The Mechanism of Scale Formation On Iron at High Temperature

Dunnington, B. W.; Beck, F. H.; Fontana, Mars G.

doi:10.5006/0010-9312-8.1.2

Cited by 59 publications

(18 citation statements)

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“…The growth of an element of the scale is always basically parabolic, but is disturbed by ever-repeating microcataclysms. Related effects have been observed in the oxidation of metals (29,30). It is proposed to denote such kinetics as the microcataclysmic scale growth.…”

Section: Continuity Of Scale Growthmentioning

confidence: 99%

Kinetics of Nickel-Sulfur and Steel-Sulfur Reactions

Dravnieks¹

1955

J. Electrochem. Soc.

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The reaction of nickel with molten sulfur between 205 ~ and 445~ follows the parabolic law. Up to 260~ the millerite form of NiS was the only sulfide detectable in the scale. At 340~ and higher, the high temperature B8 form of NiS was the only sulfide in the scale. The activation energy (Arrhenius) below approximately 300~ is in excess of 50 kcal; above this temperature, it is about 20 kcal. This compares with an activation energy of 41 kcal for the iron-sulfur reaction over the entire temperature range, where only one FeS form is known. Ni3S~, Ni6S~, two forms of NiS, and NiS~, but not NiTS~ and Ni3S4, were found to form upon exhaustive reaction of the corresponding mixtures of Ni and S. Formation of NiS2 was several thousand times slower than the formation of NiS. NiS formed continuously. In the formation of FeS, definite evidence of scale failures ~nd healings was found. A formal description of such a scale growth law is given and a term "microcataclysmic" is proposed to describe this form of kinetics.

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Section: Continuity Of Scale Growthmentioning

confidence: 99%

Kinetics of Nickel-Sulfur and Steel-Sulfur Reactions

Dravnieks¹

1955

J. Electrochem. Soc.

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“…The scales are stratified but not as on type 446; the layers are more like those which form on unalloyed iron. '· [15][16][17][18] The strueture of the scales on these lower chromi um alloys is shown in Figs. 14 to 16.…”

Section: Examination Of Scales On Types 410 and 430mentioning

confidence: 99%

High Temperature Oxidation of Some Iron-Chromium Alloys

Caplan

Cohen

1952

JOM

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The sealing eharoeteristics of three Fe-Cr alloys have been investigated by determining their weight goin vs. time curves at 1600° to 2000°F. The scoles formed thereby hove been examined using the techniques of X-ray diffraction ond speetrographic and metallographie analyses in an attempt to explain the discontinuities in the eurves and to elucidote the meehanism of scaling.D ESPITE the considerable number of investigations that have been carried out on heat resistant alloys, the characteristics of the scales formed at high temperatures are not fully known. The research reported here was undertaken in an attempt to ascertain the mechanism of scaling of the stainless steels. Scaling experiments were carried out first, the weight increase of the specimens being followed continuously with time. It was observed that, as weIl as showing the expected decrease in oxidation rate with time, the oxidation curves showed breaks corresponding to intermediate periods of accelerated oxidation, after which protectiveness again increased. This phenomenon was observed with austenitic stainless steels (types 302, 309, and 330) and with Fe-Cr alloys (types 410, 430, and 446), but only the latter are treated in this report. An examination of the scales was made using the techniques of X-ray diffr action and spectrographic and metallographie ana~ yses in an attempt to obtain a correlation between the nature of the scales and the oxidation curves.

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“…2, which was obtained by scanning the original autoradiographic plate in a direction normal to the metal/ scale boundary on an Ansco recording densitometer. The abrupt cutoff in activity at both boundaries of the OlS-marked zone allows us to conclude with confidence that the mobility of oxygen ions in the rocksalttype wiistite lattice must be at least two orders of magnitude smaller than that of iron at 1050~ It follows that, in previous investigations in which Pt wires or other types of inert markers have been found imbedded within the wfistite layer (11,(17)(18)(19)(20), the transport of oxygen past the marker must have occurred by some mechanism other than lattice diffusion. Additional experiments are described below which indicate that a vapor transport mechanism was operative.…”

Section: Results and Their Interpretationmentioning

confidence: 89%

“…It is significant, however, that, although the scale formed on the bottom surface is completely nonadherent, no internal porosity is seen except near the very edges. The nonadherent portion of the scale consists mostly of Fe304 and Fe20.~, which establishes that detachment of the scale occurred at temperature and not during subsequent cooling (15,17).…”

Section: Evidence For Vapor Phase Transport O~ Oxygenmentioning

confidence: 98%

Marker Techniques for Studying the Mechanism of Scaling of Metals Based on the Use of the O[sup 18](p,n)F[sup 18] Nuclear Reaction

Holt

Himmel

1969

J. Electrochem. Soc.

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A general mechanistic approach to the study of scaling reactions is proposed which dispenses with the conventional inert marker. Instead, radioisotopes of the reacting components are used to establish the nature of the diffusing species in the solid reaction products formed on metal surfaces at high temperatures. For investigating the mechanism of oxidation of metals, O TM is employed as a tracer and the stable isotope is subsequently activated by proton bombardment via the nuclear reaction O1S(p,n)F Is. The basis for the technique is outlined and its application to the scaling of iron and of zirconium is described. The experiments with iron establish conclusively that, at temperatures up to I050~ iron is the only diffusing component in the dense, adherent wi~stite layer which forms adjacent to the metal. Direct evidence is also presented for the vapor phase transport of oxygen by a dissociative mechanism during the growth of porous, non-adherent wfistite scales on iron in H~/H.~O atmospheres. It is shown that oxygen is mobile in thick ZrO2 scales formed on Zr in a water vapor atmosphere at 1200~ however, the unusual form of the O Is distribution in the scale indicates that open channels must have existed in the outer portion of the scale during oxidation which allowed direct penetration of oxygen to levels deep within the ZrO2 layer. The advantages and limitations of the present technique are discussed with particular reference to conventional marker methods. Major sources of difficulty in the interpretation of inert marker experiments are identified and a set of experimental requirements is given which, if satisfied, should permit reliable transport information to be obtained using conventional marker techniques.The mechanism of a heterogeneous chemical reaction, such as the oxidation of a metal, can be considered established, at least in principle, if the rate-determining step in the reaction is known and if the manner in which the reactants are transported to and from the various phase boundaries in the system can be specified. Information of this kind cannot generally be obtained from kinetic studies alone. In fact, even under conditions where diffusion-controlled kinetics are observed, it is often not possible to decide, unambiguously, whether the reaction is sustained by the outward migration of metal ions through the scale, or by the inward diffusion of the nonmetallic component. The dominant or faster diffusing species can, of course, be predicted if self-diffusion or ionic conductivity data are available for both components over the entire stability range of the product phase. Unfortunately, reliable data of this type currently exist for only a few oxide and sulfide systems (1-3).When the necessary transport data are not available, inert marker techniques are customarily employed to determine the nature of the mobile component in the growing scale. Marker methods were first introduced by Pfeil (4) in 1929 in his classic work on the scaling of iron, and they have been applied subsequently to a great many...

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The Mechanism of Scale Formation On Iron at High Temperature

Cited by 59 publications

References 0 publications

Kinetics of Nickel-Sulfur and Steel-Sulfur Reactions

Kinetics of Nickel-Sulfur and Steel-Sulfur Reactions

High Temperature Oxidation of Some Iron-Chromium Alloys

Marker Techniques for Studying the Mechanism of Scaling of Metals Based on the Use of the O[sup 18](p,n)F[sup 18] Nuclear Reaction

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