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

Definitions

• This invention relates to the art of producing corrosion resistant coatings upon the surfaces of iron, zinc, cadmium and other metals and alloys thereof.
• This invention relates more particularly to the rapid and eiiicient production of phosphate coatings upon the surfaces of metals.
• Protective phosphate coatings of this type are of great economic importance in the preparation of metal surfacesfor the reception of an organic finish.
• the object of this invention isto provide for expediting and improving the application of protective phosphate coatings on metal surfaces by subjecting the metal to a preactivating treatment.
• the phosphate coatings are of value, in that they constitute an excellent base for the application of organic finishes to the metal surfaces. talline nature of the phosphate coatings upon the metal, the organic finishes will bond and adhere more tenaciously thereto than to the bare metal surface. Peeling of the paint due to inadequate bonding is greatly diminished when protective phosphate coatings are employed. In addition, the separation of the organic finish from the metal surface due to corrosion of the surface metal beneath the organic finish is greatly reduced, since the protective phosphate coatings inhibit corrosion.
• phosphate coatings have been produced upon metal surfaces by applying a, solution containing phosphoric acid and phosphates.
• the time involved in treating the metal surface in order to secure adequate protective coatings usually has been lengthy and even within recent years has constituted a fraction of an hour.
• the treatment has been extremely lengthy. and even so the Due to the crysadequate reaction between the metal surface and a composition capable of developing a phosphate coating thereon may be greatly reduced by subjecting the metal surface to a preliminary activating treatment.
• bare metal surfaces When treated with an activating solution of the type described herein, bare metal surfaces have imparted thereto certain characteristics whereby they are activated so that the normal or modified phosphate coating compositions will form an exceedingly durable and complete phosphate film or coating thereon with great rapidity, for example, in a minute or less.
• a further advantage obtained by the activation of metal surfaces is the formation of satisfactory phosphate coatings upon metals which heretofore did not lend themselves to the formation of good phosphate coatings.
• zinc which ordinarily is not regarded as capable of being consistentl satisfactoryily treated with phosphate coating compositions, is now readily and fully treatable in a minute or less when activated by the preliminary treatment herein disclosed.
• metal surfaces to be subsequently subjected toa treatment prophosphate and oneor more compounds from the group selected from tin, lead, or arsenic the following process has been found to be most preferable.
• Orthodisodium phosphate is dissolved in water, preferably to form a nearly saturated solution.
• a small amount of one or more water soluble salts of the group consisting of tin, lead or arsenic is added to this solution in an amount ranging from /2 of 1% of the weight of the discdium phosphate up to of the weight of disodium phosphate or even more.
• I Arsenic oxides, lead acetates, tin chlorides and tin sulfates are examples of salts usable for the purpose.
• the solution so prepared is evaporated to dryness by slow heating. The residue may be broken up, preferably finely pulverized, in order to facilitate dissolving in water in subsequent operations.
• disodium orthophosphate is the most desirable material in producing the activating solution.
• Other dialkali potassium point solution and comprising 1:8 of the total phosphate content, and the remainder water is one example of a solution suitable for use with zinc.
• an oxidizing agent such as a nitrate in amount from 0.2% to 1% may bepresent in order to remove any nascent hydrogen bubbles which form on the metal surfaces.
• phosphate coating composition causes a heavy discharge of gaseous bubbles from the metal surfaces. It is believed that the cessation of such bubbling, which occurs in about 30 seconds, is a sign that the phosphate coating I microscope particularly reveals the exceptional improvement produced by applying the activating salts, for example, dipotassium phosphate, may be v employed in the same manner.
• the dried composition resulting from the evaporation described above is dissolved in water to prepare the activating solution. It has been found that the best results have been obtained when the solution contains from 0.1 to 2% of a dialkali phosphate, such as disodium phosphate, and the quantity of the soluble salt selected from the group described above ranges from 0.005% to 0.05%. However, the salt-content may be varied from this preferred range with activation being obtained.
• the pH or the solution within the range set forth will vary from 8.0 to 8.5
• the metal surface to be treated is initially thoroughly cleansed.-
• One suitable treatment is cleaning in vapors of chlorinated solvents such as trichloretlfylene and the like.
• the metal surface may be electrocleaned or subjected to alkaline detergents witlithorough washing with clean water before applying the activating solution.
• the thoroughly cleaned metal surface may be dipped into the disodium phosphate metallic salt activating solution or the solution may be sprayed over the metallic parts or applied in any desired manner.
• the surfaces need be subjected for about only 10 seconds to the activating solution in order to acquire a satisfactory degree of activation. However, applications of activating solution for seconds or more are beneficial. It is believed that the metal surface does not acquire any protective coating during this stage of the process.
• reaction is substantially complete. It is generally desirable, however, to prolong the application of the solution to themetal surface for a brief period of time beyond this point in order to insure complete formation of the phosphate coating.
• the metal may be removed from the phosphate coating composition and subjected to heat in order to dry the surface.
• the metal coming from thephosphate coating bath may be treated with chromic acid as a sealing coating and thereafter dried. Again the metal may be subjected to a hot chromic acid solution at a temperature of around 190 F. and thus acquire sufiicient heat so that the metal dries automatically in the air after removal from the solution.
• the treated dry surface will reveal on examination an almost velvety appearing crystalline coating of remarkable uniformity.
• the naked eye is unable todistinguish separate crystals. Under the microscope, ahigh magnification is necessary in order to disclose the separate. crystals.
• the coatings . are composed of relatively coarse crystals and the coverage of the metal surface is noticeably irregular. Large un'coated spaces between the crystals are dispersed at very frequent intervals.
• th metal acquires a much finer crystalline coating which under the microscope reveals very few open spaces and the coverage is more effective than that on the unactivated metal.
• Steel and iron surfaces may be subjected to the activating solution in the same manner as zinc.
• the activated ferrousmetal surfaces will respondbetter to a treatment by a phosphate solution differing somewhat from the previous solution.
• a typical formula for ferrous metals is a given herein-z Manganese phosphate pounds 1% Phosphoric acid 83% do 5 Sodium nitrate do Cupric nitrate ounce Suflicient water to make one gallon of solution.
• the gallon of solution is diluted with water to make a 3% "solution.
• 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.
• 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, 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 expedites the reaction-of the ferrous metal with the phosphate solution.
• ferrous metals and zinc other metals such as cadmium and alloys of these metals are similarly responsive to the activating treatment to acquire phosphate coatings of the finely crystalline nature herein disclosed.
• Corrosion tests have revealed a decided improvement in the corrosion resistance of the phosphate coatings as secured to the practice of the invention in this case.
• An activating solution for treating metal surfaces to improve the subsequent formation of protective phosphate coatings on the metal surfaces comprisin in combination, an aqueous solution containing as its essential components from 0.1% to 2% of disodium phosphate and from 0.005% to 0.05% of a water soluble metal salt sewill turn completely white after 12 hours.
• An activating solution for treating metal surfaces to improve the subsequent formation of protective phosphate coatings on the metal surfaces comprising, in combination, an aqueous solution containing as its essential components a dialkali metal phosphate and water soluble metal salts selected from the group of metals consisting of tin, lead and arsenic.
• An activating solution for treating metal surfaces to improve the subsequent formation of protective phosphate coatings on the metal surfaces comprising, in combination, an aqueous solution containing as its essential components from 0.1% to 2% of disodium phosphate and water soluble metal salts selected from the group of metals consisting of tin, lead and arsenic.
• a composition capable of activating metal surfaces comprising essentially, in combination, a dialkali metal phosphate and a water soluble metal salt selected from the group of metals consisting of lead, tin and arsenic.
• a composition capable of activating metal surfaces composed essentially of disodium phosphate and a .water soluble metal salt selected from the group of metals consisting of lead, tin and arsenic.
• a composition capable of activating metal surfaces composed essentially of disodium phosphate and a water soluble metal salt selected from the group of metals consisting of lead, tin and arsenic, the metal phosphate and the metal salt being derived from a water solution of both evaporated to dryness.
• the method of applying protective phosphate coatings to metal surfaces which comprises, in combination, applying an aqueous solution of a dialkali metal phosphate and a water soluble salt of a metal selected from the group consisting of lead, tin and arsenic, the aqueous solution activating the metalsurface, and thereafter subjecting the activated metal surface to a I resistant phosphate coating thereon.
• the method of applyi Protective phosphate coatings to metal surfaces which comprises, in combination, applying an aqueous solution of from 0.1% to 2% of disodium phosphate and from 0.005% to 0.05% of a water soluble salt of a metal selected from the group consisting of lead, tin and arsenic, the aqueous solution activating the metal surface, and thereafter subjecting the activated metal surface to a solution of phosphoric acid, phosphates and an oxidizing agent to produce an effective corrosion resistant phosphate coating thereon.
• the method of applying protective phosphate coatings to metal surfaces which comprises, in combination, applying an aqueous solution of disodium phosphate and a water soluble salt of a metal selected from the group consisting of lead, tin and arsenic, the aqueous solution activating the metal surface, and thereafter subjecting the activated metal surface to a solution of phosphoric acid, phosphates and an oxidizing agent to produce an effective corrosion resistant phosphate coating thereon.

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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)

Priority Applications (8)

Applications Claiming Priority (1)

Publications (1)

Family

ID=23720697

Family Applications (1)

Country Status (7)

Cited By (19)

Families Citing this family (1)

• 1942
  • 1942-03-06 US US433586A patent/US2329065A/en not_active Expired - Lifetime
• 1943
  • 1943-03-05 GB GB3661/43A patent/GB564521A/en not_active Expired
• 1945
  • 1945-11-30 NL NL122232A patent/NL62181C/xx active
  • 1945-12-27 FR FR919461D patent/FR919461A/fr not_active Expired
• 1947
  • 1947-03-17 CH CH259830D patent/CH259830A/de unknown
  • 1947-04-29 ES ES177805A patent/ES177805A1/es not_active Expired
  • 1947-04-29 ES ES177804A patent/ES177804A1/es not_active Expired
  • 1947-05-31 BE BE472648D patent/BE472648A/xx unknown

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