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
  • C25D3/22—Electroplating: Baths therefor from solutions of zinc

Definitions

• gelatin 3,4-methylene-dioxy-benzaldehyde (piperonal), 4- hydroxy-3-methoxy-benzaldehyde (vanillin), 3,4-dimethoxybenzaldehyde (veratraldehyde), protein decomposition products, and the like.
• the metal to be zinc plated Prior to the electro zinc plating process taking place, the metal to be zinc plated is usually subjected to such pretreatments as degreasing.
• a common pretreatment is for instance degreasing in organic solvents, followed by degreasing in an alkaline medium, which may be carried out electrolytically, if necessary. After rinsing with water and pickling with hydrochloric acid, there is another rinsing with water. This is followed by the zinc plating process. After this, the metal is usually passivated. Examples of conventional passivating liquids are (all per litre ofsolution):
• the temperature is somewhere between 10 and 80 C. and the dipping time between I5 and I seconds.
• the material is passivated to give extra protection against corrosion and to provide a basis for a finish such as the application of a lacquer.
• Electro zinc plating is carried out mainly either in revolving drums or in stationary containers.
• the solution in the first case the solution is automatically shaken, which is essential to prevent stationary solution can be agitated for instance by means of air.
• the current density on the objects to be zinc plated is also according to the present method between about 0.1 and l0 amperes per dmI; it is usually between about 3 and 6 amperes per dm.
• the temperature is not so very important for the present method.
• the solution is an aqueous liquid, which means that it always remains above its solidification point and, reasons, below its boiling point. In practice, the temperature will be somewhere between 20 and 80 C. It is true that at a higher temperature the electric conductivity of the solution increases and the efficiency improves, but at a lower temperature the brightness of the galvanized product is generally slightly better. The choice is therefore a matter of practice rather than theory.
• the applied zinc coat is equally thick everywhere; the I degree of difference is referred to as variance.
• the electroplating solution per litre of the bath must also contain 0.05 to 0.8 gram-atom zinc, a polyhydroxy acid or a salt thereof, as well as boric acid and/or borate.
• the molar ratio of zinc content and the polyhydroxy anion should be between about 1:1.3 and 1:22; the molar ratio of polyhydroxy anion to boric anion between about 1:1.8 and 1:22
• lt is known that sometimes a low and sometimes a high zinc content has to be used.
• a low zinc content is considered to exist in a solution with approximately 5 to 25 grams of zinc per litre, and a high zinc content in a solution with approximately 25 to 50 grams of zinc per litre.
• the three-component system which forms the essence of the invention, appears to be best if made up of approximately 2 gram-molecules polyhydroxy acid or a salt thereof, and approximately 4 gram-molecules boric acid and/or borate per gram-atom zinc 10 percent deviation possible).
• these ratios per gramatom zinc are about at 1V2 gram-molecule polyhydroxy acid or a salt thereof and 3 gram-molecules boric acid or borate (10 percent deviation possible).
• the zinc compound which is always necessary in electro zinc plating baths, is usually and also according to the present method zinc sulphate or zinc chloride, but in view of the required pH it still makes no difference whether zinc sulphate and, for instance, sulphuric acid are added as pH controlling agents or another zinc compound such as ZnO, which in this case with H 80. again brings zinc and sulphate ions into the solution anyway.
• Ammonium ions should be avoided; they give less favorable results.
• the drum was placed in a zinc solution of 185 litres, which had the following composition per litre ofsolution:
• aldehyde was added after each drum charge in such a way as to maintain the aldehyde content at about 2 grams per litre.
• Example I was repeated with a solution of the following composition per litre ofsolution:
• the charge was 15 kg. carriage bolts with a total surface of dmf"; the electroplating time was 35 minutes, at a current density of 0.85 amperes per dm. The efficiency was 78 percent and the coat thickness of the zinc after passivating was 5.2 microns.
• the cover of the objects zinc plated in accordance with the invention is excellent, and the throwing power of the solutions in accordance with the invention is good.
• An aqueous electroplating solution comprising about 0.05 to 0.8 gram-atom zinc per litre, polyhydroxy carboxylic acid or a salt thereof, and boric acid or borate, the molar ratio of zinc to polyhydroxy carboxylic acid or salt being from about 121.3 to about 1:2.2 and the molar ratio of polyhydroxy carboxylic acid or salt to boric acid or borate being from about 121.8 to about 122.2, the pH of the solution being at least about 5, and the solution being substantially free ofammonia.
• An aqueous electroplating solution according to claim 1 comprising between 5 and 25 grams per litre zinc, about 2 gram-molecules polyhydroxy carboxylic acid or salt thereof per gram-atom zinc, and about 4 gram-molecules boric acid or borate per gram-atom zinc.
• An aqueous electroplating solution according to claim 1 comprising between 25 and 50 grams per litre zinc, about 1.5 gram-molecules polyhydroxy carboxylic acid or salt thereof per gram-atom zinc, and about 3 gram-molecules boric acid or borate per gram-atom zinc.
• An aqueous electroplating solution according to claim 1 containing from about 1.8 to 2.2 parts boric acid per part polyhydroxy carboxylic acid or salt thereof.

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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)
• Electroplating And Plating Baths Therefor (AREA)

Applications Claiming Priority (2)

Publications (1)

Family

ID=25758838

Family Applications (1)

Country Status (3)

Cited By (9)

Citations (2)

• 1969
  • 1969-03-11 NL NL6903711A patent/NL6903711A/xx unknown
• 1970
  • 1970-03-09 US US17978A patent/US3642591A/en not_active Expired - Lifetime
  • 1970-03-10 GB GB1146370A patent/GB1310163A/en not_active Expired

Patent Citations (2)

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