• Title/Summary/Keyword: Degassing

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EFFECT OF DEGASSING CONDITION ON CERAMIC BOND STRENGTH OF Ni-Cr ALLOYS (Degassing 조건이 Ni-Cr 합금의 도재결합력에 미치는 영향)

  • Lee, Eun-Hwa;Jeon, Young-Chan;Jeong, Chang-Mo;Lim, Jang-Seop
    • The Journal of Korean Academy of Prosthodontics
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    • v.38 no.4
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    • pp.461-471
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    • 2000
  • This study evaluated the effect of degassing on the ceramic bond strength of two Ni-Cr alloys under varying holding time at the upper limit temperature and atmospheric conditions. Metal specimens were divided into 5 groups for each alloy according to degassing conditions prior to porcelain application no degassing, degassing under vacuum without hold, degassing under vacuum with hold for 5 min. and 10 min. respectively at the upper limit temperature and degassing in air. Total number of metal ceramic specimens was eighty and each group had eight specimens. The ceramic bond strength was measured by four-point flexural test using Instron and the fractured surface was examined under SEM. The results obtained were as follows. 1. Degassing in air improved the ceramic bond strength of Ni-Cr alloys. 2. In degassing under vacuum, hold at the upper limit temperature was advantageous to the ceramic bonding of Ni-Cr alloys. 3. After ceramic metal bond test, metal surfaces were partially covered with the thin porcelain layer, and the cohesive failures in porcelain were predominant in groups showing higher ceramic bond strength.

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Membrane Degassing Process of Sweep Gas-vacuum Combination Type for Ammonia Removal (스윕 가스-진공 혼합식 탈기막 시스템을 활용한 암모니아 제거)

  • Yoon, Hongsik;Min, Taijin;Lee, Gunhee;Kim, Hyoung-Tak;Shin, Wanho
    • Journal of the Korean Society of Industry Convergence
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    • v.25 no.5
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    • pp.835-842
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    • 2022
  • In this study, the membrane degassing process of the sweep gas - vacuum combination type was proposed for ammonia wastewater treatment. The effect of pH, initial ammonia concentration and scale-up on ammonia degassing performance was investigated. As a result, as the pH and the initial ammonia concentration increased, the degassing permeate flux was improved. On the other hand, the ammonia mass transfer coefficient increased as the initial ammonia reduced, which seems to be due to the driving force of the sweep gas-vacuum combination type membrane degassing system proposed in this study. In addition, 80 mg NH3/min of the ammonia degassing rate was achieved using a 6×28 inch size module. Better degassing performance is expected if consideration for maintaining vacuum pressure is involved in the scale-up design.

Effects of Process and Casting Variables on the Results of Degassing AC4C Aluminum Alloy Melt by Using Rotary Degasser (공정 및 주조 변수의 AC4C 알루미늄 합금 용탕의 로터리 degasser를 이용한 탈가스 처리 결과에 미치는 영향)

  • Lee, Ki-Joon;Kwon, Hae-Wook
    • Journal of Korea Foundry Society
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    • v.20 no.6
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    • pp.407-418
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    • 2000
  • The effect of various factors on the results of degassing of AC4C aluminum alloy melt by using rotary degasser were investigated. The difference between the effects of nitrogen gases of commercial pure and high purity grades on the degassing results was not significant. The optimum degassing condition was obtained. The effect of holding and degassing temperature was not significant, either. The result of degassing was deteriorated by the modification treatment of eutectic silicon, meanwhile improved by the grain refining. The effect of the latter was stronger than that of the former when the melt was treated simultaneously. The volume fractions of hydrogen porosity of the castings obtained from the molds with water moisture such as natural and green sand molds were much higher than those from the molds without that such as pep-set and $CO_2$ molds.

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Adsorption of p-Nitrophenol by Surface Modified Carbons from Aqueous Solution

  • Goyal, Meenakshi
    • Carbon letters
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    • v.5 no.2
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    • pp.55-61
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    • 2004
  • Adsorption isotherms of p-nitrophenol from its aqueous solutions on two samples of activated carbon fibres and two samples of granulated activated carbons have been determined in the concentration range 40~800 mg/L (ppm). The surface of these carbons was modified by oxidation with nitric acid and oxygen gas, and by degassing the carbon surface under vacuum at temperatures of $400^{\circ}C$, $650^{\circ}C$ and $950^{\circ}C$. The oxidation of carbon enhances the amount of carbon-oxygen surface groups, while degassing decreases the amount of these surface groups. The adsorption of p-nitrophenol does not depend upon the surface area alone but appears to be influenced by the presence of oxygen groups on the carbon surface. The adsorption decreases on oxidation while the degassing of the carbon surface enhances the adsorption. The decrease in adsorption depends upon the strength of the oxidative treatment being much larger in case of the oxidation with nitric acid, while the decrease in adsorption on degassing depends upon the temperature of degassing. The results show that while the presence of acidic surface groups which are evolved as $CO_2$ on degassing suppress the adsorption of p-nitrophenol, the presence of non acidic surface groups which are evolved as CO on degassing tend to enhance the adsorption. Suitable mechanisms compatible with the results have been presented.

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Effect of the Impeller Rotation Speed and Inert Gas Flow Rate on Degassing Rate in the A356 Aluminum Melt (임펠러 회전속도와 불활성 가스 유량이 A356 알루미늄 용탕의 탈가스 속도에 미치는 영향)

  • Hyeok-In Kwon;Hoe-Gyung Jeong;Seong-Il Jeong;Ji-Woo Park;Min-Su Kim
    • Journal of Korea Foundry Society
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    • v.43 no.6
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    • pp.271-278
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    • 2023
  • In the present study, A356 melt degassing experiments were conducted under various impeller rotation speed and inert gas flow rate conditions to determine changes in the melt temperature, composition and density during a degassing treatment. The melt temperature was found to decrease gradually as the degassing time increased, but a clear correlation between the impeller rotation speed or inert gas flow rate and the melt heat loss could not be confirmed. Regardless of the impeller rotation speed or inert gas flow rate, the Mg and Ti contents in the A356 melt scarcely changed, even after degassing for more than 10 minutes, while Sr contents decreased at the maximum degassing rate of 70 ppm. From a quantitative analysis of the degassing rate under each experimental condition based on the hydrogen concentration in the melt derived from the melt density and the degassing model equation, the inert gas flow rate was found to affect the degassing rate rather than the impeller rotation speed under the degassing operation condition employed in the present study.

Analytical Model for Predicting Degassing Pressure of the One Way Valve with Ring Type Rubber Disk for Packaging (포장용 링타입 고무막 One-way 밸브의 가스배출압력 예측을 위한 수학적 분석 모델)

  • Oh, Jae Young;Lee, Jin Yong;Yu, Ha Kyoung
    • KOREAN JOURNAL OF PACKAGING SCIENCE & TECHNOLOGY
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    • v.22 no.2
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    • pp.33-37
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    • 2016
  • One-way degassing valves usually designed for coffee packaging are recently applied to the various food packaging such as fermented health functional food or home meal replacement (HMR) packaging. The optimized degassing pressure by food product is important factor for keeping effective freshness and improving preservation of the food, therefore the development of degassing valves specified with various open pressure is needed. In this study, the mechanical characteristics of the degassing valve with ring type rubber disk were analyzed and a mathematical model was developed to predict the open pressure of the valve. The model was verified with test results derived from several available valves, and it may be useful in designing and developing a new valve.

Development of Degassing Valves for Food Packaging using Ring Type Rubber Disk (링타입 고무막을 이용한 식품 포장용 가스배출 밸브(Degassing Valve) 개발)

  • Yu, Ha Kyoung;Lee, Kyungo Ho;Oh, Jae Young
    • KOREAN JOURNAL OF PACKAGING SCIENCE & TECHNOLOGY
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    • v.20 no.2
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    • pp.35-39
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    • 2014
  • One-way degassing valves are designed to allow pressure to be released from an air-tight package while preventing air from getting back into the package. Air, especially the oxygen ($O_2$) portion of air, can have negative effects on the package contents and its freshness. The most common application of the one-way degassing valve is for fresh roasted coffee. Demands of one-way degassing valves have been increasing with the high growth of global coffee market. In this study, we have developed one-way degassing valves for coffee and food packaging using ring type rubber disk, named SP valve. Its quality and performance was verified with test results to be equal with that of global top maker's product, Goglio valve. SP valves showed 820~1200 Pa of opening pressure, 10~50 Pa of closing pressure, 1.2~1.6 L/ min of flow rate. And, the SP valve applicable to ferment food packaging is expected to contribute to globalize Korean traditional food.

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Changes in the Surface Characteristics of Gas-atomized Pure Aluminum Powder during Vacuum Degassing

  • Yamasaki, Michiaki;Kawamura, Yoshihito
    • Proceedings of the Korean Powder Metallurgy Institute Conference
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    • 2006.09b
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    • pp.1039-1040
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    • 2006
  • Vacuum degassing is essential in the preparation of RS P/M aluminum alloys to remove adsorbates and for the decomposition of hydrated-$Al_{2}O_3$ on the powder surface. Changes in the surface characteristics during vacuum degassing were investigated by X-ray photoelectron spectroscopy and temperature-programmed desorption measurement. Hydrated-$Al_{2}O_3$ decomposition to crystalline-$Al_{2}O_3$ and hydrogen desorption on the surface of argon gas-atomized aluminum powder occurred at 623 K and 725 K, respectively. This temperature difference suggests that the reaction converting hydrated-$Al_{2}O_3$ to crystalline-$Al_{2}O_3$ during vacuum degassing should be divided into the two reactions $"2Al+Al_{2}O_3{\cdot}3H_2O\;2Al_{2}O_3+6H_{surf}"and"6H_{surf}3H_2"$.

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AN EXPERIMENTAL STUDY ON THE FITNESS OF THE CERVICAL MARGIN IN THE CERAMO-METAL CROWN ACCORDING TO THE ALLOY TYPES AND THE CURVATURE OF LABIO-CERVICAL MARGIN (도재소부전장금관용 합금과 순측치경부 변연만곡도에 따른 변연적합도에 관한 연구)

  • Jeon Young-Chan;Kim Jung-Hwa
    • The Journal of Korean Academy of Prosthodontics
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    • v.29 no.3
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    • pp.181-196
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    • 1991
  • The Purpose of this study was to evaluate the marginal fit of ceramo-metal crown according to the different ceramo-metal alloy types and the curvature of labio-cervical margin. Degudent $G^{(R)}$ as precious and $Verabond^{(R)}$ as non-precious ceramo-metal alloy were used. The abutment was preparaed with two different curvature types : a normal curvature type and a pronounced curvature type. 20 crowns were farbricated using four different combinations and their marginal fits were measured at 3 consecutive stages (before degassing, after degassing, after glazing) using microscope under 200 magnification. The results were as follows: 1 . Marginal fitness before degassing. The groups of precious ceramo-metal exhibited better marginal fit than the groups of non-precious ceramo-metal with significant difference(P<0.05) . In the same ceramo-metal groups, the normal curvature group exhibited better marginal fit than the pronounced curvature group but without significant difference(P>0.05). 2. Marginal fitness after degassing. By degassing, the group of pronounced curvature and non-precious ceramo-metal was deformed the most, and the degree of margin fitness of each group was the same as before degassing. 3. Marginal fitness after glazing The group of normal curvature and precious ceramo-metal exhibited better marginal fit than the group of pronounced curvature and non-precious ceramo-metal with significant difference(P>0.05), and the degree of margin fitness of each group was the same as before degassing.

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Ammonia Wastewater Treatment and Selective Recovery Using a Sweep Gas-Vacuum Hybrid Type Membrane Degassing Process (스윕 가스-진공 하이브리드식 탈기막 공정을 활용한 암모니아 폐수처리 및 선택적 회수)

  • Hongsik Yoon;Taijin Min;Minkyu Jeon;Sungil Lim;Sechul Oh;Kyungha Ryu;Chungsung Lee;Bosik Kang
    • Journal of the Korean Society of Industry Convergence
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    • v.26 no.6_2
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    • pp.1171-1181
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    • 2023
  • In this study, a sweep gas - vacuum hybrid type membrane degassing process was proposed for ammonia wastewater treatment. In addition, the ammonia selective recovery of the hybrid type membrane degassing process was also investigated. As a result, the hybrid type membrane degassing process showed better degassing performance (54.9 mg NH3/m2min for 360 min) than the sweep gas type (32.3 mg NH3/m2min) or vacuum type (22 mg NH3/m2min). Additionally, the hybrid type membrane degassing process showed an excellent ammonia selectivity (103 times compared to Na+ Na+, 133 times compared to Ca2+). The ammonia selectivity was appeared to be due to the conversion characteristics of ammonium ion / dissolved ammonia depending on pH. The results in this study are expected to be used in the development of ammonia wastewater treatment and ammonia recovery in the future.