Corrosion inhibition effect of calcium gluconate on mild steel in artificial seawater

Figures & data

Figure 1. Molecular structure of CGN

Table 1. Results from calibration and hardware test

RAM Test	Ok
Current Test Results
Sensitivity Offset Error (0%)	0%
Gain Error	0%
Voltage Test Results
Sensitivity Offset Error	0%
Gain Error	0%

Table 2. Potentiodynamic polarization data for MS corrosion inhibition in artificial seawater at 0–2.25% CGN concentration

Sample	CGN Conc. (%)	LCS CR (mm/y)	CGN ξF (%)	CI (A)	CJ (A/cm^2)	CP (V)	Rp (Ω)	Bc (V/dec)	Ba (V/dec)
A	0	1.56	0	1.55E-04	1.37E-04	−0.989	119.30	−9.662	6.526
B	0.75	0.92	40.72	9.16E-05	8.10E-05	−0.975	358.90	−9.547	4.212
C	1.25	0.26	83.06	2.62E-05	2.32E-05	−0.931	981.50	−9.628	1.785
D	1.75	0.23	85.14	2.30E-05	2.03E-05	−0.926	1119.00	−9.785	1.358
E	2.25	0.31	80.25	3.05E-05	2.70E-05	−0.921	813.60	−9.463	2.042

Figure 2. Potentiodynamic polarization plots for MS corrosion inhibition in artificial seawater at 0–2.25% CGN concentration

Figure 3. Optical microscopic images of (a) MS surface before corrosion test and (b) MS surface after corrosion in artificial seawater at 0% CGN

Figure 4. Optical microscopic images of CGN inhibited MS surface in artificial seawater (a) at 0.75% CGN and (b) 2.25% CGN

Figure 5. Graphical plot of (a) MS corrosion rate versus exposure time and (b) CGN inhibition efficiency versus exposure time

Table 3. Data obtained from coupon measurement at 216 h

MS Specimen	MS Weight Loss (g)	CGN Concentration (%)	MS Corrosion Rate (mm/y)	CGN Inhibition Efficiency (%)
A	0.1218	0	0.00104	0
B	0.0816	0.75	0.00070	33.00
C	0.0110	1.25	0.00009	90.97
D	0.0026	1.75	0.00002	97.87
E	0.0066	2.25	0.00006	94.58

Figure 6. Langmuir plot of C_CGN/θ versus CGN concentration in artificial seawater solution

Figure 7. Frumkin isotherm plot of log[θ/(1 − θ)C_CGN] versus θ in artificial seawater solution

Table 4. Results for Gibbs free energy (∆G_ads), surface coverage (θ) and equilibrium constant of adsorption (K_ads) for CGN adsorption on artificial seawater solution

Specimen	CG Concentration (M)	Surface Coverage (θ)	Equilibrium Constant of adsorption (K)	Gibbs Free Energy, ∆G (kJmol^−1)
1	0	0	0	0
2	1.74E-02	0.330	28.3	−18.23
3	2.90E-02	0.910	346.8	−24.45
4	4.07E-02	0.979	1127.5	−27.37
5	5.23E-02	0.946	333.9	−24.35

Figure 8. Open circuit potential plot of MS corrosion in artificial seawater at 0%, 0.75% and 2.25% CGN