GREEN SOLUTION TO CORROSION PROBLEMS

Abstract

Several researchers are trying to make use of natural products as corrosion inhibitors.  Plant scientists have already established the active principles present in most of the plant materials.  The active principles form protective film on the metal surface by coordinating with the metal ion through O, S or N atoms of the functional groups present in the active principles.  When the active principles are extracted with acids or organic solvents or with water, usually a mixture of several compounds is obtained.  It is very difficult and tedious to isolate and purify them.  However, a mixture of inhibitors present in the plant extract may show synergistic effect.

The main disadvantage of using plants materials as corrosion inhibitors is their instability; they are readily biodegradable. However, this disadvantage can be minimised or avoided by adding some biocides such as N-cetyl-N,N,N-trimethyl ammonium bromide, or some plant materials which by themselves have biocidal property.  This type of approach will make the use of plant materials as corrosion inhibitors universal and versatile.

Before the 1960s inorganic inhibitors such as zinc, chromate, polyphosphate and nitrite were used as inhibitors.  They provided good corrosion protections.  However, discharge of such materials has become unacceptable, due to environmental hazards.

Between 1960 and 1980, zinc, polyphosphate, phosphonate, polymer and phosphono carboxylic acids were used as corrosion inhibitors.

After 1980 molybdate, phosphonates, phosphono carboxylic acids and polymers were used as inhibitors, along with metal ions such as Zn²⁺.  Recent trend is the search for environmental friendly inhibitors, by the researchers.  Most of the natural products are non toxic, biodegradable and readily available in plenty.  Various parts of the plants – seeds, fruits, leaves, flowers etc have been used as corrosion inhibitors.  Several studies have been published on the use of natural products as corrosion inhibitors . weight loss methods are used to measure the corrosion inhibition efficiency of the inhibitors. Electrochemical studies such as polarization study and AC impedance spectra have been employed to investigate the mechanistic aspects of corrosion inhibition. The surface morphology of the protective fims has been analysed by FTIR, SEM, AFM , EDAX and contact angle measurements. These aspects are discussed in this paper.