The Effect of Crevice‐Opening Dimension on the Stability of Crevice Corrosion for Nickel in Sulfuric Acid

Abstract

The role of the crevice-opening dimension, a, on the stability of crevice corrosion was investigated in the Ni/i N H2S04 system. The electrode potential and current distributions inside the crevice were measured and calculated, respectively. Other variables, in particular the composition of the electrolyte, were constrained from changing during the experiment. The passive/active boundary, x ass' moved further into the crevice for increasing a, and was in close agreement with the calculated value using the IR = A6I relation. A sharp upper limiting value, aim, for a given crevice depth, 1, above which crevice corrosion does not occur, was predicted and experimentally observed. The potential Epa,s at Xpass on the crevice wall corresponded approximately to the potential of the passive/active transition of the bulk solution polarization curve.

The role of electrolyte concentration on crevice corrosion of pure nickel

“…The scan rate was 0.08 mV s À1 active region of the crevice electrolyte polarization curve [4,9]. This is also consistent with recent work by Abdulsalam and Pickering [2] where it was shown that the crevice gap of 0.4 mm is the upper limit for crevice corrosion to start in 1N sulfuric acid. For the system discussed here, the results predict that an increase in the acid concentration enhances the crevice corrosion rate action manifested by the increase in the total cell current.…”

“…It is interesting to see that the location is directly at the transition point between the passive and active region of the polarization curve indicating a close agreement between the polarization curve and the behavior of the crevice corrosion inside the cavity. This is in lieu of the IR drop mechanism which predicts similar phenomenon [1,2,6,8,10].…”

“…The direction of the scan was in a passive-to-active direction, 1.1 to À 0.3 V(SCE), in deaerated H 2 SO 4 at a scan rate of 0.08 mV s À1 . This scan direction is more appropriate in studying crevice corrosion as has been demonstrated in previous works [1,2]. Two acid concentrations were used; 0.5 and 2N, prepared from regent grade chemicals and double distilled water.…”

“…These examples are seen in nearly all oil-based and chemical industries. While nickel is known to be corrosion resistant it is also susceptible to this kind of corrosion [1,2].…”

Moiré based method for real-time crevice corrosion monitoring

“…The first, addresses the change in the chemical composition of the electrolyte and the formation of a critical crevice solution with concentrations of H þ and Cl À that are large enough to breakdown the passive film [3]. The other theory is the IR voltage drop theory which attributes crevice corrosion to a significant ohmic drop that shifts the potential within the crevice to the active region of the polarization curve for the given metal/electrolyte system [6][7][8][9][10][11][12].…”