Self-diffusion in cr<sub>2</sub>o<sub>3</sub>I. Chromium diffusion in single crystals

Sabioni, Antônio Claret Soares; Lesage, B.; Huntz, A.M.; Pivin, J.C.; Monty, C.

doi:10.1080/01418619208201560

Cited by 92 publications

(49 citation statements)

References 16 publications

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“…Diffusion of metal cations and oxygen anions within the bulk oxide and oxide grain boundaries were taken into account separately. The diffusion coefficient applied are those measured by Sabioni et al 14 . Figure 7 shows the Cr 2 O 3 thickness as a function of time calculated on the basis of sole diffusion i) through the oxide bulk, ii) along oxide grain boundaries; and iii) using an effective diffusion coefficient of Cr and O, according to Sabioni et al 14 .…”

Section: Resultsmentioning

confidence: 99%

Effect of alloy grain size on the high-temperature oxidation behavior of the austenitic steel TP 347

Trindade

Krupp²,

Hanjari³

et al. 2005

Mat. Res.

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Generally, oxide scales formed on high Cr steels are multi-layered and the kinetics are strongly influenced by the alloy grain boundaries. In the present study, the oxidation behaviour of an austenite steel TP347 with different grain sizes was studied to identify the role of grain-boundaries in the oxidation process. Heat treatment in an inert gas atmosphere at 1050 °C was applied to modify the grain size of the steel TP347. The mass gain during subsequent oxidation was measured using a microbalance with a resolution of 10 -5 g. The scale morphology was examined using SEM in combination with energy-dispersive X-ray spectroscopy (EDS). Oxidation of TP347 with a grain size of 4 µm at 750 °C in air follows a parabolic rate law. For a larger grain size (65 µm), complex kinetics is observed with a fast initial oxidation followed by several different parabolic oxidation stages. SEM examinations indicated that the scale formed on specimens with smaller grain size was predominantly Cr 2 O 3 , with some FeCr 2 O 4 at localized sites. For specimens with larger grain size the main oxide is iron oxide. It can be concluded that protective Cr 2 O 3 formation is promoted by a high density of fast grain-boundary diffusion paths which is the case for fine-grained materials.

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Section: Resultsmentioning

confidence: 99%

Effect of alloy grain size on the high-temperature oxidation behavior of the austenitic steel TP 347

Trindade

Krupp²,

Hanjari³

et al. 2005

Mat. Res.

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show abstract

“…Indeed, in previous studies 1,2 , it was observed that the oxidation constant of the AISI 439 ferritic steel did not practically show significant variation with the oxygen pressure for the extreme values of 1 atm and 1.46 x 10 -20 atm. In addition, other studies 8 show that the oxygen and chromium diffusivities in Cr 2 O 3 do not depend on the oxygen pressure. As a general case, the 430A and 430E stainless steel are used for applications at low or room temperature, and the knowledge of their oxidation kinetics at high temperatures is particularly important in the field of the hot rolling.…”

Section: Discussionmentioning

confidence: 99%

High temperature oxidation behavior of the AISI 430A and AISI 430E stainless steels in Ar/H2/H2O atmosphere

Salgado

Sabioni

Huntz³

et al. 2008

Mat. Res.

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The high temperature oxidation behavior of two ferritic stainless steels type AISI 430A and AISI 430E is examined at low oxygen pressure and high temperatures. The AISI 430A steel is ferritic up to 860 °C. Above this temperature, this steel is bi-phased: presence of austenite and ferrite phases. The 430E steel is stabilized with Nb, and is ferritic at all temperatures. The oxidation experiments were performed in a thermobalance SETARAM TGDTA 92, in the range of 850-950 °C, in Ar/H 2 /H 2 O atmosphere, under oxygen partial pressures lower than 1.3 x 10 -18 atm. The microstructure and the composition of the oxide scales were analysed by scanning electronic microscopy (SEM) and energy dispersive spectroscopy (EDS). Different oxidation behaviors in AISI 430A and AISI 430E stainless steels were observed. At 850 °C, the oxidation of the 430A steel is greater than that of the 430E steel, but above 900 °C the oxidation of the 430A steels is lower than that of the 430E steel. The oxidation rate of the 430A steel shows low dependence on temperature, while the oxidation of the 430E follows an Arrhenius law, with an activation energy corresponding to the chromia scale growth.

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“…29,45 More recent studies have however indicated that oxygen diffusion is more facile, in particular along grain boundaries, thus indicating that structural defects as well as doping in Cr 2 O 3 can improve its oxygen mobility. [46][47][48] The introduction of holes through incorporating a LV dopant will lead to spontaneous formation of oxygen vacancies to compensate the lower oxidation state of the dopant compared to the host. [49][50][51][52] The resulting absence of oxygen in the lattice after the release of oxygen can be experimentally observed, as the vacancy cannot be annealed in the presence of oxygen.…”

mentioning

confidence: 99%

Low Valence Cation Doping of Bulk Cr₂O₃: Charge Compensation and Oxygen Vacancy Formation

2016

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ABSTRACT:The different oxidation states of chromium allow its bulk oxide form to be reducible, facilitating the oxygen vacancy formation process, which is a key property in applications such as catalysis. Similar to other useful oxides such as TiO 2 , and CeO 2 , the effect of substitutional metal dopants in bulk Cr 2 O 3 and its effect on the electronic structure and oxygen vacancy formation are of interest, particularly in enhancing the latter. In this paper, density functional theory (DFT) calculations with a Hubbard +U correction (DFT+U) applied to the Cr 3d and O 2p states, are carried out on pure and metal doped bulk Cr 2 O 3 to examine the effect of doping on the electronic and geometric structure. The role of dopants in enhancing the reducibility of Cr 2 O 3 is examined to promote oxygen vacancy formation. The dopants are Mg, Cu, Ni, and Zn, which have a formal +2 oxidation state in their bulk oxides. Given this difference in host and dopant oxidation states, we show that to predict the correct ground state two metal dopants charge compensated with an oxygen vacancy are required. The second oxygen atom removed is termed 'the active' oxygen vacancy and it is the energy required to remove this atom that is related to the reduction process. In all cases, we find that substitutional doping improves the oxygen vacancy formation of bulk Cr 2 O 3 by lowering the energy cost.

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Self-diffusion in cr₂o₃I. Chromium diffusion in single crystals

Cited by 92 publications

References 16 publications

Effect of alloy grain size on the high-temperature oxidation behavior of the austenitic steel TP 347

Effect of alloy grain size on the high-temperature oxidation behavior of the austenitic steel TP 347

High temperature oxidation behavior of the AISI 430A and AISI 430E stainless steels in Ar/H2/H2O atmosphere

Low Valence Cation Doping of Bulk Cr₂O₃: Charge Compensation and Oxygen Vacancy Formation

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Self-diffusion in cr2o3I. Chromium diffusion in single crystals

Cited by 92 publications

References 16 publications

Effect of alloy grain size on the high-temperature oxidation behavior of the austenitic steel TP 347

Effect of alloy grain size on the high-temperature oxidation behavior of the austenitic steel TP 347

High temperature oxidation behavior of the AISI 430A and AISI 430E stainless steels in Ar/H2/H2O atmosphere

Low Valence Cation Doping of Bulk Cr2O3: Charge Compensation and Oxygen Vacancy Formation

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Self-diffusion in cr₂o₃I. Chromium diffusion in single crystals

Low Valence Cation Doping of Bulk Cr₂O₃: Charge Compensation and Oxygen Vacancy Formation