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 a method of maintaining the efficiency of phosphate coating baths used at room temperature.
• Phosphate coating processes such as the Bonderizing and Parkerizing processes have become of considerable importance inthe modern technique of surface protection of metals, particularly of ferrous metals. Those processes are usually carried out at increased temperature of about 40 to 45 C., using phosphate coating baths of various compositions commonly based on zinc phosphate and zinc nitrate at given ratios, which may also contain other salts as accelerators, such as copper and nickel salts.
• Cold phosphate coating processes are also known (see German Patent No. 900,163). The latter processes utilize baths containing accelerators and having a pH at least 0.5 higher than those operating at higher temperatures.
• the baths are similar to hot phosphate coating baths, except that, as stated, the pH is raised to neutralize part of the acidity so that the hydrolysis equilibrium shifts to room temperature.
• the coating baths in order to accelerate the formation of the coating, the coating baths must contain an excess of the oxidizing agents, so that a P O /NO ratio of 1:2 is normally used in these baths.
• the feed salts (that is, the salts that are added to the baths to replenish the amounts of salts which have been removed) must also contain a much higher amount of oxidizing agent than that required for hot baths. Nevertheless, in practical use these cold baths have always been found to be of unsatisfactory permanency in strength. In fact, it has been found that, for example, 1 liter of such a bath, after phosphate coating therewith an area of 3 sq. meters and after regenerating the same three times by adding feed liquor having a P O /NO ratio of 1:1.4, is no longer capable of producing a good coating because the P O /NO ratio had risen to 1:7 during the coating operations.
• a cold phosphate coating bath can be made to remain efficient during a very great number of operations, even for more than one year of use, when employing feed salts at a different ratio than that of the bath; in other words, feed salt solutions containing lower amounts of oxidizing agent (N0 than those used previously and having, therefore, a composition approaching that of the feed salts for hot baths.
• Example 1 Panel sheets of soft-iron are dipped and phosphate coatedin 1 liter of a phosphate coating bath containing gr. Zn, 20 gr. P 0 and 40 gr. N03 (thus having a P O /NO ratio of 1:2). After five consecutive series of such sheets, representing a total area of 1 sq. meter, have been phosphate coated, the bath is regenerated (by adding so much feed liquor to the bath until 10 cc. of the latter consume the same number of cc. of N sodium hydroxide with phenolphthalein as the end point indicator as had been consumed by 10 cc. of the bath before beginning the phosphate coating operation).
• the feed liquor contains gr./ 1. Zn, 170 gr./-1. P 0 240 gr./l. N0 0.1 gr./l. Cu; thus having a P O /NO ratio of 121.41.
• .NaNO is also added with the feeding solution, at a proportion of 50 gr. per each liter.
• Example 2v A bath is employed as specified in Example 1, having the same initial composition and using the same operating temperature on a similar series of soft-iron sheets. Likewise, regeneration (feeding) is effected each time the bath (1 liter) has been used for phosphate coating 1 sq. meter of sheets. However, according to the present in vention, the feed liquor contains 170 gr./l. Zn, 240 gr./l. P 0 170 gr./l. N0 and 0.1 gr./l. Cu. Thus, it has a EO /N0 ratio of 1:0.73. Discontinuous or continuous addition of sodium nitrite is effected in amounts never in excess of hi of the quantity of N0 added with the feeding solution.
• the P O /NO ratio has gone down, after phosphate coating 3 sq. meters of sheet material and after three regenerations, from 1:2 to 1:7, whereas in the second example, after an initial reduction to 122.5, the P O /NO ratio remains substantially constant.
• Example 3 A bath is used which is similar to that of Example 2. The same procedures are followed, except that sodium nitrite is neither present in the initial bath nor introduced with the feeding solution. Even the first phosphating operation results in a coatingwhich is entirely inadequate a rust preventative.
• the baths and the feeding solutions are made up from zinc phosphate, zine nitrate and/er an alkali metal nitrate, while the oxidizing agent added to the feeding solution consists of sodium nitrite.
• the P O /NO ratio of the initial bath has been given as 1:2 and, in Example 2, the HO /N0 ratio of the feeding solution as 1:0.73, it is to be understood that, according to this invention, the EO /N0 ratio in theinitial solution may range from 1:1 to 1:2 and in the feed solution from 1:1 to 120.5, in order to maintain throughout the coating operations a P O /NO ratio ranging from 1:1 to 1:2.5 in the bath.
• the method of maintaining the efiiciency of phosphat comprising preparing, as coating bath, an aqueous solution of zinc phosphate and at least one nitrate selected from the group consisting of alkali metal nitrates and zinc nitrate, and during the metal coating process maintaining in said coating bath a P O /NO ratio ranging from about 112.5 to about 1:1 by replenishing the coating oath depleted in the coating operations with a feed liquor comprising an aqueous solution of zinc phosphate, at least one nitrate selected from the group consisting of alkali metal nitrates and zinc nitrate, the P O /NO ratio of the feed liquor being within a range from about 1:1 to about 1:0.5, and also adding sodium nitrite as oxidizing agent in an amount not more than about one tenth of the weight of N0 contained in the feed liquor.

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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 (4)

Publications (1)

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Family Applications (1)

Country Status (8)

Cited By (4)

Citations (4)

Family Cites Families (1)

• 0
  • NL NL206455D patent/NL206455A/xx unknown
  • IT IT532546D patent/IT532546A/it unknown
• 1956
  • 1956-04-17 US US578592A patent/US2863793A/en not_active Expired - Lifetime
  • 1956-04-19 CH CH343201D patent/CH343201A/de unknown
  • 1956-04-19 BE BE547125D patent/BE547125A/fr unknown
  • 1956-04-19 LU LU34317D patent/LU34317A1/fr unknown
  • 1956-04-19 FR FR1147796D patent/FR1147796A/fr not_active Expired
• 1959
  • 1959-04-19 DE DE1959M0030302 patent/DE1069451B/de active Pending

Patent Citations (4)

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