**2. Literature review on corrosion resistance**

Corrosion can be controlled by suitable modifications of the environment which in turn stifle, retard or completely stop the anodic or cathodic reactions or both. This can be achieved by the use of inhibitors (Blustein *et al*., 2005; Emregul *et al*., 2005; Goa *et al*., 2008). Corrosion inhibitors are substances which when added in small concentrations to corrosive media decrease or prevent the reaction of the metal with the media. Inhibitors are added to many systems, *e.g.* cooling systems, refinery units, acids, pipelines, chemicals, oil and gas production units, boiler and process waters etc. (Raja and Sethuraman, 2009).

A number of corrosion inhibitors have been developed to mitigate aluminium corrosion for the last two decades. A variety of inhibitors have been tested such as chromates, dichromates, molybdates, nitrate, nitrite and sulfate. Their high efficiency/cost ratio has made them standard corrosion inhibitors for a wide range of metals and alloys (Benthencourt *et al*., 1997).

Although chromates, dichromates, molybdates, nitrate, nitrite and sulfate were found to be the effective inhibitor for the corrosion processes taking place at the electrode/electrolyte interface of aluminium and some of its alloys in acidic and basic solutions (El-Sobki *et al*., 1981; Kassab *et al*., 1987; Badawy *et al*., 1999), unluckily a major disadvantage is their toxicity and such as their use has come under severe criticism (Bethencourt *et al*., 1997; Song-mei *et al*., 2007).

In recent days many alternative eco-friendly corrosion inhibitors have been developed, the range from rare earth elements (Neil and Garrard, 1994; Mishra and Balasubramaniam, 2007), and inorganic (Salem *et al*., 1978) to organic compounds (Onal and Aksut, 2000; Branzoi *et al*., 2002; Maayta and Al-Rawashdeh, 2004). Owing to the growing interest and attention of the world towards environmental problems and towards the protection of environment and the hazardous effects of the use of chemicals on ecological balance, the traditional approach on the choice of corrosion inhibitors has gradually changed. Researches are mainly focusing on non-toxic ''green" corrosion.

El-Etre and Abdallah (2000) study the natural honey as corrosion inhibitor for carbon steel in high saline water. It was found that natural honey exhibited a very good performance as inhibitor for steel corrosion in high saline water. The effect of fungi on the inhibition efficiency of natural honey is markedly decreased in high saline water. This is due to the high concentration of NaCl that retard the growth of fungi. This finding attracts the author to carry out further investigation on the effect of natural honey in seawater which contains NaCl.

One of the aromatic groups that showed good inhibitive effect is vanillin. The inhibition effects of vanillin on the corrosion of steel in HCl and H2SO4 solutions were investigated by Emregul and Hayvali (2002) and Li *et al.* (2008), meanwhile El-Etre (2001) studied the effect of vanillin against acid corrosion of aluminium. They were explored that an aromatic aldehyde containing carbonyl, methoxy and hydroxyl groups arranged around the aromatic ring in vanillin contributed to the inhibition mechanism process. Lack of research on the effect of this inhibitor on the corrosion of aluminium alloy in seawater has motivated the author to explore this research area as contribution to the current interest on environmentalfriendly and green corrosion inhibitors.
