• The Korean Journal of Ceramics
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• 제4권4호
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• pp.279-285
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• 1998

The $UO_2$ pellets are usually sintered under hydrogen gas atmosphere. Hydrogen gas may cause unexpected early failure of the refractory bricks in the sintering furnace. In this work, nitrogen was mixed with hydrogen to investigate the effect of nitrogen gas on a failure machanism of the refractory bricks and on the microstructure of the $UO_2$ pellet. The hydrogen-nitrogen mixed gas experiments show that the larger nitrogen the mixed gas contains, the less the refractory materials are reduced by hydrogen. The weight loss measurements at $1400^{\circ}C$ for fire clay and chamotte refractories containing high content of $SiO_2$ indicate that the weight loss rate for the mixed gas is about half of that for the hydrogen gas. Based on the thermochemical analyses, it is proposed that the weight loss is caused by hydrogen-induced reduction of free $SiO_2$ and/or $SiO_2$ bonded to $Al_2O_3$ in the fire clay and chamotte refractories. However, the retardation of the hydrogen-induced $SiO_2$ reduction rate under the mixed gas atmosphere may be due to the reduction of the surface reaction rate between hydrogen gas and refractory materials in proportion to volume fraction of nitrogen gas in the mixed gas. On the other hand, the mixed gas experiments show that the test data for $UO_2$ pellet still meet the related specification values, even if there exists a slight difference in the pellet microstructural parameters between the cases of the mixed gas and the hydrogen gas.

• 한국세라믹학회지
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• 제35권1호
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• pp.97-105
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• 1998

20mol% Gd-doped CeO2 ultrafine powders as a promising electrolyte for the low temperature solid ox-ide fuel cells were synthesized with particle sizes of 15-20 nm using glycine nitrate process(GNP) fol-lowed by sintering their pellets at 150$0^{\circ}C$ for various times in air and then the electrical properties of the sintered pellets were investigated. The sintering behaviors and electrical properties for the sintered 20 sintered mol% Gd-doped CeO2 pellets were analyzed using dilatometer and SEM and AC two-terminal impedance technique respectively. As the heating temperature increased the synthesized powder had the sintering behaviors to show the start of the significant shrink at temperature of about $700^{\circ}C$ and to show the end of the shrink at the temperature of about 147$0^{\circ}C$. When the pellets were sintered with the vaious times at 150$0^{\circ}C$ the temperatuer which the shrink had been already completed the grain sizes in the sintered 20 mol% Gd-doped GeO2 pellets increased with the increase of the sintering time but their electrical resis-tivities showed the minimum value at the sintering time of 10h. It is due that the pellet sintered for 10h had the minimum activation energy fior the electtrical conduction. Thus it is thought that the decrease of the activation energy with the increase of the sintering time to 10h is induced by the enhanced mi-crostructure like the decrease of pore amount and the grain growth and its increase with the sintering times more than 10h is induced by the increase of the amounts of the impurities such as Mg. Al and Si from the sintering atmosphere.

• 한국세라믹학회지
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• 제33권6호
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• pp.693-699
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• 1996

YIG precursor powder was obtained by homogeneous precipitation in chloride salt solution by thermal decom-position of urea. It was found that ferric ions precipitated prior to yttrium ions. The precipitate was minute and spherical in shape. The precipitate formed consisted of the mixture of amorphous and ferric oxyhydroxide. Crystallization of YIG was proceeded by solid state reaction of intermediate YFeO3 and Fe2O3 in the temperature range of 85$0^{\circ}C$ to 140$0^{\circ}C$. Single phase of YIG was obtained by heat-treatment of the powder at 140$0^{\circ}C$ for 6 hrs in air. The powder calcined was molded into pellets and sintered in air. The maximum density of 4,92 g/cm3(95.1% of theoretical density) was obtainable for the pellet sintered at 145$0^{\circ}C$ using the powder calcined at 90$0^{\circ}C$.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1998년도 가을 학술발표논문집(II)
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• pp.239-244
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• 1998

Fusion temperature of fly ash was determined with wasted glass wool and borax using ash fusion determinator, 0.5wt% of bentonite and water glass used as binder, 50wt% of wasted glass wool added to fly ash, fusion temperature of fly ash was 1, 156$^{\circ}C$. Pellet was prepared, and then sintered at 1, 00$0^{\circ}C$ and 1, 10$0^{\circ}C$. Water-absorption rate, specific gravity, porosity and pore structure of sintering aggregate was determined.

• 한국분말재료학회지
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• 제14권1호
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• pp.8-12
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• 2007

The effect of a CAM (Continuous Attrition Mill) treatment on the sinterability of ex-ADU $UO_2$ powder was investigated. As the cycles of a CAM increased, the apparent density, specific surface area and O/U of the milled powder increased, but there particle sizes decreased. However the sintered density of the $UO_2$ pellet decreased as the cycles of the CAM increased. It is considered that the decrease of the sintered density is due to the formation of $U_3O_8$, which was produced by a CAM mechanism.

• 한국결정성장학회지
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• 제34권3호
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• pp.98-102
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• 2024

본 연구에서는 ㎛ 및 nm 크기를 갖는 상용 AlN 분말을 XRD 분석을 통해 선별 후, 유도가열로를 활용하여 상이한 온도에서 소결하여 최적화된 소결 온도 및 물성 특성을 조사하였다. 소결 온도는 1,500, 1,700 그리고 1,900℃ N₂ 분위기에서 진행되었으며, 소결된 AlN 펠렛은 SEM, XRD, Raman 분석을 이용하여 최적화된 소결 온도 조건을 확립하였다. 또한 Impedance 분석을 진행하여 소결 조제 없이 제작된 AlN 펠렛의 전기적 특성을 확인하였다.

• Korean Chemical Engineering Research
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• 제43권1호
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• pp.71-75
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• 2005

초거대 자기 저항 물질인 $La_{0.5}Ca_{0.5}MnO_3$의 분말과 pellet을 졸-겔 법으로 제조하였다. 열처리 온도를 변화시켜 얻은 시료에 대해 FT-IR과 CP/MAS $^{13}C$ solid state NMR spectroscopy 그리고 XRD 등을 이용해 구조변화를 관찰하였다. 양이온 조성 비율을 알아보기 위해 ICP-AES를 이용하였으며, 입자크기와 균일도를 FE-SEM/EDS로, 미세구조와 격자 패턴은 TEM으로 관찰하였다. VSM을 이용하여 자기적 특성을 살펴보았으며 큐리온도($T_c$)는 236 K에서 측정되었다.

• 한국재료학회지
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• 제22권7호
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• pp.346-351
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• 2012

$Li_{1+x}Al_xTi_{2-x}(PO_4)_3$(LATP) is a promising solid electrolyte for all-solid-state Li ion batteries. In this study, LATP is prepared through a sol-gel method using relatively the inexpensive reagents $TiCl_4$. The thermal behavior, structural characteristics, fractured surface morphology, ion conductivity, and activation energy of the LATP sintered bodies are investigated by TG-DTA, X-ray diffraction, FE-SEM, and by an impedance method. A gelation powder was calcined at $500^{\circ}C$. A single crystalline phase of the $LiTi_2(PO_4)_3$(LTP) system was obtained at a calcination temperature above $650^{\circ}C$. The obtained powder was pelletized and sintered at $900^{\circ}C$ and $1000^{\circ}C$. The LTP sintered at $900{\sim}1000^{\circ}C$ for 6 h had a relatively low apparent density of 75~80%. The LATP(x = 0.3) pellet sintered at $900^{\circ}C$ for 6 h was denser than those sintered under other conditions and showed the highest ion conductivity of $4.50{\times}10^{-5}$ S/cm at room temperature. However, the ion conductivity of LATP (x = 0.3) sintered at $1000^{\circ}C$ decreased to $1.81{\times}10^{-5}$ S/cm, leading to Li volatilization and abnormal grain growth. For LATP sintered at $900^{\circ}C$ for 6 h, x = 0.3 shows the lowest activation energy of 0.42 eV in the temperature range of room temperature to $300^{\circ}C$.

• 한국분말재료학회지
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• 제18권3호
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• pp.256-261
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• 2011

In order to make a $Cu_2ZnSnSe_4$ (CZTSe) sputtering target sintered for solar cell application, synthesis of CZTSe compound by solid state reaction of Cu, Zn, Sn and Se mixed powders and effects of ball milling condition on sinterability such as ball size, combination of ball size, ball milling time and sintering temperature, was investigated. As a result of this research, sintering at $500^{\circ}C$ after ball milling using mixed balls of 1 mm and 3 mm for 72 hours was the optimum condition to synthesis near stoichiometric composition of $Cu_2ZnSnSe_4$ and to prepare sintered pellet with high density relatively.

• Nuclear Engineering and Technology
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• 제55권6호
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• pp.2206-2214
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• 2023

The existing wet reconversion processes for the recovery of scraps generated in manufacturing of nuclear fuel are complex and require several unit operation steps. In this study, it is attempted to simplify the recovery process of high-quality fuel-grade UO₂ powder. A novel wet reconversion process for uranyl nitrate hexahydrate solution is suggested by using a newly developed pulsed fluidized bed reactor, and the resultant chemical characteristics are evaluated for the intermediate ammonium uranate hydrate product and subsequently converted UO₂ powder, as well as the compliance with nuclear fuel specifications and advantages over existing wet processes. The UO₂ powder obtained by the suggested process improved fuel pellet properties compared to those derived from the existing wet conversion processes. Powder performance tests revealed that the produced UO₂ powder satisfies all specifications required for fuel pellets, including the sintered density, increase in re-sintered density, and grain size. Therefore, the processes described herein can aid realizing a simplified manufacturing process for nuclear-grade UO₂ powders that can be used for nuclear power generation.