• Korean Journal of Materials Research
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• v.7 no.5
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• pp.411-416
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• 1997

수소 및 산소분위기 하에서 2Y-TZP 및 3Y-PZP 세라믹스를 소결하여 각각 제조한 다음, 각 시편의 미세구조 및 25$0^{\circ}C$에서의 등온상전이 거동을 비교하여 고찰하였다. 그 결과 수소분위기에서 소결한 모든 시편의 표면에서는 Zr$_{4+}$ 이온의 환원에 의해 산화분위기에서 소결한 시편에 비하여 색이 검게 변하였으며, 장시간 소결시 시편 표면에 조대 입자의 생성 및 입계 이완이 관찰되었다. 이에따라 수소분위기 하에서 장시간 소결된 시편의 경우 냉각 시 상전이가 일어나 다량의 단사정상이 상온에서 존재하였다. 저온 aging동안 등온상전이 속도는 산소분위기에서 소결한 시편보다 수소분위기에서 소결한 시편에서 낮게 나타났으며, 이러한 경향은 $Y_{2}$O$_{3}$의 고용량이 크고, 입자크기가 적은 시편일수록 증가하였다. 또한 2Y-TZP 시편에서는 입자크기에 상관없이 대부분의 정방정상이 단사정상으로 빨리 등온상전이를 일으켰으나, 3Y-TZP 시편의 경우, 등온상전이는 입자크기가 증가함에 따라 상전이 속도도 증가하였다.

• Korean Journal of Materials Research
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• v.17 no.1
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• pp.18-24
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• 2007

Mullite-PSZ composite was prepared by sol-gel method using $Al(sec-OC_4H_9)_3,\;Si(OC_2H_5)_4,\;ZrOCl_2\;8H_2O\;and\;Y_2O_3$. The sinterability ana mechanical properties of powder compacts sintered at $1,650^{\circ}C$ for 4 hrs were investigated for various PSZ contents. In result Al-Si spinel formed at $980^{\circ}C$ from amorphous dried gel, and zirconia as well as mullite crystal formed above $1,200^{\circ}C$. The sintered body was densified to $97{\sim}98%$ except the specimen containing 25vol% PSZ which showed the relative density of about 95% obtained by sintering at $1,650^{\circ}C$ for 4 h. The flexural strength of the sintered body was a maximum value of 290 MPa in 20 vol% PSZ, which was also considerably larger than the value of 200 MPa without PSZ. The value of the fracture toughness increased linearly with increase of PSZ content and showed a maximum value of $4.3MPam^{1/2}$ in 25 vol% PSZ, Namely this value was remarkably larger than the $value(2.6MPam^{1/2})$ of pure mullite without PSZ.

• Journal of Powder Materials
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• v.29 no.5
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• pp.424-431
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• 2022

3Y-TZP ceramics obtained by doping 3 mol.% of Y₂O₃ to ZrO₂ to stabilize the phase transition are widely used in the engineering ceramic industry due to their excellent mechanical properties such as high strength, fracture toughness, and wear resistance. An additional increase in mechanical properties is possible by manufacturing a composite in which a high-hardness material such as oxide or carbide is added to the 3Y-TZP matrix. In this study, composite powder was prepared by dispersing a designated percentage of WC in the 3Y-TZP matrix, and the results were compared after manufacturing the composite using the different processes of spark plasma sintering and HP. The difference between the densification behavior and porosity with the process mechanism was investigated. The correlation between the process conditions and phase formation was examined based on the crystalline phase formation behavior. Changes to the microstructure according to the process conditions were compared using field-emission scanning electron microscopy. The toughness-strengthening mechanism of the composite with densification and phase formation was also investigated.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.3 no.1
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• pp.57-65
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• 2005

This study suggested a new method for the solidification of molten salt waste generated from the electro-metallurgical process in the spent fuel treatment. Using binary material system, sodium silicate and phosphoric acid, metal chlorides were converted into metal phosphate in the micro-reaction module formed by SiO$_{2} particles. The volatile element in the reaction module would little vaporized below 1100$^{circ}$C After the gel product was mixed with borosilicate glass powder and thermally treated at 1000$^{circ}$C, li exists as Li$_{3}$PO$_4$ separated from glass phase and, Cs and Sr would be incorporated into an amorphous phase from XRD analysis. In case of the addition of ZrCl$_{4}$ to the binary system, the gel products were transformed into NZP structure considered as an prospective ceramic waste form after heat-treatment above 700 $^{circ}$C. From these results, the gel-route pretreatment can be considered as an effective approach to the solidincation of molten salt waste by the confirmed process or waste form and this also would be an alternative method on the ANL method using zeolites in USA by the confirmation of its chemical durability as an future work.

• Transactions of the Korean hydrogen and new energy society
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• v.29 no.1
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• pp.1-10
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• 2018

The amount of biogas increases as the amount of organic waste increases. Recently, biogas from organic waste have been made much efforts to utilize as a energy. In particular, the concentration of $CH_4$ and $CO_2$ generated from sewage sludge and livestock manure treatment are 60-70% and 30-35%, and $CH_4$ and $CO_2$ generated from food wastes are 60-80% and 20-40%. In case of landfill gas, $CH_4$ and $CO_2$ have a concentration of 40-60% and 40-60% respectively. Therefore, in order to use the biogas more widely, it is necessary to convert the biogas to methanol, LNG or DME. In this study, experiments were conducted to produce hydrogen and carbon monoxide through various biogas reforming reactions on $Ni/Ce-ZrO_2/Al2O3$ catalysts. The experiment of synthetic gas synthesis was carried out on a wide concentrations of methane and carbon dioxide, which were the major constituents of biogas from various organic wastes. The effect of $(O_2+CO_2)/CH_4$ (=R') on the yields of hydrogen and carbon monoxide, the conversion rate of methane and carbon dioxide was investigated. Also simulation for syngas synthesis on the $CO_2$ reforming of $CH_4$ was computed by employing total Gibbs free energy minimization method using PRO/II simulator, and compared with the experimental results on wet and dry reforming reaction of biogas.

• Nuclear Engineering and Technology
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• v.52 no.1
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• pp.109-114
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• 2020

This work presents the results of laboratory scale tests of the CARBOFLUOREX (CARBOnate FLUORide EXtraction) process - a novel technology for the recovery of U and Pu from the solid fluorides residue (fluorination ash) of Fluoride Volatility Method (FVM) reprocessing of spent nuclear fuel (SNF). To study the oxidative leaching of U from the fluorination ash (FA) by Na₂CO₃ or Na₂CO₃-H₂O₂ solutions followed by solvent extraction by methyltrioctylammonium carbonate in toluene and purification of U from the fission products (FPs) impurities we used a surrogate of FA consisting of UF₄ or UO₂F₂, and FPs fluorides with stable isotopes of Ce, Zr, Sr, Ba, Cs, Fe, Cr, Ni, La, Nd, Pr, Sm. Purification factors of U from impurities at the solvent extraction refining stage reached the values of 10⁴-10⁵, and up to 10⁶ upon the completion of the processing cycle. Obtained results showed a high efficiency of the CARBOFLUOREX process for recovery and separating of U from FPs contained in FA, which allows completing of the FVM cycle with recovery of U and Pu from hardly processed FA.

• Journal of the Korean Ceramic Society
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• v.52 no.1
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• pp.77-82
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• 2015

The effect of the electrode type on the dielectric and piezoelectric properties of $Pb(Mg_{1/3}Nb_{2/3})O_3-PbZrO_3-PbTiO_3$ (PMN-PZT) single crystals was investigated in an effort to improve their properties for various piezoelectric applications. First, three different types of PMN-PZT single crystals [PMN-PZT-A (piezoelectrically soft type; dielectric constant ~ 10,000), PMN-PZT-B (piezoelectrically soft type; phase-transition temperature between the rhombohedral and tetragonal phases ($T_{RT}$) ~ $145^{\circ}C$), PMN-PZT-C (piezoelectrically hard type; high mechanical quality factor ($Q_m$) ~ 1,000)] were fabricated using the solid-state single crystal growth (SSCG) method. Then, four different types of electrodes [sputtered Au, sputtered Cr/Au, sputtered Ti/Au, and fired Ag] were formed on the single crystals, and their dielectric and piezoelectric properties were measured. The single crystals with a sputtered Ti/Au electrode showed the highest dielectric and piezoelectric constants but the lowest coercive electric field ($E_C$). The single crystals with a fired Ag electrode showed the lowest dielectric and piezoelectric constants but the highest coercive electric field ($E_C$). This dependence on the type of electrode was most significant in the piezoelectrically hard PMN-PZT-C single crystals. However, the effects of the electrode type on the phase transition temperatures ($T_C$, $T_{RT}$) and dielectric loss were negligible. These results clearly demonstrate that it is important to select an appropriate electrode so as to maximize the dielectric and piezoelectric properties of single crystals in each type of piezoelectric application.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2000.04b
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• pp.80-83
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• 2000

The post-annealing treatments on rf magnetron sputtered PZT($Pb_{1.05}(Zr_{0.52},\;Ti_{0.48})O_3$) thin films($4000{\AA}$) have been investigated for a structure of PZT/Pt/Ti/Coming glass(1737). Crystallization properties of PZT films were strongly dependent on RTA(Rapid Thermal Annealing) annealing temperature and time. We were able to obtain a perovskite structure of PZT at $650^{\circ}C$ and 10min. P-E curves of Pd/PZT/Pt capacitor demonstrate typical hysteresis loops. The measured values of $P_r$, $E_c$ were $8.1[{\mu}C/cm^2]$, 95[kV/cm] respectively. Polarization value decrease about 25% after $10^9$ cycles.

• Proceedings of the KIEE Conference
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• 2000.07c
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• pp.1477-1479
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• 2000

The annealing treatments on rf magnetron sputtered PZT($Pb_{1.05}(Zr_{0.52},Ti_{0.48})O_3$) thin films(4000${\AA}$) have been investigated for a structure of PZT/Pt/Ti/ITO coated glass. Crystallization properties of PZT films were strongly dependent on RTA(Rapid Thermal Annealing) annealing temperature and time. We were able to obtain a perovskite structure of PZT at 650$^{\circ}C$ and 10min. P-E curves of Pd/PZT/Pt capacitor demonstrate typical hysteresis loops. The measured values of $P_r$, $E_c$ were 15.8[${\mu}C/cm^2$], 95[kV/cm] respectively. Polarization value decrease about 10% after $10^9$ cycles.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1999.11a
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• pp.311-314
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• 1999

Ferroelectric PZT heterolayered thin films were fabricated by spin coating method on the Pt/Ti/SiO$_2$/Si substrate using PZT(10/90) and PZT(90/10) metal alkoxide solutions. All PZT heterolayered films showed a homogeneous grain structure without presence of the rosette structure. It can be assumed that the lower PZT layers a role of nucleation site or seeding layer for the formation of the upper PZT layer. Zr and Ti diffusion into the Pt electrode were mainly distributed at the surface of Pt electrode beneath the PZT/Pt interface. The PZT/Pt interfacial layer showed a microstructure characterized by a grain phase surrounded by a Pb-deficient pyrochlore matrix phase. The relative dielectric constant and the dielectric loss of the PZT-6 film were 567 and 3.6, respectively.