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35 NACE INTERNATIONAL: VOL. 56, NO. 8 MATERIALS PERFORMANCE AUGUST 2017 Electrochemical Test Apparatus The electrochemical testing system used a Zive SP1 eDAQ † potentiostat with a three-electrode arrangement consisting of a platinum coil wire counter electrode, a silver/silver chloride (Ag/AgCl) cell with a 3-M sodium chloride (NaCl) filling solution as a reference electrode, and the working electrode. Electrochemical Tests LSV measurements for both SRDE and WRDE electrodes were conducted at 20 °C at a scan rate of 2 mV/s from –1,000 to 200 mV vs. a standard hydrogen electrode (SHE). Also, ZRA experiments consisting of tim e-d e p en d ent galvani c cur rent an d potential were conducted using a rotating SRDE at 1,200 rpm positionally aligned at a 5-mm distance with a WRDE electrode sur- face fixed in the bottom. Results and Discussion Polarization Curves Measured in a RDE Glass Cell Polarization curves using SRDE elec- trodes in seawater were measured under varying rotation rates between 0 and 2,200 rpm. The experimental variability of the measured polarization was estimated as follows in Equation (1): TABLE 1. COPPER CONCENTRATE CHARACTERIZATION BY X-RAY DIFFRACTION Mineral Compound (Crystalline Phase) Chemical Composition wt% Pyrite FeS 2 19.1 Djurleite Cu 31 S1 6 31.6 Chalcopyrite CuFeS 2 9.08 Bornite Cu 5 FeS 4 9.07 Digenite Cu 9 S 5 9.03 Quartz SiO 2 5.69 Albite NaAlSi 3 O 8 4.35 Illite (K, H 3 O) Al 2 Si 3 AlO 10 (OH) 5.00 Titanomagnetite Fe 2.75 Ti 0.25 O 4 1.79 Natrojarosita NaFe 3 (SO 4 ) 2 (OH) 6 1.40 Pyrrhotite Fe 1–x S 2.07 Paligorskita (clay) Mg 5 (Si,Al) 8 O 20 (OH) 2.8 H 2 O 1.83 TABLE 2. AVERAGE (AVG.) STANDARD DEVIATION (SD) AND PARTIAL PROPAGATED ERRORS (PE) FOR STEEL AND MINERAL (A) Steel Oxygen Reduction Hydrogen Reduction Iron Oxidation Avg., SD, PE 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 Avg. 0.083 270 6.5 –0.00032 190 1,580 86 –280 0.8 SD 0.04 35 0.2 0.0002 30 610 11 15 0.2 PE 0.21 0.09 0.0054 0.0033 0.0012 2.8 4.7 Mineral Oxygen Reduction Hydrogen Reduction Mineral Oxidation Avg., SD, PE b mO2 A/m 2 t mO2 mV/dec i ml A/m 2 b mH2 A/m 2 t mH2 mV/dec b mFe A/m 2 t mo mV/dec E mcorr mV vs. SHE i mcorr A/m 2 Avg. 9.4 620 12 –0.06 200 0.7 340 130 4 SD 5.4 180 3 0.1 80 0.5 580 32 2 PE 1.8 0.63 1.5 0.9 1 0.2 0.4 (A) 0 and 100 rpm not included in the avg. and SD calculations. D D ≈ ∂ ∂ × i i x j j x x j (1) where i is a measured current density (CD) and x j is an electrochemical kinetic param- eter. Assigning standard deviation (SD) val- ues for each electrochemical parameter error ∆x j , labeled as PE in Table 2, ∆i x j values were calculated at a potential of –200 mV vs. SHE, where galvanic corrosion takes place. Polarization Curves for Carbon Steel Each measured polarization curve for CS shown in Figure 1 is expressed in terms of the mixed potential theory using Equa- tion (2): 3-4 i = A 2i l × –A + A 2 + 4 xi l 2 ⎡ ⎣ ⎢ ⎤ ⎦ ⎥ + b Fe × exp 2.3×E t Fe ⎛ ⎝ ⎜ ⎜ ⎜ ⎞ ⎠ ⎟ ⎟ ⎟ ⎟ + b H 2 ×exp – 2.3×E t H 2 ⎛ ⎝ ⎜ ⎜ ⎜ ⎞ ⎠ ⎟ ⎟ ⎟ ⎟ (2)