The corrosion protection of stainless steel in phosphate fertilizer industry

Corrosion is one of the major problems in phosphate fertilizer industry. During
processing of phosphate fertilizer strong conc. sulphuric acid is used which generates
corrosive environment that affect metal and cost of production. In phosphate fertilizer
industry, most of the equipments are made of stainless steel and when it comes in contact
of corrosive environment several types of corrosion takes place like galvanic, pitting,
crevice, stress, cracking, embitterment, blistering and soon. To check corrosion in this
abetting environment organic inhibitors are used like N, N'-di-2-amino-diphenylthiourea,
N, N'-dinaphthyllthiourea and N, N'-di-2-amino-dinaphthyllthiourea. The anticorrosive
behaviour of these inhibitors are studied at different concentrations and temperatures.
The physical and chemical adsorption phenomena of inhibitors were studied with help
of Arrhenious, Langmuir, Frundlich and Temkin equations. The corrosion rate was
determined by gravimetric and potentiostatic polarization techniques. These inhibitors
are aromatic inhibitors which are highly electronic rich compounds to work against
corrosion in acidic medium. N, N'-di-2-amino-dinaphthyllthiourea show maximum
inhibition efficiency 83% among N, N'-di-2-amino-diphenylthiourea and N, N'-
dinaphthyllthiourea. These inhibitors are adhered to the metal surface by physical bonding
indicating the result of thermodynamical parameters.