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Hydrogen in Chromium: Influence on the High-Temperature Oxidation Kinetics in O2, Oxide-Growth Mechanisms, and Scale Adherence (1999)

Tveten, Bent ; Hultquist, Gunnar ; Norby, Truls

Springer

Oxidation of metals 51 (1999), S. 221-233

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ISSN: 1573-4889

Keywords: CHROMIUM ; HYDROGEN CONTENT ; TWO-STAGE OXIDATION ; SCALE ADHERENCE

Source: Springer Online Journal Archives 1860-2000

Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics

Notes: Abstract Oxidation of chromium in 20 mbar isotopicallylabeled molecular oxygen was studied at 900°C. Thesamples comprised specimens with as-received contents ofhydrogen and specimens where this hydrogen had been eliminated by vacuum annealing. Two-stageoxidation was performed by exposure of the samples to16,16O2 and 18,18O2. Reaction rates were studied bymeasuring the change in oxygen pressure in a closedreaction-chamber with a mass spectrometer during oxidation. Theoxide formed was characterized by secondaryion massspectrometry (SIMS) and scanning electron microscopy(SEM). The adherence of the oxide scale to theunderlying metal substrate is poor and the oxidation rateis initially slightly higher when the metal containshydrogen prior to oxidation. It is shown by 18O depthprofiles that chromium diffusion within theCr2O3 scale is increased and oxygen diffusion isdecreased for metal containing hydrogen. It is believedthat the poor adherence of the oxide scale, in thiscase, is due to low anion diffusion relative to cation diffusion, which leads to an insufficientportion of oxide growth at the metal-oxideinterface.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1023/A:1018866505708

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XPS and SEM studies of Ca- and Ni-substituted LaCrO3 after quenching from reducing and oxidizing atmospheres at 800 °C (1994)

Glenne, Rita ; Horst, Jens Anton ; Jørgensen, Sissel ; [et al.]

Chichester [u.a.] : Wiley-Blackwell

Surface and Interface Analysis 22 (1994), S. 275-279

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ISSN: 0142-2421

Keywords: Chemistry ; Polymer and Materials Science

Source: Wiley InterScience Backfile Collection 1832-2000

Topics: Physics

Notes: Sintered and polished samples of La1-xCaxCrO3(x = 0.0, 0.1, 0,3, 0.5) and La1-xCaxCr1-yNiyO3(x = 0.3, y = 0.05) were annealed and quenched under reducing or oxidizing conditions at 800 °C and analysed with XPS and SEM. After annealing in H2 + H2O the surfaces of the samples with x = 0.3 and x = 0.5 were enriched in Ca in a 5 nm deep zone. Cr was not enriched and was present in the +3 state. Annealing in O2 + H2O gave Ca enrichment and crystalline outgrowths, increasing with increasing Ca contents. The Cr in the surface was in the +3 and +6 states, and the amount of Cr6+ increased with increasing Ca contents. These observations are assigned to precipitation of CaCrO4 and possibly other phases. The Ni-doped sample exhibited less grain growth during sintering and less surface recrystallization in oxidizing atmospheres than the corresponding sample without Ni.

Additional Material: 3 Ill.