The dissolution of aluminium in hydrochloric acid and sodium hydroxide solutions in the presence of dimethyltin dichloride as corrosion inhibitor has been studied using hydrogen evolution and thermometric methods. The two methods gave consistent results. The higher inhibition efficiency of this compound in acidic than in alkaline media may be due to the less negative potential of aluminium in hydrochloric acid solution, favouring adsorption of the additive. The adsorption of this compound was found to obey Frumkin adsorption isotherm.
The inhibition of the corrosion of aluminium in 1M sodium hydroxide solution by some cyclodiphosphazane derivatives has been studied using hydrogen evolution technique. The results indicate that the additives reduce the corrosion rate. The inhibitory character of these compounds depends upon the concentration of the inhibitor, as well as on its chemical composition.
of Science -A1 Azlrur Unirersify -Cairo, A.R.E.Thc dissolulion of aluminium in sodium hydroxideand hydrochloric acid in the prcscnrc of hutyltin rflchloridc ascorrosion inhibitor has been studied by hydrogcn evolution and thermometric mcihcds.
Exprinlcnlnl findings indicatc lhal the inhibition ellcct ofbulyltin lrichloridc takes place through an adsorption mechanism lollowingBucyirin trichlorrde X I S as a ucaklyadsorhcd inhihilor in NaOH and as a slrongly adsorbed inhibitor in hydrochloric acid mcdium. ihc 17rumlin's isoihurm. Table I shows that the disotulion rate, decreases with increase in BTTC concentration and hence the % inhibition efficiency increases. In thc analysis of thc isotherms having an S-shape in the % I.Evs log C chart, FrunkinYs3model was considered.
INTRODUCTION
RESULTS AND DISCUSSIONFrumkin isotherm has the formulawhere C is the concentraLm of the adsorpcd substance in the bluk of the solution md 0 is thc degree of coveragr of the investigated surface by the adsorped mofeculcs calculated from the equationwhere Ko and K are the dissohtion ratcs in absence and in presence of the investigated inhibitor. B in Eq (4) is themodiGedequilibrium constant of the adsorption process and f is constant depending on intermolecular interaction in the adsorption layer and on the heterogeneity of the surface. In the thermonetric measurements, the temperaturc changes of the systems involving Al in 2N NaOH and 2N HCI were followed in absence and presence of BTTC overthe concentration rangesviz., (1-75)x1O4M and (5x10' -lo4) M respecifvely. Aluminium dissolves readiIy in 2N NaOH. The maximum temperature is 53.2"C, and is attained within 28.5 m i , , corresponding fo a rcactian number, RN, of 1.165"C/min (Fig.3). When an increasing ing amounts of BITC were added to the NaOH solution, the thermometric curves are influcnced. The effect dcpcnds on ' _.. indicates that B'ITC behaves as inhibitor over the concentration range studied. Table 2 shows the effect of eonccntration of BTTC on the various parameters of the thermometric curves. All curves are charactcrizcd by an initial slow rise followed by asharp risc and finally by a decrease in tcmpcralure after attaining a maximum valuc. The curves for BTTC containing system fall below that of the free acid indicatc the BTTC exhibits inhibition over the conccntration r a n g studied. The parameters of the (hermomctric curves arc givcn in Table 3. It is of interest to mention that localizcd corrosion was observed during the study of thc inhibitive effect of BlTC for Al corrosion in 2N HC1 at 3YC. Figure 7 shows the A1 sample plates used duri,ng the various expcrimcnts pcrformcd by thc gasometric tcchniqucs aftcr collcction of (33 cm3 hydrogen gas with diffcrcnt inhibitor concentration.Severe corrosion was obscrved at the pcrephery of thc A1sample when the BITC concentration was 10' M/L (Fig. ( The observed high inhibition efficiency of BTTC in acidic media compared to that in alkaline media (Table 2 and 3) may be due to the low negalive potential of Al as in the fo...
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