Corrosion and additives

Corrosion, or rusting, is a well-known chemical effect. Corrosion refers to a phenomenon, in which a metal or an alloy is partly oxidized as a result of air or other gases and solutions. Corrosion may be wet (effect of a solution) or dry (effect of dry gases). Dry corrosion is less frequent and it occurs in special circumstances, as a metal surface which is in contact with air is always in contact with moisture as well.

Corrosion is classified into two categories:
Chemical corrosion and electrochemical corrosion

In electrochemical corrosion, two metals form an electric couple.
In this reaction, the metal which is more electronegative corrodes. In chemical corrosion, a metal reacts with oxygen in the air or an acid solution. This can be avoided by using corrosion inhibitors. An inhibitor forms a protective coating on the metal surface. However, there will be problems if a lot of inhibitors are required. They decompose and lose their effect as a result of heat, flow and pressure. This is how corrosion starts to take affect, although the heat transfer fluid would not otherwise have lost its properties.Another corrosion effect which is typical of heat transfer fluids is the impact of organic acids. It is possible that acid is formed in heat transfer fluids following a chemical reaction, and this acid results in corrosion in the structural material. This is particularly typical of glycols.

Thermera and corrosion:

Consequently, corrosion refers to material wear and thinning as a result of an electrochemical effect. This thinning rate is described with the term corrosion rate, and the unit used is micrometer per year, µm/a. The corrosion rate can be measured by measuring the electric current of corrosion, or directly the thinning of the raw material. To improve reliability, both of these quantities are often measured, as was done with Thermera in the product development stage. Additives With Thermera, the need of additives is considerably smaller than with conventional products. So there is no major concern about the durability or toxicity of additives as long as Thermera is used.

Neither does betaine, the main raw material, form any corrosive disintegration products, unlike conventional products. Even a Thermera product without any additives has better anti-corrosive features than water. So betaine is a natural corrosion preventing agent. Thermera is slightly scented with an odorant used in the food industry (< 1w-%). Because of its good anti-corrosion features, only a minor amount of corrosion inhibitors have been added to Thermera (< 1w-%, active ingredients total less than 0,1 w-% in the end product). The additives used do not have any effect on Thermera’s toxicity. (Cf. VTT Technical Research Centre of Finland’s statement).

As Thermera is always a ready-to-use product, each Thermera product has always the correct additives, despite varying betaine concentrations. For example: the corrosion protection of Thermera –10 corresponds thus completely with that of Thermera –40.