U.S. patent application number 17/393653 was filed with the patent office on 2022-02-24 for electrolyte composition and method of use thereof.
The applicant listed for this patent is City University of Hong Kong. Invention is credited to Paul Kim Ho Chu, King Yu Ricky FU, Liangliang LIU, Zhongzhen WU.
Application Number | 20220056610 17/393653 |
Document ID | / |
Family ID | 1000005812657 |
Filed Date | 2022-02-24 |
United States Patent
Application |
20220056610 |
Kind Code |
A1 |
Chu; Paul Kim Ho ; et
al. |
February 24, 2022 |
ELECTROLYTE COMPOSITION AND METHOD OF USE THEREOF
Abstract
Provided herein is an electrolyte composition including a metal
silicate or a metal aluminate, a metal phosphate, zinc oxide
particles, and a complexing agent useful for plasma electrolytic
oxidation treatment of a surface of a metal substrate.
Inventors: |
Chu; Paul Kim Ho; (Hong
Kong, CN) ; WU; Zhongzhen; (Hong Kong, CN) ;
LIU; Liangliang; (Hong Kong, CN) ; FU; King Yu
Ricky; (Hong Kong, CN) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
City University of Hong Kong |
Hong Kong |
|
CN |
|
|
Family ID: |
1000005812657 |
Appl. No.: |
17/393653 |
Filed: |
August 4, 2021 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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63069214 |
Aug 24, 2020 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C25D 11/06 20130101;
C25D 11/026 20130101 |
International
Class: |
C25D 11/06 20060101
C25D011/06; C25D 11/02 20060101 C25D011/02 |
Claims
1. An electrolyte composition comprising a metal silicate or a
metal aluminate, a metal phosphate, zinc oxide particles, and a
complexing agent.
2. The electrolyte composition of claim 1 further comprising an
aqueous solvent.
3. The electrolyte composition of claim 1, wherein the metal
silicate or metal aluminate is sodium silicate, calcium silicate,
tricalcium silicate, tricalcium aluminate, tricalcium iron
aluminate, potassium silicate, or a mixture thereof.
4. The electrolyte composition of claim 1, wherein the metal
phosphate is selected from the group consisting of sodium
hexametaphsophate, disodium hydrogen phosphate, sodium dihydrogen
phosphate, sodium polyphosphate, trisodium phosphate, and sodium
pyrophosphate.
5. The electrolyte composition of claim 1, wherein the zinc oxide
particles are micron-sized zinc oxide, nano-sized zinc oxide
particles, or a mixture thereof.
6. The electrolyte composition of claim 1, wherein the complexing
agent is ethylene diamine tetraacetic acid (EDTA), triethanolamine,
sodium tartrate, citrate, oxalate, or a mixture thereof.
7. The electrolyte composition of claim 1, wherein the metal
phosphate is selected from the group consisting of sodium
hexametaphsophate, disodium hydrogen phosphate, sodium dihydrogen
phosphate, sodium polyphosphate, trisodium phosphate, and sodium
pyrophosphate; the zinc oxide is micron zinc oxide, nano zinc
oxide, or a mixture thereof; and the complexing agent is EDTA,
triethanolamine, sodium tartrate, citrate, oxalate, or a mixture
thereof.
8. The electrolyte composition of claim 1, wherein the metal
silicate or the metal aluminate is sodium silicate, the metal
phosphate is sodium hexametaphosphate, and the complexing agent is
disodium EDTA.
9. The electrolyte composition of claim 2, wherein the metal
silicate or metal aluminate, the metal phosphate, the zinc oxide
particles, and the complexing agent are present in the aqueous
solution at a concentration of about 5 to about 50 g/L, about 1 to
about 30 g/L, about 2 to about 25 g/L, and about 1 to about 20 g/L,
respectively.
10. The electrolyte composition of claim 9, wherein the metal
silicate or the metal aluminate is sodium silicate, the metal
phosphate is sodium hexametaphosphate, and the complexing agent is
disodium EDTA.
11. The electrolyte composition of claim 2, wherein the aqueous
solvent has a pH of about 6 to about 12.
12. The electrolyte composition of claim 2, wherein the metal
silicate or the metal aluminate is sodium silicate, the metal
phosphate is sodium hexametaphosphate, and the complexing agent is
disodium EDTA; and the sodium silicate, sodium hexametaphosphate,
zinc oxide particles, and the disodium EDTA are present in the
aqueous solvent at a concentration of about 10 to about 20 g/L,
about 10 to about 20 g/L, about 5 to about 15 g/L, and about 10 to
about 20 g/L, respectively.
13. The electrolyte composition of claim 2, wherein the metal
silicate or the metal aluminate is sodium silicate, the metal
phosphate is sodium hexametaphosphate, and the complexing agent is
disodium EDTA; the sodium silicate, sodium hexametaphosphate, zinc
oxide particles, and the disodium EDTA are present in the aqueous
solvent at a concentration of about 15 g/L, about 15 g/L, about 10
g/L, and about 15 g/L, respectively; and the aqueous solvent has a
pH of about 6 to about 12.
14. A method of plasma electrolytic oxidation (PEO) treatment of a
surface of a metal substrate, the method comprising: providing an
anode comprising the metal substrate; an anode; and an electrolyte
solution comprising the electrolyte composition of claim 1, wherein
the electrolyte solution is in contact with the cathode and the
anode; and applying an electric current between the cathode and the
anode resulting in the PEO of at least a portion of the surface of
the metal substrate.
15. The method of claim 14, wherein the metal substrate is aluminum
or an alloy thereof.
16. The method of claim 14, wherein the step of applying the
electric current comprises applying a constant current using at
about 5 to about 20 amps/dm.sup.2 and frequency of about 50 to
about 3,000 Hz or a constant voltage of about 300 to about 800
volts at a frequency of about 50 to about 3,000 Hz.
17. The method of claim 14, wherein the step of applying the
electric current comprises applying a constant current using about
20 amps/dm.sup.2 and frequency of about 100 Hz.
18. The method of claim 14, wherein the electrolyte solution
comprises the metal silicate or metal aluminate, the metal
phosphate, the zinc oxide particles, and the complexing agent are
present in the aqueous solution at a concentration of about 5 to
about 50 g/L, about 1 to about 30 g/L, about 2 to about 25 g/L, and
about 1 to about 20 g/L, respectively.
19. The method of claim 17, wherein the electrolyte solution
comprises the metal silicate or the metal aluminate is sodium
silicate, the metal phosphate is sodium hexametaphosphate, and the
complexing agent is disodium EDTA; the sodium silicate, sodium
hexametaphosphate, zinc oxide particles, and the disodium EDTA are
present in the aqueous solvent at a concentration of about 15 g/L,
about 15 g/L, about 10 g/L, and about 15 g/L, respectively; and the
aqueous solvent has a pH of about 6 to about 12.
20. The method of claim 15, wherein the electrolyte solution
comprises the metal silicate or the metal aluminate is sodium
silicate, the metal phosphate is sodium hexametaphosphate, and the
complexing agent is disodium EDTA; the sodium silicate, sodium
hexametaphosphate, zinc oxide particles, and the disodium EDTA are
present in the aqueous solvent at a concentration of about 15 g/L,
about 15 g/L, about 10 g/L, and about 15 g/L, respectively; and the
aqueous solvent has a pH of about 6 to about 12; and the step of
applying the electric current comprises applying a constant current
using about 20 amps/dm.sup.2 and frequency of about 100 Hz.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority from U.S. Provisional
Patent Application No. 63/069,214 filed on Aug. 24, 2020, the
content of which is hereby incorporated by reference in its
entirety.
TECHNICAL FIELD
[0002] The present disclosure generally relates to an electrolyte
composition for plasma electrolytic oxidation (PEO) treatment of a
surface of a metal substrate and a method of using the electrolyte
composition in the PEO treatment of a surface of a metal
substrate.
BACKGROUND
[0003] Aluminum and its alloys are widely used in the aerospace and
transportation industries, because of their desirable properties,
such as high strength-to-weight ratio, good formability, and
lightweight. However, despite the presence of an aluminum oxide
natural passivating film on the surface of aluminum substrates,
aluminum and its alloys can still be susceptible to corrosion,
especially in the presence of oxidants and caustic agents.
[0004] Surface treatment techniques, such as anodic oxidation, PEO,
chemical conversion, electrodeposition, and laser-cladding are
viable means to mitigate corrosion of aluminum and its alloys. In
particular, PEO, a plasma-assisted electrochemical process that
tends to produce better corrosion resistance than other techniques
(due in part to the thick aluminum oxide films produced) is
environmentally friendly and efficient process for surface
treatment of aluminum and its alloys. However, the corrosion
resistance of PEO coatings is inferior to that of bulk alumina as a
result of the porous nature of the oxide coating structure, which
allows penetration of corrosive ions and results in incomplete
crystallization. As a result, the corrosion resistance of PEO
coatings normally only last for seven days as determined by the
impression test in 3.5% salt solution. Thus, there is a strong need
to develop improved methods for PEO treatment of metal substrates,
such as aluminum and its alloys that overcome at least some of the
aforementioned challenges.
SUMMARY
[0005] Provided herein is an electrolyte composition useful for PEO
treatment of a surface of a metal substrate and methods of use
thereof The methods described herein can yield substrate PEO
coatings with improved density, hardness, and wear and corrosion
resistance.
[0006] In a first aspect, provided herein is an electrolyte
composition comprising a metal silicate or a metal aluminate, a
metal phosphate, zinc oxide particles, and a complexing agent.
[0007] In certain embodiments, the electrolyte composition further
comprises an aqueous solvent.
[0008] In certain embodiments, the metal silicate or metal
aluminate is sodium silicate, calcium silicate, tricalcium
silicate, tricalcium aluminate, tricalcium iron aluminate,
potassium silicate, or a mixture thereof.
[0009] In certain embodiments, the metal phosphate is selected from
the group consisting of sodium hexametaphsophate, disodium hydrogen
phosphate, sodium dihydrogen phosphate, sodium polyphosphate,
trisodium phosphate, and sodium pyrophosphate.
[0010] In certain embodiments, the zinc oxide particles are
micron-sized zinc oxide, nano-sized zinc oxide particles, or a
mixture thereof.
[0011] In certain embodiments, the complexing agent is ethylene
diamine tetraacetic acid (EDTA), triethanolamine, sodium tartrate,
citrate, oxalate, or a mixture thereof.
[0012] In certain embodiments, the metal phosphate is selected from
the group consisting of sodium hexametaphsophate, disodium hydrogen
phosphate, sodium dihydrogen phosphate, sodium polyphosphate,
trisodium phosphate, and sodium pyrophosphate; the zinc oxide is
micron zinc oxide, nano zinc oxide, or a mixture thereof and the
complexing agent is EDTA, triethanolamine, sodium tartrate,
citrate, oxalate, or a mixture thereof.
[0013] In certain embodiments, the metal silicate or the metal
aluminate is sodium silicate, the metal phosphate is sodium
hexametaphosphate, and the complexing agent is disodium EDTA.
[0014] In certain embodiments, the metal silicate or metal
aluminate, the metal phosphate, the zinc oxide particles, and the
complexing agent are present in the aqueous solution at a
concentration of about 5 to about 50 g/L, about 1 to about 30 g/L,
about 2 to about 25 g/L, and about 1 to about 20 g/L,
respectively.
[0015] In certain embodiments, the metal silicate or the metal
aluminate is sodium silicate, the metal phosphate is sodium
hexametaphosphate, and the complexing agent is disodium EDTA.
[0016] In certain embodiments, the aqueous solvent has a pH of
about 6 to about 12.
[0017] In certain embodiments, the metal silicate or the metal
aluminate is sodium silicate, the metal phosphate is sodium
hexametaphosphate, and the complexing agent is disodium EDTA; and
the sodium silicate, sodium hexametaphosphate, zinc oxide
particles, and the disodium EDTA are present in the aqueous solvent
at a concentration of about 10 to about 20 g/L, about 10 to about
20 g/L, about 5 to about 15 g/L, and about 10 to about 20 g/L,
respectively.
[0018] In certain embodiments, the metal silicate or the metal
aluminate is sodium silicate, the metal phosphate is sodium
hexametaphosphate, and the complexing agent is disodium EDTA; the
sodium silicate, sodium hexametaphosphate, zinc oxide particles,
and the disodium EDTA are present in the aqueous solvent at a
concentration of about 15 g/L, about 15 g/L, about 10 g/L, and
about 15 g/L, respectively; and the aqueous solvent has a pH of
about 6 to about 12.
[0019] In a second aspect, provided herein is a method of plasma
electrolytic oxidation (PEO) treatment of a surface of a metal
substrate, the method comprising: providing an anode comprising the
metal substrate; an anode; and an electrolyte solution comprising
the electrolyte composition described herein, wherein the
electrolyte solution is in contact with the cathode and the anode;
and applying an electric current between the cathode and the anode
resulting in the PEO of at least a portion of the surface of the
metal substrate.
[0020] In certain embodiments, the metal substrate is aluminum or
an alloy thereof.
[0021] In certain embodiments, the step of applying the electric
current comprises applying a constant current using at about 5 to
about 20 amps/dm.sup.2 and frequency of about 50 to about 3,000 Hz
or a constant voltage of about 300 to about 800 volts at a
frequency of about 50 to about 3,000 Hz.
[0022] In certain embodiments, the step of applying the electric
current comprises applying a constant current using about 20
amps/dm.sup.2 and frequency of about 100 Hz.
[0023] In certain embodiments, the electrolyte solution comprises
the metal silicate or metal aluminate, the metal phosphate, the
zinc oxide particles, and the complexing agent are present in the
aqueous solution at a concentration of about 5 to about 50 g/L,
about 1 to about 30 g/L, about 2 to about 25 g/L, and about 1 to
about 20 g/L, respectively.
[0024] In certain embodiments, the electrolyte solution comprises
the metal silicate or the metal aluminate is sodium silicate, the
metal phosphate is sodium hexametaphosphate, and the complexing
agent is disodium EDTA; the sodium silicate, sodium
hexametaphosphate, zinc oxide particles, and the disodium EDTA are
present in the aqueous solvent at a concentration of about 15 g/L,
about 15 g/L, about 10 g/L, and about 15 g/L, respectively; and the
aqueous solvent has a pH of about 6 to about 12.
[0025] In certain embodiments, the electrolyte solution comprises
the metal silicate or the metal aluminate is sodium silicate, the
metal phosphate is sodium hexametaphosphate, and the complexing
agent is disodium EDTA; the sodium silicate, sodium
hexametaphosphate, zinc oxide particles, and the disodium EDTA are
present in the aqueous solvent at a concentration of about 15 g/L,
about 15 g/L, about 10 g/L, and about 15 g/L, respectively; and the
aqueous solvent has a pH of about 6 to about 12; and the step of
applying the electric current comprises applying a constant current
using about 20 amps/dm.sup.2 and frequency of about 100 Hz.
[0026] Other aspects and advantages of the invention will be
apparent to those skilled in the art from a review of the ensuing
description.
BRIEF DESCRIPTION OF DRAWINGS
[0027] The above and other objects and features of the present
invention will become apparent from the following description of
the invention, when taken in conjunction with the accompanying
drawings, in which:
[0028] FIG. 1 depicts the surface morphology of LY12 aluminum alloy
samples after subjecting them to PEO (a) in the absence of zinc
oxide; and (b) in the presence of 10 g/L of zin oxide. The size of
the aluminum alloy sample was 25.times.50.times.2 mm.sup.3. The PEO
treatment was conducted under 20 KW power supply with a constant
current for 15 minutes. The current density was 20 A/dm.sup.2 and
the frequency was 100 Hz. The electrolyte composition comprises
sodium silicate (15 g/L), sodium hexametaphosphate (15g/L),
Na.sub.2EDTA, and zinc oxide (0-10 g/L).
[0029] FIG. 2 depicts the surface morphology of the aluminum alloy
samples of FIG. 1 after subjecting them to the corrosion test for
14 days. (a) The sample without zinc oxide doping was eroded after
immersion in 3.5% NaCl solution for 14 days. (b) In contrast, the
aluminum alloy samples prepared with zinc oxide at a concentration
of 10 g/L were not eroded.
[0030] FIG. 3 depicts a series of optical images showing the
appearance of the surface of untreated LY12 alloy samples and
PEO-treated LY12 alloy samples treated with electrolyte composition
solutions comprising 0, 2, 4, 6, 7, and 10 g/L of zinc oxide in 3.5
wt % NaCl solution for 0, 2, 7, and 14 days. The results indicate
incorporation of zinc oxide significantly increases the corrosion
resistance of the PEO coating.
DETAILED DESCRIPTION
[0031] Definitions
[0032] The definitions of terms used herein are meant to
incorporate the present state-of-the-art definitions recognized for
each term in the field of biotechnology. Where appropriate,
exemplification is provided. The definitions apply to the terms as
they are used throughout this specification, unless otherwise
limited in specific instances, either individually or as part of a
larger group.
[0033] Throughout this specification, unless the context requires
otherwise, the word "comprise" or variations such as "comprises" or
"comprising", will be understood to imply the inclusion of a stated
integer or group of integers but not the exclusion of any other
integer or group of integers. It is also noted that in this
disclosure and particularly in the claims and/or paragraphs, terms
such as "comprises", "comprised", "comprising" and the like can
have the meaning attributed to it in U.S. Patent law; e.g., they
can mean "includes", "included", "including", and the like; and
that terms such as "consisting essentially of" and "consists
essentially of" have the meaning ascribed to them in U.S. Patent
law, e.g., they allow for elements not explicitly recited, but
exclude elements that are found in the prior art or that affect a
basic or novel characteristic of the invention.
[0034] Furthermore, throughout the specification and claims, unless
the context requires otherwise, the word "include" or variations
such as "includes" or "including", will be understood to imply the
inclusion of a stated integer or group of integers but not the
exclusion of any other integer or group of integers.
[0035] The present disclosure provides an electrolyte composition
comprising a metal silicate or a metal aluminate, a metal
phosphate, zinc oxide particles, and a complexing agent.
[0036] The electrolyte composition may comprise a metal silicate, a
metal aluminate, or a mixture thereof. The metal silicate can be an
ortho silicate, a pyro silicate, a cyclic silicate, a chain
silicate, or mixture thereof. Metal aluminates suitable for use in
the electrolyte composition described herein include, but are not
limited to, an aluminate, an aluminate hydrate, and mixtures
thereof.
[0037] The metal silicate and metal aluminate can comprise any
metal cation. Exemplary metal cations include one or more cations
selected from Group 1 and Group II of the Periodic Table of the
Elements. In certain embodiments, the metal silicate and metal
aluminate comprises one or more metal cations selected from the
group consisting of Li.sup.+, Na.sup.+, Mg.sup.2+, and Ca.sup.2+.
In certain embodiments, the metal silicate or metal aluminate is
selected from the group consisting of sodium silicate, calcium
silicate, tricalcium silicate, tricalcium aluminate, tricalcium
iron aluminate, potassium silicate, and mixtures thereof. In
certain embodiments, the metal silicate is sodium silicate.
[0038] Metal phosphates suitable for use in the electrolyte
composition described herein include, but are not limited to,
phosphate salts, metaphosphate metal salts, triphosphate salts, and
polyphosphate metal salts. Exemplary polyphosphate metal salts
include, but are not limited to, pyrophosphate salts and
polyphosphate salts, such as triphosphate salts, tetraphosphate
salts, pentaphosphate salts, trimetaphosphate salts,
tetrametaphosphate salts, and the like.
[0039] The metal phosphate can comprise any metal cation. Exemplary
metal cations include one or more cations selected from Group 1 and
Group II of the Periodic Table of the Elements. In certain
embodiments, the metal phosphate comprises one or more metal
cations selected from the group consisting of Li.sup.+, Na.sup.+,
K.sup.+, Mg.sup.2+, and Ca.sup.2+. In certain embodiments, the
metal phosphate is a sodium hexametaphsophate, disodium hydrogen
phosphate, sodium dihydrogen phosphate, sodium polyphosphate,
trisodium phosphate, and sodium pyrophosphate. In certain
embodiments, the metal phosphate is sodium hexametaphsophate.
[0040] Conjugate acids of the metal phosphate may also be used in
the electrolyte compositions described herein. Exemplary conjugate
acids of orthophosphate, pyrophosphate, and polyphosphate suitable
for use include, but are not limited to, linear polyphosphoric
acids, metaphosphoric acids, and branched polyphosphoric acids.
Exemplary polyphosphoric acids include, but are not limited to,
triphosphoric acids, tetraphosphoric acids, pentaphosphoric acids,
trimetaphosphoric acid, tetrametaphosphoric acids, and the
like.
[0041] The conjugate acids of the metal phosphate can comprise one
or more ionizable protons and thus can exist in one or more
conjugate acid protonation states. In instances in which the
electrolyte composition comprises a conjugate acid of
orthophosphate, pyrophosphate, or polyphosphate, the conjugate acid
can be in any of the possible protonation states of the phosphate
salts described herein or a combination thereof. For example,
conjugate acids of PO.sub.4.sup.3- (orthophosphate) include
HPO.sub.4.sup.2-, H.sub.2PO.sub.4.sup.-, and H.sub.3PO.sub.4; and
conjugate acids of P.sub.3O.sub.10.sup.5- (tripolyphosphate)
include HP.sub.3O.sub.10.sup.4-, H.sub.2P.sub.3O.sub.10.sup.3-,
H.sub.3P.sub.3O.sub.10.sup.2-, H.sub.4P.sub.3O.sub.10.sup.1-, and
H.sub.5P.sub.3O.sub.10. Anionic conjugate acids of the phosphate
salts can comprise any one or more of the metal cations described
herein.
[0042] Zinc oxide particles suitable for use in the electrolyte
composition described herein include nano-zinc oxide, micro-zinc
oxide, and mixtures thereof. The nano-zinc oxide can have an
average particle size between 50-1000 nm. The micro-zinc oxide can
have an average particle size between 1-10 .mu.m.
[0043] The complexing agent can be any metal complexing agent known
in the art. Exemplary complexing agents include, but are not
limited to, nitrilotriacetic acid (NTA), nitrilo(diacetic)propionic
acid (NDAP), methylglycindiacetic acid (MGDA), EDDA,
2,2'-(ethylenediimino)-dibutyric acid (EDBA), EDTA,
diethylenetriaminepentaacetic acid (DTPA), 1,2-cyclohexane
diaminetetraacetic acid (CDTA),
ethylenebis(oxyethylenenitrilo)tetraacetic acid (EGTA),
2,3,4,5,6,7-hexahydroxyheptanoic acid, triethanolamine, tartartic
acid, citratic acid, oxalic acid, or conjugate salts thereof and/or
mixtures thereof. In certain embodiments, the complexing agent is
EDTA, triethanolamine, sodium tartrate, citrate, oxalate, or a
mixture thereof. In certain embodiments, the complexing agent is a
conjugate salt of EDTA. Conjugate salts of the complexing agent can
comprise one or more one or more cations selected from Group 1 and
Group II of the Periodic Table of the Elements, such as Li.sup.+,
Na.sup.+, Mg.sup.2+, and Ca.sup.2+.
[0044] The electrolyte composition may further comprise an aqueous
solvent, such as water. The water can be distilled water or
deionized water. The pH of the aqueous solvent can range from about
6 to about 12. The ion conductivity of the electrolyte composition
further comprising the aqueous solvent can range from about 5 to
about 60 mScm.sup.-1.
[0045] The electrolyte composition can comprise the metal silicate
or metal aluminate at a concentration of about 5 to about 50 g/L in
the aqueous solvent. In certain embodiments, the electrolyte
composition comprises the metal silicate or metal aluminate at a
concentration of about 5 to about 40 g/L, about 5 to about 30 g/L,
about 5 to about 20 g/L, about 10 to about 20 g/L, or about 15 g/L
in the aqueous solvent.
[0046] The electrolyte composition can comprise the metal phosphate
at a concentration of about 5 to about 50 g/L in the aqueous
solvent. In certain embodiments, the electrolyte composition
comprises the metal phosphate at a concentration of about 5 to
about 40 g/L, about 5 to about 30 g/L, about 5 to about 20 g/L,
about 10 to about 20 g/L, or about 15 g/L in the aqueous
solvent.
[0047] The electrolyte composition can comprise the zinc oxide
particles at a concentration of about 1 to about 25 g/L in the
aqueous solvent. In certain embodiments, the electrolyte
composition comprises the zinc oxide particles at a concentration
of about 1 to about 20 g/L, about 5 to about 20 g/L, 5 to about 15
g/L, about 7 to about 13 g/L, or about 10 g/L in the aqueous
solvent.
[0048] The electrolyte composition can comprise the complexing
agent at a concentration of about 5 to about 50 g/L in the aqueous
solvent. In certain embodiments, the electrolyte composition
comprises the complexing agent at a concentration of about 5 to
about 40 g/L, about 5 to about 30 g/L, about 5 to about 20 g/L,
about 10 to about 20 g/L, or about 15 g/L in the aqueous
solvent.
[0049] In certain embodiments, the electrolyte composition
comprises the metal silicate or the metal aluminate is sodium
silicate, the metal phosphate is sodium hexametaphosphate, and the
complexing agent is disodium EDTA; the sodium silicate, sodium
hexametaphosphate, zinc oxide particles, and the disodium EDTA are
present in the aqueous solvent at a concentration of about 15 g/L,
about 15 g/L, about 10 g/L, and about 15 g/L, respectively.
[0050] Also provided herein is a method of plasma electrolytic
oxidation (PEO) treatment of a surface of a metal substrate, the
method comprising: providing an anode comprising the metal
substrate; an anode; and an electrolyte solution comprising the
electrolyte described herein, wherein the electrolyte solution is
in contact with the cathode and the anode; and applying an electric
current between the cathode and the anode resulting in the PEO of
at least a portion of the surface of the metal substrate.
[0051] The metal substrate can be aluminum, magnesium, titanium,
beryllium, zirconium, and alloys thereof. In certain embodiments,
the substrate is aluminum alloy LY12.
[0052] In certain embodiments, the step of applying the electric
current comprises applying a constant current using at about 5 to
about 20 amps/dm.sup.2 and frequency of about 50 to about 3,000 Hz
or a constant voltage of about 300 to about 800 volts at a
frequency of about 50 to about 3,000 Hz.
[0053] In certain embodiments, the step of applying the electric
current comprises applying a constant current using about 20
amps/dm.sup.2 and frequency of about 100 Hz.
[0054] Advantageously, PEO treatment of a metal substrate using the
electrolyte composition described herein incorporates zinc oxide
into the PEO coating applied to the surface of the substrate, which
fuses with the metal substrate to form a denser PEO coating. The
result of corrosion tests shown in FIG. 2 demonstrate that the zinc
oxide incorporated into PEO coatings resulted in improved corrosion
resistance compared to the substrate or PEO coating without zinc
oxide. Based on these results, it is clear that zinc oxide
incorporation into the PEO coating assists with protecting the
coating from corrosion in the NaCl solutions.
EXAMPLES
[0055] Commercial polished LY12 Al alloy was used as the substrate
for PEO. Before PEO, the substrate was cut into plates
(25.times.50.times.2 mm) and cleaned ultrasonically in acetone and
ethanol for 10 min. The deionized aqueous solution containing
sodium silicate (Na.sub.2SiO.sub.3, 15 g/L) and sodium
hexametaphosphate ((NaPO.sub.3).sub.6, 10 g/L) was used as the
electrolyte. ZnO particles (300-500 nm, Aladdin Inc., China) with
concentrations varying from 0 to 10 g/L were added to the
electrolyte and the samples were labeled as ZnO-0 (FIG. 1(a) and
FIG. 2(a)), ZnO-2, ZnO-4, ZnO-6, ZnO-8, and ZnO-10 (FIG. 1(b) and
FIG. 2(b)), respectively, where the number represented the
concentration of zinc oxide in the electrolyte. PEO was performed
on a custom system comprising a DC pulsed power supply (Plasma
Technology Ltd., Hong Kong) and stainless steel solution container
serving as the cathode. The process was conducted at a constant
positive current density of 5 A*dm.sup.-2, frequency of 100 Hz, and
duty cycle of 30% for 10 min. During PEO, the temperature of the
electrolyte was controlled to be below 55.degree. C. with a
mechanical stirrer
* * * * *