FIELD OF THE INVENTION:
The present invention relates to a novel polysiloxane compounds, which can be
used as corrosion resistance coating for the condenser tubes or more
particularly three silane compounds such as 1,2-Bis (Triethoxysilyl) Ethane
(Silane-I), Bis[3-(Triethoxysilyl) Propyl]Tetra Sulfide (Silane-II) and Bis[3-
(Triethoxysiyl)Propyl]Amine (Silane-III).
BACKGROUND & PRIOR ART OF THE INVENTION:
Patent No: WO2013029090 A1 (Application) describes Disclosed is a coating
composition comprising a bis-silane of Formula (l) (R7O)3Si-(CR3R4)m-X5-
C(X3)-X1-(CR1R2)1-X2-C(X4))-X6-(CR5R6)n-Si(OR8)3. The coating composition
can be used to form corrosion resistant coatings on metal articles, such as
aluminium or aluminium alloy containing articles.
Patent No:US2O140272420 A1 (Application) disclosed The disclosure relates to
curable polyepoxysilane compounds and compositions, methods related to
curing of such compounds via hydrolysis and/or condensation to form coatings
on a substrate, and coated articles formed from the curable polyepoxysilane
compounds. The polyepoxysilane compounds are silane functional precursors
and can be used as coatings (or pretreatments) on various substrates (e.g.,
metals such as aluminium) and provide a substantial improvement in corrosion
resistance relative to other anti-corrosion coatings.
Patent No: US20010032568 Al (Application) revealed the typical composition
which may include one or a mixture of silanes, such as methyltrimethoxysilane
and phenyltrimethoxysilane. The coating compositions may be formulated with
either acidic or basic catalysts, the latter being especially suitable for coating
steel substrates.
Patent No: US5270428 A (Granted) depicted Silane polymer coating
compositions which have excellent bonding properties for metallic surfaces and
which make such surfaces highly resistant to corrosion. The compositions are
formed by anhydrously reacting an epoxy trialkoxy silane with a primary amino
trialkoxy silane in a stoichiometric molar ratio which provides one epoxy group

for reaction with each primary amino hydrogen site to form the silane polymer
coating composition.
Patent No: US6827981A (Granted) described a method of treating a metal
surface by application of a solution containing at least one vinyl silane and at
least one bis-silyl aminosilane.
As a result of corrosion and erosion, condenser tubes degrade during course of
time which leads to untimely tube failure along with drastically fall in and
thermal efficiency. The prevailing protective measures are either eddy current
testing and plugging or retubing. Although eddy current testing with plugging
of degraded tubes is less expensive than retubing, but this is only a stop-gap
measure and cannot work for a longer time. Plugging can cause side effects
such as reduction in the heat rate efficiency, changes in flow pattern and
increased velocities, and can make re-tubing efforts difficult if solid plugs are
used. Most utilities replace condenser tubes when they reach this point at a
very high cost. Scheduling tube replacement without sacrificing service is often
difficult.
Coatings of the tube is one of the identified alternative to re-tubing. Coatings
with epoxy, polyurethane and other organic materials is being propagated by
some manufacturers. However, it is reported that epoxy, polyurethane and
other organic coatings are degraded by thermal and photo induced oxidation
and are subject to chemical attack.
Hence, there is always a long felt need to develop a suitable coating which can
substantially improve the heat transfer efficiency and prevent corrosion and
provides long life span to the tubes.
The present invention meets the long-felt need.
SUMMARY OF THE INVENTION:
A novel polysiloxane mixture for coating the condenser tubes comprises of three
silane compounds such as 1,2-Bis (Triethoxysilyl) Ethane (Silane-I), Bis[3-

(Triethoxysilyl) Propyl] Tetra Sulfide (Silane-II) and Bis[3-(Triethoxysiyl)
Propyl]Amine (Silane-III) in alcohol solution individually or in combination.
OBJECTS OF THE INVENTION:
It is therefore, the primary object of the present invention to provide novel
polysiloxane coating for the condenser tubes made up of copper alloys, which
can substantially enhance the heat transfer efficiency and prevent corrosion.
Another the object of the present invention to provide novel polysiloxane
coating to the condenser tubes, which are highly active and ale to form bonds
not only with metal and with metal oxides of the heat transfer surface of tubes
as well.
Yet another object of the present invention to provide a coating on condenser
tubes, which has thickness for filing micro cavities to a depth of upto about
2000 nanometers.
Further object of the present invention to provide a coating on condenser tubes,
whose surfaces are non-adherent to deposition of soils and microorganisms and
hence can efficiency present biofouling.
Another object of the present invention to provide a coating on condenser
tubes, which can alternative to retubing and the longer life span of condenser
tubes. i.e., upto five years.
Yet another object of the present invention to provide a coating on condenser
tubes, which provides corrosion inhibition efficiencies from 35% to 96%.
Further object of the present invention to provide a coating on condenser tubes,
which can efficiency provides physical barriers for intrusion of water and
dissolved corrosive species.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWING:
It is to be noted, however, that the appended drawings illustrate only typical
embodiments of the present subject matter and are therefore not to be
considered for limiting of its scope, for the invention may admit to other equally

effective embodiments. The detailed description is described with reference to
the accompanying figures. Some embodiments of system or methods in
accordance with embodiments of the present subject matter are now described,
by way of example, and with reference to the accompanying figures, in which:
Figure 1 illustrates Tafel plots of Admiralty brass
Figure 2 illustrates Impedance plots of Admiralty brass
Figure 3 illustrates Impedance plots of Admiralty brass
Figure 4 illustrates Tafel plots of Cupro-Nickel (70:30)
Figure 5 illustrates Impedance plots of Cupro-Nickel (70:30)
Figure 6 illustrates Impedance plots of Cupro-Nickel (90:10)
Figure 7 illustrates Tafel plots of Cupro-Nickel (90:10)
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS:
The present subject matter relates to a novel silane coatings or more
particularly polysiloxane coatings for condenser tubes, which uses heat
exchangers to substantially enhance the heat transfer efficiency and offer
effective physical barrier for intrusion of water and dissolved corrosive species
and thereby prevent or inhibit corrosion substantially.
Mainly three silane compounds such as 1,2-Bis (Triethoxysilyl) Ethane (Silane-
I), Bis [3-(Triethoxysilyl) Propyl]Tetra Sulfide (Silane-II) and Bis [3-(Triethoxysiyl)
Propyl] Amine (Silane-III) are provided which are suitable for coating of the
condenser tubes, made up of copper alloys such as Admiralty brass, Cupro-
Nickel (90:10) and Cupro-Nickel (70:30).
All the silanes are dissolved in alcohol solution such as methanol, ethanol and
isopropanol in specified concentration (99.9% (v/v) purity).
The pH of the solution is suitably adjusted with the glacial acetic acid.
The ratio of components in silane mixture is silane:isopropanol:water :: 2:5:93
(v/v).

The pH of silane I and silane III was adjusted to 4.5 to 5 and 7.5 to 8
respectively with glacial acetic acid.
The silane II solution was prepared by dissolving the same in methanol and
water mixture. The ratio of components in silane II mixture is silane
II:methanol:water :: 2:8:90 (v/v).
The silane coating I compositions are highly active and will form bonds not only
with the metal but also with metal oxides of the heat transfer surfaces.
Thereby, a parallel heat transfer pathway is formed which greatly improves the
long term efficiency of the heat exchangers.
Silane solutions were coated on the copper alloy sample.
The alloys such as admiralty brass, Cu-Ni (70/30) and Cu-Ni (90/10) were cut
and mounted in Teflon (PTFE).
Copper rod threaded in to the specimen acts as electrical connector. The
specimens were polished to the finest with emery paper started with grade-l to
grade-5 and then cleaned with alcohol and acetone.
Electrochemical studies have been conducted using electrochemical system
supplied by CH Instruments, USA. Platinum rod is used as a counter electrode
and saturated calomel electrode is used as a reference electrode. Admiralty
brass and cupro-nickel alloy specimens were used as working electrodes. The
electro chemical cell supplied along with the instrument is used for all the
studies. Equipment specific software has been used in the study of corrosion
rates and impedance measurements.
The specimens are immersed in silane solutions for 2 minutes and then dried
at Oven for 1 hr. After that, all specimens were put in desiccator for curing for
24 hrs. Tafel experiments and impedance studies were conducted for all the
specimens in 3.5% (w/w) NaCl solution. The solution is taken in the electro
chemical 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 m Hz to 100 k Hz were
applied to the specimen at the corrosion potentials. Tafel Polarisation and
Impedance plots were obtained for at the specimens immersed in different
Silane solutions.
The coated samples were evaluated by electrochemical techniques like Tafel
polarization, Impedance technique etc in 3.5% sodium chloride solution.
Figure 1 illustrates the Tafel plot of admiralty brass.
Figure 2 and 3 both discloses the graphical results of Impedance plots of
admiralty brass.
RESULTS AND DISCUSSSION
The experimental results in terms of corrosion rate, percentage inhibition,
corrosion current, polarization resistance of three silane compounds are
provided in Table 1.


Further, the figure 4 and 5 represents the experimental data graphically for the
alloys Cupro nickel (70:30).
Figure 6 and 7 also illustrate the graphical representation of Impedance plots
and Tafel plots of Cupro-nickel (90:10).
The results are presented in the table and the anodic and cathodic polarization
curves are shown in Figs respectively. It is seen that both anodic and cathodic
current densities have been largely reduced after the silane deposition
compared to the bare copper alloy specimens showing the inhibitive effect of the
silane film. It is also noted that both ECorr and the shape of the curves have not
changed much. This indicates that the silane film performs as a physical
barrier rather than a chemical barrier on the copper alloy specimen. The
electrochemical tests showed that the silane layer ensures a good barrier effect
against water and oxygen.
The applied coating thickness may be of the order of nano metre which would
will fill micro cavities to a depth of up to about 2000 nanometers. The coated
heat transfer surfaces are non-adherent to deposition of soils and
microorganisms and, therefore prevents biofouling also. Condenser tube
coating with silane can be an effective, alternative to retubing, and can extend
the lifetime of condenser up to five years. Organic upper layer of Polysiloxane
coatings are largely inorganic in nature and are more resistant to degradation
mechanisms for three principal reasons:
i) The bond strength of Si-O in the Polysiloxanes is 108 kcal/mole
whereas the bond strength of C-C bond in the Organic coatings is
approximately 83 kcal/mole. Thus, the Si-O bonds are much stronger in
polysiloxane coatings providing greater stability and superior resistance to
weathering and thermal degradation.
ii) The bonds in siloxanes are about 50% ionic in character and are
readily hydrolyzed, especially when catalyzed by acid or base.

iii) Each silicon is bonded to two to three oxygen atoms in the
Polysiloxanes. Therefore, oxidative degradation may not occur in the
polysiloxane coatings like in organic coatings.
Silane films are transparent and colourless. In most cases, silanes need to be
hydrolyzed in their diluted aqueous solutions before application. After
hydrolysis, silane solutions become "workable" as a sufficient number of active
silanols (SiOH) are generated. In the process of silane surface treatment of
metals, silane solutions are applied onto metal surfaces by dipping, spraying
and wiping, and followed by drying in air. The silane molecules initially form
hydrogen bonds between silanols (SiOH) from the silane solution and metal
hydroxyls (MeOH) from the metal surface hydroxides, and between SiOH groups
themselves. Upon heating or drying, these hydrogen bonds are condensed via
the following two reactions.
SiOH (solution) + MeOH (metal surface) = SiOMe (interface) + H2O (1)
And
SiOH (solution) + SiOH (solution) = SiOSi (silane film) + H2O (2)
Reaction (1) occurs at the silane/metal interface, forming covalent
metallosiloxane bonds (MeOSi). In general, a protective silane system should
possess the following two favourable properties. First, the silane film should
anchor to the substrate tightly by the formation of covalent bonds at the
interface via the condensation of SiOH groups in the silane solution. It is
believed that the higher the density of Silanol bonds formed at the interface, the
stronger the interfacial adhesion will be between silane films and the substrate.
The formation of a highly cross-linked SiOSi network through the condensation
reaction among SiOH groups according to Reaction (2) gives appreciable
thickness.
Since SiOSi units are hydrophobic in nature, a large number of so-formed
SiOSi units are thus expected to contribute to the hydrophobicity of the silane
system. On the other hand, a highly cross-linked SiOSi network possesses a
small porosity, which also hinders water Penetration.

The minimum to maximum corrosion inhibition efficiencies observed in all the
cases is 35 % to 96% o. In this, a protective silane film should be characteristic
of a highly cross-linked SiOSi network embedded with hydrophobic organic
substituent. Such a film is expected to offer an effective physical barrier for the
intrusion of water and dissolved corrosive species.
In accordance with another embodiment of out of silane compounds silane II
can be considered as most efficient coating with highest inhibition efficiencies.
Bis-sulfur silane is not as condensed as bis-amino silane, but it swells less in
water because of the hydrophobic nature of bridging group. By contrast, bis-
amino film is more hydrophilic since the secondary amine group form hydrogen
bonds with water. Bis-sulfur silane deposited is more porous and absorbs more
water. Bis-sulfur silane provides an adequate barrier to water penetration.
From graphical repreparation of impedance values this is also confirmed.

WE CLAIM:
1. A novel polysiloxane mixture for coating the condenser tubes comprises of
three silane compounds such as 1,2-Bis (Triethoxysilyl) Ethane (Silane-I),
Bis[3-(Triethoxysilyl) Propyl] Tetra Sulfide (Silane-II) and Bis[3-(Triethoxysiyl)
Propyl]Amine (Silane-III) in alcohol solution individually or in combination.
2. A method of preparing the silane compounds as claimed in claim 1,
comprises the steps of:
Dissolving the silane compounds in alcohol in specified concentration (2% v/v)
(please give the concentration);
adjustment of pH in a particular range with glacial acetic acid (99.5% v/v);
(kindly let us have the concentration of this acid)
applying the silane solution on the condenser tubes.
3. The polysiloxane mixture as claimed in claim 1, wherein the alcohols can be
selected from methanol, ethanol and isopropanol.
4. The polysiloxane mixture as claimed in claim 1, wherein the ratio of silane,
isopropanol and water is 2:5:93 (v/v).
5. The polysiloxane mixture as claimed in claim 1, wherein the composition of
silane II solution comprises of silane II, methanol and water in ratio of 2:8:90
(v/v).
6. The method of preparing the silane compounds as claimed in claim 2,
wherein the pH of silane I and II mixture is 4.5 to 5 and silane III is 7.5 to 8.
7. A method of applying the coating made up of the silane mixtures as claimed
1 comprises the steps of:
immersion of the copper tubes in silane solution for TWO minutes;
subjected to drying for ONE hour;
putting the specimens in a desiccator for 24 hours and after that
subjected to different experiments into an electrochemical cell to measure the
corrosion inhibiting values of the copper tubes.

8. The method of preparing the silane mixtures as claimed in claim 2, wherein
the condenser tubes are made up of such as admiralty brass Cu:Ni alloys
which further has composition of Cu:Ni::90:10 and Cu:Ni::70:30.
9. The method of applying the coating made up of the silane mixtures as
claimed in claim 7, wherein the experimentation covers Tafel experiment and
impedance technique in 3.5%.
10. The method of applying the coating made up of the silane mixtures as
claimed in claim 7, wherein the specimen is taken in 3.5% (W/W) NaCl
solution.