• 한국세라믹학회지
• /
• 제35권10호
• /
• pp.1113-1119
• /
• 1998

Crystal structure of needle-shaped maghemite(${\gamma}$-{{{{ { {Fe }_{2 }O }_{3 } }}) has been studied by the Rieveld analysis of powder X-ray diffraction patterns. The tetragonal space group P41,.3212 and cubic space group P41,.32 have been have been used for the refinement of X-ray diffraction patterns. The crystal system of maghemite is closed to tetragonal more than cubic. The tetragonal lattice parameters are a=8.3460$\AA$ and c=25.034$\AA$ The standard X-ray diffraction pattern of the tetragonal maghemite analyzed with space group P41,.3212 is proposed.

• 한국세라믹학회지
• /
• 제27권5호
• /
• pp.597-604
• /
• 1990

In Cubic ZrO2 crystal growth by Skull method, it was examined on effect of homonization on melt as keeping ZrO2(90mol%)-Y2O3(10mol%) melt with 1hr, 2hr, 4hrs, 8hrs, 16hrs, respectively. The optimum homonizing condition in this system was obtained by the examination between quality of grown crystals and soaking time of melt. It was obtained that the lower quality crystal could be produced in the longer holding melt than the optimum soaking time of melt in spite of the supposedly well homonized state, because the melt stability is sensibly dependent on the convective state of melt in skull method (cold crucible process).

• 한국전기전자재료학회논문지
• /
• 제15권4호
• /
• pp.349-355
• /
• 2002

The ionic conductivity of cubic solid solutions in the systems of CaO-$ZrO_2$, $Y_2O_3-ZrO_2$ prepared by SHS was examined. The higher conductivity appears to be related to a lower activation energy rather than to the number of oxygen vacancies dictated by composition. Conductivity-temperature data was obtained at 1000 $^{\circ}C$ in atmosphere of low oxygen partial pressure (~$10^{-40}$ atm) for $Y_2O_3-ZrO_2$ cubic solid solutions. The data indicated that these materials could be reduced, and the decree of reduction would be related with the measuring electric field.

• Journal of Ceramic Processing Research
• /
• 제17권7호
• /
• pp.763-767
• /
• 2016

The structural characterization of cubic boron nitride (c-BN) thin films was performed using a B4C target in a radio-frequency magnetron sputtering system. The deposition processing conditions, including the substrate bias voltage, substrate temperature, and base pressure were varied. Fourier-transform infrared spectroscopy and X-ray photoelectron spectroscopy were used to analyze the crystal structures and chemical binding energy of the films. For the BN film deposited at room temperature, c-BN was formed in the substrate bias voltage range of -400 V to -600 V. Less c-BN fraction was observed as the deposition temperature increased, and more c-BN fraction was observed as the base pressure increased.

• 한국세라믹학회지
• /
• 제53권1호
• /
• pp.43-49
• /
• 2016

This analyzed a Young's modulus (E), a thermal expansion coefficient (TEC, ${\beta}$) and a thermal conductivity (${\kappa}$) of the material with simple cubic particulate inclusion using two model structures: a parallel structure and a series structure of laminated layers. The derived ${\beta}$ equations were applied to calculate the ${\beta}$ value of the W-MgO system. The accuracy was higher for the series model structure than for the parallel model structure. Young's moduli ($E_c$) of sintered porous alumina compacts were theoretically related to the development of neck growth of grain boundary between sintered two particles and expressed as a function of porosity. The series structure model with cubic pores explained well the increased tendency of $E_c$ with neck growth rather than the parallel structure model. The thermal conductivity of the three phase system of alumina-mullite-pore was calculated by a theoretical equation developed in this research group, and compared with the experimental results. The pores in the sintered composite were treated as one phase. The measured thermal conductivity of the composite with 0.5-25% porosity (open and closed pores) was in accordance with the theoretical prediction based on the parallel structure model.

• 한국세라믹학회지
• /
• 제32권3호
• /
• pp.295-304
• /
• 1995

Stabilization of the perovskite phase and sequence of reactions occuring during calcination were studied with solid solutions formed between Pb(Zn1/3Nb2/3)O3 and Pb(Fe1/2Nb1/2)O3. In the PZN-PFN composition of equal molar ratio, rhombohedral type pyrochlore phase (Pb2Nb2O7) and PbO-rich distorted cubic type pyrochlore phase (Pb3Nb2O8) were coexisted as intermediate phases at temperatures below 85$0^{\circ}C$, and these phases transformed to a stable cubic type pyrochlore phase, Pb3Nb4O13 solid solution and a perovskite solid solution at temperatures above 85$0^{\circ}C$. The major stable phase as increasing sintering temperatures was a perovskite phase in this binary system and prominent suppression of the pyrochlore phase was achieved by substituting Zn2+ with Fe3+ or by increasing sintering temperature. The composition containing 20mol% PZN possessed the best dielectric properties, and the dissipation factor was lower than 5% in all compositions.

• 대한전기학회:학술대회논문집
• /
• 대한전기학회 1998년도 추계학술대회 논문집 학회본부 B
• /
• pp.675-677
• /
• 1998

In this paper, we propose the fuzzy inference algorithm with multi-layer structure. MFIS(Multi-layer Fuzzy Inference System) uses PNN(Polynomial Neural networks) structure and the fuzzy inference method. The PNN is the extended structure of the GMDH(Group Method of Data Hendling), and uses several types of polynomials such as linear, quadratic and cubic, as well as the biquadratic polynomial used in the GMDH. In the fuzzy inference method, the simplified and regression polynomial inference methods are used. Here, the regression polynomial inference is based on consequence of fuzzy rules with the polynomial equations such as linear, quadratic and cubic equation. Each node of the MFIS is defined as fuzzy rules and its structure is a kind of neuro-fuzzy structure. We use the training and testing data set to obtain a balance between the approximation and the generalization of process model. Several numerical examples are used to evaluate the performance of the our proposed model.

• 한국전자파학회논문지
• /
• 제15권3호
• /
• pp.265-270
• /
• 2004

본 논문에서는 group delay가 위성 통신 시스템에 미치는 영향을 분석한다. 일정한 상수가 아닌 group delay에서는 신호의 위상 왜곡이 발생한다. Group delay는 특성에 따라 linear, parabolic, cubic으로 모델링할 수 있다. 각각의 group delay 특성을 위성통신 시스템에 적용하여 BER(bit error rate)을 분석한다. Group delay는 신호의 대역폭이 커질수록 신호에 미치는 영향이 커지는 특성을 갖고 있으며, 위성 통신 시스템의 정보 전송속도가 1Mbps, 4Mbps, 8Mbps 의 세 가지인 경우에 대하여 BER을 분석한다. 이때 channel coding으로는 구속장이 7이고, code rate 1/2인 convolution coding과 7/8 punctured convolution coding 를 이용한다. BER = $10^{-5}$을 만족하는 요구 SNR을 관찰하였을 때, group delay의 영향을 받는 데이터는 group delay의 영향을 받지 않은 데이터에 비해 요구 SNR은 최소 0.3㏈에서 최대 4.4㏈으로 증가한다. 이들 중 group delay에 의한 영향이 가장 큰 경우는 group delay의 특성이 linear 특성이고 channel coding이 7/8 puncture convolution coding, 전송속도가 8 Mbps인 경우로서 이때 요구 SNR은 4.4㏈증가한다.

• 한국재료학회지
• /
• 제7권1호
• /
• pp.57-61
• /
• 1997

$Y_{0.8}Ta_{0.2}O_{1.7}$-MO(M=Ba, Sr, Ca 및 Mg) 계에서의 형석구조의 생성과 이와 관련된 구조에 관하여 연구하였다. BaO또는 SrO를 4mol% 첨가한 조성에서는 결함형석구조 이외에 입방정 perovskite형 규칙구조인 $Ba_{2}YTaO_{6}$ 및 $Sr_{2}YTaO_{6}$와 입방정 $Y_{2}O_{3}$가 관찰되었다. CaO를 첨가한 경우에는 8mol%이상을 첨가한 조성에서부터 단사정 $Ca_{2}YTaO_{6}$와 $Y_{2}O_{3}$의 2차상이 나타났다. MgO의 경우에는 12mol% MgO를 첨가한 조성까지는 형석구조의 단일상을 나타내어 MgO가 형석구조에 고용되는 것을 알수 있었으며, 16 mol%조성부터는 2차상으로 MgO가 관찰되었다. 그러므로 위의 계에서 형석구조의 생성은 $A_{2}$(B'B")$O_6$의 생성과 첨가된 양이온의 크기에 영향을 받는 것으로 생각된다.생각된다.

• 자원리싸이클링
• /
• 제5권3호
• /
• pp.65-72
• /
• 1996

탄산칼슘과 고분자 재료가 배합되면 서로의 계면에 대한 친화성이 결여되어 분산성이 저하하기 때문에 이를 위해 탄산칼슘을 표면처리를 하지만 이는 분체자신의 표면에너지를 저하시키는 역효과의 가능성도 있다. 따라서 표면처리를 하지 않아도 미세한 1차 입자의 상태로 유지하는 초미립체(입경 0.02~0.09$mu extrm{m}$) 입자의 콜로이드형 탄산칼슘 합성에 대한 기술이 절실히 요구되나 합성시 목적입도가 평균입도 범주에 속하고 또 그 분포가 좁아야 함이 핵심요소기술이 되는데 입경제어에 대한 인자 규명 및 최적 조건의 항구적인 합성조건에 대한 연구가 전혀 수행되지 못한 형편이다. 이에 본 연구에서는 수산화칼슘 현탁액에 탄산가스를 접촉시키는 기-액접촉방식의 CMSMPR(Continuous Mixed Suspension Mixed Product Removal)법을 이용하여 콜로이드형 탄산칼슘 합성을 목적으로 입방형 탄산칼슘과 함께 제어함으로 두 종류의 침강성 탄산캄슘을 최적 합성화 할 수 있었다. 수산화칼슘 현탁액 제조는$ 1100^{\circ}C$에서 수산화칼슘을 2시간 소성을 시켜 제조한 산화칼슘을 증류수에 600rpm으로 30분간 수화시킨 반응현탁액 2ι를 반응온도 $15^{\circ}C$와 반응교반속도 600rpm, 탄산가스 주입속도 1ι/min으로 모든 조건을 고정시키고 현탁액에 대한 산화칼슘의 농도변화만으로 입방형(0.2~0.9$\mu\textrm{m}$)과 콜로이드형($0.02~0.09\mu\textrm{m}$)을 합성하였고 이에 대한 반응현탁액의 농도 최적조건이 각각 5wt%와 2.5wt%임을 확인하였다. 결국 입경제어의 주요 인자가 현탁액의 농도임을 알았고 합성한 탄산칼슘은 Zeta sizer를 통해 측정하여 평균입도가 입방형은 223.4nm(0.223$\mu\textrm{m}$)와 콜로이드형 93.6nm(0.093$\mu\textrm{m}$)임을 확인하여 $H_2O$ 반응계에서 안정적인 균일입도제어를 할 수 있었다.