Topic
Chromia
About: Chromia is a research topic. Over the lifetime, 1860 publications have been published within this topic receiving 39167 citations.
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TL;DR: In this paper, achromia-forming 20Cr-25Ni austenitic steel was used to identify the dominant chemical-failure mechanism as a function of temperature, which is termed Mechanically Induced ChemicalFailure (MICF).
Abstract: Breakaway oxidation or chemical failure has beendescribed in this paper in terms of two possiblemechanisms and applied to the behavior of achromia-forming 20Cr-25Ni austenitic steel. Bothmechanisms relate to the depletion of chromium arisingfrom its selective oxidation and quantitative modelingof the depletion profile is used to identify thedominant chemical-failure mechanism as a function oftemperature. Intrinsic Chemical Failure (InCF) develops whenthe chromium concentration within the alloy at theoxide-metal interface is less than that in equilibriumwith chromia. This occurs at high temperatures, typically above 1390 K, but the temperature atwhich the alloy becomes susceptible to this form offailure increases as the alloy grain size decreases. Atlower temperatures, chemical failure is associated with the general depletion of chromium acrossthe specimen section to a level below which reformationof a healing chromia layer will not occur, should thesurface layer become damaged. In this regime, failure is termed Mechanically Induced ChemicalFailure (MICF).
191 citations
TL;DR: In this article, the current understanding of volatility of chromia, silica and alumina in water vapor containing combustion environments is summarized and an update on the considerable information learned in the past five years is presented.
Abstract: Many structural materials rely on the formation of chromia, silica or alumina as a protective layer when exposed in high temperature oxidizing environments. The presence of these oxide layers provides a protective diffusion barrier which slows down further oxidation. In atmospheres containing water vapor, however, reactions to form volatile hydroxide species occur which remove the surface oxide, thus, lowering the protective capability of the oxide scale. This paper summarizes the current understanding of volatility of chromia, silica and alumina in water vapor containing combustion environments. In addition unanswered questions in each system are discussed. Th current paper represents an update on the considerable information learned in the past five years for these systems.
189 citations
TL;DR: In this paper, the surface state changes in supported chromia catalysts were studied and a method was extended to determine the oxidation state of the surface in situ during reaction, and a tentative explanation was offered for the selectivity for oxygen over nitric oxide in the oxidation-reduction reactions on commonly employed catalysts.
184 citations
TL;DR: In this article, a spinel barrier layer was developed and tested on the ferritic stainless steel Crofer22 APU to protect cells from chromium poisoning and improve their performance.
Abstract: In intermediate solid oxide fuel cells, the use of cost effective chromia forming alloy interconnects such as ferritic stainless steels can lead to severe degradation in cell performance due to chromium migration into the cells at the cathode side. To protect cells from chromium poisoning and improve their performance, a Mn1.5Co1.5O4 spinel barrier layer has been developed and tested on the ferritic stainless steel Crofer22 APU. Thermal and electrical tests confirmed the effectiveness of the spinel protection layer as a means of stopping chromium migration and decreasing oxidation, while promoting electrical contact and minimizing cathode/interconnect interfacial resistance. The thermally grown spinel protection layer was well-bonded to the Crofer22 APU substrate and demonstrated stable performance under thermal cycling.
183 citations
25 Feb 2007-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this article, the oxidation behavior of stainless steels was studied at high temperatures, under various oxygen pressures and in the presence or not of water vapour, and the calculated values of the oxidation constants agree reasonably well with experimental values, therefore confirming the role of diffusion processes on the growth of chromia.
Abstract: The oxidation behaviour of AISI 304 and AISI 439 stainless steels was studied at high temperatures, under various oxygen pressures and in the presence or not of water vapour. Thermogravimetric analyses were conducted in isothermal conditions from 850 to 950 °C for 50 h and microstructural and chemical analyses of the oxide films grown by oxidation were performed by SEM and EDX. The oxide films were also analysed by grazing X-ray diffraction and by X photoelectron spectroscopy (XPS). The AISI 439 steel has higher oxidation resistance than AISI 304, above 850 °C, under high oxygen pressures. On the other hand, the AISI 304 steel has higher oxidation resistance under low oxygen pressures in the whole temperature range. In order to check whether the growth kinetics of Cr 2 O 3 formed by the oxidation of stainless steels was controlled by oxygen or/and chromium diffusion through the oxide film, the oxidation constants were theoretically calculated on the basis of diffusion data using Wagner's Theory. The calculated values of the oxidation constants agree reasonably well with experimental values, therefore confirming the role of diffusion processes on the growth of chromia on stainless steels.
182 citations