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  • 1
    Electronic Resource
    Electronic Resource
    The Sulfidation of a Cu-15 vol.% Nb Alloy in H2-H2S Mixtures at 400-600°C (1998)
    Springer
    Oxidation of metals 49 (1998), S. 169-186 
    Details
    ISSN: 1573-4889
    Keywords: NIOBIUM ; COPPER ; SULFIDATION
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The corrosion of a Cu-15 vol.% Nb alloy byH2-H2S mixtures has been studiedunder 10-12 atm S2 at 400 and500°C and under 10-10 atm S2at 500 and 600°C. The alloy is a two-phase mixtureof the two terminal solid solutions and is composed of a Cu-richmatrix containing particles of the Nb-rich phaseelongated parallel to the sample surface and isolatedmainly from each other. The alloy corroded at ratessimilar to those of pure copper at 400 and 500°Cunder 10-12 atm S2, but moreslowly than pure copper at 500 and 600°C under10-10 atm S2. The scales wereduplex, containing an external layer of pure coppersulfide and an inner very porous region composed of amixture of sulfides of the two metals in which, however,the core of the large Nb particles was stilluncorroded.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1018857703098
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  • 2
    Electronic Resource
    Electronic Resource
    The Sulfidation of a Co-15 wt.% Ce Alloy in H2-H2S Mixtures at 600-800°C (1998)
    Springer
    Oxidation of metals 49 (1998), S. 71-89 
    Details
    ISSN: 1573-4889
    Keywords: COBALT ; CERIUM ; SULFIDATION
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The sulfidation behavior of a Co-Ce alloycontaining approximately 15 wt.% Ce has been studied at600-800°C in H2-H2S mixturesproviding a sulfur pressure of 10-8 atm, butalso of 10-7 atm at 800°C. At 600 and 700°C the alloy corrodes moreslowly than pure cobalt, but more rapidly than purecerium. At 800°C under 10-8 atmS2, which is below the stability of thecobalt sulfides, the alloy corrodes quite slowly, but under 10-7 atmS2 it corrodes very rapidly and practicallyat the same rate as pure cobalt. The sulfidationkinetics are generally irregular, except for a few casesof nearly parabolic behavior. The sulfidation of the alloy produces duplexscales, containing an outermost layer of practicallypure cobalt sulfide and an inner complex layer where thetwo components are simultaneously present. Cerium is not able to diffuse out of thealloy-consumption region, where it forms a ceriumsulfide mixed with cobalt sulfide and an innermostregion where cerium sulfide is mixed with cobalt metal.The cobalt sulfide forms a continuous network which allowsthe growth of the external CoSy layer, eventhough at rates reduced with respect to pure cobalt.Thus, a cerium content of 15 wt.% is not sufficient toprevent the sulfidation of the base metal. Theseresults as well as the details of the microstructure ofthe scales grown on the alloy are interpreted by takinginto account the limited solubility of cerium in the base metal and the presence in the alloy ofan intermetallic compound rich in cerium.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1018865904916
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  • 3
    Electronic Resource
    Electronic Resource
    The Effect of Supersaturation on the Internal Oxidation of Binary Alloys (1998)
    Springer
    Oxidation of metals 49 (1998), S. 237-260 
    Details
    ISSN: 1573-4889
    Keywords: BINARY ALLOYS ; INTERNAL OXIDATION ; SUPERSATURATION
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract According to the theory of Bohm and Kahlweit ofthe internal oxidation of binary A-B alloys, theparabolic rate constant for the formation of reasonablystable internal BOν oxides as well as theconcentrations of O and B at the oxidation front arecontrolled only by the degree of supersaturationnecessary for the nucleation of new oxide particles. Theeffects of this factor on the previous parameters arecalculated for various values of the solubility product ofthe oxide and of the diffusion coefficients of O and B.Moreover, an alternative procedure for the calculationof the critical degree of supersaturation behind the precipitation front required for oxideprecipitation, which is a function of the concentrationof the reactants at the internal oxidation front, isproposed. A simple modification of Wagner's theory of internal oxidation is also presented, andits results are compared with those of the treatment byBohm and Kahlweit. Finally, the limitations of the twomethods are examined.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1018834525388
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  • 4
    Electronic Resource
    Electronic Resource
    The Criteria for the Transitions Between the Various Oxidation Modes of Binary Solid-Solution Alloys Forming Immiscible Oxides at High Oxidant Pressures (1998)
    Springer
    Oxidation of metals 50 (1998), S. 1-26 
    Details
    ISSN: 1573-4889
    Keywords: OXIDATION MODES ; BINARY ALLOYS ; HIGH TEMPERATURES
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The possible high-temperature corrosion modes ofbinary solid-solution alloys forming two immisciblecompounds by a single oxidant include (1) the exclusivegrowth of external scales of the most-noble component, which may or may not be associated with theinternal oxidation of the most-reactive component, (2)the formation of composite external scales containing amixture of the two compounds, or finally (3) the exclusive growth of the most-stable compound asan external scale. The conditions for the stability ofeach scale structure depend on a number of thermodynamicand kinetics parameters, whose effects are examined quantitatively in this paper. Theconditions for the stability of the various structuresand the criteria for the transitions among them are alsoexamined. The maximum number of possible scale structures is four, but it can reduce to threeand, in some cases, only to two. In particular, theinternal oxidation of the most-reactive component maynot occur if the stabilities of the two oxides are not sufficiently different from eachother.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1018847116670
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  • 5
    Electronic Resource
    Electronic Resource
    Sulfidation of Three Two-Phase Cu-Cr Alloys in H2-H2S Mixtures at 400-600°C (1998)
    Springer
    Oxidation of metals 50 (1998), S. 327-354 
    Details
    ISSN: 1573-4889
    Keywords: SULFIDATION ; COPPER ; CHROMIUM ; TWO-PHASE ALLOYS
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The sulfidation of three Cu-Cr alloys withnominal Cr contents of 25, 50, and 75 wt.% and of thetwo pure metals has been studied at 400-600°C inH2-H2S mixtures under sulfurpressures of 10-12 atm at 400 and 500°C and 10-10 atm at 500and 600°C, slightly above the Cu-Cu2Sequilibrium. All the alloys were two-phase, containinga mixture of the solid solution of chromium in copperwith nearly pure chromium. The corrosion rates of the three materialsunder the same conditions were similar and intermediatebetween those of the two pure metals and increased withtemperature and sulfur pressure. The scales had a complex composition, often containing anexternal Cu2S layer, which becamediscontinuous or even disappeared, in some cases,followed by an intermediate layer of the double Cu-Crsulfide CuCrS2 and an innermost complex layer, which generallyconsisted of a mixture of the double Cu-Cr sulfideCuCr2S4 with the chromium sulfideCrS and also commonly contained unsul fidized chromiummetal particles. No chromium depletion was developed in the alloys beneaththe corrosion-affected region. Moreover, no internalsulfidation of chromium was observed in the alloyrichest in copper and no exclusive external sulfidation of chromium in those richest in chromium, inspite of the large difference in the thermodynamicstabilities of the sulfides of the two pure metals.These peculiar scale features are interpreted by taking into account the special two-phase nature ofthese alloys.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1018896523030
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  • 6
    Electronic Resource
    Electronic Resource
    The Formation of Two Layers in the Internal Oxidation of Binary Alloys by Two Oxidants in the Absence of External Scales (1999)
    Springer
    Oxidation of metals 51 (1999), S. 129-158 
    Details
    ISSN: 1573-4889
    Keywords: BINARY ALLOYS ; INTERNAL OXIDATION ; TWO OXIDANTS
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract An improved treatment of the simultaneousinternal oxidation of binary solid-solution alloys bytwo different oxidants (double internal oxidation)producing two subsequent layers divided by a sharpplanar interface in the absence of external scales ofthe most-noble component has been developed by removingsome of the approximations involved in previoustheories. The kinetics of internal oxidation arecalculated, based on the assumption that all the partialprocesses follow the parabolic rate law, as expected fordiffusion-controlled processes. The overall thickness ofinternal oxidation for dual oxidants is found to be equal to or smaller than the sum of thoseproduced by the two oxidants taken separately under thesame experimental conditions. The ratio between thethickness of the two regions depends critically on the ratio between the diffusion coefficientsof the two oxidants, so that under appropriate limitingconditions, one of the two layers becomes negligible.The degree of enrichment of the most-reactive component in the region of internal oxidationby two oxidants is found to be uniform over the wholezone, but lower than what would be produced by each ofthe oxidants taken singularly. The theoretical predictions are then compared to someexperimental results. It is finally shown that theexternal layer will not contain the compound most stableon an absolute scale, but that most stable with respect to the actual composition of the gas phase,while scaling structures different from that assumedhere are also possible.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1018858303891
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  • 7
    Electronic Resource
    Electronic Resource
    The Corrosion of Co-15 wt.% Y at 600-800°C in Sulfidizing-Oxidizing Atmospheres (1999)
    Springer
    Oxidation of metals 51 (1999), S. 421-447 
    Details
    ISSN: 1573-4889
    Keywords: COBALT ; YTTRIUM ; TWO-PHASE ALLOYS ; SULFIDATION ; OXIDATION
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The corrosion of Co-15 wt.% Y has been studiedat 600-800°C inH2-H2S-CO2 mixturesproviding a sulfur pressure of 10-8 atm at600-800°C and of 10-7 atm at 800°Cand an oxygen pressure of 10-24 atm at 600°C and of10-20 atm at 700-800°C. The corrosionrates in such sulfidizing-oxidizing atmospheres werecompared with those of pure cobalt and yttrium. Theaddition of yttrium to cobalt is only slightly beneficial, sincefor a yttrium content of 15 wt.% the corrosion rate isreduced quite significantly with respect to pure cobaltat 800°C under 10-7 atm S2,only to a limited extent at 600°C, and even slightlyincreased at 700°C. Moreover, the alloy corrodesconsiderably more rapidly than pure yttrium at800°C, when the latter behaves protectively. At 600 and 700°C, yttrium exhibitedbreakaway behavior, while the alloy corroded morerapidly than yttrium at short times, but more slowly atlong times. Under all conditions, except at 800°Cunder 10-8 atm S2, the alloy formsan external layer of cobalt sulfide overlying anintermediate region of very complex compositioncontaining a mixture of the compounds of the two metalsand an innermost region of internal attack containing compoundsof yttrium with both oxygen and sulfur. Thus, cobalt canstill diffuse through the intermediate region to formthe outer cobalt-sulfide layer at nonnegligible rates. The scaling behavior of the Co-15% Yalloy is discussed by taking into account the limitedsolubility of yttrium in cobalt as well as the presenceof an intermetallic Co-Y compound in thealloy.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1018887110251
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  • 8
    Electronic Resource
    Electronic Resource
    The Sulfidation of Two-Phase Fe-Cu Alloys in H2-H2S Mixtures at 500-700°C (1999)
    Springer
    Oxidation of metals 52 (1999), S. 403-426 
    Details
    ISSN: 1573-4889
    Keywords: SULFIDATION ; IRON-COPPER ; TWO-PHASE ALLOYS
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The sulfidation behavior of three two-phaseFe-Cu alloys containing 25, 50, and 75 wt.% copper hasbeen investigated in H2-H2Smixtures at 500-700°C under gas-phase sulfur pressures, which is significantly abovethose for the dissociation of both FeS andCu2S. In all cases, the three alloyssulfidized more slowly than both pure metals under thesame conditions. At all temperatures, Fe-25Cu showed the slowestgrowth rates, whereas Fe-50Cu sulfidized more rapidlythan the other two alloys. However, the kinetics curvesfor the three alloys tended to overlap, particularly at the higher temperatures. The scales werecomplex and contained an outer layer composed of amixture of two different Cu-Fe double sulfides,Cu5FeS4 and CuFeS2,plus an inner zone containing a mixture of metalliciron with the double sulfideCu5FeS4formed by completesulfidation of the copper-rich phase and partialsulfidation of the iron-rich phase. This region also contained large voids,possibly because of outward diffusion of metal cations,whereas the iron-rich islands were mainly unattacked.The depth of internal attack increased with increasing temperature and/or iron content. Finally,particles of almost pure copper metal, probably formedduring cooling from the reaction temperature, werepresent at the scale-subscale interface, as inclusions in the scale and as whiskers protruding out ofthe external scale surface.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1018808031575
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