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

• insoluble tertiary zinc phosphate is deposited on the metal surface in the form of a coating, while iron is simultaneously dissolved off any iron-containing metal surface and enters the solution in the divalent ferrous form. It is however desirable to keep the phosphatizing solution substantially iron-free, in order to obtain good corrosion-resistant and firmly adherent phosphate coatings.
• the phosphatizing solution is therefore conventionally kept practically free from dissolved iron by the addition of an alkali-metal nitrite such as sodium nitrite or potassium nitrite. This nitrite converts the.
• the temperature of the phosphatizing solution should of course always be maintained above 45 C., and as will be indicated hereinafter the preferred temperatures are well within the range of 45-75 C.
• the process of the invention has the great advantage that it is unnecessary to add sodium nitrate at least several times daily and possibly (depending on the throughput of metal) continuouslyon the contrary, it is only necessary to add a small quantity of sodium nitrate once at the beginning of a working cycle, thus normally only once at the beginning of each week.
• the control of the process is therefore greatly simplified, and the phosphatizing solution can be used successfully despite a continuous high throughout of metal.
• the solution can be kept largely free from sodium ions, which are of course detrimental to coating formation.
• a further important advantage of the process of the invention is that coating formation proceeds so rapidly that there is practically no time for ferrous ions dissolved from the iron surface during coating formation to diffuse into the phosphatizing solution, so that sludge formation in the solution is only very slight, and significantly less than in the known phosphatizing processes which involve frequently-repeated or continuous additions of sodium nitrate. Consequently the phosphatizing solutions used in the process of the present invention need be de-sludged only very seldom, for instance when used in an immersion process at normal throughputs perhaps only every 4-6 months.
• the phosphatizing solution must also be replenished whenever necessary, and usually at least several times a day, with phosphate, zinc and nitrate ions in order to replace these as they are consumed in the coating reaction.
• the replenishment material should contain phosphate, Zinc and nitrate ions in the previously-specified ratios, but in other respects the replenishment is carried out in the usual manner, by adding a concentrate containing the necessary ratios of phosphate, zinc and nitrate ions whenever appropriate.
• the consumption of phosphate and zinc ions in the coating reaction can be monitored in the conventional manner by determining the total pointage as measured by the number of millilitres of N/ 10 NaOH needed to titrate a 10 millilitre sample of the bath to a red end-point using phenolphthalein as indicator; the total pointage thus determined may then be raised to the desired value by adding a definite quantity (dependent on the total volume of the phosphatizing solution in the bath) for each point to be restored.
• the total pointage of the solution is not critical since the process of the invention will produce good phosphate coatings to a large extent independently of the total pointage, thus both at low and high pointages, but as a general rule one replenishes so as to restore the total pointage to approximately its original value, which preferably will be in the range of 30-40.
• total pointage which is a measure of the total acidity of the solution
• free-acidity or acid pointage of the solution there is however another related factor which affects the process, namely the free-acidity or acid pointage of the solution.
• the ratio of total acidity to free acidity is a significant factor which influences both the speed of coating formation and the rate at which autocatalytic generation of nitrite takes place. In general, the lower the ratio of total acid to free acid and hence the more free acid there is present in the phosphatizing solution, the faster will coating formation take place and the more surely will nitrite be autocatalytically generated in sufficient quantities.
• the process it is not usually practicable to operate the process with a phosphatizing solution having an acid ratio of less than about 5, and indeed the freshly-prepared initial solution will preferably be made up so as to contain only such an amount of phosphate as will yield an acid ratio of from 5 to 8, the optimum acid ratio in the initial phosphatizing solution being usually 7, though this is to some extent dependent on the hardness of the water used for making up the phosphatizing solution.
• the replenishment material preferably has an acid ratio of about 2.8 to 3.7, much lower than that of the initial solution.
• the ratios of zinc and nitrate relative to phosphate in the initial solution should be at the numerically-lower end of the previously stated ranges, thus say and similarly the ratio of zinc to phosphate in the replenishment material should be at the numerically-lower end of the previously stated range, thus say Conversely, in the production of corrosion-resistant coatings the ratios of zinc and nitrate to phosphate in both the initial phosphatizing solution and also in the replenishment material can with advantage lie at the upper end of the previously-stated ranges.
• the bath-loading is increased to 65 m? per m. of solution, then the phosphatizing solution after the treatment will be found to contain iron.
• the solution is found to remain iron-free even at this higher bath loading, while at a temperature of 70 0, even at a bath-loading of to m. /m. solution, the phosphatizing solution both during and after phosphatizing contained practically no ferrous ions.
• the optimum time of treatment also varies somewhat according to the intended purpose of the fine-grained, uniform and dense zinc phosphate coatings produced.
• a treatment time of from 2 to 5 minutes at 5060 C. will usually be required with the solutions described above to produce a coating having a weight of about 2.5-4.5 g./m.
• a treatment time of from 1 to 5 minutes will usually be required with the previously-described solutions to produce a coating having a weight of 3.5-6.0 g./m. while at temperatures of 70-75 C. the treatment time may be less than 1 minute.
• a metallic catalyst such as nickel, cobalt or copper in the form of soluble salts such as sulphate, nitrate or carbonate
• the coating weights obtained are l0-20% higher.
• nickel, copper and/or cobalt in amounts exceeding 0.001%.
• Copper and/ or nickel and/or cobalt when present in greater amounts of 0.0055%-0.0l65% act not only as accelerators, but also seem markedly to promote autocatalytic nitrite-formation and may advantageously be incorporated in these amounts whenever nitrite-formation is inadequate, for instance because the bathloading is too small or the desired treatment time too short. Copper can be incorporated in the phosphatizing solution for instance by adding 1% to the concentrate as basic copper carbonate.
• a 24% (by weight) solution of sodium nitrite was added to the phosphatizing solution in an amount corresponding to 0.1% (by volume) per 100 litres, thus establishing a nitrite content of 0.014%.
• the phosphatizing solution had a total pointage of about 35, and after the addition of the sodium nitrite an acid ratio of 8.
• Iron sheet was first degreased with alkali, rinsed, pickled in sulphuric acid and once more rinsed, and was then immersed in this phosphatizing solution at a temperature of 52 C. for a period of minutes, and the coatings formed were very fine-grained, even and dense.
• the nitrite content in the solution was found to have risen to 0.024%, nearly double the initial N0 concentration-and moreover, this high nitrite content remained practically constant during the whole working day, despite even heavier loading of the bath.
• the term acid ratio is used in this example and elsewhere in its conventional sense, namely as the quotient of the total acid pointage divided by the free acid pointage--and that the total acid pointage corresponds to the millilitres of N/ NaOH which are needed for titrating 10 millilitres of the phosphatizing solution with phenolphthalein as indicator to the red end-point, while the free acid pointage corresponds to the millilitres of N/ 10 NaOH needed for titrating 10 millilitres of the phosphatizing solution using methylorange as indicator to the red/ yellow end-point.
• a phosphatizing solution was made up with a content of 7.43 g./l. P 0 12.93 g./l. Zn and 22.7 g./l. N0 having a pointage of 40.
• a 24% solution of sodium nitrite was added to this phosphatizing solution at the beginning of the working week in an amount of approximately 0.1 vol. percent so as to establish a nitrite concentration of 0.0136%.
• Steel wires (containing 0.8% C and 0.7% Mn) were phosphatized in this solution prior to cold drawing. After a throughput of 213 m. of wire surface per m. of solution, the nitrite concentration had already risen in 2% hours at 65 C. to 0.0214%, that is by about 57%.
• Example III A phosphatizing solution of the same composition as in Example II was prepared, and on the first working day of the week a 24% solution of sodium nitrite was added thereto so as to establish a concentration of 0.0118% N0 After a throughput of 91 m? of wire surface per m. of solution in 4 hours at 72 C., the concentration of nitrite in the solution had risen Without any further addition of sodium nitrite to 0.0163% N0 or about 38%, and it rose further during the rest of the day to 0.0194% N0 Overnight shutdown caused a break in working during which the nitrite concentration dropped to 0.0146% but this was still sufficient to enable the solution to be put into operation again next morning without any addition of sodium nitrite. After a further throughput of 173 m. /m. in 3 hours at 58 C., the N0 concentration had risen to 0.0243%, corresponding to an increase of 66%.
• a process for the production of coatings of zinc phosphate upon surfaces of iron, steel, zinc (including galvanized iron and steel) and cadmium and their alloys in which the surfaces are contacted until a coating is formed thereon with an aqueous acidic phosphatizing solution which contains phosphate, zinc, and nitrate ions, and a metallic accelerator selected from the group consisting of copper, nickel and cobalt and mixtures thereof, the initial phosphatizing solution containing phosphate zinc and nitrate ions in a ratio of and in which the phosphatizing solution is replenished during use whenever necessary to make good the zinc and phosphate ions consumed, replenishment being effected with a replenishment material which contains phosphate, zinc and nitrate ions in a ratio of:
• nitrite is added to the solution at the beginning of a coating cycle so as'to establish a concentration of at least 0.01% N0 therein and is thereafter maintained by autocatalytic generation throughout the coating cycle, and in which there is added from 0.0055 to 0.0165 of the metallic accelerator, and maintaining thse temperature of the phosphatizing solution below 7 C.

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• 1965
  • 1965-12-22 AT AT1152265A patent/AT282285B/de active
• 1966
  • 1966-12-20 BE BE691484D patent/BE691484A/xx not_active IP Right Cessation
  • 1966-12-21 SE SE17544/66A patent/SE340931B/xx unknown
  • 1966-12-21 NL NL6617945A patent/NL6617945A/xx unknown
  • 1966-12-21 NO NO166092A patent/NO116743B/no unknown
  • 1966-12-22 GB GB57420/66A patent/GB1164639A/en not_active Expired
  • 1966-12-22 US US603729A patent/US3520737A/en not_active Expired - Lifetime
  • 1966-12-22 FR FR88548A patent/FR1505997A/fr not_active Expired

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