Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
~05~480
BACKGROUND OF THE IN~ENTIQN
This invention relates in general to the protection of
metallic structures against corrosion and, more particularly,
to a coating uniquely adapted to effect utilization of products
of corrosion as an integral part of the protective barrier.
Heretofore numerous and extensive efforts have been
undertaken to prevent or mitigate corrosion o` metallic
structures as disposed within corrosive media, whether the
same be vapors, such as containing sulphur dioxide,salt, fog,
etc., or liquids, such as sea water brine, or underground waters.
One of the more widely and well known techniques is referred
to generally as ca~hodic protection which may comprehend the
use of sacrificial anodes or by so-called impressed current
systems. However, cathodic protection has proved to be relative- -
ly expensive in application and involves an undesired complexity.
Another technique has involved the concept of
corrosion inhibition wherein the surfaces of the structure
to be protected have been exposed to reasonably soluble compounds
so selected that certain constituents thereof react chemically
with the metal of the substrate to yield reaction products
protecting the surface against corrosion. Phosphatation is
an example of such treatment wherein the applied coating
contains phosphoric acid causing a phosphatic protective
coating to develop over the metal surface. However, such corrosion
inhibition has not in practice proved to provide the reliability
and effectiveness desired in view of the fact that the resulting
coatings are relatively thin and uneven and are imperfectly -
bonded to the underlying metal. Consequently, relatively
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l(~S04~it0
small isolated anodic area~ will occur through such unevenness
and through flaking which development will tend ~o accelerate
corrosion by generating small corresponding electric
voltage differentials or couples with cathodic surfaces
electrically shorted to the anodic areas. Furthermore,
such techniques have not succeeded in protecting immersed
metal structures because of the extreme voltage differentials
existiny between anodic and cathodic ~urface portions.
How~ver, from a theoretical ~tandpoint, the development of a
protective surface film as through normal products of
corrosion or by pa~sivation has been recognized as a fundamentally
effective corrosion inhibiting method. But to the pre~ent time
mean~ have not been achieved for eliminating or neutralizing
the disadvantages encountered in actual practice of such
¦ technique~. Thus, surface film~ of oxides as formed on iro~
or steel, and the like, are insufficiently dense to protect
the underlying metal, being porou~ in places and readily
fracturable 80 that in~tead of hindering corrosion, the same i~
actually accelerated by reducing the anodic ~urface areas through
electrical shorting to the cathodic ~urface area~.
Therefore, prior to the present inv~ht~on, there
has not been known a method or ~ystem for reliably developing
a corrosion-protective coating or barrier which effectively
embodies the normal reaction product~ of ~orrosion of the
protected ~truct~re withln ~aid coating or barrier.
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iO50480
SUMMAR~ OF THE INVENTION
Therefore, it iB a primary object of the present
invention to provide a corronion inhibiting coating for ferrou~
metal substrates which uniquely incorporate~ as fundamental
con~tituent~ of such coating reaction products re~ulting
from the corroQion of the metal to be protected.
It i~ another object of the pre~ent invsntion to
provide a corrosion inhibitor of the type 3tated which obviates
the utilization of cathodic protective system~ and overcomes
the heretofore accepted inadequacies of lnhibition treatment.
It i8 a further object of the pre~ent invention to
provide a coating which can be ea~ily applied by any
conv~ntional means to ths metal ~ubstrate to be protected:
and wherein the applic~tion i~ rapldly effected and with
limited time requlred for curing and drying.
It i~ a ~till fur*her object of the pre~ent .
invention to provide a coating which is relatively inexpensive
to produce; the u~e o~ which matsrlally enhances the ~ervice
life of the protected sub~trate; whlch ~ay be ea~ily applied
20 in varying effectlve thickneq~e~ without substantial
co~t; which i~ adapted to be applied in cold and ~nclement
weather conditlons; and whlch i~ non-reactive with agent3, such a~ -
alkalis, organic chemicals, and ultraviolet rays at temperature~
up to 1000F.
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1050480
It is another object of the present invention to
provide a coating of the character Qtated which may be used as
a primer for topcoa~ capable of inhibiting corro~ion that would
otherwi~e occur at di~continued portion3 of the topcoat.
It iS a further object of the present invention
to provide a coating which does not nece~sitate the appli~ation
of a preliminary adhe~ive coating ~ince the said coating
become~ progre~ively more adherant to the substrate as a
result of the oxidative and reductive reactions occuxring
at the sub~trate-coating interface.
It i~ a still fur~her object of the present inve~tion
to provide a corrosion inhibiting coating for a metal substxate
wh~ch 30 uniquely adheres to the latter that the same may be
fabricated, welded,or the like without damage to the
coating.
It i~ another object of the present invention to
provide a protective coating of the type stated which
does not require more than a 3ingle coating for sub~tantially
permanent protection of the metal substrate.
It i~ another object of the present invention to
provide a corro~ion inhibiting coating fox ~tal ~ubstratQs
which is effective in liquid or gaseou~ phaQe ~o that the
treated structure i~ protective under ground, above ground, or
within a corro~ive liquid medium.
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~(~50480
GENERAL STATEMENT OF THE INVENTION
The present invention comprehends the provi~ion of a
unique coating for ferrouQ metal ~ub~trates to protect same
again~t the particular ambient corrosive phage and fundamentally
comprise~ a base component intimately intermixed with a
particulate filler and a ~oluble or ionizable compound. The
ba~e component i~ polymerizable ~o that upon curing the same
will provide a porous layer permitting of reception and ab~orption
of electrolyt~c ~olution~. The filler conduce~ to the adhesion
of the ba~e to the ~ub~trate as well as to the hardening o~
the base. ~he ~oluble or ionizable compound provide3 an
anion portion which interreact~ with the metal ~ub~trate
anode for effecting inhibition thereof and a cation component
which cau~es inhibition of ~he cathodic portion~ of the
~ubstrate. The corrosion producing reaction products
developed by the ionizable compou~d or compound~ a~ well a~
by any reaction of the ~ame with ion~ in the electrolyte
are received within the pore~ of the base layer and pxogres~ively
fill the same thereby building a hard rigid barrier within the
matrix of the layer so that further moisture and oxygen
penetration i9 barred and the corroqive reaction terminated.
Thus, the pre~ent invention conte~plates the constructive
utilization of normal reaction products of corro~ion as
inherent con~tituent3 of the coating. The ba~e which i~
normally li~uid may have the ionizable compound di~solved
therein prior to in~ermixture with the parti~ulate filler;
or, if de~ired, the ~oluble compound m~y be intermixed
with the filler prior ~o ~malgamation of the latter with the
ba~e~
l(~S0~80
Thus, broadly, the invention contemplates a protective
coating on a corrodlble ferrous substrate which coating
comprises the intermixture of a base coating material constit-
uted of a prehydrolyzed polymeric material capable upon curing
to develop a hard mass having a multiplicity o~ pores, at
least one ~iller material of particulate character from the
class consistin~ of naturally occurring minerals and metals
and oxides thereof which metals are cathodic with respect
to the ferrous substrate, and at least one ionizable salt
capable upon ionization of producin~ anions interractive with
anode portions of the ferrous substrate. The pores as
formed upon curing of the base coatin~ material are receptive
of ambient corrosive electrolytic solutions so that the
reaction products of corrosion, and of the ionizable salt
and the electrolytes, fill the pores so as to develop the
intermixture into a solid barrier with the base coating
material being 20 - 60% by weight of the protective coating.
Further, the invention contemplates a method for pro-
tecting corrodible ferrous structures which comprises providing
20 a prehydrolyzed polymeric ~ase coating material from the class
consisting of alkyl silicates, acrylic resins, urethane resins
and styrene resins, providing a filler composition from the class
consisting of naturally occurring minerals and metals and metal
oxides which latter are cathodic with respect to the structure
to be protected, providing an ionizable compound from the class
consisting of the inorganlc salts of carbonic, phosphoric,
chromic~ silicic~ boric~ molybdic, and sulphuric acids,
or~anic salts of phosphoric and chromic acid and sodium nitrate,
and intimately intermixing the base coating material, the
filler composition and the ionizable compound. Then the inter-
mixed mass while in plastic form is then applied to structure
to be protected, permitting the mass to cure for providing a
hard porous coating bonded to the structure, and then
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105(~480
exposi~n~ the. co~t~ng-coyeXe~ structu~e to a cor~osi41e
env~ronment for recept~on an~ a~sorpt~on by~the coating of
ambient corrosive electrolytLc solutions whereby~reaction
products of corros~on are ~ormed by~the electrolytes and the
ions of the ionizable compound for progressively filling the
pores of the protective coating to develop a rigid barrier
preventing further recept~on and absorption of corros~ve
solutions. The base coating material const~tutes between approx-
imately 20 to 60% by weight of the protective coating.
It might be stated that to a controlled extent, corrosion
is encouraged for creating critical elements of the resultant
barrier.
As will be taught hereinbelow, substantially inert com-
pounds having good "hiding powers" may be incorporated within
the filler for obscuring any normally expected discoloration
caused by corrosion and surfactants may be utilized for
promoting the general distribution of inhibiting corrosion
products over areas substantially greater than would normally
occur.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The coating of the present invention is adapted for
protecting corrosible metal substrates of ferrous metals
as in the form of underground pipes, above ground equipment,
and the like.
For conducing to requisite bonding or adhesion,
it is preferable that prior to the application of the coating
the metal surface be freed of grease, oil, dirt, and mill
scale, as by solvent treatment or conventional abrasive
cleaning, and also including, for example, phosphatizing.
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1050480
The coating is comprised of three f ~ndamental component~,
one being referred to a~ the base, which is normally liquid,
the fill~r, which is normally of ~olid particulate character,
and a soluble or ionizable compound which may be either liquid
or ~olid, as required by the particular intermixture procedure.
The filler together with the ionized compound will jointly
vary wi~h re~pect to the base from a substantially 2 to 3 to a
4 to 1 ratio, depending upon the thicknes~ of the coating
desired.
The base is normally liquid, polymerizable material
capable of curing or hardening to pre~ent a firm, porou~
layer. Compoun~s found to be particularly ~uited for u~e as
the ba~e are the alkyl ~ilicates, ~uch as, methyl ~ilicate,
ethyl siliGate, propyl silicate, isopropyl sil~cate, butyl
~ cate, hexyl silicate, 2-ethyl hexyl silicate, tetra ortho
methyl ~ilicate and tetra ortho ethyl 3ilicate.
In additio~ to the alkyl silicates, aertain resin~
have al~o been found to posses~ the desired propert~es, such
boing variou~ acryllc resins, urethane re$ins, and styrene
resin~. $hus, the ba~e which ~erve~ as a binder for the
coat~ng cures or polymerizes to form a substantially
insoluble porou~ or foraminous matrix normally pervious
to mo~ture to conduce tb the mobility of electro ytes
tharethrough, as well a~ to form pores or lacunae for receiving
corros~on reaction product~ ormed in situ for purpo~es to be
more fully discu~sed herein~elow.
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105U41~V
The filler, as indicated above, is solia matter
in particular form, being preferably within a mesh size of
about, desirably, -325. The finer the particle ~ize the more
adherent the d~veloped coating. There is no intention to limit
the me~h size, but it i8 to be recognized that the filler should
be of finely divided dust character. The filler may be a
single pigment or a plurality of pigments. The term "pigment n
a~ used i3 intended to comprehend certain metals and oxide~
thereof having an electrochemical ralation to the particular
substrate 30 a~ to be fundamentally cathodic thereto; as well
as to variou~ chemically inert composition~, such as naturally
occurring clays and the like. The metals and metal oxides of
the foregoing would be con~idered wlthin the context of thi~
application as active pigments and the latter ' as inactive or
inert pigm~nts. As will be ~hown hereinbelow, the pigments
portion of the filler m~y comprehend either type of pigmen~
or both, as well a~ a multiplicity of compound~ falling
within either or both of such categories. The admixture
of the pigment of the filler with the ba~e cau~es the
developed hard, firm, reliably adherent porou~ layer on the
substrate upon curing of th~ base, which i~ preferably
prehydrolyzed. Apparently, the pigment particles are
interlocked by the binding character of the cured ba~e,
such as ~ilica, to promote the neces~ary poro~ity, as well
ax hardness and ~table adherence o~ the coating.
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10504~0
The other key ingredient of the coating i8 an lonizable
compound, ~uch as wa~er ~oluble ~alt capable of readily
forming ions for reaction fundamentally with the anodic portion
of the substrate for inhihiting ~ame through well known
reactions. such ions are al~o reactive with electrolytes
encountered within the particular corrosive pha~e. These
ionizable compound~ accordingly provide electrode inhibiting
propertie~, as well as control the nature of the in situ
deposition of reaction product3. As will be developed
more ~ully hereinbelow, the reaction products will gradually
fill the pores or foramina of the porou~ layer and thus,
in being held thereby, will constitute integral components
of the protective coating.
Considering now the more precise nature of the
compound3 comprising the piqments within the inert or
inactivo category thereof, they may be the following:-
~ilica, talc, mica, kaolin, bentonite, a~be~to~, fireclay,
and clay impurities, al~minum oxide and zircon.
The foregoing intimately intermix with the base coating
~0 material for developing the adherent porous layer. All of
~uoh composit~on~ are recognizedly of relat~vely low coat,
and dre capablo of reduction to desired part$cle 3ize.
~ ho~e pigments which have been referred to hereinabove as
belng active are s~lected primarily upon their cathodic orienta-
tion with re3pect to the ferrous ms~al constituting the ~ubstrate,
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1050480
that is, the ~tructure being protected. Thus, the following
are exemplary: - ferric oxide, tin, tin oxide, titanium oxide,
chromium oxide, and carbon. With iron, iron alloys, or
~teel ~ubstrate~ and the like, only those metals or metal
oxide3 which are mo~ ca~hodic than the steel or iron would
be used, ~uch as ferric oxide, chromium oxide, copper, copper
oxide, tin, and tin oxide. Accordingly, with the present
invention, the particular metal or metal oxide ~ectdd
would tend to cause oxidation of the iron or steel ~ub~trate
to ~tabil~ze anodic inhibition against corro~ion and
promote interaction with the ~oluble ~alt~, thereby
minimizing the generation of cathodic hydrogen ga~ in the
development of cathodic alkalinity of thc substrate.
As discussed more extensively hereinbelow, it i8 to
be obsexved ~hat either the active or the inact~ve pigment~
may be used for developing the protective coating of the
pr~sent invention.
With either type the ultimate rigid barr~er tightly
r~taining the produ~t~ of corrosion will re~ult. However,
with the use of the active pigment~ the production of ~uch
reaction product~ i~ a~celerated.
~ he ionizable compound i8 from the class consisting
o~ c~rtain water 901uble inorganic and organic salt~.
Carbonate~, pho~phat~s, silicates, chromates, metaborates,
molybdate~, and sulphate~ are ex~mplary of the type of 8alts
involv~d. The range with respect to any one inorganic
salt i~ relat~vely exten~ive, with 3uch being illustxated by
, ~ .. . .
~ 050480
the inorganic phospha~es, wherein there is comprehended
sodium phosphate, calcium phosphate, magnesium phosphate,
barium phosphate, iron phosphate, copper pho~phate,
lead pho~phate, alum$num pho~phate, chromium pho~phate and
dibasic calcium phosphate. Thus, an equally extensive
group of compound~ would be con~idered with respect to each
of the 8alt8 above generally listed. There i~ also to be
considexed within the ~norganic group sodium nitrite which
has proved efficaciouæ. Among the orgazic compound~
within thi~ category are the following: triethyl phosphate,
trimethyl pho~phate, tripropyl phoqphate, tributyl phosphate,
i~opropyl phosphate, tricresyl phosphate, triphenyl phosphate,
triethylammonlum phoæphate, guanidine chromate,
triethanolamine chromate, morpholine chromate, ei-phenyl
guanidine chromate, benzidine chromate, alkyl pyridine
dichromate. It should be undarstood that more than one
compound from this broad group may be utilized within the
filler.
~owever, if de~ired, for appearance or co~metic
purpose~, compoundq with ~hiding" powers may be embodied within
the filler for obscuring any diæcoloration resulting from the
corroæion p~oce~æes. Any such embod~ed ma~king comp~unds,
which are optional, may be selected for bolor but would necessarily
be of requisite particle size and be inert or resistant to
the environment. Manifestly, the same m w t be compatible
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1050480
with the absorptive properties of the base. Within this
group may be found farrous or ferric oxide, titanium
dioxide, chromium oxide. Those compounds which may
have appropriate propertie~ as a pigment within the filler
as above described would thus uniquely provide a dual capacity
in the present coating.
The general formulation for the coating of the present
invention would consist of the ba~e being 20 to 60% by weight,
and the filler, together with the ionizable compound
being jointly 40 to 80% by weight. The proportions of the
filler may be from approximately 90-99.9% pig~ent and
.1-10% ionizable compound~. In con3idering the coating,
the ~ollowing would be a general for~ulation:
BY WEIGHT
BAS~ 20% - 60~
FII.LER PIGMENT (S) 30% - 79. 9%
IONIZA33LE COMPOUND (S) ~1% - 10%
In con~idering applicatiQn of the general formula
above sot forth, it is to be rffmembered that either an
inert or active pigment or pigments may be utilized *ithin the
filler together with the ionizable compound or compound~,
and that su~h component~ may act~ally comprise a plurality
of compound~ within each of such particular group.
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105~480
EXAMPLE I
A coating havlng the requisite characteri~tics may
be formulated a~ follow~:
BY WEIGHT
BASE:
Prehydrolyzed methyl ~ilicate20%
FILLER ACTIVE PIGMENT:
Chromium Oxide 70
FILLER INER.T PIGMENT:
Asbestos Powder 5%
IONIZABLE COMPOUN~:
Diba~ic Calc~um Phosphate 5
~0~ ,
The forego~ng demon3trates the versatility of ~he
present coating in that both active and inactive pigments
are ~ncorporated in the filler and with the ba~e being at
the lower end of it~ ~ffective proportion and the filler
as its maximum.
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1050480
EXAMPLE II
BY WEIGHT
BASE
Prehydrolyzed ethyl silicate 52%
EILLER ACTIV~ PIGMENT:
Ferric Oxide 47
IONI~ABLE COMPOUND:
Iron Pho~phate l~
In thi~ formula only the so-called active type of
pigment i~ u~ed and the ionizable compound i~ at the lower
end of its range.
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~OS~480
EXAMPL II I
BY WEIGHT
BASE:
Prehydrolyzed methyl silicate 45
FILLER INERT PIGMENT:
Silica 25%
FILLER INERT PIGMENT:
Kaolin 25%
IONIZABLE COMPOUND:
Zinc Chromate 5%
10 0% ~
This formulation demon~trate~ the fillex as having
only tha iner~ type o pigment but with two different
compo~itions in this category.
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lOS0480
EXAMPLE IV
BY WEIGHT
BASE:
Prehydrolyzed ethyl silicate 47%
FILLER ACTIVE PIGMENT:
Ferric Oxide 41%
FILLER INACTIVE PIGMENT:
Clay Impurities 7%
IONIZABLE COMPO~ND:
Strontium Chromate 5%
~00%
This formulation i~ related to Example I in that
both the active and inactive types of pigments are :~
incorporated.
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lOS04~0
EXAMPLE V
BY WEIGHT
BASE:
Prehydrolyzed ethyl ~ilicate 40%
FILLER INACTIVE ~IGMENT:
Silica 48%
FILLER ACTIVE PIGMENT:
:
Titanium Oxide 5%
IONIZABLE COMPOUNDSs
Zinc Phosphate 5%
Calcium Phosphate Dibasic 2%
100%
The foregoing ~ 8 of interest in that it demonstrates a ~-
preponderance of the..insert-or inactive pigment over the
active pigment, but the latter being ~itanium oxide will also
provide a discoloration masking attribute.
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1050480
EXAMPLE VI
BY WEIGHT
BASE:
Prehydrolyz~d ethyl ~ilicate 50
FII~ER INACTIVE PIGMENTS:
Silica 25%
Talc 15%
IONIZABLE COMPOUNDS:
-
Iron Pho3phate 5%
Zinc Pho~phate 5%
This formula demon~trate~ the maximum percen~age
of ionizable compounds and wherein two such compound~ are
incorporated.
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10504~30
The ionizable compounds used in the present invention
may be either intermixed with the filler as in dry solid
particulate form or may be intermixed with the base by means of
a suitable solution. Accordingly, the ionizable compounds may
be used either in a liquid or a dry solid form and intermixed
with the base or the filler if desired.
As an example of intermixing the ionizable compou~d
with the base, prior to the amalgamation of the la~ter with the
filler, a predetermined quantity of sodium chromate may be
predissolved in 85% phosphorix acid thereby providing both sodium
chromate and sodium phosphate for ionizing in accordance with
this invention. Exemplary of such a composition would be as
follow~:
BY WEIGHT
BASE:
Prehydrolyzed ethyl silicate 40%
FILLER: ACTIV~ PIGMENT
Ferr~c Oxide 30%
FIILER: INACTIVE PIGMENT
S~ 29~ 5~6%
IONI2A~LE COMPOUNDs :
Sodium Chromate
Sodium Phosphate .404%
prepared by predissolving
.004~ sodium chromate ~ -
(.004~ by weight of coating)
in a5% pho~phoric acid
.4~ ~y weight of coating~
The provision of the ionizable compound or compounds in
liquid state for intarmixture with the ba~e may be easily
accomplished through obvious ~election of ~uitable acid with one
--~0--
1050480
or more of the compounds to be predissolved. ~owever, th~ fore-
going does demonstrate the ver~atility of the present invention
in that it can be prepared in several easily performed methods.
In order to prepare coating~ conforming to the invention
set forth herein,~-the ba~e and filler portions, either of which
incorporate the ionizable compount or compounds as above dis-
cussed, are intermixed under room atmo~pheric and temperature
condition~ and then applied by any suitable means whether by
spraying or by bru~h and the like to thesUbstrate to be protected.
As ~ndicated above, the ~ubqtrate will be in a sub~tantially
cleaned condition 80 as to be freed of grea~e, oil, and like
foreign matter. The liquid film i~ then allowed to cure, or
polymerize, with the development as brought out above, of a hard,
porouJ layer or coating which i8 reliably bonded to the substrate.
The lonizable compound or compounds incorporated in the aoating
are malntained thereby pending the reception of moisture by the
coating which i~ thus readily absorbed therein. The said
ionizable compounds ionize within the moisture and are available
for lnterreaction with electrolytes normally contained within
2Q the moi~ture such as sulfides, aulfite~ car~onic acid, etc.,
as well as oxidized iron discharged at the anode being the
sub~trate in this instance. Th~s, corrosion or ru~t formation
is actually promoted with the customary precipitation of
ferrous and ferric hydroxides which gradually are converted into
hydroxy carbonates. Thu~, the porosity or foraminous character
of the coating conduces to mobiIity of corrosion inhibiting ion~
so that the actual development of corrosion products is
encouraged together with the other reaction products caused by
the ioni~ab1e compound or compounds and the compositions
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~050480
within the ambient corrosive phase. The aforesaid reaction
products, whether corrosion, or otherwise, wïll progressively
be accepted within the pores or voids of the coating and com-
pletely fill same to result in a tightly packed condition
creating an ultimate barrier against further incursion of
moisture w-ithin the coating to effectively discontinue corrosion
and chemical interreaction beyond such juncture. It will be
seen that the products of corrosion as well as the simultaneous
accompanying reaction products will actually constitute an
integral component of the protective coating. By this unique
concept the products of corrosion are adapted to protect the
very substrate from which such products were formed. The
coating of the present invention presents a matrix which retains
such products so that the same may effectively perform a pro-
tectionary role which has not hitherto been achieved.
As pointed out above, the ionizable compound may
actually be but a single compound from the group indicated,
or may actually be constituted of a multiplicity of such
compounds. Calcium salts, such as calcium phosphate dibasic,
calcium carbonate, etc. are of especial interest in that the
same tend to cause a calcareous build-up about the cathodic
portion for cathode inhibition. However, the primary function
of the ionizable compound or compounds is to effect the develop-
ment of an electrolytic solution with the ions thereof facili-
tating chemical reactions productive of compounds which
constitute integral elements of the ultimate coating.
Both the inert or inactive pigments and the active
pigments have the property when in particulate form to conduce
to the rigidity of the porous layer as well as to its assured
.
lOS0481)
adherence to the s-ubstrate. In this respect there is an
identification of fundamental properties-. However, with
the utilization of the active pigments, as above categorized~
an electrical potential ïs created which hastens or accelerates
the involved chemical reactions. Thus, by using metals or
metal oxides- which are cathodic to the substrate, driving
potentials develop which promote ~he formation of the reaction
products which constitute protection for the anodic substrate.
It has been found preferable to utilize a metal or metal oxide
which would result in the least driving potential between same
and the anode of the substrate so that the potential would be
less likely to break through any films that might develop on
the anodic substrate. For instance, with an iron substrate,
it would be preferable to utilize iron oxides and more desirably
ferric oxide as the active pigment rather than copper or copper
oxide which latter are more cathodic to the substrate and
thereby develop a driving potential which might tend to disrupt
or prevent protective films from developing on the anodic
substrate.
- Therefore, in view of the foregoing, it will be seen
that the coating of the present invention is of low cost, both
from the standpoint of components, as well as in preparation
and application; and that in actual use the same provides a
reliable barrier which uniquely comprehends the constructive
utilization of corrosion products.
As indicated above, any discoloration brought about
by use of the present invention may be hidden by incorporation
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105~480
within the filler of a masking compound; with the de~ired
co~o~ being determinative of the compound u~ed.
Surface active agents may be incorporated within
the filler such a~ in the nature of 1% or thereabouts by
weight for reduction of ~urface ten~ion upon ab~orption
of moisture by the coating 80 as to conduce to diffu~ion
and relatively increased wetting.
It i~ particularly noteworthy that the ionizable
compound is in a relatively limited concentration ~o a3 to
preclude the development of osmosi~ a~ a cau~e for coating
blistering. In coatings usea heretofore there ha~ been a
relatively high concentration of solubl~ corro~ion inhibitors
which cau~e osmotic water bl~stering to occur in applied top
coat~ in the pre~ence of fresh water by rea on of the ~alt con-
centration under the top coat being greater than that in the water.
Also, the present coating encourages relatively harmless anodic
reactions which in the preQence of inhibitor~ stabilize the
anode against corrosion, and the generation of hydrogen gas
is minimized through the oxidation of hydrogen by oxidizing
compounds, e.g., chromate~, thereby eliminating another cause
for blistering.
Coatings developed in accordance with the foregoing
are inert to sunlight, high temperature~, and organic
chemicals. When the coating ia to be used in ~trong acid
environment~ the same may be controlled by incorporation
of buffer compounds, Yuch as, dicalcium pho~phate, which tends
to neutralize the acid~ present. Thus, the hydrogen ion
concent*ation or pH control may be effected by the following
ormulation which is purely exemplary:
-24-
~ - . . . . - .. , . , . . .- :
~OS0480
BY WEIGHT
B _ :
Ethyl silicate 37-1/2%
FILLER (Pigment) INERT
Silica 50 %
FILLER ACTIVE PIGMENT:
_
Ferric Oxide 5 %
IONIZABLE COMPOUND:
Iron Phosphate 2-1/2%
BUFFERING AGENT:
-
Dicalcium Phosphate 5 %
Also strong acid conditions can be controlled by theapplication of suitable topcoats which prevent acid~ from
penetrating to the coating. The coating of the present
invention ha~ extreme breadth of usage but for purposes of
illu~tration only may be u~ed as corrosion control ~ystems
for bridge structure~, water tank lining~, ship~ and barges,
farm machinery, reaction ves~els, railway equipment, off~hore
~tructures, power plant~, petroleum ~torage tank~, ~tacks,
automotive equipment, steel silos, etc., etc.
25-
. . : - . . . : . ~ . .: ,
