction of magnetite by Al and Ti if a relatively simple reaction, involving one intermediate phase of FeAl$_{2}$O$_{4}$ or Fe$_{3}$Ti$_{3}$O$_{10}$. The average grain size of $\alpha$-Fe in Fe-TiO$_{2}$ composite powders is in the range of 30 nm. From magnetic measurement, we can also obtain indirect information about the details of the solid-state reduction process during MA.

• Metals and materials international
• /
• v.24 no.6
• /
• pp.1285-1292
• /
• 2018

Microstructural properties of as-grown and annealed CoCrFeMnNi high entropy alloy (HEA) oxynitride thin films were investigated. The CoCrFeMnNi HEA oxynitride thin film was grown by magnetron sputtering method using an air gas, and annealed under the argon plus air flow for 5 h at $800^{\circ}C$. The as-grown film was homogeneous and uniform composed of nanometer-sized crystalline regions mixed with amorphous-like phase. The crystalline phase in the as-grown film was face centered cubic structure with the lattice constant of 0.4242 nm. Significant microstructural changes were observed after the annealing process. First, it was fully recrystallized and grain growth happened. Second, Ni-rich region was observed in nanometer-scale range. Third, phase change happened and it was determined to be $Fe_3O_4$ spinel structure with the lattice constant of 0.8326 nm. Hardness and Young's modulus of the as-grown film were 4.1 and 150.5 GPa, while those were 9.4 and 156.4 GPa for the annealed film, respectively.

• Korean Journal of Materials Research
• /
• v.11 no.9
• /
• pp.733-739
• /
• 2001

In Al-25Nb binary system, it was observed only formation of $D0_{22}$ $Al_3Nb$ intermetallic compound after 5hr milling but it was not observed formation of meta stable phase like L1$_2$ phase. In this state, $D0_{22}$ $Al_3Nb$ fabricated had nano sized grain of approximately 20nm. Ternary systems, transition metals such as Cr, Cu, Fe, Mn were added 6~12at.% as substitution of Al, showed formation of $D0_{22}$ $Al_3Nb$ like Al-25Nb binary system. In Al- l2Cu-25Nb system, it was observed that broad XRD pattern like amorphization of Al and not observed formation of $D0_{22}$ $Al_3Nb$ after 5hr milling. But there was mixed phase of a lot of amorphous Al and little $D0_{22}$ $Al_3Nb$ through TEM. In the states of unalloyed, 5~7hr milling time, those showed exothermic reaction at 35$0^{\circ}C$, which was formation of $D0_{22}$ $Al_3Nb$ like Al-25Nb binary system. With increasing milling time to 10hr, $D0_{22}$ $Al_3Nb$ was transformed to mixed phase of amorphous and nanocryatlline, having approximately 10nm grain but the meta stable $Al_3Nb$ was not fabricated by adding transition metals.

• Environmental Engineering Research
• /
• v.19 no.3
• /
• pp.255-259
• /
• 2014

In this research, we compared the COD removal efficiencies of titanium dioxide ($TiO_2$) thin films coated on the surfaces of borosilicate glass that prepared by three different numbers of coating layer; i) 3 layers ii) 4 layers and iii) 5 layers by sol-gel method. All of the prepared $TiO_2$ thin films consisted of pure anatase crystalline structure with grain sizes in the range 20-250 nm. The calculated optical band gaps of the $TiO_2$ thin films were 3.24. The total apparent surface area per total weight of $TiO_2$ thin films were 4.74, 3.86 and $2.79m^2g^{-1}$ for 3, 4 and 5 layers coating, respectively. The kinetics of the photodegradation reactions of COD under UVA light source were described by the Langmuir-Hinshelwood (L-H) kinetic model. The specific rates of the photodegradation of $TiO_2$ thin films at 3 layers coating was $1.40{\times}10^{-4}min^{-1}mW^{-1}$, while for the 4 layers coating and the 5 layers coating were $1.50{\times}10^{-4}$ and $4.60{\times}10^{-4}min^{-1}mW^{-1}$, respectively. The photocatalytic performance of COD degradation was higher with smaller grain size, higher surface area and narrow optical band gaps. Moreover, the numbers of coating layer on substrate also have great influence for kinetic of COD removal.

• Journal of the Korean Ceramic Society
• /
• v.42 no.1
• /
• pp.43-49
• /
• 2005

YSZ layer containing nano-sized particles has been deposited on the commercial A1203 substrate by Electron Beam Physical Vapor Deposition (EB-PVD). The role of coating rnjcrostructures of YSZ to indentation damage is studied. The different coating microsouctures are prepared by varying the substrate temperatures from $600^{circ}C$ to $800^{circ}C$ during the deposition. Microhardness test and Hertzian indentation are conducted on the $YSZ/Al_{2}O_{3}$ layered systems. The damage and flilure behaviors have been investigated according to the effect of microstructures and indentation loads. With increasing the substrate temperature during EB-PVD, the overall grain sizes are coarser and more faceted, which microsoucture ultimately influences on the indentation behavior, thus, YSZ/Al_{2}O_{3}$ layered system prepared at the substrate temperature of $800^{circ}C$ shows relatively higher damage tolerance.