• Journal of the Korean Ceramic Society
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• v.49 no.5
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• pp.432-437
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• 2012

Electrical properties of the laminated SMD-type PTC thermistor for microcircuit protection were investigated as a function of calcination and sintering temperature. $BaTiO_3$ with $Y_2O_3$ and $MnO_2$ were calcined at 1000 to $1150^{\circ}C$ for 2h and the laminated SMD-type PTC thermistor was sintered at 1350 to $1400^{\circ}C$ for 2h in a reduced atmosphere (1% $H_2/N_2$). Sintered density of the sample was dependent on the calcination and sintering temperature. Electrical properties of the sintered samples were strongly dependent on the densities of samples. For the samples with density below 4.6 g/$cm^3$, the insulator characteristics were observed, while PTC jump characteristics (R150/R30) were disappeared for the sample with density above 5.05 g/$m^3$. Optimal PTC characteristics were obtained for the sintered samples with density of 5.05 g/$m^3$. The laminated SMD-type PTC thermistor prepared by calcination at $1100^{\circ}C$ for 2h and sintering at $1270^{\circ}C$ for 2h showed the room temperature resistivity of $11{\Omega}{\cdot}cm$ and PTC jump characteristics of $10^2$ order.

• Nuclear Engineering and Technology
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• v.30 no.2
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• pp.128-139
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• 1998

The effect of UO$_2$ powder property and oxygen potential on characteristics of sintered UO$_2$-Gd$_2$O$_3$ fuel pellets has been investigated. Two types of powder, mixture of AUC-UO$_2$ and Gd$_2$O$_3$powders (type I) and mixture of ADU-UO$_2$ and Gd$_2$O$_3$powders (type II), have been prepared, pressed, and sintered at 168$0^{\circ}C$ for 4 hours. Four sintering atmospheres with different mixing ratios of $CO_2$to H$_2$ gas ranging from 0 to 0.3 have been used. UO$_2$-Gd$_2$O$_3$ fuel has lower sintered density than UO$_2$ fuel, and the density drop is larger for powder type I than for powder type II. As the oxygen potential increases, the sintered density of UO$_2$-2wt% Gd$_2$O$_3$pellets increases but that of UO$_2$-10wt% Gd$_2$O$_3$ pellets decreases. It is found that pores are newly formed in UO$_2$-10wt% Gd$_2$O$_3$ pellets in accordance with the decrease in density. The grain size of UO$_2$-Gd$_2$O$_3$ fuel increases and a short range G4 distribution becomes homogeneous as the oxygen potential increases. A long range ed distribution and grain structure are inhomogeneous for powder type II. The lattice parameter of (U,Gd)O$_2$solid solution decreases linearly with Gd$_2$O$_3$ content. The dependence of UO$_2$-Gd$_2$O$_3$fuel characteristics on powder type and sintering atmosphere have been discussed.

• Proceedings of the Korea Association of Crystal Growth Conference
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• 1998.06a
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• pp.81-86
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• 1998

The light aggregates were fabricated by sintering green bodies made form the fly ash-clay alip. The content of fly ashes in the slip could be increased up to 70wt.% due to controlled rheological behavior of the slip, and the green body of uniform microstructure could be obtained by DCC(Direct Coagulation Casting)method. The apparent density, microstructure and compressive strength for sintered bodies fired at 1100∼1200$^{\circ}C$ were evaluated. The properties of light aggregates fabricated depend on slip density, particle behavior in the slip and sintering conditions. The sintered body prepared by firing a green body made from slip of density 1.60 at 1150$^{\circ}C$/2hr satisfied conditions of a light aggregate as apparent density of 1.49${\pm}$0.02 and compressive strength of 584${\pm}$62kg/$\textrm{cm}^2$.

• Journal of the Korean Ceramic Society
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• v.21 no.2
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• pp.121-126
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• 1984

The dielectric properties of $BaTiO_3$ containing 0~0.3mol% and ZnO respectively as additives were investigated as a function of temperature from $25^{\circ}C$ to 14$0^{\circ}C$ and frequency from 24 KHz to 15MHz. The density of sintered $BaTiO_3$ was increased with addition of increasing to 0.15mol% amounts of $Sb_2O_3$ and the dielectric constant was also increased. This is due to space charge polarization with Ba vacancies. Above 0.15mol% $Sb_2O_3$ the density was decreased and the dielectric constant was also decreased due to occuring the discharge through voids. The density of sintered $BaTiO_3$ was decreased with addition of increasing to 0.15mol% amounts of ZnO and the dielectric constant was decreased due to occuring the discharge through voids. Above 0.15mol% ZnO the density was increased and the dielectric constant was also increased.

• Transactions of Materials Processing
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• v.7 no.5
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• pp.426-431
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• 1998

This study is concerned with cold repressing of sintered preforms by the rotary forging process. An experiment has been carried out using the rotary powder forging press(500kN) which was designed and constructed in the authors' laboratory. The effect of process variables and aspect ration of sintered preform on the densification behavior during the rotary repressing was studied by several mechanical test such as working force hardness distribution density and microstructures of the specimens. Since a higher densification can be achieved by applying the rotary repressing on presinted preforms it was successively demonstrated that the cold rotary powder forging is an effective operation to improve quality of P/M parts.

• Transactions of the Korean Society of Mechanical Engineers
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• v.17 no.5
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• pp.1115-1122
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• 1993

Several yield criteria for porous materials are compared with each other, defining the apparent yield stress as the yield stress of the porous material in simple compression. It was found that the plastic Poisson's ratio is the parameter needed to define the yield criterion, rather than the relative density. The plastic Poisson's ratio is regarded as a material characteristic that is obtained from a simple compression test. A new form of yield criterion was suggested, and it was applied to hydrostatic compression as well as uniaxial strain compression of sintered Al-2024 powder. The crossover point in the mean stress vs volume change curves of the processes was predicted. It is presented that the flow stress of the fully densed material can be obtained from that of the porous material using relations obtained from the yield criterion.

• Journal of the Korean Magnetics Society
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• v.4 no.2
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• pp.89-93
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• 1994

Effects of density, inner-stress, and grain size on B-H hysteresis loop properties of Mg-ferrite were investigated. As the sintered bulk density increase, coercive force($H_c$) decreasand squareness ratio increase. Coercive force was very dependent on inner-stress in sintered body, so coercive force increase from 1.95[Oe] to 4.35[Oe] when inner stress present in bulk, however, the squareness ratio was almost not changed Coercive force and squareness ratio were independent on grain size of sintered body which is between 6-11[$\mu\textrm{m}$]

• Journal of the Korean Ceramic Society
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• v.16 no.2
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• pp.69-76
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• 1979

This study attempted to characterize the powder and sintered specimen of Mn-Zn ferrite that was prepared by Hot Petroleum Drying Method. The results of the experiment were as follows: 1. The mixed sulfate powder prepared by Hot Petroleum Drying Method was homogeneous and very reactive. The ferrite formation of this powder occurred at lower temperature than the one prepared by Sulfate Dry Mixing Method. 2. The calcined oxide powder prepared by Hot Petroleum Drying Method was found to be agglomerated, and therefore it was very difficult to compact this powder. 3. The sintered density was 4.95g/㎤, 97% of the theoretical density, when the specimen was prepared by Hot Petroleum Drying method, calcined at 90$0^{\circ}C$ in air for 3h, sintered at 1,30$0^{\circ}C$ in air for 3h, and then cooled in nitrogen. 4. The discontinuous grain growth occurred at lower temperature in the specimen prepared by Hot Petroleum Dyring Method than in the one prepared by Sulfate Dry Mixing Method. The discontinuous grain growth was considered to be due to the presence of liquid formed by addition of CaO and $SiO_2$.

• Journal of the Korean Ceramic Society
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• v.31 no.6
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• pp.595-600
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• 1994

Ni0.3Zn0.7Fe2O4 ferrite specimens were fabricated by dry pressing and tape casting method. The properties of each specimen were measured and compared. In order to design and manufacture the chip devices effectively, one important criterion can be that the sintered density of the laminated body should approach close to that of the dry pressed body which is regarded as standard. This requirement could be satisfied by controlling the solid loading of the ferrite sheet, lamination temperature and pressure. Using the optimum conditions (solid loading 55 wt%, lamination temperature 6$0^{\circ}C$, lamination pressure 400 kg/$\textrm{cm}^2$, sintered at 125$0^{\circ}C$ 2h) a sintered ferrite, with the density of 5.18g/㎤ and permeability of 1390 at 0.5 MHz, were obtained.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1988.05a
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• pp.10-12
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• 1988

High Tc Y-Ba-Cu-O Superconductors were fabricated by sintering, sintering + HIP and Hot Pressing. Specimens were sintered at $940^{\circ}C$ and $960^{\circ}C$. In case that sintered specimens were treated by HIP, the relative density was increased 5-6% in comparison with sintered ones. X-ray analysis of each specimens represented orthorhombic phase and Tc measurements showed a sharp drop in the temperature range $95-88^{\circ}K$. The relative density of hot pressed samples was lower than 80%.