Oxide Films Formed on Alloys at Moderate Temperatures. Electron Diffraction and Electron Microscope Study

Gulbransen, Earl A.; Phelps, R.T.; Hickman, Jared

doi:10.1021/i560158a019

Cited by 18 publications

(6 citation statements)

References 7 publications

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“…The diffraction patterns were made at room temperature using a 9 cm Unicam camera. Oxide samples were removed from the alloy by electrochemical stripping (16). After washing sev-era1 times in distilled water, the oxide films were rolled on to small glass capillary tubes for mounting in the x-ray camera.…”

Section: Methodsmentioning

confidence: 99%

Oxidation Studies on the Iron-Chromium-Aluminum Heater Alloys

Gulbransen

Andrew

1959

J. Electrochem. Soc.

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are interposed between it and the nitro group. It is also seen that the addition of successive chloro or nitro groups to a primary nitro carbon atom increases the potential of the parent nitroalkane compound with each succeeding addition of the electron attracting group.2. Coulometric studies in a MgBr2 electrolyte indicate electrode efficiencies of 36-52% can be obtained from a number of solid nitroalkane compounds, assuming a 6-electron change per nitro group. The latter assumption is in doubt, however, since the reduction mechanism is not known.3. Magnesium-nitroalkane dry cells have been assembled, and the performance characteristics of these cells indicate that nitroalkane compounds show promise for use as cathodes in primary cells. ABSTRACTThe oxidation behavior of three iron-chromium-aluminum alloys was studied using sensitive weight gain techniques. In addition, x-ray diffraction methods were used to determine the crystal structure and composition of the oxide films. The adhesion characteristics of the oxide film to the metal were tested by introducing strains into the metal oxide system during oxidation.Rate studies show a change in rate for the three alloys near 900~ Between 900 ~ to 1050~ the rate of oxidation remained nearly constant; above 1050~ it increased again. X-ray diffraction studies suggest that a crystal structure ,transformation was occurring in the oxide. At 1050~ a-A120~ was the main oxide in the scale.The parabolic rate law was used to interpret the rate data. Deviations occurred during the initial reaction period as a result of crystal structure transformations in the film. Heats of activation of 76 to 77 kcal/mole were calculated for the range 700~176Strain oxidation studies showed the oxide scale on the high aluminum alloy to be less susceptible to damage than the lower aluminum content alloys. These studies were correlated directly with practical performance tests.Thermodynamic analyses of the several types of solid-solid and solid-gas reactions were used to interpret the rate and structure studies. Preliminary design principles were proposed for heat resistant alloys.Heater alloys have been characterized by three important properties: (a) high melting point, (b) high resistance to oxidation, and (c) good mechanical properties. For extreme service conditions, two types of alloys have been used: (a) Ni-Cr alloys of nominal composition 80% Ni and 20% Cr, and (b) Fe-Cr-A1 alloys of nominal composition 20-25% Cr, 4-6% A1, balance Fe. Both alloy systems consist of a single phase with the Ni-Cr alloys having the austenitic structure and the Fe-Cr-A1 alloys the ferritic structure.The maximum operating temperature in the final analysis is limited by the alloy's solidus point. This is about 1440~ for the Fe-Cr-A1 alloys and 1380~ ) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 147.188.128.74 Downloaded on 2015-06-06 to IP ABSTRACTA new bath composition and its operating conditions are described for electrodepositio...

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Section: Methodsmentioning

confidence: 99%

Oxidation Studies on the Iron-Chromium-Aluminum Heater Alloys

Gulbransen

Andrew

1959

J. Electrochem. Soc.

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“…In summary, most of the somewhat vague statements in the literature, regarding deviations from parabolic growth (1,8) and the presence of NiO in late and early stages of oxidation (1, 2, 11-14, 16, 31-33), appear to fit in with the theories developed above but this is not true of protection by NiCr204 (1-6) which seems something of a myth. Protection is by Cr203, as has been previously suggested (7)(8)(9)(10)(11)(12)(13)(14). Where NiO has not been observed outside, this may have been due to spalling, preferential oxidation effects, or to it forming a small percentage of the scale after long runs, particularly with Ni-60% Cr and Ni-80% Cr (9).…”

Section: Mechanism Of Oxidation Of Ni-cr Alloy~--beforementioning

confidence: 55%

“…Protection is by Cr203, as has been previously suggested (7)(8)(9)(10)(11)(12)(13)(14). Where NiO has not been observed outside, this may have been due to spalling, preferential oxidation effects, or to it forming a small percentage of the scale after long runs, particularly with Ni-60% Cr and Ni-80% Cr (9).…”

Section: April 1966mentioning

confidence: 58%

Characteristic Scales on Pure Nickel-Chromium Alloys at 800°–1200°C

Wood

Hodgkiess

1966

J. Electrochem. Soc.

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Thermogravimetric measurements, metallography, and electron-probe microanalysis have revealed the nature of characteristic scales produced on pure 27.4, and 40.2 w/o (weight per cent) Cr in oxygen at 800 ~ 1200~ The growth kinetics are relatively independent of the surface preparation but are critically affected by the method of heating the specimen to temperature. Preferentially oxidized specimens usually produce only Cr203 scales, but samples immediately located in the hot zone possess an outer layer which is largely NiO. For high chromium contents and low temperatures the inner layer is Cr20~, but under the opposite conditions it is multiphase. Cr203, subscale formation is extensive and can stop rapid development of stratified scale by joining up to give a complete layer. Cr20~ is definitely the oxide which renders scales on these alloys protective. Extensive chromium depletion in the underlying alloy has serious consequences if protective scale fails. The mechanism of oxidation of Ni-Cr alloys is discussed and briefly compared with that of Fe-Cr alloys, from which there are distinct differences.A surprising feature of the alloy oxidation field is the extensive disagreement about the nature of protective scale on Ni-Cr alloys rich in chromium when they are oxidized in air or oxygen (1-15). It is also curious that this system has been neglected during the recent trend to study the behavior of pure materials by topographical and microanalytical methods, which can scarcely fail to resolve such problems.Except for quite low-chromium alloys (15-16), scarcely any optical micrographs of scales on reasonably pure materials have been published. In addition, no detailed electron-probe microanalyses have appeared yet. Use of these techniques, in conjunction with kinetic measurements, provides a close characterization of the scaling behavior, with precise details of scale topography and analysis, and data regarding the location and time of appearance of the various oxides, information lacking in previous studies. This paper presents such data for Ni-Cr alloys containing respectively 14.6, 27.4, and 40.2% chromium over a wide range of exposure times at 800~176 This allows a more precise description of the mechanism of scaling than given previously (9), without arbitrary divisions according to composition. Experimental ProcedureThe Ni-14.6, 27.4, and 40.2 w/o (weight per cent) Cr alloys were made from nickel of 99.97% purity (C 0.008, Fe < 0.03, S < 0.002, Pb < 0.002, B < 0.001, Cr, Co, Mo, Ti, A1, Si, Mn, Zr, lVig, and Cu < 0.01%) and from pure chromium (C < 0.005, O 0.035, H 0.01%; N 7, Pb 3, Sn 4, A1 4, Fe 2, Na 4, Mg, Cu, Ni, Ag, Sb and B < 1 ppm) by rapid vacuum melting and were rolled to strip 0.06 cm thick. They were then given a preliminary annealing treatment in an inert gas at 1000~176 which produced a coarse, heavily twinned, equiaxed grain structure with few Cr203 inclusions and a homogeneous bulk composition.Specimens 2.0 x 0.5 x 0.06 cm were annealed "in vacuo" (10 -5 mm Hg) for 8 hr at 1050~ in a further ef...

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“…In a systematic study of the controlled oxidation of polished tungsten specimens at high temperature, Gulbransen (19) showed that the oxidation of tungsten started with the adsorption of a layer of oxygen on the surface and the rapid formation of a thin oxide film. This action was followed by the growth of the oxide from crystallization nuclei such that thicker films were nonuniform.…”

Section: Properties Of Freshly Reduced Powdersmentioning

confidence: 99%