• Journal of the Korean Ceramic Society
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• v.33 no.5
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• pp.563-571
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• 1996

In order to fabricate solid electrolyte CaO-stabilized ZrO2 of high density sintered body economically 13 mol% CaO-stabilized ZrO2 powders were synthesized by the coprecipitation method. The characteristics and sintering behavior of fine powder were investigated. The precipitates has the specific surface area of 193 m2/g and apperaed to be fine and spherical primary particles with a size of approximately 5nm. The crystalliza-tion temperture of CaO-stabilized ZrO2 was 462$^{\circ}C$. The tetragonal phase was stable in the low calcining tempe-rature regions and the cubic zirconia solid solution was formed from above 120$0^{\circ}C$ through an intermediate stage of formation of CaZrO3 By introducing fine powders washed with alcohol and ball-milling process after calcination the sintered body was possible to attain the value of above 92% of the theoretical density at low temperature of 120$0^{\circ}C$.

• Journal of the Korean Ceramic Society
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• v.31 no.1
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• pp.1-10
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• 1994

Monodispersed alumina and Mg-doped alumina fine particles were prepared by controlled hydrolysis of alkoxides. Aluminium alkoxide and magnesium alkoxide were dissolved into complex solvent which was composed of hydrophobic n-octanol and hydrophilic acetonitrile. Hydroxypropyl cellulose(HPC) was used as a dispersant for the alumina particles. The size of these prepared powders was approximately 0.3 ${\mu}{\textrm}{m}$. In the case of sintering above 100$0^{\circ}C$, most of these prepared powders were transformed to $\alpha$-alumina. The relative density of the sintered body of these prepared powders at 1$600^{\circ}C$ was 98%. The sintered body of the Mg-doped alumina powder had more uniform grain size than that of the undoped alumina podwer.

• Proceedings of the Korea Association of Crystal Growth Conference
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• 1998.09a
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• pp.73-77
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• 1998

Langasite(La3Ga5SiO14) is a new piezoelectric material which is similar to quartz, LN(LiNbO3) and LT(LiTaO3) in its acoustic behavior. In this study, pure Langasite and Langasite family groups were synthesized by the solid state reactions in air. For the synthesis process, diffusion species were investigated and sintered body of synthesized powders were studied on dielectric property according to surface microstructures.

• Archives of Metallurgy and Materials
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• v.65 no.4
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• pp.1269-1272
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• 2020

In this study, a molybdenum alloy with dispersed high-entropy particles was fabricated using the powder metallurgy method. The high-entropy powder, composed of Nb, Ta, V, W, and Zr elements with a same atomic fraction, was prepared via high-energy ball milling. Using this powder, an ideal core-shell powder, composed of high-entropy powder as core and Mo powder as shell, was synthesized via the milling and reduction processes. These processes enabled the realization of an ideal microstructure with the high-entropy phase uniformly dispersed in the Mo matrix. The sintered body was successfully fabricated via uniaxial compaction followed by pressureless sintering. The sintered body was analyzed by X-ray diffraction and scanning electron microscope, and the high-entropy phase is uniformly dispersed in the Mo matrix.

• Journal of Powder Materials
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• v.22 no.4
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• pp.271-277
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• 2015

As wrought stainless steel, sintered stainless steel (STS) has excellent high-temperature anti-corrosion even at high temperature of $800^{\circ}C$ and exhibit corrosion resistance in air. The oxidation behavior and oxidation mechanism of the sintered 316L stainless was reported at the high temperature in our previous study. In this study, the effects of additives on high-temperature corrosion resistances were investigated above $800^{\circ}C$ at the various oxides ($SiO_2$, $Al_2O_3$, MgO and $Y_2O_3$) added STS respectively as an oxidation inhibitor. The morphology of the oxide layers were observed by SEM and the oxides phase and composition were confirmed by XRD and EDX. As a result, the weight of STS 316L sintered body increased sharply at $1000^{\circ}C$ and the relative density of specimen decreased as metallic oxide addition increased. Compared with STS 316L sintered parts, weight change ratio corresponding to different oxidation time at $900^{\circ}C$ and $1000^{\circ}C$, decreased gradually with the addition of metallic oxide. The best corrosion resistance properties of STS could be improved in case of using $Y_2O_3$. The oxidation rate was diminished dramatically by suppression the peeling on oxide layers at $Y_2O_3$ added sintered stainless steel.

• Journal of Powder Materials
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• v.23 no.4
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• pp.282-286
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• 2016

A sintered body of $TiB_2$-reinforced iron matrix composite ($Fe-TiB_2$) is fabricated by pressureless-sintering of a mixture of titanium hydride ($TiH_2$) and iron boride (FeB) powders. The powder mixture is prepared in a planetary ball-mill at 700 rpm for 3 h and then pressurelessly sintered at 1300, 1350 and $1400^{\circ}C$ for 0-2 h. The optimal sintering temperature for high densities (above 95% relative density) is between 1350 and $1400^{\circ}C$, where the holding time can be varied from 0.25 to 2 h. A maximum relative density of 96.0% is obtained from the ($FeB+TiH_2$) powder compacts sintered at $1400^{\circ}C$ for 2 h. Sintered compacts have two main phases of Fe and $TiB_2$ along with traces of TiB, which seems to be formed through the reaction of TiB2 formed at lower temperatures during the heating stage with the excess Ti that is intentionally added to complete the reaction for $TiB_2$ formation. Nearly fully densified sintered compacts show a homogeneous microstructure composed of fine $TiB_2$ particulates with submicron sizes and an Fe-matrix. A maximum hardness of 71.2 HRC is obtained from the specimen sintered at $1400^{\circ}C$ for 0.5 h, which is nearly equivalent to the HRC of conventional WC-Co hardmetals containing 20 wt% Co.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.5 no.2
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• pp.135-141
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• 1995

Abstract The sintering behavior and the electrical properties of sintered PZT ceramics using 2.45 GHz microwave energy were investigated. The ceramics were sintered between $1050 ~ 1130^{\circ}C$ for 5 min. Sintered body with high density and good electrical properties were achieved as the sintering temperature increases. Above $1090^{\circ}C$, however, the bulk density was decreased due to the volatilization of PbO component, and also electrical properties were decreased. The relative dielectric constant, mechanical Quality factor, electro- mechanical coupling factor of microwave sintered body at $1090^{\circ}C$ without PbO atmosphere were 1900, 80, 0.53 respectively, which were comparable to conventional sintering values. The sintering process completed within 20 min using microwave hybrid energy. The processing time and the amount of energy con-sumption could be reduced by microwave hybrid energy assisted rapid sintering.

• Korean Journal of Materials Research
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• v.17 no.2
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• pp.100-106
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• 2007

The effects of $MgO-P_2O_5$ based sintering additive on the microstructure and material and biological properties of hydroxyapatite $(HAp,\;Ca_{10}(PO_4)_6(OH)_2)$ ceramic were investigated using XRD, SEM and TEM techniques. The $MgO-P_2O_5$ sintering additive improved the material properties and increased the grain size in the sintered HAp bodies. As the content of sintering additive increased over 4 wt%, a small amount of the HAp phase was decomposed and transformed to ${\beta}-TCP$. In the 2 wt% $MgO-P_2O_5$ content HAp sintered body, the maximum values of density and hardness were respectively about 3.10 gm/cc and 657 HV. However, the maximum fracture toughness in the HAp body containing 8 wt% $MgO-P_{2}O_{5}$ was about $1.02MPa{\cdot}m^{1/2}$ due to the crack deflection effect. Human osteoblast like MG-63 cells and osteoclast like raw 264.7 cells were well grown and fully covered all of the HAp sintered bodies. The osteoblast cells were grown with spindle-shaped and the osteoclast cells had a grape-like round shape.

• Journal of Powder Materials
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• v.9 no.3
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• pp.148-152
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• 2002

The microstructures and indentation fracture of pressureless-sintered $DyNbO_4$ crystalline were investigated as a basic study for the application of weak phase of fibrous monolithic composites. They were comprised with many lamella twins as well as micro-cracks at the grain boundaries. The hardness at room temperature was remarkably low value(575 Hv) due to the low relative density and existence of microcracks at grain boundaries. The main fracture mode was a typical intergranular fracture, and showed remarkable micro-cracking effect. The heavy plastic deformation was observed around the site of indentation. In addition, the $DyNbO_4$ was expected to apply as a weak phase in the fibrous monolithic composites because of the low hardness and easily plastic deformation that could be led the preferable pulled-out and microcracking toughening under the failure.

• Journal of Powder Materials
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• v.1 no.2
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• pp.135-144
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• 1994

Silicon carbide powder was prepared from mixtures of Sangdong silica sand and carbon black by SHS (Self propagating High temperature Synthesis) method which utilizes magnesiothermic reduction of silica. In the powder preparation process, the reacted powder was leached by chloric acid to remove the magnesium oxide and was subsequently roasted to remove free carbon. The impurities were mostly eliminated by hot acid treatment. The resultant SiC powder showed the mean particle size of 0.22 ${\mu}{\textrm}{m}$ and the specific surface area of $66.55 m^2/g$. The SiC powder was mixed with 1 wt% of boron and of carbon to increase densification rate. The mixed powder was pressed and sintered pressurelessly at $2100^{\circ}C$ for 30 min in argon gas. The sintered body showed the hardness of $2550 kg{\cdot}f/mm^2$ and the fracture toughness, KIC of $3.47 MN/m^{3/2}$.