TITLE:
PLANT EXTRACTS AS CORROSION INHIBITORS FOR CU-ALLOYS IN RIVER
WATER
FIELD OF INVENTION:
This invention relates to a process for the preparation of herbal corrosion inhibitors for
copper alloy.
This invention also relates to corrosion is the deterioration of metal by chemical attack or
reaction with its environment. It is a constant and continuous problem, often difficult to
eliminate completely. The use of corrosion inhibitors is one of the best options of protecting
metals and alloys against corrosion. The environmental toxicity of organic corrosion
inhibitors has prompted the search for green corrosion inhibitors as they are biodegradable,
do not contain heavy metals or other toxic compounds. As in addition to being
environmentally friendly and ecologically acceptable, plant products are inexpensive, readily
available and renewable. Investigations of corrosion inhibiting abilities of tannins, alkaloids,
organic, amino acids, and organic dyes of plant origin are of interest.
BACKGROUND AHT & PRIOR ART:
The consequence of metal corrosion is considered a serious problem in industries. A
corrosion inhibitor is a substance which when added in small concentration to cooling water,
effectively reduces the corrosion rate of a metal exposed to it. Generally used cheap inorganic
metal corrosion inhibitors, such as chromates, is banned because of toxicity to the
environment after discharge hazards they create. Hence there is a strive to make use of
environmental friendly, non toxic /less toxic, extracts of naturally occurring plant materials as
corrosion inhibitors.

Large numbers of organic/ inorganic compounds have been studied and are still being studied
to assess their corrosion inhibition potential. However, most of these substances are not only
expensive but also pose health and environmental hazards prompting the search for their
replacement.
Plants have been recognized as sources of naturally occurring compounds that are generally
referred to as 'green' compounds, some with rather complex molecular structures and having
a variety of physical, chemical and biological properties. Furthermore, there has been a
growing trend in the use of natural products as corrosion inhibitors for metals in various
corrosive media. In fact, plants have become important as environmentally acceptable,
readily available and renewable source of a wide range of chemicals. Due to bio-
degradability, ecofriendliness, low cost and easy availability, the extracts of some common
plants based chemicals and their by-products have been tried as inhibitors for metals under
different environments.
Over the years, considerable efforts have been deployed to find suitable corrosion inhibitors
of organic origin in various corrosive media. In acid media, nitrogen-base materials and their
derivatives, sulphur-containing compounds, aldehydes, thioaldehydes, acetylenic compounds,
and various alkaloids, for example, papaverine, strychnine, quinine, and nicotine are used as
inhibitors. In neutral media, benzoate, nitrite, chromate, and phosphate act as good inhibitors.
Inhibitors decrease or prevent the reaction of the metal with the media. They reduce the
corrosion rate by
(i) adsorption of ions/molecules onto metal surface.
(ii) increasing or decreasing the anodic and/or cathodic reaction.
(iii) decreasing the diffusion rate for reactants to the surface of the metal.
(iv) decreasing the electrical resistance of the metal surface.
(v) inhibitors that are often easy to apply and have in situ application advantage.
Several factors including cost and amount, easy availability and most important safety to
environment and its species need to be considered when choosing an inhibitor.

To replace the environmentally hazardous chromates, several non-chromates have been used
as corrosion inhibitors. Among those, extracts of plant materials are top on the list. The plant
extracts are environmentally friendly, non-toxic and readily available. These extracts contain
many ingredients. They contain several organic compounds which have polar atoms such as
O, N, P and S. They are adsorbed onto the metal surface through these polar atoms and
thereby protective films are formed. Adsorptions of these ingredients obey various adsorption
isotherms. The films have been analyzed by many surface analysis techniques such as AFM,
FTIR, UV, Fluorescence spectra and SEM. Some of the patented works on development of
ecofriendly green biodegradable corrosion inhibitors and their effects on metals are described
below
1) Patent No EP 2386338 Al (Application type)describes the use of fruit skin extracts as
corrosion inhibitors and process for producing same . This invention says more particularly to
ihe use of the skin of fruits such as mango, cashew, passion-fruit and orange, inter alia, more
specifically as corrosion inhibitors for steel in an acid medium, preferably carbon steel 1020
in a I mole/L"1 hydrochloric acid medium.
2) Patent No US 20140345871 Al (application type) discloses the use of a corrosion
inhibitor selected from the group consisting of; (a) the leaves of henna, jewelweed, or any
combination thereof; (b) an extract of the leaves of henna, jewelweed, or any combination
thereof; (c) a plant source of a hydroxynaphthoquinone; (d) a hydroxynaphthoquinone; and
(e) any combination an any of the foregoing for Acid in a Well of oil rig.
3) Patent No US 8409340 Bl ( Application type) claims a bio-based corrosion inhibitor
composition includes a com stillage product, and may be a substantially water insoluble
fraction of com stillage. The corrosion inhibitor composition is useful in protecting metal
articles from corrosion.
4) Patent No US 6602555 Bl( Granted) reveals a method of extracting corrosion inhibiting
constituents from tobacco comprises the steps of soaking tobacco in an extraction solution
under certain extraction conditions, followed by filtration to remove tobacco residue from the
resultant aqueous tobacco solution. This tobacco solution is used as a corrosion inhibitor to
minimize the amount of corrosion occurring at galvanic corrosion cells that are established at
areas of union of metals having different electrochemical potentials.

5) Patent no: US 8790457 Bl (granted) describes a bio-based corrosion inhibitor
composition includes a com stillage product, and may be a substantially water insoluble
fraction of com stillage.
6) Patent No 223621 (Indian patent; granted) claims Musa Paradisica Peel Extract as
Green Corrosion Inhibitor for Mild Steel in HC1.
OBJECTS OF INVENTION:
An object of the present invention is to propose a process for the preparation of herbal
corrosion inhibitor for copper alloy.
Another object of the present invention is to propose a process for the preparation and
evaluation of inhibition efficiencies of environmental friendly plant extracts from Neem
leaves, Turmeric, Coffee and Tea.
Further, object of the present invention is to propose a process for evaluation of herbal
corrosion inhibitors efficiencies by electrochemical polarization and impedance techniques
for copper alloys in river water.
Still further object of the present invention is to propose a process to use herbal corrosion
inhibitors for copper alloys, Cu-Ni(70/30) and Cu-Ni(90/10) which are common materials for
condenser tubes.

BRIEF DESCRIPTION OF THE INVENTION:
This invention relates to a process for the preparation of herbal corrosion inhibitors for
copper alloy comprising:
cutting neem leaves and green tea leaves into small pieces;
drying the small pieces of the said leaves,
subjecting the dried leaves to the step of grinding,
drying turmeric powder and roasted coffee powder,
refluxing 50 gm of each sample
filtering the refluxed sample to produce the solution.
DESCRIPTION OF DRAWINGS:
Fig I: Tafel Plots of Admiralty Brass with and without Inhibitors
Fig: II: Tafel Plots of Cu/Ni 70/30 with and without Inhibitors
Fig: III: Tafel Plots of Cu/Ni 90/10 with and without Inhibitors
Fig IV: Impedance Plots of Admiralty Brass with and without Inhibitors
Fig .V: Impedance Plots of Cu/Ni 70/30 with and without Inhibitors
Fig VI: Impedance Plots of Cu/Ni 90/10 with and without Inhibitors
Fig VII:Variation of Impedance Plots of Admiralty brass with Different immersion time in
Turmeric Extract.
DETAILED DESCRIPTION OF INVENTION:
In power utilities, cooling water management is vital and one of the tasks is to combat
corrosion in heat exchanger tubes. It is a general practice in power stations to add inhibitors
to the cooling water to reduce the corrosion of the metals. Commercial inhibitors

are very much effective but at the same time, disposal of such chemicals is considered to be
hazardous to the environment. Hence, a need exists for environmental friendly corrosion
inhibitors. From the little information available in literature, extracts of some plant materials
have been found to inhibit corrosion of steels and copper alloys in river water as well as in
sea water.
This process describes the evaluation of corrosion inhibition efficiencies of environment
friendly plant extracts such as Neem leaves, Turmeric, Coffee and Tea for copper alloys in
river water. These extracts are evaluated by electrochemical polarization and impedance
techniques. Admiralty brass, Cu-Ni (70/30) and Cu-Ni (90/10) were chosen as copper alloys.
Water finds extensive use as a cooling medium in power plants and the quality of water
changes continuously because of seasonal variations, natural contaminants and diverse
pollutants introduced by human activity. The usage of open recirculation towers is increasing,
as the water shortage limits the usage of once through cooling systems. The treatment of raw
water is essential to maintain heat-transfer efficiency and prolong the life of the equipment.
The objective of cooling water treatment is of paramount importance to operate at higher
Cycles of Concentration (COC) to save waters Proper treatment should be selected so as to
control or minimize scaling, corrosion and microbiological growth.
Choice of a treatment program depends on the type of cooling system, characteristics of
water and the metallurgy of the system. Environmental regulations should be given due
consideration, since the compounds in some of the dosing chemicals are hazardous and can
not be discharged directly. It is a general practice in power stations to add commercial
inhibitors to the cooling water (CW) to reduce the corrosion of the metals. Commercial
inhibitors are very much effective but at the same time, disposal of such chemicals is
considered to be difficult because of environmental regulations. Hence, a need exists for
environmental friendly corrosion inhibitors. Innovative studies to use plant extracts as
inhibitors is gaining importance and accordingly environmental friendly plant extracts of
Neem leaves, Turmeric, Coffee and Tea have been chosen as corrosion inhibitors for copper
alloys in river water.

These plant extracts contain alkaloids like lignin, tannin, limonoids, salanin, pectin, nimbin,
meldenindiol, azadirachtin, curcumin etc.; hence their inhibition property is a logical
consequence of the complex organic nature of the compounds. The neem and turmeric are
known to have antibacterial property; hence their usage as inhibitors in CW systems has an
additional value as biocide. The present study is to evaluate aqueous leaf extract of
Azadirachta indica (Neem), rhizome extract of Curcuma longa (turmeric), leaf extract of
Thea (tea), and seed extract of Coffea arabica (coffee beans) as corrosion inhibitors for
condenser tube materials of copper alloys. The Copper alloys taken for this study are
Admiralty Brass, Cu/Ni 90/10, Cu /Ni 70/30 and the medium is river water.
Experimental Set-up:
Preparation of the Specimen:
Area of the specimen for electrochemical studies was chosen as 1.0 sq cm for convenience.
Keeping this in mind, each alloy i.e admiralty brass, Cu-Ni (70/30) and Cu-Ni (90/10) were
cut and mounted on circular PTFE (Teflon) base. Copper rod direaded in to the specimen
acted as electrical connector. The specimens were polished with emery paper from grade-1
(Coarsest) to grade-5 (Finest) and then cleaned with acetone.
Preparation of the Extract:
Neem leaves and green tea leaves were taken and cut into small pieces and they were dried
in natural circulation air oven at 70°C for 1.5 hrs. They were ground well into powder.
Turmeric powder, and roasted coffee powder were dried in air oven at 50°C for 1 hrs. From
these, 50g ofeach sample was refluxed in 200mL-distilled water for 40 minutes. The refluxed
solution was cooled then filtered carefully through nylon membrane filter of pore size 0.45
^im and 0.20 urn at 100 mm Hg vacuum. The filtrate volume was made up to 500 mL using
DM water. The concentration of the stock solution is expressed in term of %(v/v). These
solutions are stored in refrigerator. From these concentrates, 1%, 0.1% and 0.01% dilutions
were made using Manjeera river water.

Equipment used:
Electrochemical studies were conducted using "Auto-lab" supplied by Ecochemie,
Netherlands. Platinum rod was used as a counter electrode and saturated calomel electrode
was used as a reference electrode. Admiralty brass and cupro-nickel alloy specimens were
used as working electrodes. The electrochemical cell supplied along with the instrument was
used for all the studies. Equipment compatible specific software was used in the study of
corrosion rates and impedance measurements.
Experimental procedure:
Tafel experiments and impedance studies were conducted for all the specimens in river water
with and without the plant extracts. The solution was taken in the electrochemical cell. In
the Tafel experiments, the specimens were polarized from -250mv to +250mv through the
corrosion potential. The programming was done using the software. Cathodic and anodic
polarization curves were recorded. In the impedance technique, different frequencies from 10
mHz to 100 k Hz were applied to the specimen at the corrosion potentials. Impedance plots
were obtained with and without these extracts for all the specimens.
Results:
Values of various electrochemical parameters like corrosion potentials (E^n), polarization
resistance (Rp) and the corrosion current (1^) for all the alloys in the presence and absence
of inhibitors were given in Table-1. Cathodic and anodic polarization curves for Admiralty
brass in the presence and absence of plant extracts were shown in Fig. I. The same curves for
cupronickel (70/30) and cupronickel (90/10) were shown in Fig.II and Fig.III.
Impedance studies were also conducted for these alloys in the presence and absence of plant
extracts. The solution resistance (R5), charge transfer resistance (Rr), admittance (Y0) and
empirical constant (n) values were tabulated in Table-2. The impedance plots were shown in
Fig. IV, V and VI. The Impedance is nothing but the resistance of an AC circuit. Normally
the parts of an electrochemical cell resemble a resistance. For instance the electrolyte
solution, in this case river water behaves as an ohmic resistance. The interface between the
metal and the

electrolyte ideally behaves like a capacitor. At high frequencies, the impedance equals to the
solution resistance and at low frequencies the impedance equals to the total of solution
resistance and the charge transfer resistance. Both limits show a phase shift equal to 0 . The
impedance plot is usually a semi circle. But in the actual situation the impedance spectrum is
much more complicated and it is like a suppressed semi circle. This is due to the fact that the
surface is heterogeneous and the porosity of the surface that makes the surface to behave as a
leaky capacitor. In such cases the phase angle is less than 90 .

WE CLAIM:
1. A process for the preparation of herbal corrosion inhibitors for copper alloy comprising:
curling neem leaves and green tea leaves into small pieces;
drying the small pieces of the said leaves,
subjecting the dried leaves to the step of grinding,
drying turmeric powder and roasted coffee powder,
refluxing 50 gm of each sample
filtering the refluxed sample to produce the solution.
2. The process as claimed in claim 1, wherein the neem and green tea leaves were dried in an
air oven at 70°C for 1.5 hrs.
3. The process as claimed in claim 1, wherein the turmeric and coffee powder was dried in air
oven at 50°C for 1 hr.
4. The process as claimed in claim 1, wherein the sample was refluxed in 200 ml distilled
water for 40 minutes.
5. The process as claimed in claim I, wherein the refluxed sample was filtered through nylon
membrane filter of pore size 0.45µm and 0.20µm at 100 mm Hg Vacuum.
6. The process as claimed in claim I, wherein the filtrate after filtration was madeup to 500
mL using DM water.