US2197611A - Method of producing protective coatings on magnesium and the alloys thereof - Google Patents

Method of producing protective coatings on magnesium and the alloys thereof Download PDF

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Publication number
US2197611A
US2197611A US80908A US8090836A US2197611A US 2197611 A US2197611 A US 2197611A US 80908 A US80908 A US 80908A US 8090836 A US8090836 A US 8090836A US 2197611 A US2197611 A US 2197611A
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United States
Prior art keywords
magnesium
group
protective coatings
alloys
electrolyte
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Expired - Lifetime
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US80908A
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English (en)
Inventor
Fischer Johannes
Richter Werner
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Siemens and Halske AG
Siemens Corp
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Siemens Corp
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Classifications

    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
    • C25D11/00—Electrolytic coating by surface reaction, i.e. forming conversion layers
    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
    • C25D11/00—Electrolytic coating by surface reaction, i.e. forming conversion layers
    • C25D11/02—Anodisation
    • C25D11/30—Anodisation of magnesium or alloys based thereon

Definitions

  • the electrolyte must contain according to the invention at least three components in order to attain satisfactory coatings that may be reproduced at will.
  • the three electrolytic components necessary according to the invention must be taken from the groups of compounds which present a certain chemical affinity with one another.
  • the first group belongs besides the alkali metal hydroxides, which are preferably employed, also the alkaline-earth hydroxides and the aqueous solution of ammonia.
  • the second group comprises water soluble carbonates, silicates and borates; also the salts of the polyboric acids may be employed.
  • the third group in cludes cyanides, thiocyanides and cyanates.
  • sealing means varnish, grease, oil, wax, colloidal hydroxide, silica gel, etc., may be employed.
  • the porosity of the novel layers enables the application of a color which may be desirable for certain purposes.
  • any other filling material solutions may, of course, be utilized for treating the electrolytically prepared objects of magnesium. It should be considered that the porosity of the novel layers decreases with time.
  • the newly produced protective coatings present a considerably-greater adsorptive power with respect to coloring substances of any kind than seasoned protective coatings. This fact renders it possible to regulate the depth of color.
  • coloring substances all organic dye solutions may be utilized as well as colored inorganic substances precipitated in the layer.
  • the voltage is preferably taken as 16 volts.
  • good results may also be attained with a gradual change in voltage.
  • a coating was produced at a voltage of 16 volts and then the coating was strengthened at or 110 volts.
  • the strengthening of the coating is possible owing to the greater residual current resulting from the higher voltages.
  • gradualy increasing voltages may under certain circumstances be employed; for instance, by gradually increasing the voltage from 1 volt to 60 or 110 volts, While maintaining the intensity of the current constant.
  • the temperature during the treatment is preferably chosen between 20 and 25 centigrade, since at a higher temperature a pitting occurs, It is, therefore, necessary to cool the object to be treated during the passage of the current. At temperatures which lie considerably below 20 the current is blocked too quickly so that the formation of a good thick absorbing layer is prevented. This phenomenon is due to the fact that the residual current at low temperatures becomes considerably weaker. The .current density decreases by suddenly during the first seconds of the treating period. It is kept at this .low value preferably for 60 minutes.
  • the electrolytical process may be considered as terminated.
  • the objects are then treated with the dye solution and finally they are sealed; forlnstance,
  • This fourth group of substances includes the water soluble sulphates, nitrates, phosphates, halogenides, halogenates, fiuosilicates, chromates,-tungstates, etc.
  • concentration to be used a great advantage is obtained from the industrial point of view, since the so-called degreasing baths for electroplating obtainable on the market present the desired concentration for the novel method.
  • Soda for instance, may be used with success in a 5% solution, pure caustic soda in a 6% solution of NaOH and potassium cyanide in a 2% solution of KCN.
  • the cations, panticularly the alkalies, may be replaced by one another or uniformly chosen from all three groups; only ammonium forms an exception, since a very bad coating was attained in connection with ammonium compounds.
  • Example 1 In an aqueous electrolyte containing 5% of NaOH, 5% of NazCOs, 2% of KCN and 0.1% of Na2WO4 a sheet metal consisting of an alloy of magnesium was subjected anodically at a temperature of 20 C. to the action of the current. At a voltage of 16 volt a current density of 5 amp./dm. was attained in the first moment and this decreased to 1 amp./dm. within the following 30 seconds. The current treatment lasted an hour. The sheet metal provided with the fresh layer was dipped" into a dye solution and then coated and varnished. The layer thus produced was extremely tight and uniformly colored.
  • Example 2 Instead of the sodium tungstate employed in Example 1 as electrolytic admixture, potassium iodide, potassium chromate, sodium chloride, potassium chlorate, potassium nitrate, sodium silicate and sodium sulphate were alternately used in succession as electrolytic admixture at a concentration of 0.1%. Particularly good absorbing layers were obtained when admixing potassium iodide, potassium chlorate and potassium nitrate. Experiments have shown that an admixture of potassium iodide and sodium silicate caused a pitting at the surface of -the liquid. Inthe last-mentioned'example a relatively slight porosity of the coating resulted.
  • Example 3 The method according to the invention was carried out without admixing a substance of the fourth group.
  • 5% of NaZCOa instead of 5% of NaZCOa, 5% of borax (NazBiov) or 5% of water glass (NazSiOa) was used.
  • the electrolyte consisting of potash lye, soda and potassium cyanide gave without any admixture excellent results which, however, could be further improved by substituting borax for soda; that is to say-the porosity of the coating is improved.
  • borax for soda
  • Example 4 Provided in an electrolyte which contained 2% of KCNS and 2% of KCNO instead of 2% of KCN. In the first case a very hard coating which was substantially free of pores was produced, whereas when using 'KCNO as electrolytic component a good average result was obtained.
  • Example 5 Finally the same cation was employed forall components. An experiment was carried out with 5% of KOH, 5% of K2CO3, 2% of KCN a d'0.1% of K2804. The absorptive power of he layer thus produced was above average.
  • the method of producing non-metallic protective coatings on magnesium which comprises anodically treating the magnesium in an aqueous solution of a mixture consisting substantially of hydroxide selected from the group consisting of alkali metal hydroxides, alkaline earth hydroxides and aqueous ammonia, and salt selected from the group consisting of water soluble carbonates, silicates and borates, and salt selected from the group consisting of the simple cyanides, thiocyanides and cyanates of the alkali metals.
  • the method of producing non-metallic protective coatings on magnesium which comprises anodically treating the magnesium at between 1 and volts at a temperature of about 20 to 25 C. in an aqueous solution of a mixture consisting substantially of hydroxide selected from the group consisting of alkali metal hydroxides, al-
  • salt selected from the group consisting of water soluble carbonates, silicates and borates, and salt'selected from the group consisting of the simple cyanides, thiocyanides and cyanates of the alkali metals.
  • the method of producing non-metallic protective coatings on magnesium which comprises anodically treating the'magnesium at about 16 volts in an aqueous solution of a mixture consisting substantially of hydroxide selected from the group consisting of alkali metal hydroxides, alkaline earth hydroxides and aqueous ammonia, and salt selected from the group consisting of water soluble carbonates, silicates and borates,
  • the method of producing non-metallic protectivecoatings on magnesium which comprises anodically treating the magnesium at a voltage increasing from less than 16 volts to at least about 60 volts in an aqueous solution of a mixture consisting substantially of hydroxide selected from the group consisting of alkali metal hydroxides, alkaline earth hydroxides and aqueous ammonia, and salt selected from the group consisting of water soluble carbonates, silicates and borates, and salt selected from the group consisting of the simple cyanides, thiocyanides and cyanates of the alkali metals.
  • the method of producing non-metallic pro- 15 aroma a 3 tective coatings on magnesium which comprises anodically treating the magnesium in an aqueous solution of a mixture consisting substantially of hydroxide selected from the group consisting of I alkali metal hydroxides, alkaline earth hydroxides and aqueous ammonia, salt selected from the group consisting of water soluble carbonates,
  • silicates and borates selected from the group consisting of thesimple cyanides, thiocyanides highly dissociated acid, the concentration of said 5 latter ingredient being lower than that of said three groups.

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Chemical Treatment Of Metals (AREA)
  • Other Surface Treatments For Metallic Materials (AREA)
US80908A 1935-06-01 1936-05-20 Method of producing protective coatings on magnesium and the alloys thereof Expired - Lifetime US2197611A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
DE459017X 1935-06-01

Publications (1)

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US2197611A true US2197611A (en) 1940-04-16

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US80908A Expired - Lifetime US2197611A (en) 1935-06-01 1936-05-20 Method of producing protective coatings on magnesium and the alloys thereof

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US (1) US2197611A (en(2012))
BE (1) BE415398A (en(2012))
FR (1) FR808289A (en(2012))
GB (1) GB459017A (en(2012))

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2426254A (en) * 1943-04-23 1947-08-26 Turco Products Inc Anodic treatment of magnesium and its alloys to form protective coatings thereon

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2512563A (en) * 1946-11-09 1950-06-20 Dow Chemical Co Method of electrolytically coating magnesium and its alloys

Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2426254A (en) * 1943-04-23 1947-08-26 Turco Products Inc Anodic treatment of magnesium and its alloys to form protective coatings thereon

Also Published As

Publication number Publication date
GB459017A (en) 1936-12-31
BE415398A (en(2012))
FR808289A (fr) 1937-02-02

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