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
  • C23C22/46—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 oxalates

Definitions

• This invention relates to the provision of firm, non-porous, adherent, insoluble rotective coatings on iron and steel artic es and comprises a process oftreating the surfaces of iron and steel articles to produce such coatings thereon.
• the protective coatings in accordance with our invention consist essentially of insoluble compounds consisting essentially of oxalates of iron, formed in situ on the articles by interaction between the iron of the article and ferric oxalate, in a solution or bath which ordinarily is more or less acidified to accelerate the reaction as more fully described hereinafter.
• oxalic acid has occasionally been used for cleaning and pickling iron and steel, and particularly for brightwork.
• it has the disadvantage that its aci it is not as great as that of sulphuric and by rochloric acids and evolution of hydrogen is not rapid. It does, however, have the advantage of great solvent power for ordinaryiron rust; a property to which it owes its well known use for remov ing rust stains.
• pickling and scouring iron its action in practice 15 found to be erratic. Under some circumstances it leaves a coating on the iron, which has led to the proposal that it be used for forming a protectlve coating for iron and steel.
• ferrous oxalate seems to predominate.
• the material of the coating is insoluble in. solutions of we acids, such as acetic acid (vinegar). It. is highly resistant to attack.
• the coating is ferrous oxalate, two-thirds of it can be regarded as coming from the solution and only one-third from the iron of the article being coated.
• the operation of the ferric oxalate bath is regular and there is not the annoying development of hydrogen to dislodge the coating which is incident to the use of most coating baths of acid nature.
• ferric 0xalate for coating iron and steel% dipping processes, better and quicker resu ts are obtained if a small amount of free acid, such as sulfuric, phosphoric, oxalic or other suitable acid, is added.
• All ferric salts, including the oxalates, show a tendency to hydrolyze in water; h drolysis tending to produce ferric hydroxi e in solution or suspension.
• Ferric oxalate is comparatively poorly ionized and displays little tendency to form free oxalic acid as a result of hydrolysis.
• the presence of ferric hydroxide is disadvantageous, as tending to contaminate the coating or the metal surface to be coated.
• the acidulatingl acid should be one which is at least as ighly ionized as acetic acid and may be either an organic acid or a mineral acid.
• the quantity of free acid in the coating bath should not be sufficient to give free evolution of hydrogen with the iron of the article being treated, i. e. it should not exhibit substantial pickling properties, but on the other hand it shoul e suflicient to prevent harmful hydrolysis of the ferric oxalate and to promote the formation of the coating.
• a ferric oxalate concentration of about 5%
• the use of 0.5% of sulphuric acid in the bath is ample. If oxalic acid is used in place of sulphuric acid, at least 1% is desirable. More oxalic acid may be used.
• ferric oxalate and oxalic acid present in about equirnolecular proportions.
• a greater proportion of oxalic acid is objectionable because of its interaction with metallic iron and consequent liberation of gaseous hydrogen.
• the bath may be replenished as'required with ferric oxalate and adjustment of its composition may be accomplished in case of need by suitable additions of oxalic acid or hydrated ferric oxide of a good reactive grade.
• the coating operation withdraws both iron and oxalate from the bath.
• the article to be coated is sometimes made the anode, in a solution of ferric oxalate, a moderate E. M. F. being applied. This accelerates the action and greatly reduces the time necessary to obtain satisfactory coatings.
• the particular concentration of the bath is not greatly important. Good results are obtained with a coating bath containing 50 parts of ferric oxalate and 25 parts of oxalic acid per liter at a temperature around 90 C.
• the ferric oxalate may be the ordinary commercial grade used for making blueprints; the yellow-brown scale preparation.
• the temperature used varies. In general the speed of formation of coating increases as the temperature, but boiling the bath should be avoided.
• the iron or steel article to be coated is immersed in the bath at a suitable temperature, allowed to remain until a fine grained, satiny coating is obtained, withdrawn, washed and dried. The article can then be used without further treatment, or can be painted, varnished or lacquered.
• the coatings produced by practicing the process of the present invention find many obvious a plications in the arts.
• a special use to which they admirably are adapted is in the preparation of laminations for electromagnets, laminated cores of transformers,
• Such equipment serving as an insulating layer or 1m in p ace of-mill scale or other insulating coating between laminae.
• Such equipment is made up of superposed thin, flat pieces of iron, out to size, mill scale or other insulating material on the contacting surfaces of the pieces serving to insulate them from each other and reduce eddy current losses. It has been found that in a certain transformer core construction in which mill scale serves i as the insulator, and in which the electrical resistance perpendicular to the plane of the laminations is ohms, the resistance in an otherwise identical core made up of laminae coated in accordance with the present invention is 4,000,000 ohms.

Landscapes

• 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)
• Other Surface Treatments For Metallic Materials (AREA)
• Cleaning And De-Greasing Of Metallic Materials By Chemical Methods (AREA)
• Chemical Treatment Of Metals (AREA)
• Soft Magnetic Materials (AREA)

Priority Applications (5)

Applications Claiming Priority (1)

Publications (1)

Family

ID=24368563

Family Applications (1)

Country Status (5)

Cited By (8)

Families Citing this family (1)

• 0
  • BE BE393417D patent/BE393417A/xx unknown
• 1932
  • 1932-02-09 US US591932A patent/US1895569A/en not_active Expired - Lifetime
  • 1932-12-29 FR FR748192D patent/FR748192A/fr not_active Expired
  • 1932-12-30 GB GB36848/32A patent/GB401908A/en not_active Expired
  • 1932-12-30 DE DEC47360D patent/DE642191C/de not_active Expired

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