# Crude Glycerol as an Innovative Corrosion Inhibitor
## 3 Results and Discussion
### Potentiodynamic Polarization Measurements  
The Potentiostat samples for electrochemical experiments were machined into test electrodes of dimension \(1\times 1\) cm and fixed in polytetrafluoroethylene (PTFE) rods by epoxy resin in such a way  
Figure 8: SEM images of (**a**) a new steel specimen, (**b**) the corrosion of a steel specimen with 0.5 M HCl, (**c**) a steel specimen after corrosion inhibition with 0.3 wt % waste glycerol, and (**d**) a steel specimen after corrosion inhibition with 0.5 wt % waste glycerol.  
that only one surface, with an area of 1 cm\({}^{2}\), was left uncovered. The exposed surface was cleaned. Electrochemical experiments were conducted in a conventional three-electrode glass cell of 400 mL using a complete DC voltammetry and corrosion system. A graphite rod was used as a counter electrode and a saturated calomel electrode (SCE) as a reference electrode.  
The effect of crude glycerol concentration in the polarization curves for steel specimens in 0.5 M HCl is shown in Figure 9. This curve represents the anodic and cathodic polarization curves of the steel specimens. Both anodic and cathodic polarization curves are shifted to lower current density values in the presence of crude glycerol. This behavior suggests the inhibitive action of the inhibitor. The extent of the shift in current density increases with increasing glycerol concentrations. The values of corrosion current density (icorr), corrosion potential (Ecorr), anodic Tafel constants (\(\beta\)a), and cathodic Tafel constant (\(\beta\)c), excluded from polarization curves are given in Table 6.  
Table 6 reveals that the corrosion potential of steel specimens in the acid solution is largely shifted to more negative values (the noble direction) upon the addition of crude glycerol. On the other hand, the corrosion current density is greatly reduced upon the addition of the inhibitor. These results suggest the inhibitive effects of the crude glycerol. The data in Table 6 reveal that the values of inhibition efficiency obtained by polarization are comparable to those obtained by weight loss measurements. The inhibition efficiency increases with increasing inhibitor concentration. The addition of increasing concentrations of crude glycerol decreases both the anodic and cathodic Tafel constants. This result indicates that the inhibitor acts as a mixed inhibitor [42]. This means that the inhibitor molecules are adsorbed on both the anodic and cathodic sites, resulting in the inhibition of both anodic dissolution  
\begin{table}
\begin{tabular}{c c c} \hline \hline  & **Without Inhibition** & **With Inhibition** \\ \hline E (I = 0) (mV): & \(-914.082\) & \(-884.460\) \\ Icorr (\(\mu\)A): & 602.7 & 212.5 \\ Ca. Beta (mV): & 108.714 & 149.183 \\ An. Beta (mV): & 120.478 & 108.848 \\ Co. Rate (mpv): & 56.66 & 19.97 \\ Chi-Square: & 0.58 & 5.96 \\ Fit Range (mV): & \((-1005)\), \((-811)\) & \((-1021)\), \((-785)\) \\ Fit Mode: & Auto & Auto \\ \hline \hline \end{tabular}
\end{table}
Table 6: Tafel fit minimizing x error (no inhibitor).  
Figure 9: E versus log I for steel in 0.5 M HCl without and without inhibitor. Corrosion rate (mpy) of 0.5 M HCl solution = 56.6; corrosion rate (mpy) of 0.5 M HCl + crude glycerol (0.1%) = 16.9; corrosion rate of (mpy) of 0.5 M HCl + crude glycerol (0.8%) = 19.97.  
and cathodic reduction reactions. As the metal surface area occupied by adsorbed molecules increases, inhibition efficiency increases.