SHS 공정에 의해 제조된 Mo_xW_1-xSi₂ 발열체의 열화메커니즘

이동원,이상헌,김용남,이성철,구상모,오종민,Lee, Dong-Won,Lee, Sang-Hun,Kim, Yong-Nam,Lee, Sung-Chul,Koo, Sang-Mo,Oh, Jong-Min 한국전기전자재료학회 2017 전기전자재료학회논문지 Vol.30 No.10

The degradation mechanism of $Mo_xW_{1-x}Si_2$ ultrahigh-temperature heating elements fabricated by self-propagating high-temperature synthesiswas investigated. The $Mo_xW_{1-x}Si_2$ specimens (with and without post-annealing) were subjected to ADTs (accelerated degradation tests) at temperatures up to $1,700^{\circ}C$ at heating rates of 3, 4, 5, 7, and $14^{\circ}C/min$. The surface loads of all the specimen heaters were increased with the increase in the target temperature. For the $Mo_xW_{1-x}Si_2$ specimens without annealing, many pores and secondary-phase particles were observed in the microstructure; the surface load increased to $23.9W/cm^2$ at $1,700^{\circ}C$, while the bending strength drastically reduced to 242 MPa. In contrast, the $Mo_xW_{1-x}Si_2$ specimens after post-annealing retained $single-Mo_xW_{1-x}Si_2$ phases and showed superior durability after the ADT. Consequently, it is thought that the formation of microcracks and coarse secondary phases during the ADT are the main causes for the degraded performance of the $Mo_xW_{1-x}Si_2$ heating elements without post-annealing.

Effect of post annealing on the microstructure, mechanical properties, and failure of Mo_xW_1-xSi₂ heaters produced by self-propagating high-temperature synthesis

Cho, Myung-Yeon,Lee, Sung-Chul,Park, Chulhwan,Lee, Daeseok,Koo, Sang-Mo,Moon, Kyoung-Sook,Lee, Dong-Won,Oh, Jong-Min Elsevier 2019 INTERMETALLICS Vol.110 No.-

<P><B>Abstract</B></P> <P>High-performance tungsten molybdenum disilicide (Mo<SUB>x</SUB>W<SUB>1-x</SUB>Si<SUB>2</SUB>) heating elements were prepared using a self-propagating high temperature synthesis process. The effect of post annealing on the degradation behavior of the alloy was experimentally investigated. Increasing the attrition milling time up to 20 min during powder preparation resulted in Mo<SUB>x</SUB>W<SUB>1-x</SUB>Si<SUB>2</SUB> heaters with the highest density, which increased the fracture strength compared to samples with shorter attrition times. Such samples were annealed and evaluated as heating elements using accelerated degradation tests and failure analysis in order to compare their structural characteristics and flexural strength with as-fabricated samples. The annealed Mo<SUB>x</SUB>W<SUB>1-x</SUB>Si<SUB>2</SUB> heater showed a relatively dense structure with few pores and no secondary phases, apart from a SiO<SUB>2</SUB> layer. This favorable structure prevented bubble formation, which can result in fracturing of the heater, as revealed by evaluation at high temperatures with various heating rates. The flexural strength of the annealed specimen was 2.5-times higher than that of the as-fabricated specimen, which was attributed to removal of secondary phases during annealing. Failure time and surface load analyses were used to investigate the fracture mechanism of the Mo<SUB>x</SUB>W<SUB>1-x</SUB>Si<SUB>2</SUB> heaters in detail at 1790 °C by quantifying bubble formation and the presence of secondary phases.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Self-propagating high temperature synthesis of Mo<SUB>x</SUB>W<SUB>1-x</SUB>Si<SUB>2</SUB> heaters demonstrated. </LI> <LI> Post-annealed Mo<SUB>x</SUB>W<SUB>1-x</SUB>Si<SUB>2</SUB> heaters were highly dense, with good flexural strength. </LI> <LI> Bubble formation (the main cause of fracture) suppressed at ultra-high temperature (above 1700 °C). </LI> <LI> Surface load, failure time, and bubble formation used to study fracture mechanisms. </LI> </UL> </P>

SHS 공정으로 제조된 Mo<SUB>x</SUB>W<SUB>1-x</SUB>Si₂ 발열체의 가속수명시험과 고장분석

이동원(Dong-Won Lee),이상헌(Sang-Hun Lee),김용남(Yong-Nam Kim),이희수(Heesoo Lee),이성철(Sung-Chul Lee),구상모(Sang-Mo Koo),오종민(Jong-Min Oh) 한국전기전자학회 2017 전기전자학회논문지 Vol.21 No.3

고온자전합성과 후열처리 공정으로 MoxW1-xSi₂ 발열체를 제조하였다. MoxW1-xSi₂ 발열체의 신뢰성을 검증하기 위해 가속수명시험을 수행하였으며, 수명시간을 Minitab 프로그램으로 추정하였다. 또한, 가속수명시험 후의 MoxW1-xSi₂ 발열체의 고장분석을 전기적과 구조적 특성으로부터 수행하였다. 그 결과, MoxW1-xSi₂ 발열체의 지배적인 고장 유형은 발열체 내부의 크랙 형성과 SiO₂ 보호층의 박리임을 확인하였다. MoxW1-xSi₂ heaters were fabricated by self-propagating high-temperature synthesis (SHS) process and post sintering process. To validate the reliability of the MoxW1-xSi₂ heaters, the accelerated life test (ALT) was conducted, and then lifetime to MoxW1-xSi₂ heaters was estimated by using Minitab programs. Also, the failure analysis of MoxW1-xSi₂ heaters after ALT was performed through electrical and structural properties. As the results, it was confirmed that the dominant failure mode of MoxW1-xSi₂ heaters is the crack formation in heaters and the delamination of protective SiO₂ layers.

물류산업 종사자의 임금격차에 관한 요인분석 -생산성에 직접적 영향을 주지 않는 요인을 대상으로-

구경모(Koo, Kyoung?mo) 한국항만경제학회 2021 韓國港灣經濟學會誌 Vol.37 No.2

텔레비전의 장과 문학의 장

구모룡 국어국문학회 2004 국어국문학 Vol.- No.137

Nothing is more influential than television, when considered in terms of time spent and information received by people. It is not too much to say that we live in the field of television. This may seem a realization of Marshal McLuhan's prediction that the age of letters would put to an end due to televisions. Currently it is not unreasonable to say that the death of literature is prevalent. Succeeding McLuhan, Alvin Kernan wrote <The Death of Literature> whose theme is the revolutionary power of the television. Literature is a representative area of printing culture. The high crisis in literature is a natural outcome of electronic culture emergence. Above all, reading and writing skills necessary for literal art are being degraded. Such skills have something to do with cognitive aspects, so they require mental concentration on previous texts. Such concentration is in contrast to mental dispersion by which entertainments are characterized. Unlike art and literature both of which require mental concentration, such new media as film and television 8provide interpretation of entertainments which are mentally dispersing. Strongly appealing to the public, those media are changing cultural geographies and severely swinging the arena of literature. Then, is <the death of literature> an inevitable history ? It is fact that changes in technology would bring those in media and culture. However, it is exaggerative to say that book culture, which has long been a necessary pattern of life, would disappear due to the emergence of electronic technology as completely different. Printing and electronic technologies should not be replaced with each other, but coexist. But it is inevitable that the hegemony of culture is being gradually held by electronic culture. In nature, television is an entertainment technology whose aim is at fulfilling demands of the public. Because of their attractive functions and powerful audiovisual penetration, Jacques Ellul criticizes, television is becoming a device that destroys personality and human relations most seriously. Nevertheless, television is already a stuff that overwhelms the life of modern people. It is a critical technology that mediates daily aspects of modern society. That television is in the center of daily life suggests that television is in the very center of social culture. Symbols and signs provided by television are various extending beyond space and time. They provide both much information and much pleasure. Images reproduced by television are excessive, far from reality. Such reproduction is a specific formation of the world. This is true of cyber space. People tend to mistake things reproduced by television with realities. In this sense, interpreting originals behind channels is emerging as a main issue. Television programs are things that form the world specifically, rather than just reproducing the world. They provide specific forms of knowledge about the world. Thus it is needed for us to know processes through which television form and distribute specific discourses of the world. <Media Literacy> regarding television may be developed in different ways. The field of literature is facing crisis in the field of television. Under this situation, there's a tendency to seek literacy whose aim is at integrating literature, television and other media as literature publication is growing as an industry. In the era of new media or digital period, literature research cannot avoid being carried out in relation to other media. This suggests the necessity of integrated cultural studies seeking towards non-fragmental management of culture and non-closeness of culture. In this field of television, there are three main opinions about literature. The first opinion refers to negative effects of television. According to it, television ruling discourse and image is changing literature very negatively. The second opinion indicates the death of literature and transition to the field of television. Television indicates the emergence of new culture and new human image in advance. Finally, there's an opinion that television, literature and other media should be integratively understood with the concept of literature as a cultural part based. Any of these opinions acknowledges the overwhelming power of television.

Sialic acid-speciflc lectin from legume Maackia fauriei

Kim HaHyung,Park Hyun Joo,Kim Bum Soo,Koo Wan Mo 대한약학회 2004 大韓藥學會 總會 및 學術大會 Vol.2004 No.1

Nonstop Monomer-to-Aramid Nanofiber Synthesis with Remarkable Reinforcement Ability

Koo, Jun Mo,Kim, Hojun,Lee, Minkyung,Park, Seul-A,Jeon, Hyeonyeol,Shin, Sung-Ho,Kim, Seon-Mi,Cha, Hyun Gil,Jegal, Jonggeon,Kim, Byeong-Su,Choi, Bong Gill,Hwang, Sung Yeon,Oh, Dongyeop X.,Park, Jeyoung American Chemical Society 2019 Macromolecules Vol.52 No.3

<P>Aramid nanofibers (ANFs), typically produced by exfoliating aramid microfibers (Kevlar) in alkaline media, exhibit excellent mechanical properties and have therefore attracted increased attention as nanoscale building blocks. However, the preparation of aramid microfibers involves laborious and hazardous processes, which limits the industrial-scale use of ANFs. This work describes a facile and direct monomer-to-ANF synthesis via an as-synthesized intermediate low-molecular-weight poly(<I>p</I>-phenylene terephthalamide) (PPTA) without requiring the environmentally destructive acids and high-order shearing processes. Under the employed conditions, PPTA immediately dissociates and self-assembles into ANFs within a time period of 15 h, which is much shorter than the time of 180 h (not including the Kevlar preparation time) required for the Kevlar-to-ANF conversion. Interestingly, the fabricated ANFs exhibit nanoscale dimensions and thermoplastic polyurethane (TPU) reinforcing effects similar to those of Kevlar-derived ANFs; i.e., a 1.5-fold TPU toughness improvement and a maximum ultimate tensile strength of 84 MPa are achieved at an ANF content of only 0.04 wt %. Remarkable reinforcement ability investigated by comprehensive analytical data comes from ANFs, which disturb ordered hydrogen bonding in hard segments and induce strain hardening along the elongation pathway. Thus, the developed approach paves the way to industrial-scale production of ANFs and related nanocomposites.</P> [FIG OMISSION]</BR>

CONTROLLED LYSIS OF ESCHERICHIA COLI DOUBLE - LYSOGEN OF BACTERIOPHAGES λHL1 AND φ434

Koo, Yoon Mo,Parekh, Bhavin S,Hatfield, G Wesley,Lim, Henry C 한국화학공학회 1996 Korean Journal of Chemical Engineering Vol.13 No.2

A novel phage double-lysogen was developed to produce an intracellular protein and disrupt the host cell in the same reactor. Using this double-lysogen, we could simplify the recovering processes without cell harvest and disruption. Construction of the double-lysogen is based on the fact that a lysogen of a phage can be superinfected by another phage with different immunity. The single-lysogen of Escherichia coli, P90c/λHL1, was superinfected with bacteriophage Φ434 to produce a double-lysogen, in which phage genomes from each phage coexisted in the host chromosome. Two different inducers were used to induice the double-lysogen to produce a protein and to lyse the host cell. The first phage genome, λHL1, the prophage of the original lysogen, containing the temperature sensitive cI_(857), lacZ and defective Q genes was induced by increasing temperature to produce β-galactosidase, an intracellular reporter protein. The overproduction of β-galactosidase was carried out without experiencing the cell lysis due to the defective Q gene. After the temperature shift, the second prophage from the lysogen MS21/Φ434 was induced by mitomycin C or ultra-violet light to lyse the cell. The lysis of the cell releases the intracellular protein to the outer space. The cell lysis was confirmed by the decrease of cell density and the increase of the extracellular activity of β-galactosidase at the same time.

MATHEMATICAL MODELING FOR THE ESTIMATION OF LIPASE ACTIVITY BY AGAR DIFFUSION METHOD

Koo, Yoon Mo,Chang, Woo Jin,Moon, Yoon Hee 한국화학공학회 1997 Korean Journal of Chemical Engineering Vol.14 No.3

A mathematical model was developed to estimate the lipase activities from the experimentally obtained physical dimension of halo, formed by a diffusing lipase through agar media. A diffusion equation based upon the mass balance was derived in cylindrical coordinates, the integration of which was carried out by using finite difference method. A regressional analysis of the experimental data using the proposed model has brought the values for the hindered diffusivity of lipase through agar media and the minimum effective lipase concentration of 0.817 x 10^(-6) ㎠/s and 2.86 unit/㎤, respectively. The procedures, delineated in this work are considered to be useful for the quantitative analysis of haloforming enzymes at predetermined standard conditions.

Controlled Lysis of Escherichia coli Double - Lysogen of Bacteriophages λHL1 and φ434

Koo, Yoon Mo,Lim, Henry C,Parekh, Bhavin S,Hatfield, G Wesley 한국화학공학회 1996 NICE Vol.14 No.3

A novel phage double-lysogen was developed to produce an intracellular protein and disrupt the host cell in the same reactor. Using this double-lysogen, we could simplify the recovering processes without cell harvest and, disruption. Construction of the doutrle-lysogen is based on the fact that a lysogen of a phage can be superinfected by another phage with different immunity. Thc single-lysogen of Escherichia coli, P90c/λHL1, was superinfected with bacteriophage Ø434 to produce a double-lysogen, in which phage genomes from each phage coexisted in the host chromosome. Two different inducers were used to induce the double-lysogen to producx a protein and to lyse the host cell. The first phage gercome, λHL1, the prophage of the original lysogen, containing the temperature sensitive cles, lacZ and defective Q genes was induced by increasing temperature to produce p-galactosidase, an intracellular reporter proteitc. The overproduction of 3-galactosidase was carried out without experiencing the cell lysis due to the defective Q gene. After the temperature shift, the second praphage from the lysogen MS21/Ø434 was induced by mitomycin C or ultra-violet light to lyse the cell. The lysis of the cell releases the intracellular protein to the outer space. The cell lysis was confirmed by the decrease of cell density and the increasev of the extracxllular activity of galactosidase at the same time.