US2863793A - Method of maintaining the efficiency of phosphate coating baths used at room temperature - Google Patents

Method of maintaining the efficiency of phosphate coating baths used at room temperature Download PDF

Info

Publication number
US2863793A
US2863793A US578592A US57859256A US2863793A US 2863793 A US2863793 A US 2863793A US 578592 A US578592 A US 578592A US 57859256 A US57859256 A US 57859256A US 2863793 A US2863793 A US 2863793A
Authority
US
United States
Prior art keywords
coating
bath
phosphate
ratio
maintaining
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired - Lifetime
Application number
US578592A
Inventor
Cerma Paolo De
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Montedison SpA
Original Assignee
Montedison SpA
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority to IT532546D priority Critical patent/IT532546A/it
Priority to NL206455D priority patent/NL206455A/xx
Priority to US578592A priority patent/US2863793A/en
Application filed by Montedison SpA filed Critical Montedison SpA
Priority to BE547125D priority patent/BE547125A/en
Priority to LU34317D priority patent/LU34317A1/en
Priority to FR1147796D priority patent/FR1147796A/en
Priority to CH343201D priority patent/CH343201A/en
Application granted granted Critical
Publication of US2863793A publication Critical patent/US2863793A/en
Priority to DE1959M0030302 priority patent/DE1069451B/en
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

Links

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.

Description

c 2,863,793 v Patented Dec. 9, 1958 No Drawing. Application April 17,
Serial No. 578,592
Qlaims priority, application April 20, 1955 4 Claims. (Cl. 148-6.15)
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. In such processes, 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. However, when using cold phosphate 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.
in case of cold phosphate coating 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.
Now I have found that 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.
However, I found that if the baths are to maintain the necessary metal-attacking power at normal temperature, another suitable oxidizing agent, such as sodium nitrite, must be added, from time to time or continuously, in amounts not exceeding of the N0 comprised in the feed salts. The addition of the foregoing amount, which maintains the concentration of the oxidizing nitrites, is an indispensable condition but one should not go above this established limit, if the efficiency of the bath is to be'preserved. Accelerators in the form of copper or nicltel salts may be added to the bath.
The advantages of the present invention in comparison with prior processes will beshown in the following examples which are presented to illustrate the present invention, but not to limit the scope of the appended claims.
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.
After using 1 liter of the bath for phosphate coating 3 sq. meters of soft-iron sheets which, therefore, includes three intermittent regenerations by means of the foregoing feed liquor, the bath must be considered unsuitable for further service since it yields quite poor phosphate coatings.
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.
After 1 liter of the bath has been used for phosphate coating 4 sq. meters of sheets and, therefore, has been regenerated for four times with the foregoing solution, it continues indefinitely to give a protective coating of excellent properties, similar to the coatings applied to the panels constituting the first square meter.
In these two examples, the variations of the concentration of P 0 clue to the coating action and the feeding, are as follows:
In the first example, 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.
in the foregoingexamples, 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.
While in the examples 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.
1 claim:
1. The method of maintaining the efiiciency of phosphat: coating baths used to coat a metallic surface in the cold, 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.
2. The method of claim I, wherein the P O /NO ratio of the feed liquor is adjusted between 120.7 and 120.8.
3. The method of claim 2, wherein said coating bath and said Iced liquor comprise as accelerators small amounts of a salt selected from the group consisting of copper and nickel salts.
4. The process of claim 1 in which the feed liquor comprises zine phosphate and zinc nitrate, the amount of s dium nitrite being about one tenth of the weight of N0 contained in the feed liquor, the i O /NQ, ratio of the initial coating bath being in the ratio range from 1:1 to 1:2.
References Cited in the file of this patent UNITED STATES PATEIJTS

Claims (1)

1. THE METHOD OF MAINTAINING THE EFFICIENCY OF PHOSPHATE COATING BATHS USED TO COAT A METALLIC SURFACE IN THE COLD, 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 P235/NO3 RATIO RANGING FROM ABOUT 1:2.5 TO ABOUT 1:1 BY REPLENISHING THE COATING BATH 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 P2O5/NO3 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 NO3 CONTAINED IN THE FEED LIQUOR.
US578592A 1955-04-20 1956-04-17 Method of maintaining the efficiency of phosphate coating baths used at room temperature Expired - Lifetime US2863793A (en)

Priority Applications (8)

Application Number Priority Date Filing Date Title
IT532546D IT532546A (en) 1955-04-20
NL206455D NL206455A (en) 1955-04-20
US578592A US2863793A (en) 1955-04-20 1956-04-17 Method of maintaining the efficiency of phosphate coating baths used at room temperature
LU34317D LU34317A1 (en) 1955-04-20 1956-04-19 METHOD FOR MAINTAINING THE EFFECTIVENESS OF PHOSPHATING BATHS AT AMBIENT TEMPERATURE
BE547125D BE547125A (en) 1955-04-20 1956-04-19 PROCESS FOR CONSERVING THE EFFICIENCY OF PHOSPHATION BATHS AT ROOM TEMPERATURE
FR1147796D FR1147796A (en) 1955-04-20 1956-04-19 Process for maintaining the efficiency of phosphating baths at room temperature
CH343201D CH343201A (en) 1955-04-20 1956-04-19 Process for maintaining the effectiveness of phosphating baths
DE1959M0030302 DE1069451B (en) 1955-04-20 1959-04-19 METHOD OF SUPPLEMENTING COLD PHOSPHATING BATHS

Applications Claiming Priority (4)

Application Number Priority Date Filing Date Title
US2863793XA 1955-04-20 1955-04-20
IT343201X 1955-04-20
IT1147796X 1955-04-20
US578592A US2863793A (en) 1955-04-20 1956-04-17 Method of maintaining the efficiency of phosphate coating baths used at room temperature

Publications (1)

Publication Number Publication Date
US2863793A true US2863793A (en) 1958-12-09

Family

ID=61187843

Family Applications (1)

Application Number Title Priority Date Filing Date
US578592A Expired - Lifetime US2863793A (en) 1955-04-20 1956-04-17 Method of maintaining the efficiency of phosphate coating baths used at room temperature

Country Status (8)

Country Link
US (1) US2863793A (en)
BE (1) BE547125A (en)
CH (1) CH343201A (en)
DE (1) DE1069451B (en)
FR (1) FR1147796A (en)
IT (1) IT532546A (en)
LU (1) LU34317A1 (en)
NL (1) NL206455A (en)

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3294593A (en) * 1961-12-07 1966-12-27 Hoechst Ag Solution and process for producing a phosphate coating on a metal body
US3516875A (en) * 1966-06-11 1970-06-23 Hooker Chemical Corp Process for coating ferrous surfaces
US3520737A (en) * 1965-12-22 1970-07-14 Amchem Prod Processes for the production of zinc phosphate coatings
US4293349A (en) * 1979-03-16 1981-10-06 Parker Italiana S.A.S. Protective compositions for steel surfaces and the process for their preparation

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2315605A (en) * 1942-06-29 1943-04-06 Hugo J Ehrenfeld Venetian blind structure
DE900163C (en) * 1943-07-01 1953-12-21 Metallgesellschaft Ag Phosphating process
DE900162C (en) * 1943-07-01 1953-12-21 Metallgesellschaft Ag Phosphating process
DE910165C (en) * 1943-01-15 1954-04-29 Hoechst Ag Process for the production of sulphonic acids

Family Cites Families (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE859843C (en) * 1949-02-28 1952-12-15 Metallgesellschaft Ag Process for the phosphating of metals

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2315605A (en) * 1942-06-29 1943-04-06 Hugo J Ehrenfeld Venetian blind structure
DE910165C (en) * 1943-01-15 1954-04-29 Hoechst Ag Process for the production of sulphonic acids
DE900163C (en) * 1943-07-01 1953-12-21 Metallgesellschaft Ag Phosphating process
DE900162C (en) * 1943-07-01 1953-12-21 Metallgesellschaft Ag Phosphating process

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3294593A (en) * 1961-12-07 1966-12-27 Hoechst Ag Solution and process for producing a phosphate coating on a metal body
US3520737A (en) * 1965-12-22 1970-07-14 Amchem Prod Processes for the production of zinc phosphate coatings
US3516875A (en) * 1966-06-11 1970-06-23 Hooker Chemical Corp Process for coating ferrous surfaces
US4293349A (en) * 1979-03-16 1981-10-06 Parker Italiana S.A.S. Protective compositions for steel surfaces and the process for their preparation

Also Published As

Publication number Publication date
DE1069451B (en) 1959-11-19
LU34317A1 (en) 1956-06-19
FR1147796A (en) 1957-11-29
NL206455A (en) 1900-01-01
BE547125A (en) 1956-05-15
IT532546A (en) 1900-01-01
CH343201A (en) 1959-12-15

Similar Documents

Publication Publication Date Title
CA1200470A (en) Low zinc content, replenishment
US4865653A (en) Zinc phosphate coating process
EP0018841B1 (en) Composition and process for zinc-phosphate coating a metal surface, coated metal surface and a process for painting the coated surface
US3090709A (en) Phosphate coating of metals
US2487137A (en) Producing coatings on metal
US4824490A (en) Process of producing phosphate coatings on metals
US2293716A (en) Metal treating solution
JPS5751266A (en) Method and composition for forming phosphate coating
US2702768A (en) Ferrous surface coating process using alkali metal phosphates and hydroxylamines
US2462196A (en) Protective phosphate coatings for metal surfaces
US2375468A (en) Phosphate coating of metals
GB2224516A (en) Phosphate conversion treatment liquid
US2863793A (en) Method of maintaining the efficiency of phosphate coating baths used at room temperature
CN103695881A (en) Normal-temperature sludgeless fast phosphating liquid and preparation method thereof
US2813812A (en) Method for coating iron or zinc with phosphate composition and aqueous solution therefor
US2733199A (en) Electrolytic treatment of metal
Pearlstein et al. Electroless cobalt deposition from acid baths
US3895969A (en) Composition and process for inhibiting corrosion of non-ferrous metal surfaced articles and providing surface for synthetic resin coating compositions
US2835617A (en) Composition and method for coating metallic surfaces
US3755018A (en) Composition and process for inhibiting corrosion of non-ferrous metal surfaced articles and providing receptive surface for synthetic resin coating compositions
US3607453A (en) Metal treating process
US3404046A (en) Chromating of zinc and aluminum and composition therefor
US3161549A (en) Solution for forming zinc phosphate coatings on metallic surfaces
US3127279A (en) Aqueous black coating composition con-
US3632452A (en) Oxalate conversion coating method for stainless steel