Description:TECHNICAL FIELD
The present disclosure relates to the field of electroplating. Particularly, the present disclosure
relates to electroplating compositions comprising zinc and aluminium nanoparticles, methods
of preparing them, a direct current method of depositing these electroplating compositions on
steel substrates and steel substrates obtained 5 therefrom.
BACKGROUND OF THE DISCLOSURE
Hot dip galvanised (zinc coating) steel is the most popular coated steel product used in
automotive segment. The conventional zinc coating can be modified to zinc alloy coatings to
10 further improve the corrosion resistance properties. Electrodeposition technology offers higher
flexibility than hot dip technology to coat steel with a variety of zinc alloys which can offer a
higher corrosion resistance along with a better control over coating thickness (much lower
thickness is possible), superior surface finish and possibility of only one-sided coating.
However, there is a lot of scope to introduce special functionalities in the coating as demanded
15 by the automotive segments. At present, the functionalities like self-passivation and selflubrication
properties are achieved through an additional inorganic or organic coating over and
above the zinc metallic coating.
In earlier works, Zn has been studied for manufacturing metal matrix composite coatings with
20 reinforcements in terms of oxides, nitrides, polymeric particles and carbonaceous
incorporations. Zn along with other metal matrix based composite coatings has been studied in
terms of the design of the deposition line for shaped components. Metallic matrix of Ag, Au,
Cu, Co, Cr, Ni, Fe, Pb, Pd, Pt, Rh, Ru, Sn, V, W and Zn with alloying elements selected from
C, P, S and Si with oxide powders of Al, Co, Cu, In, Mg, Ni, Si, Sn, V, and Zn; nitrides of Al,
25 B and Si; C (graphite or diamond); carbides of B, Cr, Bi, Si, W; and organic materials such as
PTFE and polymer spheres have been studied. Properties like wear resistance, corrosion
resistance, abrasion resistance, and the like, materials such as silicon carbide, aluminium oxide,
tungsten carbide, titanium carbide, zirconium oxide, boron carbide, chromium carbide, iron
oxide, thorium oxide, uranium oxide, rare earth oxides, or diamonds and for lubrication
30 molybdenum disulphide have been studied through DC deposition.
Metallic particles especially aluminium (Al) could be an interesting category of material that
can be used as reinforcements for composite coatings to improve corrosion resistance
3
properties. Al may be added to the plating bath as nanoparticles, and further co-deposited with
a metal or alloy matrix. However, the main challenge for incorporation of Al reinforcement
particles in the coating is the dispersion and stability of these Al particles in the electroplating
bath. Nanoparticles have a high specific surface area; hence they tend to agglomerate and settle
down in the bath. Various studies have been carried out to study the dispersion 5 of Aluminium
oxides (Al2O3) particles with and without surfactants but no study was found on Al particles
incorporation as metal due to the aforementioned challenges.
Therefore, there is a need in the art to provide a comprehensive coating solution where
10 multifunctional requirements (e.g., self-passivation and self-lubrication that are currently
achieved through an additional inorganic or organic coating over and above the zinc metallic
coating) of the automotive industry can be achieved through a single coating system using
Aluminium reinforcement particles. The present disclosure attempts to address this need.
15 STATEMENT OF THE DISCLOSURE
The present disclosure relates to an electroplating composition comprising zinc sulphate in an
amount of about 200-300 g/L, zinc chloride in an amount of about 5-8 g/L, boric acid in an
amount of about 22-35 g/L, and aluminium nanoparticles in an amount of about 1-10 g/L,
wherein the electroplating composition has a pH of about 3.5.
20
The present disclosure also relates to a method for preparing the electroplating composition
described herein, comprising: a) adding zinc sulphate, zinc chloride, and boric acid to
demineralized water followed by stirring to prepare an electrolyte solution; b) adding
aluminium nanoparticles to a portion of the electrolyte solution followed by stirring and
25 ultrasonication for about 1-1.5 hours to obtain an ultrasonicated solution; c) mixing the
ultrasonicated solution with remaining portion of the electrolyte solution to obtain a second
solution; and d) stirring the second solution for about 20-30 hours followed by ultrasonication
to obtain the electroplating composition.
30 The present disclosure also provides a method for depositing the electroplating composition
described herein on a steel substrate, comprising: a) providing the steel substrate as a cathode;
and b) depositing the electroplating composition on the steel substrate at a constant current
with a current density of about 170-190 mA/cm2 and at a stirring rate of about 250-350 rpm to
provide a steel substrate comprising a zinc-aluminium (Zn-Al) composite coating.
4
The present disclosure further relates to a steel substrate comprising the Zn-Al composite
coating deposited by the method described herein.
BRIEF DESCRIPTION OF THE ACCOMPANYING FIGURES
Figure 1 shows the transmission electron microscopy (TEM) and X-ray 5 diffraction (XRD)
analysis of Al particles.
Figure 2 shows Gallic acid non-compatibility in Zn electrolyte.
10 Figure 3 shows TEA compatibility in Zn electrolyte.
Figure 4 shows the Zeta potential of Al nano particles with varying concentrations of
surfactants.
15 Figure 5 shows a schematic of an exemplary method of preparing the electroplating
composition without surfactant.
Figure 6 shows a schematic of an exemplary method of preparing the electroplating
composition containing surfactant.
20
Figure 7 shows the corrosion properties and morphology of physically dispersed Zn-Al DC
composite coating.
Figure 8 shows the corrosion properties of anionic dispersed Zn-Al composite coating.
25 Figure 9 shows the corrosion properties of cationic dispersed Zn-Al composite coating.
Figure 10 shows the top surface and cross-section morphologies of anionic (SDS) and cationic
(TEA) dispersed Zn-Al coatings.
30 Figure 11 shows SST results for Zn-Al DC composite coatings (rinsed).
Figure 12 shows the SST results for pure Zn coating.
5
Figure 13 shows the SST results of rinsed Zn-Al composite coating with anionic dispersion
(SDS).
DETAILED DESCRIPTION OF THE DISCLOSURE
With respect to the use of substantially any plural and/or singular terms herein, 5 those having
skill in the art can translate from the plural to the singular and/or from the singular to the plural
as is appropriate to the context and/or application. The various singular/plural permutations
may be expressly set forth herein for sake of clarity. The use of the expression “at least” or “at
least one” suggests the use of one or more elements or ingredients or quantities, as the use may
10 be in the embodiment of the disclosure to achieve one or more of the desired objects or results.
Throughout this specification, the word “comprise”, or variations such as “comprises” or
“comprising” or “containing” or “has” or “having”, or “including but not limited to” wherever
used, will be understood to imply the inclusion of a stated element, integer or step, or group of
elements, integers or steps, but not the exclusion of any other element, integer or step, or group
15 of elements, integers or steps.
Reference throughout this specification to “some embodiments”, “one embodiment”, “an
embodiment”, “some exemplary embodiments”, “some preferred embodiments”, or “some
non-limiting embodiments” means that a particular feature, structure or characteristic described
20 in connection with the embodiment may be included in at least one embodiment of the present
disclosure. Thus, the appearances of the phrases “in some embodiments”, “in one
embodiment”, “in an embodiment”, “in some exemplary embodiments”, “in some preferred
embodiments”, or “in some non-limiting embodiments”, in various places throughout this
specification may not necessarily all refer to the same embodiment. It is appreciated that certain
25 features of the disclosure, which are, for clarity, described in the context of separate
embodiments, may also be provided in combination in a single embodiment. Conversely,
various features of the disclosure, which are, for brevity, described in the context of a single
embodiment, may also be provided separately or in any suitable sub-combination.
30 As used herein, the term “electroplating composition” refers to an electroplating bath
comprising electrolytes (Zn salts) and aluminium nanoparticles. In some embodiments, the size
of the nanoparticles ranges from about 30 nm to about 50 nm, including values and ranges
6
thereof, for example, about 30 nm, about 32 nm, about 34 nm, about 36 nm, about 38 nm, about
40 nm, about 42 nm, about 44 nm, about 46 nm, about 48 nm, or about 50 nm.
The term “about” as used herein encompasses variations of +/-5% and more preferably +/-
2.5%, as such variations are appropriate for practicing the 5 present invention.
The present disclosure provides electroplating compositions for depositing Zn-aluminium (Zn-
Al) coatings on steel substrates. The electroplating compositions of the present disclosure
provide a single coating solution for steel substrates and obviate the need of additional organic
10 or inorganic coatings that are currently employed to provide various functionalities. Further,
the present disclosure provides an improved method for preparing electroplating compositions
comprising zinc salts and aluminium nanoparticles that enables proper dispersion of aluminium
in the electroplating composition. The present disclosure also provides methods for
depositing/electroplating said compositions on steel substrates by a direct current (DC) method.
15 The coatings of the present disclosure show improved corrosion resistance.
In some embodiments, the present disclosure provides an electroplating composition
comprising zinc sulphate in an amount of about 200-300 g/L, including values and ranges
therebetween; zinc chloride in an amount of about 5-8 g/L, including values and ranges
20 therebetween; boric acid in an amount of about 22-35 g/L, including values and ranges
therebetween; and aluminium nanoparticles in an amount of about 1-10 g/L, including values
and ranges therebetween, wherein the electroplating composition has a pH of about 3.5.
For example, in some embodiments, the electroplating composition comprises zinc sulphate in
25 an amount of about 200-300 g/L, about 220-270 g/L, about 240-280 g/L, about 210-260 g/L,
about 240-260 g/L, about 250-290 g/L, about 270-300 g/L, about 200 g/L, about 210 g/L, about
220 g/L, about 230 g/L, about 240 g/L, about 250 g/L, about 260 g/L, about 270 g/L, about 280
g/L, about 290 g/L or about 300 g/L, including values and ranges therebetween; zinc chloride
in an amount of about 5-7 g/L, about 5 g/L, about 5.2 g/L, about 5.4 g/L, about 5.6 g/L, about
30 5.8 g/L, about 6 g/L, about 6.2 g/L, about 6.4 g/L, about 6.6 g/L, about 6.8 g/L, about 7 g/L,
about 7.2 g/L, about 7.4 g/L, about 7.6 g/L, about 7.8 g/L or about 8 g/L, including values and
ranges therebetween; boric acid in an amount of about 22-35 g/L, about 30-35 g/L, about 22-
30 g/L, about 25-29 g/L, about 22 g/L, about 23 g/L, about 24 g/L, about 25 g/L, about 26 g/L,
7
about 27 g/L, about 28 g/L, about 29 g/L, about 30 g/L, about 31 g/L, about 32 g/L, about 33
g/L, about 34 g/L, or about 35 g/L, including values and ranges therebetween; and aluminium
nanoparticles in an amount of about 1-10 g/L, about 1-2.5 g/L, about 5-10 g/L, about 1-5 g/L,
about 2-7 g/L, about 4-8 g/L, about 1 g/L, about 2 g/L, about 2.5 g/L, about 3 g/L, about 4 g/L,
about 5 g/L, about 6 g/L, about 7 g/L, about 8 g/L, about 9 g/L, or about 5 10 g/L, including
values and ranges therebetween.
In some non-limiting embodiments, the electroplating composition of the present disclosure
comprises zinc sulphate in an amount of about 250 g/L, zinc chloride in an amount of about 6
10 g/L, boric acid in an amount of about 30 g/L, and aluminium nanoparticles in an amount of
about 1-10 g/L.
In some non-limiting embodiments, the electroplating composition of the present disclosure
comprises aluminium nanoparticles in an amount of 5 g/L.
15
Accordingly, in some exemplary, non-limiting embodiments, the electroplating composition of
the present disclosure comprises zinc sulphate in an amount of about 250 g/L, zinc chloride in
an amount of about 6 g/L, boric acid in an amount of about 30 g/L and aluminium nanoparticles
in an amount of 5 g/L.
20
In some embodiments, aluminium nanoparticles are pre-treated with a surfactant prior to
mixing them with the rest of the electrolyte components (zinc sulphate, zinc chloride, and boric
acid) to enhance dispersion of the nanoparticles in the composition. The surfactant employed
in the present disclosure can be a non-ionic, cationic, or an anionic surfactant.
25
Accordingly, in some embodiments, the electroplating composition of the present disclosure
comprises a surfactant selected from triethanolamine (TEA) or sodium dodecyl sulphate (SDS).
In some embodiments of the present disclosure, the electroplating composition comprises TEA
30 in an amount of about 0.01-0.1 g/L, including values and ranges therebetween.
For example, in some embodiments, TEA is present in an amount of about 0.01-0.1 g/L, about
0.01-0.05 g/L, about 0.05-0.1 g/L, about 0.03-0.09 g/L, about 0.02-0.07 g/L, about 0.01 g/L,
8
about 0.02 g/L, about 0.03 g/L, about 0.04 g/L, about 0.05 g/L, about 0.06 g/L, about 0.07 g/L,
about 0.08 g/L, about 0.09 g/L or about 0.1 g/L, including values and ranges therebetween.
In some exemplary, non-limiting embodiments of the present disclosure, TEA is present in an
amount of about 0.1 g/L.
5
Accordingly, in some embodiments, the present disclosure provides an electroplating
composition comprising zinc sulphate in an amount of about 200-300 g/L, including values
and ranges therebetween as described above; zinc chloride in an amount of about 5-8 g/L,
including values and ranges therebetween as described above; boric acid in an amount of about
10 22-35 g/L, including values and ranges therebetween as described above; aluminium
nanoparticles in an amount of about 1-10 g/L, including values and ranges therebetween as
described above; and TEA in an amount of about 0.01-0.1 g/L, including values and ranges
therebetween as described above; and wherein the electroplating composition has a pH of about
3.5.
15
In some non-limiting embodiments, the present disclosure provides an electroplating
composition comprising zinc sulphate in an amount of about 250 g/L, zinc chloride in an
amount of about 6 g/L, boric acid in an amount of about 30 g/L, aluminium nanoparticles in an
amount of about 1-10 g/L and TEA in an amount of about 0.1 g/L.
20
In some non-limiting embodiments, the present disclosure provides an electroplating
composition comprising zinc sulphate in an amount of about 250 g/L, zinc chloride in an
amount of about 6 g/L, boric acid in an amount of about 30 g/L, aluminium nanoparticles in an
amount of 10 g/L and TEA in an amount of about 0.1 g/L.
25
In some embodiments, the electroplating composition comprises about 250 g/L zinc sulphate,
about 6 g/L zinc chloride, about 30 g/L boric acid, and about 10 g/L aluminium nanoparticles
pre-treated with about 0.1 g/L TEA.
30 In some embodiments of the present disclosure, the electroplating composition comprises SDS
in an amount of about 1.2-1.4 g/L, including values and ranges therebetween.
For example, in some embodiments SDS is present in an amount of about 1.2 g/L, about 1.22
g/L, about 1.24 g/L, about 1.25 g/L, about 1.26 g/L, about 1.28 g/L, about 1.3 g/L, about 1.32
9
g/L, about 1.34 g/L, about 1.36 g/L, about 1.38 g/L, or about 1.4 g/L, including values and
ranges therebetween.
In some exemplary, non-limiting embodiments of the present disclosure, SDS is present in an
amount 5 of about 1.25 g/L.
Accordingly, in some embodiments, the present disclosure provides an electroplating
composition comprising zinc sulphate in an amount of about 200-300 g/L, including values
and ranges therebetween as described above; zinc chloride in an amount of about 5-8 g/L,
10 including values and ranges therebetween as described above; boric acid in an amount of about
22-35 g/L, including values and ranges therebetween as described above; aluminium
nanoparticles in an amount of about 1-10 g/L, including values and ranges therebetween as
described above; and SDS in an amount of about 1.2-1.4 g/L, including values and ranges
therebetween as described above; and wherein the electroplating composition has a pH of about
15 3.5.
Accordingly, in some non-limiting embodiments, the present disclosure provides an
electroplating composition comprising zinc sulphate in an amount of about 250 g/L, zinc
chloride in an amount of about 6 g/L, boric acid in an amount of about 30 g/L, aluminium
20 nanoparticles in an amount of about 1-2.5 g/L and SDS in an amount of about 1.25 g/L.
Accordingly, in some non-limiting embodiments, the present disclosure provides an
electroplating composition comprising zinc sulphate in an amount of about 250 g/L, zinc
chloride in an amount of about 6 g/L, boric acid in an amount of about 30 g/L, aluminium
25 nanoparticles in an amount of 1 g/L and SDS in an amount of about 1.25 g/L.
In some embodiments, the electroplating composition comprises about 250 g/L zinc sulphate,
about 6 g/L zinc chloride, about 30 g/L boric acid, and about 1 g/L aluminium nanoparticles
pre-treated with about 1.25 g/L SDS.
30
Also provided herein is a method of preparing the electroplating compositions of the present
disclosure.
10
The main challenge for incorporation of Al reinforcement particles in the coating is its
dispersion and stability in the electroplating bath. Nanoparticles have a high specific surface
area; hence they tend to agglomerate and settle down in the bath. The specific order of steps in
preparing the electrolytic composition of the present disclosure allows proper dispersion of the
aluminium nanoparticles in the bath. Particularly, the inventors found 5 that if aluminium
nanoparticles are first treated with a small volume of electrolyte comprising Zn salts and boric
acid (concentrated emulsion), the particles get a chance to interact with a small volume of the
operating environment and to get adjusted with the same.
10 Further, for the compositions comprising a surfactant, the inventors found that if aluminium
nanoparticles are first emulsified by treating with a small volume of a surfactant solution
followed by treating with a small volume of the electrolyte comprising Zn salts and boric acid
(concentrated emulsion), the particles get a chance to interact with a small volume of the
operating environment and to get adjusted with the same. When these pre-treated aluminium
15 nanoparticles are added to the remaining electrolyte, it is found that the aluminium particles
are dispersed well in the bath and they do not agglomerate and settle down.
Figure 5 shows an exemplary flowchart of the method steps for preparing the electroplating
composition of the present disclosure where a surfactant is not added to the compositions.
20 Figure 6 shows an exemplary flowchart of the method steps for preparing the electroplating
composition of the present disclosure where a surfactant is added to the compositions.
In some embodiments, the method for preparing the electroplating composition of the present
disclosure comprises the steps of:
25 a. adding zinc sulphate, zinc chloride, and boric acid to demineralized water followed by
stirring to prepare an electrolyte solution;
b. adding aluminium nanoparticles to a portion of the electrolyte solution followed by
stirring and ultrasonication for about 1-1.5 hours to obtain an ultrasonicated solution;
c. mixing the ultrasonicated solution with a remaining portion of the electrolyte solution
30 to obtain a second solution; and
d. stirring the second solution for about 20-30 hours followed by ultrasonication to obtain
the electroplating composition.
11
The above method allows a uniform physical dispersion of the aluminium nanoparticles in the
electroplating composition by treating the aluminium nanoparticles to a small portion of an
electrolyte solution, such as about 200-300 mL or about 250 mL of the electrolyte solution
followed by stirring and ultrasonication for about 1-1.5 hours before mixing the aluminium
nanoparticles into the remaining portion of the electrolyte and then making 5 up the volume.
In some embodiments of the present disclosure, the electrolyte solution is obtained by stirring
zinc sulphate, zinc chloride, and boric acid in demineralized water, for about 1-1.5 hours,
including values and ranges therebetween, for example, for about 1 hour, about 1.1 hours, about
10 1.2 hours, about 1.3 hours, about 1.4 hours or about 1.5 hours.
In some embodiments of the present disclosure, pH of the electrolyte solution is adjusted to
about 3.5.
15 In some embodiments of the present disclosure, the aluminium nanoparticles and the portion
of the electrolyte solution are stirred and ultrasonicated for about 1-1.5 hours, including values
and ranges therebetween, for example, for about 1 hour, about 1.1 hours, about 1.2 hours, about
1.3 hours, about 1.4 hours or about 1.5 hours.
20 In some non-limiting embodiments of the present disclosure, once the aluminium nanoparticles
are added to the portion of the electrolyte solution, the pH is adjusted to about 3.5 followed by
stirring the solution for about 15-20 minutes, including values and ranges therebetween,
followed by ultrasonication for about 1 hour to obtain the ultrasonicated solution.
25 The ultrasonicated solution is mixed with the remaining portion of the electrolyte solution, such
as about 200-300 mL or about 250 mL of the electrolyte solution, to obtain a second solution.
The second solution is stirred overnight, such as for about 20-30 hours, followed by
ultrasonication to obtain the electroplating composition.
30 In some embodiments, the second solution is stirred for about 20-30 hours, including values
and ranges therebetween, for example, for about 20 hours, about 21 hours, about 22 hours,
about 23 hours, about 24 hours, about 25 hours, about 26 hours, about 27 hours, about 28 hours,
about 29 hours, or about 30 hours, including values and ranges therebetween.
12
In non-limiting embodiments of the present disclosure, the second solution is stirred for about
24 hours, followed by ultrasonication for about 30 minutes to obtain the electroplating
composition.
In some embodiments, the stirring step in the method of the present disclosure is carried out at
a rate of about 250-350rpm, including values and ranges therebetween, for 5 example at about
250-300 rpm, at about 300-350 rpm, at about 270-320 rpm, at about 290-340 rpm, about 250
rpm, about 260 rpm, about 270 rpm, about 280 rpm, about 290 rpm, about 300 rpm, about 310
rpm, about 320 rpm, about 330 rpm, about 340 rpm, or about 350 rpm.
In some embodiments, the ultrasonication in the method of the present disclosure is carried out
10 at a frequency of about 15-25 kHz, including values and ranges therebetween, for example, at
about 15 kHz, about 16 kHz, about 17 kHz, about 18 kHz, about 19 kHz, about 20 kHz, about
21 kHz, about 22 kHz, about 23 kHz, about 24 kHz, or about 25 kHz.
In some embodiments of the present disclosure, pH is adjusted by H2SO4 to 3.5.
In some embodiments, the method for preparing the electroplating composition of the present
15 disclosure comprises steps of:
a. adding zinc sulphate, zinc chloride, and boric acid to demineralized water
followed by stirring for about 1-1.5 hours and adjusting the pH to prepare an
electrolyte solution;
b. adding aluminium nanoparticles to a portion of the electrolyte solution and
20 adjusting the pH followed by stirring and ultrasonication for about 1-1.5 hours,
including values and ranges therebetween, to obtain an ultrasonicated solution;
c. mixing the ultrasonicated solution with remaining portion of the electrolyte
solution to obtain a second solution; and
d. stirring the second solution for about 20-30 hours, including values and ranges
25 therebetween, followed by ultrasonication for about 30 minutes to obtain the
electroplating composition.
For compositions comprising a surfactant, the inventors found that when the particles are first
emulsified in a surfactant solution prepared in water, the particles get a chance to interact with
30 surfactants by modifying the particle surface and to get adjusted with the same. When this
emulsion is treated with a small volume of the electrolyte comprising Zn salts and boric acid
13
(concentrated emulsion) followed by treating with the remaining electrolyte, it is found that the
aluminium particles are dispersed better and they do not agglomerate and settle down.
Accordingly, in some embodiments, the method of preparing the electroplating compositions
of the present disclosure comprises first adding the aluminium nanoparticles 5 to a surfactant
solution followed by stirring and ultrasonication to obtain an ultrasonicated aluminium
particles solution, which is then added to the portion of the electrolyte solution.
In some embodiments of the present disclosure, the surfactant solution is prepared by adding
10 the surfactant to demineralized water followed by heating the demineralized water to about 30-
40°C, including values and ranges therebetween, and stirring to provide the surfactant solution.
In some embodiments of the present disclosure, the surfactant is TEA or SDS.
In some embodiments of the present disclosure, the surfactant containing demineralized water
15 is heated to about 30°C, about 31°C, about 32°C, about 33°C, about 34°C, about 35°C, about
36°C, about 37°C, about 38°C, about 39°C or about 40°C.
Accordingly, the present disclosure provides a method of preparing the electroplating
compositions of the present disclosure comprising steps of:
20 a. adding zinc sulphate, zinc chloride, and boric acid to demineralized water
followed by stirring to prepare an electrolyte solution;
b. adding a surfactant to demineralized water followed by heating the
demineralized water to about 30-40°C, including values and ranges
therebetween, and stirring to provide a surfactant solution;
25 c. adding aluminium nanoparticles to the surfactant solution followed by stirring
and ultrasonication for about 1-1.5 hours to obtain an ultrasonicated aluminum
particles solution;
d. adding the ultrasonicated aluminium particles solution to a portion of the
electrolyte solution followed by stirring to obtain a second solution;
30 e. mixing the second solution with remaining portion of the electrolyte solution to
obtain a third solution; and
f. stirring the third solution for about 20-30 hours, including values and ranges
therebetween, followed by ultrasonication to obtain the electroplating
composition.
14
An exemplary flowchart of this method is shown in Figure 6. This method allows chemical
dispersion of the aluminium nanoparticles in the electroplating composition as it is aided by a
surfactant.
In some embodiments, the electrolyte solution is obtained by stirring zinc sulphate, zinc
chloride, and boric acid in demineralized water (DM), such as about 500 mL 5 of DM water, for
about 1-1.5 hours, including values and ranges therebetween, for example, for about 1 hour,
about 1.1 hours, about 1.2 hours, about 1.3 hours, about 1.4 hours or about 1.5 hours.
In some embodiments, a surfactant solution is prepared by adding the surfactant such as TEA
or SDS to DM water, such as about 100-250 mL of DM water, followed by heating the DM
10 water to about 30-40°C and stirring at about 300 rpm to obtain the surfactant solution. The pH
of the surfactant solution may be adjusted at this step, if required. Aluminium nanoparticles are
added to the surfactant solution followed by stirring and ultrasonication to obtain an aluminium
nanoparticles solution.
After adding the aluminium nanoparticles, the surfactant solution is stirred for about 20-30
15 minutes and ultrasonicated for about 1-1.5 hours, including values and ranges therebetween,
for example, for about 1 hour, about 1.1 hours, about 1.2 hours, about 1.3 hours, about 1.4
hours or about 1.5 hours.
In some non-limiting embodiments, once the aluminium nanoparticles are added to the
surfactant solution, the solution is stirred for about 20 minutes, followed by ultrasonication for
20 about 1 hour and the pH is adjusted may be adjusted to about 3.5 (if required) to obtain an
ultrasonicated aluminium particles solution.
In some embodiments of the present disclosure, once the ultrasonicated aluminium particles
solution is added to a portion of the electrolyte solution, such as about 250 mL of the electrolyte
solution, the pH is adjusted and stirred for about 30 minutes to obtain the second solution.
25 The second solution is mixed with the remaining portion of the electrolyte solution to obtain a
third solution.
In some embodiments of the present disclosure, the third solution is stirred for about 20-30
hours, including values and ranges therebetween, for example, for about 20 hours, about 21
hours, about 22 hours, about 23 hours, about 24 hours, about 25 hours, about 26 hours, about
30 27 hours, about 28 hours, about 29 hours, or about 30 hours, including values and ranges
therebetween.
15
In non-limiting embodiments of the present disclosure, the third solution is stirred for about 24
hours, volume and pH of the solution are adjusted, followed by ultrasonication for about 30
minutes to obtain the electroplating composition.
In some embodiments of the present disclosure, pH is adjusted by H2SO4 to 3.5.
5
Accordingly, in some embodiments, a method for preparing the electroplating compositions of
the present disclosure comprises the steps of:
a. adding zinc sulphate, zinc chloride, and boric acid to demineralized water
followed by stirring for about 1-1.5 hours and adjusting the pH to prepare an
10 electrolyte solution;
b. adding a surfactant to demineralized water followed by heating the demineralized
water to about 30-40°C, including values and ranges therebetween, stirring and
adjusting the pH to provide a surfactant solution;
c. adding aluminium nanoparticles to the surfactant solution followed by stirring and
15 ultrasonication for about 1-1.5 hours and optionally adjusting the pH to obtain an
ultrasonicated aluminum particles solution;
d. adding the ultrasonicated aluminium particles solution to a portion of the
electrolyte solution, adjusting the pH followed by stirring to obtain a second
solution;
20 e. mixing the second solution with remaining portion of the electrolyte solution to
obtain a third solution; and
f. stirring the third solution for about 20-30 hours, including values and ranges
therebetween, adjusting the pH and solution volume, followed by ultrasonication
to obtain the electroplating composition.
25 In some embodiments, the method for preparing the electroplating compositions of the present
disclosure comprises the steps of:
a. adding zinc sulphate, zinc chloride, and boric acid to demineralized water followed
by stirring for about 1-1.5 hours and adjusting the pH to prepare an electrolyte
solution;
30 b. adding a surfactant to demineralized water followed by heating the demineralized
water to about 30-40°C, including values and ranges therebetween, stirring and
adjusting the pH to provide a surfactant solution;
16
c. adding aluminium nanoparticles to the surfactant solution followed by stirring for
about 20 minutes and ultrasonication for about 1 hour and optionally adjusting the
pH to provide an ultrasonicated aluminum particles solution;
d. adding the ultrasonicated aluminium particles solution to a portion of the
electrolyte solution, adjusting the pH followed by stirring for about 5 30 minutes to
provide a second solution;
e. mixing the second solution with remaining portion of the electrolyte solution to
obtain a third solution; and
f. stirring the third solution for about 24 hours, adjusting the pH and solution volume,
10 followed by ultrasonication for about 30 minutes to obtain the electroplating
composition.
In the methods of the present disclosure, stirring is carried out to dissolve components into DM
water. The duration of stirring can vary for different steps. For dissolution of Zn salts and boric
15 acid to prepare an electrolyte solution, stirring is carried out for 60-120 minutes, including
values and ranges therebetween, such as about 60-100 minutes, or about 60-90 minutes, about
60 minutes, about 70 minutes, about 80 minutes, about 90 minutes, about 100 minutes, about
110 minutes, or about 120 minutes.
20 After addition of aluminium nanoparticles into a small portion of the electrolyte solution or
into a surfactant solution, the nanoparticles are mixed by stirring for about 15-30 minutes,
including values and ranges therebetween, such as about 15-25 minutes, about 20-30 minutes,
about 15 minutes, about 20 minutes, or about 30 minutes.
25 For compositions comprising the surfactant, when the ultrasonicated surfactant solution
comprising aluminium nanoparticles is mixed with a small portion of the electrolyte solution,
the contents are stirred for about 20-40 minutes or for about 30 minutes.
For both compositions – compositions without a surfactant and compositions with a surfactant
30 - once the nanoparticles containing solution is added to the main electrolyte solution, the
volume of the solution is made to a total desired volume, and then this volume-adjusted solution
is stirred overnight such as for about 20-30 hours, about 20-28 hours, about 20-24 hours, about
20 hours, about 24 hours, or about 30 hours.
17
In some embodiments, the ultrasonication in the method of the present disclosure is carried out
at a frequency of about 15-25 kHz, including values and ranges therebetween, for example, at
about 15 kHz, about 16 kHz, about 17 kHz, about 18 kHz, about 19 kHz, about 20 kHz, about
21 kHz, about 22 kHz, about 23 kHz, about 24 kHz, or about 25 kHz.
5
In the methods of the present disclosure, ultrasonication is carried out i) after addition of the
aluminium nanoparticles to a small portion of the electrolyte solution or after addition of the
aluminium nanoparticles to the surfactant solution and ii) after overnight stirring step.
10 For ultrasonication after addition of the aluminium nanoparticles to a small portion of the
electrolyte solution or after addition of the aluminium nanoparticles to the surfactant solution,
it is carried out for about 60-80 minutes, including values and ranges therebetween, for
example, about 60 minutes, about 70 minutes, or about 80 minutes.
15 For ultrasonication performed after overnight stirring step, it is carried out for about 10-40
minutes, including values and ranges therebetween, for example, about 20-40 minutes, about
30-40 minutes, about 10 minutes, about 15 minutes, about 20 minutes, about 25 minutes, about
30 minutes, about 35 minutes, or about 40 minutes.
20 The present disclosure also provides a method for depositing the electroplating compositions
described herein on steel substrates to provide substrates with a coating comprising zinc-based
matrix reinforced with aluminium nanoparticles. This coating is referred to herein as a zincaluminium
(Zn-Al) composite coating. In some embodiments, the electroplating composition
is deposited using a direct current (DC) method.
25
In some embodiments, the method for depositing the electroplating composition on a steel
substrate, comprises:
a. providing the steel substrate as a cathode; and
b. depositing the electroplating composition on the steel substrate at a constant
30 current with a current density of about 170-190 mA/cm2 and at a stirring rate of
about 250-350 rpm to provide a steel substrate comprising a zinc-aluminium (Zn-
Al) composite coating.
18
In some embodiments, the current density employed in the DC method of deposition is about
170, 175, 180, 185, or 190 mA/cm2, including values and ranges thereof. In some embodiments,
the current density employed in the DC method of deposition is about 175-185 mA/cm2,
including values and ranges thereof. In an exemplary embodiment, the current density for the
DC deposition is 5 about 180 mA/cm2.
In some embodiments, the electroplating composition is deposited on the steel substrate at a
stirring rate of about 250-350 rpm, including values and ranges therebetween, for example at
about 250-300 rpm, at about 300-350 rpm, at about 270-330 rpm, at about 290-340 rpm, at
10 about 260-310 rpm, about 250 rpm, about 260 rpm, about 270 rpm, about 280 rpm, about 290
rpm, about 300 rpm, about 310 rpm, about 320 rpm, about 330 rpm, about 340 rpm or about
350pm. In an exemplary embodiment, the stirring rate for the DC deposition is about 300 rpm.
In some embodiments, an electroplating composition comprising about 250 g/L zinc sulphate,
15 about 6 g/L zinc chloride, about 30 g/L boric acid, and about 5 g/L aluminium nanoparticles
and having a pH of about 3.5 is deposited on a steel substrate at a current density of about 180
mA/cm2 and a stirring rate of about 300 rpm to provide a steel substrate comprising a Zn-Al
composite coating.
20 In some embodiments, an electroplating composition comprising about 250 g/L zinc sulphate,
about 6 g/L zinc chloride, about 30 g/L boric acid, about 1 g/L aluminium nanoparticles and
about 1.25 g/L SDS and having a pH of about 3.5 is deposited on a steel substrate at a current
density of about 180 mA/cm2 and a stirring rate of about 300 rpm to provide a steel substrate
comprising a Zn-Al coating.
25
In some embodiments, an electroplating composition comprising about 250 g/L zinc sulphate,
about 6 g/L zinc chloride, about 30 g/L boric acid, about 10 g/L aluminium nanoparticles and
about 0.1 g/L TEA and having a pH of about 3.5 is deposited on a steel substrate at a current
density of about 180 mA/cm2 and a stirring rate of about 300 rpm to provide a steel substrate
30 comprising a Zn-Al coating.
The inventors found that the electroplating compositions of the present disclosure when
deposited by a direct current provide a coating with corrosion properties superior to the pure
19
Zn coating and in some embodiments, with corrosion properties superior to the commercial
Zn-Ni coating with a passivation (shown as “benchmark” coating in Figures 7-9 and 11-12).
In some embodiments of the present disclosure, the Zn-Al composite coating provided by the
method described herein exhibits a corrosion rate of about 0.02-0.05 mm/year, 5 including values
and ranges therebetween, for example, about 0.02 mm/year, about 0.03 mm/year, about 0.04
mm/year or about 0.05 mm/year.
In some embodiments of the present disclosure, the electroplating composition comprising
10 about 250 g/L zinc sulphate, about 6 g/L zinc chloride, about 30 g/L boric acid, and about 5
g/L aluminium nanoparticles and having a pH of about 3.5, when deposited by the method
described herein provides a Zn-Al coating exhibiting a corrosion rate of about 0.03 mm/year.
In some embodiments of the present disclosure, the electroplating composition comprising
15 about 250 g/L zinc sulphate, about 6 g/L zinc chloride, about 30 g/L boric acid, and about 1
g/L aluminium nanoparticles treated with about 1.25 g/L of SDS and having a pH of about 3.5,
when deposited by the method described herein provides a Zn-Al coating exhibiting a corrosion
rate of about 0.04 mm/year.
20 In some embodiments of the present disclosure, the electroplating composition comprising
about 250 g/L zinc sulphate, about 6 g/L zinc chloride, about 30 g/L boric acid, and about 10
g/L aluminium nanoparticles treated with about 0.1 g/L of TEA and having a pH of about 3.5,
when deposited by the method described herein provides a Zn-Al coating exhibiting a corrosion
rate of about 0.02 mm/year.
25
In some embodiments of the present disclosure, the Zn-Al composite coating provided by the
method described herein exhibits a corrosion current density of about 1.9-2.4 μA/cm2,
including values and ranges therebetween, for example about 1.9 μA/cm2, about 1.95 μA/cm2,
about 2.0 μA/cm2, about 2.1 μA/cm2, about 2.2 μA/cm2, about 2.3 μA/cm2, about 2.35 μA/cm2,
30 or about 2.4 μA/cm2.
In some embodiments of the present disclosure, the electroplating composition comprising
about 250 g/L zinc sulphate, about 6 g/L zinc chloride, about 30 g/L boric acid, and about 5
g/L aluminium nanoparticles and having a pH of about 3.5, when deposited by the method
20
described herein provides a Zn-Al coating exhibiting a corrosion current density of about 1.95
μA/cm2.
In some embodiments of the present disclosure, the electroplating composition comprising
about 250 g/L zinc sulphate, about 6 g/L zinc chloride, about 30 g/L boric 5 acid, and about 1
g/L aluminium nanoparticles treated with about 1.25 g/L of SDS and having a pH of about 3.5,
when deposited by the method described herein provides a Zn-Al coating exhibiting a corrosion
current density of about 2.35 μA/cm2.
10 In some embodiments of the present disclosure, the Zn-Al composite coating provided by the
methods described exhibits a corrosion potential of about -0.8 to -0.9 V, including values and
ranges therebetween, for example, about -0.8 V, about -0.81 V, about -0.82 V, about -0.83 V,
about -0.84 V, about -0.85 V, about -0.86 V, about -0.869 V, about -0.87 V, about -0.88 V,
about -0.89 V or about -0.9 V.
15
In some embodiments of the present disclosure, the electroplating composition comprising
about 250 g/L zinc sulphate, about 6 g/L zinc chloride, about 30 g/L boric acid, and about 1
g/L aluminium nanoparticles treated with about 1.25 g/L of SDS and having a pH of about 3.5,
when deposited by the method described herein provides a Zn-Al coating exhibiting a corrosion
20 potential of about -0.869 V.
In some embodiments of the present disclosure, the Zn-Al composite coating provided by the
methods described herein exhibits a Salt Spray Test (SST) 5% Red Rust life of about 200 hours
or more, such as about 200-350 hours, about 200-320 hours, or about 250-350 hours, including
25 values and ranges therebetween.
In some embodiments of the present disclosure, the electroplating composition comprising
about 250 g/L zinc sulphate, about 6 g/L zinc chloride, about 30 g/L boric acid, and about 1
g/L aluminium nanoparticles treated with about 1.25 g/L of SDS and having a pH of about 3.5,
30 when deposited by the method described herein provides a Zn-Al coating exhibiting a Salt
Spray Test 5% Red Rust life of more than 300 hours, such as about 312 hours.
21
The present disclosure also provides a steel substrate comprising a zinc-aluminium (Zn-Al)
composite coating.
In some embodiments, the steel substrate comprises a zinc-aluminium (Zn-Al) composite
coating, wherein the coating comprises about 1.5-5.2% by weight of aluminium, 5 including
values and ranges therebetween. For example, in some embodiments, the steel substrate
comprises a Zn-Al composite coating comprising about 2.6-4.9, about 2.6-4.3, about 1.5, about
1.54, about 2.5, about 2.54, about 2.64, about 2.78, about 3, about 3.28, about 3.5, about 3.7
about 4, about 4.23, about 4.28, about 4.82, about 5, about 5.1 or about 5.2 percent by weight
10 of aluminium.
It is to be understood that the foregoing descriptive matter is illustrative of the disclosure and
not a limitation. While considerable emphasis has been placed herein on the particular features
of this disclosure, it will be appreciated that various modifications can be made, and that many
15 changes can be made in the preferred embodiments without departing from the principles of
the disclosure. Those skilled in the art will recognize that the embodiments herein can be
practiced with modification within the spirit and scope of the embodiments as described herein.
Similarly, additional embodiments and features of the present disclosure will be apparent to
one of ordinary skill in art based upon description provided herein.
20
Descriptions of well-known/conventional methods/steps and techniques are omitted so as to
not unnecessarily obscure the embodiments herein. Further, the disclosure herein provides for
examples illustrating the above-described embodiments, and in order to illustrate the
embodiments of the present disclosure certain aspects have been employed. The examples used
25 herein for such illustration are intended merely to facilitate an understanding of ways in which
the embodiments herein may be practiced and to further enable those of skill in the art to
practice the embodiments herein. Accordingly, the following examples should not be construed
as limiting the scope of the embodiments herein.
30 EXAMPLES
Example 1: Characterization of aluminium nanoparticles
Aluminium (Al) particles were characterised through transmission electron microscopy (TEM)
and X-ray diffraction (XRD) as shown in Figure 1 to check the particle size, agglomeration
tendency and diffraction pattern. The particle size was analysed through TEM and found to be
22
in the range of 30-50 nm. The phase of Al particles was analysed through X-ray diffraction
(XRD) and detected to have a crystalline structure.
Example 2: Determination of surfactants to be used
After a thorough search for surfactants, the most common surfactants in cationic, 5 anionic and
non-ionic ranges, namely: gallic acid (non-ionic surfactant), cetyl trimethyl ammonium
bromide (CTAB) and TEA (cationic surfactants) and SDS (anionic surfactant) were selected
to understand the dispersing of the nano particles.
These surfactants were studied for the compatibility in a composition of sulphate-based Zn
10 electrolyte comprising zinc sulphate, zinc chloride and boric acid, having a pH of about 3.5 by
Hull Cell Studies. Among these surfactants, gallic acid was found to be incompatible with the
electrolyte as shown in Figure 2 whereas CTAB was discarded due to very high foaming. TEA
(Figure 3) and SDS were found to be compatible with the electrolyte in the presence of the
metallic ions. These two surfactants were taken forward for the zeta potential studies with Al
15 particles in desired pH range.
Example 3: Zeta Potential Measurement
Al reinforcement particles were first studied for physical dispersion tendency through zeta
potential measurement in 100 ml of Demineralized (DM) water in a range of pH from 3 to 12
20 at 1% concentration i.e., with 1 g/l of particles. It is always suggested to have a zeta value more
than ±30 mV to have better dispersion of the particles. The Zn electroplating bath employed in
these experiments had a pH of 3.5. It was observed that Al has zeta potential more +30 mV at
3.5 pH making it very well dispersed in physical dispersion. Cationic surfactant such as TEA
was taken for chemical dispersion whereas SDS was considered for anionic dispersion in the
25 working range of pH as shown in Figure 4. It was observed that beyond 0.1 g/L of TEA, desired
zeta potential was achieved, which with further increase in the concentration of the same, did
not improve, but instead created foaming disturbances in DM water. The best zeta potential
results were obtained with an SDS concentration of 1.25 g/l as seen in Figure 4.
30
23
Example 4: Preparation of the electroplating composition
(a) Electroplating Composition without Surfactant
The electroplating bath/compositions containing electrolyte salts (250 g/L zinc sulphate, 6 g/L
zinc chloride, 30 g/L boric acid) and 1, 2.5, 5, or 10 g/L Al nanoparticles were prepared as
shown in Figure 5. To 500 ml/L of demineralized water, boric acid, zinc 5 sulphate, and zinc
chloride were added; the solution was stirred for about 1 to 1.5 hours; and the pH was adjusted
to obtain the main electrolyte. 250 ml of the main electrolyte was taken in a separate beaker
and stirring was continued for the rest of the electrolyte. Al particles were added to 250 ml of
the main electrolyte, the pH was adjusted to 3.5 and the solution was stirred for 15-20 minutes
10 followed by ultrasonication for 1 hour. The ultrasonicated solution was added to the rest of the
electrolyte. The whole solution was stirred overnight and the stirring was continued for 24
hours. After 24 hours, the solution was ultrasonicated for 30 minutes to obtain the
electroplating composition containing dispersed Al particles. The particle dispersion was
achieved through self/physical dispersion, ultrasonication and magnetic stirring.
15
(a) Electroplating Composition with Surfactant
Figure 6 depicts the method for preparing the electroplating bath/composition of the present
disclosure containing electrolyte salts (250 g/L zinc sulphate, 6 g/L zinc chloride, 30 g/L boric
acid), 1-10 g/L Al nanoparticles and surfactant (TEA or SDS).
20 (i) Preparation of Electroplating Composition with TEA as Surfactant
TEA was added to about 100-250 ml of demineralized water depending on the solubility of the
surfactant and the pH was adjusted to 3.5. The water was heated to 30-40℃ and stirred at 300
rpm to dissolve the surfactant and the pH was adjusted. The entire amount of Al nanoparticles
was added to the surfactant solution and the solution was stirred for about 20 minutes. The Al
25 containing surfactant solution was ultrasonicated for about 1 hour and the pH was adjusted, if
required, to obtain the ultrasonicated TEA solution containing 0.1 g/L of TEA and 1, 2.5, 5, or
10 g/L Al.
To 500 ml/L of demineralized water, boric acid, zinc sulphate, and zinc chloride were added;
30 the solution was stirred for about 1 to 1.5 hours; and the pH was adjusted to obtain the main
electrolyte. 250 ml of the main electrolyte was taken in a separate beaker and stirring was
continued for the rest of the electrolyte. The ultrasonicated Al containing surfactant solution
was added to 250 ml of the main electrolyte, the pH was adjusted to 3.5 and the solution was
stirred for 30 minutes. The rest of the electrolyte was added to the ultrasonicated Al containing
24
surfactant solution. The volume of the solution was adjusted to 1 L, pH was adjusted to 3.5 and
the stirring was continued for 24 hours. After 24 hours, the solution was ultrasonicated for 30
minutes to obtain the electroplating composition. The Al particle dispersion was achieved
through the TEA treatment of Al nanoparticles, ultrasonication and magnetic stirring.
5
(ii) Preparation of Electroplating Composition with SDS as Surfactant
SDS was added to about 100-250 ml demineralized water depending on the solubility of the
surfactant and the pH was adjusted to 3.5. The water was heated to 30-40℃ and stirred at 300
rpm to dissolve the surfactant and the pH was adjusted. The entire amount of Al nanoparticles
10 was added to the surfactant solution and the solution was stirred for about 20 minutes. The Al
containing surfactant solution was ultrasonicated for about 1 hour and the pH was adjusted, if
required, to obtain the ultrasonicated SDS solution containing 1.25 g/L of SDS and 1, 2.5, 5,
or 10 g/L Al.
15 To 500 ml/L of demineralized water, boric acid, zinc sulphate, and zinc chloride were added;
the solution was stirred for about 1 to 1.5 hours; and the pH was adjusted to obtain the main
electrolyte. 250 ml of the main electrolyte was taken in a separate beaker and stirring was
continued for the rest of the electrolyte. The ultrasonicated Al containing surfactant solution
was added to 250 ml of the main electrolyte, the pH was adjusted to 3.5 and the solution was
20 stirred for 30 minutes. The rest of the electrolyte was added to the ultrasonicated Al containing
surfactant solution. The volume of the solution was adjusted to 1 L, pH was adjusted to 3.5 and
the stirring was continued for 24 hours. After 24 hours, the solution was ultrasonicated for 30
minutes to obtain the electroplating composition. The Al particle dispersion was achieved
through the SDS treatment of Al nanoparticles, ultrasonication and magnetic stirring.
25
Example 5: Dispersion Studies of the Al particles in the Electrolyte/Electroplating
Composition
To understand the dispersion of the particles in the electrolyte, the hydrodynamic diameter was
measured for the surfactants’ combinations. Hydrodynamic diameter is actually the particle in
30 the dispersing medium with a coat of surfactant molecule and the ions present on top of it.
Lesser the diameter indicates better dispersion for the particles. By this strategy, the surfactants
showed an excellent reduction in the diameter of the Al nano particles in DM water as shown
in Table 1 below. When introduced into the ionic medium of electrolytes, they showed a slight
increase in the diameter due to metallic ion accumulation on top.
25
Table 1: Hydrodynamic diameters of Al particles with different surfactants
Example 6: Determination of the Stirring and Ultrasonication Conditions
The duration and sequences of stirring and ultrasonication were decided by 5 the hydrodynamic
diameter ranges of Al particles in electrolyte. It is suggested that with a very high
hydrodynamic diameter, the particles go to a stage of settling down from electrolyte. After
thorough agitation either by magnetic stirring or ultrasonication, the agglomerates of these
particles break down to small segments, thus tending towards a situation called dispersion state
10 where the particles remain suspended. To have a better electroplating medium, it is better as
the particle get more dispersed. But after more agitation, these hydrodynamic particle sizes
reduce further. Due to this, the particles get out of the dispersed state and go into the
flocculation state where these particles create a muddy mixture which get separated out from
the dispersing medium floating on top of it. To avoid both the settling down and flocculating
15 up states, it is important to find a condition at which the hydrodynamic diameters are such that
the Al particles get to the dispersed state keeping the particles suspended in the medium. Tables
2 and 3 below show the variation of hydrodynamic diameters (nm) of Al particles surface
treated with SDS and TEA respectively, in Zn electrolyte with the variation of agitation type
and time.
26
Table 1: Hydrodynamic diameter (nm) of Al particles with SDS in Zn electrolyte
Table 2: Hydrodynamic diameter (nm) of Al particles with TEA 5 in Zn electrolyte
Example 7: Direct current (DC) deposition of Zn-Al coating
The Electroplating compositions of the present disclosure were prepared as shown in Example
4. These compositions were further deposited on steel substrates using direct current. The
10 CRCA steel substrate was used as a cathode and pure Zn (99.5% pure) was used as an anode.
Prior to deposition, the steel samples were degreased to remove surface oil and then dipped in
27
a dilute HCl solution to remove any oxide film which might be present. The samples were
rinsed in distilled water and the deposition was carried out. The electroplating compositions
were deposited on the steel substrate at a constant current with a current density of 180 mA/cm2
and at a stirring rate of about 300 rpm to provide the steel substrate comprising a zinc-Al (Zn-
Al) composite coating. During deposition, the electrolyte was stirred at a constant 5 rate of 300
rpm using a magnetic stirrer. The current was supplied through a potentiostat. After
plating/deposition, the coated samples were rinsed with distilled water and dried.
Example 8: Characterization of the Zn-Al composite coating
10 The concentration of the Al nanoparticles in the electrolyte was varied from 1 to 10 g/l and the
corrosion resistance properties of the composite coatings were studied. For a physical
dispersion composition (i.e., a composition where a surfactant was not added), it was observed
that at 5 g/l Al, DC coatings showed excellent corrosion properties (Figure 7). The
corresponding top surface morphologies along with the Al content in the coating is shown in
15 the right panel of Figure 7. It can be observed through the cross-section morphologies that the
Al particles got incorporated into the coating. It was observed that without any additive or
secondary coatings, only Al particles embedded in the metallic matrix were able to improve
the corrosion properties compared to a pure Zn coating. The data point in Figure 7 shown as
Zn (additive) refers to a bath containing Zn salts and an additive such as Benzylidene acetone
20 (BA).
Zn-Al composite coatings were further studied by preparing an anionic dispersion (SDS of 1.25
g/l) and a cationic dispersion (TEA of 0.1 g/l) in Figures 8 and 9 respectively. Anionic
dispersion showed that at lower concentration of Al particles, the corrosion properties were
better, with the best corrosion properties shown at 1 g/L of Al (Figure 8). Whereas, for cationic
25 dispersion, the corrosion properties remained in a good range for all the concentrations of Al
particles tried out, with the best corrosion properties shown at 10 g/L of Al (Figure 9).
The top surface morphologies for the best combination for DC parameters are shown in Figure
10. It was observed that anionic dispersion (SDS) of Al had reduced the grain size of the deposit
with a good incorporation of Al particles into the coating as visible in the cross-section.
30 Cationic dispersion (TEA) showed bigger grain size of the deposited Zn layer, but more
compact and dense deposit compared to the variant without surface treatment (as shown in
Figure 7). Clear indication of particle incorporation is visible from the cross-sectional
morphology of the coating.
28
From the above results, the coatings were upscaled from 20 cm2 samples in 500ml/L bath
volume to 100 cm2 samples in 5/10 L bath volume with air agitation. The 100 cm2 samples
were exposed to SST chambers to further check the self-passivation properties of the composite
coatings. Figures 11 shows the SST results for all the dispersion strategies of Zn-Al DC
composite 5 coatings.
For pure Zn, the red rust hour was found to be 48 to 72 hours as shown in Figure 12. Physical
dispersion did not have much impact on the red rust hours and similarly, cationic dispersion
with TEA was also not found to improve the red rust hours much. Among all the dispersion
routes, anionic dispersion with SDS for a 3-5 μm thick coating showed maximum red rust
10 resistance with Al nano particles (Figure 13), of 312 hours with 5% red rust coverage on top
surface on consecutive three samples as per the ASTM B117.
Table 4 below shows all the combinations tried for Zn-Al composite coating system via both
physical dispersion and chemical dispersion.
Coating compositions Strategy
Thickness
(μm)
Al concentration
(%)
SST red
rust hours
Pure Zn
Rinsed
3.26 - 72
Pure Zn+BA (0.15 g/l) 3.76 - 96
Zn-Al (5 g/l)-BA (0.15 g/l) 3.48 2.64±1.86 48
Zn-Al (10 g/l)-TEA (0.01 g/l) 3.78 4.28±2.73 48
Zn-Al (1 g/l)-SDS (1.25 g/l) 3.48 2.78±0.06 312
Table 3: SST results along with the coating thickness and particle concentration , Claims:We Claim:
1. An electroplating composition comprising zinc sulphate in an amount of about 200-300
g/L, zinc chloride in an amount of about 5-8 g/L, boric acid in an amount of about 22-35
g/L, and aluminium nanoparticles in an amount of about 1-10 g/L, wherein the
electroplating composition has 5 a pH of about 3.5.
2. The electroplating composition as claimed in claim 1, wherein zinc sulphate is present in
an amount of about 250 g/L, zinc chloride is present in an amount of about 6 g/L, and boric
acid is present in an amount of about 30 g/L.
3. The electroplating composition as claimed in claim 1 or 2, wherein the aluminium
10 nanoparticles are present in an amount of 5 g/L.
4. The electroplating composition as claimed in any one of claims 1-3, comprising a surfactant
selected from triethanolamine (TEA) or sodium dodecyl sulphate (SDS).
5. The electroplating composition as claimed in claim 4, wherein TEA is present in an amount
of about 0.01-0.1 g/L or SDS is present in an amount of about 1.2-1.4 g/L.
15 6. The electroplating composition as claimed in claim 5, wherein zinc sulphate is present in
an amount of about 250 g/L, zinc chloride is present in an amount of about 6 g/L, boric acid
is present in an amount of about 30 g/L, the aluminium nanoparticles are present in an
amount of 1-10 g/L and TEA is present in an amount of about 0.1 g/L.
7. The electroplating composition as claimed in claim 5, wherein zinc sulphate is present in
20 an amount of about 250 g/L, zinc chloride is present in an amount of about 6 g/L, boric acid
is present in an amount of about 30 g/L, the aluminium nanoparticles are present in an
amount of 1-2.5 g/L and SDS is present in an amount of 1.25 g/L.
8. The electroplating composition as claimed in claim 7, wherein the aluminium nanoparticles
are present in an amount of 1 g/L.
25 9. A method for preparing the electroplating composition as claimed in any one of claims 1-
8, comprising the steps of:
a. adding zinc sulphate, zinc chloride, and boric acid to demineralized water
followed by stirring to prepare an electrolyte solution;
b. adding aluminium nanoparticles to a portion of the electrolyte solution
30 followed by stirring and ultrasonication for about 1-1.5 hours to obtain an
ultrasonicated solution;
30
c. mixing the ultrasonicated solution with remaining portion of the electrolyte
solution to obtain a second solution; and
d. stirring the second solution for about 20-30 hours followed by ultrasonication
to obtain the electroplating composition.
10. The method as claimed in claim 9, wherein in step b), the aluminium nanoparticles 5 are first
added to a surfactant solution followed by stirring and ultrasonication to obtain an
aluminium particles solution and the aluminium particles solution is added to the portion
of the electrolyte solution.
11. The method as claimed in claim 10, wherein the surfactant solution is prepared by adding
10 the surfactant to demineralized water followed by heating the demineralized water to about
30-40°C and stirring to provide the surfactant solution.
12. The method as claimed in any one of claims 9-11, wherein stirring is carried out at a rate
of about 250-350 rpm for about 30-180 minutes.
13. The method as claimed in any one of claims 9-12, wherein ultrasonication is carried out at
15 a frequency of about 15-25 kHz.
14. A method for depositing the electroplating composition as claimed in any one of claims 1-
8 on a steel substrate, comprising:
a. providing the steel substrate as a cathode; and
b. depositing the electroplating composition on the steel substrate at a constant
20 current with a current density of about 170-190 mA/cm2 and at a stirring rate of
about 250-350 rpm to provide a steel substrate comprising a zinc-aluminium
(Zn-Al) composite coating.
15. The method as claimed in claim 14, wherein the current density is about 180 mA/cm2.
16. The method as claimed in claim 14 or 15, wherein the Zn-Al composite coating provided
25 by the method exhibits a corrosion rate of about 0.02-0.05 mm/year.
17. The method as claimed in any one of claims 14-16, wherein the Zn-Al composite coating
provided by the method exhibits a corrosion current density of about 1.9-2.4 μA/cm2.
18. The method as claimed in any one of claims 14-17, wherein the Zn-Al composite coating
provided by the method exhibits a corrosion potential of about -0.8 to -0.9 V.
31
19. The method as claimed in any one of claims 14-18, wherein the Zn-Al composite coating
provided by the method exhibits a Salt Spray Test 5% Red Rust life of about 200 hours or
more.
20. The method as claimed in any one of claims 14-19, wherein the Zn-Al composite coating
provided by the method comprises aluminium particles in an amount of 5 about 1.5-5.2% by
weight.
21. A steel substrate comprising the Zn-Al composite coating deposited by the method as
claimed in any one of claims 14-20.