[001] The present invention relates to synthesizing and characterizing of metal oxide-conducting polymer composite as corrosion inhibitor for acidic environment with advanced corrosion resistance, better mechanical potency and thermal constancy for mild steel in acidic medium.
BACKGROUND AND PRIOR ARTS OF THE INVENTION
[002] Mild steel is widely applied as the constructional materials in many industries due to its excellent mechanical properties and low cost. Hydrochloric acid solutions are widely used in several industrial processes, some of the important fields of the application being acid pickling of steel, chemical cleaning and processing, ore production and oil well acidification, Because of the general aggression of acid solutions, inhibitors are commonly used to reduce the corrosive attack on metallic materials. The selection of the inhibitor is controlled by its economic availability, its efficiency to inhibit the substrate material and its environmental side effects. So most of the excellent acid inhibitors for corrosion of steel in acidic medium, are organic compounds containing nitrogen, oxygen and/or sulfur atoms. The inhibiting action of these compounds is attributed as a first stage, to the adsorption of the additives to the metal/solution interface. The adsorption process depends upon the nature and surface charge of the metal, the type of aggressive media, the structure of the inhibitor and the nature of its interaction with the metal surface. There are several types of corrosion inhibitors which are widely used to control the corrosion problem of low carbon steel upon exposure to acidic solutions, which vary from organic macromolecules to nanocomposites. These compounds are adsorbed onto the metallic surface, blocking the active corrosion sites. The applicability of these materials as corrosion inhibitors for metals in acidic media has been recognized for a long time. However, most of these materials are heavily toxic and environmentally hazardous; therefore, attempts have been carried out to search for eco-friendly

treatment materials for metals in acid solutions. In the past few years, conducting polymers composites have been recognized as excellent corrosion inhibitors for metals in the acid environment. A small quantity of polymer composite may be effective in inhibiting the corrosion of metals in acidic medium. Oxidative polymerization may be used for the synthesis of polymeric (oligomeric) products from several classes of monomers (aromatic amines, phenols, thiophenols, aromatic hydrocarbons and heterocyclic (Higashimura & Kobayashi, 2004; Sapurina IY & Shishov MA) products.
[003] Following are the works done so far in the field of conductive polymers based corrosion inhibitors.
[004] US patent- 6942899 B2 relates to coating for inhibiting corrosion of metallic substrate (aluminum or alloys composed of aluminum) by using conducting polymer with certain inhibiting ions. Inhibiting ions comprise of mono-thiol, di-thiol, poly-thiol, or combinations such as 2,5-dimercapto-l,3,4-thiadiazole; 6-ethoxy-2-mercaptobenzothiazole; 1,3,4 thiadiazole; 6-ethoxy-2-mercaptobenzothiazole, dimethyldithiocarbamic acid; o-ethylzanthicacid; 2-mercaptobenzothiazole; 2-mercaptoethanesulfonic acid; diethyldithiocarbamic acid. The coating composed of cationic electrically conductive carrier (polymer) able to conduct an electric current and anions of the thiol. The invention claims when any damage to coating occurred coating exhibits anticorrosive properties by releasing anions of the thiol in reducing environment.
[005] US Patent 6150032 A claims synthesis of anti-corrosive polymeric complex which is comprised of a plurality of double-stranded molecular complexes. These complexes strands were non-covalently attached with each other and are soluble in organic solvents. One strand is of conducting polymer like polyaniline, polypyrrole, polythiophene, poly(phenylene sulfide), poly(p-phenylene) and poly(phenylene vinylene), and other was copolymer such as of poly(acrylic acid-co-methylacrylate), poly(acrylic acid-co-ethylacrylate), poly(acrylic acid-co-acrylamide), poly(acrylic acid-co-methylvinylether) and

poly(acrylic acid-co-ethylvinylether). These complexes were blended with epoxies polyurethanes, polyamides, polyimides, polyaramids, polyacrylates, and poly(vinyl alcohol) and coated over aluminum and steel substrates.
[006] US Patent 5532025 A relates an anticorrosion coating for preventing steel materials from corrosion by using polyaniline, polypyrrole, blended with binder materials. The blends exhibit anticorrosive properties in alkaline, acidic and marine environment The present invention provides a corrosion inhibiting blends. The invention provides a bilayer coating to the substrate. The First coating comprising of intrinsically conducting polymer (polyaniline) blended with inorganic silicates or organic resins. Secondary coatings is mainly consist inorganic fillers and organic resin. The organic resin is mainly consist of shellac, phenolic resins, alkyd resins, aminoplast resins, epoxy resins, urethane, resins, acrylic resins, unsaturated polyester resins, vinyl resins, silicones, polyimides, unsaturated olefin resins, fluorinated olefin resins, crosslinkable styrenic regins, crosslinkable polyamide resins, rubber, elastomer, ionomers, mixture and there cross linkers.
[007] EP 0294013 A2 describes the preparation of cavitation-resistant polymer and coating for the metal substrates. The composition contains 24 to 48 wt.% of a liquid epoxy resin, 24 to 48 wt.% of a blocked isocyanate prepolymer, 4.2 to 12 wt.%) of a rheological additive (amorphous silica flatting agent), 1 to 4 wt.% of a plasticizer (dibutyl phthalate), 10 to 14 wt.% of a curing agent (alkyleneamine) and 0.1 to 0.6 wt.% of a silane (gamma-aminopropyltriethoxysilane). The formulation contains certain fillers, pigments and auxiliary agents. The invention claims composition, polymers, and coatings provide excellent protection against the degrading effects of cavitation.
OBJECTS OF THE INVENTION:
[008] The principal objective of the present invention is to design metal oxide doped conducting polymer by chemical oxidative polymerization.

[009] Another objective of the present invention is to illustrate the process of synthesis of metal oxide doped conducting polymer by selecting specific monomer which shows corrosion inhibition response which is the novelty of the invention.
[0010] Yet another objective of the present invention is to synthesize and design metal oxide-conducting polymer composite as corrosion inhibitor for acidic environment and synthesized in a specific medium.
[0011] Further objective of the present invention is to utilize the metal oxide doped conducting polymer as excellent corrosion inhibitors for metals in acidic environment.
SUMMARY OF THE INVENTION
[0012] Accordingly, the present invention provides a process for synthesis and designing of metal oxide doped conducting polymer as excellent corrosion inhibitors in a reaction medium containing metal oxide as dopant within the polymerization process. The method comprising:
(a) Synthesis of metal oxide doped conducting polymer Polyaniline by a facile chemical oxidative polymerization method in aqueous medium.
(b) Loading of metal oxide into polymer matrix within the polymerization process.
(c) Analysis of corrosion resistance performance of the metal oxide doped conducting polymer by weight loss test and potentiodynamic polarization test (Tafel Plots).
[0013] Precisely, the present invention discloses and claims a process for synthesizing conducting polymer of aniline comprising the steps of preparing aqueous solution of 0.05 - 0.2 M, preferably 0.1 M aniline monomer; mixing said aqueous solution of aniline monomer oxide of a transition metal as a dopant, said

oxide is vanadium (V) oxide (V2O5) in 0.05 - 0.2 M, preferably 0.1 M; adding dropwise aqueous solution of 0.1 M ammonium peroxydisulfate (APS) as an oxidant; isolating said synthesized metal doped conducting polymer from reaction mixture by filtration; and washing the resultant product with distilled water in order to remove oxidant and oligomers, followed by drying in the vacuum oven at 60°C. The polymerization is carried out at a temperature of 0-5 ±1.0°C for a period of 6-8 h.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] In the drawings accompanying this specification
Fig. 1: Schematic of the synthesis of Vanadium oxide doped Polyaniline composite by chemical oxidative polymerization process, electrochemical workstation and galvanostatic polarization curves of sample in 1M HC1
Fig. 2: XRD graph of V2O5-PANI composite
Fig. 3: SEM image of V2O5-PANI composite
Fig. 4: Tafel plots of V2O5-PANI composite in different concentration (a) without inhibitor, (b) 50 ppm, (c) 100 ppm, (d) 150 ppm and (e) 200 ppm
DETAILED DESCRIPTION OF THE INVENTION
[0015] At the very outset of the detailed description, it may be understood that the ensuing description only illustrates a particular form of this invention. However, such a particular form is only exemplary embodiment, and without intending to imply any limitation on the scope of this invention. Accordingly, the description is to be understood as an exemplary embodiment and teaching of invention and not intended to be taken restrictively.

[0016] Throughout the description and claims of this specification, the phrases
“comprise” and “contain” and variations of them mean “including but not limited
to”, and are not intended to exclude other moieties, additives, components,
integers or steps. Thus, the singular encompasses the plural unless the context
5 otherwise requires. Wherever there is an indefinite article used, the specification is
to be understood as contemplating plurality as well as singularity, unless the context requires otherwise.
[0017] Features, integers, characteristics, compounds, chemical moieties or groups described in conjunction with a particular aspect, embodiment or example
10 of the invention are to be understood to be applicable to any other aspect,
embodiment or example described herein unless incompatible therewith. All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at
15 least some of such features and/or steps are mutually exclusive. The invention is
not restricted to the details of any foregoing embodiments. The invention extends to any novel one, or any novel combination, of the features disclosed in this specification including any accompanying claims, abstract and drawings or any parts thereof, or to any novel one, or any novel combination, of the steps of any
20 method or process so disclosed.
[0018] The reader's attention is directed to all papers and documents which are
filed concurrently with or previous to this specification in connection with this
application and which are open to public inspection with this specification, and
the contents of all such papers and documents are incorporated herein by
25 reference. Post filing patents, original peer reviewed research paper shall be
published.
Materials and Reagents Used:
[0019] Aniline (Sigma Aldrich Germany), Divanadiumpentaoxide (V2O5, Sigma Aldrich Germany) are of high purity and analytical grade. Ammonium
7

persulphate and Hydrochloric Acid were procured from Across Organics and Merck Chemicals.
[0020] The present invention basically discloses a process for synthesizing metal oxide doped conducting polymer, polyaniline in the presence of metal oxide as 5 dopant in the presence of suitable medium, said method comprises designing of metal oxide doped conducting polymers (polyaniline) by chemical oxidative polymerization which when incorporated with suitable metal oxides; analysing electrochemically the metal oxide doped conducting polymer as corrosion inhibitors; verifying said anticorrosive properties of metal oxide doped conducting
10 polymer by potentiodynamic polarization studies; and further weight loss study for Mild Steel in presence of inhibitors in 1.0 M HCl. The conducting polymer selected for the corrosion inhibitor was selected from polyaniline and the like. The one of the monomer at least have a bulky group at ortho position of cyclic ring. The medium of polymerization was chosen from aqueous or acidic media. If acid
15 is chosen for said media, said acid may be either of Hydrochloric acid, Sulphuric acid and the likes either standalone or in combination. The polymerization of monomer has been carried out in presence of ammonium per sulphate, ferric chloride and the like. For the required polymerization, oxidants like, ammonium persulfate (APS)/ FeCl3, ferric phosphate and the like has been used for
20 polymerization.
[0021] For the purpose of polymerization monomer aniline and the like are first adsorbed on metal oxide layer and then added in aqueous solution. The samples were analyzed by Tafel Plot methods and by weight loss study for Mild Steel in presence of inhibitors in 1.0 M HCl and the like, wherein the samples show 95% 25 inhibition efficiency.
[0022] Generally, polyaniline is synthesized by oxidative polymerization of aniline. However, other methods like polycondensation of aniline derivatives with reactive functional groups (Y-n- = (-n-)n + Y), may also be exploited. The monomers used in oxidative polymerization are characterized by pronounced
8

electron donor properties and high oxidation tendency. These properties, in
particular, are inherent to aromatic amines, phenols and thiophenols or sulphur-
and nitrogen-containing heterocycles due to the presence of electron donor
substituent in benzene or heterocyclic ring. Oxidation of monomer takes place
5 under the action of inorganic (or organic) oxidizing agent or the applied potential.
During this process, cation or cation radical sites are generated in monomer of said polymer molecule, thus initiating the desired polymer growth. Technically, oxidative polymerization may be considered as formation of covalent bond between monomer molecules at the expense of abstracting two protons, wherein
10 there are several types of linkage between monomer units. In case of aniline,
“head-to-head”, “tail-to-tail” and “head-to-tail” configurations may be possible. In addition to that, in the last two cases chain assembly may occur due to substitution in phenyl ring with the formation of ortho-, para- and meta- monomer units. Thereby, oxidative polymerization yields chains with a wide variety of monomer
15 unit structures.
[0023] Since chain growth is accompanied by the formation of low-molecular products, oxidative polymerization may also be considered as a kind of polycondensation,. However, there might be deviation from afore mentioned principle as the formation of chain may proceed in two ways, whereas the first
20 one is recombination of cation radical oxidation sites, wherein further polymer
growth process is classed as polycondensation, since fragments of any length may recombine; and the second way of chain growth belongs to electrophilic substitution; in the case of aniline, oxidized nitrogen-containing structure attacks phenyl ring of another aniline molecule and substitutes one proton of the ring.
25 These ring and nitrogen-containing structure lose one proton; which is followed
by monomer units binding with each other, and lengthening of the chain. In the case of electrophilic substitution, both variants namely polycondensation and chain-growth processes are possible. To determine the type of addition, measurement of the molecular mass of the polymer throughout the reaction may
30 be performed. In the course of polycondensation, fragments with any molecular
9

mass may react with each other; therefore, average molecular mass of the product
increases in a slower pace, wherein monomer is rapidly transformed into low
molecular weight oligomers coexisting with the high molecular weight fraction up
to high conversion. Different molecular weight distribution may be observed
5 during chain-growth processes. In the course of chain-growth polymerization,
monomer units may be sequentially added to the polymer chain bearing active end group(s). Here, during oxidation, monomer may coexist with high molecular weight fraction of the product, and the content of low molecular weight oligomers may become minimal.
10 [0024] The process undertaken during the formation of poly-conjugated chains is
considered as electrophilic substitution reactions as the attacking species is oxidized and may act as an electrophilic agent, which may be considered that the most probable structure of monomer unit during electrophilic substitution process. Due to the presence of electron donor (heteroatom) in the monomer, this
15 heteroatom will most likely be oxidized, and monomer units may be linked in the
“head-to-tail” fashion. However, even when this type of linkage is repeated, the structure of the resultant polymer may be heterogeneous. Monomer units with ortho-, para- and meta-structure may be formed as a result of attacks of the electrophilic agent directed to different atoms of the central phenyl ring. Contents
20 of different types of units in the polymer may vary. The probability of the
formation of meta-structures is low, since aniline possesses electron donor substituent in its phenyl ring. Donor substituent creates excess negative charge on ortho- and para- carbon atoms of phenyl ring, and electrophilic attack is thus directed to ortho- and para-atoms. Therefore, according to the existing theory of
25 organic reactions, in the case of aniline oxidation, the most probable monomer
structures are ortho- and para-units linked in the “head-to-tail” fashion.
[0025] The active site or the terminal active group responsible for the
polymerization of aniline was assumed to be nitrenium cation or radical cation.
Studies on the aniline oxidation in the presence of “traps” for both types of
30 structures showed that alkyl-substituted phenols (2,6- di-tert-butyl-4-
10

methylphenol) and electron-enriched alkenes (2,3-dimethoxybuta-1,3-diene)
inhibit the polymerization by acting as scavengers of radical cations. At the same
time, aniline polymer is readily formed in the presence of electron-enriched arenes
(1,3- and 1,4- dimethoxybenzene), widely known as “traps” of nitrenium cations.
5 The activated terminal group of the chain is generated by an oxidant.
[0026] In the initial step, it is the monomer that is oxidized; however, upon formation of oligomers, these are terminal amino groups of the oligomer (polymer) that are oxidized because of having lower oxidation potential, which contributes to the polymer. In the course of polymerization, the polymer chain
10 performs the function of a mediator in the oxidation of monomer by oscillating
between the highest and intermediate oxidation states, i.e., pernigraniline and emeraldine. The active site formed at the end of the chain attacks the monomer molecule, specifically directed at a hydrogen atom in the aromatic ring and results in replacing hydrogen by a polymeric fragment. The chain propagates due to the
15 addition of new monomer units.
[0027] Polymerization of aniline and synthesis of its conducting polymer may be performed by electrochemical or chemical methods, wherein for the electrochemical method, electrode potential is increased. A wide range of oxidants may be used in the chemical synthesis of aniline polymer. As a rule, compounds
20 with high oxidation potentials exceeding +1.0 V including but not limited to
persulfates, dichromates, cerium (IV) salts, aurates etc. This is associated with the fact that the onset of the propagation of the polymer chains in acidic media requires overcoming energy barrier corresponding to a definite oxidation potential of +1.05 V. Upon beginning of the propagation, the oxidation potential of the
25 reaction decreases. In the chemical synthesis of polyaniline, persulfates (having an
oxidation potential of +2.01 V) are used most widely. However, experiments showed that aniline is also oxidized under the action of weak oxidants with a potential close to +1 V or even lower (Sapurina & Stejskal, 2012; Sapurina IY & Shishov MA). Such agents can oxidize aniline not only in basic and neutral
30 media, but also, strange as it may seem, in acidic media where potential barrier of
11

oxidation is high. However, the use of weak oxidants causes some problems because it does not necessary lead to the formation of conducting products.
[0028] Conducting polymer polyaniline have been synthesised by chemical
oxidative polymerization using oxide of a transition metal as a dopant. For
5 preparation of metal oxide doped polyaniline different molar ratio of monomer
like aniline was taken in aqueous solution. The monomer solution was then mixed
dopant. The polymerization was initiated by the drop wise addition of aqueous
solution of an oxidant. The polymerization was carried out at a temperature of 0-
5 ±1.0oC for a period of 6-8 h. The synthesized metal doped conducting polymer
10 was isolated from reaction mixture by filtration and washed with distilled water to
remove oxidant and oligomers, followed by drying in the vacuum oven a definite temperature ranged between 40-80oC.
Embodiments
15 [0029] In one embodiment of the invention, the monomer selected for study is
aniline.
[0030] In another embodiment of the invention, Vanadium (V) Oxide/ Vanadium pentoxide (V2O5) is dissolved in the reaction medium.
[0031] In another embodiment of the invention, the ammonium per sulphate
20 (APS) acts as oxidant used for the polymerization process.
[0032] In a yet another embodiment of the invention, the reaction medium for polymerization selected is aqueous and the like.
[0033] In a yet another embodiment of the invention, the oxidant such as
ammonium persulphate or potassium persulphate, ferric chloride and the like has
25 been used.
[0034] In a still another embodiment of the invention, the polymerization reaction condition was maintained at 0 to 5oC temperature.
12

[0035] In a still another embodiment of the invention, the ratio loading of Vanadium oxide metal ions in the polymeric matrix with respect to monomer was kept 1 to 1.
[0036] In a further embodiment of the invention, the content of oxidant to
5 monomer was kept between 0.1 moles to 0.1 moles.
[0037] In a further embodiment of the invention, the reaction time of polymerization was kept between 4-6 hours.
[0038] In a still further embodiment of the invention, the powder obtained after filtration was dried in vacuum oven at 50-60oC.
10 [0039] In a still further embodiment of the invention, the inhibiting performance
of metal doped polymer was evaluated by weight loss test and galvanostatic polarization curves (Tafel Plots).
[0040] The following examples are given to illustrate the process of the present
invention and should not be construed to limit the scope of the present invention.
15 However, the best mode requirement is served through the below example.
Example 1
Synthesis of Vanadium oxide doped Polyaniline
[0041] Conducting polymer polyaniline have been synthesised by chemical
20 oxidative polymerization using vanadium oxide (V2O5) as a dopant. For the
preparation of metal oxide doped polyaniline different molar ratio of monomer
such as 0.05 – 0.2 M aniline, preferably 0.1 M aniline was taken in aqueous
solution. The aniline monomer solution was then mixed with 0.05 – 0.2 M,
preferably 0.1 M vanadium oxide solution. The polymerization was initiated by
25 the drop wise addition of aqueous solution of 0.05 – 0.2 M, preferably 0.1 M
ammonium peroxydisulfate (APS) acting as an oxidant. The polymerization was
carried out at a temperature of 0-5 ± 1.0oC for a period of 6-8 h. The synthesized
13

metal doped conducting polymer was isolated from reaction mixture by filtration and washed with distilled water to remove oxidant and oligomers, followed by drying in the vacuum oven at 60oC. The prepared sample was designated as V2O5-PANI.
5 [0042] The corrosion protection performance study was carried out at room
temperature in aqueous solution 1.0 M HCl by using potentiodynamic polarization
technique. Experiments were carried in a conventional three electrode cell
assembly using Autolab Potentiostat/ Galvanostat, PGSTAT100 (Nova Software).
In three electrode cell assembly, pure iron of dimension 1 cm x 1 cm is taken as
10 working electrode, Pt as counter electrode and saturated calomel electrode (SCE)
as reference electrode.
Table 1: Tafel parameters for Mild Steel in 1.0 M HCl containing different concentration of inhibitor
15

Inhibitor’s name Inhibitor’s Ecorr icorr I.E (%)
concentration
---50 (Volts)
-7.7 -6.7 (μA/cm2)
590 305
Without inhibitor


--



69
V2O5-PANI 100 -5.5 255 75
150 -4.5 187 82
200 -3.3 103 95
14

Table 2: Weight loss study for Mild Steel in presence of inhibitors in 1.0
MHC1

Inhibitor's name Inhibitor cone, (ppm) Initial Weight of iron (mg)
before immersion Final weight
after immersion
(mg) Weight loss
(%)
Without inhibitor - 32350.5 19720.2 42.00
V2O5-PANI 50 32970.2 20770.6 39.11

100 32997.6 25995.6 22.70

150 34776.2 29637.6 16.55

200 32657.0 28741.5 14.15

100 32567.6 28336.3 13.77

150 32841.0 29832.5 11.25

200 33604.5 32507.3 2.90

We Claim:

A process for synthesizing conducting polymer of aniline comprising the steps of:
a) preparing aqueous solution of 0.05 - 0.2 M aniline monomer;
b) mixing said aqueous solution of aniline monomer oxide of a transition metal as a dopant;
c) adding dropwise aqueous solution of 0.1 M ammonium peroxydisulfate (APS) as an oxidant;
d) isolating said synthesized metal doped conducting polymer from reaction mixture by filtration; and
e) washing the resultant product with distilled water in order to remove oxidant and oligomers, followed by drying in the vacuum oven at 60°C.
The process as claimed in claim 1, wherein 0.1 aniline monomer is taken for the required preparation of aqueous solution.
The process as claimed in claim 1, wherein said dopant is 0.05 - 0.2 M vanadium (V) oxide, preferably 0.1 M vanadium (V) oxide.
The process as claimed in claim 1, wherein the polymerization is carried out at a temperature of 0-5 ±1.0°C for a period of 6-8 h.