An improved mathematical solution for the calculation of the parabolic rate constant for the growth of nonuniformly doped oxides on dilute alloys

1983 ◽  
Vol 19 (1-2) ◽  
pp. 31-36
Author(s):  
V. Dov� ◽  
F. Viani ◽  
F. Gesmundo
Keyword(s):  
Rate Constant ◽  
Parabolic Rate Constant ◽  
Mathematical Solution ◽  
Dilute Alloys ◽  
Parabolic Rate

Effects of Yttrium on Cyclic Oxidation Resistance of Co-10Cr-5Si Alloy

2013 ◽  
Vol 785-786 ◽  
pp. 914-917
Author(s):  
Jun Huai Xiang ◽  
Xian Chao Xu ◽  
Ling Yun Bai ◽  
Yun Xiang Zheng ◽  
Huai Shu Zhang
Keyword(s):  
Oxidation Resistance ◽  
Rate Constant ◽  
Cyclic Oxidation ◽  
Oxidation Behavior ◽  
Parabolic Rate Constant ◽  
Cooling Process ◽  
Parabolic Rate

The cyclic oxidation behavior of Co-10Cr-5Si alloys with and without Y in atmosphere at 800 °C was investigated. The addition of 0.3 at.% Y decreased the average parabolic rate constant from 4.45×10-10g2cm-2s-1to 3.58×10-10g2cm-2s-1. The thin scales grown on Co-10Cr-5Si alloys were mainly composed of an outer CoO layer, followed by an inner protective SiO2layer. However, the scales can not be observed for Co-10Cr-5Si-0.3Y alloy, probably due to the spallation of the scales during the cooling process. The addition of 0.3 at.% Y improved the cyclic oxidation resistance of the Co-10Cr-5Al alloy.

On the Defect Structure and Transport Properties of Co3O4 Spinel Oxide

2012 ◽  
Vol 31 (4-5) ◽  
pp. 371-379 ◽  
Author(s):  
A. Kaczmarska ◽  
Z. Grzesik ◽  
S. Mrowec
Keyword(s):  
Transport Properties ◽  
Rate Constant ◽  
Oxygen Pressure ◽  
Defect Structure ◽  
Pressure Range ◽  
High Pressures ◽  
Parabolic Rate Constant ◽  
Cation Sublattice ◽  
Low Oxygen ◽  
Parabolic Rate

AbstractDefect structure and transport properties of Co3O4 cobalt oxide have been studied as a function of temperature and oxygen pressure, using marker and thermogravimetric techniques. It has been found that the oxidation of CoO to form Co3O4 follows parabolic kinetic, being thus diffusion controlled. Marker experiments have demonstrated that cation sublattice of Co3O4 oxide is predominantly disordered, but the defect structure is rather complex. At very low oxygen pressures, close to the dissociation pressure of the oxide, interstitial cations are the predominant point defects, while at high pressures cation vacancies predominate. This behavior is reflected in complex dependence of the parabolic rate constant of CoO oxidation on oxygen pressure. At low pressures, namely, parabolic rate constant of the reaction increases with oxygen pressure, reaching then virtually constant value in intermediate pressure range and increases again in highest pressure range. Theoretical analysis of kinetic results in terms of point defect thermodynamics confirmed the above conclusion, concerning complex defect structure of Co3±yO4 oxide. Finally, self-diffusion coefficient of cations in the discussed oxide has been calculated as a function of temperature and oxygen pressure from kinetic rate measurements, using Wagner's theory of metals oxidation.

Ni Layer Evolution of FeCrAl Substrate Treated by Ultrasonic and Electroplating Methods in Long Term Oxidation at 900°C

2011 ◽  
Vol 181-182 ◽  
pp. 501-506 ◽  
Author(s):  
Darwin Sebayang ◽  
Putrasari Yanuandri ◽  
Firdianto Ade ◽  
Sulaiman B. Hasan ◽  
Ashraf Bin Otman ◽  
...  
Keyword(s):  
Nickel Oxide ◽  
Rate Constant ◽  
Ultrasonic Treatment ◽  
Parabolic Rate Constant ◽  
Nickel Layer ◽  
Time To Failure ◽  
Nickel Electroplating ◽  
Oxidation Exposure ◽  
Parabolic Rate

The long term oxidation test of FeCrAl substrate treated by ultrasonic and electroplating methods was performed at 9000C in air environment for 100 hours. The purpose of this paper is to show the nickel layer evolution of that substrate. Oxide scale and layer evolution were assessed on specimens using scanning electron microscope (SEM) coupled with energy dispersive X-ray spectroscopy (EDX). The nickel layer disappeared and fully converted to be nickel oxide on FeCrAl treated using ultrasonic and nickel electroplating after oxidation exposure at 9000 C in air for 100 hours. In this condition, the nickel oxide still existed. Not only nickel oxide and Al2O3 were occurred when oxidation exposure at this condition but also Cr2O3 and Fe2O3. The lowest parabolic rate constant was obtained from FeCrAl ultrasonic treatment with SiC for 50 minutes at 1.21 x 10-4 mg2mm4h-1, and FeCrAl ultrasonic treatment with Al2O3 for 30 minutes at 1.15 x 10-4 mg2mm4h-1. The lower parabolic rate constant indicated the higher long time to failure of the FeCrAl substrate.

Intermediate-temperature oxidation behavior of Ti2AlC in air

2002 ◽  
Vol 17 (11) ◽  
pp. 2974-2981 ◽  
Author(s):  
X. H. Wang ◽  
Y. C. Zhou
Keyword(s):  
Raman Spectroscopy ◽  
Rate Constant ◽  
Oxidation Behavior ◽  
Parabolic Rate Constant ◽  
Oxidation Products ◽  
Scale Morphology ◽  
Temperature Oxidation ◽  
Good Oxidation Resistance ◽  
Parabolic Rate ◽  
Anomalous Oxidation

The isothermal oxidation behavior of Ti2AlC at intermediate temperatures of 500, 600, 700, 800, and 900 °C in flowing air was investigated by means of thermogravimetric analysis, x-ray diffraction (XRD), Raman spectroscopy, and scanning electron microscopy (SEM)/energy dispersive spectroscopy. An anomalous oxidation with higher kinetics at lower temperatures of 500 and 600 °C was observed although Ti2AlC exhibited good oxidation resistance at higher temperatures. As revealed by SEM scale morphology observation, oxidation-induced cracks present at temperatures of 500 and 600 °C resulted in poor protectivity of scales and accounted for the anomalous oxidation. The weight gain data for the remaining temperatures were analyzed with an instantaneous parabolic rate constant method by assuming a parabolic rate law. The variations of instantaneous parabolic rate constant with time reflected the complexity of the oxidation behavior of Ti2AlC at intermediate temperatures. These variations were discussed from the viewpoint of phase transformation of oxidation products on the basis of XRD, Raman spectroscopy, and SEM scale morphology observation. As indicated by XRD and Raman spectra, the scale formed on Ti2AlC at higher temperature was stable α–Al2O3 and rutile TiO2, while transition aluminas of γ–Al2O3, δ–Al2O3, θ–Al2O3, and TiO2 (anatase) were detected at lower temperatures. The whisker morphology of θ–Al2O3 at 800 °C and ridged morphology of α–Al2O3 at 800 and 900 °C were confirmed by SEM.

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