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36 AUGUST 2017 MATERIALS PERFORMANCE NACE INTERNATIONAL: VOL. 56, NO. 8 where n equals electrons involved in the oxygen reduction reaction; F is the Faraday number, 96,500 C/eq-mol; D is the oxygen diffusion coefficient in seawater as m 2 /s; ν is the kinematic viscosity of seawater as m 2 /s; and C o is the dissolved oxygen con- centration in seawater as mol/m 3 . Here, ω must be expressed in rad/s. From data listed in Table 4, Equation (4), the expression for i l , is obtained: v = × i 0.64 l 1/2 (4) with a linear regression coefficient of r 2 = 0.97. Polarization Curves for Copper Concentrate Mineral About 80% wt/wt% of the constituent minerals of the concentrate are sulfides (Table 1) having rest potentials signifi- cantly more positive than those of CS in chloride solutions. 6 In this regard , it is assumed that the mineral concentrate will behave as a single mineral exhibiting a spe- cific electrochemical behavior. Discarding experimental data measured at potential values more positive than 250 mV vs. SHE, it is observed that polarization curves for the mineral in seawater exhibit similar variational patterns to those for CS, but with much higher SD and with a shift TABLE 3. ELECTROCHEMICAL KINETIC PARAMETERS FOR CS IN SEAWATER AT VARYING ROTATION RATES Rotation Rate Oxygen Reduction Hydrogen Reduction Iron Oxidation ω rpm b O2 A/m 2 t O2 mV/dec i l A/m 2 b H2 A/m 2 t H2 mV/dec b Fe A/m 2 t Fe mV/dec E corr mV vs. SHE i corr A/m 2 0 0.00 3,740 0.00 –0.0000010 127 102 103 –672 0.00 100 0.0010 181 0.63 –0.000025 160 398 87.6 –332 0.07 200 0.021 189 2.4 –0.000025 166 2,350 80.2 –288 0.61 400 0.048 230 3.5 –0.000042 169 2,320 76.8 –272 0.66 600 0.052 256 4.9 –0.00022 202 844 102 –309 0.77 800 0.077 288 5.7 –0.000019 163 1,950 86.6 –295 0.77 1,000 0.13 303 7.0 –0.0000086 152 467 107 –283 1.0 1,200 0.088 284 6.9 –0.0012 240 1,260 91.4 –289 0.88 1,400 0.057 253 7.4 –0.00061 221 1,910 73.3 –283 0.58 1,600 0.085 271 8.3 –0.00014 192 1,700 79.4 –289 0.78 1,800 0.12 284 8.7 –0.00067 221 1,340 82.5 –258 0.93 2,100 0.15 299 11 –0.00025 200 1,630 83.4 –265 1.1 FIGURE 1 Polarization curves between 0 to 2,200 rpm. Black curves represent CS and red curves represent mineral-wax graphite. where i is the total CD, E is the applied potential in mV, A equals b O 2 × exp (–2.3 × E/t O 2 ), b j equals i 0j × exp (±2.3 × E eqj /t j ), "+" stands for oxidation and "–" stands for reduction, t j is the Tafel slope, E eqj is the equilibrium potential, i 0j is the exchange CD, and j denotes either O 2 , Fe, or H 2 . All parameters of Equation (2) deter- mined by a numerical method 3-4 are shown in Table 3. The Tafel slope values (Table 3) present the lowest relative variations at different rotational speeds (ω). Also, the parameter i l shows a strong dependence on the rotation rate. Equation (3), the Levich equation, is used for oxygen convection diffusion: 5 n v = × × × × × × i 0.62 n F D C l 2/3 –1/6 o 1/2 (3) CATHODIC PROTECTION