The scales of iron oxide formed on the surface of the strip are insoluble in water, and when they are immersed in acid or sprayed on the surface, they undergo a series of chemical reactions with the acid. Due to the loose, porous and cracked properties of the iron oxide scale on the surface of carbon structural steel or low-alloy steel, and the repeated bending of the iron oxide scale on the pickling unit, these pores and cracks are further increased and enlarged, so the acid solution is in contact with While the iron oxide scale reacts chemically, it also reacts with the steel through cracks. Therefore, the pickling principle can be summarized into the following four aspects.
Various paste oxides in the iron oxide scale on the surface of the strip are dissolved in the acid solution to generate ferric and ferrous chlorides or sulfates that can be dissolved in the acid solution, thereby removing the iron oxide scale from the surface of the strip. This effect is generally called dissolution.
2. Mechanical peeling effect
In addition to the various oxides of iron, the iron oxide scale on the surface of the strip is also mixed with some metallic iron, and the iron oxide scale is porous, so the acid solution can pass through the gaps in the iron oxide scale. and produce a lot of hydrogen. The expansion pressure generated by this part of the hydrogen can separate the iron oxide scale from the surface of the strip. We call this reaction mechanical exfoliation.
The acid solution enters through the gap of the iron oxide scale and reacts with FeO. Since FeO and Fe2O3 are easy to react with the operator, the phenomenon that the iron oxide scale falls off due to the dissolution of the lower FeO in the acid occurs. This phenomenon is called osmosis.
When metallic iron reacts with acid, hydrogen atoms are first produced. Part of the hydrogen atoms combine with each other to form hydrogen molecules, which promotes the separation of the iron oxide scale. The other part of the hydrogen atoms reduces the oxides and salts of high-valent iron to low-valent iron oxides and salts that are easily soluble in acid solutions by virtue of their reducing power.
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