Nt1310 Lab Report

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All the data was fitted satisfactorily using the equivalent circuit shown in Fig. 7. Where, Rs, CPE1 and R1 represent solution resistance, a constant- phase element corresponding to the double layer capacitance and the charge transfer resistance, respectively. CPE2 and R2 were added to account for the electrical elements of the outer layer. The following formula expressed the electrode impedance, Z, as follow: Z = Rs + [Rct/ {1 +(2 π f Rct Cdl)α }] (8) Where α is an empirical parameter (0 ≤α≤1) and f is the frequency in Hz. This formula considered the deviation from the ideal RC-behavior due to surface inhomogeneties, roughness effects, and different compositions of surface layers 40, 41. The first time constant at low frequency range was claimed to the presence of an inhomogeneous passive film 42. A constant phase element (CPE) was used instead of a pure capacitance due to these inhomogenities, which were found at the oxide/electrolyte interface and under the oxide film. CEE can be introduced in terms of impedance from the following equation: Zw= Zo i(W)-n Where Zo is the CPE constant, W is the angular frequency (in rad/s), i2 = -1 is the imaginary number and (n) is the CPE exponent. Based on (n), CPE can represent resistance (n = 0, Zo = R),…show more content…
With respect to the influence of albumin, it increased the charge transfer resistance and the outer layer resistance of titanium and copper alloy and slightly decreased the capacitance. This was mainly due to the blocking effect of the organic molecule and the adsorption effect 48. R2 value of Ti increased from 592.2 kΩ cm2 in SBF solution to 1080 kΩ cm2 in SBF + Albumin and from 168.5 kΩ cm2 to 292 kΩ cm2 for the copper alloy. On contrary was the effect of KF, where it decreased significantly the impedance resistance of both samples with respect to SBF solutions (cf. Tables 3, 4, 6 and
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