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7 *- t v Li Current technology review Received JUN 2 6 1975 ZINC-RICH COATINGS have been finding increased use in the protection offerrous metal substrates against corrosion. Here is a review of the technology behind these important coatings, and an insight to their potential in today's expanding markets. BY DEAN M. BERGER GILBERT ASSOCIATES, INC., READING, PENNA. The use of zinc in coatings to protect iron and steel substrates goes back at least 135 years. In 1840, a French en gineer named Sorel suggested in a pat ent that iron rusting could be con trolled by coating the ferrous substrate with zinc. The galvanizing industry since that time has shown an ever-increasing growth. The most popular method of protecting structural steel with zinc has been hot dip galvanizing, which protects steel surfaces very well. In corrosive environments, however, top coating is usually desired to protect the zinc from eroding too quickly. The selection of corrosion resistant topcoats for galvanized surfaces has presented innumerable problems of adhesion. Furthermore, not all sur faces can easily be galvanized. The construction industry, therefore, wel comed the invention and development of zinc-rich coatings. Zinc-rich paints fall into two major classes; some are based on inorganic vehicles, while others are based on or ganics. The best known example of the successful use of an early inorganic type is the coating of sodium silicatebased zinc-rich paint on an above ground pipeline between Whyalla and .Morgan in South Australia. This coating was applied in 1941 and was guaranteed to give satisfactory protec tion for 20 years. According to a report more than 20 years later, the coating was still in excellent condition. This early coating consisted of a simple mixture of zinc dust and sodi um silicate solution and had to be baked for half an hour at 350 F. to be converted to an insoluble film. Since then, numerous modifications to im prove handling, film formation and durability have been described in the patent and trade literature. Typical early sodium silicate-based zinc-rich paints are described in pat ents by V. C. J. Nightingall and A. McDonald. In U.S. Patent No. 2,462,763 issued on February 22, 1949, and assigned to Di-Met Propri etary Ltd. of Melbourne, Australia, Nightingall discloses a zinc-rich paint formula consisting of 100 parts by vol ume of sodium silicate solution (1.4 specific gravity) and 12 parts by vol ume of sodium bicarbonate solution (saturated at 60 F.) mixed with an equal weight of zinc dust. This paint is promptly applied to clean steel, al lowed to air-dry for six hours and then baked for two hours at 450F. After cooling, the coating is washed with warm water to remove free alkali. McDonald, in U.S. Patent No. 2,509.875 issued on May 30, 1950, and assigned to Industrial Metal Protectivcs, Dayton. Ohio, discloses the V.ODERN PAINT AND COATINGS, JUNE 1975 use of a sodium silicate solution having an Si02 to Na20 ratio of 1.33 to produce a vehicle having a specific gravity of 1.3. This vehicle is then diluted to a specific gravity of 1.26 and mixed with zinc dust (100 grams of dust to 30 ml of vehicle). After application, this paint is baked at 250F. to attain insolubility. Improvements Since the original formulations were patented, various changes have been made that resulted in improved appli cation characteristics, methods of curing and over-all performance. Today's coating products contain a pigment that is substantially zinc dust of specially blended commercial super fine grades and high metallic zinc con tent produced - by the distillation process. Various additives, such as red lead, lead peroxide, lead chromate and lead sulfides, have been used to successfully increase pot life by delaying or preventing hydrogen evolution and re tarding the tendency to thicken. The addition of lead compounds produces other advantages for most uses and increases the hardness of the cured coating. In water-based silicates, purity of the zinc dust has a marked effect on pot life. An oxide layer on the zinc 19 Photomicrograph of zinc dust: process, condensation; shape, spherical; relative magnification, 10. Zinc powder: process, atomization; shape, irregular; relative magnification, 1. All photomicrographs courtesy Dr. A. W. Kennedy, research manager, Metal Coatings Division, Diamond Shamrock Chemical Co. dust particles, with suitable particle size distribution, is necessary. Zinc dust that has been exposed to atmospheric carbon dioxide and mois ture for extended periods, and has thus developed a basic zinc carbonate or hydroxide film, will produce a signifi cant reduction in the pot life of the mixed material (/). Those reactions responsible for short pot life are not fully understood. It must be assumed, however, that they involve the reaction between metallic zinc powder and water to form zinc hydroxide or hydrated zinc oxide, with the simultaneous liberation of hy drogen. perhaps according to the equa tion: Zn + 2 H20 = Zn(OH)2 + H2 Also involved is the reaction of zinc hydroxide with sodium silicate to yield polymer zinc silicate. The former reac tion would be expected to cause foaming, and the latter would result in a consistency increase and eventually in solidification of the mixture (2). Potassium silicate coatings, which on atmospheric exposure do not de velop the white carbonate film of efflo rescence characteristic of sodium sili cate coatings, were among the first self-curing zinc-rich paints. The lower alkalinity of these paints may have been a major consideration. They were quickly outdistanced, however, by paints based on lithium silicate solu tions, which offered impressive prac tical advantages and which became an important tool in the fight against cor rosion. Napko (Houston, Tex.) offers a fast curing zinc-rich primer based on potassium silicate. Lithium silicate solutions, which produce stable vehicles and paints, can be prepared at significantly higher Si02 to Li20 ratios (six to more than eight, for example). The coatings ob tained with such vehicles cure readily upon exposure to the atmosphere and yield films of good abrasion resistance and durability. U.S. Patent 3,180,746. to Cox et al of Exxon, describes this water-based self curing inorganic zincrich coating, and U.S. Patent 3,130,061, to Walter McMahon of Ameron, contains the original technol ogy. Many paint companies are li censee producers. Ethyl or Alkyl Silicates An important class of self-curing zinc-rich paints, which occupies a place between inorganic and organic paints, is based on alkyl silicates. These paints are grouped in the inor ganic category, exhibiting all of the film properties of the silicates, but consist of partially hydrolyzed. members of the series methyl through hexyl or gylcot ether silicates. Of the-.^. the ethyl silicate type is most widely known and used. The First known disclosure re garding the effective use of zinc powder with a partially hydrolyzed alkyl silicate was found by <;t,,nrl'"'1Paint & Varnish. It is credited to H. Anders in 1904 (3). Although galvanic protection is not mentioned, good rust inhibition is claimed. According to Loomans and Van Leberghe (4), hydrolyzed ethyl silicate in various states of hydrolyzation has been used as a binder for paints, and especially for heat resistant paints, for some time. Upon partial hydrolysis, some of the ethoxy groups in the ethyl orthosilicate are replaced by hydroxyl groups, thereby liberating ethanol. Some of the hydroxyl groups react with each other, giving off water and tying silicon atoms together by oxygen bridges. The partially hydrolyzed, polycondensed ethyl silicate contains about 40 per cent Si02 and continues to hydrolyze upon exposure to the atmo sphere. Zinc dust paints made with this vehicle are said to be easily applied by either brush or spray, to adhere well to iron and steel, and to give excellent protection against rusting, even when immersed in salt solution (2). Another method for preparing an ethyl silicate-based vehicle for zincrich paint is described in a British pat ent (5). It is suggested that an equal volume of monoethanolamine and ethyl silicate be blended and allowed to stand for 12 hours, after which an additional nine volumes of ethyl sili cate are added. Twenty volumes of the mixture are then mixed with ten vol umes of mineral spirits and 100 parts by weight of zinc dust to yield the paint. A small amount of butyl phthalate may be added as a plas ticizer. One of the most widely used zincrich paints based on ethyl silicate is described in U.S. Patent No. 3,056,684 (6) by Stan Lopata and W. R. Kcithler. This patent was dedicated to the public in October. 1972. According to the patent, partial hydrolysis of tetraethyl orthosilicate may be carried out by dissolving the alkyl silicate in a suitable organic sol vent, adjusting the pH to between 1.5 and 4.0 by the addition of any conven tional acid, and adding a quantity of xvater less than that required for complete hydrolysis. The reaction is then allowed to run its course, while 20 MODERN PAINT AND COATINGS. JUNE IP75 Ad 2 x /-/? /c /y / r the mixture is stirred until a homo i geneous. oily liquid has been obtained. l"his liquid is then mixed with filler- component consisting essentially of finely divided metal. The zinc dust to vehicle ratios given in the examples disclosed in this patent range from 8:3 to 7:1 by weight. To improve film hardness or resiliency, zinc chloride, magnesium chloride or similar acid metal salts may be added in concentrations of from five to 30 per cent of the particular hydrolyzed retraethyl orthosilicate. Depending on the pH of the medi Zinc flake: process, ball milling; shape, platelet; relative magnification. 3.3 um. the reaction of ethyl silicate with water follows two different paths, each of which is useful in the preparation of zinc-rich paints. In theory, the hydrolysis of ethyl sil icate should show two distinct steps: first, the hydrolytic reaction to give silicic, acid, followed by the condensa zinc. In fact, it must be packaged in metal-free containers and is usually supplied in plastic bottles. When the paint is finally mixed there is an ade quate pot life and, in the paint film, moisture from the atmosphere com pletes the hydrolysis to silica and the (1) 200-proof ethanol should be added to ES-40. (2) Specially denatured alcohol is acceptable. (3) Keep under constant agitation at all times. (4) Partial hydrolysis usuatly takes tion reaction to give polysilicic acids and. finally, silica. formation of a typical silica-zinc sili cate coating results. two or three days. (5) Always add alcohol to ES-40. OEt I Eto - Si - OEI HjO OH I HO - Si - OH - H,0 (SiO,ln The same type of reaction occurs, of course, if one starts with a polycondensed ethyl silicate, such as ethyl sili Ethyl alcohol is a fairly rapidly evaporating solvent with a low flash point. The partial hydrolysis can be I - OEt I OH -* cate 40. This product, a partially polymerized form of ethyl silicate, is somewhat altered by transesterifying glycol ethers or higher alcohols into However, Bechtold (J. Phys. Chem., Voi. 59. pp. 532-41; 1955) and also a completely esterified polysilicic acid of the following general structure: the system. Such partially hydrolyzed silicates offer the manufacturer of zinc o 1 1 Audsley (Chem. Soc. of London, 1962, pp. 2320-29) have shown that in an acidic environment all the ester groups of ethyl silicate are not equally reac tive; that is, two ester groups show a much faster rate of hydrolysis than the other groups so that, to a limited ex tent. ethyl silicate reacts with water as if it were a difunctional monomer -ather than a tetrafunctional one. Moreover, in a very slightly acidic me dium, the silunol groups, which are the initial products of hydrolysis, are relaively stable and the self-condensation reaction that leads eventually to silica quite slow. In consequence, it is possible to -lydrolyze ethyl silicate with a limited quantity of water at a slightly acidic H and obtain low polymers of a par;:illy hydrolyzed ethyl polysilicate ith the following general structure: Oil O11 il - Si - OEt 1i OEt OEt Ibis product, a partial ester of poly- OEt I EtO - Si - - OEt I OEt n n 5- 7 When this material is partially hydrolyzed with an acid catalyst, some further condensation occurs and the final product again contains a certain number of free Si-OH groups, which give it the properties of a partially es terified polysilicic acid. A different type of hydrolytic reac tion occurs between silicate esters and water in an alkaline environment. In this case, the reaction with water is very rapid for all the ester groupings, as is the subsequent condensation reac tion that leads to silica, so that under these conditions one cannot isolate any partially hydrolyzed ester. Therefore, alkaline catalyst and water react im mediately to give a more highly con densed product, which is. again, a completely esterified polysilicic acid, and this reaction will continue as water becomes available until silica it self is produced: primers better application properties. A per U.S. Patent 3.730.743 hy Oorrjpn^^ McLeod of/Stauffer Chemica~y$uch zinc-rich primers are made by South ern Imperial Coatings. New lT~ ' In U.S. Patent 3,392.036, McLeod offers several vehicle modifications using trimethyl borate with a siloxane. It can be shown that these materials will react with partially hydrolyzed ethyl silicate in the presence of mois ture to form a complex borosilicate. A boron content of five to 20 per cent of the silica is useful. The ethyl dimethyl- siloxane is used to help prevent mudcracking of the applied zinc-rich primer. Many paint companies incor porate this technology, including Mobil, Carboline. International and Standard Paint. The first polyvinyl butyralmodified, ethyl silicate zinc-rich paint is described by Robert A. Rucker of Zinclock in U.S. Patent 3.392,130. This product, which is now produced by Porter Paint, Louisville, Ky., offers extremely good flexibility of the final ;cic acid, can be used as the silicate rtion of a zinc-rich paint. However, OEt OEt OEt I II 2 Et - 0 - Si - OEt + H,0 EtO - Si - 0 - Si - OEt + ZttOH film. In addition. Zinclock is easy to apply and to top coat. It will not. how -c by virtue of the silanol OH ups the material is a polysilicic I OEI *I OEt OEt ever. withstand high temperatures. D. P. Boaz (Standard Paint) also uses d. it will react with heavy metals The hydrolysis of ethyl silicate 40 this technology, plus borates and I it cannot be packaged with the involves the following: silanes, in U.S. Patent 3.730.746. fRN PAINT AND COATINGS. JUNE 1975 21 Combinations of Cellosolve silicates with borates, glycols and silanes are mentioned as vehicles for zinc paints in various foreign patents: in Germany, Patent 2,147,299 to Anderson and 2,147,804 and 2,147,865 to Gordon McLeod, and in South Africa, Patent 71/3993 to Nils Trulsson. Aaron Oken of Du Pont, in U.S. Patent 2,649,307, describes a borosilicate vehicle for zinc-rich paint. Dean Jarboe of Plaskem describes a tri methyl borate and aluminum oxide modified zinc-rich paint in U.S. Patent 3,412,063. The use of 2 ethylhexoic acid and monoethanolamine is described by Blake F. Mago in U.S. Patent 3,634,109 to Union Carbide. The amine salt is used to partially hydro lyze the ethyl silicate. W. R. Keithler of Plaskem describes the use of di-2ethylhexylamine in U.S. Patent 3,202,517, and describes the first zincrich based on an amine hydrolysis. Various colored zinc-rich paints are described by Robinson in British Pat ent 1,205,394. These coatings have become very popular. Recently Napko Chemical and Carboline have also in troduced zinc-rich paints of various colors. One-coat protection is offered and a topcoating is not required. Nuclear Power Facilities One interesting application of inor ganic zinc is in the protection of nuclear power plants. The protection of steel surfaces within the reactor building requires a coating with a 40year expected life. In fact, it is hoped that such surfaces will never have to be painted after the plant goes into opera tion. The Utilities Nuclear Coating Work Committee and ASTM DO1.43 meet quarterly to establish specifi cations and guides for coating these fa cilities. Alkyl silicate inorganic zinc-rich primers are used in nuclear applica tions for many reasons. These primers are applied at 3.0 mils minimum thickness, mainly at the steel plate manufacturer's facility before ship ment to the job site. Recent technology involves the use ot on-site paint facilities to blast clean and coat the steel. This allows for the steel plate to be shipped bare and for improved inspection and quality con trol on-site. After the building is erected, the topcoat is applied. An epoxy-phenolic or epoxy-polyamid is used at 5.0 mils minimum. This coating system meets the rugged requirements of DBA (Design Basic 22 Accident) testing as found in ANSI 5.12 and 101.4. Such a system is pres ently offered by three suppliers: Carboline. Ameron and Mobil Chemi- Une-Package Primer The most promising recent develop ments involve preconstruction primers. These products are normally applied 0.75 to 1.0 mils over sand blast cleaned steel. At Sun Ship and various other shipyards, a single coat of the one-package zinc-rich primer is ap plied. The plate is handled immedi ately and stored. After fabrication the final coating is applied. Weld-thru primers are being devel oped to provide better welding charac teristics. These include the use of "Ferrophos" (Hooker). Ferrophos may be added in amounts up to 30 per cent of the zinc content without losing the ef fectiveness of the protective qualities of the zinc-rich primer. Ferrophos offers good welding qualities and little tendency for gas evolution during welding. Weldalloy 505 T, by Southern Imperial Coatings, contains a combina tion ot zinc and various metallic oxides designed to match the charac teristics of a welding flux. Gabriel H. Law and Walter M. McMahon of Ameron describe amine initiated hydrolysis and colloidal sus pension of silica in various solvents in U.S. Patents 3,615,730 and 3.653,930, and Dutch Patent 6,900,749. This technology led to the first commer cially produced, single-package zincrich paint, Dimetcote E-Z and Dimetcote D-l, by Ameron. Some interesting aspects of U.S. Patent 3,653,930 include the use of amines, such as cyclohexylamine or triethanolamine. These amines provide a hydroxyl source that is non-reactive with the organic polysilicate vehicle. When the coating is applied, the amine reacts with atmospheric mois ture to yield OH ions. The alkyl polysilicate then undergoes basic hy drolysis to form the polysilica matrix, and the resultant alcohol by-product is lost by vaporization. RAH, + H;0 5= RNHj + OH "0C,Hs C.H-,0------- Si-------- 0 C.H, OH + H,0 M - CiHjU n NiSiO!, + NlC-HjOH) It has been found that gas evolution may be controlled by adding a few per cent of l-nitropropane. Thus, it is sug gested: Zn + 2H-0--Zn(OH)* + H*and CHj - CH* - CH* - NO* + 3Hj-- CH3CH*CH*NHi + 2H*0 Close examination, however, indicates the following combined reactions like ly: 3 Zn + 4H*0 + RNOi-*-3 Zn(OH)* + RNH* Red lead has also been found to reduce the gas evolution of such inor ganic single-package systems. The patent described by Mr. Law further claims the use of non-polar solvents, which contribute to non-settling char acteristics of the paint. In addition, a cyclic ketone is also claimed as a hydrogen scavenger. Single ethyl silicate 40 contains no free OH groups, it is unreactive with metals, and with it one can prepare a single-container zinc-rich paint. This is the basis of a patent, U.S. 3,660.119, to Aaron Oken, which claims a single container, storage-stable, highly reac tive zinc-rich paint from a composi tion of ethyl silicate 40. zinc dust and an alkali metal alkoxide catalyst, such as sodium methoxide. As an example, the following for mulation shows no gassing or deterio ration on prolonged storage at 130F., is non-settling, will harden rapidly after being painted out and gives ex cellent protection to steel exposed to salt spray. Material Ethyl silicate 40 Zinc dust Bentone 34 Micro mica C-3000 Chrome oxide pigment Xylene 100% sodium methoxide powder Ib/gal 1.60 12.40 .22 .22 .27 4.43 .03 19.17 The paint is made very simply in a high shear stirrer with a portion of the xylene to provide a workable consis tency and. when maximum thixotropy is obtained, is reduced with the remaining xylene. In addition, a polyol silicate or a polyol hydrocarbon ether silicate is available. This interesting vehicle pro vides unlimited stability and good flex ibility and welding characteristics. Gordon McLeod has patents pending concerning this Silzinc vehicle. The implication is that silicone hydrocarbon is grafted onto the ethyl silicate partially-hydrolyzed backbone. It is expected that the fast drying flexi bility and package stability wilt be useful in coil coating applications, as MODERN PAINT AND COATINGS. JUNE 19/5 1 Table I -- Zinc-Rich Primer Specifications, July 1974 Dote of Lest Federal Spec Amendment Specification Nov., 197! Aug., 1966 TTP-64IF Type 1 Type II Type III TT-P-001046 June, 1973 CE1409VZI08C June, 1973 CE1409 E303o Moy, 1961 July, 1970 MIL-P-15145B MIL-P-21035 Dec., 1965 Mll-P-23236 Type 1 and II Class 3 War., 1972 Mar., 1966 Mar., 1966 MIL-P*26915A Type 1 Class A & 8 Type If Class A Class B MIL-P-38336 MIL-P-46105 May, 1971 (omend 6) Nov., 1968 Moy, 1974 1 -GP-171a Type 1 Type II igpi8Io TTP-I561A Suggested Vehicle Linseed oil Alkyd Phenolic vornish Chlorinated rubber Vinyl Epoxy-polyomid Phenolic varnish Phenoxy No-Li silicote Ethyl silicate Phosphates Silicones Phenoiic vornish or Chlorinated rubber Phenolic varnish Styrene butadiene copolymer Alkyl silicates Acrylic MOD epoxy ester, urea formaldehyde Alkyl silicate No, Li, silicate Phenoxy Petroleum/hydrocorbon V/T butodiene Solvent Number of Govt Pockoges Agency Minerol spirits Mineroi spirits Mineral spirits Xylene 2 GSA 2 2 1 GSA Ketones Alcohols Mineral spirits Cellosolve acetate Water Alcohol Water Sol vent (xylene) Xylol 3 US Army Corps Eng. 3 US Army Corps Eng. 2 Navy 2 Navy 2 Navy 2 2 2 2 Air Force Xylol Xylol 2 2 End Use Repoir galvonized surfaces Primer for steel and gofvanized Primer for locks and dom< Primer, steel, potable water Interior potable woter tanks Regotvonizing welds in galvanized steel QPl, fuel tanks, misc. storage tanks Steel ground support equipment gofvonic protection Primer for other finish coots Alcohols or glycol ethers 2 Air Force Xylol 2 Army Corrosive environments Weld-thru primer outomotive. truck equip. Alcohols Woter, post cure 2 DOD Ottawa Morine tank QPL 2 Canada interiors Cellosolve 2 DOD Ottawa Repoir QPl acetate ketone Ef benzene Mineral spirits 1 GSA Choin-link fence repair (aluminum modified) ;! as in single-package structural 1 formulations. he three main organic binders used e mulate zinc-rich paints are chlou\l rubber, epoxy-polyamide and .:ioxy. nenoxy resins are high molecular `.grit, thermoplastic materials that ihine the application and handling .icieristics of a thermoplastic with : of the outstanding physical and :al properties of a thermosetting They may be characterized by 'owing molecular structure: , H H H III o-c-c-c- III H0H I n = --100 H ; resins are made from bis\ and cpichlorhydrin. and ic chemical structure is simihai of epoxy resins. ;ur difference between organic y.mic zinc-rich primers is in the adhesion between topcoat and primer. Epoxy, vinyl, chlorinated rubber and other topcoats adhere to the inorganic zinc-rich primer mainly by mechanical or polar bonding, while the organic zinc primer may be soft ened by the solvents used in the top coat. Care should be taken, therefore, in topcoat selection. Vinyls are incompat ible with phenoxy and require modifi cations with acrylic to adhere. Wash primer tie coats are frequently recom mended. Organic zinc primers have no criti cal application requirements. They are commonly applied over blast cleaned steel to a dry film thickness of 2.5 to five miles by brush, air spray or airless spray. Any reasonable thickness, how ever, can be applied without danger of cracking or flaking. Organic zinc primers come close to being ideal in that they combine a high order of permanence, easy application characteristics and economy. 'Nr AND COATINGS, JUNE 197S Chlorinated rubber has been a pop ular vehicle for zinc-rich primers. Fed eral specifications TT-P-001046 and MIL P-26915A are used extensively. Subox (BASF-Wyandotte) offers such a primer. The most effective organic zinc-rich primer is based on an epoxy polyamide vehicle. This versatile primer can be applied to a variety of substrates and offers maximum adhe sion and protection; In addition, it is easily topcoated with a variety of chemical resistant finishes. PPG In dustries. Steelcote, Sherwin-Williams. Mobil Chemical and many other manufacturers offer epoxy-polyamide zincrich primers. Other organic vehicles find special uses for temporary protection and are not recommended for high perfor mance. These include such oilmodified vehicles as alkyds. phenolics and epoxy esters. A summary of Government zincrich primers is shown in Table I. Com- 23 Table II -- Commercial Inorganic Zinc-Rich Primers for Structural Steel Supplier Ameron \V A. Bruder Conirox ltd. Corboline Corroline Corp. Cook Copon Deorbom Celanese (Devoe) Debevoise Du Pont Exxon Parboil Glidden Grow (Prufcoat) Grow (BW) Industrial Metol Prot. International Koppers (A Brown Div.) Mafcote McCleaster Mobil Chem. McLeod & Sons Nopko PPG Industries Philadelphia Quortz Ploskem (Eagle-Picher) Porter Rust-Oleum Sea Guard Sherwin-Williams Southern Imperial Standard Paint & Varnish (Gen. Dynamics) Steekote Subox (BASF-Wyandotte) Tnemec Wisconsin Protective SSPC Class IA (Post Cure) SSPC Class IB Water-Base Self Cure SSPC Classic Solvent-Base Dimetcote 3 Dimetcote 8 Dimetcote 2 Dimetcote 4 Dimetcote 5 Dimetcote 6 Dimetcote 1 and lM Dimetcote EZ Camrox Carbozinc 33 Rust O lostic 24A 111 Carbozinc 11 Carbozinc 12 Metal Plate Z Corrozinc Galvapoc 100 Galvapoc 101 Endcor 831 Catha Cote 300 Catha Cote 305 Catha Cote 302 Catha Cote 304 Debzinc-Galv Ganicin 347-936 Gonicin 347-931 Rustban 190 Rustban 186 Rustban 191 Rustban 193 Rustban 188 Forbozinc 76 Bolt O Zinc Glidzinc 5545 Zinc Prime 200 Zinc Prime 600 Zinc Prime 500 Met l Plate Z Zincilate 101C Zincilate 101R Interzinc 2410/2411 Interzinc 2410/2411/2415 Inorganic (Post cured) Inorganic Zinc # 3 P1500 Matcote 289 Dox-Anode Mobilzinc 1 1 3-F-l Mobilzinc 7 13-F-9 Mobilzinc 10 13-R-76 Mobilzinc 7 13-F-122 Mobilzinc 7 13-F-l2 3Z 4Z Post Cure Zincitf 4Z Metalhide 100 306 Silzinc 5Z Qu RAM 3365 WZ Zincite G Super Zincite Zinc Lock 351 Zinc Sele 56-8501 Zincguard 4 Zincguord 3 Zinc Clad 8 Zinc Clad B69AC50 Durozinc 500 Durozinc 525 Duro?inc 555 Inzinc MK 1 Golvanox VI 92 Tnemezinc 95 T Z Stoncoot 7-1 I Golvanox V Plasite 1000-1002 mercial zinc-rich primers are listed ac cording to their SSPC class!fication in Tables II and III. A new development using zinc flake has been incorporated in an aqueous product licensed by Diamond 24 Shamrock Chemical Corp. Trade named Dacromet 320 (7), the coating is applied to preformed small steel parts in a double coat at about 0.2 mils. At equal coating thickness,. Dacromet 320 contains less than half the weight of zinc than do plated metal parts, yet imparts more than twice the salt spray resistance. The surface provides an-excellent base for further painting, including clcctrodeposited coatings for automotive parts. Dacromet 200 (7) is a zinc dust aqueous dispersion applied at 0.1 mils and baked. This is followed by a sec ond coat of Zincromet at 0.4 mils, which is also baked. This product, called Zincrometal, is applied by reverse roll coating at speeds up to 500 feet per minute. Such products can be applied to one or both sides of the steel surface. Several steel companies are licensees of Diamond Shamrock. Photomicrographs show the dif ferences in the physical characteristics of particulate zinc, zinc dust and zinc flake. The plate-like nature of zinc flake is expected to account for the ability to lower the total zinc content to 25 to 30 per cent of zinc dust formulations and still maintain ade quate protection for thin film precon struction primers. Zinc Chemistry Chatalov has described the influ ence of pH on the corrosion rate of zinc (Figure 1). It is for this reason that zinc must be topcoated in agressive environments. Zinc is amphoteric and reacts quickly with chemicals. Numerous salts, many of which are insoluble, are formed. Some of these are identified in Tables IV. V and VI. Most chemical reactions with zinc occur in the presence of moisture. Therfore, in such aggressive environ ments as coastal areas, one such reac tion might be described in a simplified form as follows: 2 Zn + 2 NaCI + 3H20- ZnOZnCl- + 2NaOH + 2H2 Many other reactions do occur, however. Since this reaction liberates sodium hydroxide, such paint vehicles as alkyds. which are alkali sensitive, should never be specified as topcoats over zinc in marine environments. Reliability Factors The reliability of a good zinc-rich coating svstem depends upon many important factors: (1) Adequate surface preparation with proper anchor pattern (SPPC 10 near white blast). (2) Proper film thickness of zincrich coatings -- 3.0 mils minimum. (3) Selection of a high quality zincrich primer. (4) Good application of a tie coat modern paint and COATINGS, JUNE W75  -*3! over an adequately cured zinc-rich primer. Toble 111 -- SSPC Class II Commercial Organic Zinc-Rich (5) Selection of a chemical resistant Primers for Structural Steel topcoat. ... (6) Total film thickness of eight mils. minimum. Supplier Phenoxy Cot Epoxy CMonnate-it Rubber Otbjr The world shortage of zinc dust is Arrvron 62 6H 39 expected to prevail for many years. American Abrus*w> AAV. z.nr 1 2 Considerable effort will he made to Briiit'f Duroxy 3395 4395 Durojmc ' r j conserve the available supply. When 150 zinc is topcoated with chemical resis .W A. Srovkr 520 A 244 tant finishes, it is reasonable to lower Corbolme 6/6 655 the zinc content of the primer from 85 Con Lux Zinc Plate i to 75 per cent based on total film weight. Some companies offer such a Cook Oeorbom 920 G-140 Endcore 860 Epic^n 2 system. The Steel Structures Painting i Council (SSPC) has developed an ex i Ii tensive specification for z.inc-rich primers. The Zinc-Rich Committee has worked very hard since 1963 in preparing this document. The SSPC zinc-rich primer specifi cations arc listed: SSPC P5J2.01: One-coat zinc-rich paint system. Devoe (Cdanese) Devcon Detroit Grophite Diamond Du Pont Exxon Chidden Grow (Prufcoat) Hughson International towa Paint RBI457 Z Pnenoxy ZR CRI05G Gonazin 347-937 5699 1934 300 444) Epoxy Zinc Dut 5662 100 9927 6375 400 Vinyl Z'ncR.ch VZ 103.' < SSPC PS 12.02: Topcoated inorganic zinc-rich paint system. 41Vi SSPC 1\S 12.03: Topcoated organic zinc-rich paint system. Many panels are being prepared by 11 SSPC in a rather extensive topcoat study. This study will include many of 4 the systems proposed in PS12.02 and 1 12.03. Tie coats will also be used. Panels will be exposed in marine and Jones 8lo'f Koppers Matcote Mobil Napko PPG Industries 35504 Organic Zinc 235 I3-G-5 Mobilzinc 5 2Z Mobilz.r.; 4 Zinc Rich Aquopon Mobilzinc 2 IZ Inerlol 632 Iner.'o) 640 Bitumostic Gray other environments. In addition, SSPC Ploskem Zincor 7 has other field exposures involving zinc rich primers. Porter 309 303 19600 Epoxy Ester ASTM subcommittee DO1.46.09 is studying the adhesion of topcoats over zinc-rich primers. This committee is also examining the problems of pinholing and blistering of topcoats applied to zinc-rich primers after various time intervals. Pmholing and blistering of the topcoat usually occur when such topcoats are applied too 'Oun; inorganic zinc must have suf ficient time to cure. Application of steam may be required. Such applica tion characteristics are described by NASA (X). Reports of topcoat adhesion failures Reliance Ruit Oleum Sh-r-.viM V/ilI'ams Southern Imperial S'eelcote Subox Tnemec US Sitel Wisconsin Protective Wit to 50 29 la? Metobox 92 92-8504 92-3305 Zinc Clue! 9 Imperial 51 2 Gal szoriox 1! t 93 Tnemezinc no Plositf 1 704 963*. 7035 Zinc CUi'i 7 Epot-js I03E li - GdvonOx fl 94 Tnemeznic Pcfmadnc 520 HR54.140 Gclv'inox 1 and In Zme CL>d 5 -IR-S4 193 Vinyl 1636 7UD 7141 VZ ?03C Vnyl /inc by the states nf California and Florida ;::;c the n...:d :n c'.ami.ic this phe ft-r rr c:S-, v- .u* .-'oH vf * , z. . 2. ' W ; - mo-"*- K j.-.ri* Ir r: I j'v 5-2:r t* i- - ..C:cfuref, yifO'L'fis moy h::.- r* jen o;.. "v J d * o c.f it*rarmofior nomenon. Tin: results ol testing an ex tensive ser ies of topcoats and zinc-rich primers was reported by NASA (9). Another investigation, by Parker subsequent X-ray emission, spec- chemical fumes penetrate the topcoat. Helms and John Bryzinski of Union trophotometric analysis. The chemical reaction force exert.-.! Carbide, of the topcoat -- zinc-rich The salts caused by H-SO.i. H-SOa upon the zinc primer is stronger than primer interface has shown unusual and INS are believed to be responsible the adhesive Kind. This causes the top salt formation but failed to detect amines. These salts were identified by lor the lack of topcoat adhesion. Those zinc salts are formed as a result of coat to peel off. W. J. Francis (10) has reported that only three harrier coals scanning election microscope and chemical exposure: moisture and may be selected tor use over inoig.uuc !V. I .'.in < i iArt.'ajs. lu.'.'F t'/Z.s 5 Grams Per dm- Per Day Table IV -- Zinc Complexes Amine Cyonide Thiocyani de Oxylate HydrocMorote Table V -- Water Insoluble Zinc Salts Ethylene diamine Pyri dine Aniline Hydrozine Sulfate Aluminafe Arsonate Carbonate Ferrocyonide Formaldehydesulfoxylate (basic) Olcate Phosphote Cyanide Silicate Stearote Table VI --Zinc Complexes Identified in Corrosion ZnO HZnO* ~ Zn02-------7.nOH + Zri lC,rl)a Zinc oxide Bizincate Zincate Zincyl 5 forms V N 1 i zincs: vinyl red loud. epoxy-polyamide and epoxy-polyamino adduct typ-!s.. The National Association of Cor rosion Engineers has issued a Tech nical Committee report: T-6H-18. Or ganic and Inorganic Zinc Filled Coatings for Atmospheric Service. Also. Technical Committee T-6G-14 is studying the effect of flash rust inhibitors used in wet sand blast procedures. In this study, zinc-rich primers were applied to various chemi cally inhibited steel panels. The effects these inhibitors have on the zinc-rich performance is measured by undercut ting at the scribe after 1,000 hours of salt fog testing. Amine and chromate inhibitors were tested. These indicated the chromate inhibitor to be superior. Further studies are continuing. References (1) McKenzie, M. G., "Development and Case History Data on ZincDust-Sodium Silicate Coatings in Australia." Mat. Prot., April. 1965. (2) Elm, A. C., "Zinc Dust Metal Protective Coating," N. J. Zinc publication. (3) Anders. H,, "Ethyl Silicate as a Base Body for Paints and Colors," Deutsche Farbert Zeitschrift, Nov., 1954. (4) Loomans, J., and van Leberghe, K.. Chimie des Peinturcs, Vol. 12, pp. 184-190 (1949). (5) I.angrish-Smith. W. E., Shaw. C.. and Wheeler-Hill, D. A., British Patent. (6) Lopata, S.. Keithler, W. R.. U.S. Patent 3.056.684. (7) U.S. Patents 3,382,08 1; 3,519.501; 3.535,166; 3,535.167; 3,671.331; 3.687.738; 3.687.739; 3.708,350; 3.717.509; 3.799.815. among others, to Diamond S!''iir.rock Chemical Cwp.. A. W. Kennedy, et al. (8) NASA MAB154-70: "Application Characteristics of Zinc-Rich Coatings." Kennedy Space Center, Fla., March, 1971. (9) NASA T N D-7336: -Perfor mance Characteristics of ZincRich Coatings Applied to Carbon Steel." Wm. Patton, Kennedy Space Center, Fla., July. 1973. (lO)NNSY P10360-1: "Inorganic Zinc Primers and Topcoat Com patibility." W. J. Francis. Norfolk Naval Shipyard, Norfolk. Va. Airless spraying of a riveted tank with inorganic ethyl silicate zinc-rich primer. 26 A\ODERN PAINT AND COATINGS. ION; 1*75