Tin-iron couple

A reversal of potential of the tin—iron couple occurs when tin-coated steel (tin-plate) is in contact with acid solutions in the absence of air. The tin coating acts as an anode it is the tin that is slowly attacked and not the steel. This unique property is the keystone of the canning industry because dissolved iron affects the flavor and appearance of the product. Thus, the presence of tin protects the appearance and flavor of the product. 

Steel coated with tin (tinplate) is used to make food containers. Tin is more noble than steel therefore, well-aerated solutions will galvanically accelerate attack of the steel at exposed areas. The comparative absence of air within food containers aids in preserving the tin as well as the food. Also the reversible potential which the tin-iron couple undergoes in organic acids serves to protect exposed steel in food containers. 

Canned foods may take up metals from the container, tin and iron from the tin plate, and tin and lead from the solder. There are several types of internal can corrosion. Rapid detinning is one of the most serious problems of can corrosion. With most acid foods, when canned in the absence of oxygen, tin forms the anode of the tin-iron couple. The tin under these conditions goes into solution... 

To ensure maximum continuity of the tin-iron compound layer between tin and steel. This layer is itself corrosion resistant and appears to act as a nearly inert screen limiting the area of steel exposed as tin is removed by corrosion. Its effectiveness is measured by the Alloy-Tin Couple (A.T.C.) test, in which the current flowing is measured between a sample of tinplate from which the unalloyed tin layer has been removed, and a relatively large tin electrode immersed in an anaerobic fruit juice. ... 

Changes in corrosion resistance of the electrolytic tin coatings were determined by the iron-solution-value test and the alloy-tin-couple test (6). Corrosion resistance data for the 43 kg (95 lb), Type MR-TU, No. 25 tinplate are presented in Table VIII. These data show that there is no significant difference in the corrosion resistance of the unirradiated... 

The great advantage of Mossbauer spectroscopy is that it can be applied in situ. The major limitation of the technique is that it can only be applied to a couple of elements, among which iron and tin are the easiest to study. 

Most electrodes are metallic. Sometimes the metal of an electrode can also be one component part of a redox couple. Good examples include metallic iron, copper, zinc, lead or tin. A tin electrode forms a couple when in contact with tin(IV) ions, etc. Such electrodes are called redox electrodes (or non-passive). In effect, a redox electrode has two roles first, it acts as a reagent and, secondly, it measures the energy of the redox couple of which it forms one part when connected to a voltmeter. 

F. J. Copa-Rodriguez and M. I. Basadre-Pampin, Determination of iron, copper and zinc in tinned mussels by inductively coupled plasma atomic emission spectrometry (ICP-AES), Fresenius J. Anal. Chem., 348(5-6), 1994, 390-395. 

This potential, adjusted as a function of the pH of the solution and of the hydrogen pressure, is easily fixed between +0 1 V and — 0.9V/NHE (Normal Hydrogen Electrode). The H2/H+ couple was used to prepare supported catalysts with platinum, palladium, ruthenium, and rhodium modified with deposits of tin, lead, iron, germanium, and bismuth [50-54]. These catalysts were proposed for their good selectivities for different reactions in specialize organic chemistry. 

By using cyclic voltammetry, Schiffrin and coworkers [26, 186, 187, 189] studied electron transfer across the water-1,2-dichloroethane interface between the redox couple FefCNls /Fe(CN)6 in water, and lutetium(III) [186] and tin(IV) [26, 187] diphthalocyanines and bis(pyridine)-me50-tetraphenylporphyrinato-iron(II) or ru-thenium(III) [189] in the organic solvent. An essential advantage of these systems is that none of the reactants or products can cross the interface and interfere with the electron transfer reaction, which could be clearly demonstrated. Owing to a much higher concentration of the aqueous redox couple, the pseudo-first order electron transfer reactions could be analyzed with the help of the Nicholson-Shain theory. However, though they have all appeared to be quasireversible, kinetic analysis was restricted to an evaluation of the apparent standard rate constant o. which was found to be of the order of 10 cm s [186, 189]. Marcus [199] has derived a relationship between the pseudo-first-order rate constant for the reaction (8) and the rate... 

The metals can be activated toward alkalies by coupling them with other metals, just as they are activated toward water and acids. When zinc is in contact with iron the former reacts rapidly with a warm solution of sodium hydroxide. Hydrogen is evolved from the iron and the zinc passes into solution as sodium zincate, NagZnOg. Tin behaves in a similar way and sodium stannite, NagSnOa, is formed. It should be noted that in these cases the metal that dissolves is the one which forms a hydroxide soluble in sodium hydroxide. When two metals are coupled in neutral or acid solution hydrogen is evolved from the metal having the lower solution pressure— that is, the one lower in the electromotive series. When the solution contains an alkali, this is not always the case. Zinc is above and tin is below iron in the electromotive series, but when activated by iron in the presence of an alkali they each dissolve. The solubility of the hydroxide in alkalies is the determining factor in the reaction. The zinc that passes into solution is not presnt in the form of zinc ions, but as zincate ions, ZnOo— which result from the ionization of the salt formed. 

Iron was known to the British at least a couple of centuries before Julius Ca ar visited our shores in b.c. — one of the few dates we all remember. None of the earliest furnaces have been discovered but it is thought probable that the first iron furnace of the Britons was similar to those used so successfully in the extraction of tin it would thus be a simple low hearth resembling the Catalan furnace of the Pyrennees which has been in use there from very remote times down to the present. ... 

Many metals are used as chromophores. These can include, but are not limited to, cobalt, nickel, iron, chromium, tungsten, ruthenium, gold, copper, vanadium, titanium, manganese, zinc, aluminum, zirconium, palladium, and tin. Organometallic complexes with these metals are often used as coloring agents for a variety of materials. Coupled with the appropriate ligands, they can be made soluble in a slew of solvents and so can be distributed to wherever they are needed. 

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