• Title/Summary/Keyword: pack-cementation process

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Kinetic Analysis of Diffusion Aluminide Coating (확산 알루미나이드 코팅의 속도론적 해석)

  • 손희식;김문일
    • Journal of the Korean institute of surface engineering
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    • v.28 no.3
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    • pp.152-163
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    • 1995
  • A theoretical model which combines gaseous transport and solid state diffusion with the multi-component equilibrium at the gas/pack and gas/coating interfaces was used to study the kinetics of diffusion aluminide coating. The diffusion aluminide coatings were applied by pack cementation with Ni substrate under argon atmosphere in the high activity and the low activity pack containing $NH_4CL$ or $AlF_3$ activator. On the basis of the process conditions, the suggested model allows the surface composition, the growth rate of coating layers and the aluminium concentration profiles in coatings to be calculated. In the case of $NH_4$Cl activator, careful consideration was required in the analysis, because activator contains nitrogen and hydrogen as well as halogen element to activate the pack. A good agreement is obtained between the theoretical predictions and the experimental results.

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Microstructure and Hot Corrosion Resistance of Aluminide and Chromium-Aluminide Coatings for Inconel 600 (Inconel 600에 있어서 Al 및 Al-Cr擴酸浸透 被覆處理에 따른 被覆層의 特性과 耐蝕性)

  • Chung In-Sang;Park, Kyeung-Chae;Park, Soo-Ho
    • Journal of the Korean institute of surface engineering
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    • v.20 no.3
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    • pp.95-105
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    • 1987
  • For the purpose of improving the hot corrosion resistance of Ni-base superalloy, Inconel 600, aluminide and chromium-aluminide coatings by pack cementation process were studied. The morphology of these coatings is dependent on the type of process employed. And their overall composition depends on the composition of the base alloy and on the nature of the cement. Therefore the different aluminide and chromium-aluminide coatings obtained on a superalloy do not possess the same resistance to oxidation and hot corrosion. The mechanisms governing the formation of the coatings and the composition of the coating were varied by pack composition and temperature, and cyclic hot corrosion resistance of the auluminide coating formed by one-step process was inferior to that of the coating formed by two-step process. and Cr-Al composite coating showed good resistance for cyclic hot corrosion.

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Evaluation of Corrosion Resistance on Al-Cr Coated Stainless Steel Separator for MCFC at Anode Side (MCFC 양극측에서 Al-Cr피복 스테인레스강 분리판의 내식성평가)

  • Lee, M.H.;Yoon, J.S.;Bae, I.S.;Yoon, D.J.;Kim, B.I.;Park, H.H.
    • Korean Journal of Materials Research
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    • v.13 no.2
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    • pp.126-132
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    • 2003
  • In order to evaluate the corrosion resistance at the anode side separator for molten carbonate fuel cell, STS316 and SACC-STS316 (chromium and aluminum were simultaneously deposited by diffusion into STS316 authentic stainless steel substrate by pack-cementation process) were applied as the separator material. In case of STS316, corrosion proceeded via three steps ; a formation step of corrosion product until stable corrosion product, a protection step against corrosion until breakaway occurs, a advance step of corrosion after breakaway. Especially, STS316 would be impossible to use the separator without suitable surface modification because of rapid corrosion rate after formation of corrosion product, occurs the severe problem on stability of cell during long-time operation. Whereas, SACC-STS316 was showed more effective corrosion resistance than the present separator, STS316 due to the intermetallic compound layer such as NiAl, Ni3Al formed on the surface of STS316 specimen. And it is anticipated that, in order to use SACC-STS316 alternative separator at the anode side, coating process, which can lead to dense coating layer, has to be developed, and by suitable pre-treatment before using it, very effective corrosion resistance will be achieved.

High Temperature Combustion Behavior of Carbon/Carbon Composites Coated with SiC (탄화규소로 도포된 탄소/탄소 복합재의 고온 연소거동)

  • Choi, Don-Mook;Kim, Joung-Il
    • Journal of the Korean Society of Hazard Mitigation
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    • v.1 no.1 s.1
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    • pp.127-138
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    • 2001
  • Although Carbon/Carbon Composites(CFRCs) have excellent mechanical properties at high temperature, the disadvantage of combustion in air restricts their applications. Thus a lot of investments have been studied to improve the drawback of CFRCs. In this study, SiC used as a thermal protective coating material possesses almost the same expansion coefficient compared to that of carbon, so SiC was coated on 4D (directional) CFRCs by Pack-Cementation process. For the 4D CFRCs coated with SiC, optical microscopy observations were performed to estimate the coating mechanism involved and TGA tests were also performed to evaluate the improvement of combustion resistance. And their high temperature combustion properties were investigated by the arc torch plasma test. From the results, it is found that the mechanical properties and high temperature combustion properties of the 4D(directional) CFRCs coated with SiC were much better than bare 4D CFRCs.

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Ablative Mechanism of SiC Coated Carbon/carbon Composites with Ratio of Oxygen to Fuel at Combusion Test (연소시험에서 산소와 연료 비에 따른 탄화규소로 코팅된 탄소/ 탄소 복합재의 삭마 메커니즘)

  • Zhang, Eun-Hee;Kim, Zeong-Baek;Joo, Hyeok-Jong
    • Applied Chemistry for Engineering
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    • v.18 no.3
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    • pp.227-233
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    • 2007
  • Carbon/carbon (C/C) composites as unique materials possess exceptional thermal resistance with light weight, high stiffness, and strength even at high temperature. However, one serious obstacle for application of the C/C composites is their poor oxidation resistance in high temperature oxidizing environments. SiC coating has been employed to protect the composites from oxidation. This study explored combustion characteristics of 4-directional (4D) carbon/carbon composites using liquid fuel rocket engine to investigate ablative motion of the materials. C/C composites were made of coal tar pitch as a matrix precursor, and heat-treated at $2300^{\circ}C$. Throughout repeated densification process, the density of the material reached $1.903g/cm^3$. After machining 4D C/C composites, the nozzle surface was coated by a SiC layer by pack-cementation method to improve oxidation resistance. Erosion characteristics of SiC-coated C/C composites were measured as function of the ratio of oxygen to fuel. The morphological change of the composites after combustion test was investigated using SEM and erosion mechanism also was discussed.

The Aluminizing of Boronized Low Carbon Steel (침붕처리한 저탄소강의 알루미늄 확산처리에 관한 연구)

  • 윤영식;김한삼;김수식
    • Journal of the Korean institute of surface engineering
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    • v.29 no.2
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    • pp.120-131
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    • 1996
  • In order to improve the mechanical properties and the high temperature oxidation resistance, aluminizing was carried out at a temperature range between $850^{\circ}C$ and $1050^{\circ}C$. The pack cementation process was used to produce uniform layer. After each treatment, the microhardness and the characteristics of high temperature oxidation were tested to evaluate the properties of the aluminide layer. The aluminide layer consisted of FeAl above $1000^{\circ}C$, and $Fe_2Al_5$ below $900^{\circ}C$, and the mixed phase of FeAl and $Fe_2Al_5$ between 90$0^{\circ}C$ and $1000^{\circ}C$ in case of the mixture powder consisted of 5%Al+5%$NH_4Cl+90%AL_2O_3$. The microhardness of $Fe_2Al_5$ was obtained much as the twice as that of FeAl. As the aluminizing temperature and time increased, the thickness of aluminide increased. After aluminizing, the high temperature oxidation resistance was remarkably improved. The high temperature oxidation resistance of FeAl was superior to the resistance of high temperature oxidation of $Fe_2Al_5$.

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Effect of Heat Treatment on the Microstructural Evolution of Pt-aluminide Coated Ni-based Superalloy (Pt-Aluminide로 코팅된 초내열합금의 열처리에 따른 미세조직변화)

  • Joo, D.;Park, S.H.;Jung, Y.G.;Lee, K.H.;Kim, C.S.
    • Journal of the Korean Society for Heat Treatment
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    • v.19 no.2
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    • pp.103-108
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    • 2006
  • Microstructural evolution of Pt-aluminide coated Ni-based superalloy has been investigated with ductilization heat treatment. The Pt coat was prepared on the superalloy and then aluminide coating was conducted using a pack cementation process. Samples were heat-treated at $1050^{\circ}C$ for 2 hrs and the microstructure and element analysis were preformed. A various precipitated compounds were observed within the coating layer and the diffusion region in the Pt-aluminide coating and heat treatment, indicating that the bi-phase compounds of $PtAl_2$ and NiAl were performed during the Pt-aluminide coating, whereas $M_{23}C_6$, MC, $Ni_3Al$ and ${\sigma}$ phases were precipitated in the inter-diffusion region. The bi-phase compounds of $PtAl_2$ and NiAl were transformed into the single phase compound of $PtAl_2$ with the heat treatment, increasing the amount of carbide and ${\sigma}$ phase.

CASE REPORTS OF TREATMENT OF ERUPTION-DISTURBED MX. FIRST MOLAR BY SURGICAL EXPOSURE (맹출 장애를 가진 상악 제1대구치의 외과적 노출을 이용한 치험례)

  • Seok, Choong-Ki;Nam, Dong-Woo;Kim, Hyun-Jung;Kim, Young-Jin;Nam, Soon-Hyeun
    • Journal of the korean academy of Pediatric Dentistry
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    • v.31 no.1
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    • pp.11-18
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    • 2004
  • The eruption of permanent teeth represents the movement in the alveolar bone before appearance in oral cavity, to the occlusal plane after appearance in oral cavity, and additive movement after reaching th the occlusal plane. Tooth eruption is mostly controlled by genetic signals. The eruption stage is divided to preeruptive alveolar stage, alveolar bone stage, mucosal stage according to the process of growth and development. If the disturbance is occured in any stage of eruption, tooth does not erupt. The cause of eruption disturbance are ectopic position of the tooth germ, obstruction of the eruption path and defects in the follicle or PDL. In the treatment of eruption disturbance, surgical procedures are commonly used. There are three kind of surgical procedure ; surgical exposure, surgical repositioning, surgical exposure and traction Surgical exposure is basic procedure. This involves removal of mucosa, bone, lesion that are surrounding the teeth, dental sac when necessary to maintain a patent channel between the crown and the normal eruptive path into the oral cavity. To ensure this patency, many techniques including cementation of a celluloid crown, packing with gutta-percha or zinc oxide-eugenol, or a surgical pack, are used. When surgical exposure is conducted, operators should not expose any part of cervical root cement and not injure periodontium or root of adjunct tooth. After surgical exposure, tooth should be surrounded by keratinized gingiva. There is direct relationship between the extent of development of pathophysiologic aberrations and the intensity of the manipulative injury inflicted on the tooth by surgical treatment, so operator should consider this thing. In these cases, surgical exposure is conducted on Maxillary 1st milars that have a eruption disturbance and improve the eruption disturbance effectively.

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