• Proceedings of the Korean Institute of Surface Engineering Conference
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• 1999.05a
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• pp.5-5
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• 1999

A novel process is proposed to improve oxidation resistance of Ti-Al intermetallic compounds at elevated temperatures by both Cr addition and pre-sulfidation, where TiAl alloys withlor without Cr addition were sulfidized at 1173K for 86.4ks at a 1.3 Pa sulfur partial pressure in a $H_2-H_2S$ gas mixture. The pre-sulfidation treatment formed a thin Cr-Al alloy layer as well as 7~10 micrometer $TiAl_3$ and $TiAl_2$ layer, due to selective sulfidation of Ti. Oxidation resistance of the pre-sulfidation processed TiAl 4Cr alloy was examined under isothermal and heat cycle conditions between room temperature and 1173K in air. Changes in $TiAl_3$ into $TiAl_2$ and then TiAl phases as well as their effect on oxidation behavior were investigated and compared with the oxidation behavior of the TiAl-4Cr alloy as TiAl and pre-sulfidation processed TiAl aHoys. After oxidation for up to 2.7Ms a protective $Al_2O_3$ scale was formed, and the pre-formed $TiAl_3$ changed into $TiAl_2$ and the $Al_2Cr$ phase changed into a CrAlTi phase between the $Al_2O_3$ scale and $TiAl_2$ layer. The pre-sulfidation processed TiAl-4Cr alloy had very good oxidation resistance for longer times, up to 2.7 Ms, in contrast to those observed for the pre-sulfidation processed TiAl alloy where localized oxidation occurred after 81 Oks and both the TiAl and TiAl-4Cr alloys themselves corroded rapidly from the initial stage of oxidation

• Journal of Korea Foundry Society
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• v.25 no.6
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• pp.233-239
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• 2005

Contact material is widely used in the field of electrical parts. Ag-CdO has a good wear resistance and stable contact resistance. We studied a lifetime of Ag-CdO material because of getting better properties of Ag-CdO using Post-oxidation. The experimental procedure were melting using high frequency induction, heat treatment, rolling and internal oxidation. And we experimented on difference process, Post-oxidaion. Then we tested a lifetime and analysed. We obtained the optimizing oxidation temperature was $750^{\circ}C$. Using Pre-oxidation, coarse oxide and depleted oxidation layer existed but finer oxides were existed and depleted oxidation layer was not using Post-oxidation. In Post-oxidation, The density was 10 $g/cm^{3}$, the hardness was Hv 80 and the adhesive strength was 9000N. The specimen of Post-oxidation had better lifetime properties than that of Pre-oxidation. We predicted that the lifetime of Post-oxidation specimen is more longer twice than that of Pre-oxidation one.

• Electrical & Electronic Materials
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• v.7 no.6
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• pp.511-519
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• 1994

The effect of the deposition conditions, such as the base pressure, working pressure, sputtering power, pre-sputtering, and deposition thickness in facing targets sputtering system(FTS), on the oxidation of the TbFeCo thin films was studied by investigating the magneto-optical properties as well as oxygen analysis by the AES depth profiles. The results showed that the base pressure did not affect the magnetic properties so much, probably due to the short flight distance of the sputtered particles. At the higher sputtering power and lower working pressure with pre-sputtering the oxidation of TbFeCo thin films was decreased. As the film thickness increased the TbFeCo thin films showed the perpendicular anisotropy from in-plane anisotropy overcoming the oxidation effect at the beginning of the sputtering.

• Journal of Korean Society on Water Environment
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• v.38 no.6
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• pp.267-274
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• 2022

This paper is a result of research conducted on the 800,000 m³/d capacity of A Water Treatment Plant (WTP) and 400,000 m³/d capacity of B WTP plant in operation in the Nakdong River region. We evaluated the effect of algae broom on the WTP operation based on the running data of both WTP and the data on the pre-oxidation process field test for algae control using sodium permanganate (SPM) at the B WTP. The study results showed that during the algal bloom period, the coagulant dose increased by 102% in A WTP and 58% in B WTP, respectively, and the chlorine dose also increased by 38% and 29%, respectively, which may affect Total trihalomethane (THM) production. Data such as algal populations and Chl-a, residual chlorine and THM, algal populations, and ozone dose appeared also highly correlated, confirming that algal broom affects WTP operations, including water quality and chemical dosage. As a result of the field test of B WTP, THMs appeared lower than that of the control, suggesting the possibility of the SPM pre-oxidation process as an alternative to algae-related water quality management. Furthermore, in terms of GHG emissions due to energy consumption, it was observed that the pre-oxidation process using SPM was approximately 10.8%, which is a very low ratio compared to the pre-ozonation process. Therefore, these results suggest that the SPM pre-oxidation process can be recommended as an alternative to low-carbon water purification technology.

• Journal of the Korean Applied Science and Technology
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• v.22 no.3
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• pp.250-256
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• 2005

This study was aimed to investigate treatment feasibility of leachate from D landfill that is located in gyr대ungbuk. From the analytical results of leachate, organic and nonbiodegradable matters were contained in high concentration. Thus chemical treatment was introduced to degrade nonbiodegradable matters in pre or post biological process. Two types of Fenton oxidation were adapted in this study. The first one is pre treatment process before biological treatment. The second one is post treatment process after biological treatment. The optimal conditions of both treatment methods were investigated as follows. In case of pre treatment process, the optimal conditions appeared in $Fe^{+2}/H_2O_2$(mmol/mmol): 0.1, $H_2O_2/CODcr$(mg/mg): 27.0, pH: 3 and reaction time: 2hrs. On the other hand, in case of post treatment process, the optimal conditions appeared in $Fe^{2+}$(mmol/mmol): 0.14, $H_2O_2/COD_{cr}$(mg/mg): 57.4, pH: 3 and reaction time: 1.25hrs. In the above optimal conditions, high COD removal was obtained in pre and post treatment process. Also it can expect that Fenton oxidation converted nonbiodegradable matters into biodegradable matters.

• Corrosion Science and Technology
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• v.4 no.4
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• pp.136-139
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• 2005

The effect of oxidation and hot corrosion on the solid particle erosion was investigated for hot-pressed silicon nitride using as-polished, pre-oxidized and pre-corroded specimens by molten sodium sulfates. Erosion tests were performed at 22, 500 and $900^{\circ}C$ using angular silicon carbide particles of mean diameter $100{\mu}m$. Experimental results show that solid particle erosion rate of silicon nitride increases with increasing temperature for as-polished or pre-oxidized specimens in consistent with the prediction of a theoretical model. Erosion rate of pre-oxidized specimens is lower than that of as-polished specimens at $22^{\circ}C$, but it is higher at $900^{\circ}C$. Lower erosion rate at $22^{\circ}C$ in the pre-oxidized specimens is attributed due to the blunting of surface flaws, and the higher erosion rate at $900^{\circ}C$ is due to brittle lateral cracking. Erosion rate of pre-corroded specimens decreases with increasing temperature. Less erosion at $900^{\circ}C$ than at $22^{\circ}C$ is associated with the liquid corrosion products sealing off pores at $900^{\circ}C$ and the absence of inter-granular crack propagation observed at $22^{\circ}C$.

• Applied Science and Convergence Technology
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• v.25 no.6
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• pp.149-153
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• 2016

Thermal oxidation has significant potential for use in synthesizing metal-oxide nanostructures from metallic materials. However, this method has limited applicability to the synthesis of multi-morphology NiO from Ni foil. Techniques consisting of mechanical and chemical approaches were used to pre-treat the Ni foil (prior to oxidation) to promote the formation of nanowires and nanoplates on the NiO layer. These morphologies were realized on the Ni foils scratched by sand paper and a knife, respectively, and subsequently heat-treated at $500^{\circ}C$ for 24 h. Small nanowires (diameter: <10 nm) formed on the Ni foil treated by absolute $HNO_3$ and then oxidized at $500^{\circ}C$ for 24 h. The formation of various morphologies (on the pre-treated Ni foil), which differ from that formed in the case of pristine Ni foil after oxidation, may be attributed to the surface melting phenomenon that occurs during the nucleation process.

• Carbon letters
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• v.12 no.2
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• pp.107-111
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• 2011

Polyacrylonitrile (PAN) fibers were pre-oxidized in a temperature range of 180-275$^{\circ}C$. The effects of positive and negative stretching on the structure and morphology of PAN fiber in the pre-oxidation process were studied by FTIR spectroscopy, XRD, and SEM. Mechanical property changes were also investigated. No changes in the movement and intensity of functional groups of PAN fibers were caused by positive stretching of up to 10% and negative stretching down to -8%. The crystal structure can be affected by the positive stretching and negative stretching. The maximum strength is 479.81 MPa when the stretching is positive, and the maximum strength is 420.55 MPa when the stretching is negative.

• Advances in environmental research
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• v.5 no.4
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• pp.251-262
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• 2016

The biodegradability and decomposition efficiencies increase with the pre-treatment of sludge in a digestion process. In this study, the feasibility of ultrasound coupled with potassium permanganate oxidation as a disintegration method and digestibility of aerobic reactor fed with disintegrated sludge with ultrasound coupled potassium permanganate were investigated. The first stage of the study focused on determining the optimum condition for ultrasonic pre-treatment for achieving better destruction efficiency of sludge. The second part of the study, the aerobic digestibility of sludge disintegrated with ultrasound and potassium permanganate oxidation alone and combined were examined comparatively. The results showed that when 20 min of ultrasonic pre-treatment applied, the specific energy output was 49384 kJ/kgTS with disintegration degree of 58.84%. During the operation of aerobic digester, VS/TS ratios of digesters fed with disintegrated sludge decreased indicating that disintegration methods could obviously enhance aerobic digestion performance. The highest reduction in volatile solids was 75% in the digester fed with ultrasound+potassium permanganate disintegrated sludge at the end of the operation compared to digester fed with raw sludge. Total Nitrogen (TN) and Total Phosphorus (TP) levels in sludge supernatant increased with this combined method significantly. Besides, it promoted the production of ${\bullet}OH$, thus enhancing the release of Carbon (C), Nitrogen (N) and Phosphorus (P) from the sludge. Disintegration with all methods used in this study could not improve Capillary Suction Time (CST) reduction in disintegrated digesters during the operation. The results demonstrated that the combined ultrasound treatment and potassium permanganate oxidation method improves the biodegradability compared to control reactor or their single application.

• Preventive Nutrition and Food Science
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• v.18 no.3
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• pp.175-180
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• 2013

The purpose of this study was to determine the effects of a pre-exercise meal on the plasma human growth hormone (hGH) response and fat oxidation during walking. Subjects (n=8) were randomly provided with either 1 g/kg body weight of glucose in 200 mL water (CHO) or 200 mL water alone (CON) 30 min prior to exercise and subsequently walked on a treadmill at 50% of VO2max for 60 min. Plasma hGH concentrations were significantly higher in subjects who received CHO compared to those who received CON at 15 and 30 min. The fat oxidation rate in the CHO was significantly lower than the CON while walking for 5~15, 25~35 and 45~55 min. Plasma FFA levels were also significantly lower in the CHO compared to the CON at 30, 45 and 60 min. Plasma glucose levels in the CHO were significantly lower while plasma insulin levels were significantly higher than in the CON at 15 and 30 min. Therefore, the results of this study suggest that the elevation of plasma hGH levels due to the intake of a pre-exercise meal may not be strongly related to fat oxidation and plasma free fatty acid (FFA) levels during low-intensity exercise.