**5. Conclusions**

392 Corrosion Resistance

The observations mentioned above were confirmed by EDS analysis (Figure 12). The EDS spectra showed an additional line characteristic for the existence of C (due to the carbon atoms of the VL). These data show that carbonaceous material has covered the specimen surface. This layer is absolutely due to the VL compound, because the carbon signal is

Fig. 12. EDS analysis of Al-Mg-Si alloy immersed in seawater containing 1000 ppm of VL.

Figure 13 depicts the SEM of specimen surface after 60 days of immersion in seawater with the addition of 600 ppm of tapioca starch. TS had shown similar characterization as NH and VL. From the micrograph, it can be seen that the flakes in the surface of the specimen are

Fig. 13. SEM of specimen surface after immersion in seawater with presence of 1000 ppm TS

lessen when compared with that of the micrograph of uninhibited specimen.

**4.4.5 Inhibited specimen with TS** 

absent on the specimen surface exposed to uninhibited seawater.

The corrosion inhibition studies of the aluminium alloy were carried out at room temperature using seawater and the results indicate that NH, VL and TS are an effective corrosion inhibitor of aluminium alloy in that particular solution.

The electrochemical studies of the corrosion inhibition process of Al-Mg-Si alloy in seawater using three selected natural products as corrosion inhibitors show that the corrosion rate of the alloy significantly reduced upon the addition of studied inhibitors. PP measurement reveals that the studied inhibitors can be classified as mixed-type inhibitors without changing the anodic and cathodic reaction mechanisms. The inhibitors inhibit both anodic metal dissolution and also cathodic hydrogen evolution reactions.

EIS measurements clarifying that the corrosion process is mainly charge-transfer controlled and no change in the corrosion mechanism occurred due to the inhibitor addition to seawater. It also indicates that the *R*ct values increase with addition of inhibitor whilst, the capacitance values decrease indicating the formation of a surface film. The EIS measurement also confirms the similar corrosion process and mechanism occurs in PP measurements. According to LPR data, the values of *R*p of Al-Mg-Si after addition of the studied inhibitors increase with the following order: NH < VL < TS.

Improvement of Corrosion Resistance of Aluminium Alloy by Natural Products 395

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It can be concluded that the corrosion parameters result obtained from PP, LPR and EIS measurements show the inhibitive effect on the corrosion behaviour of aluminium alloy in seawater by the studied inhibitors. The performance of natural products as corrosion inhibitors was evaluated by inhibition mechanism. The results reveal that inhibition efficiency increases with the increase in concentration of the studied inhibitors. Similar to the findings reported previously (Yurt *et al.,* 2006; Bhrara and Singh, 2006; El-Etre and Abdallah, 2000) the adsorption corrosion inhibitor mechanism is related to the presence of heteroatom such as nitrogen, oxygen, phosphorous, sulphur and long carbon chain length, as well as triple bond or aromatic ring in their molecular structures.

The studied natural products give above 90% of inhibition efficiency in their tested solutions. The comparison of present results with the results of reviewed paper by the other researchers on the same studied inhibitors proves that NH, VL and TS are comparable to the other natural products as corrosion inhibitor for aluminum alloy.

The use of SEM-EDS techniques provide good insight into the surface corrosion products grown on Al-Mg-Si alloy during the immersion test in seawater with and without the natural products as corrosion inhibitors. The SEM results indicate that the natural products (NH, VL and TS) absolutely minimized the corrosion products on the specimen surfaces. They also protect the passive film from dissolution in aggressive solution like seawater.

The EDS spectrums reveal that the presence of C, O, and S for NH as elements which take place in the inhibition mechanism. The carbonyl, methoxy and hydroxyl groups arranged around the aromatic ring are determined as functional groups of VL in inhibition process. The C atoms in TS are recognized by the EDS analysis, where these atoms involve in the adsorption process in alloy surface. The formation of precipitates of oxides/hydroxides of these inhibitors results in improved corrosion resistance.

Based on the results from SEM and EDS studies, it can be concluded that the TS gave the best protection of Al-Mg-Si alloy from the corrosion attack in seawater, following by VL and NH. The protection of passive film is increased with the increasing in inhibitor concentrations.

It is explored and proven in this research that NH, VL and TS carry tremendous potential for industrial usage. Unlike the pure synthetic product that requires enormous investment scale; NH, VL and TS can be produced at any type of industrial scale, which is potentially capable of eradicating the disparity among the communities, especially in the third world. Furthermore, the potential usages of these natural products discussed in this research are in line with the recent trend of the environment-friendly concept. However, resolution of the problem of whether the origin of these effects is associated with an application of aluminium alloys must await the results of further experimental studies.

#### **6. References**


It can be concluded that the corrosion parameters result obtained from PP, LPR and EIS measurements show the inhibitive effect on the corrosion behaviour of aluminium alloy in seawater by the studied inhibitors. The performance of natural products as corrosion inhibitors was evaluated by inhibition mechanism. The results reveal that inhibition efficiency increases with the increase in concentration of the studied inhibitors. Similar to the findings reported previously (Yurt *et al.,* 2006; Bhrara and Singh, 2006; El-Etre and Abdallah, 2000) the adsorption corrosion inhibitor mechanism is related to the presence of heteroatom such as nitrogen, oxygen, phosphorous, sulphur and long carbon chain length,

The studied natural products give above 90% of inhibition efficiency in their tested solutions. The comparison of present results with the results of reviewed paper by the other researchers on the same studied inhibitors proves that NH, VL and TS are comparable to the

The use of SEM-EDS techniques provide good insight into the surface corrosion products grown on Al-Mg-Si alloy during the immersion test in seawater with and without the natural products as corrosion inhibitors. The SEM results indicate that the natural products (NH, VL and TS) absolutely minimized the corrosion products on the specimen surfaces. They also protect the passive film from dissolution in aggressive solution like seawater.

The EDS spectrums reveal that the presence of C, O, and S for NH as elements which take place in the inhibition mechanism. The carbonyl, methoxy and hydroxyl groups arranged around the aromatic ring are determined as functional groups of VL in inhibition process. The C atoms in TS are recognized by the EDS analysis, where these atoms involve in the adsorption process in alloy surface. The formation of precipitates of oxides/hydroxides of

Based on the results from SEM and EDS studies, it can be concluded that the TS gave the best protection of Al-Mg-Si alloy from the corrosion attack in seawater, following by VL and NH. The protection of passive film is increased with the increasing in inhibitor

It is explored and proven in this research that NH, VL and TS carry tremendous potential for industrial usage. Unlike the pure synthetic product that requires enormous investment scale; NH, VL and TS can be produced at any type of industrial scale, which is potentially capable of eradicating the disparity among the communities, especially in the third world. Furthermore, the potential usages of these natural products discussed in this research are in line with the recent trend of the environment-friendly concept. However, resolution of the problem of whether the origin of these effects is associated with an application of

Aballe, A., Bethencourt, M., Botana, F.J. & Marcos, M. (2001). CeCl3 and LaCl3 binary

Al-Juhni, A.A. & Newby, B.Z. (2006). Incorporation of benzoic acid and sodium benzoate

solutions as environment-friendly corrosion inhibitors of AA5083 Al-Mg alloy in

into silicone coatings and subsequent leaching of the compound from the

aluminium alloys must await the results of further experimental studies.

NaCl solutions. *Journal of Alloys and Compounds* 323:855–858.

incorporated coatings. *Progress in Organic Coatings* 56:135–145.

as well as triple bond or aromatic ring in their molecular structures.

other natural products as corrosion inhibitor for aluminum alloy.

these inhibitors results in improved corrosion resistance.

concentrations.

**6. References** 


**18** 

Maria Trzaska

*Poland* 

**Studies of Resistance** 

*Warsaw University of Technology* 

**to Corrosion of Selected Metallic** 

**Materials Using Electrochemical Methods** 

One of the main causes of degradation of metallic products during their operation time is their corrosion. The destruction by corrosion arises from spontaneous adverse chemical reactions in metallic materials with the surrounding environment. Irreversible corrosive processes damage any metallic products both, during their operation, and their storage. Economic losses due to destructive corrosive actions are very important and still growing due to increasing environmental pollution. The annual cost of corrosion and corrosion protection in the world is estimated to be in excess of hundred billion dollars. Reducing the continuing degradation of metallic materials by corrosion is one of the fundamental objectives of modern technological solutions and is still the subject of intensive research in

Metallic products in operational conditions are primarily exposed to electrochemical corrosion. Corrosion processes, which include oxidation and reduction reactions, mainly occur at the interface between the metal and the environment. Both, the structure and the properties of the metal as well as the characteristics of the environment affect the corrosive processes. The rate of corrosion processes depends on the electrochemical susceptibility of a given metal, its chemical composition, homogeneity and surface topography, on the type and chemical composition of the environment, the concentration of aggressive agents, temperature, as well as the type of corrosion products themselves. Electrochemical corrosion processes are accompanied by mass transport and flow of electric charge through the metal corrosive environment boundary. To characterize the susceptibility of metallic materials to electrochemical degradation modern research techniques increasingly use the relationship between voltage and current intensity occurring in corrosive systems. Such studies rely on computerized measuring system, in which suitable electrical stimulation is generated numerically while the system analyzes simultaneously the response. The results are presented in the form of graphs showing the current - voltage relationships (Trzaska, 2010). In this chapter we present the results of investigations of corrosion properties of metallic materials with different chemical susceptibilities and different crystalline structures. The

main focuses are materials playing important roles in current technologies.

**1. Introduction** 

many research centers in the world (Yang, 2008).

