• International Journal of Automotive Technology
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• 제7권3호
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• pp.261-267
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• 2006

Understanding the mechanism of carbon oxidation is important for the successful modeling of diesel particulate filter regeneration. Carbon oxidation characteristics were investigated by temperature programmed oxidation(TPO) method as well as constant temperature oxidation(CTO) with a flow reactor including porous bed. The activation energy of carbon oxidation was increasing with temperature and had two different constant values in the early and the later stage of the oxidation process respectively in TPO experiment. Kinetic constants were derived and the reaction mechanisms were assumed from the experimental results and a simple reaction scheme was proposed, which approximately predicted the overall oxidation process in TPO as well as CTO.

• 한국군사과학기술학회지
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• 제25권6호
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• pp.580-585
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• 2022

In this study, the high-temperature dielectric constant of Si₃N₄ ceramics, a representative non-oxide-based radome material, was evaluated and the cause of the dielectric constant change was analyzed in relation to the oxidation behavior. The dielectric constant of Si₃N₄ ceramics was 7.79 at room temperature, and it linearly increased as the temperature increased, showing 8.42 at 1,000 ℃. As results of analyzing the microstructure and phase for the Si₃N₄ ceramics before and after heat-treatment, it was confirmed that oxidation did not occur at all or occurred only on the surface at a very insignificant level below 1,000 ℃. Based on this, it is concluded that the increase in the dielectric constant according to the temperature increase of Si₃N₄ ceramics is irrelevant to the oxidation behavior and is only due to the activation of charge polarization.

• 열처리공학회지
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• 제14권5호
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• pp.282-285
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• 2001

Based on the mass balance of anion and cation fluxes, the parabolic rate constant ($K_p$) of oxide grown during the high-temperature oxidation of metal is theoretically calculated. It is assumed that the diffusion of oxygen anion and metal cation through oxide scale obeys the Fick's 1st law, the growth of oxide is controlled by the diffusion of ions, electrical potential gradient as driving force for diffusion of ions is ignored, and oxidation occurs within an existing oxide layer. Then, the parabolic rate constant can be expressed by $K_p=[2{\rho}_{MmOn}{M^2}_{MmOn}(mD_oC_o{^e}+nD_MC_M{^e})/nm]$.

• 한국세라믹학회지
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• 제31권7호
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• pp.753-758
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• 1994

(100) Si and 4$^{\circ}$off (100) Si were oxidized in dry oxygen, and the differences in thermal oxidation behavior and electrical characteristics between two specimens were investigated. Ellipsometer measurements of the oxide thickness produced by oxidation in dry oxygen from 1000 to 120$0^{\circ}C$ showed that the oxidation rates of the 5$^{\circ}$ off (100) Si were more rapid than those of the (100) Si and the differences between them decreased as the oxidation temperature increased. The activation energies based on the parabolic rate constant, B for (100) and 4$^{\circ}$off (100) Si were 25.8, 28.6 kcal/mol and those on the linear rate constant, B/A were 56.8, 54.9 kcal/mol, respectively. Variation of C-V characteristics with the oxidation temperature showed that the flat band voltages were shifted positively and surface state charge densities decreased as the oxidation temperature increased, and the surface state charge density of the 4$^{\circ}$off (100) Si was lower than that of the (100) Si. Also considerable decrease in the density of oxidation induced stacking faults (OSF) for the 4$^{\circ}$off (100) Si was observed through optical microscopy after preferentially etching off the oxide layer.

• 한국식품위생안전성학회지
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• 제9권4호
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• pp.199-203
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• 1994

The oxidation of cholesterol in tallow heated at three frying temperatures, 130, 150 and 18$0^{\circ}C$ was studied by assaying cholesterol oxidation products(COP)by GC-MS. The correlation between levels of COP and changes of physicochemical parameters (peroxide value, polymer, polar components and dielectric constant) in tallow heated were studied. As temperature increased, the amount of cholesterol was decreased proportionally with heating time. However, the levels of COP did not increase considerably with increased frying temperature. The rate of cholesterol disappearance was the greatest at 18$0^{\circ}C$ and the smallest at 13$0^{\circ}C$. Larger amounts of COP formed were found at 15$0^{\circ}C$ than at 18$0^{\circ}C$. The levels of COP formed in tallow heated showed highly correlation with(r=0.94, n=30, p<0.01) polymer, polar components and dielectric constant, respectively.

• Nuclear Engineering and Technology
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• 제28권4호
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• pp.366-372
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• 1996

The simulated spent PWR fuel pellet which is corresponding to the turnup of 33,000 MWD/MTU is prepared by adding 11 fission-product elements to UO$_2$. The simulated spent fuel pellet is treated at 40$0^{\circ}C$ in air (oxidation), at 110$0^{\circ}C$ in air (high-temperature treatment), and at $600^{\circ}C$ in hydrogen (reduction). The product is treated through additional addition and reduction up to 3 cycles. Pellets are completely pulverized by the first oxidation, and the high-temperature treatment causes particle and crystallite to grow and surface to be smooth, and thus particle size significantly increases and surface area decreases. The reduction following the high-temperature treatment decreases much the particle size by means of the formation of intercrystalline cracks. The particle size decreases a little during the second oxidation and reduction cycle and then remains nearly constant during the third and fourth cycles. Surface area of pounder increases progressively with the repetition of oxidation and reduction cycles, mainly due to the formation of Surface cracks. The degradation of surface area resulting from high-temperature treatment is restored by too subsequent resulting oxidation and reduction cycles.

• 한국자동차공학회논문집
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• 제19권3호
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• pp.52-56
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• 2011

Active regeneration in CDPF requires $O_2$ which regenerates soot at high temperature. However, small amount of NO can interrupt $O_2$ regeneration in CDPF. To verify this phenomena, soot oxidation experiments using a flow reactor with a $Pr/CeO_2$ catalyst are carried out to simulate Catalyzed Diesel Particulate Filter (CDPF) phenomena. Catalytic soot oxidation with and without small amount of NO is conducted under tight contact condition. As the heating rate rises, the temperature gap of maximum reaction rate is increased between with and without 50ppm NO. To accelerate the $NO_2$ de-coupling effect, CTO process is performed to eliminate interfacial contact for that time. As CTO process is extended, temperature which indicates peak reaction rate increases. From this result, it is found that small amount of NO can affect tight contact soot oxidation by removal of interfacial contact between soot and catalyst.

• 한국표면공학회지
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• 제28권6호
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• pp.333-342
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• 1995

Stainless steels are widely selected as commercial engineering materials mainly because of their excellent corrosion resistance, oxidation resistance and strength. Because the manufacturing temperature of stainless steels is relatively high, the chemical and physical properties of the oxide film which was formed on the stainless steels are of importance in determining the rate of oxidation and the life of equipment exposed to high temperature oxidizing environments. In this study, the oxidation behavior of S. S. 304 and S. S. 430 added by a small amount of oxygen active elements(each +0.5wt% Hf and Y) was studied to improve oxidation resistance. The results of cyclic and isothermal oxidation on S. S. 304 added by OAE showed relatively poor oxidation resistance due to spallations and cracks of $Cr_2O_3$ layer. But all S. S. 430+0.5wt% OAE maintained constant oxidation rates and stable oxide layers at high temperature environment. Especially S. S. 430+0.5wt% Y formed a $Cr_2O_3$ oxide layer and improved cyclic oxidation resistance preventing loss of protective layers about 1000 hours at $1000^{\circ}C$

• Nuclear Engineering and Technology
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• 제41권2호
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• pp.163-170
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• 2009

In order to evaluate high-temperature oxidation behavior of the advanced alloy cladding under LOCA conditions, isothermal oxidation tests in steam were performed with cladding specimens prepared from high burnup PWR fuel rods that were irradiated up to 79 MWd/kg. Cladding materials were $M5^{(R)}$ and $ZIRLO^{TM}$, which are Nb-containing alloys. Ring-shaped specimens were isothermally oxidized in flowing steam at temperatures from 1173 to 1473 K for the duration between 120 and 4000s. Oxidation rates were evaluated from measured oxide layer thickness and weight gain. A protective effect of the preformed corrosion layer is seen for the shorter time range at the lower temperatures. The influence of pre-hydriding is not significant for the examined range. Alloy composition change generally has small influence on oxidation in the examined temperature range, though $M5^{(R)}$ shows an obviously smaller oxidation constant at 1273 K. Consequently, the oxidation rates of the high burnup $M5^{(R)}$ and $ZIRLO^{TM}$ cladding are comparable or lower than that of unirradiated Zircaloy-4 cladding.

• 한국표면공학회지
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• 제29권4호
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• pp.268-277
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• 1996

Boronizing treatment of Microalloyed steel has been investigated by mean of Boronizing paste mainly consisted of $B_4C$ at various temperatures and times. The micro hardness of the boride layers were about HV 1200~1500. The thickness of the boride layer were increased with an increase of square root of treatment time at constant temperature. The activation energy for diffusion of boron in the specimen obtained from the slope of Arrhenius plots was 254 kJ/mol, but 197 kJ/mol for the induction heated specimen. The boride layer had a good corrosion resistance in solutions of 20% HCl and 20% $H_2SO_4$, solution. In 20% $HNO_3$ solution, however, its corrosion resistance increased. The boride layer had a good high temperature oxidation resistance at below $800^{\circ}C$, but at temperature above $900^{\circ}C$, the oxidation resistance decreased as the oxidation temperature.