YBa₂Cu₃O_(7-x) 세라믹과 YBa₂Cu₃O_(7-x)/Ag 복합체에서의 영率 對 氣空率의 상관관계

윤존도,초우예 경남대학교 신소재연구소 1995 論文集 Vol.5 No.-

YBa₂Cu₃O_(7-x) 초전도 세라믹 재료와 YBa₂Cu₃O_(7-x)/Ag 복합체의 명율에 미치는 기공율의 효과에 대하여 연구하였다. 서로 다른 기공율을 갖는 소결 시편의 영율을 상온에서 衝擊?? 起法(Impulse Excitation Technique)으로 측정하였다. 측정된 데이터를 영율과 기공율과의 상관관계에 대한 두 가지의 관계식-선형방정식과 스프리그스의 지수함수 방정식-과 비교함으로써 적합한 정량적 관계식을 구하고자 하였는데, 표준오차로 볼 때, 후자가 상대적으로 양호한 것으로 나타났다. 스프리그스의 관계식에 포함되어 있는 상수를 구해본 결과, 세라믹의 경우 3.7 복합체의 경우 3.84로 매우 근사한 것으로 밝혀져, 두 물질이 유사한 기공구조를 갖는다는 것을 보였다. 복합체의 영율은 세라믹의 그것보다 낮았는데, 이론적 영율의 상한과 하한과 비교함으로써 그 정량적 관계에 대한 이해가 시도되었다. The effect of porosity on the Young's modulus in YBa₂Cu₃O_{7-x} ceramics and YBa₂Cu₃O_{7-x}/25%Ag composites was studied. Young's moduli of the samples with various porosities were measured with the Impulse Excitation Technique. When the experimental data were fitted with the linear equation and the Spriggs exponential equation, both were found to be reasonably good with a little superioty in the latter, represented by the lower standard error. The b constant in the Spriggs equation was determined t o be 3 . 7 and 3.8 for the ceramics and the composites. respectively, implying the similarity of the pore structures of two different materials. The understanding of the effect of the addition of silver on a decrease in the Young's modulus was attempted by comparing the data with theoretical upper and lower bound of the modulus in the composites.

테이프 캐스트法에 의해 제조된 세라믹 초전도 厚膜에서의 배향성에 관한 연구

윤존도 경남대학교 신소재연구소 1996 論文集 Vol.6 No.-

Y-Ba-Cu-O 산화물 초전도체를 후막으로 성형하기 위한 테이프캐스트법에 대한 연구와 성형과정과 성형후과정에 의한 후막내 세라믹입자의 배향에 관한 연구가 수행되었다. 결합제, 가소제, 해교제, 빛분산매의 첨가량에 대한 최적조성비가 실험적으로 결정되었으며, 성형도중 발생하는 세포모양(cell狀)의 후막표면의 결함과 니장조성 및 공정변수와의 관계가 조사되었다. 성형 및 성형후 과정 동안 세라믹 입자의 배향도를 엑스선 회절도에서 00L 회절선의 강도合과 기타면들의 회절선 강도合과의 비로 정량화하여 측정하였는데, 테이프캐스트 성형, 적층압착, 소결을 거치는 동안 계속 배향도는 증가하였다. 배향도는 분말의 입도와 적층압착시 압력과 관계가 있는 것으로 나타났으나, 캐스트속도와 블레이드간극과는 연구된 범위내에서는 큰 관계가 없는 것으로 나타났다. Y-Ba-Cu-O ceramic superconductor thick tapes were prepared by tape casting, during which the composition of slips and the processing variables were optimized. The degree of preferred orientation(DPO) as a function of processing variables, such as powder size, casting speed, doctor-blade opening size, and laminating pressure, were examined by XRD analysis on the casted. laminated, and sintered tapes. It was found that the DPO increased as the processing steps proceeded, with highest DPO in the as-sintered tapes. It was also found that the DPO was a function of powder size and laminating pressure. but was not affected by the casting speed and blade opening size in the range studied.

Al6061 Bulk재에서 압축시험에 의한 상온가공성 분석 및 마찰인자 측정

김국주,박종수,윤존도 경남대학교 신소재연구소 2003 신소재연구 Vol.15 No.2

부피성형(bulk forming)은 가공속도, 소재 회수를 및 가공 후의 조직 미세와 등의 유리한 점이 많아 대량 생산에 적합한 가공 방식이다. 그러나 금형형상과 가공조건들이 적절하지 못할 경우 형상오차 및 연성파괴 등의 성형결함이 발생하게 된다. 이 성형결함 없이 성형될 수 있는 한계를 부피 성형한계(bulk forming limit)라고 하는데, 이것은 가공성(workability)과 의미가 비슷하다. 가공성은 공정종류 금형과 소재사이의 마찰, 변형속도 등에 의해 좌우되므로 예측하기 어렵다. 따라서 본 실험에서는 가공성을 Al6061의 소재에서 가공온도, 마찰 및 변형을 속도에 따른 성형한계도(forming limit diagram)로 작성하여 정량화하고자 하였다. 또 압축시험에서 금형과 소재사이의 마찰효과에 의한 베럴링(barreling) 현상이 생기므로 신빙성 있는 실험결과를 얻기 힘들다. 따라서, 각 마찰조건에서 링 압축시험을 통한 마찰인자를 구해서 압축시험으로 구한 측정웅력을 보정하여 유동웅력(flow stress)을 구하는데 사용하고자 한다. Bulk forming process is widely used for a large plastic deformation in a metal industry, which has a lot of advantages at processing speed, raw material utilization, fine microstructure, etc. But if die shape and process conditions are selected improperly, forming defects can be found due to geometric errors and ductile fracture. Bulk forming limit is defined as it is deformed without these defects which is similar to the workability. Prediction of workability is difficult because of dependence on a type of processes, friction of die and material, deformation rate, etc. Therefore, in this study, forming limit diagram is made depending on forming temperature, friction and strain rate to analyze the workability of A16061 bulk material. Also, it is difficult in measuring of reliable result exactly because the barreling is caused by interfacial friction between die and material at the compression test. So, friction factor is measured at the different friction conditions by ring compression test and then flow stress will be calculated from the measured stress by compression test.

Effects of the nano-sized clay on rheological behavior of ρ-alumina bonded castable

( Jon Do Yun ),( Sung Ho Cheon ),( Soon Ho Kim ),( Byung Sei Jun ) 경남대학교 신소재연구소 2012 신소재연구 Vol.24 No.-

The advantages of refractory castables regarding ease of installation and thermome- chanical behavior have made the replacement of conventional brick. Such advantages result form improvements of rheological behavior of the castable during working and from a significant reduction of liquid phase formation at high temperature. The conventional castables typically contain 10 to 30% calcium alumina cement as the binder for the curing strength. The curing strength of conventional castables is due to the gel formation of hydrated phases of alumina cement binder. Alumina cement permits a large amount of the water in the castables and a liquid phase at the low temperature formed by the reaction between CaO of the cement and aluminosilicate aggregates. To prepare the alumina cement free vibrated alumina castable, ρ-alumina is employed as a binder material, and nano-sized clay is added to enhance a curing strength and give thixotropic behavior. The rheological behavior of matrix of castable is controlled by investigating the influences of ultrafines, ρ-alumina, and nano-sized clay on the viscosity of matrix. The microsilica and ultrafine alumina were added 3wt% and 4wt%, respectively to the matrix, which showed that the viscosities tends to be lowest values. The rheological property of the matrix is well estabilished by adding ρ-alumina as 8wt% and clay as 4wt%. The thixotropic behavior of the ρ-alumina bonded castable was appeared by introducing nano-sized clay into the matrix and adjusting the pH near to the PZC of the clay suspension.

Transparent Bioceramics Prepared by Spark Plasma Sintering

( Jon Do Yun ),( Byung Nam Kim ),( Su Kyoung Kim ),( Young Hwan Han ) 경남대학교 신소재연구소 2012 신소재연구 Vol.24 No.-

1. Introduction Hydroxyapatite (HA), Ca10(PO4)6(OH)2, is one of the most attractive bioceramics. HA ceramic promotes bone apposition and growth on its surface [1, 2]. But HA ceramic has been hardly used in orthopaedic and dental clinic due to their intrinsic poor mechanical properties[3]. However, efforts have been made for the development of dense bulk HA ceramics with good mechanical properties by microstructure modification. Also, transparency and nano structure make its application to confocal microscopy allowing direct observation of bio-interfacial reactions with improved spatial and temporal resolution. This work is to prepare transparent HA ceramics with nano-scale microstructure and to characterize them by microscopy. 2. Experimental procedure Hydroxyapatite ceramics were prepared by spark plasma sintering technique. The spark plasma sintering was carried out at temperatures between 900 and 1000oC under a pressure of 80 MPa for 10minutes in a vacuum. Microstructure was observed by scanning electron microscopy, transmission electron microscopy, scanning transmission electron microscopy, and energy dispersive x-ray spectrometry. 3. Result and Discussion Sintered ceramics reached almost full density over 99%, showing high transparency and improved mechanical properties. TEM analysis showed that they had grain size of about 100 nm and porosity of extremely low level. Grain boundaries were clean without any amorphous or second phase. Intragranular nanovoids of about 10 nm size were generated inside grains. The voids were generated during rapid heating of SPS process and stabilized during slow cooling forming flat boundaries. Growth behavior of nanovoids during post-annealing was examined.

수열합성을 통한 제철 , 제강 슬래그의 건자재 활용

윤존도(Jon Do Yun),전병세(Byung Sei Jun) 경남대학교 신소재연구소 2000 신소재연구 Vol.12 No.-

베르코비치 나노인덴테이션에 대한 3차원 유한요소해석과 탄소성 변형에 관한 연구

양현윤(Hyeon-Yun Yang),조상봉(Sang-Bong Cho),김지수(Ji-Soo Kim),윤존도(Jon-Do Yun) Korean Society for Precision Engineering 2005 한국정밀공학회지 Vol.22 No.10

Poster Presentation : Fabrication of Dense ZnAl2O4 by Spark Plasma Sintering

( Ah Rong Jeong ),( Jon Do Yun ),( Byung Nam Kim ) 경남대학교 신소재연구소 2013 신소재연구 Vol.25 No.-

Zinc aluminate (ZnAl2O4), naturally occurring as the mineral gahnite, is a member of the spinel family. At present zinc aluminate is used as a catalyst for the dehydration of saturated alcohols to olefins, methanol and higher alcohol synthesis, preparation of polymethylbenzenes, synthesis of styrenes from acetophenons, and double bond isomerisation of alkenes. Furthermore, zinc aluminate can also be used as a catalyst support, since it has a high thermal stability, low acidity and a hydrophobic behavior. In this study, we fabricated dense ZnAl2O4 using Spark Plasma Sintering (SPS) at 1200℃. Through the XRD analysis, we identify ZnAl2O4 of the single phase. Also Optical, physical properties and microstructure were measured.

The Differences of Influencing Factors on IOS Usage Intention between Adopters and Non-Adopters in Small- and Medium-Sized Firms

Ryu Il,Kim Jae-Jon,Cho Geon,Kim Do-Goan,Lee Yun-Hee 한국정보기술응용학회 2005 한국정보기술응용학회학술대회 Vol.2005 No.1

Preparation of Superhydrophobic Coating Films

( A Rong Jeong ),( Jun Su Kim ),( Jon Do Yun ) 경남대학교 신소재연구소 2012 신소재연구 Vol.24 No.-

As the nano technology is developed, the nano materials with a super hydrophobic surface has been studied. Self-cleaning function of Lotus leaf to wipe clean the impurities on its surface is excellent because it has a unique nanostructure. By using the effect to solar panels, it may clean surface itself by rain. In this study, coating films were prepared by the 2 step process. To provide surface roughness, we prepared silica form of sphere by self-assembly monolayer. By changing the composition and processing variables optimum condition was determined. Contact and sliding angles were measured using contact angle analyzer. Microstructure was observed by LOM and FE-SEM.