Title of Invention

ANTI-CORROSIVE HYBRID SOL-GEL FILM ON METALLIC SUBSTRATES AND METHOD OF PRODUCING THE SAME

Abstract A method of preparing anti-corrosive hybrid sol-gel film coating on zinc or zinc alloy coated metallic substrates comprising the steps of preparing a mixture of sol-gel from hydrolisable silicon alkoxides, sodium venadate such as herein described solution combined with colloidal silica in a beaker and vigorously stirred; adding within 20 seconds of two separated phase formation between silica precursors and colloidal silica, acid selected from acetic acid and nitric acid which acts as a catalyzer to initiate hydrolysis reaction of silicon alkoxides and condensation reaction in the sol gel composition, continuously stirring the mixture for about 24 hours to form a single phase solution, applying the solution on cleaned zinc or zinc alloy coated metal substrates to form a transparent sol-gel coating film and drying the coated substrates at 50° to 200°C for 10 to 60 minutes.
Full Text FIELD OF THE INVENTION
The present invention relates to the development of sol-gel coating on metal
surface especially zinc alloys coated steel substrate, which provide a durable,
corrosion resistant, hydrophobic coating.
BACKGROUND OF THE INVENTION
The zinc and zinc alloy coatings are highly susceptible to corrosion and therefore
chromate passivation is usually applied directly after galvanizing in line to
enhance the corrosion protection properties of zinc and zinc alloy. This method
is widely applied as an effective and economical method of corrosion prevention.
However, chromate conversion coating contains hexavalent chromium which is
carcinogenic and they are environmentally and toxicologically hazardous.
Therefore, alternative coating development for protecting zinc and zinc alloys is a
growing need of industries.


In recent trend, thin organic protective coating formulation by sol-gel process
has found a most suitable alternative to chromate passivation. In sol-gel
method, small molecules can be converted into polymeric or ceramic materials
depending upon the monomers selection. Silance sol-gel chemistry consists
primarily of hydrolysis and condensation reactions of alkoxysilane precursors that
form macro- or nanoporous gel as the reaction proceed. The hydrolysis reaction
are typically catalyzed by base or acid conditions, producing partly or completely
hydrolyzed silanol and then condensation reaction occur to form siloxane bridge
resulting in a polymerization to form molecules of a glass-like oxide or ceramic
network.
US Patent No. 6162498, has described a sol-gel coating formulation consisted of
precursors methyltriethoxy silane, tetraethoxy silane, silica sol and then it was
catalysed by orthophosphoric acid addition. This coating gives colourless coating
formulation on cleaned substrate. However, this sol-gel formulation required
filtration prior to application on substrate. Furthermore, after coating
formulation, it started to become viscous and then became gel very fast.
Similarly the US Patent No. 6579472 has described the uses of triethylphosphate
as a preferable corrosion inhibitor but it was also not found suitable for zinc and
zinc alloy steel substate.


The present invention is aimed to develop a sol-gel coating formulations on
removing the above difficulties of prior art.
The present invention describes a sol-gel coating formulations which after
application on zinc and zinc alloy coated substrate enhances the corrosion
resistance properties of the substrate. The coating performance of the sol-gel
formulation is further enhanced by addition of inorganic compound, particularly
sodium metavanadate. The sol-gel coatings enhance the corrosion resistance as
well as give a hydrophobic surface characteristic on metal surface.
OBJECTS OF THE INVENTION
One objective of the invention is to develop an hybrid anti-corrosive sol-gel
coating to be applied in the zinc and zinc alloy substrates by preparing a
synergestic solution consisted of silicon alkoxides along with colloidal silica and
sodium metavenadate.
According to another objective of the invention zinc and zinc alloy substrate
samples are prepared on which the novel coating formulation is applied.


An yet another objective of the invention is to prepare a sodium venadate
solution separately to be added to sol-gel formulation to enhance the corrosion
resistance properties of sol-gel formulations.
A still another objective of the invention is to add acetic acid or dilute nitric acid
used as a catalyzer to initiate hydrolysis reaction of sol-gel solution.
DETAILED DESCRIPTION OF THE INVENTION
The proposed invention relates to development of an anti-corrosive sol-gel
formulation consisted of silicon alkoxides particularly Trimethoxymethylsilane,
Tetraethyl orthosilicate, ethyltriethoxysilane, methyltriethoxysilane and
Tetramethoxysilane, along with colloidal silica and sodium metavenadate. The
colloidal silica used in this formulation provides SiO2 particles of average particle
size less than 30 µm. The sodium metavenadate used in the formulation is first


made soluble in water and then added in required quantity in the sol-gel
formulation. The acetic acid or dilute nitric acid is used as an acid catalyser to
initiate hydrolysis reaction. Colloidal silica used in preparing the anticorrosive
composition has a nano particle silica sol of surface area 200 - 300 meter square
per gram and pH in the range of 8.5 - 10 thickness of the resulting sol-gel film is.
maintained between 1 µm to 10 µm.

According to the invention there is provided a method of preparing anti-corrosive
hybrid sol-gel film coating on zinc or zinc alloy coated metallic substrates
comprising the steps of preparing a mixture of sol-gel from hydrolisable silicon
alkoxides, sodium venadate solution combined with colloidal silica in a beaker
and vigorously stirred; adding within 20 seconds of two separated phase
formation between silica precursors and colloidal silica acetic acid or dilute nitric
acid as a catalizer to initiate hydrolysis reaction of silicon alkoxides and
condensation reaction in the sol gel composition, continuously stirring the
mixture for about 24 hours to form a single phase solution, applying the solution
on cleaned zinc or zinc alloy coated metal substrates to form a transparent sol-
gel coating film and drying the coated substrates at 50° to 200° C for 10 to 60
minutes.
Sample Preparation: The zinc and zinc alloy substrate commercially known as
galvanized and galvannealed materials respectively were used in the present
investigation. The galvanized material is a pure zinc coating where as the
galvannealed material is a zinc-iron alloy containing about 10 % iron in coating
formulation. The material was first alkali cleaned followed by washing under tap
water then further washed in demineralized water and dried. The substrate may
be further cleaned optionally by ultrasonically in an organic solvent such as
isopropanol.


Sodium vanadate solution preparation: 1.5. gm of sodium venadate
compound was added in 10 ml of distilled water. Sodium vanadate is insoluble in
water and therefore 1 drop of nitric acid was added under vigorous stirring
condition. The above solution was heated upto 50° C and kept under continuous
stirring till the sodium vanadate is completely dissolved in water. A light yellow
colour solution of sodium venadate was observed which is kept in a glass
container at ambient temperature. This sodium venadate solution was added in
appropriate amount in sol-gel formulation to enhance the corrosion resistance
properties of sol-gel formulation to enhance the corrosion resistance properties
of sol-gel formulation.
The proposed invention relating to preparations of sol-gel coating formulation is
illustrated in the following examples.
Example 1
A mixture of 30 ml of Trimethoxymethylsilane (TMMS) and 8 ml of Tetraethyl
orthosilicate (TEOS) combined in a beaker and with vigorous stirring 23 g of


colloidal silica (sigma Aldrich product, ludox AM 30 colloidal silica 30 wt %
suspension in water) was added. Initially, two phase separation was observed
between silica precursors and colloidal silica. Within 20 second of the colloidal
silica addition, 0.3 to 0.5 ml of acetic acid was added in the formulation. The
above solution was kept under stirring condition for about 24 hours and in this
time period the two phases disappear to become a single phase sol formulation.
This sol formulation was applied by dip coating process on zinc or zinc alloy
coated steel substrate. This gave a clear transparent sol-gel coating film. The
coated substrate was then dried in oven at 60 to 200° C for 20 to 30 minutes.
If required in the above sol formulation, viscosity may be reduced by adding
ehanol or methanol under stirring condition. This sol formulation is applied by
dip coating process on zinc or zinc alloy coated steel substrate to give a clear
transparent sol-gel coating film. The coated steel substrate is then oven dried at
60 to 70 degree centigrade for 20 to 30 minutes.


Example 2
A mixture of 30 ml of Trimethoxymethylsilane (TMMS) and 12 ml of Tetraethyl
orthosilicate (TEOS) combined in a beaker. Under vigorous stirring condition 16
gm of colloidal silica (sigma Aldrich product, ludox AM 30 colloidal silica 30 wt %
suspension in water) was added. Thereafter, 1 ml of sodium vanadate solution
was added in the above sol mixture. Acetic acid of 0.2 ml was added in the
formulation within 20 second of colloidal silica addition.
After 30 minutes of continuous stirring, again 1 ml of sodium vanadate solution
was added. The above solution was kept under stirring condition for about 20
hours and in this time period the two phases disappear to become a single phase
sol formulation. This sol formulation was applied by dip coating process on zinc
or zinc alloy coated steel substrate. This gave a clear transparent sol-gel coating
film. The coated substrate was then dried in oven at 60 to 100° C for 20 to 30
minutes.
If required the above sol formulation viscosity may be reduced by adding
methanol or ethanol under stirring condition. This sol formulation was applied by
dip coating process on zinc or zinc alloy coated steel substrate. This gave a clear
transparent sol-gel coating film. The coated substrate was then dried in oven at
60° to 100° C for 20 to 30 minutes.


The invention as herein described and illustrated should not be read and
construed in a restrictive manner as various adaptations, alterations and
modifications are possible within the scope and limit of the invention as defined
in the encompassed appended claims.

WE CLAIM:
1. A method of preparing anti-corrosive hybrid sol-gel film coating on zinc or
zinc alloy coated metallic substrates comprising the steps of preparing a
mixture of sol-gel from hydrolisable silicon alkoxides, sodium venadate
such as herein described solution combined with colloidal silica in a
beaker and vigorously stirred; adding within 20 seconds of two separated
phase formation between silica precursors and colloidal silica, acid
selected from acetic acid and nitric acid which acts as a catalyzer to
initiate hydrolysis reaction of silicon alkoxides and condensation reaction
in the sol gel composition, continuously stirring the mixture for about 24
hours to form a single phase solution, applying the solution on cleaned
zinc or zinc alloy coated metal substrates to form a transparent sol-gel
coating film and drying the coated substrates at 50° to 200°C for 10 to
60 minutes.
2. The method as claimed in claim 1, wherein the silicon alkoxides are
Trimethoxymethylsilane (TMMS) and Tetraethyl orthosilicate (TEOS),
Methyltriethoxysilane (MTES), Ethyltriethoxysilane (ETES) and
Tetramethoxysilane (TMOS) when added singular or in combination.
3. The method as claimed in claim 1, wherein colloidal silica is a nano
particle silica sol of surface area 200-300 meter square per gram and pH
of the colloidal silica is in range of 8.5 - 10.
4. The method as claimed in the preceding claims, wherein the said sol gel
film coating solution is prepared by mixing solutions of TMMS and TEOS,
combined with colloidal silica and vigorously stirred,

adding within 20 seconds of two separate phase formation in the mixture
of solutions acetic acid or dilute nitric acid acts as a catalyzer to initiate
hydrolysis reaction, continuously stirring the mixture for at least eight
hours to form a single phase solution, applying the resulted solution on
zinc or zinc alloy coated metal substrates and drying the substrate at
70°C.
5. The method as claimed in claim 1, wherein the ratio of total silanes
alkoxides to sodium vanadate solution are in a ratio of 100:1 to 100:10.
6. The method as claimed in claim 1, wherein the ratio of total si atoms in
silicone alkoxide to total Si atoms in the colloidal silica is in the ratio of
5:1 and 1:1.
7. The method as claimed in claim 1, wherein the metallic surface is zinc,
zinc alloy coated steel, the zinc and zinc alloy steel being galvanized and
galvannealed material respectively.
8. The method as claimed in claim 1, wherein the sol-gel coating is applied
on zinc or zinc alloy steel surface and subsequently dried at 50 to 200°C
for 10 to 60 minutes, wherein the thickness of the resulting sol-gel film is
maintained between 1µm to 10µm.
9. The method of preparing an anti-corrosive hybrid sol-gel film on metallic
substrate, as herein described and illustrated.


A method of preparing anti-corrosive hybrid sol-gel film coating on zinc or zinc
alloy coated metallic substrates comprising the steps of preparing a mixture of
sol-gel from hydrolisable silicon alkoxides, sodium venadate such as herein
described solution combined with colloidal silica in a beaker and vigorously
stirred; adding within 20 seconds of two separated phase formation between
silica precursors and colloidal silica, acid selected from acetic acid and nitric
acid which acts as a catalyzer to initiate hydrolysis reaction of silicon alkoxides
and condensation reaction in the sol gel composition, continuously stirring the
mixture for about 24 hours to form a single phase solution, applying the
solution on cleaned zinc or zinc alloy coated metal substrates to form a
transparent sol-gel coating film and drying the coated substrates at 50° to
200°C for 10 to 60 minutes.

Documents:

00304-kol-2007-correspondence-1.1.pdf

00304-kol-2007-form-1-1.1.pdf

0304-kol-2007 abstract.pdf

0304-kol-2007 assignment.pdf

0304-kol-2007 claims.pdf

0304-kol-2007 correspondence others.pdf

0304-kol-2007 description(complete).pdf

0304-kol-2007 form-1.pdf

0304-kol-2007 form-2.pdf

0304-kol-2007 form-3.pdf

304-KOL-2007-(29-11-2011)-FORM-27.pdf

304-kol-2007-abstract.pdf

304-kol-2007-amanded claims.pdf

304-kol-2007-amanded pages of specification.pdf

304-kol-2007-cancelled pages.pdf

304-kol-2007-correspondence.pdf

304-kol-2007-description (complete).pdf

304-kol-2007-examination report.pdf

304-kol-2007-form 1.1.pdf

304-kol-2007-form 1.pdf

304-kol-2007-form 18.pdf

304-kol-2007-form 2.pdf

304-kol-2007-form 3.pdf

304-kol-2007-form 5.1.pdf

304-kol-2007-form 5.pdf

304-kol-2007-gpa.pdf

304-kol-2007-granted-abstract.pdf

304-kol-2007-granted-claims.pdf

304-kol-2007-granted-description (complete).pdf

304-kol-2007-granted-form 1.pdf

304-kol-2007-granted-form 2.pdf

304-kol-2007-granted-specification.pdf

304-kol-2007-reply to examination report.pdf

304-kol-2007-reply to examination report1.1.pdf


Patent Number 247791
Indian Patent Application Number 304/KOL/2007
PG Journal Number 20/2011
Publication Date 20-May-2011
Grant Date 18-May-2011
Date of Filing 01-Mar-2007
Name of Patentee TATA STEEL LIMITED
Applicant Address RESEARCH AND DEVELOPMENT AND SCIENIFIC SERVICES DIVISION, JAMSHEDPUR
Inventors:
# Inventor's Name Inventor's Address
1 SINGH ,A.K. TATA STEEL LIMITED. RESEARCH AND DEVELOPMENT AND SCIENTIFIC SERVICES DIVISION, JAMSHEDPUR-831 001
2 NARAYAN, RAMANUJ TATA STEEL LIMITED. RESEARCH AND DEVELOPMENT AND SCIENTIFIC SERVICES DIVISION, JAMSHEDPUR-831 001
3 VERMA, ANIL KUMAR TATA STEEL LIMITED. RESEARCH AND DEVELOPMENT AND SCIENTIFIC SERVICES DIVISION, JAMSHEDPUR-831 001
4 BANDYOPADHYAY, N. TATA STEEL LIMITED. RESEARCH AND DEVELOPMENT AND SCIENTIFIC SERVICES DIVISION, JAMSHEDPUR-831 001
5 RANI, NITU TATA STEEL LIMITED. RESEARCH AND DEVELOPMENT AND SCIENTIFIC SERVICES DIVISION, JAMSHEDPUR-831 001
6 ROUT, TAPAN KUMAR TATA STEEL LIMITED. RESEARCH AND DEVELOPMENT AND SCIENTIFIC SERVICES DIVISION, JAMSHEDPUR-831 001
PCT International Classification Number G03G5/04
PCT International Application Number N/A
PCT International Filing date
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 NA