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
  • C23C22/07—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 phosphates
  • C23C22/08—Orthophosphates
  • C23C22/12—Orthophosphates containing zinc cations
  • C23C22/13—Orthophosphates containing zinc cations containing also nitrate or nitrite anions

Definitions

• This invention relates to the production of phosphate coatings on metal surfaces and relates more particularly to a method of replenishing the solutions which are used for that purpose.
• the presence of sodium dihydrogen phosphate also has disadvantages.
• the coating efiiciency of the solution will be impaired by the accumulation of an appreciable amount of sodium phosphate because it increases the solubility of normal zinc phosphate which comprises the bulk of the coating formed on the metal surface.
• the sodium phosphate will be calculated as a coating material along with zinc phosphate. This will occur whenever the usual titrating methods are employed.
• the true coating phosphate content of the bath therefore, must be determined by other less convenient means whenever an appreciable amount of sodium phosphate is present.
• An object of this invention is a method of using a nitrite, such as sodium nitrite, or any similar nitrite which by decomposition in an acid phosphate solution results in a neutralizing action, as an accelerator and at the same time avoid the build up of more than insignificant amounts of the objectionable sodium salt, and at the same time avoid the neutralizing effect which would otherwise be obtained.
• a nitrite such as sodium nitrite, or any similar nitrite which by decomposition in an acid phosphate solution results in a neutralizing action, as an accelerator and at the same time avoid the build up of more than insignificant amounts of the objectionable sodium salt, and at the same time avoid the neutralizing effect which would otherwise be obtained.
• Another object is the avoidance of sludge formation and the consequent loss of coating chemicals such as occurs in phosphate solutions when the neutralizing effect of a nitrite is not counteracted.
• a further object is to enable the operator of a solution to determine by a. simple titration the true coating strength present.
• a coating dihydrogen phosphate such as zinc phosphate
• a nitrite such as sodium nitrite
• an acid with which the nitrite will react with the liberation of nitrous acid and in amount at least equivalent to that required to form a substantially neutral salt by reaction with the nitrite present.
• the coating metal and the phosphate content of the,replenishing materials be added in substantially the proportions to form zinc dihydrogen phosphate.
• phoric acid would, of course, result in the presence of sludge, while more than is required would be available to form sodium phosphate.
• Sodium nitrite being unstable in the presence of acid, must be added separately from the acid phosphate.
• the nitrite will vary in efliciency within limits, with the rate of production, that is, the greater the amount of surface treated in a given time, the less the amount of nitrite required for a given area coated, because there is less chance for decomposition to occur in the absence of coating formation. It can be seen, therefore, that the amount of acid to be added to combine with the sodium of the sodium nitrite will vary somewhat depending on operating conditions.
• this factor is compensated for by a more or less corresponding change in consumption of coating chemicals, and .for variations ordinarily encountered the acid may be' incorporated with the coating phosphate material so that the addition of the acid as a separate ingredient is avoided.
• the acid may be' incorporated with the coating phosphate material so that the addition of the acid as a separate ingredient is avoided.
• Less phosphate phosmaterial for the purpose of the invention. This may be added along with the acid phosphate as a single mixture.
• the water in the tank isflrst heated to 110-130 F.
• processing bath may be prepared by adding in i the proportion of 40 pounds to 100 gallons of water a concentrated solution of the following composition:
• The' coating solution may be applied to the metal to be coatedby any of the usual methods,
• the metal for example, fenders, wheels, or other automotive steel parts
• the other steps incident to this coating operation that is, the necessary cleaning and rinsing operations, are also carried out by the spray method.
• the metal is carried on a conveyor through a tunnel in which the various steps are performed.
• a spraying time of approximately one minute in the coating section is usually sufficient to cause a uniform conversion of the steel surface to an insoluble phosphate.
• the sodium nitrite is preferably added in the same manner.
• the amount reqired in the solution will vary not only with the rate of production, as has been pointed out, but also to some extent with the ease with which any given kind of steel is coated.
• the processing time is standardized as it is in the usual spraying installations, it is sometimes necessary to slightly increase the amount of nitrite in order to obtain a satisfactory coating in a given time, since it is impractical to increase the processing time.
• a range of nitrite, calculated as N02, from .006 to .05% is very satisfactory.
• the nitrite content of the solution can permanganate in accordance with usual methods.
• the amount of N02 required varies with the temperature, that is, 006% is satisfactory when operating at around 130 F., while approximately .02-.05% is required at a temperature in the neighborhood of 110 F. 7
• the amount of nitric acid in the above replenishing formula is sufficient to avoid the formation of sodium dihydrogen phosphate when the higher amounts of nitrite are used and, at the same time, there is insufllcient to cause excessive acidity when only small amounts are employed.
• nitric acid has been dealt with somewhat in detail. However, it is to be underi stood that other acids may be used in place of it. For example, sulfuric and hydrochloric acid are also capable of counteracting the neutraliz- The nitrite appears to have some catalytic action on the nitrate with the formation of some additional nitrite which also aids in accelerating the coating action.
• the principle of the invention may be employed in connection with any phosphate solution whose coating action is accelerated by nitrite and is not restricted to instances where ferrous surfaces are coated, since various non-ferrous metals, such as zinc, cadmium, magnesium, copper, and aluminum may also be phosphate coated with the aid of. nitrite.
• the invention is also applicable to other metallic phosphate solutions; for example, dihydrogen phosphates of manganese, cadmium, and calcium may also be accelerated by a nitrite.

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)
• Chemical Treatment Of Metals (AREA)

Priority Applications (4)

Applications Claiming Priority (2)

Publications (1)

Family

ID=61187030

Family Applications (1)

Country Status (4)

Cited By (7)

Families Citing this family (1)

• 1942
  • 1942-03-02 US US433014A patent/US2351605A/en not_active Expired - Lifetime
• 1946
  • 1946-08-10 CH CH260320D patent/CH260320A/fr unknown
• 1950
  • 1950-10-01 DE DEP4132A patent/DE845135C/de not_active Expired
• 1952
  • 1952-10-11 AT AT186083D patent/AT186083B/de active

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