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
  • C23C22/47—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 containing also phosphates
• • 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

• the present invention relates to a process for producing surface layers on iron and steel articles.
• the objective .of my present invention is to produce a strongly acid aqueous solution suitable for producing surface layers on iron and steel articles.
• This solution contains one or several alkali metal chlorates, oxalic acid radicals and phosphoric acid radicals, and as cations potassium, sodium and ammonium.
• alkali metal chlorates there come into consideration, for instance, potassium chlorate or sodium chlorate.
• phosphoric acid radicals comprises the radicals of all the acids which may be obtained by hydration of phosphorus pentoxide such as, for instance, meta-phosphoric, orthophosphoric, pyro-phosphoric, tripoly-phosphoric, tetrapoly-phosphoric acid and other poly-phosphoric acids.
• the treating solution contains potassium, sodium or ammonium in the form of cations.
• the oxalic acid and/ or phosphoric acid radicals may be present in the solution in the form of oxalic acid or of one of the phosphoric acids mentioned above. When such acids are present in the solution, it contains as cations potassium or sodium, e. g. in a quantity corresponding to that of the alkali metal chlorate. Moreover, it is also possible further to add to the solution alkali metal or ammonium radicals in the form of their soluble salts as, for instance, their chlorides and sulfates.
• the oxalic acid and/or phosphoric acid radicals may also, either totally or partially, be present in the form of potassium, sodium or ammonium salts of the above named oxalic and/or phosphoric acid. Oxalic acid radicals in the form of oxalic acid may, ofcourse, likewise be present in addition to phosphoric acid radicals in the form of alkalic metal or ammonium salts of the above named phosphoric acids or vice versa.
• the strongly acid solutions have a pH-value ranging from about 1.0 to about 2.5. It is of particular advantage to use solutions having a pH-value from between 1.5 and 2.0. By an appropriate selection of the acid ingredients and the quantity of said ingredients contained in the treating solution, the latter may be adjusted to the desired pH-value.
• a treating solution which contains, at the beginning of the treatment, per 1 mol of oxalic acid radical about 1 atom of the cation, e. g. sodium, potassium or ammonium.
• the oxalic acid radical is used up by the reactions occurring during the treatment; thereby the proportion of alkali radical to oxalic radical is altered in favor of the alkali radical. It is of importance that the cations sodium, potassium 2,832,707 Patented Apr.
• the solution When repeatedly used, the solution shows a certain reduction of its ingredients since they have been used up for the production of the surface layer. For this reason the used up substances are replaced at a rate corresponding to their consumption by introducing solutions containing the corresponding ingredients into the original solution.
• the treatment according to the invention may be carried through as follows: the article to be treated, either made of iron, steel or alloy steel, as for instance sheet iron, is dipped into the solution. During this dipping process the bath liquid may be agitated by means of mechanical devices or by blowing in air or other gas.
• the treatment may also be carried out in a stationary bath by moving the articles to be coated. As articles to be treated there come into consideration, in addition to sheet iron, for instance, small working pieces such as screws, bolts, etc. They are most advantageously treated by placing them into a perforated drum which slowly rotates in the bath (rotation rate about /2 to 2 per minute).
• Bulky and large pieces are treated by placing them into Wire baskets and dipping the latter into the treating solution or by fixing the articles to wire and dipping them into the bath liquid.
• the treatment may also be effected by spraying the solution by means of nozzles on the surface of the articles, it being of advantage that in the absence of sludge formation clogging of the nozzles is avoided. It is understood that automatic sprayers may be applied.
• a surface layer containing iron oxalate, in addition to iron phosphate is produced on iron and steel articles.
• the layers so obtained have a fine crystalline structure and a grey to black coloration; they mayalso' be produced in the form of very thin layers having a thickness of about 1 1 to about 2,1.
• This is of special advantage for layers which are needed for small articles as they are used in the construction of typewriters or telephone apparatus.
• the surface layers according to the invention are of adavntage if the treated articles are exposed to bending stress or when, in additionto improving the corrosion resistance, special importanceis attached to facilitating the application of color or lacquer coatings.
• Surface layers according to the invention can be produced at room temperature, i. e. at temperatures ranging from 15 C. to 20 C.
• the process can also be effected at elevated temperatures up to about 50 C.
• the proportion of the concentrations of the compounds contained in the solutions may vary within wide limits.
• the proportion of oxalic acid radical to phosphoric acid radical may vary within the limits of about 1:3 and about 221, that of oxalic acid radical to chlorate radical within thelimits of about 1:1 and about 3:1, and that of phosphoric acid radical to chlorate radical within the limits of about 4:1 and about 1:2.
• the process according to the invention may be applied on iron and any kind of non-alloyed steel; however, alloy steels having minor proportions of other elements, e. g. proportions of up to about 3 percent, may also come into consideration.
• alloy steels having minor proportions of other elements e. g. proportions of up to about 3 percent
• the time of reaction during which the articles to be treated are subjected to the action of thesolution depends on the composition of the iron or steel, the nature of the surface, and the purpose which the treated workingpiece shall serve. As a rule the articles need only be treated for a short time until the reaction is complete. The treatment is finished as soon as a noticeable layer having the desired thickness has been formed. Quite generally, it is suflicient, when operating at a temperature of between about 15 C. and 20 C., to treat the surfaces for several minutes, i. e. l-5 minutes. An increase ofthe temperature does not require a substantial alteration of the treating period.
• alloy steels having minor proportions of up to about 3 percent of other elements it may be necessary to pro long the time of treatment, for instance, to about to about minutes.
• the degreasing may be accomplished with known agents, for instance, with agents containing meta-silicate, carbon tetrachloride, trichlor-ethylene, etc.
• the articles may be after-treated by thoroughly rinsing them with water in order to remove adhering ingredients of the bath; thereupon the articles may be dried by means of hot air.
• solutions which also contain both oxalic acid and alkali metal or arm monium oxalate these two substances together being present within the limits of about 5 to about 25 grams per liter of solution.
• solutions which also contain both ortho-phosphoric or pyro-phosphoric or metaphosphoric or tripoly-phosphoric or tetrapoly-phosphoric acid and alkali metal or primary ammonium ortho-phosphates or pyro-phosphates or meta-phosphates or tripolyphosphates or tetrapoly-phosphates in a total concentration of about 5 to about 60 grams per liter may likewise be used.
• An especially advantageous solution contains, per liter of solution, for instance, 7-15 grams of sodium or potassium chlorate, 5-60 grams of sodium or potassium tripoly-phosphate and 5-25 grams of oxalic acid.
• the substances used for the preparation of this solution are solid products, thus simplifying the manipulation of the ingredients.
• a further possibility consists in using solutions which, at first, have a low content of alkali metal chlorate.
• alkali metal chlorate as a solid product or in the form of an aqueous suspension is introduced into the solution, continuously or discontinuously, at a rate corresponding to its consumption.
• the alkali metal chlorate contained in the starting solution may thus be decreased to a content of about 1 to about 2 grams per liter of solution.
• alkalitripoly-phosphate or alkali tetrapoly-phosphate is present in the treating solution, an addition of sulfuric acid is unnecessary since, as a rule, these poly-phosphates prevent the precipitation of calcium.
• the single components may be dissolved in water and added separately in the desired quantities.
• the components required for the preparation of the bath may be chosen so that all the substances are present in the-solid form.
• these granular or powdery substances separately, one package containing alkali metal chlorate, for instance sodium chlorate, and alkali tripoly-phosphate, for instance sodium tripoly-phosphate, and the other package containing oxalic acid.
• alkali metal chlorate for instance sodium chlorate
• alkali tripoly-phosphate for instance sodium tripoly-phosphate
• oxalic acid oxalic acid
• Other solid substances suitable for the process of the present invention may also .be packed.
• the packages contain the substances in such quantities that, when they are dissolved in water, they are present in the proportion required for-the solution of this invention, i. e., a solution is obtained at the desired pH-value.
• the solid substances may be despatched in iron or wooden drums.
• the process of producing surface layers on metal according to the present invention constitutes a great improvement over the hitherto known processes because-it is possible now to prepare the bath solution from solid substances.
• Example 1 '1 liter of a solution according to the invention is prepared for the treating bath.
• a sheet iron of non-alloyed steel having a surface of cm? is cleaned in the usual manner and degreased with an agent containing sodium meta-silicate and then brought "into 1 liter of this solution. Duration of treatment: '3 minutes. Temperature of the bath: 20 C.
• the treatment is complete, i. e. as soon as the surface 'layer'has been formed, the sheet iron is removed from the bath, thoroughly rinsed with water in order to remove the adhering ingredients of the bath, and dried with hot air.
• the thickness of this Iayer is 2a.
• the layerhaving a fine crystalline structure consists of equally formed crystals.
• Example 2 1 liter of a solution according to the invention is prepared for the treating bath. The solution obtained contains per liter 10.0 grams of oxalic acid. 7
• a sheet iron having a surface of 100 cm. is cleaned in the usual manner and degreased with an agent containing' sodium meta-silicate. 1 liter of the aforementioned solution is used for spraying (by means of a nozzle) said sheet iron. Duration of treatment: 2 minutes. Temperature of the bath: 20 C. When the treatment is complete, i. e. as soon as the surface layer has been formed, the sheet iron is thoroughly rinsed with water in order to remove the adhering ingredients of the bath, and dried with hot air. A black layer is obtained having a thickness of l-Z and a fine crystalline structure consisting of equally formed crystals.
• Example 3 1 liter of a solution according to the invention is prepared for the treating bath.
• the solution obtained contains per liter 15.0 grams of oxalic acid 10.0 grams of sodium chlorate 10.0 grams of sodium tripoly-phosphate and has a pH-value of 1.6.
• a sheet iron of non-alloyed steel having a surface of 100 cm. is cleaned and degreased with trichlor-ethylene and then treated in 1 liter of this solution.
• the sheet iron is brought into the solution and part of the solution is removed by pumping, i. e. the solution is filtered off with suction at one place and reintroduced into the bath at another place, so that the solution is constantly agitated. Duration of treatment: 2 minutes. Temperature of the bath: 22 C.
• the sheet iron is removed from the bath, thoroughly rinsed with water in order to remove the adhering ingredients of the bath, and dried with hot air.
• a dark grey layer is obtained having a thickness of 1 /22 and a fine crystalline structure of equally formed crystals.
• Example 4 1 liter of a solution according to the invention is prepared for the treating bath.
• the solution obtained contains per liter 22.7 grams of oxalic acid 7.2 grams of potassium chlorate 10.0 grams of sodium tripoly-phosphate 8.4 grams ofortho-phosphoric acid calculated as H PO of pH-value of 1.0.
• a sheet iron of alloyed steel having a surface of 100 cm. and a content of nickel of 0.3 percent is cleaned in the usual manner and degreased with carbon tetrachloride and then treated with this solution.
• the treatment is effected by immersing the sheet iron for 5 minutes in the bath solution having a temperature of 24 C.
• the sheet iron is removed from the bath, thoroughly rinsed with water in order to remove the adhering ingredients of the bath, and dried with hot air.
• a grey layer is obtained having a thickness of 1 and a fine crystalline structure consisting of equally formed crystals.
• Example 5 100 percent strength and has a Example 5 1 liter of a solution according to the invention is prepared for the treating bath.
• the solution obtained contains per liter 10.0 grams of oxalic acid 12.5 grams of sodium chlorate 7.5 grams ofortho-phosphoric acid calculated as H PO of 100 percent strength, and has a pH-value of 1.0.
• a sheet iron having a surface of 100 cm. is cleaned in the usual manner and degreased with trichlor-ethylene and then immersed in '1 liter of this solution. Duration of treatment: 2. minutes. Temperature of the bath: 18 C. When the treatment is completed. e. as soon as the surface layer has been formed,- the'sheet iron is removed from thebath, thoroughly rinsed with water in order to remove the adhering ingredients of the bath, and dried with hot air. A grey layer is obtained having a thickness of 1.5; and a fine crystalline structure of equally formed crystals.
• Example 6 1 liter of a solution according to the invention is prepared for the treating bath.
• the solution obtained contains per liter 10.0 grams of oxalic acid 7.2 grams of sodium chlorate 20.0 grams of primary ammonium phosphate and has a pH-value of 2.0.
• a sheet iron having a surface of 100 cm. is cleaned in the usual manner and degreased with an agent containing sodium meta-silicate and then immersed in 1 liter of this solution. Duration of treatment: 5 minutes. Temperature of the bath: 20 C. When the treatment is complete, i. e. as soon as the surface layer has been formed, the sheet iron is removed from the bath, thoroughly rinsed with water in order to remove the adhering ingredients of the bath, and dried with hot air. A dark grey layer is obtained having a thickness of 1-2p. and a fine crystalline structure consisting of equally formed crystals.
• a process for producing surface layers on iron and steel articles in a strongly acid bath which comprises exposing the surface of such article at a temperature ranging between about 15 C. and about 50 C. to the reaction of an aqueous solution having a pH of from about 1.0 to about 2.5 and containing per liter of solution (a) an alkalimetal chlorate in a concentration of from about 7 to about 15 grams, (b) a substance selected from the group consisting of oxalic acid, alkali metal oxalates, and ammonium oxalate, in a concentration of from about 5 to about 25 grams; and (c) a compound selected from the group consisting of meta-phosphoric, ortho-phosphoric, pyro-phoshoric, and poly-phosphoric acids, and the alkali metal and primary ammonium salts thereof in a concentration of from about 5 to about 60 grams.
• a process for producing surface layers on iron and steel articles in a strongly acid bath which comprises exposing the surface of such article at a temperature ranging between about 15 C. and about 50 C. to the reaction of an aqueous solution having a pH of from about 1.0 to about 2.5 and containing per liter of solution from about 7 to 15 grams of an alkali metal chlorate, 5 to 60 grams of alkali metal tripoly-phosphate, and to 25 grams of oxalic acid.

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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)

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Citations (5)

• 0
  • BE BE536618D patent/BE536618A/xx unknown
  • NL NL105857D patent/NL105857C/xx active
• 1954
  • 1954-03-19 US US417515A patent/US2832707A/en not_active Expired - Lifetime
• 1955
  • 1955-03-16 CH CH335916D patent/CH335916A/de unknown
  • 1955-03-18 FR FR1120983D patent/FR1120983A/fr not_active Expired
  • 1955-03-18 GB GB8030/55A patent/GB810546A/en not_active Expired

Patent Citations (5)

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