Лаборатория иши №5

LABORATORY WORK №6
STUDY OF CORROSION RESISTANCE OF METALS AND METALS
The purpose of the work. Determination of corrosion resistance of steel in hydrochloric or sulfuric acid.

Corrosion of metals occurs mainly due to the polarization of hydrogen by the electrochemical mechanism. In cathodic reactions, the penetration of a hydroxy ion through a double electric layer occurs, the discharge of which occurs when the atoms separate the hydrogen into its molecule and desorb it from the metal surface. The anode reaction depends on the adsorption of active anions on the metal surface, which also forms intermediate complexes. In the final stage of the anode process, the metal ion passes into the solution in a hydrated state.

Corrosion retardants are substances that are adsorbed in the cathode or anode areas, slowing down the anodic or cathodic process. Some inhibitors form a spatial protective layer on the metal surface. For example, the slowing down of the melting of titanium in the presence of cupferron in hydrochloric acid is explained by the formation of a thin but less soluble and less conductive titanium cupferronate on the surface.
One of the simplest and most reliable methods is to determine the corrosion resistance of metals by gravimetric method. Corrosion can occur slowly or rapidly. In such cases, the gravimetric method allows to determine the average rate of corrosion over a certain period of time. The experiment can be carried out by hanging on chemical rods, glass plates on metal plates. The volumetric method is based on measuring the amount of hydrogen released by the reaction of a metal with an acid. This method is a more accurate method than the gravimetric method.
In this case, if certain conditions are not met, the results will be slightly wrong. This can be explained by the fact that some of the oxygen dissolved in the acid reacts with the atoms of hydrogen. If the melting of the metal occurs much faster and the acid surface is in contact with air, 93-95% of the steel will accelerate due to hydrogen polarization. In this case, the experimental results are reduced by 5-7%.
If the reaction occurs slowly, the amount of molten metal is sharply reduced due to hydrogen polarization and can be as high as 20-30%. In this case, the dissolved oxygen must be removed from the acid and prevented from diffusing into the acid. For this purpose, a very small amount of hydrogen is passed through the kilo for 10-15 minutes and a corrosimeter is used to prevent the ingress of oxygen into the acid.
The corrosimeter funnel is lowered to the bottom of the beaker, which prevents oxygen from entering the sample surface.