The Tin Iron Alloy in Tin Plate¹

Abstract

A series of,lots of tin:plate were made by varying the time a n d temperature that the plate was held in molten tin. These lots of tin plate were then made into enameled cans, whose service value for canning fruits was determined. By increasing the time a n d temperature the amount of tin which alloyed with the base plate was increased. The free tin coating was kept reasonably constant by passing the several lots successively through the same tin pot after the preliminary holding period. Cans were also made from the untinned base plate by electrically welding the side seams. For comparison, HERE is a scarcity of published data on the structure and composition of the metal a t the junction of the T tin and iron in commercial tin plate and no correlation of such data with service value for fruit cans. Even within recent years doubt as to the existence of a tin-iron alloy has been expressed.Mayer2 has shown that under certain conditions the two metals do alloy when iron is coated with tin by immersion in molten tin. He held steel of varying carbon content (electrolytic carbon-free iron and two steels containing, respectively, 0.06 and 0.41 per cent carbon) for 30 minutes in molten tin, respectively, a t 300", 500°, 750", and 950" C., and removed the specimens without subjecting them to rolls as is done in commercial tinning. Under these conditions photomicrographs disclosed an intermediate layer of crystals between the tin and iron, the thickness of which increased with the temperature of the tin pot, but which evidently was independent of the carbon content of the iron. The appearance of this intermediate layer of crystals was accompanied by a recession of the pearlite away from the tin coat, except in the specimen held a t 950" C., in which the pearlite was again in evidence adjacent to the tin layer. I n the carbonfree iron small crystals were in evidence within the large ferrite crystals adjacent to the tin coat. Mayer thus believes he has shown the diffusion of tin into the iron by a microscopic examination of the pearlite and ferrite crystals.From a patent granted to DavisS it is evident that the existence of tin-iron alloy between the tin and iron is recognized by manufacturers of tin plate. In this patent the following picture is presented:When the ferrous base and molten tin first come into contact. a layer of an iron-tin alloy forms on the surfaces of the base, this alloy having a melting point higher than that of the molten tin itself. The result of this action is that fine needle-like crystals of this iron-tin alloy are formed which protrude from the surfaces of the iron base and form a fine spongy or porous network of crystals, the interstices of which are filled with the molten tin. When the iron base and adherent alloy layer of crystals later pass between the exit rolls of the tin pot, which are located within a body of palm oil, the network of crystals is crushed and flattened against the iron base, and a large portion of the molten, interstitial tin is squeezed out and flows off the plate. The body ...

The Canning of Grapefruit and Grapefruit Juice

“…As has been shown by Kohman (6), Bohart (1), and others, the storage temperature of the canned product, the vacuum obtained in the cans when packed, and the amount of head space in the cans are factors affecting the rate of development of hydrogen springers. The lower the storage temperature, the greater (within the limits of commercial practice) the head space in the can; and the higher the partial vacuum, the less the difficulty with hydrogen springers.…”

Factors Controlling the Corrosion of Tinplate. Fifty-Year Search for the Abominable Snowman

“…Earlier, Kohman and Sanborn (1927) had studied the effect of the alloy in hot-dipped tinplate and reached the conclusion that it had but little influence on shelf life, a deleterious one if any. Covert and Uhlig (1937), observing the electrochemical relations of massive alloy to tin and steel, concluded that while it was cathodic to both metals, it was of minor importance to shelf life, because of its high hydrogen overvoltage.…”

The determination of tin coating weights on tinplate

“…The usual procedure in volumetric determination of tin coating wights is to dissolve a sample of plate in hydrochloric acid and to estimate the stannous tin by iodimetric titration.ls 20 (a) Sohrtion of the sa?npk.-A number of acid mixtures were compared with concentrated hydrochloric acid, the usual reagent, as media for the solution of tinplate samples. However, concentrated hydrochloric acid proved to be most generally suitable and was employed throughout the investigation.…”