PIGMENT GRADE CORROSION INHIBITOR HYBRID COMPOSITIONS AND PROCEDURES

Abstract: A corrosion-inhibiting composition for application to a metal substrate, such as steel, silver, copper or aluminum, includes a film-forming organic coating composition, and, a pigment phase of a stable unitary hybrid material which contains organic and inorganic solid phase constituents interfaced at a crystallite level, that are inseparable by physical separation procedures and which display uniphase behavior. The inorganic phase includes a cation selected from Zn, Al, Mg, Ca, Sr, Ti, Zr, Ce and Fe and an anion selected from phosphates, polyphosphates, phosphites, molybdates, silicates and cyanamides. The organic phase includes zinc or alkyl-ammonium (for example: cyclohexyl-ammonium, di-cyclohexyl-ammonium, octyl-ammonium) salts of organic mercapto- and thio- compounds or their alkyl-substituted derivatives, as follows: mercaptobenzothiazole, mercaptothiazoline, mercaptobenzimidazole, mercaptoimidazole, 2,5-dimercapto-1,3,4-thiodiazole, 5,5-dithio-bis(1,3,4-thiadiazole-2(3H)-thione, mercaptobenzoxazole, mercaptothiazole, mercaptotriazole, mercaptopyrimidine, mercaptopyridine, mercaptoquinoline, alkyl- and cyclo-alkyl mercaptanes, N-alkyl- or N-cycloalkyl-dithiocarbamates, O-alkyl- or O-cycloalkyl-dithiocarbonates, O,O-dialkyl- and O,O-dicycloalkyl-dithiophosphates.

Description: Pigment Grade Corrosion Inhibitor Hybrid Compositions and Procedures Field of Invention The present invention relates to compositions and processes for inhibition of corrosion of metals. Background of the Invention Atmospheric corrosion of metals is the most visible form of occurrence of the spontaneous process fueled by 0_, H.O and various airborne pollutants always present in industrial or urban environments. Among numerous alternatives for corrosion preventive techniques, organic protective coatings are certainly the most versatile and economical. Structurally, corrosion inhibitive primers are solid composites, comprising finely divided, usually multi- component, inorganic pigment phases dispersed into continuous organic polymer phases, which are strongly adherent to the protected metal substrates. Although all physical characteristics relevant to primers' protective performance are reinforced by the dispersed inorganic pigment phase, they nevertheless remain permeable to 0 2 , H.O and air-born pollutants. As a consequence, organic coatings do not prevent atmospheric corrosion of metals, unless they are specifically formulated with active corrosion inhibitor pigment constituents, included in the pigment phase. Contrary to appearances, a metal substrate- protective primer, in equihbrium with its environment is a dynamic medium: it accommodates several concurrently occurring physical and chemical processes, in which water, always present due to the resin phase's permeabihty, plays a critical role. Coatings' water contents are variable, a function at any time of the resin components' chemical compositions, formulation parameters and humidity of the surrounding air. Under condensing humidity conditions, this moisture content reaches a i-_a_dmum value determined by pertinent formulation parameters. Water content affects the physical integrity of organic coatings in several ways. Most importantly, it promotes hydrolytic degradation of the resin phases, dissolves all soluble components (inclusive of pigments) to saturation concentrations and supports in situ diffusional transport processes of dissolved constituents. Water accumulates preferentially at metal-coating interfaces, causing loss of interfacial adhesion and more specifically supporting the electrochemical processes of metal corrosion. Paradoxically, in actively pigmented organic coatings water supports the inhibition of metal substrates' atmospheric corrosion, as well, by in situ solubilization of active pigments. Further, by diffusion, active species are transported toward both interfaces and made available for corrosion inhibition at metal- coating interfaces. Considering the dynamic nature of atmospheric corrosion, effective inhibition performance requires a critical irriiiimum or higher concentration of inhibitor species, continuously supplied to the substrate-coating interfaces. Evidently, substantial but limited solubility is a critical property of active corrosion inhibitive pigments, functionally as important as chemical composition and related molecular structure. Consequently, inhibitor pigment constituents of protective primers can be regarded as built in reservoirs of corrosion inhibitive species. Electrochemically active corrosion inhibitor pigments generally used for Fe, Al, or Cu protection, belong exclusively to only a few generic types of inorganic materials, such as chromates, phosphates, molybdates, borates, silicates and phosphites of Zn, Ca, Sr, Ba, Al, Mg, Pb, Cr, Fe, or diverse combinations of the same. Transition metal derivatives of hydrogen cyanamide, particularly ZnNCN are also known for pigment grade application, limited, however, to special mirror backing coatings intended for Ag protection. The active inhibitor species generally are the anionic constituents. The cations present, however, determine important physical properties of such pigments, i.e: solubility or kinetic availability of the effective species. Chromates and particularly SrCrCv (characterized by desirable combination of relatively high CrQ, 8 content and optimal solubihty) are regarded in the art, as being the most versatile, being compatible with all vehicles, highly effective on all metal substrates, and thus being effective, although toxic, pigment grade corrosion inhibitors. It is the redox activity of chromate species, accountable for their inhibitive efficiency, which allows interference with both anodic and cathodic corrosion processes. As a consequence, chromates are considered anodic-cathodic or "mixed" type inhibitors. A direct result of Cr(VI) reduction by corrosion processes, the formation of Cr(III) species in situ of metal substrates' protective oxide layer is a distinctive feature of chromates corrosion inhibitive mechanism. In contrast with chrornates, all the other above specified active corrosion inhibitive pigments, and more specifically the pertinent anionic constituents of phosphates, molybdates, silicates, borates, phosphites and cyanamides are "redox inactive" under normal conditions of metal corrosion. Consequently they do not qualify as electiOchemically active materials in that sense. A characteristic feature of "redox inactive", so called "anodic" pigments' inhibitive mechanism is the related anionic species' limited ability to interfere, restricted exclusively to anodic corrosion processes, which presumably include insoluble precipitate formation, involving anodically solubilized metal cations. There are far reaching consequences of anodic pigments' less efficient corrosion inhibitive mechanism. In this sense, generally, it can be stated, that pigment grade anodic corrosion inhibitors are quaUtatively inferior, less effective and versatile, but, however, non-toxic alternatives to the chromates. In contemporary industrial practice pigment grade non-toxic alternatives to chromates enjoy commercial acceptance, limited practically, however, to apphcations intended for iron or steel protection. This situation also applies to diverse, multi-phase pigment systems which contain various combinations of anionic and cationic species as above disclosed. In view of these considerations, it can be concluded that expectations regarding development of effective, non- toxic inorganic alternatives to pigment grade chromates are not justifiable. As is well known, there is a large arsenal of organic corrosion inhibitors employed in industrial practice. These are limited, however, to gas phase and Uquid medium apphcations. Logically, it would be expected that the same would generally be appropriate for paint and coating apphcations, as weU, which paradoxically is not the case. This apparent contradiction is understandable by considering that paint and coatings' related apphcations, in addition to corrosion inhibitive efficiency, require pigment grade quaUties as weU. In addition to general quaUty requirements such as low toxicity, competitive price, physical and chemical stabihty, non-reactivity with paint systems, pigment grade quaUty is defined by an additional, quite limiting set of parameters. The more important of them are: non- volatiUty, soUd consistency, specific gravity of 2.5-5.0, substantial, but limited solubility in water, virtual insolubiUty in organic solvents, moderately alkaline hydrolysis pH, and a lack of interference with coating curing processes. It is thus apparent that coatings-related appUcations are incompatible with physical properties such as volatiUty and excessive solubiUty in water or organic mediums which are critical requirements, respectively, of gas phase or Uquid medium related appUcations of organic corrosion inhibitors. Diverse organic compounds, such as nitrogen- containing heterocycUc mercapto derivatives, i.e: 2- mercaptobenzothiazole (hereinafter "MBT"), are well known corrosion inhibitors, employed practicaUy exclusively in dissolved form, as functional components of aqueous, polar organic or hydrocarbon-based Uquid systems. Typical appUcations of organic corrosion inhibitors in water, polar organic solvents or hydrocarbons include heat exchangers, anti-freeze systems, steam condensers, hydraulic oils, or metal cutting liquids lubricants. Water soluble, related sodium or potassium salts (as for example Na-MBT) or "thio" compounds in their more hydrocarbon soluble acidic form (such as MBT) are preferred in many of these latter appUcations. However, the aforementioned appUcations are not paint or protective coating related and are not intended for control of atmospheric corrosion. U.S. Patent No. 4,329,381 (1982) discloses the use Pb or Zn salts of selected, five or six membered, nitrogen-containing organic heterocycUc mercapto derivatives, as additives to paint and coating formulations intended for anti-corrosion protection of metals, particularly of iron or steel. More specificaUy, the aforementioned selected heterocycUc compounds include, among others, Pb or Zn salts of mercaptobenzothiazole, iiiercaptopyridine, mercapto thiazole and mercaptotriazine derivatives, employed in preferred concentrations of 1-3% by weight of the paint formulations. Several examples given in the '381 patent are based on one modified medium oil alkyd paint formulation of about 39% PVC, containing usual ratios of organic solvents, driers, fiUer pigments (talc, Ti0 2 , BaS0 4 ) and, more importantly, in one particular case, 2.3% by weight of Zn(MBT).. Further examples disclose comparative experimental data regarding variations of the above- specified formula. These tests involved corrosion inhibitive performance on steel, which, based on the results of limited salt spray exposure of only 200 hours, showed Zn(MBT) a to be the best performer. Several shortcomings of the concept and procedures set forth in the '381 patent can be identified, as foUows: In respect of synthesis of MBT derivatives selected according to the patent, it will be noted, that essentially two procedures, for Zn(MBT) a preparation are disclosed; A. "Direct conversion" into Zn(MBT). of mixed aqueous suspension, containing ZnO, or alternatively basic zinc carbonate, and MBT, performed by extensive agitation and heating at approximately 100°C, in the presence of catalytic amounts of acetic acid. B. By double decomposition or precipitation, using aqueous solutions of Na-MBT and of zinc salts. As it will be demonstrated in Example 1 of the present disclosure, procedure "A", as disclosed in the '381 patent, is not practicable, generaUy, and especially not in relation to paint appUcations, for it does not yield a reasonably pure Zn(MBT). as is necessary. Rather a mixture containing quite high ratios of unreacted MBT and ZnO results. This is expUcable by the diffusionaUy controUed, heterogeneous nature of the process, which, even if ZnO of high specific surface area is employed, obstructs the raw materials' total conversion and is basicaUy accountable for the presence of MBT in technical grade Zn(MBT produced by this process. It is interesting to observe that Zn(MBT) a formation by direct conversion, which occurs according to: ZnO + 2 MBT - (1-x) Zn(MBT) 2 + 2xMBT + x-ZnO+(l-x)H } 0 (1) a heterogenous reaction, wherein the reaction mixture's equiUbrium composition is primarily controUed by the ZnO phase specific surface area. In that respect, it was learned, pursuant to the present invention, that if the required ZnO/MBT «= 1/2 molar ratio is appUed, then x > > 0, even if ZnO of high specific surface area is used and the equiUbrium reaction mixture contains substantial amounts of unreacted MBT and ZnO. As subsequently demonstrated in Example 1 hereof, technical grade Zn(MBT) 2 prepared according to procedures proposed by the '381 patent could have Zn contents practicaUy corresponding to Zn(MBT). chemical composition and paradoxicaUy, at the same time, high MBT contents, detectable by IR spectroscopy. For example, if x = 0.2 according to Reaction 1., the correspondent reaction mixture contains 4.0% ZnO, 16.6% MBT and it is characterized by Zn - 16.28% (in comparison with Zn - 16.35% in pure Zn(MBT) 2 ). Experimental data obtained pursuant to the present invention are consistent with these considerations: aqueous mixed suspension of highly reactive ZnO (such as AZO-66 from American Smelting and Refining Co. with specific surface area value of 4.7 Sq.m./g., average particle diameter of 0.25 micron) and MBT in 1:2 molar ratio, processed at 95-100°C for 2.5 hours and intense agitation, yields a reaction mixture ∞nt___αing Zn = 16.41% and 32.7% of unreacted MBT. (See Table 1.1.) The obtained products' MBT content was estimated by IR spectroscopy, which, by an intense absorption band situated at 1496 and 1425 cm 1 of the related spectrum, characteristic for MBT, confirmed the presence of the same. Notably, the absorption bands characteristic for Zn(MBT) 2 are situated at 1369 and 543 cm 1 (see Fig.1). Quantitative deterniination of unreacted MBT contents were performed by repeated extraction in ethanol and gravimetric evaluation of the consecutively filtered and dried samples. Zn(MBT) 2 and unreacted ZnO contents were calculated, considering related, experimentaUy determined Zn and unreacted MBT contents. Pertinent analytical data are presented in Table 1.1. Similar conclusions are apphcable with respect to the alternative procedure specified by the '381 patent, namely Zn(MBT)_ preparation by double decomposition (precipitation), according to: 2Na-MBT + Zn(X) t + 2x-H 3 0 = (1-x) ■ Zn(MBT) 2 + 2xMBT +x-Zn(0H) . + 2NaX, (2) where x > 0, and where X = Cl , NO a , etc. It was found experirnentaUy, according to the present invention, that such product, produced pursuant to the recommendations of the art, contains large amounts of unreacted MBT (see 1.3 of Example 1 and Table 1.1) detectable by IR spectroscopy. It is assumed, that concurrent hydrolysis reactions of Zn* + and MBT-species are accountable for it. (See Fig. 2.) The above disclosed considerations regarding purity of technical grade Zn(MBT) 2 , and more specificaUy the unreacted MBT content, have limiting impUcations in respect of appUcabiUty of such materials in paint formulations, as subsequently presented. The '381 patent promotes the concept of employing Pb and Zn salts of diverse organic compounds, notably Zn(MBT) a , as corrosion inhibitor components of organic coatings, more specifically by formulating such compounds as finely divided, distinct soUd phases into related paint systems. A significant limitation of this concept observed pursuant to the present invention, is that technical grade Zn(MBT) 2 (produced according to any of the above identified procedures), when formulated as a finely divided, distinct soUd component in paint systems, interferes with and inhibits the curing process of oil alkyd resin based coatings. Remarkably, it is estimated that about 60% of aU primers intended for metal protection are oil alkyd resin based. Supporting experimental data, pertinent to solvent based medium oil alkyd and chain-stopped water reducible short oil alkyd resin based paint formulations, are presented in Example 1. Notably, it was experimentaUy proven, that curing of short oil alkyd paint appUcations, performed at 70 °C for 30 minutes, is inhibited by very low concentrations of 0.2 to 0.3 weight per cent MBT, which observation is consistent with the foregoing statements. Thus, it is plausible that technical grade Zn(MBT) a , which commonly contains in excess of 10 weight % of un-converted MBT, at a generaUy low concentrations of 2.5 to 3.0% by weight, could inhibit the curing process of such paint systems. As for the chemical mechanism of the curing process's inhibition, it is known that alkyd resins, both solvent or water reducible, are cured by oxygen supported radicaUc mechanism, promoted usuaUy by Co, Ca, Pb, or Zr based dryers. Thus, it is plausible that the free radical scavenging abiUty of MBT, probably related to the -SH functional group's known oxidizabiUty, is accountable for it. In this respect it will be noted again, that apparently, MBT is present in considerable amounts in any technical grade Zn(MBT) 2 unless the latter product is specificaUy purified, which is generaUy not the case. Relevant solubiUty data indicate that MBT is quite soluble in organic solvents typicaUy present in oU alkyd based paint formulations. SolubiUty values, as g/lOOg, are: 10.0; 2.0; and 1.0 in acetone, ethanol and benzene, respectively. Consequently, it is assumed, that the MBT content of technical grade Zn(MBT). is solubiUzed by Uquid phases of related paint systems and thus causes unwanted curing inhibition. Furtherπiore, considering that the presence of -SH functional groups, in addition to thiols, provides similar free radical scavenging capacity to several thio-organic compound families such as derivatives of dithio-carbonic and dithio-phosphoric acids, the above outlined limitation should be extended to those materials, as weU. GeneraUy, technical grade heavy metal salts, and more specificaUy zinc salts of diverse organic compounds containing -SH functional groups, due to the presence of un-neutraUzed such species, if appUed according to the recommendations of the '381 patent, are expected to display inhibitive activity in respect to radicaUc curing processes which are typical for alkyd resin based coatings. An additional limitation of the '381 patent relates to the fact that the specific gravity of Zn(MBT) 2 (1.5-1.7) is quite low in comparison with such values typical for other components of a paint system's dispersed inorganic phase, which range from 2.5 to 5.0, or with density values of cured coatings of about 2.0. As is known, shelf-stable paint systems dispersed soUd phases, usuaUy multi-component constituents of the same, tend to segregate by "flooding", if they contain components with appreciably different specific gravity values. Caused by convective processes related to solvent evaporation, flooding occurs during the cniring period of freshly appUed coatings, resulting in predominant accumulation, at the coating-air interface, of the dispersed soUd phase's low specific gravity components and ultimately, in an anisotropic composition of the resultant coatings. Observing that low specific gravity values are typical for zinc salts formed by relatively "bulky" organic moieties, such as Zn(MBT) 2 , it is considered that segregation by flooding has relevance to the apphcation of such compounds as paint additives and constitutes a considerable shortcoming of the concept promoted by the '381 patent. It is a principal object of the present invention to provide corrosion inhibitors for metals which, avoid the foregoing problems related to inhibition of paint and coating curing processes. In accordance with an important aspect of this invention, the above discussed limitations related to the preparation, consequent curing process inhibitive activity and comparatively low specific gravity of thio-organic zinc salts, specificaUy of Zn(MBT) a , among others, are eliminated, by synthesis and employment, of pigment grade organic-inorganic hybrid materials. It was learned pursuant to the present invention, that technical grade Zn(MBT). purified by solvent extraction with ethanol at approximately a 1:3 soUd-Uquid ratio, does not display the same inhibitive activity even at considerable higher concentrations of > 10% by weight. It is the organic-inorganic interface, formed concurrently with the constituent organic and inorganic phases, which is the characteristic structural feature of hybrid materials obtained pursuant to the present invention. As a consequence, the organic and inorganic soUd phase constituents, interfaced at a crystalUte level, form unitary hybrid materials, which display typical uniphase behavior in respect of physical properties, critical in paint appUcations. Most typicaUy in this sense, in contrast with multi-phase organic-inorganic mixtures, finely divided pigment grade hybrid materials of the present invention do not segregate in phase components by physical procedures such as flotation or flooding. Furthermore, as a direct consequence of pigment grade hybrid material's uniphase behavior, pertinent specific gravity, pH and solubiUty values are approximately weighed averages of the phase components' characteristic values. In this sense, it wiU be observed, that pigment grade hybrid materials' pH, measured in saturated leachets of the same, are the result of the phase components' acid-base interaction occnirring at an intra-granular level. In similar fashion, measured solubilities are cumulative values. It is particularly important to note, that pigment grade hybrid materials according to the present invention, and particularly those contεdning Zn(MBT) 2 , do not display cure inhibitive activity in alkyd resin based paint systems. Consequently, they are actual pigment grade materials, compatible with aU paint vehicle systems, as documented hereinafter. More importantly, however, pigment grade hybrids produced according to the present invention display synergistic behavior with respect to metal corrosion inhibition. Manifestations of pigment grade hybrids' synergistic behavior are their abihty to effectively retard aU of the important metals' corrosion, particularly of Fe, Al, Cu and Ag, as weU as their compatibiUty with aU paint vehicle systems, inclusive of water reducible and solvent based alkyds. More specificaUy, effective corrosion inhibition and synergistic behavior is understood as the capacity of pigment grade hybrid materials to display, in identical coating formulations, essentially similar or enhanced corrosion inhibitive performance in comparison with state of the art corrosion inhibitor pigments typically appUed on all the above specified metal substrates. The comparison in this sense refers to all individual phase components of related hybrid compositions, as weU. In contrast, aU known electrochemicaUy active pigment grade corrosion inhibitors, which as above discussed, representing the state of the art, display some degree of substrate specific behavior. For example, chromates and particularly SrCr0 4 , highly effective pigment grade inhibitors apphcable practicaUy on aU metals (such as Fe, Al, Cu) are known to actually promote Ag corrosion and consequently are incompatible with such substrates. Non-toxic alternatives to chromates such as phosphates, molybdates, borates, siUcates and diverse combinations of the same, are valued, although less efficient inhibitors of Fe corrosion, which however, perform poorly on Al, Cu and are just as incompatible with Ag. Their industrial apphcation is thus limited practically to anti-corrosive protection of Fe. Pigment grade metal cyanamides and more specificaUy ZnNCN of salt-free quaUty (see my U.S. Patents Nos. 5, 176,894 and 5,378,446), represent the state of art in non-lead corrosion inhibitor pigment technology recommended for Ag protection, but their industrial apphcation is limited to the same. Brief Description of Drawings Figures 1-12 are graphical prints representing IR spectra obtained from analysis of materials produced pursuant to the invention. Detailed Description The synthesis of pigment grade organic- inorganic hybrid materials, pursuant to the present invention is preferably accompUshed by combining selected constituents according to procedures which promote formation of organic-inorganic interfaces. Inorganic constituents preferred according to the present invention are as foUows: Cations: Zn, Al, Mg, Ca, Sr, Ti, Zr, Ce, Fe; Anions: phosphate, polyphosphates, phosphites, molybdates, siUcates and cyanamides. Accordingly, inorganic compounds typicaUy present in corrosion inhibitive hybrids synthesized pursuant to the present invention, are: Zn 3 (P0 4 ) a (H 2 0)., x-2-4; MgHP0 4 .(H 8 0) a , A1P0 4 , CaSiO a , Sr- or CaMo0 4 , ZnNCN and combinations of the same. Selected organic constituents of hybrid pigments synthesized according to the present invention are the zinc salts or _dkyl-a_τ_παoniuι_ (For example: cyclohexyl- εcαααrioniuin, di-cyclohexyl-ai-rjmonium, octyl-aι__tnomum) salts of organic mercapto- and thio- compounds or their alkyl-substituted derivatives, as foUows: mercaptobenzothiazole, mercaptothiazoline, mercaptobenzimidazole, mercaptoimidazole, 2,5- dii-_ercapto-l,3,4-thiodiazole, 5,5-dithio-bis(l,3,4- thiadiazole-2(3H)-thione, mercaptobenzoxazole, mercaptothiazole, mercapto triazole, mercaptopyrimidine, mercaptopyridine, mercaptoquinoline, alkyl- and cyclo- alkyl mercaptanes, N-alkyl- or N-cycloalkyl- dithiocarbamates, O-alkyl- or O-cycloalkyl- dithiocarbonates, O.O-dialkyl- and O.O-dicycloalkyl- dithiophosphates. The preferred practical realization of the synthesis of organic-inorganic hybrids in heterogeneous processes, is exemphfied by Reaction 3 and Reaction 4, the former being an adaptation of Reaction 1, which is performed in aqueous medium and extensive heating at 85-95 °C, as foUows: ZnO + 2xMBT > xZn(MBT) 2 /(l-x)ZnO + xH 2 0 (3) where x < 0.25, and ZnO is finely divided with average particle size of 0.25 micron or less. It will be observed, that in contrast with Reaction 1, Reaction 3 is carried out with a large stoichiometrical excess of ZnO of at least 100 mole %. As a result, the equilibrium reaction mixture does not contain unreacted MBT, which, as above discussed, is one of the major objectives of the present invention. It was further learned pursuant to the present invention that the equiUbrium mixture of Reaction 3, which contains Zn(MBT)- and ZnO, reacts readily with H a NCN, as foUows: xZn(MBT)/(]-x) ZnO + (1-x) H 1 NCN—> xZn(MBT) ,/(l-x)ZnNCN + (1-x) H } 0 (4) Reaction 4, or a variation thereof, is the process generaUy preferred for the formation of organic-inorganic interfaces, characteristic to pigment grade hybrid materials according to the present invention. As hereinafter further disclosed, this procedure offers significant advantages, the absence of soluble by-products being one of the most important. It is important to observe as weU, that certain useful characteristics of Reaction 4 observed pursuant to the present invention, are essentiaUy unpredictable on the basis of common theoretical considerations, as foUows: A. Reaction 4, even if performed at about 15 mole% of H a NCN stoicihiometrical excess and 80-85 °C, does not reverse Reaction 3 and consequently does yield pigment grade organic-inorganic hybrid material free of unreacted MBT. B. Zn(MBT) 2 , the final product of Reaction 3, which is present in the related reaction mixture presumably as an adsorbed layer on a ZnO core, does not obstruct the completion of Reaction 4. C. The above specified process sequence, symbolized by Reaction 3 > Reaction 4 is reversible; it having been experimentaUy proven that ZnNCN in aqueous suspension reacts readily with MBT. Notably, it was learned that attempts to produce 0.2Zn(MBT ZnNCN type pigment grade hybrid, essentiaUy by reverse process sequence (see Example 1.4.1 and IR spectrum 3), yielded a product which contained no unreacted MBT, according to: ZnO + HJΪCN + H20 ~(85°C)-> ZnNCN + 2H 2 0 (5) ZnNCN + 0.2 MBT + H 2 0 ~(heat)~-> 0.9 ZnNCN/0.1 Zn(MBT) 2 + 0.1 H.NCN+H.O (6) It appears reasonable to suppose that diffusing abiUty, affinity to form ZnΝCΝ and the very weak acidic character (K=4.04 10 ,1 )/20°C) of H2ΝCΝ, comparative to the stronger acidity of organic thiol compounds, aU contribute to the feasibiUty of pigment grade hybrid synthesis according to Reactions 3 and 4. It is important to emphasize, that Reaction 6, unknown by the prior art, and Reaction 4 constitute the basic chemical process of pigment grade organic-inorganic hybrid synthesis, pursuant to the present invention. For the aforementioned reasons and also due to its appropriate solubiUty and corrosion inhibitive activity, ZnNCN is an irreplaceable functional component of pigment grade organic-inorganic hybrids with synergistic behavior in providing corrosion inhibition. These considerations are supported by further observations made pursuant to incorporation of salts of stronger acids, such as H 8 P0 4 or HgPO a and MoO a , into pigment grade hybrids of the present invention. For example, efforts to incorporate Zn a (P0 4 ) a (H a O) a or ZnMo0 4 by introduction of H 3 P0 4 or Mo0 3 into the characteristic reaction equiUbrium mixture of Reaction 3, have yielded pigment grade hybrids with substantial, undesired content of free MBT. It is assumed, that concurrently with zinc phosphate formation, H 3 P0 4 (and strong acids, generaUy) to some extent promotes the undesirable side reaction, as foUows: 3 Zn(MBT) . + 2H } PO 4 + H 2 0 > Z 3 (P0 J 2 (H 2 0) ^ + 6 MBT (7) As a consequence, the preferred technique to incorporate aU constituents of a multi-component hybrid pigment of 0.2Zn(MBTyZnNCN/0.2 zinc phosphate/0.5 CaSiOg phase composition formula, can be represented as foUows: A. Reaction 3 is performed at x ■= 0.2; B. Reaction 8 is performed separately on a mixed suspension of ZnO and CaSiO s , as foUows: ZnO/0.5CaSiO, + 0.53H,PO 4 + H 2 0 -(ambient temp.)~-> 0.2ZnO/0.26Zn } (PO i ) 2 (H 2 O) 4 /0.5CaSiO i (8) C. equiUbrium mixtures of Reaction 3 and Reaction 8 are mixed together; D. ZnNCN is incorporated by H2NCN addition: (EquiUbrium mixture of Reaction 3 + 8) + H2NCN - (ambient temp. )—- > 0.2Zn(MBT) /ZnNCN/ 0.26Zn } (P0 J 2 (H20) 4 /0.5CaSiO^ H 2 O (9) It is particularly interesting to observe, that, quite unexpectedly, the ZnO component of the equiUbrium mixture of Reaction 8 (presumably present as zinc phosphate coated core) is available for reaction with ELjNCN; the case is specificaUy documented in Example 17.1. NaturaUy occurring WoUastonite or CaSiO β is preferred for incorporation of silicate species into pigment grade hybrids according to the present invention. As for molybdate species, it is comfortable to produce Zn-, Ca- or Sr-molybdate without soluble by¬ products, by reacting MoO a with ZnO, Ca(OH) a or preferably Sr(OH) a , according to the foUowing: Sr(0H) 2 + MoO, + H 2 0 > SrMo0 4 + 2H 2 0 (10) Reaction 10 is preferably performed as a variation of Reaction 8, wherein Sr(OH) 2 (or alternatively, Ca(OH) 2 ) is a partiaUy soluble component of the reaction precursor (a mixed suspension of ZnO and CaSi0 8 ) and MoO a introduction precedes or is performed concurrently to HgP0 4 . The phase composition of a such typical multi- component hybrid pigment can be represented by the following formula: 0.2Zn(MBT) ,/ZnNCN/0.25Zn ,(P0 4 ) 2 (H 2 0) . / 0.5CaSiO,/0.2SrMoO , An alternative procedure for synthesis of multi- component, organic-inorganic hybrid pigments involves coprecipitation by double decomposition of mixtures of soluble salts, containing the above specified selected anionic and cationic species. Accordingly, soluble salts of organic thiol derivatives and mercaptans are co-precipitated selectively as Zn- derivatives, aUowed by the rule of solubiUty, with phosphates, molybdates, phosphites, poly-phosphates and cyanamides of Zn, Al, Ca, Sr, Mg, Ti, Zr and Ce. Cyanamide species are also selectively precipitated as ZnNCN, pursuant to the present invention. Formation of soluble by-products constitutes, however, a severe limitation of the latter procedure, for it requires extensive washing of the synthesized pigments. The apphcation of coprecipitation by double decomposition however, is inevitable in cases of thiol- organic compounds which are not available in an acid form, such as derivatives of dithio-carbonic and dithio- phosphoric acid. In order to minirnize the inconvenience caused by of by¬ products formation, coprecipitation by double decomposition is preferably employed in combination with the earUer disclosed heterogeneous procedure, as exemplified below. For example, the synthesis of a five component pigment grade hybrid is accompUshed according to a combined procedure as foUows: A. An aqueous suspension of Sr(OH) 2 , ZnO and WoUastonite is treated with Mo0 3 and H^NCN according to the heterogeneous process: ZnO+0.5CaSiO 3 +0.2Sr(OH) 2 +0.2MoO 3 +H 2 NCN+H 2 0 -(70-85°C)~> ZnNCN/0.5CaSiO/0.2SrMoO +2.2H 2 O (11) B. Without soUd-Uquid phase separation, the equiUbrium mixture of Reaction 11 is further processed by co-precipitation of mixtures of selected anionic and cationic species, such as POΛ NCN 8 , thio-organic compounds (as sodium salts) and Zn 2+ , AT* (usuaUy as nitrates), respectively: (Reaction 11 product) + [0.4°DT + O.JςNCN + 0.5°PO?] + 2.9Na" + 1.45 Zn(NOJ 3 ~(70-85°C)~> 0.2Zn(DT) 2 / 1.5ZnNCN/0.5CaSiO, /0.2SrMoO 4 / 0.25Zn , (PO J 2 (H 2 0) . + 2.9 NaNO } (12) where DT symboUzes thio-organic compounds, such as 0,0-di-alkyl-dithiophosphates, O-alkyl-dithiocarbonates, Ν- alkyl-(or Ν-aryl-) dithiocarbamates or mercaptans. It will be noted, that alkyl-ammomum salts of mercapto derivatives, as for example di-cyclohexyla___r__omum-2- naercaptobenzothiazolate, are preferably incorporated into hybrid compositions as aqueous suspensions. The following examples demonstrate the feasibiUty of synthesis procedures according to the present invention, to produce pigment grade organic-inorganic hybrid compositions. The experimental evidence also demonstrates the same materials' synergistic behavior in respect to inhibition of corrosion in commerciaUy significant metal substrates including iron, steel, silver, copper and alui-ύnum. Other aspects of the invention also wiU be further iUustrated by the foUowing examples, wherein aU percentages are given by weight unless otherwise indicated. Examples Experimental data presented under Example 1 are intended to demonstrate the above specified limitations of the concept and practice promoted by U.S. Patent No. 4,329,381. Comparative Example 1 Preparations of varieties of technical grade Zn-2- mercaptobenzothiazolate were performed pursuant to the recommendations of the above identified '381 patent, foUowing procedures essentiaUy known by the art. 1.1. In order to obtain Zn(MBT) 2 by "direct conversion", a weU dispersed and hydrated, highly reactive suspension of ZnO was prepared, by introducing 1.0 moles of such product (AZO 66 grade, with an average particle size of 0.25 micron, from American Smelting and Refining Co.) into 500 ml of intensively stirred hot water (80-85 oC) and keeping the same conditions for 1 hour. Concurrently, aqueous suspension, containing 2.0 moles of finely groimd MBT in 1000 ml. water, (341.2 g. of 98%, available from Aldrich Chemical Co.) was prepared in similar fashion, using however a substantiaUy small, but effective amount of non-ionic surfactant (Igepal-CA 630, distributed by Hydrite Chemical Co., WI). The "conversion" process was performed by the ZnO suspension's gradual introduction into the MBT suspension, 25g of glacial Acetic acid addition (as catalyst), and intense agitation of the reaction mixture at 98-100oC for 2.5 hours. Subsequently, the solid phase of the resultant suspension was separated by filtration, dried at 105-110oC overnight and pulverized to a fineness of 100% +270 mesh. Pertinent analytical data are presented in Table 1. 1.2. Preparation of Zn(MBT) a by converting a mixed suspension, containing basic zinc carbonate and MBT, was performed in identical fashion as above described, except that no glacial acetic acid was used and the previously obtained ZnO suspension was first converted into basic zinc carbonate suspension, by cooling it to about 40oC and introducing continuously into it for about 1 hour, CO s gas at a manageable rate and intense agitation. Related analytical data are presented below. 1.3. Technical grade Zn(MBT), by "precipitation" was produced according to the foUowing: Aqueous solutions of 1.0 mol ZnSO 4 /1000 ml at pH- 4.0-4.3 and of 2.0 mol. Na-MBT /1000 ml were prepared, using high purity ZnO and technical grade MBT with 98% assay. Particularly, the latter solution was obtained by adding, in small increments, 341.2g of MBT and 81.0g NaOH into intensively stirred 800 ml of water at ambient temperature and subsequently completing the volume of the solution. Technical grade Zn(MBT) a was precipitated by introducing the above solutions, simultaneously at identical deUvery rate (in about 30 min.), into weU agitated 300 ml. of water, at ambient temperature. After 1 hour of stirring at that temperature, the obtained slurry was filtered, washed intensively to salt- free conditions and further processed in identical fashion, as disclosed above. Related analytical data are presented below. 1.4. Purified grade Zn(MBT) 2 , containing no unreacted MBT, was produced by solvent extraction. For that purpose, 200.0g of technical grade Zn(MBT) a (produced by precipitation according to 1.3) was suspended in 600 ml. of 98% ethanol, stirred intensively for 30 min. at about 45° C, filtered, dried overnight at 105oC and pulverized. Related analytical data are presented below. 1.4.1 Pigment grade hybrid of 0.2ZN(MBT) 2 / O.δZnNCN composition, was synthesized according to Reaction 6 of the present invention and the foUowing procedure: Aqueous ZnO slurry, containing 1.0 moles (81.38 g.) of AZO 66 grade such product in 500 ml. H a O, was prepared by intense agitation of the suspension at 80-85°C, for one hour. Keeping the reaction conditions the same, ZnO suspension was converted into ZnNCN suspension (foUowing appUcable procedure according to my U.S. Patent 5,176,894), by introducing into it in about 15 min., 1.1 moles (46.5 g) of I^NCN as aqueous solution of 25%. After processing it for one hour in the same conditions and without soUd Uquid separation, the ZnNCN suspension was subsequently converted into pigment grade hybrid suspension (as specified), by introduction of aqueous suspension, containing 0.2 moles (34.0 g.) of finely ground 2-mercaptobenzothiazole. The conversion process according to Reaction 6, was finaUzed by intense agitation of the suspension, at 85-90°C for 2.5 hours and finaUy, the filtered soUd phase, dried overnight at about 100°C, was subsequently pulverized to + 325 mesh fineness. Pertinent analytical data are as foUow: % ZN = 47.8; % NCN-22.6; Yield - 135.0 g; Notably, the related IR Spectrum presented in Fig. 3, indicates that the product does not contain unreacted MBT. It is important to observe, that test results presented below in Table 1.3 support the above statement: pigment grade hybrid of 0.2°ZNz(MBT) a /0.8ZnNCN, synthesized according to the present invention, does not possess cure inhibitive activity. Table 1.1 QuaUty parameters of Zn(MBT). varieties Determined Produced/Example No. parameters: 1.1 1.2 1.3 1.4 Zn% MBT% , (unreacted) ZnO% .(calculated) Zn(MBT) 2 % .(calculated) Carbonate as CO2% Specific gravity pH, (aqueous leachet) Yield, g. IR spectra of Zn(MBT) 2 produced according to 1.1 and 1.3 are presented in Figs. 1 and 2, respectively. 1.5. In order to evaluate the cure-inhibitive activity of various technical grade Zn(MBT) 2 samples produced according to 1.1.-1.4., solvent-based medium oU alkyd (1.5.1.) and water-reducible, chain stopped short oil alkyd resin based paint formulations (1.5.2.) were employed, as subsequently presented. Table 1.2. Kelsol 3962 (6) 310.0 Driers Noury (7) Cobalt, 6% Co 2.2 4.2 Zirconium, 6% Zr 21.0 Manganese, 6% Mn 9.3 961.9 891.0 Raw material supphers: (1) U.S.Oxides; (2) Pfizer Inc., Chemical Div.; (3) Columbian Chemical Co.; (4) Rheox, Inc.; (5) McWhorther Technologies; (6) Reichold Chemicals, Inc. ; (7) Interstab Chemicals, Inc. ; 1.6. Curing inhibitive activity of technical grade Zn(MBT) a varieties, synthesized pursuant to 1.1-1.4 and of technical grade MBT, was evaluated by deterrnining the xnininauzn concentration of the above materials, necessary to inhibit the curing process of solvent and aqueous alkyd resin based paint formulations, according to 1.5.1 and 1.5.2, respectively. For that purpose, 3 mil thick appUcations of the above paint formulations, containing variable amounts of Zn(MBT) 2 varieties, were appUed on draw-down boards, subsequently dried at 70oC for 30 minutes and evaluated for cure; tack-free appUcations were considered cured. Zn(MBT) 2 varieties' cure inhibitive activity was estimated by observing the pertinent minimal concentration necessary for partial cure inhibition. Data are presented below. Table 1.3 Tested Technical Grade Zn(MBT)2 Inhibitive Concentration, wght.% Varieties and MBT (minimal) / paint system 1.5.1 1.5.2 Observation As observable, aU technical grade Zn(MBT) 2 varieties, inclusive 1.3. the one produced by precipitation, and MBT, display cure inhibitive activity in solvent based alkyd systems, at very low concentration range of 0.3-0.5 weight %; in comparison, purified Zn(MBT). does not present such activity even at > 10.0 weight % concentration. Tested materials display similar behavior in water reducible alkyd systems, at higher minimum inhibitive concentration, however. EXAMPLES OF EMBODIMENTS OF THE PRESENT INVENTION. AU examples of reaUzation hereafter presented, disclose manufacturing procedures and pertinent chemical compositions of pigment grade organic-inorganic hybrid compounds obtainable pursuant to the present invention; experimental data regarding appUcabiUty of the formers in various and more specificaUy, in alkyd based paint systems as weU as regarding their synergistic behavior in respect of corrosion inhibition, are also presented. Example 2. Pigment grade, organic-inorganic hybrid material, characterized by synergy in respect of Ag, Cu, Al, Fe corrosion inhibition and symbohzed by phase- composition formulas: 2.1. 0.05Zn(MBT) a /ZnNCN, and 2.2. 0.05Zn(MBT) 2 /ZnNCN/0.5CaSiO3 where 2.1. contains about 17% by weight of Zn(MBT) 2 , were produced according to the foUowing procedures: To synthesize 2.1, highly reactive, hydrated and finely divided ZnO suspension was prepared by introducing 1.0 mole of ZnO (AZO 66 grade, characterized by 0.25 micron average particle size, assay: > 99.9%, from American Smelting and Refining Co.) into 500 ml. of hot water, with intensive agitation. The dispersion and hydration process was completed by maintaining the same conditions (85-90 °C)f or one additional hour. Concurrently, aqueous suspension of MBT, (technical grade 98% 2-Mercaptobenzothiazole, available from Aldrich Chemical Co.) was obtained in similar fashion, containing 0.1 moles (17.0 g. of 98%) of the same in 200 ml. of water at ambient temperature, using, however, a small but effective amount of non-ionic surfactant (Igepal-CA 630, distributed by Hydrite Chemical Co., WI.)as a wetting aid. By introducing the latter suspension into the former, a mixed suspension was formed and converted, at 85-90oC and intense agitation for 2.5 hours, into a Zn(MBT) 8 -ZnO suspension. Subsequently, pigment grade hybrid material, according to the above specified phase- composition, was produced by introducing in about 30 min. into the reaction mixture, 1.05 moles of HjNCN (as aqueous solution of 50 weight %, available from S.K.W., Germany) and keeping the same conditions (80-85 oC, intense agitation) for one hour. The resultant product suspension's soUd phase was separated by filtration. The presscake, without washing, was dried at 105-110oC for 12 hours and pulverized to a fineness of 100% +270 mesh. Organic-inorganic hybrid pigment according to phase-composition formula 2.2, was synthesized, in identical fashion as disclosed for Example 2.1, with addition of a mixed suspension of 1.0 moles (81.38 g.) ZnO and 0.5 moles (58.0 g.) WoUastonite grade CaSi03 in 1000 ml. Of water. (See Example 3 for specific data regarding CaSiOa). Pertinent analytical data and IR spectra characteristic to Example 2.2 are presented in Table 2 and Fig. 4, respectively. Table 2. Measured Parameters Determined Values 2.1. 2.2. Appearance Zn totak. % NCN % pH (ASTM D 120881/6.1.1) Specific Gravity Oil absorption, lbs/100 lbs; (ASTM D 281-84) 34 32 Yield, g. 114.3 181.5 Example 3 Pigment grade, organic-inorganic hybrid materials, characterized by corrosion inhibitive properties similar to Example 2 and symboUzed by phase-composition formulas: 3.1. 0.05 Zn(MBI) 2 / ZnNCN / 0.5 CaSi0 3 3.2. 0.05 Zn(MTH) 2 / ZnNCN / 0.5 CaSi0 3 where Zn(MBI). and Zn(MTH) 2 stand for zinc salts of 2- Mercaptobenzimidazol or 2-Mercaptothiazoline, respectively (both materials are commerciaUy avaUable with assays of 98% from Aldrich Chemicals Co.) were obtained according to the procedure as foUows: Mixed suspension, containing 160.0 g CaSiO a (NYAD 1250 grade WoUastonite from NYCO Minerals Inc.) and 224.0 g. (2.75 moles) of ZnO in 2500 ml. H^O, was prepared in similar fashion as described in the appUcable part of Example 2, at lower temperature however, of 65 - 85oC. Subsequently, hybrid pigment varieties according to 3.1. and 3.2. were produced by introducing into the mixed suspensions of CaSi0 3 /ZnO, in about 15 minutes, previously prepared aqueous solutions of Zn(N0 3 ) 2 (0.15 moles as approximately 25% solution). Simultaneously with the former appropriate amounts of Na-MBI and Na-MTH. respectively were added. After one hour of intense agitation at 65-75o C, 3.0 moles of HjNCN (as 20% solution) were introduced in about 30 min. into the reaction mixture, after which, the same reaction conditions were extended for about 60 additional minutes. Aqueous solutions of Na-MBI and Na-MTH were prepared by solubiUzing 0.30 moles of 2- Mercaptothiazoline (36.5g of 98%) or 2- Mercaptol_e_____midazo_e (46.0g of 98%), respectively, in 300 ml. HgO, containing 0.30 moles of NaOH. The conversion was finaUzed and the obtained composite pigments were further processed in identical fashion as presented in the appUcable section of Example 2, except that the slurry was cooled to ambient temperature before performing soUd-Uquid separation. Pertinent analytical data and IR spectra characterisic to Example 3.1 are presented in Table 3 and Fig. 5, respectively. Table 3 Measured QuaUty Parameters Appearance Zn total,% NCN,% PH Specific gravity Oil absorption, lbs/lOOlbs Yield, g. Example 4 Pigment grade, multi-component, organic- inorganic hybrid material, characterized by synergistic behavior in regard of metal corrosion inhibition and symboUzed by phase-composition formula of Q.06Zn(MBT) 2 I 0.06 Zn(MTH) 2 I ZnNCN I 0.21 Zn P0 A ) 12 Hp was produced pursuant the foUowing procedure: Dispersion(A), containing 138.5 g. (1.7 moles) of ZnO /1000 ml. H.O and solution (B) of 2.4 moles ZnS0 4 / 1500 ml., at approximately pH -= 4.0, were prepared foUowing the appUcable section of Example 2. and common procedure, respectively. Concurrently, solution (C), comprising anionic species, was prepared by dissolving 0.3 moles of each, MBT (36.5g of 98%)and MTH (51.2 g. of 98%), as weU as 1.0 moles of HaP0 4 in 1000 ml. aqueous solution of 4.8 moles NaOH. After cooling to ambient temperature, 0.6 moles of H s NCN were added and the volume completed to 1500 ml. Pigment grade hybrid material, according to the above specified phase-composition formula, was produced by introducing first, in about 30 min., 1.8 moles of aqueous H.NCN and subsequently (in about 30 min.) solutions (B) and (C) (simultaneously) into intensively stirred dispersion (A); The pH of the reaction medium was observed to be 7-8. The same reaction conditions were held for an additional 60 min. at 60-65oC and subsequently, the suspension's soUd phase was separated by filtration, washed to soluble salt-free conditions and further processed in identical fashion as disclosed in the appUcable section of Example 2. Pertinent analytical data are presented in Table 4. Table 4. Measured parameter Determined value Zn total% 46.7 NCN% 13.6 pH 8.4 Oil absorption, lbs/100 lbs Spec, gravity 2.63 Yield, g. 550.0 Example 5. Pigment grade, organic-inorganic hybrid material, characterized by similar corrosion inhibitive behavior as the compositions described in previous examples, symboUzed by phase composition formula of 0.075 Zn-DMTD / ZnNCN where Zn-DMTD is Zn-2,5-_-_rnercapto-l,3,4-thiadiazolate, was produced according to the foUowing procedure: Highly reactive ZnO suspension (A ), containing 2.0 moles of such product in 1000 ml. of water, was prepared as described in the pertinent section of Example 2. Concurrently, solution (B) of 0.15 moles ZnS0 4 in 200 ml. of water and solution (C) of 0.15 moles disodium 2,5- dimercapto-l,3,4-thiadiazolate in 200 ml. of water, were obtained foUowing common procedure, or by dissolving the appropriate amount of DMTD (available from Aldrich Chemical Co.)in aqueous solution of 0.3 moles NaOH, respectively. Hybrid material, according to the above specified phase composition was produced by simultaneous introduction, in about 30 minutes, of solutions (B),(C) and at a comparatively higher rate, of 200 ml. of a solution containing 2.1 moles of H.NCN, into intensively stirred suspension (A), at about 50-60o C. After the reactants' introduction was completed, the reaction medium's pH, if necessary, was adjusted to pH » 8.0 and the same conditions were kept for one hour. Subsequently, the obtained pigment suspension was processed in identical fashion as described in the appUcable section of Example 1. Related analytical data, IR spectra are presented below and in Fig. 6, respectively. Table 5. Measured parameter Determined value Appearance white powder Zn total,% 57.4 NCN% 26.6 pH 8.11 Sp. gravity 2.94 Oil absorption, lbs/lOOlbs Yield, g. 235.0 Example 6. Pigment grade hybrid material of similar characteristics as disclosed in previous examples, symboUzed by a phase-composition formula of 0.13 Zn(CyDQ 2 / ZnNCN I 0.21 Zn 3 (P0^ 2 2H 2 0 where Zn(CyDC) 8 stands for Zn-(-S(S)-NH-C β H u ) 2 , Zn- Cyclohexyl-dithiocarbaπiate, was produced in identical fashion as described in Example 4, except that solution (C), in this case contained 1.0 moles of Na 8 P0 4 and 0.6 moles of both, Na a NCN and Na-Cyclohexyl-_Ut_ύoc__rba_nate. Latter was synthesized pursuant the procedure weU known by the art, as foUows: 0.65 moles of CS- were slowly introduced, at normal temperature, into an aqueous solution comprising 0.6 moles of cyclohexylamine and 0.6 moles of NaOH in 400 ml. water. Pertinent analytical data and IR spectrum are presented below and Figure 7, respectively. Table 6. Measured parameter Determined value Appearance pale yellow Zn total % 49.0 NCN% 14.2 pH 7.7 Oil absorption, lbs/100 lbs Spec, gravity 2.62 Yield, g. 270.0 Example 7. Pigment grade organic-inorganic hybrid material of similar corrosion inhibitive characteristics as those described in previous examples, symboUzed by the phase-composition formula of where Zn(n-pDC) 2 is (n-C 3 H--0-C(S)S-) 2 -Zn, Zinc-n-propyl-O- dithiocarbonate, was synthesized in identical fashion as described in Example 4, except that solution (B) and (C ), in this case contained 0.5 moles Sr(N0 3 ) 2 , 1.65 moles Zn(NO a ) 2 /1500 ml. KL.O and 0.5 moles Na 3 P0 4 , 0.5 moles Na 2 Mo0 4 , 0.6 moles Na 2 NCN, 0.6 moles Na-S(S)C-0-C 3 H 7 -n/ 1500ml. H a O, respectively. The necessary amounts of Na-n-propyl- dithiocarbonate was synthesized pursuant the procedure known by the art, as foUows: into a mixture of 0.61 moles n-propanol and 0.6 moles NaOH / 100 ml. H.O, 0.61 moles of CS 2 were graduaUy introduced under moderate agitation and at 40-50° C, after which the same conditions were kept for one hour; the obtained aqueous solution was subsequently incorporated into solution (C). Pertinent analytical data are presented below. See IR spectrum in Fig.8. Table 7. Measured parameter Determined value Appearance white powder Zn total % 41.08 NCN% 12.3 pH 7.3 Oil absorption, lbs/100 lbs Spec, gravity 2.84 Yield, g. 525.0 Example 8 Multi-phase pigment grade hybrid material, appUcable for corrosion inhibition of Ag, Cu, Al, Fe, characterized by phase-composition formula of 0.05 dCy-MBT / ZnNCN / 0.5 CaSi0 3 (where dCy-MBT stands for di-cyclohexylammoriium 2- mercaptobenzothiazolate) was produced according to the foUowing procedure: CaSi0 8 /ZnO mixed suspension (A), containing 165.0 g. of CaSi0 8 and 224.0 g.(2.75 moles) of ZnO in 2000 H s O, was prepared in identical fashion as described in the appUcable part of Example 3. Concomitantly, an aqueous suspension (B) of di- cyclohexyl__mι_ιoniurn 2-mercaptobenzothiazolate was produced by introducing simultaneously into 200 ml. H a O, (under agitation and normal temperature conditions) 0.15 moles of Na-2-mercaptobenzothiazolate (as aqueous solution, prepared by dissolving the appropriate amount of technical grade MBT in 200 ml. solution containing 0.15 moles NaOH )and aqueous solution of di- cyclohexyl_u-_ιr_oniuιn sulfate, previously prepared by neutralizing 27.5 g.(0.15 moles)of di-cyclohexlamine (technical grade with 98% assay, avaUable from Aldrich Chemical Co.) in 150 ml. H.O, with 0.08 moles of H 2 S0 4 . Subsequently, pigment grade hybrid material corresponding to the above specified phase composition formula, was produced by introducing into suspension (A), under intense agitation, suspension (B) and simultaneously 3.0 moles of H 2 NCN (as aqueous solution of 25%), in about 30 minutes. During (B) and H 2 NCN introduction, the intensively stirred reaction system's temperature was kept at 65-75oC and consecutively the conversion process was finaUzed under the same conditions in one additional hour. The obtained pigment slurry was subsequently cooled to normal temperature, filtered, washed to salt-free conditions and further processed according to the appUcable part of Example 2. Pertinent analytical data and characteristic IR Spectrum are presented in Table 8 and Fig. 9, respectively. Table 8. Parameter Measured Determined value Appearance white powder Zn total.% 39.0 NCN,% 35.7 pH 8.95 Specific Gravity 2.72 Oil absorption, lbs/100 lbs Yield, g. 492.0 Example 9. Pigment grade organic-inorganic hybrid composition, corresponding to the phase-composition formula of 0.05 Zn(CyM) 2 / ZnNCN /0.5 CaSiO a (where Zn(CyM) 2 stands for Zn(-S-(C β H n ) 2 , Zn-cyclohexyl- thiolate) appUcable as corrosion inhibitor pigment component of paint and coating formulations intended for Ag, Cu, Al, Fe protection, was obtained in aU details according to the procedure described in Example 3/3.2., except that in this case, (instead of 2-mercaptothiazoline), 0.28 moles (33.5 g., 97%)of cyclohexyl mercaptan, (available from ELF Atochem North America, Inc.), was used. AU operations involving cyclohexyl mercaptan were performed in closed apparatus equipped with caustic scrubber. Pertinent analytical data and characteristic IR Spectrum are presented in Table 9 and Fig. 10, respectively. Table 9. Parameter measured Determined value Appearance white powder Zn total,% 37.5 NCN,% 40.8 Specific gravity 2.57 pH. 8.4 Oil absorption, Ibs/lOOlbs Yield, g. 493.0 Example 10. Organic-inorganic hybrid material, appUcable as pigment grade corro-sion inhibitor, corresponding to the phase-composition formula of 0.06Zn(DTP) 2 / ZnNCN / 0.4 CaSiO a / 0.2Zn 3 (PO 4 ) a 2H a O where Zn(DTP) a symboUzes Zn-(S(S)P[-OCH 2 -CH(CH a )CH 3 ] 2 or Zn-O, O-di-i-butyl-dithiophosphate, was synthesized according to the foUowing procedure: Mixed dispersion (A), containing 138.5 g. (1.7 moles)of ZnO, 116.5 g.(1.0 moles) of CaSiOa/1000 ml. H-O and solution (B) of 2.25 moles ZnSO.,/1500 ml., the latter at approximately pH = 4.0, were prepared foUowing the appUcable section of Example 2. and common procedure, respectively. Concurrently, solutions (C) and (D), comprising 1.0 mole Na 8 P0 4 , 0.6 moles Na_NCN /1000 ml HaO and 0.3 moles of Na-DTP/500 ml H a O, respectively, were prepared at ambient temperature. Pigment grade hybrid material, according to the above specified phase-composition formula, was produced by introducing first, in about 30 min., 1.8 moles of aqueous HaNCN and subsequently (in about 30 min.) solutions (B), (C) and (D) (simultaneously) into intensively stirred dispersion (A); pH = 7-8 of the reaction medium was observed. Same reaction conditions were hold for additional 60 min. at 60-65 °C and subsequently, the suspension's soUd phase was separated by filtration, washed to soluble salt-free conditions and further processed in identical fashion as disclosed in the appUcable section of Example 2. Pertinent analytical data and IR spectra are presented in Table 10 and Fig. 11. Table 10. Measured parameter Determined value Appearance white powder Zn total % 50.05 NCN % 10.7 pH 8.2 OU absorption, lbs/100 lbs Spec, gravity 3.23 Yield, g. 230.0 Example 11. In order to evaluate the cure-inhibitive activity of various organic-inorganic hybrid pigments produced according to the present invention, the medium oil alkyd resin based paint formulation presented under 1.5.1 /Table 1.2 of Example 1 and the test procedure according to 1.6/Example 1, were employed. In this case, however, all hybrid pigments were tested at 4% by weight of paint formulation and, again, tack-free appUcations were considered cured. Data are presented below. Table 11. Hybrid Pigment Example No. Observation: 0.05Zn(MBTyZnNCN 2.1 No cure inhibition 0.05_-n(MBTy__ι_NCN/0.5CaSiO 3 2.2 0.05Zn(MBiyZn CN/05°CaSiO 3 3.1 0.05Zn(MTHyZnNCN/0.5CaSiO. 3.2 0.075Zn DMTD/ZnNCN 5 0.05Zn(CyM),/ZnNCN/0.5CaSiO a 9 0.06Zn(DTP)_/ ZnNCN/ 0.4CaSiO s /0.2Zn 3 (PO.) ~ 2H 3 O 10 005dCy-MBT/Zz_NCN/0.5CaSiO_ 8 0.06Zn(n pDCyZnNCN/ 0.21SrMoO^0.1Zn 3 (FO 4 ) a 2H 3 O 7 As observed, no hybrid pigment (tested at 4% by weight) displayed cure inhibitive activity in the radicaUy cured, solvent based medium oil alkyd paint system; such behavior indicates, that hybrid pigments synthesized according to the present invention are essentiaUy free of un-complexed thiol compounds. Notably, aU technical grade Zn(MBT) a prepared pursuant to U.S. Patent 4,329,381 displayed cure inhibition. (See Table 1.3 & Example 1 for detaUs). Example 12. Selected pigment grade hybrid composites synthesized according to the present invention, were tested (comparatively to strontium chromate), as a pigment component of protective primer formulations, specificaUy for their inhibitive activity to metal corrosion. Two such solvent based epoxy/polyamide (two component) test formulations (identified as 12.1 and 12.2) and corresponding control formulations, were appUed and tested on alurninurn and copper substrates. DetaUs are presented below in Table 12. It wiU be observed, that in both cases pigment grade strontium chromate was employed as corrosion inhibitor component of the respective control forrnulations. Table 12 Components of Parts by Weight of Formu- Trade name* _. lationβ Suppliers of 12.1. 12.2 12.1 in 12.2 Components Test Control Test Control Epox Base Epoxy Resin Shell Epon 1001-CX-75 320.0 same 320.0 same as test as test Corrosion Inhibitor Pigments Zn(MBTyZnNCN/ CaSi0 3 (See Example 2.2) 95.0 __n-DMTD/ZnNCN (See Ex 5) 95.0 Strontium Chromate SrCr04-176 (4) 50.0 50.0 Catalyst Hardener Aramide 220 Polyamide 160.0 " Shell 3115-X-70 Polyamide- - 160.0 Solvents Toluene 168.0 " 168.0 MIBK 222.0 " 222.0 PM Aoetate 141.0 " 141.0 Butanol 40.0 " 40.0 Volumes: Approximately 100 gal. * PM Acetate - Propylene glycol methyl ether Acetate; Raw material supphers: (1) Qmya, Inc.; (2) DeGussa Co.; (3) American Cyanamide; (4) Wayne Pigment Co. Example 13. Test formulation 12.1 (see Example 12) was employed to evaluate effectiveness on aluixiinurn of the corrosion inhibitive activity of pigment grade hybrid symboUzed by 0.05Zn(MBT) a /ZnNCN/0.5CaSiO 3 phase composition formula synthesized according to Example 2.2 For that purpose, the 12.1 and related control formulations were appUed by wire-wound rod on Type A 3003 H14 Aluminum panels (from The -Panel Co.), at 0.6- 0.8 mils thickness, aged for 7 days at room temperature, verticaUy scribed and subsequently subjected to salt spray exposure (according to ASTM B-117). It wiU be noted, that the coatings' observed corrosion inhibitive performance is considered being directly proportional with the tested pigment components' corrosion inhibitive activity. Test results are summarized in Table 13. Table 13. Formulation / Salt spray exposure Observation pigment inhibitor time Test 12.1/hybrld, Example 2.2 7000 hours No blisters, coating intact Control 12.1/SrCrO. 7000 hours " Based on the above presented experimental results it can be concluded that hybrid pigment of 0.05Z_ι(MBT) 8 /ZnNCN/0.5CaSiθ 3 phase composition possesses exceUent corrosion inhibitive activity on aluminum, being equaUy effective as SrCr0 4 , which is regarded the industrial standard for such appUcations. Example 14 Test formulations 12.1 and 12.2 (see Example 12) were used to assess on copper the corrosion inhibitive activity of pigment grade hybrids symboUzed by 0.05Zn(MBT) 2 / ZnNCN/0.5.CaSiO 3 (Example 2.2) and 0.075.Zn-DMTD/ZnNCN phase composition formulas, the latter being synthesized according to Example 5. Both test and the pertinent control formulation were appUed on commerciaUy available copper panels, baked, aged for 7 days at room temperature, verticaUy scribed and subsequently tested. The evaluation of corrosion inhibitive activity of the above specified hybrid pigment varieties, comparatively to SrCr0 4 , was performed according to an electrolytic procedure, (of NIKE- TECH, Inc., of Alvarado TX.) as foUows: AnodicaUy polarized test and control panels, as weU as an inert cathode, are simultaneously immersed in an aqueous electrolyte solution containing NaCl, a___r__onia, Na,S0 4 and surfactant; 6 Volts DC is appUed for 30 min at ambient temperature after which the physical integrity of the coatings are visually evaluated and performance graded on a 1 (worst) to 5 (best) scale. It is noted again that coatings' protective performance is considered to be directly proportional with the tested pigment component corrosion inhibitive activity. Test results are summarized in Table 14. Table 14. Formulation/inhibitor Performance grade pigment of inhibitor pigment Test 12.1/hybrid, according to Example 2.2 4 Control 12.1/SrCr0 4 1 Test 12.2/hybrid, according to Example 5. 4 Control 12.2/SrCr0 4 1 Based on these test results it can be concluded that hybrid pigments having 0.05 Zn(MBT) ϊ yZnNCN/0.5 CaSiO 3 and 0.075-Zn- DMTD/ZnNCN phase composition formulas display exceUent corrosion inhibitive activity on copper, substantiaUy better than SrCrO, which is the industry standard for such appUcations. Example 15. Pigment grade hybrids of 0.05Zn(MBT) ZnNCN, 0.05Zn(MBT)./ ZnNCN/0.5CaSiOa, 0.05Zn(MBI) s ZnNCN/0.5CaSiO 3 and 0.05.Zn(MTH)_/ ZnNCN/0.5CaSiO 8 phase composition formulas, synthesized according to Examples 2.1, 2.2, 3.1 and 3.2, of the present invention, were tested for their corrosion inhibitive activity on sUver, as pigment components of "mirror backing" coating formulations. The test formulation employed, which is weU known by the industry, is presented below: Table 15.1 Components of Trade names & Parts by weight formulation suppliers Resin component Acryloid B-67 (1) 33.0 Solvent Xylene 42.0 Corrosion inhibitor Pigment Hybrids as above disclosed * 25.0 100.0 * Pigment grade ZnNCN, manufactured according to U.S. Patents 5,176,894 and 5,378,446 by Wayne Pigment Co., MUwaukee, Wi; was used in the control formulation, (1) - suppUed by Rohm & Haas; The experimental work was performed by Nike- Tech, Inc. (located at FM 1807 Nike North, Alvarado, Tx., 76009). It did include preparation of Ag mirror substrates, apphcation by dipping of test and control coatings at approximately 1.0 mil dry thickness, 24 hours air drying and vertical scribing of the test panels. The evaluation of corrosion inhibitive activity of the above specified hybrid pigment varieties, comparatively to ZnNCN, was performed according to the electrolytic procedure described in detail in Example 14. Test results are summarized below. Table 15.2 Inhibitor pigment tested/ According to Performance (phase composition formula) Example grade accorded 0.05Zn(MBT)JZnNCN 2.1. 5 0.05Zn(MBT) 2 /ZnNCN/0.5CaSiO, 2.2. 5 0.05Zn(MBI)_/ZnNCN/0.5CaSiO- 3.1. 4 0.05 Zn(MTH)_/ZnNCN/0.5CaSIO-3.2. 4 ZnNCN * 4 * Produced by Wayne Pigment Co. Based on the presented experimental results it can be concluded that pigment grade hybrid materials produced specifically according Examples 2.1 and 2.2 possess high corrosion inhibitive activity on silver, being superior in that respect to ZnNCN, a state of the art lead- free pigment recommended for such appUcations. Example 16. Pigment grade organic-inorganic hybrid, according to Example 2.2, described by phase composition formula of 0.05Zn(MBT)_/ZnNCN/0.5CaSiO 3 , was evaluated in solvent based medium oil alkyd formulation for synergistic behavior in respect of inhibition of steel corrosion. Distinct test formulations, containing the pigment grade hybrid composition, its phase constituents (pigment grade ZnNCN, CaSiO a -WoUastonite grade, technical grade Zn(MBT) 2 produced according to Example 1.3), pigment grade SrCr0 4 and zinc phosphate dihydrate, respectively, were sprayed on cold roUed steel panels (from The Q-Panel Co.), at 1.5 mil film thickness. The exhibits were air dried, aged overnight at 130°F, scribed, and subsequently exposed to salt spray conditions for 670 hours, foUowing to ASTM B-117 and evaluated by ASTM D-714; the test coatings' overall corrosion inhibitive performances, considered directly proportional with pertinent pigments' corrosion inhibitive activity, were comparatively evaluated and graded on 0 (worst) to 10 (best) scale. The test formulations and results are presented below in Table 16.1 and 16.2, respectively. Table 16.1 Components of test Trade names β. Parts by weight formulation suppliers Raw material supphers: (1) McWhorther Technologies; (2) SCM; (3) Pfizer Inc., Chemical Div.; (4) Harcros; (5) Rheox, Inc.;(6) Interstab Chemicals, Inc.; Table 16.2 Results of the evaluation of pigments' corrosion inhibitive activity Pigment grade hybrid according to Example 2.2, displays synergisticaUy enhanced corrosion inhibitive activity on cold roUed steel, perfomaing substantiaUy better in that sense, than pigment grade Zn 8 (P0 4 ) a (H.O) a and at comparative level to SrCr0 4 . It is as weU the manifestation of synergy, that the same pigment composition evidently outperforms the components which is constituted of. Example 17 17.1: Multi-component pigment grade composition, characterized by synergistic behavior in respect of inhibition of steel corrosion, symboUzed by the phase composition formula of ZnNCN/0.77ZnO/0.77Zn a (PO 4 ) a (H _0) 4 /2.42CaSiO a / 0.3SrCO 8 was synthesized according to the foUowing procedure: Mixed suspension, containing finely ground 1.0 moles ( 81.38 g.) of ZnO, 0.075 moles (11.0 g.) SrC0 3 , 0.6 moles (69.5g.) of CaSiO, in 1000 ml. water, was prepared by overnight agitation at normal temperature of the above mixture. Aqueous solution of about 50%, containing 0.38 moles H 8 P0 4 was introduced first, at ambient temperature, into the intensively stirred mixed suspension in approximately 60 minutes; subsequently, 0.25 moles of H-NCN (as aqueous solution of 25%) were introduced into the reaction mixture, after which, by keeping the same reaction conditions, the process was finaUzed in one hour. The synthesized multi- component pigment was further processed in identical fashion as described in the appUcable section of Example 2, except that it was dried at a moderate temperature of 70-80°C, in order to preserve the tetrahydrate composition of the zinc phosphate constituent. Related analytical data and IR spectra are presented in Table 17.1 and Fig. 11, respectively. Table 17.1 Measured parameter Determined value Appearance white powder Zn total % 32.0 NCN % 10.7 pH 7.5 Oil absorption, lbs/100 lbs 34 Spec, gravity 2.95 H-O % (by loss at 200 °C) 5.0-6.0 Yield, g. 210.0 17.2: Multi-component pigment grade composition according to Example 17.1 was evaluated in a solvent-based medium oU alkyd formulation for synergistic behavior with respect to inhibition of steel corrosion, in identical fashion as described in detail at the introductory section of Example 16. In this case, however, the distinct test formulations contained the multi-component pigment composition, its phase constituents (pigment grade ZnNCN, CaSiO B - WoUastonite grade, Zn 3 (P0 4 ) a (H a O) 4 ), coprecipitated mixtures of ZnNCN/Zn a (P0 4 ).(H_0) 4 , respectively, ZnO/Zn 3 (P0 4 ) a (H a O) 4 and pigment grade SrCr0 4 (see Table 17.3). The test formulation employed and the results of corrosion inhibitive activity evaluation are presented below in Table 17.2 and 17.3, respectively. Table 17.2 Components of test Trade names & formulation suppliers Parts by Weight Raw material supphers: (1) McWhorther Technologies; (2) U.S.Oxides; (3) Pfizer Inc., Chemical Div.; (4) Rheox, Inc.;(5) Interstab Chemicals, Inc.; Table 17.3 Results of the evaluation of pigments' corrosion inhibitive activity. Inhibitor pigment Status of test Overall grading Observation component of test coatings after of pigments' coatings. 240 hours. inhibitive performance. None Extensive Control. delamination, dense blisters; ZnNCN Extensive Component of delamination, pigment accord¬ medium dense ing to Example blisters 17.1 CaSlO, Extensive 0 delamination, dense blisters; Zn_(PO.)_(H.O). " 0 ZnNCN / Extensive 0 Zn J (PO < )_(H.O) 4 delamination, medium dense blisters; ZnO / __u_(P0 4 )_(H.O) 4 Pigment 5 mm creapage 8 Pigment displays according at scribe; few blisters synergy at scribe to Example 17.1 SrCrO, Limited creepage at 9 Control pigment, scribe; few blisters; standard of the industry; Based on the above presented results of the comparative evaluation, it can be concluded, that the multi- component pigment composition according to Example 17.1, displays synergy in respect of corrosion inhibition on steel.

Claims: 1. A corrosion-inhibiting composition for apphcation to a metal substrate comprising a film-forming organic coating composition having a pigment phase which comprises a stable hybrid organic/inorganic suspension which contains suspended ZnNCN and an organic zinc or alkyl-aix-cαoniuin salt of mercapto- and/or thio- compounds or their alkyl-substituted derivatives. 2. A composition according to claim 1 which comprises a mixture of said organic zinc salts. 3. A composition according to claim 1 wherein the organic salt comprises a zinc or alkyl-__α_rr_oniurn salt of a compound selected from mercaptobenzothiazole, mercapto thiazoline, mercaptobenzimidazole, mercaptoimidazole, 2,5-diι_-ercapto-l,3,4-t__iodiazole, 5,5- dithio-bis( 1 ,3,4-thiadiazole-2(3H)-thione, mercaptobenzoxazole, mercapto thiazole, mercapto triazole, mercaptopyririiidine, mercaptopyridine, mercaptoquinoline, alkyl- and cyclo-alkyl mercaptanes, N-alkyl- or N- cycloε-Lkyl-chthiocarbainates, O-alkyl- or O-cycloalkyl- dithiocarbo nates, 0,0-dialkyl- and 0,0-dicycloalkyl- dithiophosphates. 4. A method of providing corrosion resistance to a metal surface which comprises applying to said surface a film-forming organic coating containing a suspended pigment phase, said pigment phase containing a hybrid organic/inorganic suspension which comprises a hybrid organic/inorganic material according to claim 1 in a corrosion-protecting amount. 5. A con >sion-irιhibiting composition for apphcation to a metal substrate comprising a film-forming organic coating composition, and, a pigment phase which comprises a stable unitary hybrid material containing organic and inorganic soUd phase constituents interfaced at a crystaUite level, being inseparable by physical separation procedures and displaying uniphase behavior, said inorganic phase including a cation selected from Zn, Al, Mg, Ca, Sr, Ti, Zr, Ce and Fe and an anion selected from phosphates, polyphosphates, phosphites, molybdates, siUcates and cyanamides, and said organic phase including a zinc or alkyl-anunoniuin salt of a compound selected from mercaptobenzothiazole, mercaptothiazoline, inercaptobenzii-iidazole, mercaptoimidazole, 2,5- d-mercapto-l,3,4-thiodiazole, 5,5-dithio-bis(l,3,4- thiadiazole-2(3H)-thione , mercaptobenzoxazole , mercaptothiazole, mercaptotriazole, ιr_ercaptopyrirnidine, mercaptopyridine, mercaptoquinoline, alkyl- and cyclo¬ alkyl mercaptanes, N-alkyl- or N-cycloalkyl- dithiocarbaxnates, O-alkyl- or O-cycloalkyl- dithiocarbonates, 0,0-dialkyl- and 0,0-dicycloalkyl- dithiophosphates.

Inventors: SINKO JOHN, SINKO, JOHN
Applicants: WAYNE PIGMENT CORP, WAYNE PIGMENT CORP.
Application year: 1997
Main classification: C01C3
IPC codes: C09D5