The inhibitive effect of 4-((4-formyl-3-hydroxyphenyl)diazenyl)-3-hydroxynaphthalene-1-sulfonic acid on carbon steel
corrosion in hydrochloric acid solution was investigated using chemical and electrochemical techniques. It was found
that the compound acts as good corrosion inhibitor with inhibition efficiency more than 98.5%. The inhibition efficiency
was found to increase with inhibitor concentration and exposure time. On the other hand, it decreases by rising the
temperature. The inhibition action was discussed in view of adsorption of the organic compound molecules on the carbon
steel surface. It was found that the adsorption of 4-((4-formyl-3-hydroxyphenyl)diazenyl)-3-hydroxynaphthalene-1-
sulfonic acid on carbon steel surface follows Langmuir adsorption isotherm. The thermodynamic parameters for the
corrosion process in free and inhibited media were calculated and interpreted. Corrosion of metals and alloys is a disaster
which causes a large economic loss in different human activities. The corrosion process is thermodynamically
spontaneous and cannot be totally stopped anyhow. However, there are continuous trials to develop methods for
decreasing the corrosion to its minimum rate. One of the methods used to achieve this goal was using inhibitors. The
corrosion inhibitors act either by adsorption on the metal surface or reaction with it producing a passive film. The former
ones are most likely organic compounds (Azo compounds) with atoms in their structures carrying lone pair of electrons
capable of electrostatic attraction of the vacant orbitals of the metal.