Oxides in Caustic

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Cross section of the oxide layer formed in aerated 0,5 n NaOH. The inner layer is magnetite with many cracks and on the outside hematite (alpha -Fe2O3) platelets. (foto KEMA, ref 10).
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Detail of picture 3561. In the magnetite layer clear perlite islands are still present. (foto KEMA, ref 10).
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Pitting with the hematite caps was found on C-steel exposed in NaOH (pH=10) at 250 gd C (40 atm) in oxygen containing solution. The experiment was under electrochemical controll at a high corrosion potential. (foto KEMA, ref 10).
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Magnetite formed on a perlite area in 0.01 n NaOH at 250 gd C during 17 hours. (foto KEMA, ref 10).
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Very minor magnetite formation on a perlite area in NaOH (ph=9.0) at 250 gd C during 17 hours. The perlite area was marked by means of Vickers hardness indents. (foto KEMA, ref 10).
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MnS inclusions are solved in 0.01 n NaOH and near the inclusion places magnetite is not present. (foto KEMA, ref 10).
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SEM-picture of the alpha-Fe203 crystals, formed in aerated 0,5 n NaOH. See Figure 3008. (foto KEMA, ref 10).
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Oxidation of pure iron in oxygen free NaOH (pH 12.5) at 310 gr C and 100 atm. A break-away is present in the oxidation curve, indicating cracing of the oxide. (ref 10)
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SEM picture of the magnetite grown in the NaOH after 50 days. After the break-away point cracks are formed in the adherent magnetite. (foto KEMA, ref 10).
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Second example of a cracked surface at an oxidation time of 50 days. (foto KEMA, ref 10).
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Cross sections of the magnetite layers on 3 steels: 15Mo3, 14Mn4 and C-35. (Foto KEMA, ref 23).
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"Weight losses after a 4-day exposure to NaOH under non-deaerated conditions at 250°C (experiment 1 ) (ref 23)."
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Oxide layers formed on C-steel after a 31-day exposure to NaOH (A) and LiOH (B) in 10-molar solutions under non-deaerated conditions at 310 ° C. In LiOH (at such high concentration) a very open non protective scale is formed. (foto KEMA, ref 23, 61).
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Oxidation of C steel during 4 days in increasing caustic concentration. (ref 23).
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SEM picture of a fracture surface of a corrosion scale. On the steel surface a porous topotactical magnetite layer and on the outer surface a epitactical layer of coarse magnetite octaeders have been formed. Caustic environment onder bopiler conditions. (foto KEMA, ref 11, 61).
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SEM picture of a post-break-away sample exposed in deaerated 0.03 NaOH at 310°C. (foto KEMA, ref 8).
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Blistered oxide formed in 0,5 n NaOH at 360 °C in an autoclave test. (foto KEMA, ref 8).