Classifications

• • C—CHEMISTRY; METALLURGY
  • C23—COATING 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
  • C23C—COATING 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
  • C23C22/00—Chemical 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
  • C23C22/05—Chemical 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
  • C23C22/06—Chemical 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
  • C23C22/24—Chemical 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 containing hexavalent chromium compounds
  • C23C22/30—Chemical 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 containing hexavalent chromium compounds containing also trivalent chromium
• • C—CHEMISTRY; METALLURGY
  • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
  • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
  • C04B28/00—Compositions of mortars, concrete or artificial stone, containing inorganic binders or the reaction product of an inorganic and an organic binder, e.g. polycarboxylate cements
  • C04B28/34—Compositions of mortars, concrete or artificial stone, containing inorganic binders or the reaction product of an inorganic and an organic binder, e.g. polycarboxylate cements containing cold phosphate binders
• • C—CHEMISTRY; METALLURGY
  • C23—COATING 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
  • C23C—COATING 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
  • C23C22/00—Chemical 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
  • C23C22/05—Chemical 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
  • C23C22/06—Chemical 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
  • C23C22/24—Chemical 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 containing hexavalent chromium compounds
  • C23C22/33—Chemical 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 containing hexavalent chromium compounds containing also phosphates
• • C—CHEMISTRY; METALLURGY
  • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
  • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
  • C04B2111/00—Mortars, concrete or artificial stone or mixtures to prepare them, characterised by specific function, property or use
  • C04B2111/00474—Uses not provided for elsewhere in C04B2111/00
  • C04B2111/00482—Coating or impregnation materials
  • C04B2111/00525—Coating or impregnation materials for metallic surfaces

Definitions

• the invention relates to a process for treating zinciferous surfaces to give them an excellent resistance to both blackening and white rusting.
• the process which uses a one-step chromate treatment that does not require a preliminary flash treatment with, e.g., Ni or Co, is particularly useful for the manufacture of zinciferous-plated steel sheet.
• zinciferous-plated refers to elec- trogalvanization, hot-dip zinc plating, hot-dip 5% Al/Zn plating, hot-dip 55% Al/Zn plating, and the like.
• the process is largely described below with respect to zin ⁇ ciferous-plated steel sheet, but is equally applicable to any other surface with the same chemical composition. Background Art
• Galvanized steel sheet is used in a variety of applications, for example, as a construction ma ⁇ terial, in automobiles, and for household electrical appliances.
• the sacrificial cor ⁇ rosion resistance conferred by zinc is based on the formation of a galvanic cell by bringing two different metals into contact, in this case zinc and steel (or iron). The zinc, as the baser metal, forms an anode and thereby cathodizes the iron.
• Flash treatment for example, with an aqueous solution containing Ni 2+ and/or Co 2+ as described in, e.g., Japanese Laid Open [Kokai or Unexamined] Patent Application Number Sho 59-177381 [177,381/1984], is currently regarded as a very effective countermeasure for solving this post-chromating black rust problem.
• flash treatment is taken to mean the chemical deposi ⁇ tion of very small quantities of metal.
• the above-refer ⁇ enced invention concerns a means for inhibiting black rust through the pre-chro- mating flash treatment of the surface of zinc-plated or zinc alloy-plated steel sheet.
• the surface of the steel sheet is flash- treated with an aqueous solution (pH 1 to 4 or 11 to 13.5) that contains Ni + and/or Co 2+ metal ions.
• This treatment results in the deposition of these metal ions on the plating surface as the metal or oxide.
• This treatment is followed by a water wash and then the formation of a chromate film.
• the mechanism for black rust inhibition on zinc-plated or zinc alloy-plated steel sheet that has been flash-treated with Ni and/or Co and then chromated has yet to be clearly established.
• Zinc black rust like the corresponding white rust, is thought to be a basic zinc carbonate (ZnC0 3 ) x [Zn(OH) 2 ] y ; however, it differs from white rust in that it is stoichiometrically oxygen deficient. Black rust is therefore a corrosion product occurring under oxygen-deficient conditions, and in particular it is thought that black rust is formed in association with the development of corrosion from the grain boundaries. As a result, it can be postulated that the chromium compounds concentrated at the grain boundaries by the flashed metal contribute to an inhibi- tion of black rust development by inhibiting corrosion originating from the grain boundaries.
• the invention offers a one-step process that consists of only a chromate treatment and that does not employ a pretreatment, but is able to simultaneously inhibit both blackening and white rust.
• This one-step process renders unneces ⁇ sary the two-step prior art process of a flash treatment with Ni and/or Co plus a chromate treatment.
• This process yields zinciferous-plated steel sheet that ex ⁇ hibits a satisfactory corrosion resistance, blackening resistance, and white rust resistance.
• being a one-step process it avoids the drawbacks in the prior art due to the use of a two-step treatment process (pretreatment followed by chromate treatment).
• This novel one-step chromate treatment process is the subject of Japanese Patent Application Number Hei 4-164083 [164,083/1992].
• the invention in Japanese Patent Application Number Hei 4-164083 re ⁇ lates to a process for fabricating zinciferous-plated steel sheet that has an excel- lent resistance to both blackening and white rusting, wherein said process is characterized by the formation on zinciferous-plated steel sheet of a 10 - 200 mg/m 2 (calculated as chromium metal) film by: (I) application to zinciferous-plated steel sheet of a chromate bath that contains hexavalent chromium ion, trivalent chromium ion, and inorganic acid comprising at least one selection from nitric acid, boric acid, and sulfuric acid, and in which the trivalent chromium ion/hexavalent chromium ion weight ratio is 1/9 to 4/1 and the inorganic acid/total chromi ⁇ um ion
• the subject of this ap- plication is a process characterized by the formation on zinciferous-plated steel sheet of a solid 10 - 200 mg/m 2 (calculated as chromium metal) film by: (I) application to zinciferous-plated steel sheet, so as to form a liquid coating thereon, of a chromate bath that comprises, preferably consists essential ⁇ ly of, or still more preferably consists of: (A) hexavalent chromium ions,
• the entire stoichiometric equivalent as phos ⁇ phate ions of any phosphoric acid and/or anions produced by ionization thereof that are added to the chromate bath are counted as phosphate ions, irrespective of the actual degree of ionization of the added acid.
• the acid added is orthophosphoric acid H 3 P0 4 , but other inorganic phosphoric acids such as HP0 3 , H 4 P 2 0 7 , H 5 P 3 O 10 may also be used.
• the constituents specified in ionic form must be accompanied by counterions so that the composition as a whole is electrically neutral.
• Such counterions preferably are chosen from other specified constituents of the invention to the extent possi ⁇ ble, and otherwise may be freely chosen, except for avoiding counterions that are detrimental to the purposes of the invention.
• the trivalent chromium ion/hexavalent chromium ion molar ratio in the subject chromate treatment bath is preferably 1/9 to 4/1 and more preferably is 1/4 to 7/3.
• Trivalent chromium ion/hexavalent chromium ion molar ratios below 1/9 are undesirable because such values usually result in excessive chromium ion elution in corrosive environments and thus in pollution of the environment.
• the trivalent chromium ion/hexavalent chromium ion molar ratio exceeds , 4/1 , the corrosion resistance becomes inadequate.
• Sulfate and/or nitrate ions as required for the chromating treatment ac ⁇ cording to the invention are preferably added at least partially in the form of the corresponding acids.
• These anions are added in a quantity that yields values preferably of 0.1 to 2.0 and more preferably of 0.2 to 1.6 for the sulfate + nitrate + phosphate anions/total chromium ions molar ratio.
• the blackening resistance is usually inadequate when the inorganic anions/total chromium ions molar ratio is less than 0.1.
• Inorganic anions/total chromium ions molar ratios in excess of 2.0 are undesirable because such values usually result in a degraded corrosion resistance due to a deficient chromium immobilization ratio in the resulting chro- mate film.
• the metal ion/inorganic anion molar ratio in the subject chromate bath is to be 0.05 to 1.
• the pH of the chromate bath is too low when the metal ion/inor- ganic anion molar ratio is below 0.05.
• the reaction is too vig ⁇ orous when the chromate bath and zinciferous-plated steel sheet are brought into contact, so that there is a whitening of the zinciferous-plated steel sheet and a degraded corrosion resistance due to an elevated chromium immobilization ratio in the resulting chromate film.
• this ratio has a value in excess of 1 , the chromate bath has a reduced stability and precipitation readily occurs.
• Any metal ion can be used that is capable of dissolving in the chromate bath of the present invention, but Zn, Ni, Co, and Al are particularly preferred. Alkali metals such as Na and K are undesirable because they cause a substan- tial decline in the chromium immobilization ratio of the chromate film.
• the addi ⁇ tional presence of phosphoric acid as inorganic acid in the subject chromate treatment bath functions to raise the chromium immobilization ratio of the chrom ⁇ ate film. When phosphoric acid is added, it is preferably added in a quantity such that the phosphate ions/total chromium ions molar ratio does not exceed 0.3.
• the instant chromate treatment bath may of course optionally contain col- loidal silica as known from the art, for example, silica sol, fumed silica, and the like.
• the chromate film is formed by coating the coating-type blackening-resist- ant chromate bath prepared as described above on the surface of zinciferous- plated steel sheet followed by drying without a water wash.
• the film weight pref- erably falls in the range of 10 to 200 mg/m 2 calculated as chromium metal.
• a sat ⁇ isfactory corrosion resistance is not usually obtained when the chromate film weight falls below 10 mg/m 2 as chromium metal.
• the anti ⁇ corrosion performance is saturated at chromate film weights in excess of 200 mg/m 2 as chromium metal, and such values are therefore uneconomical.
• the first essential step in treatment according to the invention begins by applying the treatment bath to the surface of the zinciferous plating, e.g., by spraying the treatment bath on the workpiece or immersing the workpiece in the treatment bath, followed in either case by a roll or air wipe, or by applying the treatment bath to the surface of the zinciferous plating by known coating meth ⁇ ods, for example, by roll coating.
• the final pro- tective film is formed by drying the liquid film without any water wash or rinse. The drying conditions should be sufficient to evaporate the water in the coating, and drying is generally carried out at a sheet temperature of 40° C to 100° C.
• each of the constituent components of the in ⁇ vention are not known with certainty.
• the sulfate and/or nitrate anions present in the coating-type chromate treatment bath appear to suppress blacken ⁇ ing by inhibiting the production of basic zinc carbonate (ZnC0 3 ) x [Zn(OH) 2 ] y through the formation of the corresponding salts, for example, Zn(N0 3 ) 2 , etc., between zinc and the inorganic acid.
• the instant coating-type chromate bath containing hexavalent chromium ion, trivalent chromium ion, inorganic acid, and metal ion is able to pro ⁇ vide both a blackening-inhibiting activity (based on the inorganic acid and metal ion) and a white rust-inhibiting activity (based on the hexavalent chromium ion and trivalent chromium ion).
• the mechanism underlying the white rust-inhibiting activity of chromate films is generally thought to consist of an inhibitor effect in which the hexavalent chromium ion inhibits zinc corrosion.
• Another mechanism as reported in Zairyo to Kankyo, Volume 41 , pp. 244-245 (1992), consists of a self-repair activity exer ⁇ cised by hexavalent chromium ion that elutes from the film. In this mechanism, the eluted hexavalent chromium ion repairs damaged regions in the film.
• the ab ⁇ solute amount of hexavalent chromium ion available to function as inhibitor will be inadequate.
• the inhibitor effect cannot be maintained, i.e., is not durable, when the chromium immobilization ratio is too low.
• the white rust-inhib ⁇ iting activity is inadequate in either case.
• the chromium immobilization ratio and the Cr'VCr 6 * ratio are closely re- lated, and it is known that the presence of trivalent chromium ions is essential for inhibiting hexavalent chromium ion elution and raising the chromium immobiliza ⁇ tion ratio.
• the Cr'VCr 6 * molar ratio must be held below 2/3 in order for Cr 3 * ions to remain in the aqueous solution as ions without precipitation.
• Cr'VCr 6* ratios in excess of 2/3 are de ⁇ sirable in order to improve the white rust-inhibiting activity.
• the addition of an acid component other than chromic acid is a tactic that can be considered for the purpose of raising the Cr 3 7Cr 6+ ratio.
• the chromium immobilization ratio is also affected by the reactivity pre- vailing when the chromate bath and zinciferous-plated steel sheet are brought into contact (abbreviated below as the contact reactivity).
• the addition of even very small quantities of the nitric acid or sulfuric acid that are added to the chromate bath of the present invention causes a sharp drop in the pH of the chromate bath, which increases the contact reactivity and ultimately results in a higher than necessary chromium immobilization ratio.
• the chromate bath pH will clearly have an optimal range.
• the following methods can be considered for adjusting the pH of a chromate bath whose pH has been reduced by the addi ⁇ tion of inorganic acid: (i) the addition of a metal oxide, hydroxide, or carbonate to the reduced pH chromate bath; (ii) in the case of addition of nitric acid or sul- furic acid to the chromate bath, the addition of metal salts of these acids.
• the inventors carried out detailed investigations into the effects obtained when the specified inorganic anions and metal ions stipulated in the present specification are added to chromate baths at particular molar ratios relative to the total chromium ions. These investigations determined that the addition of both inorganic anions and metal ions as reported below resulted in the same activity as for Ni or Co flash treatment followed by chromate treatment. The reasons for this have yet to be satisfactorily resolved, but it is thought that an anti-blackening activity is produced by the concentration of chromium compounds at the grain boundaries of the zinc crystals and by the formation of Zn(N0 3 ) 2 , etc.
• An anti- blackening effect also appears to be produced by an inhibition of cathodic reac ⁇ tions on the galvanized surface by the metal ion.
• White rust prevention is thought to be based on a persistent or continuing elution of hexavalent chromium ion that is induced by holding the chromium immobilization ratio within an optimal range.
• the process of the present invention is able, as described above, to render these two effects or activities compatible.
• Each sample test sheet in the examples and comparative examples was alkaline degreased, water washed, and dried as described in items (2), (3), and (4) below. The sample test sheet was then subjected to a chromate treatment using the procedures outlined in items (5) and (6) below. Each sample test sheet, after treatment as specified above, was subjected to accelerated black rust testing and accelerated white rust testing as described below. The stability of the treatment baths was also tested.
• sample test sheets hot-dip zinc-plated steel sheet hot-dip 5% Al/Zn-plated steel sheet hot-dip 55% Al/Zn-plated steel sheet (2) alkaline degreasing:
• the chromate film weight was controlled through the wet pick-up in roll coating.
• the chromate-treated zinciferous-plated steel sheet was alkali- washed under the conditions given below, and the chromium add-on in mg/m 2 was measured using an X-ray fluorescence analyzer both before and after this alkali wash.
• the alkali wash consisted of a 2 minute spray at 60° C with a 2 % aqueous solution of a sodium silicate-based alkaline degreaser (PalklinTM
• ABST accelerated black rust testing
• test coupons were cut from each sample test sheet.
• the test surfaces of two test coupons were laid against each other to give a pair, and 5 to 10 pairs were stacked.
• the stack was wrapped with vinyl-coated paper, the four corners were tightened down with bolts, and a 0.67 kgf»cm load was applied with a torque wrench.
• This assembly was held in a humidistat for 240 hours at 70° C/RH 80 %. After removal, blackening of the counterfacing areas was visually evaluated. The evalu- ation standards are given below. 5: no blackening
• a 70 x 150 mm test coupon was cut from each sample test sheet and submitted to salt-spray testing as specified in JIS Z2371.
• the area of white rust development was visually inspected after 72 hours for the hot-dip zinc-plated steel sheet, after 240 hours for the 5 % Al/Zn-plated steel sheet, and after 600 hours for the 55 % Al/Zn-plated steel sheet.
• the evaluation standards are given below. 5: no white rust
• Tables 1 - 4 report the composition of the chromate treatment baths, the component ratios for the treatment baths, the pH, the film weight, the chromium immobilization ratio, and the results of accelerated black rust testing and acceler ⁇ ated white rust testing.
• compositions of the chromating treatment baths are given in Table 4.
• the wet pick-up mass of the treatment bath was about 1.2 milliiiters/meter 2 .
• the film mass was measured as its stoichiometric equivalent as chromium metal.
• the wet pick-up mass of the treatment bath was about 2.5 milliliters/meter 2 .
• the wet pick-up mass of the treatment bath was about 4 milliliters/meter 2 .
• Other notes are the same as for Table 1.
• the basic nickel carbonate used has the chemical formula 3 NiCO 3 • Ni(OH) 2 • 20 H 2 O and contains 29 % Ni.
• the basic cobalt carbonate used is believed to contain cobalt carbonate and cobalt hydroxide along with water and contains 44 % Co.
• the silica used was SNOTEXTM O, a colloidal silica commercially supplied by Nissan Kagaku Kabushiki Kaisha.
• Comparative Example 2 does provide an anti-black rust activity, white rust resistance is poor.
• Comparative Examples 3 and 4 produce a moderate activity with regard to the chromium immobilization ratio and white rust resistance, but they lack any anti- black rust activity.
• the composition in Comparative Example 1 performs poorly in all areas (chromium immobilization ratio, anti-black rust activity, and anti-white rust activity) Benefits of the Invention
• the chromate treatment process of the present invention offers very substantial practical results for zinciferous- plated steel sheet. Not only does the invention process improve both the resist ⁇ ance to black rust and the resistance to white rust, it also stabilizes and improves the chromium immobilization ratio and the appearance of the chromate film.

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• Mechanical Engineering (AREA)
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• Ceramic Engineering (AREA)
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• Chemical Treatment Of Metals (AREA)
• Electroplating Methods And Accessories (AREA)
• Coating With Molten Metal (AREA)
• Other Surface Treatments For Metallic Materials (AREA)

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• 1993
  • 1993-08-14 JP JP22222993A patent/JP3288152B2/ja not_active Expired - Lifetime
• 1994
  • 1994-08-05 TW TW083107191A patent/TW247321B/zh active
  • 1994-08-11 AU AU77141/94A patent/AU7714194A/en not_active Abandoned
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