**4.4 Surface morphology studies**

388 Corrosion Resistance

The adsorption of vanillin onto the surface of the aluminium alloy may take place through all these functional groups. The simultaneous adsorption of the three functional groups forces the vanillin molecule to be horizontally oriented at the surface of the aluminium alloy (Li *et al*., 2008). As the inhibitor concentration increases, the area of the metal surface

Similar to the findings reported previously (El-Etre, 2001; Emregul and Hayvali, 2002; Li *et al*., 2008) the adsorption of vanillin mechanism is related to the presence of carbonyl, methoxy,

The inhibition process of tapioca starch can be explained as follows: FTIR spectrum shows that TS is composed of mixture of two molecular entities (polysaccharides), a linear fraction, amylase and highly branched fraction, amylopectin (Figure 5). Both of them are polymers of

Amylose is constituted by glucose monomer units joined to one another head to tail forming alpha–1, 4 linkages; these are linked with the ring oxygen atoms all on the same side. Amylopectin differs from amylase in that branching occurs, with an alpha–1, 6 linkages every 24–30 glucose monomer units. Amylopectin has phosphate groups attached to some

500 1000 1500 2000 2500 3000 3500 4000 Wavenumbers (cm-1)

The peak at 923.4, 2931.3 and 3322.3 cm−1 in the FTIR spectrum are characteristic of hydroxyl group (OH). The adsorption of TS on Al-Mg-Si alloy surface would take place through all these functional groups. As the concentration of corrosion inhibitor increases, the part of the metal surface covered by the corrosion inhibitor molecule also increases, leading to an

covered by the inhibitor molecule also increases, leading to an increase in the IE.

and hydroxyl groups arranged around the aromatic ring in their molecular structures.

**4.3.3 Inhibition mechanism of TS** 

Fig. 5. FTIR spectrum of TS.

923.4 [OH]

hydroxyl group (Wu *et al*., 2009).

increase in the IE.

glucose.

%Transmittance

Uninhibited and inhibited samples were analyzed by SEM and EDS in order to identify the morphology and composition of the corrosion products before and after immersion in seawater at 25°C.
