[No.3/17] The functions of the anti-corrosion inhibitor contained in the rust preventive oil (1)
Let me explain, this time and next time as a series, about the corrosion inhibitor used in rust preventive oil. The thickness and the toughness of the oil film greatly contribute to prevent the corrosion occurrence on iron and steel when using the rust preventive oil, as the chemical substance called the corrosion inhibitor is contained. What does the corrosion inhibitor mean and how does it work?
Please refer to Figure 1, in which the regularly lined corrosion inhibitor molecules have been shown on the surface of the steel. This phenomenon is described that the corrosion inhibitor molecules are adsorbed on the surface of the steel. As a matter of course, nobody can see with the naked eyes as this absorption is occurred in nano-scale world, and therefore it is difficult to see even if enlarged with electron microscope. But, it is turned out as per Figure 1 by the study of the surface chemistry.
The corrosion inhibitor molecules are described as pink-top in Figure 1. Most of the corrosion inhibitor has been this kind of elongated shape actually. The head part of the pink-top (referred as hydrophilic group) has better affinity with iron and steel. The stick part of pink-top (referred as hydrophobic group or lipophilic group) does not have affinity with iron and steel has better affinity conversely with oil. Due to such kind of properties, the corrosion inhibitor can be adsorbed in the regular figure for by making the head part face towards the steel surface.
The corrosion inhibitor disturbs the water slightly solved in the rust preventive oil, which contacts with the steel by being adsorbed on the steel surface. Incidentally, the water solved in the rust preventive oil will be adsorbed by the steel and will generate corrosion on the surface, in the case that the corrosion inhibitor is not contained in the rust preventive oil.