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
  • C25D11/02—Anodisation
  • C25D11/026—Anodisation with spark discharge
• • 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
  • C25D11/04—Anodisation of aluminium or alloys based thereon
• • 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
  • C25D11/04—Anodisation of aluminium or alloys based thereon
  • C25D11/14—Producing integrally coloured layers

Definitions

• the invention relates to electrolytes for producing uniformly thin, matte black conversion layers as functional surfaces of components or groups made of light metal materials or their alloys by the process of anodic oxidation with spark discharge (ANOF).
• ANOF anodic oxidation with spark discharge
• they represent a coating variant especially for complex shaped construction parts or groups and are therefore particularly suitable for use in optical precision device construction.
• a number of electrolytes for producing conversion layers by means of the ANOF process on lightweight materials, especially on valve metals such as Ti, Ta, Zr, Nb or AI, are known from the specialist and patent literature (see PS-DD 229 163, PS-DD 236 978 , PS-DD 142 360, PS-EP 0 280 886).
• electrolytes are used which mainly contain subgroup elements which are bound as hydroxo, amino or complexone complexes.
• PS-DD 229 163 describes electrolyte solutions for producing black or gray-black conversion layers on light metals, such as Al.
• electrolyte solutions mainly contain fluorides as NaF or NH4F, dihydrogen phosphates as NaH2PO4, tetraborates as Borax Na2B4O7 and chromates as well as other foreign additives.
• fluorides as NaF or NH4F
• dihydrogen phosphates as NaH2PO4
• tetraborates as Borax Na2B4O7
• chromates as well as other foreign additives.
• the disadvantage here is that the use of fluorides necessitates special work, environmental protection and disposal measures.
• the PS-DD 257 275 refers to decorative coatings, inter alia, on titanium materials which are produced by means of the ANOF process and an electrolyte consisting of NaF, NaH2PO4, Na2B4O7 and potassium hexacyanoferrate-K4 [Fe [CN] 6] are produced.
• this solution contains the great problems of health and environmental protection due to the toxic cyanide-containing electrolyte.
• the black color is achieved only through the use of hexacyanoferrate, which, like the black iron-aluminum spinel, forms a tita spinel and only serves decorative purposes.
• PS-DD 236 978 describes solar-selective absorption layers which consist of dark-colored, chromadotized oxide layers on valve metals such as Ti, Ta, Zr, Nb, Al and which are also produced by means of an electrolyte containing fluoride and dihydrogen phosphate, tetraborate and chromate in the ANOF process .
• These electrolytes also have the already mentioned disadvantage of fluoride content and the layers obtained with them also have such a rough surface structure effect that when used, for example as a functional surface for complexly shaped structural parts or assemblies, there is such abrasion that dimensional accuracy is no longer guaranteed .
• these layers have a high ABsorption capacity ⁇ , they also record multiple reflections of the incident radiation due to the rough surface structure effect, which emits its energy in the form of heat to the absorption layer and transfers it to the collector body. In relation to the optical absorption ⁇ , a very low thermal emission ⁇ is achieved.
• the aim of the invention is to provide an easy-to-use electrolyte for the production of uniformly thin, matte black conversion layers as functional surfaces of components or groups, which open up a large amount of constructive freedom even in the case of complicatedly shaped structural parts or groups.
• the invention has for its object to develop a low-pollutant, environmentally friendly electrolyte that enables the production of optically black layers with a layer thickness ⁇ 10 microns and almost the same optical absorption and thermal emissivity using the ANOF process.
• the object is achieved by an electrolyte for producing thin black conversion layers on light metals or their alloys by means of anodic oxidation with spark discharge in that the electrolyte consists of an aqueous solution which contains potassium dihydrogen phosphate, potassium chromate, acetates, ammonium citrate and ethylenediamine.
• mol / l potassium dihydrogen phosphate 0.03 to 0.08 mol / l potassium chromate; Acetations in concentrations from 0.08 to 0.5 mol / l; 0.1 to 0.3 mol / l ammonium citrate and 0.5 to 0.9 mol / l ethylenediamine mixed to form an aqueous solution.
• An advantageous embodiment of the solution consists in that the ions of the copper acetate are used as acetations.
• An essential result of the use of the electrolyte according to the invention is that it can be used to produce the thin black conversion layers by the light metal or its alloys using plasma-chemical anodic oxidation in an aqueous electrolyte at a current density of 0.005 to 0.05 A. cm ⁇ 2 and a voltage of 100 - 200 V is coated.
• a degreased and alkaline pickled sheet made of AlMg 5 was also made using plasma-chemical anodic oxidation with spark discharge in an already known aqueous electrolyte, consisting of a 4.5% by volume ammoniacal solution with 0.5 mol / l KH2PO4; 0.1 mol / l K2crO4 and 0.35 mol / l Cu [CH3COO] 2 at a current density of 0.045 A. cm ⁇ 2 coated.
• a deep black colored conversion layer is also obtained in the one-step process.
• the new electrolyte gives a conversion layer of approximately 4 ⁇ m in thickness. It is therefore about 30% of the layer thickness of conventional black ANOF layers. This is particularly advantageous for constructive solutions in which coatings have to be applied without changing the fit tolerances. Even thread fits up to H6 tolerances are manageable. The release of particles when fitting parts is minimized. The good spreading capacity of cylindrical parts up to an inner diameter / length ratio of 1:10.
• the reflectance at 540 nm is 6% and is therefore comparable to conventional black ANOF layers.
• the roughness number is 1.6 ⁇ m, while for conventional black ANOF layers it is 5.4 ⁇ m - with the same initial roughness of 0.7 ⁇ m.
• the layers obtained therefore have a lower particle generation and are therefore suitable as a coating variant for complexly shaped construction parts or assemblies with higher requirements for their dimensional accuracy.
• the dielectric strength test is to be understood here as a laboratory method for determining the current / voltage curve up to the breakdown of the layer under high vacuum conditions (10 ⁇ 2Pa). The results obtained show that the dielectric strength is maintained or even increases slightly as the layer thickness decreases due to the specific morphology of the layer. However, it would have been assumed that the dielectric strength of layers of chemically similar composition decreases with decreasing layer thickness (see Kahle, M.-Elektro Isoliertechnik, VEB Verlagtechnik, Berlin, 1988).

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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)
• Application Of Or Painting With Fluid Materials (AREA)

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• 1990
  • 1990-06-14 DD DD34163790A patent/DD295198B5/de not_active IP Right Cessation
• 1991
  • 1991-04-25 US US07/691,629 patent/US5094727A/en not_active Expired - Lifetime
  • 1991-06-13 EP EP91810453A patent/EP0462073B1/fr not_active Expired - Lifetime

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