• Title, Summary, Keyword: preoxidation

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CONTROL OF DIATOM BY PREOXIDATION AND COAGULATION IN WATER TREATMENT

  • Seo, Jeong-Mi;Kong, Dong-Soo;Ahn, Seoung-Koo;Kim, Hyun-Ook
    • Environmental Engineering Research
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    • v.11 no.1
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    • pp.45-53
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    • 2006
  • Conventional coagulation is still the main treatment process for algae removal in water treatment. The coagulation efficiency can be significantly improved by the preoxidation of algae-containing water. Jar test was conducted to determine the optimal condition for the removal of diatoms, especially Cyclotella sp. by preoxidation and the subsequent coagulation. The effects of various concentration of PAC (Polyaluminum chloride) on coagulation with and without preoxidation using chlorine or potassium permanganate at different pHs (7.7 and 9.0) were evaluated. At pH 7.7, preoxidation with 2ppm $Cl_2$ followed by coagulation with 7.5 ppm PAC coagulant could reduce Cyclotella sp. concentration by 86%. At pH 9.0, preoxidation with 1 mg $KMnO_4/L$ followed by coagulation with 12.5 ppm PAC coagulant reduced Cyclotella sp. concentration by 85%. Non-linear regression was applied to determine the optimal condition. At pH 7.7 and 9.0, R was over 0.9, respectively. The pH of algal blooming water is over 9.0. Algae (diatom; Cyelotella sp.) can be controlled in the following ways: preoxidation with 1 mg $KMnO_4/L$ followed by coagulation with 12.5 ppm PAC coagulant can remove 80% algae from water. If water pH is adjusted to 7.7, it was expected that less amount of coagulant (7.5 or 10 mg PAC /L) after preoxidation ($Cl_2$ 2 ppm or $KMnO_4$ 0.33, 1 ppm) would be needed to achieve similar level of algae removal. The oxidation with 0.33ppm $KMnO_4$ followed by coagulation with 7.5 ppm PAC coagulant was preferable due to cost-effectiveness of treatment condition and color problem after treatment.

Effects of Preoxidation on High Temperature Wear of Piercing Plug Tool Steel Sliding Against SA210C Steel Used for Production of Seamless Tube (심리스 튜브 제조용 피어싱 플러그 공구강과 SA210C강의 고온 미끄럼 마모에 미치는 예비산화의 영향)

  • Choi, Byung-Young;Gu, Yoon-Sik
    • Journal of the Korean institute of surface engineering
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    • v.46 no.6
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    • pp.264-270
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    • 2013
  • Effects of preoxidation on high temperature wear of piercing plug tool steel sliding against SA210C steel used for production of seamless tube have been studied using a pin-on-disc CETR tribometer, under applied normal load of 20 N at $900^{\circ}C$ in air. It was found in the preoxidized pin specimens of piercing plug tool steel that the coefficient of friction decreased to about 0.4 at an initial stage followed by showing nearly constant value of about 0.4 during high temperature wear testing. On the other hand, it was also found in the pin specimens without preoxidation that the coefficient of friction increased and fluctuated, ranging from about 0.3 to 0.6 during the tests until the running period of about 800 sec. The compact and continuous Fe-oxide layer was formed on the contact surface of the preoxidized pin specimens after high temperature wear testing followed by penetrating along the grain boundaries of coarse ferrite in the decarburized region beneath the oxide layer due to the lower hardness of the region.

Preparation and Analysis of Activated Carbon Fiber from PAN Precursor(I) (PAN 선구체로부터 활성 탄소섬유의 생산과 분석(I))

  • 김진홍;이화선;박병기;정경락;김공주
    • Textile Coloration and Finishing
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    • v.4 no.4
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    • pp.90-96
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    • 1992
  • In the PAN-based ACF manufacturing system stabilization step was improved with chemical treatment (preoxidation) in order to yield higher carbon content and to avoid excessive fragmentation during carbonization and activation process. The optimal condition of preoxidation was at 18$0^{\circ}C$ for 4 minutes in sodium glyceroxide in glycerine (concentration of NaOH was 0.02 meq/g). To investigate low temperature stabilization effect, preoxidized PAN fiber heated 22$0^{\circ}C$ to 26$0^{\circ}C$ as a function of treatment time and oxidative gas atmosphere, and analysed by infrared spectrum and TGA. As a results of IR and TGA, it was clear that impregnated[preoxidative] PAN had 14% higher residual than untreated PAN at 100$0^{\circ}C$ and the optimal condition of stabilization was at 26$0^{\circ}C$ for 3.5 hours within $N_2$ atmosphere.

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Effect of Preoxidation on the Zircaloy-4 Oxidation Behavior in a Steam and Water Mixture between $700^{\circ}C$ and 85$0^{\circ}C$ (수증기와 물의 혼합 분위기에서 기산화층이 지르칼로이 -4의 산화 거동에 미치는 영향)

  • Yoo, Jong-Sung;Kim, In-Sup
    • Nuclear Engineering and Technology
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    • v.19 no.2
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    • pp.122-129
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    • 1987
  • Experiments and numerical analysis have been performed to investigate the effect of preoxidation by oxidizing Zircaloy-4 specimens at a higher temperature after a period of exposure at a lower temperature. The oxidation experiments were performed between $700^{\circ}C$ and 85$0^{\circ}C$ after Preoxidation at $650^{\circ}C$ in a steam and water mixture for 600 seconds and 1,800 seconds. As the thickness of preoxidized layer increased, the oxidation rate of preoxidized specimens at higher temperature became lower than that of as-received claddings. A transition region of oxidation rate exist in the preoxidized specimens, and the region disappeared rapidly as the oxidation temperature increased. This effect appeared more clearly at lower temperatures. According to the results of numerical analysis performed in this study, the growth rate of oxide layer thickness and weight gains were similarly affected by the thickness of preoxidized layer.

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METAL SURFACE CHANGES BY HEAT TREATMENT OF Ni-Cr ALLOYS (열처리에 의한 도재용 Ni-Cr합금 표면의 변화에 관한 연구)

  • Kim, Young-Han;Lee, Sun-Hyung;Yang, Jae-Ho;Jung, Heon-Young
    • The Journal of Korean Academy of Prosthodontics
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    • v.27 no.2
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    • pp.219-248
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    • 1989
  • The purposes of this study were to analyze the microstructural and compositional changes of metal surfaces following different conditions of preoxidizing heat treatment, to investigate the composition of metal oxides, and to evaluate the effect of preoxidation and removal of surface oxides on microstructure and diffusion profiles. The techniques of EDAX (energy-dispersive analysis of x-ray), ESCA (electron spectroscopy for chemical analysis), and EPMA (electron probe micro analysis) were used, along with SEM (scanning electron microscopy). The obtained results were as follows : 1. A surface of the specimen became rough and the amount of the metal oxides increased with increasing the heat treatment time and temperature and the partial pressure of oxygen. 2. At an air pressure of 28' vacuum, the higher the temperature and the longer the time of preoxidation, the higher Ni concentration was detected. 3. Cr concentration in the specimen heat treated with air was higher than that of with vacuum. 4. The oxides in the specimens were mainly composed of Ni and Cr oxides. On the globular growth particles, significant rises in Al concentration of Rexillium III and Ti concentration of Verabond were noted. 5. Atomic diffusion occurred at the ceramic-metal interface, furthermore the amount of the flux was increased with preoxidation heat treatment.

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Glass to Metal Bonding by Electric Field (전장에 의한 유리와 금속의 접합)

  • 정우창;김종희
    • Journal of the Korean Ceramic Society
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    • v.20 no.1
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    • pp.70-78
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    • 1983
  • This paper discusses the application of Si-Borosilicate glass sealing to a new sealing method which utilizes a large electrostatic field to pormote bound formation at relatively low temperature. Bonding mechanism and the effect of bonding time bonding temperature glass thickness and surface roughness on the bond strength were investigated. Application of a de voltage across bonded specimen gradually produced a layer of glass adjacent silicon which was depleted of mobile ions. As a consequence a n increasingly larger fraction of the applied voltage appeared across the depleted region and very large electric field resulted This field accompanyed by large electrostatic force acted as driving force the of strong bond. And stronger bond was formed with increasing bonding time and temperature. A low temperature preoxidation is advantageous for the Si surface having a rougher surface finish that 1 microinch.

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Time-Dependent Dielectric Breakdown Characteristics of Thin $SiO_2$ Films and Their Correlation to Defects in the Oxide (얇은 산화막의 TDDB 특성과 막내의 결함과의 상관성)

  • Sung, Yung-Kwon;Choi, Jong-Ill;Kim, Sang-Yung;Han, Sung-Jin
    • Proceedings of the KIEE Conference
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    • pp.147-150
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    • 1988
  • Since the integration level of VLSI circuits progresses very quickly, a highly reliable thin $SiO_2$ film is required to fabricate a small-geometry MOS device. In the present study we have attempted to eliminate the failure-causing defects that develop in thin oxide films during the oxidation step by performing a long-time preoxidation and postoxidation annealing. The TDDB test and the copper decoration method were used to calculate the oxide defects density of MOS device. The dielectric reliability of high-quality thin oxides have been studied by using the time-zero-dielectric-breakdown (ramp-voltage-stressed I-V) and time-dependent-dielectric -breakdown (Constant-stressed I-V) tests. Failure times against temperature and electric field are examined and acceleration factors are abtained for each parameter. Based on the data obtained, breakdown wearout limitation for thin oxide films is estimated.

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A Study on Elongation/Contraction Behavior and Mechanical Properties of Oxy-Polyacrylonitrile(PAN) Fiber in Basic/Acidic Solution for Artificial Muscle Applications (산화된 폴리아크릴로니트릴 섬유의 인공근육 응용을 위한 염기/산 용액에서의 신장/수축 거동과 기계적 특성 연구)

  • 이영관;김상완;이경섭;조인희;이주화
    • Polymer Korea
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    • v.26 no.4
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    • pp.468-476
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    • 2002
  • Oxy-PAN fiber prepared from the preoxidation and saponification of raw PAN fiber is known to elongate and contract when immersed in basic and acidic solutions, respectively. In this study, about 30% elongation in NaOH solution and 30∼50% contraction in HCl solution have been observed. In mechanical test, the mechanical properties of oxy-PAN fiber in the contracted state was stronger than that in the elongated state. These behaviors and mechanical properties are compared to those of living muscle and linear actuator. The change of length in NaOH and HCl solutions is due to switching between a hydrophilic and a hydrophobic structure. Other reasons are exchange of ion and water in/out of oxy-PAN fiber, and osmotic pressure difference associated with relevant ions. Much studies are needed to clarify the effective factors on but the oxy-PAN fiber's elongation/contraction behavior and mechanical properties, but the oxy-PAN fiber perpared in our laboratory has a sufficient potential for application as artificial muscle and linear actuator.

Effect of Acanthopanacis cortex Water Extract on Antioxidative Activity, Lipid Profile and Epidermal Thickness in DNCB-induced Allergic Contact Dermatitis Animal Model (오가피열수추출물이 DNCB로 유도된 알레르기성 접촉피부염 흰쥐의 지질대사, 항산화능 및 표피회복능에 미치는 영향)

  • Kim, Yoon-Hee;Park, Young-Sook
    • Korean Journal of Food Science and Technology
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    • v.38 no.5
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    • pp.668-673
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    • 2006
  • The effects of Acanthopanacis cortex water extract on allergic contact dermatitis (ACD) in Sprague-Dawley male rats treated with 2.5% 1-chloro-2,4-dinitrochlorobenzene (DNCB) on the dorsal skin were evaluated. The concentration of TBARS in plasma and liver was increased in ACD rats and was significantly decreased in Acanthopanacis cortex fed group (ACFG) compared to CG (control group). Serum Ig E level was significantly increased in CG compared to normal group, while that of ACFG was significantly decreased. The epidermal thickness of CG was significantly increased compared to that of normal group, while that of ACFG was significantly decreased compared to that of CG These results indicated that the Acanthopanacis cortex water extract administration improved lipid preoxidation, antioxidative activity, serum Ig E level and epidermal thickness in rats with ACD.