Classifications

• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D3/00—Electroplating: Baths therefor
  • C25D3/02—Electroplating: Baths therefor from solutions
  • C25D3/04—Electroplating: Baths therefor from solutions of chromium
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D3/00—Electroplating: Baths therefor
  • C25D3/02—Electroplating: Baths therefor from solutions
  • C25D3/56—Electroplating: Baths therefor from solutions of alloys
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D3/00—Electroplating: Baths therefor
  • C25D3/02—Electroplating: Baths therefor from solutions
  • C25D3/04—Electroplating: Baths therefor from solutions of chromium
  • C25D3/10—Electroplating: Baths therefor from solutions of chromium characterised by the organic bath constituents used

Definitions

• chromium for surface finishing has long been used in the industry.
• the range of application extends from thin layers for decorative purposes to the formation of hard chrome layers.
• high hardness and wear resistance, resistance to chemical influences, corrosion resistance and high temperature resistance are desirable advantages.
• metallic coatings serve, in particular, the functional coating of workpieces in order to take into account the stress mechanisms occurring during normal use by suitable surface properties, such as, for example, hardness, wear resistance, corrosion resistance, friction properties or thermal and chemical resistance. These properties can be influenced in particular by the use of alloys of defined composition. Furthermore, the electrolytes used often contain special additives which additionally influence the properties of the coatings.
• the present invention is therefore based on the object to provide a method for producing an alloy, which overcomes the disadvantages known in the prior art and ensures the production of a layer which is characterized by a compared to the pure Chromium layers higher corrosion and especially chloride resistance is characterized, and overall has a high gloss and shows an increased crack density for advantageous influence on the corrosion resistance. Furthermore, the method should ensure high current yields. Furthermore, to be proposed with the invention, an electrolyte for carrying out the method.
• a chromium alloy from an electrolyte which, in addition to chromic and sulfuric acid, also contains an isopolyanion-forming metal, e.g. Molybdenum, vanadium, tungsten or niobium.
• Molybdenum which is added to the electrolyte in the form of molybdic acid or of molybdenum salts, has proved to be particularly advantageous.
• the method according to the invention makes it possible, with a low level of analytical process controls, to guarantee the production of a technically usable layer of constant composition, which has the advantageous chromium-molybdenum alloy properties and is distinguished by a decorative gloss and a smooth surface.
• the combined addition of an organic compound with an isopolyanion-forming element therefore surprisingly leads to an improved chromium alloy deposition.
• the organic compound not only affects the current efficiency, but also has a direct, advantageous effect on the formation of the alloy, which manifests itself in particular in the gloss and not least in the constant composition of the layer formed according to the invention.
• the layer formed according to the invention has further advantageous properties which distinguish it from both the pure chromium coatings and the chromium-molybdenum alloys known in the prior art.
• the method according to the invention therefore makes it possible to use the matt and gray chromium-molybdenum alloys, which are otherwise too heavily influenced by the working conditions. This is also an advantage over pure chrome coatings, which also have a high sensitivity to the deposition conditions.
• the method according to the invention is particularly economical, since the product quality has a higher consistency and thus produces a small amount of waste. Further advantageous properties of the deposited with the method according to the invention layer are mentioned below.
• the use of in the DE 34 02 554 proved organic compounds. These compounds are added as catalysts - in addition to sulfuric acid and / or optionally fluorides. Compared to the fluorides or the complex fluorides short-chain sulfonic acids have the advantage that, for example, steel is not attacked as the base material. Particularly advantageous is the use of saturated aliphatic sulfonic acids having a maximum of two carbon atoms and a maximum of six sulfonic acid groups or their salts or halogen derivatives.
• the method according to the invention therefore for the first time offers the possibility of producing chromium-molybdenum alloys of low cost, which have many advantageous properties of pure chromium layers, as well as having additional properties favored by the alloy, resulting in a total of a lustrous layer which is superior in many respects to both the pure chromium layers and the known chromium-molybdenum layers.
• Chromium-molybdenum layers deposited from a sulfuric acid electrolyte have wide cracks at low cracking density, which can range from the surface to the base material, which deteriorates the corrosion resistance.
• the inventive method overcomes this disadvantage by adding an organic compound, in particular by adding a sulfonic acid, as this significantly increases the crack density.
• the cracks of the deposited with the method according to the invention layers are therefore very fine and no longer reach the base material. This greatly affects the corrosion resistance and causes a clear advantage of the deposited with the inventive method layers over the known chromium-molybdenum layers.
• pure chromium coatings permit significantly higher anodic currents than the coating of chromium, molybdenum and a short-chain aliphatic sulfonic acid produced by the process according to the invention. It has also been found that when molybdenum compounds are used together with organic compounds, layers are deposited which have significantly lower anodic corrosion currents compared to the pure chromium layers. This shows that the layers deposited according to the invention have a significantly higher corrosion resistance than pure hard chrome layers. This marked difference also results in a better chemical resistance of the layer produced by the process according to the invention to chlorides. Furthermore, the layers deposited by the method according to the invention are advantageously characterized by high hardness and high abrasion resistance. The hardness of the coating produced by the process according to the invention is in the range of hard chrome coatings.
• molybdic acid may be added to the electrolyte in an amount of 10 g / l up to the limit of solubility.
• the addition of 50-70 g / l molybdic acid has proven to be particularly advantageous.
• the electrolyte contains chromic acid in an amount of 100 g / L to 400 g / L depending on the desired incorporation rate.
• the electrolyte has catalysing sulfuric acid in a quantity range of 1 g / l to 6 g / l, but preferably it contains 2 g / l.
• the organic compound is added to the electrolyte at a concentration of more than 0.1 g / l, and has proved to be particularly advantageous in an amount of 2 g / l.
• halides preferably complex halides, may be added to the electrolyte.
• the method according to the invention enables the operating parameters of electrolyte composition, electrolyte temperature and / or current density to be set as a function of the desired molybdenum incorporation rate.
• a coating according to the invention can be provided specifically.
• the electrolytically deposited chromium-molybdenum alloy layers have a molybdenum incorporation rate between 0.1% by weight and 10% by weight. It was found that optimized deposition results can be achieved when chromium and Sulfuric acid in a ratio of about 100: 1 and chromic and molybdic acid in a ratio of about 3: 1 to 4: 1 are contained in the electrolyte.
• the electrolyte is connected to an external power source.
• the method according to the invention allows a wide current density working range, while ensuring a very shining layer deposition.
• an energization with a current density in the range of 5 A / dm 2 to at least 200 A / dm 2 are performed so that a high-speed chrome plating is easily possible.
• the method according to the invention enables a securely adhering, corrosion-resistant and glossy layer to be deposited at a high cathodic current yield.
• a cathodic current yield of not less than 15%, preferably more than 20%.
• a coating has proven to be advantageous, which is formed according to the invention at a current density operating range of 20-50 A / dm 2 with very bright deposition and a molybdenum incorporation rate of 1%.
• an element of the VI main group selected according to the invention will be added to the electrolyte.
• this additive may be added as a salt or as mixtures thereof.
• a salt e.g. Sulphates, halides, carbonates, chromates, dichromates, oxides, hydroxides, acetates, sulfonates and compounds in which the element is present as an anion referred to.
• the amount of additive is in a range of 0.25 mmol to 2.5 mol / l, but preferably less than or equal to 0.1 mol / l.
• the addition of selenium or tellurium has proved particularly advantageous.
• the addition of selenium or tellurium as elements selected according to the invention for the process according to the invention advantageously affects the crack density.
• the following embodiment shows a base electrolyte, which differs from the electrolyte according to the invention by the absence of selenium and tellurium.
• This embodiment is illustrative and not limiting.
• the amounts of individual catalysts to be added may vary and depend on the bath composition and deposition conditions.
• all materials, in particular metallic can be coated with a chromium-molybdenum alloy which is distinguished in particular by its smooth, shiny appearance compared to conventional chromium-molybdenum alloys, as well as pure chromium layers by their better corrosion resistance, in particular their chemical resistance towards chlorides, as well as further highlighted by their little susceptible to interference deposition. Furthermore, the inventive method ensures constant working conditions and high current efficiency.

Landscapes

• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Electrochemistry (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Electroplating And Plating Baths Therefor (AREA)
• Removal Of Specific Substances (AREA)
• Electrolytic Production Of Non-Metals, Compounds, Apparatuses Therefor (AREA)
• Electrolytic Production Of Metals (AREA)

Priority Applications (13)

Applications Claiming Priority (1)

Publications (2)

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• 2000
  • 2000-11-11 ES ES00124672T patent/ES2310985T3/es not_active Expired - Lifetime
  • 2000-11-11 DE DE50015318T patent/DE50015318D1/de not_active Expired - Lifetime
  • 2000-11-11 AT AT00124672T patent/ATE405694T1/de active
  • 2000-11-11 DK DK00124672T patent/DK1205582T3/da active
  • 2000-11-11 EP EP00124672A patent/EP1205582B1/de not_active Expired - Lifetime
• 2001
  • 2001-11-03 CN CNB018036236A patent/CN1306069C/zh not_active Expired - Fee Related
  • 2001-11-03 CA CA002396946A patent/CA2396946C/en not_active Expired - Fee Related
  • 2001-11-03 WO PCT/EP2001/012747 patent/WO2002038835A1/de active IP Right Grant
  • 2001-11-03 EP EP01980543A patent/EP1250472A1/de not_active Withdrawn
  • 2001-11-03 KR KR10-2002-7008837A patent/KR100503210B1/ko active IP Right Grant
  • 2001-11-03 BR BR0107473-3A patent/BR0107473A/pt not_active Application Discontinuation
  • 2001-11-03 US US10/169,959 patent/US6837981B2/en not_active Expired - Lifetime
  • 2001-11-03 JP JP2002541146A patent/JP3873025B2/ja not_active Expired - Fee Related

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