• Journal of Chest Surgery
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• 제20권3호
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• pp.458-472
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• 1987

A heart supplies bloods of about 15, 000 liters to each human organ in a day. A normal function of heart valves is necessary to this act of heart. The disease of heart valve develops to a narrowness of a closure, resulting in an abnormal circulation of bloods. In an attempt to eliminate the affliction of heart valves, the operation method to repair with artificial heart valves has been developed and saved numerous patients over past 30 years. This replacement operation has been performed since early 1960`s in Korea, but all the artificial heart valves used are imported from abroad with very high costs until recent years. The artificial heart valve using pyrolytic carbon has been developed at KAIST, which was proved to be stable in the mechanical performance and durability. Therefore, the in viva performance of this valve was examined through animal tests. The artificial heart valves used in this study are tilting disc type valves, in which the disc were made of graphite coated with pyrolytic carbon and the cages were made of titanium. In viva testings of these valves were performed in 12 dogs, in which right ventriculo-pulmonary arterial [Croup I] or inter-aortic [Croup IV] valved conduit was implanted using polytetrafluoroethylene conduits containing KAIST valve and aortic valve [Group II] or pulmonary valve [Croup III] was replaced by a KAIST valve with a 21mm or 19mm tissue annulus diameter. In group I and II, pre-and post-operative transvalvular pressure gradient was measured and compared with other prosthetic valves. During post operative period laboratory examination was performed including hemoglobin, hematocrit, red cell count, white cell, lactic acid dehydrogenase and platelet. The eight surviving dogs were sacrificed and autopsy was performed at 2, 6, and 8 weeks. KAIST valve has low transvalvular gradient and relatively high orifice area. Average ventriculo-aortic peak systolic transvalvular gradient was 14 mmHg in 21 mm valve and 19 mmHg in 19 mm valve. The valve has slight intravascular hemolysis effect. Thrombogenic effect of low polishing quality and eddy currents around small orifice is high. The valve has vulnerability of disc movement. These animal tests suggest that the improvement of the heart valve design, surface polishing state and prescription methods.

• Journal of Chest Surgery
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• 제22권1호
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• pp.42-49
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• 1989

A total of 420 pyrolytic carbon mechanical valves were implanted in 336 patients from January, 1984, through Jung, 1988. Of the valves implanted, 131 were Bjork-Shiley, 250 St-Jude, and 39 Duromedics. The cumulative follow-up was 398 patient-years with a mean follow-up of 14.4 months per patients. Among 336 patients, 175 had mitral, 68 aortic, 82 multiple, 10 tricuspid, and one pulmonary valve replacement. The hospital mortality figures were 9 of 336[2.67%] in all, 5 of 175[2.85%] in isolated mitral, 1 of 68[1.47%] in isolated aortic and 3 of 82[3.65%] in multiple valve replacement. The causes of hospital mortality were myocardial failure in 5, sepsis in 2, bleeding in 1, cerebral embolism in l. There was no late valve related mortality. The actuarial survival rate at 4.5years was 99.4*0.1%. The complications occurred in 15 of 336[4.46%]; 7 of 175[4.0%] in isolated mitral, 4 of 68[5.88%] in isolated aortic, and 4 of 82[4.89%] in multiple valve replacement. The causes of complications were thromboembolism in 4, hemorrhage in 4, paravalvular leakage in 4, hepatitis in 2, and complete AV block in l. Actuarial probability of survival at 4.5 years was 95.0*0.1%. The low mortality and complications encourage us to applicate these valves to any patient including children and young women.

• The Korean Journal of Ceramics
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• 제2권4호
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• pp.184-187
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• 1996

Diamod nucleation by mw assisted CVD was examined various conditions namely, (1) diamond nucleation on variour substrate materials, such as Si, cubic BN, pyrolytic BN and AIN, (2) AST(Activated species transport) method which promote nucleation of diamond on single crystal and polycrystalline alumina substrate was developed. (3) Effect of bias enhancement of nucleation on single crystalline Si was examined, and finally (4) DST (Double step treatment) method was developed to enhance diamond nucleation on Ni. In this method, we separated carbon diffusing process into Ni, carbon precipitating process from the inside of Ni and diamond precipitation process.

• Carbon letters
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• 제6권2호
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• pp.101-105
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• 2005

Like bamboo-sprouts after rains, numerous sub${\mu}m$-sized pyrocarbon whiskers growth on the Mullite ($3Al_2O_3{\cdot}2H_2O$) substrate could be observed through a looking glass during methane pyrolysis at the temperature of $1050^{\circ}C$ in this study. If the surface of substrate would be scrubbed strongly with iron metals, then finely sticked iron particles were more effective catalytic for nm-sized whisker growth. Numerous fine flakes of pyrolytic carbon were hanging by invisible nm-whiskers as like as small spiders hanging by a spiderweb. This is the identification of nm-sized whisker growth. Therefore if the pyrolysis would be stopped at the initial stage of the whisker growth, the primary lengthening growth was nm-sized whisker. So could we vary arbitrarily sizes of whisker from nm- to ${\mu}m$-sizes. But ${\mu}m$- and nm-whiskers grown with the different growth mechanism; the former was straight and the latter has twigs, The lengthening growth of whisker was depended on the flow pattern pyrolysis species on the active sites of substrate and on the growth duration. We could obtained straight whisker length of 10~20 ${\mu}m$/min during the primary growth and laboratory spiral whisker of 30~40 ${\mu}m$-diameter/hr during the secondary growth.

• 한국지하수토양환경학회지:지하수토양환경
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• 제27권2호
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• pp.41-49
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• 2022

To abate the environmental burdens arising from CO₂ emissions, biochar offers a strategic means to sequester carbons due to its recalcitrant nature. Also, biochar has a great potential for the use as carbon-based adsorbent because it is a porous material. As such, developing the surface properties of biochar increases a chance to produce biochar with great adsorption performance. Given that biochar is a byproduct in biomass pyrolysis, characteristics of biochar are contingent on pyrolysis operating parameters. In this respect, this work focused on the investigation of surface properties of biochar by controlling temperature and reaction medium in pyrolysis of pine sawdust as case study. In particular, CO₂ was used as reaction medium in pyrolysis process. According to pyrolytic temperature, the surface properties of biochar were indeed developed by CO₂. The biochar engineered by CO₂ showed the improved capability on CO₂ sorption. In addition, CO₂ has an effect on energy recovery by enhancing syngas production. Thus, this study offers the functionality of CO₂ for converting biomass into engineered biochar as carbon-based adsorbent for CO₂ sorption while recovering energy as syngas.

• 에너지공학
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• 제19권1호
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• pp.16-20
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• 2010

본 연구에서는 바이오매스로 커피원두를 이용하여 합성한 카본재료에 도전재로 주석을 이용하였다. 주석을 첨가하는 방법에 따라 단순 혼합, 화학적인 방법을 이용하여 혼합체를 만들어 시료를 합성하였다. 시료에 대한 XRD를 이용하여 주석과 탄소가 혼합된 구조를 가지고 있음을 확인하였고 SEM을 통한 합성된 시료구입자크기($12{\sim}85\;{\mu}m$)와 형태를 확인하였다. 충 방전 테스트를 실시하여 15사이클에서 카본블랙을 사용했을 때(105 mAh/g)보다 주석을 화학적으로 혼합을 시킨 시료의 경우(191 mAh/g)가 방전용량이 더 높게 나타나는 것을 볼 수 있었고, 주석을 단순 혼합을 실시한 경우에서는 카본블랙과 비슷한 용량(131 mAh/g)을 보였다.

• 공업화학
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• 제31권5호
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• pp.581-584
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• 2020

The effect of a chemical pretreatment on the surface carbon was investigated using a scanning electron microscope (SEM) and electrochemical methods. Primitive carbon has a reducing power likely due to incompletely oxidized functional groups on the surface. We aim to control this reducing power by chemical treatment and apply for the spontaneous deposition of nanoparticles (NPs). Highly ordered pyrolytic graphite (HOPG) was initially treated with a reducing agent, NaBH4 or an oxidizing agent, KMnO₄, for 5 min. Subsequently, the pretreated carbon was immersed in a platinum (Pt) precursor. Unexpectedly, SEM images showed that the reducing agent increased spontaneous PtNPs deposition while the oxidizing agent decreased Pt loading more as compared to that of using bare carbon. However, the amount of Pt on the carbon obviously decreased by NaBH₄ treatment for 50 min. Secondly, spontaneous reduction on pretreated glassy carbon (GC) was investigated using the catalytic hydrogen evolution reaction (HER). GC electrode treated with NaBH4 for a short and long time showed small (onset potential: -640 mV vs. MSE) and large overpotential for the HER, respectively. Although the mechanism is unclear, the electrochemistry results correspond to the optical data. As a proof-of-concept, these results demonstrate that chemical treatments can be used to design the shapes and amounts of deposited catalytic metal on carbon by controlling the surface state.

• 한국세라믹학회지
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• 제55권4호
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• pp.392-399
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• 2018

$C_f/SiC$ composites were prepared via a process combining chemical vapor infiltration (CVI) and precursor infiltration pyrolysis (PIP), wherein silicon carbide matrices were infiltrated into 2.5D carbon preforms. The obtained composites exhibited porosities of 20 vol % and achieved strengths of 244 MPa in air at room temperature and 423 MPa at $1300^{\circ}C$ under an Ar atmosphere. Carbon fiber pull-out was rarely observed in the fractured surfaces, although intermediate layers of pyrolytic carbon of 150 nm thickness were deposited between the fiber and matrix. Fatigue fracture was observed after 1380 cycles under 45 MPa stress at $1000^{\circ}C$. The fractured samples were analyzed by transmission electron microscopy to observe the distributed phases.

• 한국정밀공학회지
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• 제19권7호
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• pp.106-115
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• 2002

Growth characteristics of micro carbon structures fabricated by laser-assisted chemical vapor deposition are studied. Argon ion laser and ethylene were used as the energy source and reaction gas, respectively, to grow micro carbon rod through pyrolytic decomposition of the reaction gas. Experiments were performed at various conditions to investigate the influence of process parameters on growth characteristics such as the diameter or growth rate of the micro carbon rod with respect to reaction gas pressure and incident laser power. Reaction gas pressure in experiments ranges from 200 to 600Torr and the incident laser power from 0.3 to 3.8W. For these conditions, the diameter of the rod increases linearly with respect to the laser power but is almost independent of the reaction gas pressure. Growth rate of the rod changes little with gas pressure when the laser power remains below IW. For a constant reaction gas pressure, the growth rate increase with Increasing laser power, but the rate of increase decreases gradually, implying that the chemical vapor deposition condition changes from a kinetically-limited regime to a mass-transport-limited regime. When the carbon rod was grown at near threshold laser power, a very smooth surface is obtained on the rod. By continuously moving the focusing lens in the direction of growth, a micro carbon rod with a diameter of 287${\mu}{\textrm}{m}$ and aspect ratio of 100 was fabricated..

• 청정기술
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• 제21권2호
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• pp.108-116
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• 2015

황화수소와 암모니아는 많은 하수처리장과 산업 플랜트로부터의 배출가스에서 발견되어질 수 있는 가장 흔한 악취성분이다. 이들 유해물질들은 인간에게 건강 문제를 일으키고 촉매에 악영향을 미치기 때문에 생활환경과 산업 현장에서의 제거는 매우 중요하다. 본 연구에서는 황화수소와 암모니아에 대한 우수한 흡착능력을 가지는 흡착제를 개발하기 위하여 폐타이어의 열분해 생성물인 카본블랙을 이용하였다. 카본블랙, 금속산화물과 산 또는 염기를 혼합하여 펠렛형 흡착제를 제조하였고, 상온상압에서 고정층 흡착탑의 파과곡선을 이용하여 황화수소와 암모니아에 대한 흡착성능을 평가하였다. 카본블랙, 산화철(III)과 수산화나트륨 혼합물로 제조된 흡착제가 황화수소에 대한 가장 우수한 작업능력을 나타내었다. 암모니아에 대해서는 카본블랙, 산화구리(II), 염산의 혼합물로 제조된 흡착제가 우수한 작업능력을 보였다.