Corrosion of copper by food acids containing colourants and sweetening agents – Part IV: Corrosion by lactic acid

Abstract

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...

Adsorption and Corrosion Inhibition Studies of Some Selected Dyes as Corrosion Inhibitors for Mild Steel in Acidic Medium: Gravimetric, Electrochemical, Quantum Chemical Studies and Synergistic Effect with Iodide Ions

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Recovery of palladium from waste fashion items through food waste by-products

“…Lactic acid is known to dissolve copper 31,32 but also to complex metal ions, thereby providing an extra driving force for base metal leaching. If HL indicates lactic acid in the acidic pH range, copper can be solubilized as Cu 2+ , CuL + , and, especially, CuL 2 according to the following reactions:2HL + Cu → CuL 2 + H 2 HL ⇌ H + + L − Cu 2+ + L − ⇌ CuL + Cu 2+ + 2L − ⇌ CuL 2 …”

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