GB2032465A - Non-chromate Conversion Coating Solutions - Google Patents

Non-chromate Conversion Coating Solutions Download PDF

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GB2032465A
GB2032465A GB7932620A GB7932620A GB2032465A GB 2032465 A GB2032465 A GB 2032465A GB 7932620 A GB7932620 A GB 7932620A GB 7932620 A GB7932620 A GB 7932620A GB 2032465 A GB2032465 A GB 2032465A
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solution according
acid
solution
conversion coating
sodium
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Dart Industries Inc
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Dart Industries Inc
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Priority claimed from US06/045,162 external-priority patent/US4225351A/en
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    • CCHEMISTRY; METALLURGY
    • C23COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23CCOATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C22/00Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
    • C23C22/05Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions
    • C23C22/06Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6
    • C23C22/48Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6 not containing phosphates, hexavalent chromium compounds, fluorides or complex fluorides, molybdates, tungstates, vanadates or oxalates
    • C23C22/53Treatment of zinc or alloys based thereon
    • CCHEMISTRY; METALLURGY
    • C23COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23CCOATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C22/00Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
    • C23C22/05Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions
    • C23C22/06Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6
    • C23C22/48Chemical surface treatment of metallic material by reaction of the surface with a reactive liquid, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using aqueous solutions using aqueous acidic solutions with pH less than 6 not containing phosphates, hexavalent chromium compounds, fluorides or complex fluorides, molybdates, tungstates, vanadates or oxalates

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  • Chemical & Material Sciences (AREA)
  • General Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Mechanical Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Chemical Treatment Of Metals (AREA)
  • Preventing Corrosion Or Incrustation Of Metals (AREA)
  • Paints Or Removers (AREA)

Abstract

Improved brightness and corrosion resistance are imparted to metal surfaces such as zinc plated surfaces, by treatment with an aqueous non-toxic conversion coating solution comprising 0.2-45 g/l sulfuric acid, 1.5-58 g/l hydrogen peroxide, 3-33 g/l SiO2, certain primary organophosphorus compound promoters and 2-20 g/l of at least one secondary promoter selected from ascorbic acid, boric acid, gluconic acid, glycolic acid, tartaric acid and salts of said acids. The solution is free of chromate and may be used for coating Zn, Cd, Ag, Cu, Al, Mg surfaces.

Description

SPECIFICATION Non-chromate Conversion Coating Solutions The formation of chromate conversion coatings on surfaces of various metals, such as zinc and cadmium, is presently the most common technique of imparting increased brightness and corrosion resistance to the metal. In a typical process, the metal work pieces are immersed in an acidic solution hexavalent chromium compounds, which react with the metal causing the precipitation of a complex gel-like coating or film of trivalent chromium and entrapped soluble hexavalent chromium compounds onto the metal surface. The coated work pieces are then rinsed and dried under controlled conditions.
There are several serious disadvantages common to all chromate conversion coating processes.
One of these is the relatively short life of the process bath expressed in terms of unit surface area coated per unit volume of bath. The main reason for the short life is the continuous build-up in the bath of dissolved trivalent chromium resulting from the oxidation-reduction reactions that occur between the metal and the hexavalent chromium. Trivalent chromium is a contaminant in the process affecting the coating efficiency. Thus, when reduced coating activity is noted, or when the contaminants have built up to a certain predetermined level, a process solution of this type is at least partially replaced with freshly prepared solution, and ultimately completely discarded in favor of a fresh bath.
The disposal of the spent process solution is wasteful, as the solution still contains considerable quantities of hexavalent chromium. Not only does the loss of these values contribute significantly to the overall cost of the coating process, but disposal also adds to this cost in that the solutions present a substantial waste treatment problem. Hexavalent chromium is highly toxic and must be reduced to the trivaient form, e.g. by reaction with sodium hydrosulfite or sodium bisulfite, and is thereafter precipitated from solution by addition of alkalies, such as sodium carbonate or lime. After dewatering of the precipitate by settling or filtration, the concentrated sludge of trivalent chromium hydroxide must be disposed of in specially designated areas, since trivalent chromium is still too toxic to be used as landfill.Substantial waste treatment requirements of spent rinse waters are also created due to dragout of toxic chemicals from the process bath into subsequent rinse waters. Although there are integrated processes for the reoxidation and regeneration of spent chromate solutions and rinse water, the small processor usually finds that the refined and sophisticated techniques involved are neither practical nor economically feasible for solving his waste treatment problems.
In Application No. 7932624 (N. 31675) of even date we describe and claim a non-toxic conversion coating solution which comprises sulfuric acid, hydrogen peroxide and a soluble silicate and optionally a primary promoter, i.e. certain organophosphorus compounds, for further enhancement of corrosion resistance of metal surfaces treated with the solution.
Although these acidic silicate solutions (which need not be true solutions but may be in the form of hydrosols so that the term "solution" is intended to cover a hydrosol as well as a truce solution) not only provide conversion coatings of excellent properties, but also have many other important advantages. One of these is the extremely long life of the conversion coating solution before it need be discarded in favor of a fresh solution. It has been found that the solutions are capable of treating up to approximately 1 85 m2 of surface area per liter, which is far superior to the typical value of approximately 20 m2/l obtained with conventional chromate conversion coating baths.
Another and related advantage is that, apart from some build-up of dissolved metal in the solution, there are no detrimental by-products forming and accumulating therein during use, as is the case with conventional chromate conversion coating solutions, in which trivalent chromium rapidly builds up.
The most important advantage, however, is the non-toxic nature of the system, which greatly facilitates waste disposal of spent solutions from the conversion coating process. Rinse waters can usually be disposed of without any treatment required. Spent conversion coating baths are merely treated with lime for neutralization and removal of dissolved metal ions and phosphorus as a precipitate. After settling or other separation, the liquid phase may be disposed of safely in common sewers, while the dewatered sludge mainly composed of silicate can be dumped in municipal landfill areas.
The present invention provides a novel conversion coating solution which can be used to provide a coating which exhibits brightness and further improved corrosion resistance.
In accordance with the present invention there is provided a novel conversion coating solution which comprises an aqueous solution of from about 0.2 g/l to about 45 g/l of free H2SO4, from about 1.5 g/l to about 58 g/l of H202, from about 3 g/l to about 33 g/l of SiO2, from about 0.15 g/l to about 10 g/l of at least one of the organophosphorus compound promoters specified below and from about 2 g/l to about 20 g/l of at least one secondary promoter selected from the group consisting of ascorbic acid, boric acid, gluconic acid, glycolic acid, tartaric acid and salts of said acids, wherein the organic phosphorus compound is one having the general formula:: [X(Ri)min. [R2]p . [X(R1)m]q, wherein X is a group of the formula
in which Z1 and Z2 independent from each other are hydrogen, sodium or potassium; m is either 0 or 1; p is either 0 or 1; n+q is either (a) 1 when p=O, or (b) equal to the number of available bonds provided by R2 when p=1; R1 is a (a) C1-C4 alkyl or a C1-C4 hydroxy-substituted alkyl and p=O; and (b) C1-C4 alkylene or a C1-C4 hydroxy-substituted alkylene and p=1; R2 is selected from (a) N=, m=1 (b) =N(CH2)rN=, m=1 and r is an integer from 2 to 6
and (d) a C1-C4 alkylene or a C1-C4 hydroxy-substituted alkylene, m=O or 1.
The SiO2 component is conveniently provided in the form of a soluble silicate, e.g. sodium silicate or potassium silicate, of predetermined contents of SiO2 and Na2O or K2O. The mole ratios of SiO2 to either Na2O or K20 generally range between 1 and 4, and it is preferred to use those silicates wherein the mole ratio is at least about 1.8 and most preferabiy at least about 2.2. Ammonium or lithium silicates are also useful in providing the SiO2 component.
Examples of the organophosphorus compounds include C1-C4 alkyl phosphonic acids, C1-C4 hydroxyalkalenephosphonic acids, amino tri-C1-C4 alkylene phosphonic acids, C2-C8alkylene diamine-tetra (C1-C4 alkylene phosphonic acid), diethylenetriamine-penta (C1-C4 alkylene phosphonic acid) as well as the acid or neutral sodium or potassium salts of any of the above-listed phosphonic acids. 1 -hydroxyethylidene-1 ,1 -diphosphonic acid is a preferred compound.
The secondary additives can either be provided in the acid form or as a salt, e.g. of sodium, potassium, zinc, etc.
The solution is easily prepared, e.g. by first adding sufficient sulfuric acid to at least a major portion of the makeup water under agitation to provide the desired free H2S04 content and taking into account that some of the free acid will be subsequently neutralized by the Na2O or K20 portions introduced with the silicate. The silicate is added under agitation to the cooled acidic solution until it is completely dispersed. The remaining components are then added. Preferably the peroxide is added last, however, the sequence of addition can be changed without any detrimental effect, provided that the silicate is acidified with sulfuric acid prior to mixing with the hydrogen peroxide, or peroxide decomposition will occur.
The preferred concentrations of the components in the aqueous solution are from about 1.8 g/l to about 18 g/l of free H2SO4, from about 7 g/l to about 29 g/l of H2O2, from about 8 g/l to about 18 g/l of SiO2, from about 0.5 to about 2 g/l of the primary organophosphorus promoter and from about 3 to about 10 g/i of the aforementioned secondary promoters.
In order to impart pleasing and lasting colors to the conversion coated work pieces without detrimentally affecting the corrosion resistance of the coating or the stability of the coating solution, it has been found necessary to employ cationic triarylmethane dyes which heretofore predominantly have been used in the dyeing of natural fibers such as paper, cotton, wool, silk, etc. Conventional metal dyes or conversion coating dyes either affect the stability of the system or do not impart any color to the coatings.
The triarylmethane dyes used in this invention are well known in the art and are recognized as a separate generic group of dyes having a Colour Index (C.I.) in the range from 42,000 to 44,999. They are commercially available in a wide variety of colors both in solid form or as aqueous soluton concentrates with solids contents typically in the 40-50% range. The effective amount of dye to be added to the conversion coating solution depends obviously on the desired depth of color. Typically, this amount ranges between about 0.05 and about 2 gIl.
The solution is useful for forming conversion coatings on various metallic surfaces, such as those of zinc, cadmium, silver, copper, aluminum, magnesium, and zinc alloys.
The most common application is, however, in the formation of conversion coatings on zinc plated articles such as zinc plated steel articles. The zinc plate provides the steel with cathodic protection against corrosion, and the conversion coating further improves the corrosion resistance, reduces the susceptibility to finger markings and enhances the appearance by chemical polishing of the article and by the color imparted by the dye. It is important that the zinc plate deposit is relatively smooth and finegrained prior to coating, and that the thickness of the plate deposit is at least 0.005 mm since some metal removal occurs when the film is formed. The preferred plate thickness is between about 0.005 mm and about 0.02 mm.
Usually the formation of the conversion coating follows immediately after the last rinse in the plating cycle. Thus, the freshly plated articles are immersed for a period of from about 5 seconds to about 300 seconds into the solution which is maintained at ambient temperatures. For best results, the immersion treatment is carried out for a duration of from about 20 seconds to about 50 seconds in a bath maintained at temperatures not less than about 200C and not more than about 350C. The coated articles are subsequently rinsed, first in cold water and then briefly in warm water to aid drying of the films. The hot water rinse typically has a temperature in the range of from about 60 to about 7O0C.
The final step of the coating process is a drying step, which is carried out by any means that will neither abrade the soft and then rather fragile film, nor expose it to excessive temperatures, i.e. temperatures higher than about 7O0C. The use of circulating warm air or an airblast are examples of suitable means in the drying operation. After drying, the conversion coatings are quite resistant to damage from abrasion and generally do not require the 12-24 hour aging necessary with conventional chromate conversion coatings.
The resulting conversion coatings have very good resistance to corrosion as determined by the accepted accelerated corrosion test ASTM B-l 17-64.
During the course of the coating process, the coating solution becomes depleted in both free sulfuric acid and hydrogen peroxide values and must be replenished. Therefore, monitoring of these values should be carried out on a regular basis to assure that the respective concentrations have not fallen below their minima and to assess the amounts needed for replenishment. Free sulfuric acid can be determined by conventional titration methods using sodium hydroxide or by pH determinations. In order to maintain the free sulfuric acid within the broad ranges of about 0.2 to about 45 g/l the pH should be controlled between about 0.5 and about 3.5 and preferably between about 1.0 and about 3.0 which approximately corresponds to a free sulfuric acid concentration of from about 1.8 to about 18 g/l.The hydrogen peroxide concentration levels are advantageously monitored by conventional titration with ceric ammonium sulfate. The silicate (SiO2) consumption is relatively small compared to the consumptions of either the free sulfuric acid or the hydrogen peroxide, and generally neither monitoring (which can be carried out using e.g. colorimetric principles involving the reaction of silicate with ammonium molybdate to form a yellow-colored molybdo silicate solution) nor replenishment is required during the practical life of the conversion coating bath. The rates of consumption (i.e. percent decrease in concentration per unit time) of the primary and secondary additives have been found to be approximately of the same order as that of the hydrogen peroxide consumption.Therefore, replenishments of the solutions with these additives are suitably carried out at the time of hydrogen peroxide replenishment in amounts proportional to the hydrogen peroxide addition. The dye, if present, generally does not need to be replenished during the practical lifetime of the conversion coating bath.
Monitoring of the color depth quality of the coating is easily carried out by visual inspection of the coated article and comparison against a reference color.
The following examples are provided to illustrate but not to limit the invention.
The general procedures used in the examples for preparing the conversion coating solutions, test specimens and forming the conversion coatings are described below.
The aqueous conversion coating solutions were each prepared to contain 2.4 g/l free H2SO4, 1 6.2 g/l SiO2, 11.7 g/l H202 and 0.85 g/l of 1-hydroxyethylidene-1 ,1-diphosphonic acid. The Si02 ingredient was added in the form of sodium silicate (SiO2=33.2% w/w; Na20=13.85% w/w) and a sufficient excess of sulfuric acid was provided to result in the indicated free H2SO4 content after neutralization of the Na2O in the sodium silicate.
Standard Hull cell steel panels (10 cmx6.8 cmx0.03 cm) were plated with zinc using a cyanide electrolyte. After thorough rinsing and drying, the samples were then immersed for 40 seconds in the conversion coating solution maintained at room temperature. The treated samples were then rinsed in water and then dried with a hot air gun.
The dried coated test specimens were then subjected to the accelerated salt spray corrosion tests in accordance with the ASTM test B-1 1 7-64. The tests were carried out for various periods of time, i.e.
6, 1 6, 24 and 30 hours. After each test the specimens were examined for evidence of corrosion on a rating scale from 1 (heavy corrosion) through 10 (no corrosion).
Examples 1-3 The beneficial effects of boric acid and zinc gluconate as secondary additives are demonstrated in these examples. The general procedures described above were followed except that the solutions of Examples 2 and 3 also contained the additives indicated in Table 1, which includes the results of the corrosion tests performed on the bright, coated test samples.
Table 1 Add.
Ex. Conc. Extent of corrosion after No. Additive gll 6 hrs. 24 hrs.
Control 1 None - 9 7 2 Boric Acid 5 10 8 3 ZnGluconate 5 9 8 Examples F12 In this series of experiments all the conversion coating solutions contained triarylmethane dyes in addition to the secondary additives shown in Table 2. These dyes used were a mixture of E.l. DuPont de Nemours' liquid dyes Victoria Pure Blue BOP solution (0.2 ml/l, Basic Blue 7, C.l. 42,595) and Paper Blue R Liquid (0.1 ml/l, Basic Violet 3, C.l. 42,555).
The results of corrosion tests on the bright, colored, coated test specimens are shown in Table 2.
Table 2 Add.
Conc. Extent of corrosion after Ex. No. Additive gll 16 hrs. 24 hrs. 30 hrs.
Control 4 None - 7 6 6 5 Boric Acid 5 9 8 7 6 Boric Acid 20 9 8 7 7 Ascorbic Acid 5 9 8 7 8 Potassium Sodium Tartrate 5 10 8 9 Glycolic Acid 5 9 9 - 10 Zn Gluconate 5 9 8 7 11 Na Gluconate 5 9 7 12 Na Gluconate+ Zn Sulfate1 3.2 9 8 The amount of Zn in 3.2 g ZnSO4. 7H20 is equivalent to that in 0.5% Zn gluconate.
In Application No. 7932621 (N. 31677) of even date we describe and claim conversion coating solutions which contain free H2SO4, H2O2, SiO2 and at least one cationic triarylmethane dye.

Claims (22)

Claims
1. A conversion coating solution (as defined herein) which comprises an aqueous solution of from 0.2 g/l to 45 g/l of free H2SO4, from 1.5 g/l to 58 g/l of H2O2, from 3 g/l to 33 g/l of Six,, from 0.15 g/l to 10 g/l of at least one organophosphorus compound promoter, and from 2 g/l to 20 g/l of at least one secondary promoter selected from ascorbic acid, boric acid, gluconic acid, glycolic acid, tartaric acid and salts of said acids, the organophosphorus compound being of the general formula:: [X(R,)m]n . [R2]p [X(Rj)miq, wherein X is a group of the formula
in which Zr and Z2 independently are hydrogen, sodium or potassium; m is either 0 or 1; p is either 0 or 1; n+q is either (a) 1 when p=O, or (b) equal to the number of available bonds provided by R2 when p=1; R, is a (a) C1-C4 alkyl or a C1-C4 hydroxyalkyl and p=O; and (b) C1-C4 alkylene or a C1-C4 hydroxyalkylene and p=1; R2 is selected from (a) N=, m=1, (b) =N(CH2)rN=, m=1 and r is an integer from 2 to 6
(d) a C1-C4 alkylene or a C1-C4 hydroxyalkylene, m=O or 1.
2. A solution according to claim 1, wherein the free H2SO4 concentration is between 1.8 g/l and 18 g/l.
3. A solution according to claim 1 or 2, wherein the H202 concentration is between 7 g/l and 29 girl.
4. A solution according to claim 1,2 or 3, wherein the SiO2 concentration is between 8 g/l and 1 8 girl.
5. A solution according to any one of the preceding claims, in which the SiO2 is provided in the form of a sodium silicate or a potassium silicate.
6. A solution according to claim 5, wherein the molecular ratio of SiO2 to either Na2O or K20 in the sodium silicate or potassium silicate is between 1:1 and 4:1.
7. A solution according to claim 6, wherein said molecuiar ratio is at least 2.2:1.
8. A solution according to any one of the preceding claims, containing from 0.5 to 2 g/l of said organophosphorus compounds.
9. A solution according to any one of the preceding claims, wherein the organophosphorus compound is a hydroxy-alkylene diphosphonic acid.
1 0. A solution according to claim 9, wherein the organophosphorus compound is 1 hydroxyethylidene-l ,l-diphosphonic acid.
11. A solution according to any one of the preceding claims, wherein the secondary promoter is added in an amount between 3 and 10 g/l.
12. A solution according to any one of claims 1 to 11, containing zinc gluconate as secondary promoter.
13. A solution according to any one of claims 1 to 11, containing sodium gluconate as secondary promoter.
14. A solution according to any one of claims 1 to 11, containing a sodium-potassium tartrate as secondary promoter.
1 5. A solution according to any one of the preceding claims containing additionally an effective amount of at least one cationic triarylmethane dye.
1 6. A solution according to claim 1 5, in which the dye concentration is from 0.05 to 0.3 grams/liter on a dry basis.
1 7. A solution according to claim 1 5 or 1 6, in which at least one dye is Basic Violet 3 having a Coiour Index of 42,555.
18. A solution according to claim 15 or 16, in which at least one dye is Basic Blue 7 having a Colour Index of 42,595.
19. A solution according to claim 1 substantially as described in any one of Examples 2, 3 and 5 to 12.
20. A process for the formation of a corrosion resistant conversion coating on a metallic surface selected from zinc, cadmium, silver, copper, aluminum, magnesium and zinc alloy surfaces, which process comprises immersing said surface in a conversion coating solution as claimed in any one of the preceding claims, and subsequently rinsing and drying.
21. A process according to claim 20 wherein the metal surface is a zinc plate surface.
22. A process according to claim 20 substantially as described in any one of Examples 2, 3 and 5 to 12. ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
GB7932620A 1978-10-30 1979-09-20 Non-chromate conversion coating solutions Expired GB2032465B (en)

Applications Claiming Priority (2)

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US95581278A 1978-10-30 1978-10-30
US06/045,162 US4225351A (en) 1979-06-04 1979-06-04 Non-chromate conversion coatings

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GB2032465B GB2032465B (en) 1982-09-29

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2504156A1 (en) * 1981-04-16 1982-10-22 Hooker Chemicals Plastics Corp PASSIVATION PRODUCT SOLUTION HAVING CHROMIC ASPECT AND METHOD OF USE

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US9677031B2 (en) 2014-06-20 2017-06-13 Ecolab Usa Inc. Catalyzed non-staining high alkaline CIP cleaner

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JPS5210834A (en) * 1975-06-02 1977-01-27 Nippon Packaging Kk Surface treatment of metal

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2504156A1 (en) * 1981-04-16 1982-10-22 Hooker Chemicals Plastics Corp PASSIVATION PRODUCT SOLUTION HAVING CHROMIC ASPECT AND METHOD OF USE
DE3213384A1 (en) * 1981-04-16 1982-12-09 Hooker Chemicals & Plastics Corp., 48089 Warren, Mich. AQUEOUS ACID SOLUTION AND METHOD FOR THE TREATMENT OF RECEIVABLE METAL SUBSTRATES FOR THE AWARD OF A PASSIVATION FILM

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NL7907964A (en) 1980-05-02
CA1134726A (en) 1982-11-02
DE2943835A1 (en) 1980-05-08
IT7926890A0 (en) 1979-10-29
FR2440413A1 (en) 1980-05-30
IT1124815B (en) 1986-05-14
GB2032465B (en) 1982-09-29

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