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The performance of triethylenetetramine-tribenzylidene (TTTB) and triethylenetetramine-trisalicylidene (TTTS) as corrosion inhibitors for zinc in hydrochloric acid is investigated. At lower concentrations, both inhibitors accelerate the attack but inhibit corrosion at higher concentrations, e.g., 96-100% with 1.0% concentration in 0.5 M and 1.0 M HCl. The efficiency of TTTB decreases while that of TTTS remains almost constant (≥ 99.7%) up to 120 minutes and in the temperature range 35 -65 ºC. The activation energies are higher in inhibited than in plain acid with both inhibitors. The free energy of adsorption (∆G ads ) and heat of adsorption (Q ads ) are negative, which suggests that there is spontaneous adsorption on metal surface, and from the values of (∆G ads ) and (Q ads ), the values of entropy of adsorption (∆S ads ) were calculated. Galvanostatic polarization shows that corrosion is under mixed control with predominance of the cathodic part. In uninhibited 1.0 M HCl, complete cathodic protection is achieved at a current density of 4.2224 Adm -2 , but in presence of these inhibitors, much lower current densities are required. Plot of log (θ/1-θ) versus log C inh gives a straight line, suggesting that inhibitors cover both the anodic and cathodic regions through general adsorption following Langmuir isotherm. The mechanism of inhibition has been proposed.

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The corrosion of copper in lactic acid containing various colourants and sweetening agents has been studied. In plain lactic acid the corrosion increases with acid concentration up to 0.5 M and then decreases, but it increases continuously with the time of immersion and temperature. Pure buffalo milk (pH 6.45) and curd (pH 3.70) have almost no effect on copper. Addition of food dyes to lactic acid increases corrosion, the order of corrosivity being: amaranth < fast red E S sunset yellow < tartrazine d ponceau 4 R < carmoisine. Saccharin in plain as well as coloured lactic acid has an accelerating effect. The other sweeteners have an inhibitive effect, in the order: glycerol < glucose s fructose < sucrose in plain lactic acid, while in coloured acid the effect increases in the order: glycerol < sucrose < glucose < fructose.Copper in 0.1 M plain as well as coloured and/or sweetened lactic acid shows a corrosion potential of -70 mV (+ 5 mV) vs SCE. Galvanostatic polarisation curves show very little anodic but appreciable cathodic polarisation. Preservatives like sodium benzoate confer 30% protection.Untersucht wurde die Korrosion von Kupfer in Milchsaure mit verschiedenen Farbstoffen und SiiBstoffen. In Milchsaure allein steigt die Korrosion mit der Saurekonzentration bis 0,5 M und nimmt dann wieder ab, sie steigt jedoch kontinuierlich mit der Versuchsdauer und der Temperatur. Reine Biiffelmilch (pH 6,45) und Quark (pH 3,70) haben fast keine Wirkung auf Kupfer. Zusatz von Lebensmittelfarbstoffen zu Milchsaure verstarkt die Korrosion, und zwar steigt die Aggressivitat in der Reihenfolge: Amaranth > Echtrot E S Sunset yellow Tartracin 4 Ponceau 4R < Carmoisine. Saccharin wirkt sowohl in der reinen als auch in der farbstoffhaltigen Milchsaure beschleunigend. Die iibrigen verwendeten SiiDstoffe wirken inhibierend, und zwar in der Reihenfolge: Glycerin < Glucose 6 Fructose < Saccharose in reiner Milchsaure, Glycerin < Saccharose < Glucose < Fructose in farbstoffhaltiger Milchsaure.Das Potential des Kupfers in 0,l m Milchsaure auch mit Farbstoffen undfoder SuDstoffen liegt bei -70 mV (+5 mV) (SCE). Die galvanostatischen Polarisationskurven zeigen sehr geringe anodische, jedoch betrachtliche kathodische Polarisation. Konservierungsmittel wie Natriumbenzoat erreichen einen Hemmwert von 30%.particularly on long standing. The corrosion of copper and brass by food acids and souring substances has been studied by some workers [l, 7-13]. However, data regarding the effect of various food dyes and sweetening agents on corrosion of copper by edible acids are not much available. In the present communication the corrosion of electrolytic copper by lactic acid solutions containing various food dyes (e. g. ponceau 4 R, tartrazine, amaranth, carmoisine, sunset yellow, fast red E) and sweetening agents (e. g. glucose, fructose, sucrose, glycerol, saccharin) has been reported. The study is an extension of the earlier work [14-171 and forms part of the project to study corrosion of different metals and alloys by solutions of food acids co...

The corrosion of copper in tartaric acid solutions containing various food colourants and/or sweetening agents has been studied with respect to the concentration of the acid and the colourant, and temperature. At constant acid concentration the corrosion increases with the concentration of the colourant whereas at constant colourant concentration it increases with acid concentration. In acid solutions the corrosivity of the colourant increases in the order: tartrazine < ponceau 4R < carmoisine < amaranth < fast red E < sunset yellow. The addition of sweetening agent also increases the corrosion of copper, the corrosion increasing in the order: saccharin < fructose < glycerol < sucrose < glucose. In acid containing the colourant as well as the sweetening agent the order of corrosivity is: sucrose < glucose < fructose < saccharin < glycerol.Copper in 0.05 M tartaric acid develops a corrosion potential of -40 mV (vs SCE). The addition of colourants or sucrose do not appear to have any effect on the corrosion potential. Galvanostatic polarisation curves show very little anodic but appreciable cathodic polarisation.Additives like sodium benzoate, raspberry essence, gum tragacanth, dextrin, and potato starch appear to confer some protection to copper in tartaric acid containing colourants like carmoisine.