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
  • C23C22/78—Pretreatment of the material to be coated
  • C23C22/80—Pretreatment of the material to be coated with solutions containing titanium or zirconium compounds

Definitions

• This invention relates to the art of producing corrosion-resistant coatings on the surfaces of iron, zinc and other metals and alloys.
• the object of this invention is to provide for treating metal surfaces to expedite the process of forming corrosion-resistant phosphate coatings thereon.
• Another object of this invention is to provide a composition capable of activating metal surfaces to improve the formation of corrosion-resistant phosphate coatings thereon.
• a protective phosphate coating is practiced extensively. Not only do these phosphate coatings protect the underlying metal from corrosion, but they constitute excellent surfaces for the successful application of organic finishes.
• the phosphate coatings occur as crystalline deposits to which organic finishes will bond and adhere more tenaclously than to the bare metal surface.
• metal surfaces particularly surfaces of ferrous metal
• a protective phosphate coating by applying an aqueous solution containing phosphoric acid and metal phosphates.
• the time required to produce a satisfactory phosphate coating on the metal surface has usually been relatively lengthy but within recent years the time of treatment has been reduced to a fraction of an hour.
• the time necessary to produce a satisfactory phosphate coating on a metal surface by applying thereto a phosphate solution may be greatly reduced by pretreating the metal surfaces in order to activate the surface metal. It is my theory that under ordinary conditions the metal crystals exposed at the surface of a body of metal are characterized by different degrees of activity whereby some crystals are in a highly active state and will react speedily with a chemical applied thereto whereas other crystals on the same surface are in a. relatively inactive state and react much more slowly or may not react at all with the given chemical applied thereto. The state of relative activity of a crystal probably determines the speed with which it will react with a phosphate solution to produce a phosphate coating.
• the pre-treatment of this invention is believed to activate the metal at the surface of a body so that a large proportion orall of the exposed crystals are in a highly active state, whereby they react with a phosphate coating solution at a rapid rate.
• metals that did not satisfactorily react with phosphate solutions to produce a protective phosphate coating will, when so pre-activated, acquire highly satisfactory coatings of phosphate.
• Zinc metal ordinarily does not react with phosphate coating solutions to form satisfactory coatings.
• zinc will react at a high rate with an applied phosphate solution to produce a fine crystalline coating having excellent protective properties.
• the pre-treatment of the invention comprises the application to metal surfaces of an aqueous solution of ortho-disodium phosphate and zirconium dissolved in water.
• an aqueous solution of ortho-disodium phosphate and zirconium dissolved in water In some cases the addition of titanium to the solution produces unexpectedly improved results. In the absence of the zirconium or titanium, the disodium phosphate has negligible activating effect.
• ortho-disodium phosphate is the only material that may be combined compound or zirconiumselected need not be very soluble in water.
• a portion of the zirconium may be replaced by titanium with good results.
• titanium compounds suitable for this purpose are titanium tetrachloride, titanium trichloride, titanium hydroxide, titanium nitride -and titanium potassium oxalate.
• the disodium phosphate and zirconium, with or without the titanium are combined by dissolving to form an initial aqueous solution and slowly evaporating the solution to dryness.
• the zirconium and tita- 3 nium do not form an appreciably effective pretreating solution if simply added to the disodium phosphate without the step of evaporating to dryness.
• the evaporated and dried disodium phosphate and zirconium composition so prepared may contain from about 0.005% up to 20% by weight of zirconium, the balance being disodium phosphate. It is used in a powdered form to faciiitate dissolution in water.
• the dried composition may be stored indefinitely until desired for use.
• the dried composition is dissolved in water to produce an aqueous solution containing from about 0.1% to 2% of disodium phosphate and from about 0.001% to 0.1% of zirconium. If titanium is present, the total quantity of titanium and zirconium present may be from 0.001% to 0.1%. Zirconium and titanium may be present in larger amounts but no advantage is obtained due to the presence of such excess.
• a satisfactory commercial composition has been found to contain 1% disodium phosphate and 0.01% of zirconium or zirconium and titanium combined.
• the percentage of zirconium and titanium is that of the metal radical alone.
• a solution in the range of concentrations given will have a pH of from 8 to 8.5.
• the pre-treatment' solution prepared as indidicated is particularly eflective when applied to iron, steel and other ferrous metals.
• a pre-treatment solution containing titanium was disclosed as particularly satisfactory in treating zinc.
• the present invention is based on a zirconium solution which exhibits desirable characteristics in treating zinc but its major advantages are revealed when applied to iron and steel surfaces.
• the zirconium present in the pretreating solution activates the ferrous metal to a much greater extent than titanium alone.
• titanium is added to the zirconium, particularly to produce a solution having approximately 30% of titanium and 70% zirconium, exceptional results are obtained in treating ferrous metal.
• Ferrous metal may be treated with the solution of 'disodium phosphate and zirconium either by spraying the solution on the metal surface or dipping the metal in the solution or in any other convenient manner.
• the time of treatment need be very brief. Usually, 10 to 15 seconds, is all that is required to satisfactorily activate the surface. In some cases, the activating solution may be applied for 45 seconds or even longer to the metal with some benefit.
• the pretreated ferrous metal is treated with a conventional type of phosphate coating solution to cause the formation thereon of a protective phosphate coating.
• a typical coating producing solution for treating ferrous metal is the following:
• the main purpose of the sodium nitrate in the above formula is to provide an oxidizing agent to react with small amounts of nascent hydrogen which are produced when the solution reacts with the metal surface. Unless the hydrogen is oxidized or removed as large bubbles of hydrogen gas. the nascent hydrogen adheres to the metal surface and blankets the action of the solution. Therefore, a non-uniform coating may result as well as a slower rate of reaction.
• the oxidizing agent will immediately react with the bubbles of nascent hydrogen and remove them from the surface of the metal.
• Other oxidizing agents such as sodium or potassium nitrite, chlorates, and the like are suitable for this purpose.
• Zinc phosphate may. be introduced to replace a part of the manganese phosphate in the solution for treating ferrous metals.
• the presence of one or more of the group consisting of zinc, copper and manganese greatly expedite: the reaction of the ferrous metal with the phos" phate solution.
• the preactivated metal When the preactivated metal is treated with the phosphate coating solution, a large quantity of gaesous bubbles appear when the solution is first applied.
• the bubbles consist mainly of hydrogen gas.
• the bubbling ceases after a fraction of a minute and it is believed that the coating reaction is substantially to assure the complete coating of the metal surface.
• the crystals are probably a ferro-ferric phosphate, though it is difllcult to analyze the crystals with a sufficient accuracy to be certain of their exact chemical composition.
• the metal surface may be rinsed with clear water.
• the surfaces may be subjected to a sealing treatment by applying chromic acid solution thereto.
• An aqueous solution containing 7 /2 ounces of chromic acid per gallons of water is generally satisfactory for the purpose.
• a water rinse may not be necessary in this case since the chromic acid sealing treatment performs a rinsing function.
• the chromic acid solution need be applied to the metal surface for only a few seconds.
• the metal after rinsing or after the application of the chromic acid solution, may be dried by passing through a drying oven to Prepar the surface for subsequent operations such as the application of an organic finish.
• the drying operathe preactivating treatmentherein disclosed areof a much coarser structure and usually require two or more coats oi organic finish to give a smooth surface and to furnish adequate corrosion protection.
• the zirconium preactivating treatment is particularly beneficial for treating iron, steel and other ferrous metal members, inthe form of sheets, tubes, ,punchings, castings, for'gings, and the like, it has advantages when applied to zinc, cadmium and other alloys and metals.
• the pretreating solution may be of the same composition as for treating iron and steel and the like, but the subsequently applied phosphate coating solution is usually modified to operate more satisfactorily with the lar'iriztal being treated.
• An aqueous solution for treating ferrous zinc and cadmiummetal surfaces to provide for improving the formation of protective coatings on the metal'surface consisting of from 0.1% to 2% by weight of ortho-disodium phosphate and a total from 0.001% to 0.1% by weight of titanium and zirconium combined, the balance being water, the titanium and zirconium being present as water soluble compounds, the ortho-disodium phosphate, titanium compound and zirconium compound having been previously combined by dissolving them in water and evaporating. to dryness. 4
• a composition capable of activating metal surfaces when in aqueous solution consisting of from 0.005% to 20% by weight of zirconium and titanium, the zirconium and titanium being present as water soluble compounds, and the balance being ortho-disodium phosphate, the composition being the residue derived by dissolvingin water the zirconium and titanium compounds and the ortho-disodiuin phosphate and evaporating the water solution to dryness.
• aqueous solution consisting of from 0.1% to 2% by weight of ortho-disodium phosphate, and a total of from 0.001% to 0.1% of titanium and zirconium combined present as a. water soluble compound, the ortho-disodlum phosphate and the zirconium compound having been previously combined by dissolving them in water and evaporating to dryness, and the balance being water, to provide for activating the metal surface and thereafter applying to the activated metal surface a solution comprising phosphoric acid, phosphates and an oxidizing agent to produce a phosphate coating thereon.
• a solution for treating ferrous metal surfaces toprovide for improving the formation of protective coatings on the metal surface comprising an aqueous solution consisting of from 0.1% to 2% by weight of ortho-disodium phosphateland a. total of from 0.001% to 0.1% of titanium and zirconium each present as a water soluble compound, the ortho-disodium phosphate and the zirconium and titanium compounds having been previously combined by dissolving them in water and evaporating to dryness, the ratio of weight of titanium to the weight of the zirconium being about 3 to '7, and the balance being water.

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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)
• Chemically Coating (AREA)

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Cited By (13)

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Citations (3)

• 0
  • IT IT432445D patent/IT432445A/it unknown
  • NL NL62521D patent/NL62521C/xx active
• 1943
  • 1943-07-29 US US496619A patent/US2462196A/en not_active Expired - Lifetime
• 1944
  • 1944-07-21 GB GB13976/44A patent/GB587176A/en not_active Expired
• 1946
  • 1946-01-07 FR FR919823D patent/FR919823A/fr not_active Expired
• 1947
  • 1947-03-31 CH CH270548D patent/CH270548A/de unknown
  • 1947-04-17 BE BE472618D patent/BE472618A/xx unknown
  • 1947-05-13 ES ES0178007A patent/ES178007A1/es not_active Expired

Patent Citations (3)

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