• 한국결정성장학회지
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• 제12권1호
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• pp.31-35
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• 2002

상용 스피넬 분말(0.94$\mu$m)을 $1300^{\circ}C$ 2시간 열처리한 후 30분 동안 습식혼합하여 3.29$\mu$m의 최종분말을 제조하여 die-press법을 이용하여 $1100^{\circ}C$에서 2시간 1차 소결하여 다공성 전성형체를 제조하고 $1080^{\circ}C$에서 0~2시간가지 $La_2O_3-A1_2O_3-SiO_2$계 유리를 용응 침투시켜 유리 침투 깊이와 시간간의 kinetic을 조사하였다 유리 침투시간이 증가할수록 침투깊이는 모세관압에 의하여 parabolic하게 증가하였다. 유리-스피넬 복합체의 강도와 인성값은 각각 317MPa, 3.56MPa . $m^{1/2}$이 었으며 $1300^{\circ}C$의 높은 하소온도로 인한 재결정에 의하여 스피넬은 침상과 다각형 조직이 동시에 존재하는 이중 미세조직 이 관찰되었다.

• Journal of the Korean Physical Society
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• 제73권12호
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• pp.1863-1866
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• 2018

The sodium-iron phosphate maricite-$NaFe_{0.9}Mn_{0.1}PO_4$ was synthesized using the ball mill method. The crystal structure and magnetic properties of the prepared materials were studied using X-ray diffraction (XRD), vibrating sample magnetometer (VSM), and $M{\ddot{o}}ssbauer$ spectroscopy. Structural refinement of maricite-$NaFe_{0.9}Mn_{0.1}PO_4$ was analyzed using the FullProf program. From the XRD patterns, the crystal structure of maricite-$NaFe_{0.9}Mn_{0.1}PO_4$ was found to be orthorhombic with the space group Pmnb. The lattice parameters of maricite-$NaFe_{0.9}Mn_{0.1}PO_4$ are as follows: $a_0=6.866{\AA}$, $b_0=8.988{\AA}$, $c_0=5.047{\AA}$, and $V=311.544{\AA}^3$. Maricite-$NaFePO_4$ has an edge-sharing structure that consists of $FeO_6$ octahedral. Under an applied field of 100 Oe, the temperature dependences of zero-field-cooled (ZFC) and field-cooled (FC) curves were measured from 4.2 to 295 K. $M{\ddot{o}}ssbauer$ spectra were also recorded at various temperatures ranging from 4.2 to 295 K. We thus confirmed that the $N{\acute{e}}el$ temperature of $NaFe_{0.9}Mn_{0.1}PO_4$ ($T_N=14K$) was lower than that of maricite-$NaFePO_4$ ($T_N=15K$).

• 한국자기학회지
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• 제17권1호
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• pp.38-42
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• 2007

단일상의 $KFeO_2$ 분말을 ball-mill법을 이용하여 제조 하였다. 결정학적 및 자기적 성질을 x-선 회절법, 중성자 회절 실험, 뫼스바우어 분광법으로 연구 하였다. x-선 및 중성자 회절실험 분석 결과 $KFeO_2$ 시료의 결정구조는 격자상수 $a_0=5.557{\AA},\;b_0=11.227{\AA},\;c_0=15.890{\AA}$을 갖는 단일상의 orthorhombic구조로 분석 되었다. 또한 시간변화에 따른 $KFeO_2$의 강한 흡습성으로 인한 급격한 변화를 확인할 수 있었다. 뫼스바우어 스펙드럼 결과 1 set(6-line)으로 분석되었다. 극저온(4.2 K)과 상온에서의 초미세자기장값(hyperfine field)은 각각 519, 489 kOe이었으며, 이성질체 이동치(isomer shift)는 0.19, 0.05 mm/s로 나타났다. $KFeO_2$의 스핀과 여기에 의한 T/Tc<0.7 이하의 초미세자기장 $H_{hf}(T)$의 변화는 $[H_{hf}(T)-H_{hf}(0)]/H_{hf}(0)=-0.16(T/Tc)^{3/2}-0.25(T/Tc)^{5/2}$로 얻어졌다.

• 한국광학회지
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• 제5권4호
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• pp.466-472
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• 1994

아르곤 레이저에 의해 광펌핑 되는 티타늄 사파이어 레이저를 제작하고 이를 자체 모드록킹 시켰다. 모드록킹은 볼 슬라이더 위에 장착된 공진기 거울의 이동에 의해 시작되었으며 티타늄 사파이어 결정내의 자체 집속 효과와 공진기내에 설치된 조리개에 의해 모드록킹이 유지 되었다. 공진기내의 군속도를 보상하기 위하여 프리즘쌍을 사용하였으며, 모드록킹된 펄스의 대역폭은 11nm, 펄스폭은 $1000\pm20fs$였다.

• Journal of Advanced Marine Engineering and Technology
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• 제24권6호
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• pp.139-146
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• 2000

The development of high performance materials is very important subject in order to enhance the properties of bearings whose role is to transfer energy harmoniously by reducing the problem of friction and wear down, etc. between the interacting solid surfaces in relative motion under high loads in comply with mechanical operating mechanism of engines. In this study, several (100-x)Al-xSn coating films (where x=85, 75, 65 atomic % at Al) on substrates which are abt. 2mm thickenss of Kelmet layer sintered back steel were prepared by using RF sputtering system. These coating films were observed the morphology by SEM(Scanning Electron Microscope) and investigated the crystal structure by XRD(X-ray Diffractor) for their properties. And friction coefficient of these films was measured by ball-on-disc tester for their tribological properties. From the experimental results, it was shown that high performance properties of bearing can be improved greatly by controlling the composition and morphology of material surface with effective use of the plasma-assisted sputtering process.

• Wind and Structures
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• 제18권4호
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• pp.323-345
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• 2014

Less than 30 years ago a new method was introduced in wind-tunnel testing of tall buildings, known variously as the High-Frequency Base Balance or High-Frequency Force Balance, which revolutionized the determination of design wind loads using model studies. The method is reviewed in hindsight, in the perspective of the present, and with a crystal ball to speculate on future developments. These viewpoints focus on various technical issues that have been solved, are being solved, and need to be solved. The intent is to assist the uninitiated develop appreciation for the technology involved, to identify various pitfalls awaiting those who embark in the method, and to identify areas of need so that practicing design engineers-the users of such studies-can appreciate the limitations and collaborate on future advances while promoting improved communication between executor and user.

• 국제학술발표논문집
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• The 2th International Conference on Construction Engineering and Project Management
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• pp.130-139
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• 2007

This paper presents a study on risk analysis in terms of contractor's costs in construction phase in which Crystal ball (software of Decisioneering, UK) has been utilized as a main tool. To realize it, a questionnaire survey has been carried out to identify the dominant factors that strongly influence contractor costs in Vietnam. Based on results of questionnaire investigation, the survey identified three factors which were duration of each construction task, costs of reinforcing steel, and cement. Then a spreadsheet model was created in order to analyze risks. The study also indicates that the cost of reinforcing steel and cement are the cause of risks for contractors. According to the suggested model, contractors may foresee the probability of completion within the approved budget, and the possibility of earning in accordance with owner's payment conditions.

• 한국전기전자재료학회논문지
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• 제21권12호
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• pp.1077-1082
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• 2008

To fabricate a multi-layered piezoelectrics/electrodes structure, the piezoelectrics should be sintered at the temperature lower than $950^{\circ}C$ to use the silver electrode, which is cheaper than the electrodes containing noble metals such as Pd and Pt. Therefore, in this study, we modified the composition of $Pb(Zr,Ti)O_3$-based material as $(Pb_{0.98}Cd_{0.02})(Ni_{1/3}Nb_{2/3})_{0.25}Zr_{0.35}Ti_{0.4}O_3$ to lower the sintering temperature and to improve the piezoelectric properties. Small amount of $MnCO_3$, $SiO_2$, and $Pb_3O_4$ were also added to lower the sintering temperature of the ceramic. The prepared raw powders were mixed by using a ball mill for 24 hours. And then the mixed powders were calcinated for 2 hours at $800^{\circ}C$. The calcinated powders were again crushed with the ball mill for 72 hours. The final powders were pressed for making the shape of ${\emptyset}15\;mm$ disk. The disk-type samples were sintered at temperature range of $850{\sim}950^{\circ}C$. The crystal phases of the sintered specimens were perovskite structure without secondary phases. All of the measured electrical properties such as electromechanical coupling coefficients ($k_p$), mechanical quality factors ($Q_m$), and piezoelectric charge constants ($d_{33}$) were decreased with decreasing the sintering temperatures. The electrical properties measured at the sample sintered at $950^{\circ}C$ were 54% of $k_p$, 503 of $Q_m$, and 390 pC/N of $d_{33}$, respectively. These properties were considered to be fairly good for the application of multi-layered piezoelectric generators or actuators.

• 한국자기학회지
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• 제22권3호
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• pp.85-90
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• 2012

$Nd_2Fe_{14}B$ 화합물 결정의 산화 및 미세 $Nd_2Fe_{14}B$ 결정입자의 보자력에 미치는 산화의 영향을 조사하였다. $Nd_2Fe_{14}B$ 화합물 결정의 산화속도는 $Nd_{15}Fe_{77}B_8$ 합금 잉곳 중의 과잉 성장시킨 $Nd_2Fe_{14}B$ 결정립을 이용하여 조사하였다. $Nd_2Fe_{14}B$ 화합물 결정의 산화는 이 결정상의 ${\alpha}$-Fe, $Fe_3B$, 및 Nd 산화물 복합상으로의 분해에 의해 일어 났다. $Nd_2Fe_{14}B$ 화합물 결정의 산화속도는 결정 방위와는 무관하였다. 산화반응 속도 식은 단순한 직선관계로 나타났다. $Nd_2Fe_{14}B$ 화합물 결정의 산화에 대한 활성화에너지는 약 26.8 kJ/mol로 계산되었다. HDDR 처리한 $Nd_{15}Fe_{77}B_8$ 합금을 볼밀링하여 임계단자구 크기에 유사한 미세한 $Nd_2Fe_{14}B$ 결정입자를 제조하고, 이 입자들을 이용하여 보자력에 미치는 산화의 영향을 조사하였다. 임계단자구 크기에 유사한 미세한 $Nd_2Fe_{14}B$ 결정입자(${\fallingdotseq}0.3\;{\mu}m$)는 9 kOe 이상의 높은 보자력을 가졌다. 그러나, 이 보자력은 공기 중에서 온도 상승에 따라 급격하게 저하하였다($200^{\circ}C$에서 2 kOe 이하). 이러한 급격한 보자력의 감소는 산화에 의해 미세 입자의 표면에 형성된 연자성 ${\alpha}$-Fe 및 $Fe_3B$ 상 때문으로 판단되었다.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2008년도 춘계학술대회 및 기술 세미나 논문집 디스플레이 광소자
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• pp.63-64
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• 2008

Electrokinetic motion of fullerene ($C_{60}$) particles in liquid crystal (LC) medium under an in-plane electric field has been studied for the application to the electronic paper display. Fullerenes move in the direction of applied electric field due to interaction between the induced dipole moment on $C_{60}$ and external electric field at lower threshold voltages compared to other devices such as QR-LPD (Quick Response Liquid Powder Display) and TBD (Twisting Ball Display). We also confirmed the bistability of fullerene particles in LC medium and the results showed that the 87% and 81% of original reflectance or transmittance of image was retained after 24 hours and 48 hours respectively. Our studies show the possibility that fullerenes can be used for electronic paper display.