PDF file - Facultatea de Chimie şi Inginerie Chimică

- Imaginary part / kΩ.cm 2
- Imaginary part / kΩ.cm 2
20
(A)
10
240
0.1
SIMONA VARVARA, MARIA POPA, LIANA MARIA MURESAN
10m
10m
Glu (mM)
0
0.01
0.1
1
0
0 10 20
Real part / kΩ.cm
30 40
2
1
0.1k
18
12
Arg (mM)
0
0.1
1
10
0.1
10m
(C)
6
0.1
10m
10m
0
0 12 24
Real part / kΩ.cm
36
2
1
0.1k
- Imaginary part / kΩ.cm 2
- Imaginary part / kΩ.cm 2
9
6
3
1
1
10m
0.1
10m
0.1
10m
0.1k
0
0
1
0.1
6 12
Real part / kΩ.cm
18
2
(B)
His (mM)
0
1
10
18
12
6
10m
0.1
0
0
1
9 18
Real part / kΩ.cm
27 36
2
Met (mM)
0
(D)
0.01
0.1
10m
1
0.1
1
0.1k
Figure 2. Nyquist plots of bronze electrode in 0.2 g/L Na2SO4 + 0.2 g/L NaHCO3
(pH=5) solution, in the absence and in the presence of different amino acids:
(A) glutamic acid; (B) histidine; (C) arginine; (D) methionine. The symbol (—+—)
corresponds to the simulated spectra. Frequencies are expressed in Hz.
R e
R f
R t
C f, n f
C d, n d
R F
C F, n F
Figure 3. Equivalent electrical circuit used for computer fitting of experimental data
In the present work, the (3RC) electrical circuit was also adopted for
carrying out a non-linear regression calculation of the impedance data obtained
in the presence of the amino acids (Glu, His, Arg, Met) using a Simplex method.
The origin of the various variables used in the equivalent circuit from
Figure 3 were ascribed as follows [5, 28]: Re-electrolyte resistance; Rf -
resistance representing the ionic leakage through pores of a dielectric thin
film formed on the surface that is reinforced in the presence of the inhibitors
and by the ionic conduction through its pore; Cf - capacitance due to the
dielectric nature of the surface film (corrosion products); Rt - charge transfer
resistance; Cd - double layer capacitance at the bronze|electrolyte interface;