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EcorrCorrosion Potential
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7,8 The free corrosion potential was stabilised in he same way for both plates.
As can be seen for the uncoated 2524-T3 aluminum alloy, the pitting potential, [E.sub.pitting], and corrosion potential, [E.sub.corr], are nearly the same and a small increase of the potential E above [E.sub.corr] will lead to the initiation or acceleration of pitting with a large increase of the anodic current density j [12, 13].
Samples Corrosion potential Corrosion current density ([E.sub.corr]) (V/SCE) ([I.sub.corr]) (A/[cm.sup.2]) AZ31 substrate -1.387 8.796 x [10.sup.-5] Bulk pure Al -0.7276 7.335 x [10.sup.-7] Coating 0 -1.146 5.79 x [10.sup.-6] Coating 10 -1.04 6.66 x [10.sup.-7] Coating 20 -0.9 6.04 x [10.sup.-7] Coating 40 -0.826 4.87 x [10.sup.-7]
Table 3 shows the corrosion potential ([E.sub.corr]) and corrosion current densities (7corr) of phosphate coatings.
(i) The values of corrosion rate, and corrosion potential and resistivity, which show a steady-state plateau in corrosion data for CAC-reinforced mortars exposed to chloride environments, have been stated.
Three main periods were differentiated in the ZRP's lifetime after immersion in 3% NaCl solution: (a) the "activation" period, corrosion potential shifts to cathodic values; (b) in a second period, the electrode potential shifts to more anodic value and then reached the limit of CP; (c) at the third period, the corrosion potential is out of the CP range, and the coating provided barrier protection, depending on the formed zinc oxide products and coating morphology.
In general, when the corrosion potential is more positive, the polarization resistance is larger, and the corrosion current is lower, the coating has better anticorrosion properties.
The polarization curves were measured after 1 hour of immersion with a sweep rate of 1 mV/s and at a voltage range from -250 mV to +1250 mV with respect to the corrosion potential ([E.sub.corr]).
The open circuit corrosion potential (OCP) is continuously recorded owing to a saturated calomel electrode (SCE) as a reference (Fig.
The corrosion potential and corrosion current density were obtained from cathodic curves and the calculated anodic Tafel lines, respectively.
As can been seen from Figure 2 and Table 1, the corrosion potential of bare copper in 1 mol/L HCl is -0.44 V, while the corrosion current density is 3.18 x [10.sup.3] [micro]A/[cm.sup.2].
Alloys Mean Improvement Mean Mean Thermal Creep Percentage% Dimensional Conductivity (%) Change Mm/cm (W/m.k) 7 days M 0.7 -- +5.3 78.9 0.5% 0.4 42.8 + 4.6 63.6 1% 0.2 71.4 +4.1 50.4 1.5% 0.08 88.5 +3.8 39.1 2% 0.05 92.3 +3.2 27.3 2.5% 0.03 95.9 +2.7 18.9 3% 0.01 98.6 + 2.1 10.5 Alloys Improvement Percentage% M -- 0.5% 19.3 1% 35.9 1.5% 50.5 2% 65.4 2.5% 76.1 3% 86.6 Table 4: Illustrates the corrosion potential ([E.sub.corr]), corrosion current ([i.sub.corr]), corrosion rate and improvement percentage.
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