Tin sulfuration in food cans

Tin sulfiding is a phenomenon that occurs in tinplate, a material widely used in the manufacture of metal containers. This chemical reaction occurs when the tin present on the surface of the tinplate reacts with sulfur compounds present in the contents of the container, generating tin sulfide (SnS) and iron sulfide (FeS).

Tin sulfiding can be problematic as it can affect the quality and appearance of metal containers. In some cases, it can lead to the formation of dark tin sulfide stains on the surface of the tinplate, which adversely affects the appearance of the packaged product.

There are different factors that can influence tin sulfiding. One of them is the amount of tin deposited on the tinplate. Although the amount of tin is not a determinant in the formation of tin sulfide, it has been observed that a higher tin deposit can help reduce sulfidation. However, an excess of tin can affect the adhesion of the varnishes used in the protection of tinplate.

Another important factor is the presence of sulfur compounds in the contents of the container. Some products, especially those with an acidic pH or containing sulfurized proteins, can promote tin sulfuration. In these cases, measures can be taken to prevent the formation of tin sulfide, such as adjusting the pH of the product or avoiding contamination with sulfur compounds.

To prevent or reduce tin sulfidation, different techniques and protective coatings are used in the manufacture of metal containers. One of them is the use of varnishes applied on tinplate, which act as a protective barrier against attacks from the packaged product. These varnishes must have good adhesion and be sufficiently dense to prevent the penetration of sulfur compounds.

In addition to varnishes, surface treatments such as passivation, which consists of depositing a layer of chromium oxide on the tinplate to protect it against the formation of tin sulfide, are also used. Passivation helps to create a physical and chemical barrier that prevents oxidation and reaction with sulfur compounds.

In summary, tin sulfuration is a phenomenon that can occur in tinplate used in metal containers. To prevent or reduce this problem, different techniques and protective coatings, such as varnishes and passivation treatments, are used. However, it is important to keep in mind that tin sulfuration can be influenced by several factors, and its prevention may require a multifaceted approach.