CA1050480A - Protective coating for ferrous bodies - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
A corrosion protective coating for a ferrous metal substrate of iron, iron alloys, steel. and the like, comprising a base ingredient consisting of a prehydrolyzed, polymerizable compound capable of developing A porous layer upon curing, a filler of particulate material intimately intermixed with said base ingredient such as a pigment which may be inert or active, or combinations thereof, and a soluble salt, capable of producing ions when in solution which react with anodic portions of the metal substrate to inhibit same. The reaction products of corrosion progressively fill the interstices of the porous layer which uniquely retains same as integrated components of the developed coating for preventing further corrosion.

Description

~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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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 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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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.
-_g_ .. . . . .. .. , ., .,.. ~ .. . - . - .

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, 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 ~-12-.. . ... . .. .
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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.

~.

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.

' 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.

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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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.

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--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 ~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 . .

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:

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~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.

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Claims (22)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A protective coating on a corrodible ferrous substrate, said coating comprising an intermixture of a base coating material constituted of a prehydrolysed polymeric material capable upon curing to develop a hard mass having a multiplicity of pores; at least one filler material of particulate character from the class consisting 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 producing anions interreactive with anode portions of the ferrous sub-strate, said pores as formed upon curing of said base coating material being receptive to ambient corrosive electrolytic solutions so that the reaction products of corrosion and of said ionizable salt and said electrolytes will fill said pores so as to develop the intermixture into a solid barrier, said base coating material being 20 - 60% by weight of said prot-ective coating.

2. A coating on a corrodible ferrous substrate as defined in Claim 1 and further characterized by said base coating material being from the class consisting of alkyl silicates, acrylic resins, urethane resins, and styrene resins.

3. A coating on a corrodible ferrous substrate as defined in Claim 1 and further characterized by said ionizable salt being from the class consisting of organic and inorganic salts capable of ionizing in moisture absorbed into the mass through the pores thereof.

4. A coating on a corrodible ferrous substrate as defined in Claim 1 and further characterized by said filler material constituting between 30 - 79.9% by weight of said protective coating and said ionizable salt constituting between .1-10% by weight of said protective coating.

5. A coating on a corrodible ferrous substrate as defined in Claim 4 and further characterized by said base coating material being from the class consisting of methyl silicate, ethyl silicate, propyl silicate, isopropyl silicate, butyl silicate, hexyl silicate, 2-ethyl hexyl silicate, tetra ortho methyl silicate and tetra ortho ethyl silicate.

6. A coating on a corrodible ferrous substrate as defined in Claim 5 and further characterized by said filler material being from the class consisting of silica, talc, mica, kaolin, bentonite, asbestos, fireclay, clay impurities, ferric oxide, tin, tin oxide, titanium oxide, carbon, and chromium oxide.

7. A coating on a corrodible ferrous substrate as defined in Claim 1, Claim 4 or Claim 6 and further characterized by said ionizable salt being from the class consisting of the inorganic salts of carbonic acid, phosphoric acid, chromic acid, boric acid, molybdic acid, sulphuric acid, or silicic acid, and organic salts of phosphoric acid, or chromic acid, and sodium nitrite.

8. A structure protected against corrosion in the presence of an electrolyte comprising a corrodible ferrous substrate having a protective coating provided thereon, said protective coating comprising a prehydrolysed polymeric base coating material capable upon curing to develop a hard mass having a multiplicity of pores, at least one filler material, and at least one ionizable salt, said base coating material and said filler material and said ionizable salt being intimately intermixed, so that the developed pores permit absorption and retention of ambient corrosive electro-lytic solutions therein, said ionizable salt being capable of forming ions within the said solutions which ions are reactive with the electrolytes in said solutions to form reaction products for reception and retention within the aforesaid pores so as to develop a rigid barrier against further moisture penetration, said base coating material constituting between approximately 20 to 60% by weight of the protective coating.

9. A structure as defined in Claim 8 and further characterized by said base coating material being from the class consisting of alkyl silicates.

10. A structure as defined in Claim 8 and further characterized by said filler being of particulate character and from the class consisting of naturally occurring minerals and metals and metal oxides, which latter are cathodic with respect to the metallic substrate.

11. A structure as defined in Claim 10 and further characterized by said base coating material being from the class consisting of alkyl silicates.

12. A structure as defined in Claim 11 and further characterized by said ionizable salts being from the class consisting of organic and inorganic salts.

13. A structure as defined in Claim 12 and further characterized by said inorganic salts being the salts of carbonic, phosphoric, chromic, silicic, boric, molybdic and sulphuric acid.

14. A structure as defined in Claim 12 and further characterized by said organic salts being salts of phosphoric and chromic acid.

15. A structure as defined in Claim 8 and further characterized by said filler composition comprising 30-79.9%
by weight of the protective coating and said ionizable salt comprising .1-10% by weight of said protective coating.

16. A structure as defined in Claim 8 and further characterized by said base coating material being ethyl silicate, said filler material being an inert mineral, and said ionizable salt being dibasic calcium phosphate.

17. A structure as defined in Claim 8 and further characterized by said base coating material being ethyl silicate, said filler material being from the class consisting of silica, talc, mica, kaolin, bentonite, asbestos, fireclay and fireclay impurities, and said ionizable salt being dibasic calcium phosphate.

18. A structure as defined in Claim 8 and further characterized by said base coating material being methyl silicate, said filler material being ferric oxide and said ionizable compound being strontium chromate.

19. A structure as defined in Claim 8 and further characterized by a buffering agent provided in the protective coating.

20. A method for protecting corrodible ferrous structures comprising providing a prehydrolyzed polymeric base 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 inorganic salts of carbonic, phosphoric, chromic, silicic, boric, molybdic, and sulphuric acids, organic salts of phosphoric and chromic acid and sodium nitrite, intimately intermixing said base coating material, said filler composition and said ion-izable compound, then applying said intermixed mass while in plastic form to said structure to be protected, permitting said mass to cure for providing a hard porous coating bonded to said structure, and then exposing said coating-covered structure to a corrosive environment for reception and absorption by said coating of ambient corrosive electrolytic solutions whereby reaction products of corrosion are formed by the electrolytes and the ions of said ionizable compound for progressively filling the pores of said protective coating to develop a rigid barrier preventing further reception and absorption of corrosive solutions, said base coating material constituting between approximately 20 to 60% by weight of the protective coating.

21.
The method as defined in claim 20 and further characterized by said organic salts of phosphoric and chromic acid comprising triethyl phosphate, trimethyl phosphate, tripropyl phosphate, tributyl phosphate, isopropyl phosphate, tricresyl phosphate, triphenyl phosphate, triethyl ammonium phosphate, guanidine chromate, triethanolamine chromate, morpholine chromate, di-phenyl guanidine chromate, benzidine chromate, and alkyl pyridine dichromate.

22.
The method as defined in claim 20 and further characterized by said filler composition comprising 30 - 79.9%
by weight of said protective coating and said ionizable compound comprising .1 - 10% by weight of said protective coating.