硫酸塩を含むアルカリ溶融塩化物中 (700℃) のクロムの不働態

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タイトル別名
  • Passivation phenomena of Chromium in Fused Alkaline Chloride Containing Sulfate at 700°C
  • リュウサンエン オ フクム アルカリ ヨウユウ エンカブツチュウ 700ドC
  • Passivation phenomena of Chromium in Fused Alkaline Chloride Containing Sulfate at 700°C

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It is well-known that increase in the chromium content of Ni-base heat-resistant alloys improves their anti-corrosive properties in the fused chloride containing sulfate anions, However, few mechanistic works on the effect of chromium on corrosion behavior of the alloys have been done in detail. From the fundamental approach to this subject, the passivation behavior of chromium was investigated in fused KCl-NaCl eutectic containing the sodium sulfate at 700°C, The current flown during anodic polarization of chromium in the salt containing sulfate consisted of the anodic currents due to oxidation of the sulfate and that of chromium. In order to separate these two currents, the rotating ring-disk electrode technique was employed. The passivation mechanism of chromium was discussed through studying on the effect of the sulfate concentration on the spearated anodic polarization curves and the potentiostatic transient behavior, The results were as follows. (1) When chromium was anodically polarized in fused KCl-NaCl containing sodium sulfate, a current peak was observed above the rest potentials. The current peaks were depressed with increase in the sulfate concentration. (2) When the ring potential was kept 0V, the oxidized sulfate species which were produced at the disk electrode were reduced at the ring electrode with a collection number of 0.20. Therefore, the anodic current for the sulfate oxidation could be evaluated using the ring current. (3) The real anodic current for chromium which were separated from the anodic current for sulfate gave a typical polarization curve called passivation and the current in the passive region decreased with increase in the concentration of sodium sulfate. (4) It is found that the current in the passive region was in proportion to the molar concentration of the sodium sulfate with the order of -0.72. It is concluded that the passive current was due to the chemical dissolution of the passive oxide Cr2O3.

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