The Evaluation of Corrosion Susceptibility of a Metal Student Corrosion Experiment II A. I. Onuchukwu Bayero University, Kano, Nigeria I t has long been recognized that metallic material will corrode on exposure t o a moist-air environment. Thus, industries, in pa>ticular those producing chemicals and petroleum, spend huge sums of money providing corrosion monitoring and p r ~ t & t i ~devices n for their machines and components. Advocates of corrosion control suggest that ah initio corrosion orevention measures are best ~ r o v i d e dfor hv adequate material selection during the deAgn stage of fabrication of any mechanical device (1).In the literature, there are various briefly described laboratory tests for the assessment of corrosion susceptibility of metals prior to deployment in service (2,3).But, there seems to be an oversight since these principles are not included in our chemistry laboratory manuals used in the training of chemists and material scientists for the evaluation of materials. In mv earlier reoorts (3). ahd ealvano. . . the notentiostatic . " static corrosion experimental principles (4.5)were presented for inclusion in our electrochemistrv lahoratorv teachine. This paper seeks to present the principles of the weight-lo& method of corrosion evaluation of a metal in aqueous media. This is a part of our electrochemistry labora&ry, which is taueht to final-vear chemistrv students in an electrochemistry course in ~ a y e r university. o Experimental
Aluminum alloy (A.41060)failof 0.10-mm thicknesswas press-cut into 20- X 20-rnm squares. These aluminum samples were degreased in absolute ethanol, dried in warm air, weighed, and stored in a moisture-free desiccator prior to the laboratory session. The analaR-grade reagents of 5 M KOH, HCI, and H2S04solutions were each diluted separately to 0.5, 1.0, 2.0, 3.0, and 4.0 mol dm-3. Into each of the three sets of six beakers were placed 250 mL of these earrodine..arents. The weiehts of the aluminum sauares were record,. ed,nnd they wereintroduced intc, therurrodingagents and made to t wallrof the beaker. l'hrw pirresofnlumi.itand inclined a ~ s i n i the num were retrieved from the corrodingagents after an hour, washed, dried over warm air, and reweighed. The weight loss was recorded for each concentration of the corroding agents. Results and Dlscusslon The weight losses of the pieces of aluminum foil were calculated by weight difference: aw(mglcm2/h)= (w,- wi)l(~)(t)
(1)
where wi and wr are weights of aluminum before and after corrosion. while ( A )and ( t )are the eeometric area and time of aluminum in the corroding (h) of exposure bf 'the aeent. res~ectivelv.The fieure compares the corrosion susceptibilitiof the tbree corroding agents studied. The results of the experiment and explanations adduced hv the students after cofiective discussio~are collated and s k n a r i z e d as follows: (1) the three corroding agents depicted increase in corrosion susceptihility with increase in corroding agent concentrations; (2) corrosion rates of AAlO6O in these media are H2SOa HCl>> .>?SO*: . .. thus. inhihition was fairly attained in HzSOI: ( 4 ) H? gas evolutim ( 6 )at the cathode sites enhanced the dispersal of the prod934
Journal of Chemical Education
Corrosion rate vs. concentration (mol dm-')of A, Hd04:0 ,HCI: and A, KOH corroding agents for 4.0-cm2AAIOBO pieces of aiumlnum at 27 '6.
uct(s) and consequently facilitated the exposure of the aluminum s a m ~ l surface e to continued vieorous reaction characterized h i g a s bubbles. In conclusion, the students realized that, in actual use, AA1060 would he most stable in a sulfuric acid environment, preferably at very low acid concenrrations. This laborator; provided the class with a group interaction that is desirahle for solving field problems.
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Acknowledgment The author is grateful to the Principal Technologist, Mrs. M. A. Akinhede, for orovidine the facilities that ensured the completion of this work witlhin the three-hour laboratory session. Literature Cited
I. Keith, E.; Harttey, P. a. Moterid Seloelor and n..".""
Design Guide; Morgan-Grsmpian:
IG?d
2. Uhlip, H. H.Chem. E w . News 1949.27.276P2767: Corr. Sei. 1950,6,29-34 8. Onuchukwu,A. I. J . C h m . E d u c . 1986.63.269-270. 4. Onuchukwu,A.I.:Oppong-B0achie.F.K. Corr Sci. 1986.26.919-926. 6. 0nuchukwu.A.1,;Lori.J. A. Corr. Sci. 1981.24, 833.841. 6. Onuchukwu, A. I.: J. Elelroehem. See. 1983,130,1077-1079.
