U.S. patent application number 14/911996 was filed with the patent office on 2016-09-08 for inorganic phosphate corrosion resistant coatings.
The applicant listed for this patent is LATITUDE 18, INC.. Invention is credited to Benjamin Chaloner-Gill, Anthony V. Collins, Sameerkumar Vasantlal Patel.
Application Number | 20160258067 14/911996 |
Document ID | / |
Family ID | 52468623 |
Filed Date | 2016-09-08 |
United States Patent
Application |
20160258067 |
Kind Code |
A1 |
Patel; Sameerkumar Vasantlal ;
et al. |
September 8, 2016 |
INORGANIC PHOSPHATE CORROSION RESISTANT COATINGS
Abstract
This disclosure relates to compositions for protecting a
metallic surface susceptible to corrosion, the composition
comprising a first component comprising an aqueous mixture of an
acid-phosphate of chemical formula
A.sup.m(H.sub.2PO.sub.4).sub.m.nH.sub.2O, where A is hydrogen ion,
ammonium cation, metal cation, or mixtures thereof; where m=1-3,
and n=0-6; the first component solution adjusted to a pH of about 2
to about 5, the first component having a particle size distribution
between 0.04 to 60 micron; and a second component, configured for
combination and at least partial reaction with the first component
to provide a phosphate ceramic, the second component comprising an
aqueous solution or suspension of an alkaline oxide or alkaline
hydroxide represented by B.sup.2mO.sub.m, B(OH).sub.2m, or mixtures
thereof, where B is an element of valency 2m (m=1, 1.5, or 2) the
second component solution adjusted to a pH of between 9-14.
Inventors: |
Patel; Sameerkumar Vasantlal;
(Sims, NC) ; Chaloner-Gill; Benjamin; (Sims,
NC) ; Collins; Anthony V.; (Sims, NC) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
LATITUDE 18, INC. |
Sims |
NC |
US |
|
|
Family ID: |
52468623 |
Appl. No.: |
14/911996 |
Filed: |
August 12, 2014 |
PCT Filed: |
August 12, 2014 |
PCT NO: |
PCT/US2014/050707 |
371 Date: |
February 12, 2016 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61865115 |
Aug 12, 2013 |
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C04B 35/447 20130101;
C09D 5/084 20130101; C04B 2111/00525 20130101; C23C 22/68 20130101;
C04B 28/34 20130101; C23C 22/22 20130101; C04B 28/34 20130101; C04B
14/043 20130101; C04B 14/106 20130101; C04B 14/304 20130101 |
International
Class: |
C23C 22/22 20060101
C23C022/22; C09D 5/08 20060101 C09D005/08; C04B 35/447 20060101
C04B035/447 |
Claims
1. A phosphate ceramic precursor composition comprising: a first
component comprising an aqueous mixture of an acid-phosphate of
chemical formula A.sup.m(H.sub.2PO.sub.4).sub.m.nH.sub.2O, where A
is hydrogen ion, ammonium cation, metal cation, or mixtures
thereof; where m=1-3, and n=0-6; the first component solution
adjusted to a pH of about 2 to about 5, the first component having
a particle size distribution between 0.04 to 60 micron; and a
second component, configured for combination and at least partial
reaction with the first component to provide a phosphate ceramic,
the second component comprising an aqueous mixture of an alkaline
oxide or alkaline hydroxide represented by B.sup.2mO.sub.m,
B(OH).sub.2m, or mixtures thereof, where B is an element of valency
2m (m=1, 1.5, or 2) the second component solution adjusted to a pH
of between 9-14.
2. The phosphate ceramic precursor composition of claim 1, wherein
about 50 percent of the particle size distribution of the first
component is particles having a particle size less than 50 microns,
less than 40 microns, less than 30 microns, or less than 20
microns.
3. The phosphate ceramic precursor composition of claim 1 wherein
about 90 percent of the particle size distribution of the first
component is particles having a particle size less than 50 microns,
less than 40 microns, or less than 30 microns.
4. The phosphate ceramic precursor composition of claim 1, wherein
the first component average particle size is about 20 microns to
about 30 microns.
5. The phosphate ceramic precursor composition of claim 1, wherein
the first component comprises at least one of mono potassium
phosphate and mono calcium phosphate, water, and optionally about 2
to about 10 wt % phosphoric acid, and wherein the second component
is at least one of magnesium oxide, calcium oxide, magnesium
hydroxide, and calcium hydroxide, and water.
6. (canceled)
7. The phosphate ceramic precursor composition of claim 5, further
comprising at least one of a mineral silicate, wollastonite, talc,
amorphous magnesium silicate, amorphous calcium silicate,
diatomaceous earth, silicon dioxide, amorphous silicon dioxide, a
rheology modifier/suspending agent, the rheology
modifier/suspending agent is at least one of guar gum, diutan gum,
welan gum, and xanthan gum present in an amount of 0.15-15 weight
percent.
8. The phosphate ceramic precursor composition of a claim 5,
wherein either of the first component or the second component is
present in an amount of at least about 60 wt % to about 80 wt
%.
9. (canceled)
10. A method of providing corrosion protection to a metal surface,
the method comprising: contacting a metal surface with a first
component and a second component, in any order or in combination;
wherein the first component comprises an aqueous mixture of an
acid-phosphate of chemical formula
A.sup.m(H.sub.2PO.sub.4).sub.m.nH.sub.2O, where A is hydrogen ion,
ammonium cation, metal cation, or mixtures thereof; where m=1-3,
and n=0-6; the first component solution adjusted to a pH of about 2
to about 5, the first component having a particle size distribution
between 0.04 to 60 micron; and wherein the second component
comprises an aqueous mixture of an alkaline oxide or alkaline
hydroxide represented by B.sup.2mO.sub.m, B(OH).sub.2m, or mixtures
thereof, where B is an element of valency 2m (m=1, 1.5, or 2) the
second component solution adjusted to a pH of between 9-14; and
providing corrosion protection to the metal surface.
11. The method of claim 10, wherein about 50 percent of the
particle size distribution of the first component is particles
having a particle size less than 50 microns, less than 40 microns,
less than 30 microns, or less than 20 microns.
12. The method of claim 10 wherein about 90 percent of the particle
size distribution of the first component is particles having a
particle size less than 50 microns, less than 40 microns, or less
than 30 microns.
13. The method of claim 10 wherein the first component average
particle size is about 20 microns to about 30 microns.
14. The method of claim 10, wherein the first component comprises a
dihydrogen phosphate salt of formula M.sup.m(H.sub.2PO.sub.4).sub.m
and its hydrates, or mixtures thereof; where M sodium, potassium,
magnesium, calcium, aluminum, or mixtures thereof, and m is
1-3.
15. The method of claim 10, wherein the first component comprises
water, at least one of mono potassium phosphate and mono calcium
phosphate, and optionally, about 2 to about 10 wt % phosphoric
acid, and wherein the second component is at least one of magnesium
oxide, calcium oxide, magnesium hydroxide, and calcium hydroxide,
and water.
16. (canceled)
17. The method of claim 10, wherein the second component further
comprises wollastonite, talc, Class C fly ash, Class F fly ash,
kaolin clay, kaolinite, meta kaolin, mullite, calcium aluminate
minerals, calcium silicate minerals, aluminum silicate minerals,
calcium aluminum silicate minerals, or mixtures thereof, in a
weight ratio of between 1:0.05 to 1: 6 of the second component.
18. The method of claim 10, wherein the first component or the
second component is present in an amount of at least about 60 wt %
to about 80 wt %.
19. (canceled)
20. A product coated by the method of claim 10.
21. An inorganic phosphate compound of the general formula: i)
B.sup.s(A.sub.3-mPO.sub.4).sub.s; wherein A has a valency of m=1 or
2; and B has a valency of s=1, or 2; ii)
B.sup.s(A.sub.(2/m)PO.sub.4).sub.s; wherein A has a valency of m=1
or 2; B has a valency of s=1, or 2; iii)
.sup.(2/m)A.sub.3B.sub.m(PO.sub.4).sub.2; wherein A has a valency
of m=1 or 2; B has a valency of 3; or iv) B(AOPO.sub.4).sub.s;
wherein A has a valency of 4 and s=1 or 2; and B has a valency of
1, or 2; wherein the inorganic phosphate i-iv has less than
0.000001 to 10 percent of unreacted, crystalline inorganic acid
phosphate of an average particle size greater than about 60
microns.
22. The inorganic phosphate compound of claim 21, wherein the
compound is at least one of the following: MgKPO.sub.4;
Mg(ZnPO.sub.4).sub.2 Mg(K.sub.2PO.sub.4).sub.2; Mg.sub.2KPO.sub.4;
Mg(ZnPO.sub.4).sub.2; Mg(K.sub.2PO.sub.4).sub.2;
Al.sub.2Mg.sub.3(PO.sub.4).sub.2; Mg(ZrOPO.sub.4).sub.2;
Mg[Zr(OH).sub.2PO.sub.4).sub.2].sub.2; and calcium/magnesium
phosphate.
23. The inorganic phosphate ceramic of claim 21, wherein less than
0.000001 to 10 percent of the unreacted, crystalline inorganic acid
phosphate is of an average particle size distribution greater than
about 50 microns, less than 40 microns, or less than 30
microns.
24. The inorganic phosphate compound of claim 21, wherein the
inorganic phosphate has a density less than 1.8 g/cm.sup.3.
25. The inorganic phosphate compound of claim 21, wherein the
inorganic phosphate has a density less than 1.5 g/cm3.
Description
TECHNICAL FIELD
[0001] This disclosure relates to coatings comprising
acid-phosphate and alkaline metal oxide/hydroxide components that
inhibit corrosion of metals, and specifically, the manufacture and
method of coating phosphate ceramics on metal.
BACKGROUND
[0002] Corrosion of structural steel and other metals is a serious
problem in construction and utility industry. When exposed to humid
and saline environments, especially at elevated temperatures, steel
deteriorates. To minimize or reduce the extent of this corrosion,
alloys of steel, such as galvanized (zinc coated) compositions, or
chrome plated compositions are used. While this approach may solve
the problem in the short run, the problem persists when the steel
is exposed to the above-mentioned environments over long periods of
time. This invention discloses uniquely-suited phosphate-based
composite coatings that minimize or reduce the corrosion of steel
or other metals and make it unnecessary to use alloys of steel such
as galvanized (zinc coated) compositions or chrome plated
compositions.
[0003] Phosphating to passivate a steel surface is generally known
in the steel industry. Typically, well polished steel is immersed
in phosphate bath of pH between 4-4.5 containing 2-3 g/L phosphoric
acid, 2-3 g/L of ammonium or zinc dihydrogen phosphate as buffer,
and a small amount (<0.5 g/L) of oxidizer, to produce an iron
phosphate passivation layer. In the process, however, hydrogen gas
is liberated by the reaction of elemental iron with water in the
extremely acidic environment. This produces a very thin passivation
layer that is porous and not abrasion resistant, and as a result,
an additional coating is required to make the surface of the
passivated steel inaccessible to atmospheric oxygen and/or abrasion
resistant. This process has, therefore, at least the following
disadvantages: (i) an acid immersion bath/tank, which generates
sludge as formed by accumulating reaction products--making the bath
less effective and creating environmental disposal issues for the
sludge and the acidic solution; (ii) oxidizers used in the
passivation process produce toxic gases. For example, chlorates
produce chlorine, meta nitro benzene sulfonic acid produces nitrous
oxide, potassium permanganate presents occupational health risks;
(iii) resultant passivation layers are not abrasion resistant,
therefore, abrasion resistance must be augmented by additional
coating(s).
SUMMARY
[0004] In a first embodiment, a phosphate ceramic precursor
composition is provided. The composition comprising a first
component comprising an aqueous mixture of an acid-phosphate of
chemical formula A.sup.m(H.sub.2PO.sub.4).sub.m.nH.sub.2O, where A
is hydrogen ion, ammonium cation, metal cation, or mixtures
thereof; where m=1-3, and n=0-6; the first component solution
adjusted to a pH of about 2 to about 5, the first component having
a particle size distribution between 0.04 to 60 micron; and a
second component, configured for combination and at least partial
reaction with the first component to provide a phosphate ceramic,
the second component comprising an aqueous mixture of an alkaline
oxide or alkaline hydroxide represented by B.sup.2mO.sub.m,
B(OH).sub.2m, or mixtures thereof, where B is an element of valency
2m (m=1, 1.5, or 2) the second component solution adjusted to a pH
of between 9-14.
[0005] In a first aspect of the first embodiment, about 50 percent
of the particle size distribution of the first component is
particles having a particle size less than 50 microns, less than 40
microns, less than 30 microns, or less than 20 microns. The minimum
of particle sizes being about 0.04 micron, about 0.4 micron, or
about 4 micron.
[0006] In a second aspect, alone or in combination with any one of
the previous aspects of the first embodiment, about 90 percent of
the particle size distribution of the first component is particles
having a particle size less than 50 microns, less than 40 microns,
or less than 30 microns.
[0007] In a third aspect, alone or in combination with any one of
the previous aspects of the first embodiment, the first component
average particle size is about 20 microns to about 30 microns.
[0008] In a fourth aspect, alone or in combination with any one of
the previous aspects of the first embodiment, the first component
comprises at least one of mono potassium phosphate and mono calcium
phosphate, water, and optionally about 2 to about 10 wt. %
phosphoric acid.
[0009] In a fifth aspect, alone or in combination with any one of
the previous aspects of the first embodiment, the second component
is at least one of magnesium oxide, calcium oxide, magnesium
hydroxide, and calcium hydroxide, and water.
[0010] In a sixth aspect, alone or in combination with any one of
the previous aspects of the first embodiment, the composition
further comprising at least one corrosion inhibitor precursor of a
mineral silicate, wollastonite, talc, amorphous magnesium silicate,
amorphous calcium silicate, diatomaceous earth, silicon dioxide,
and amorphous silicon dioxide.
[0011] In a seventh aspect, alone or in combination with any one of
the previous aspects of the first embodiment, either of the first
component or the second component is present in an amount of at
least about 60 wt % to about 80 wt %.
[0012] In an eighth aspect, alone or in combination with any one of
the previous aspects of the first embodiment, the composition
further comprising further comprising a rheology
modifier/suspending agent, the rheology modifier/suspending agent
is at least one of guar gum, diutan gum, welan gum, and xanthan gum
present in an amount of 0.15-15 weight percent.
[0013] In a second embodiment, a method of providing corrosion
protection to a metal surface is provided. The method comprising
contacting a metal surface with a first component and a second
component, in any order or in combination; wherein the first
component comprises an aqueous mixture of an acid-phosphate of
chemical formula A.sup.m(H.sub.2PO.sub.4).sub.m.nH.sub.2O, where A
is hydrogen ion, ammonium cation, metal cation, or mixtures
thereof; where m=1-3, and n=0-6; the first component solution
adjusted to a pH of about 2 to about 5, the first component having
a particle size distribution between 0.04 to 60 micron; and wherein
the second component comprises an aqueous mixture of an alkaline
oxide or alkaline hydroxide represented by B.sup.2mO.sub.m,
B(OH).sub.2m, or mixtures thereof, where B is an element of valency
2m (m=1, 1.5, or 2) the second component solution adjusted to a pH
of between 9-14.
[0014] In a first aspect of the second embodiment, about 50 percent
of the particle size distribution of the first component is
particles having a particle size less than 50 microns, less than 40
microns, less than 30 microns, or less than 20 microns.
[0015] In a second aspect, alone or in combination with any one of
the previous aspects of the second embodiment, about 90 percent of
the particle size distribution of the first component is particles
having a particle size less than 50 microns, less than 40 microns,
or less than 30 microns.
[0016] In a third aspect, alone or in combination with any one of
the previous aspects of the second embodiment, the first component
average particle size is about 20 microns to about 30 microns.
[0017] In a fourth aspect, alone or in combination with any one of
the previous aspects of the second embodiment, the first component
comprises at least one of mono potassium phosphate and mono calcium
phosphate, water, and optionally about 2 to about 10 wt %
phosphoric acid.
[0018] In a fifth aspect, alone or in combination with any one of
the previous aspects of the second embodiment, the second component
is at least one of magnesium oxide, calcium oxide, magnesium
hydroxide, and calcium hydroxide, and water.
[0019] In a sixth aspect, alone or in combination with any one of
the previous aspects of the first embodiment or the second
embodiment, further comprising at least one of a mineral silicate,
wollastonite, talc, amorphous magnesium silicate, amorphous calcium
silicate, diatomaceous earth, silicon dioxide, and amorphous
silicon dioxide.
[0020] In a seventh aspect, alone or in combination with any one of
the previous aspects of the second embodiment, either of the first
component or the second component is present in an amount of at
least about 60 wt % to about 80 wt %.
[0021] In an eighth aspect, alone or in combination with any one of
the previous aspects of the second embodiment, further comprising
further comprising a rheology modifier/suspending agent, the
rheology modifier/suspending agent is at least one of guar gum,
diutan gum, welan gum, and xanthan gum present in an amount of
0.15-15 weight percent.
[0022] In a ninth aspect, alone or in combination with any one of
the previous aspects of the second embodiment, a product produced
by the method is provided.
[0023] In a third embodiment, an inorganic phosphate compound is
provided of the general formula: [0024] i)
B.sup.s(A.sub.3-mPO.sub.4).sub.s; wherein A has a valency of m=1 or
2; and B has a valency of s=1, or 2; [0025] ii)
B.sup.s(A.sub.(2/m)PO.sub.4).sub.s; wherein A has a valency of m=1
or 2; B has a valency of s=1, or 2; [0026] iii)
.sup.(2/m)A.sub.3B.sub.m(PO.sub.4).sub.2; wherein A has a valency
of m=1 or 2; B has a valency of 3; or [0027] iv)
B(AOPO.sub.4).sub.s; wherein A has a valency of 4 and s=1 or 2; and
B has a valency of 1, or 2;
[0028] In a first aspect of the third embodiment, the inorganic
phosphate i-iv has less than 0.000001 to 10 percent of unreacted,
crystalline inorganic acid phosphate of an average particle size
greater than about 60 microns.
[0029] In a second aspect, alone or in combination with any one of
the previous aspects of the third embodiment, the inorganic
phosphate is at least one of the following: MgKPO.sub.4;
Mg(ZnPO.sub.4).sub.2 Mg(K.sub.2PO.sub.4).sub.2; Mg.sub.2KPO.sub.4;
Mg(ZnPO.sub.4).sub.2; Mg(K.sub.2PO.sub.4).sub.2;
Al.sub.2Mg.sub.3(PO.sub.4).sub.2; Mg(ZrOPO.sub.4).sub.2;
Mg[Zr(OH).sub.2PO.sub.4).sub.2].sub.2; and calcium/magnesium
phosphate.
[0030] In a third aspect, alone or in combination with any one of
the previous aspects of the third embodiment, less than 0.000001 to
10 percent of the unreacted, crystalline inorganic acid phosphate
is of an average particle size distribution greater than about 50
microns, less than 40 microns, or less than 30 microns.
[0031] In a fourth aspect, alone or in combination with any one of
the previous aspects of the third embodiment, the inorganic
phosphate has a density less than 1.8 g/cm.sup.3 or less than 1.5
g/cm.sup.3.
BRIEF DESCRIPTION OF THE DRAWINGS
[0032] FIG. 1 is an illustration of a corrosion protection layer of
a phosphate ceramic coating composition.
[0033] FIG. 2 is an illustration of a corrosion protection layer of
a phosphate ceramic coating composition as disclosed and described
herein.
DETAILED DESCRIPTION
[0034] In general, disclosed herein are multi-component
formulations comprising at least one acidic phosphate first
component and at least one alkaline second component, the first and
second components being suitable for providing, upon combination,
an inorganic phosphate composition.
[0035] As used herein, the phrase "aqueous mixture" refers to a
combination of at least a quantity of water and at least one of the
sparingly soluble acid phosphate or basic component. For example,
the aqueous mixture can contain mostly water and suspended,
dispersed, or slurried components, and may also contain non-aqueous
components such as alcohols and other solvents. Preferably, water
is the major liquid phase. The amount of solids (e.g., the
sparingly soluble acid phosphate or basic component and/or other
solids) present in the aqueous mixture can be between 1 wt. % to
about 80 wt. %, preferably 50-80 wt. % solids.
[0036] As used herein, the phrases "sparingly soluble acidic
phosphate component" and "acidic phosphate precursor" and "acid
component" and "acid-phosphate component" and "Part A" are used
interchangeably unless otherwise indicated. As used herein, the
phrase "sparingly soluble acidic phosphate component" refers to
inorganic acid-phosphates of chemical formula
A.sup.m(H.sub.2PO.sub.4).sub.m.nH.sub.2O, where A is metal cation,
or mixtures thereof; where m=1-3, and n=0-6. Such inorganic
phosphates typically have low solubility constants characteristic
of low aqueous solubility, e.g., solubility constants (Ksp) of at
least 10.sup.-6, 10.sup.-7, 10.sup.-8, 10.sup.-9 or smaller. In one
aspect, the phrase "sparingly soluble acidic phosphate component"
excludes phosphoric acid or ammonium phosphates, however,
non-stoichiometric amounts (e.g., less than 10 weight percent to
that of the acid phosphate component) of phosphoric acid can be
used to adjust pH of the aqueous phosphate precursor compositions.
Because solubility product constants may be pH dependent, the above
phrase includes the addition of small amounts of phosphoric acid to
the aqueous mixture of sparingly soluble acidic phosphate component
to provide a target solubility product constant relative to that of
the basic component.
[0037] As used herein phrases "sparingly soluble basic metal oxide
and sparingly soluble basic metal hydroxide component" and
"sparingly soluble basic component" and "sparingly soluble alkaline
component" and "sparingly soluble alkaline precursor" are used
interchangeably unless otherwise indicated. The phrases "sparingly
soluble basic component" and "sparingly soluble alkaline component"
and "sparingly soluble alkaline precursor" are inclusive of
materials that are sparingly soluble, e.g., have low solubility
product constants in aqueous media, e.g., solubility constants
(Ksp) of at least 10.sup.-6, 10.sup.-7, 10.sup.-8, 10.sup.-9 or
smaller. In one aspect, the phrases "sparingly soluble basic metal
oxide and sparingly soluble basic metal hydroxide component" and
"sparingly soluble basic component" and "sparingly soluble alkaline
component" and "sparingly soluble alkaline precursor" are exclusive
of materials that are readily soluble, e.g., have high solubility
product constants in aqueous media. In one aspect, the sparingly
soluble acid phosphate has a solubility product constant that is
greater than the sparingly soluble basic component when used in
forming the acid/base phosphate coating.
[0038] The uniquely-suited formulations and methods disclosed and
described herein are based in one aspect on acid-base inorganic
phosphate compositions. It is believed that similar principles are
applicable for other acid/base pair compositions other than
inorganic phosphates. Examples of the inorganic phosphate coatings
provided herein include a magnesium potassium phosphate coating,
and calcium potassium phosphate coating. These compositions are
disclosed herein for coatings on steels, aluminum, and other metals
as corrosion inhibitors. When applied to a metal surface as a
paste, spray or vapor coating, the compositions react depending on
their solubility product constants, e.g., where the more soluble
component (e.g., preferably the acidic component) reacts with ions
associated with the bulk metallic surface substantially or to an
extent before the less soluble component (e.g., the basic
component). After reactions of the more soluble component with the
ions of the bulk metallic surface, the second component reacts
providing an alloying surface zone that is chemically bound to the
metallic surface and includes the reaction products of the ions
associated with the metallic surface (e.g., metal ions), and in
combination, the acid/base components, bonding therewith and
forming a thin layer/coating to the metallic surface. The bonded
layer is hard and inhibits corrosion of the metal surface. A range
of phosphate-based formulations may be used to coat and prevent or
minimize the corrosion of metallic surfaces. The metallic surface
can be pristine, polished, and/or contain pre-existing corrosion.
By selecting the acid component and basic component based on their
solubility in the media used to apply them to the metallic surface,
the aforementioned reaction products form that provide an improved
corrosion coating for the bulk metal.
[0039] The instant compositions can be configured as atomizible,
sprayable inorganic phosphate precursor compositions that can be
sprayed at a relatively thin thickness. The compositions can hold
high solids contents and yet still hold the solids until setting
and thus avoiding the solids migrating or dislodging from the point
of application, e.g., down a wall, beam, curved surface, or from a
ceiling surface. Such spray coated phosphate ceramic compositions
produce high-strength, rapid-setting phosphate ceramic coatings
that provide corrosion protection and/or be used as an undercoating
in combination with a polymeric coating or paint, such as an
acrylic- or urethane-based coating or paint. In one aspect, said
phosphate spray coating compositions are suitable for spray coating
on metal surfaces, for example, structural elements such as tanks
and other storage structures, as well as chassis of transportation
vehicles such as automobiles, trains, cycles, aerospace vehicles,
trucks, and buses.
[0040] Proper particle size selection of one or more of the
precursor materials provides improved corrosion protection relative
to conventional phosphate coatings. Proper selection of solubility
of one or more of the precursor materials provides improved
corrosion protection relative to conventional phosphate coatings.
Dense, hard, large crystals are likely to go into solution and/or
react slower and therefore may not completely dissolve and/or react
during the formation the ceramic coating and/or inhibit or alter
the formation of the passive layer on the metal surface. If they
remain behind after the coating has set up such dense, hard, large
crystals are likely to cause corrosion if in proximity to the metal
surface. Of course, the use of acid-phosphate precursors that are
completely soluble or are rapidly solubilized cause excessive
exothermic heat generation and/or react violently resulting in poor
coating properties. Thus, the combination of proper particle size
selection and solubility of one or more of the precursor materials
as disclosed and described herein provides improved corrosion
protection relative to conventional phosphate coatings. Unreacted
crystals of acid phosphate precursor (e.g., first component) that,
for example, do not dissolved in the formulation prior to set-up,
or do not react with a stoichiometric amount of base component will
eventually dissolve and leave a void in the coating and/or if in
contact with a metal surface, commence with an acid-metal reaction
that can lead to pitting and other corrosion-related issues.
[0041] It has now been determined that proper selection of particle
size commensurate with solubility of the acid-phosphate component
precursor effectively reduces or eliminates corrosion caused by the
precursors themselves as well as providing an improved corrosion
coating for the metal surface.
[0042] In one aspect, the average particle size of the
acid-phosphate precursor material is less than 600 microns.
Preferably, the average particle size of the acid-phosphate
precursor material is less than 60 microns, less than 50 microns,
less than 40 microns, less than 30 microns, or less than 20
microns.
[0043] Very small particle size phosphate acid (or acid-phosphate)
precursors are achievable with milling or other commutation
techniques alone or in combination with surfactants. The present
method is particularly advantageous with certain low solubility or
"sparingly soluble" components, e.g., monopotassium phosphate (MKP)
solid in particulate form.
[0044] By way of example, the particle size of the acid-phosphate
component can determine whether the resultant ceramic coating is
going to provide corrosion protection or actually contribute to
localized corrosion after coating. Whatever solid phosphate
component is chosen, it is preferred that it go completely into
solution and/or react with the basic component before or during
set-up. While some chemistry of the phosphate component and the
metal surface is desirable and indeed, beneficial, if un-reacted
phosphate component is localized in the solid ceramic and in
proximity to the metal surface, and in this localized environment
the basic component is substantially absent or of a
non-stoichiometric amount relative to the acid component, overtime
and via egress of water, corrosion and/or pitting of the steel
surface will likely result. This problem is exacerbated by the
presence of large, unreacted particles (e.g., greater than 70
micron, and especially greater than 100-1000 micron average
diameter particles) of an acid phosphate components present
throughout the hardened ceramic that ultimately react with residual
base and/or water that has seeped into the coating leaving behind
in the ceramic a porous structure that further promotes water
egress. Balancing this is the observation that very small particles
of acid and base components tend to react rather quickly reducing
setup time and shelf-life, which has diverted interest in pursuing
extremely small particle size formulations without the need for
additional chemistries to retard or otherwise inhibit fast reaction
rates and exothermic phenomena that likely would otherwise
occur.
[0045] The above is schematically depicted in FIG. 1, which depicts
a conventional phosphate chemistry formulation having particles of
acid component 600 greater than about 70 micron and base component
700 combined as a coating 400 on metal surface 500. After set-up
and over a time period less than the average useable life of the
metal object having the coated surface, the unreacted, crystalline
base components and the acid components of coating 405 react or
dissolve, leaving behind porous voids 650 of approximate size or
slightly smaller or larger of that of the crystal(s) present at set
up. Of particular concern is the acid-phosphate crystals left in
proximity 610 to the metal surface-coating interface, which is
capable of undergoing the acid-metal reaction and generating
hydrogen gas. These particular localized, unreacted acid-phosphate
crystals contribute to pitting 625 and other types of corrosion of
the metal surface and are undesirable in a coating designed for
corrosion protection. It is therefore provided herein in at least
one embodiment of the present disclosure to eliminate or reduce the
number of large, unreacted acid-phosphate crystals that can be
present in the corrosion coating prior to and during setup and
subsequently thereafter.
[0046] Thus, as depicted in FIG. 2, the phosphate chemistry
formulation of the present disclosure, having particles of acid
component 602 less than about 60 micron, and base component 702
combined and cast as a coating 402 on metal surface 500. After
set-up and over a time period less than the average useable life of
the metal object having the coated surface, the unreacted,
crystalline base components and the acid components of coating 405
react or dissolve, leaving behind significantly smaller porous
voids 652 of approximate size to that of the crystal(s) present at
set up or slightly smaller or larger and with substantially less
crystals present at the metal surface-coating interface so as to
prevent or eliminate post-coating pitting or other types of
corrosion of the metal surface.
[0047] In various aspects, a multi-component formulation is
provided, comprising at least one acidic component and at least one
alkaline component. Both components of the multi-component
formulation are provided as solutions, emulsions, dispersions,
pastes, or combinations thereof. Each of the components can be
produced separately and stored separately, and may be dispensed
separately or in combination. The components ultimately are
combined prior to or during application and are allowed to react to
form an inorganic phosphate composition.
[0048] Thus, in one aspect, a phosphate ceramic precursor
composition is provided comprising a first component comprising an
aqueous mixture of an acid phosphate having a particle size
distribution between 0.04 to 60 micron. In another aspect, about
50% of the particle size distribution of the first component is
particles of less than 50 micron, less than 40 micron, less than 30
micron, or less than 20 micron. In another aspect, about 90% of the
particle size distribution of the first component is particles
having a particle size less than 40 micron, less than 30 micron, or
less than 20 micron. In yet another aspect, the first component
average particle size is between about 20 micron to about 30
micron. The present coatings provide excellent corrosion resistance
and also improved resistance to pitting and other corrosion related
phenomenon as well as providing a more dense, less porous phosphate
ceramic by virtue of the reduction in size of voids typically
created by the post-set reaction and/or dissolution of the acid
phosphate crystals.
[0049] The phosphate ceramic composition can comprise an acidic
phosphate component comprising an aqueous solution, suspension, or
slurry of an acid-phosphate, for example, of chemical formula
Am(H.sub.2PO.sub.4)m.nH.sub.2O, where A is hydrogen ion, ammonium
cation, metal cation, or mixtures thereof; where m=1-3, and n=0-6;
the first component solution adjusted to a pH of about 2 to about
5; a basic component, comprising, for example, an aqueous solution,
suspension, or slurry of an alkaline oxide or alkaline hydroxide
represented by B.sub.2mOm, B(OH).sub.2m, or mixtures thereof, where
B is an element of valency 2m (m=1, 1.5, or 2) the second component
solution adjusted to a pH of between 9-14; and a rheology
modifier/suspending agent in an amount capable of providing shear
thinning of either the first component or the second component and
further capable of suspending a high solids content of either the
first component or the second component for atomization.
Optionally, pigments and/or aggregate material can be present in an
amount in at least one of the acidic phosphate and the basic
component capable of imparting an observable color and/or texture.
The above composition can be configure as an atomizible spray
coating that can provide a thin, paint-like coating for imparting
corrosion resistance to metallic surfaces. The rheology
modifier/suspending agent can be at least one of guar gum, diutan
gum, welan gum, and xanthan gum. By using an optional rheology
modifier/suspending agent in an amount capable of providing shear
thinning of the basic component and further capable of suspending a
high solids content of either the acidic component or the basic
component for atomization, excellent paint-like coatings for
imparting corrosion resistance to metallic surfaces are
obtained.
[0050] Processes and articles prepared by coating with the
aforementioned formulation are disclosed and described herein and
such coated articles overcome many if not all of the problems
related to conventional passivation processes of iron, steels,
aluminum, and other corrodible metals. The instant processes also
provide a more economical, environmentally-friendly method of
coating steel and other metal surfaces with acid-base inorganic
phosphate based coatings that not only passivate the layer but also
provide abrasion resistance along with good aesthetics in one
step.
[0051] The instant coatings disclosed herein can comprise, in part,
the formation of poly phosphates, and in particular, poly
phosphates formed by phosphites at the interfacial regions of the
substrate surface in the instant coating. Polyphosphate can provide
abrasion resistance and impermeablity to water and humidity, thus
improving abrasion resistance as well as improving corrosion
resistance to the substrate surface.
[0052] In one aspect, an acid-phosphate composition, one acidic
with a pH between about 3 to about 4.5, and the other, an alkaline
component with a pH between about 10 and about 11. These two
components are contacted with the substrate surface, where they
combine form a coating. For example, mono potassium phosphate
(KH.sub.2PO.sub.4) and a magnesium hydroxide (Mg(OH).sub.2, or its
brine) composition with or without fillers such as wollastonite
(CaSiO.sub.3) or fly ash, can be combined and contacted with a
corrodible metal surface (e.g., steel). Once the compositions
contact the surface, a coating forms that bonds instantly to the
substrate. While not wishing to be held to any particular theory,
it is believed that the contact by the acidic phosphate and an
alkaline oxide or hydroxide, or oxide mineral components provides
an initial passivation layer (sub-, primer, or bottom layer) as
well as the corrosion protective layer.
[0053] In certain aspects of the present disclosure, the metallic
surface is that of a transition metal or its alloy, for example,
iron, chromium, aluminum, copper, etc.
[0054] Acidic phosphate component--The acidic phosphate component
consists of an acid-phosphate representative of the formula,
A.sup.m(H.sub.2PO.sub.4).sub.m.nH.sub.2O, where A is an m-valent
element such as sodium (Na, m=1), potassium (K, m=1), magnesium
(Mg, m=2), calcium (Ca, m=2), aluminum (Al, m=3) etc. A may also be
a reduced oxide phase when higher-valent oxides are used. For
example, for iron, which exists in valence state of +2 and +3 (FeO
and Fe.sub.2O.sub.3 as oxides), A can be the metal of lower
oxidation state. It can also be a cation of oxides of four-valent
metal oxide such as ZrO.sup.2+, in which case m=2. nH.sub.2O in the
formula above is simply the bound water, where n can be any number,
normally ranging from 0 to 25.
[0055] It is possible to use hydro phosphates of trivalent metals
such as aluminum, iron and manganese represented by the formula
AH.sub.3(PO.sub.4).sub.2.nH.sub.2O, where A is a transition metal
that includes aluminum, iron, manganese, yttrium, scandium, and all
lanthanides such as lanthanum, cerium, etc.
[0056] In case the pH of the acidic precursor is higher than needed
for instant reaction, phosphoric acid may be added and the pH may
be adjusted to bring down the pH. A preferred pH selected is
between 3 and 4, and the most preferred pH is between 3 and 3.5.
either elevating the pH of phosphoric acid or that of an
acid-phosphate such as magnesium dihydrogen phosphate
(Mg(H.sub.2PO.sub.4).sub.2) or aluminum trihydrogen phosphate
(AlH.sub.3(PO.sub.4).sub.2) by neutralizing partially using an
alkaline oxide, hydroxide, or a mineral, or by acidifying a
dihydrogen phosphate such as mono potassium phosphate
(KH.sub.2PO.sub.4) that has a pH>3.5 by adding a small but
appropriate amount of phosphoric acid or a low pH acid phosphate
such as Mg(H.sub.2PO.sub.4).sub.2 or aluminum trihydrogen phosphate
AlH.sub.3(PO.sub.4).sub.2. Examples described later in this
document provide the art of adjusting this pH.
[0057] Often the acid-phosphate solid used as the precursor is only
partially soluble. In such a case, the acid-phosphate precursor is
milled (wet or dry milling or other grinding or size-reduction
technique) so that the particles pass through 325 mesh sieve (less
than 50 micron), 400 mesh sieve (less than 38 micron), 450 mesh
sieve (less than 32 micron), 500 mesh sieve (less than 25 micron),
or 635 mesh sieve (less than 20 micron). In one aspect, the acid
phosphate has a solubility product constant that is greater than
the basic component used in forming the acid/base phosphate
coating.
[0058] Water may be added to the precursor component to reduce the
viscosity thereof, or other types of viscosity reducing agents may
be used. Commercial additives that prevent algae growth may also
added to this precursor so that no algae growth occurs during
storage of this precursor.
[0059] The Basic component or precursor comprises one or more basic
oxides, hydroxides and basic minerals. The basic component
generally consists of a sparsely soluble oxide, or preferably a
hydroxide with a solubility product constant less than the acid
phosphate precursor. In one aspect, a particle size less than 230
micron or of a size commensurate with that of the acid component
discussed above. The oxide may be represented by the formula
B.sup.2mO.sub.m or B(OH).sub.2m, where B is a 2m-valent metal. All
divalent metal oxides (m=1), and some trivalent metal oxides in
reduced state fall into this category of small solubility product
constant oxides. Examples of divalent oxides are, but not limited
to, magnesium oxide, barium oxide, zinc oxide, calcium oxide and
copper oxide. Examples of trivalent oxides in reduced state are
iron oxide (FeO), and manganese oxide (MnO). In preferred aspects
of the instant disclosure, 0 to about 10 molar excess of basic
component relative to acidic component is used. For example, about
0-10 molar excess of Mg(OH).sub.2 based on MKP acidic phosphate can
be used. In one aspect, the molar ratio of acid:base components can
be between about 0.9:1.0 to about 1.0:3.0; preferably about
1.0:2.0; and most preferably, about 1.0:1.8. For example, the
composition comprising Mg(OH).sub.2:KH.sub.2PO.sub.4 =1.8:1.0
provides equal volumes of Parts A and B during spraying. In other
aspects, spray coatings of the instant compositions having a molar
ratio of about 1:2 or about 1:1.5 (acid:base) with mixing, sprayed
well and corrosion protected effectively.
Inorganic Phosphate Coating Compositions
[0060] A range of phosphate compositions may be used as the
corrosion inhibitor coatings commensurate with the spirit and scope
of that disclosed and described herein, the following three
exemplary, non-limiting examples are provided: [0061] 1. Magnesium
potassium phosphate coating formed by the combination and/or
reaction of magnesium oxide (MgO) and mono potassium phosphate
(KH.sub.2PO.sub.4), which in the presence of water combine to
produce magnesium potassium phosphate ceramic, comprising
MgKPO.sub.4.6H.sub.2O. Magnesium potassium phosphate is also
referred to hereafter as "MKP". [0062] 2. Magnesium hydrogen
phosphate (newberyite) coating formed by the combination and/or
reaction of magnesium oxide (MgO) and phosphoric acid solution
(H.sub.3PO.sub.4 solution), which when mixed well and allowed to
dry, combine to produce a magnesium hydrogen phosphate coating
comprising MgHPO.sub.4.3H2O. [0063] 3. Magnesium hydrogen phosphate
(newberyite) coating formed by the combination and/or reaction of
magnesium dihydrogen phosphate compositions usually have an aqueous
pH between about 2.5 and about 5.0. Magnesium hydrogen phosphate is
also referred to hereafter as "MHP". MHP solutions with a pH of
about 3 or slightly higher are generally believed more effective in
the production of corrosion resistant products and, for at least
that reason, tend to be preferred.
[0064] Under ambient conditions, aqueous mixtures of magnesium
potassium phosphate compositions and magnesium hydrogen phosphate
compositions exhibit a paste-like consistency that can be shear
thinned to be atomizable for spraying. When these compositions are
applied to a surface, e.g., steel, as coatings, it is believed that
one or more reaction occurs, and/or the one or more reaction occur
at different rates, and a thin layer of the above compositions
bonds to the metallic surface. The remaining parts of the coatings
distal from the metallic surface can be loosely bound and can be
easily scraped off, but the layer or coating is thin it remains and
is very hard, resistant to abrasion, and inhibits corrosion of the
surface. Thus, in one aspect, this thin layer provides protection
of the metallic surface from corrosion. Similar results are
observed when these compositions are applied to the surface of
other metals besides steel, such as aluminum. It is believed that
the same effects would be observed for copper, nickel, tungsten,
vanadium and other transition metals prone to oxidation at pH's of
between about 2 to about 11, and potentials of about 2eV to about
-2eV.
[0065] In another aspect, the above phosphate ceramic precursor
components are utilized to form an inorganic phosphate compound.
The inorganic phosphate compound comprises less than 1%, less than
0.1%, less than 0.01%, less than 0.001%, less than 0.0001%, less
than 0.00001%, less than 0.000001% unreacted, crystalline inorganic
acid phosphate of an average particle size greater than about 60
micron, 50 micron, 40 micron, 30 micron, or 20 micron. Residual
unreacted inorganic acid phosphate can be determined using a number
of techniques including but not limited to x-ray crystallography,
Raman spectroscopy, FT-IR spectroscopy, optical microscopy,
porosity measurements, density measurements, and the like. In one
aspect, the inorganic phosphate prepared in accordance with the
present disclosure as a density less than 1.8 g/cm.sup.3. In
another aspect, the inorganic phosphate prepared in accordance with
the present disclosure as a density less than 1.5 g/cm.sup.3.
[0066] In another aspect, the instant corrosion resistant coatings
can be formulated to provide aesthetic properties, such as color,
proper shine, and texture. This effect may be achieved, for
example, by adding pigments, color aggregate, crushed glass, sand,
etc, to the instant acidic phosphate/alkaline metal oxide/hydroxide
formulations. For example, the resulting coating comprising crushed
glass prepared by the processes disclosed herein provides a very
dense glassy surface. Additional suitable ceramic pigments may be
further added to produce colored paints. Soluble glass in
combination with the instant compositions above can also be used in
formulations for coating of solid objects, to provide very dense,
glassy solid coatings having corrosion resistance.
Experimental Section
[0067] The following examples are illustrative of the embodiments
presently disclosed, and are not to be interpreted as limiting or
restrictive. All numbers expressing quantities of ingredients,
reaction conditions, and so forth used herein may be understood as
being modified in all instances by the term "about." Accordingly,
unless indicated to the contrary, the numerical parameters set
forth herein may be approximations that may vary depending upon the
desired properties sought to be obtained. At the very least, and
not as an attempt to limit the application of the doctrine of
equivalents to the scope of any claims in any application claiming
priority to the present application, each numerical parameter
should be construed in light of the number of significant digits
and ordinary rounding approaches. Several experimental examples,
listed below, were conducted in order to formulate, coat, and
demonstrate the attributes of the instant compositions disclosed
herein.
[0068] A range of phosphate compositions may be used as the
corrosion inhibitor coatings commensurate with the spirit and scope
of that disclosed and described herein, the following exemplary,
non-limiting examples are provided:
TABLE-US-00001 TABLE 1 Exemplary Phosphate Ceramic Compositions
Part A Part B Sample Weight percent (%) of Part A Weight percent
(%) of Part B A mono potassium phosphate (MKP) magnesium hydroxide
(~38-39%) (~63-64%) of an average particle size wollastonite
(~20-21%) of about 20 micron xanthan gum (0.07%) phosphoric acid
(~8%) remainder water ~27-28% xanthan gum (0.15%) crystalline
SiO.sub.2 (~1.5%) remainder water B Mono Potassium Phosphate (MKP)
magnesium hydroxide (~40%) (~63-64%) of an average particle size
xanthan gum (0.07%) of about 20 micron K.sub.3PO.sub.4 (~3.5%)
phosphoric acid (~6%) remainder water xanthan gum (0.15%)
crystalline SiO.sub.2 (~1%) calcined kaolin (~12%) remainder water
Control mono potassium phosphate (MKP) magnesium hydroxide
(~38-39%) (~63-64%) average particle size about wollastonite
(~20-21%) 200-700 microns xanthan gum (0.07%) phosphoric acid (~8%)
remainder water ~27-28% xanthan gum (0.15%) crystalline SiO.sub.2
(~1.5%) remainder water
[0069] Samples A and B and Control when field tested on storage
tanks showed that the Control samples containing larger average
particle size MKP were more likely, if not consistently, prone to
pitting, galling, cracking, and staining that was visible upon
inspection after four months. In contrast, Samples A and B, using
smaller average particle size MKP, did not show visible signs of
coating-induced corrosion or pitting and further, provided
excellent resistance to environmentally-caused corrosion events
such as salt spray, rain, and humidity.
* * * * *