Classifications

• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D5/00—Electroplating characterised by the process; Pretreatment or after-treatment of workpieces
  • C25D5/34—Pretreatment of metallic surfaces to be electroplated
• • 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
  • C25D11/36—Phosphatising
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D5/00—Electroplating characterised by the process; Pretreatment or after-treatment of workpieces
  • C25D5/10—Electroplating with more than one layer of the same or of different metals
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10S205/00—Electrolysis: processes, compositions used therein, and methods of preparing the compositions
  • Y10S205/917—Treatment of workpiece between coating steps
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T428/00—Stock material or miscellaneous articles
  • Y10T428/12—All metal or with adjacent metals
  • Y10T428/12493—Composite; i.e., plural, adjacent, spatially distinct metal components [e.g., layers, joint, etc.]
  • Y10T428/12708—Sn-base component
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T428/00—Stock material or miscellaneous articles
  • Y10T428/12—All metal or with adjacent metals
  • Y10T428/12493—Composite; i.e., plural, adjacent, spatially distinct metal components [e.g., layers, joint, etc.]
  • Y10T428/12771—Transition metal-base component
  • Y10T428/12785—Group IIB metal-base component
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T428/00—Stock material or miscellaneous articles
  • Y10T428/12—All metal or with adjacent metals
  • Y10T428/12493—Composite; i.e., plural, adjacent, spatially distinct metal components [e.g., layers, joint, etc.]
  • Y10T428/12771—Transition metal-base component
  • Y10T428/12785—Group IIB metal-base component
  • Y10T428/12792—Zn-base component

Definitions

• a large number of permanent coatings are known, which can be applied to metallic materials in order to protect them against corrosion in the atmosphere or the like, caused by the presence of various aggressive products. These treatments can be adopted for various purposes, for exmple for decorative coverings, for adhesive carriers for an organic covering or lubricant, for protecting resistant surfaces against wear or for such surfaces which have special electrical or thermal properties, or finally for protecting layers against corrosion.
• phosphates are currently used, which serve mainly as carriers for paints.
• the relatively porous surface obtained in this manner possesses excellent adhesive power for paints, and if the phosphate protecting layer becomes damaged, corrosion is prevented below the surface sldn.
• Hitherto these coverings have been obtained by simply bringing the metallic carrier into contact with aqueous solutions which generally contain phosphates, phosphoric acid and various reaction accelerators.
• the known methods for applying phosphates are dipping, spraying with a spraying gun, as well as brushing on or scouring.
• the metallic coverings adopted for protecting against corrosion consist essentially of bringing at least two metals onto each other, the basic metal and at least one protecting metal.
• corrosion is in general an electrochemical process, and this allowed a known theory to he established concerning the mechanism of protection against corrosion, based on the metals arranged in series in accordance with their electrochemical potentials.
• electro-negative and electropositive are naturally relative terms between the metals in question.
• the metals currently used for its protection are zinc, cadmium and tin.
• Cadmium is electro-negative with respect to iron. It is therefore the cadmium that will be first attacked in the case of corrosion later.
• Tin on the other hand is electro-positive, unless organic acids are present, whereby it becomes electro-negative.
• Anodic coverings i.e. electro-nega-tive metals, give selfprotection, i.e. protection against corrosion is ensured even in cases of breakage, cracking, porosity or too little thickness of the protecting metal.
• the duration of protection is thus limited; it is essentially proportional to the thickness of the covering.
• cathodic coverings of electro-positive metals have unlimited duration of protection, as long as the covering is not damaged mechanically. In the case of cracks, porosity or other damage, rapid decomposition occurs in consequence of the attack from below of the basic metal to be protected.
• the metals described as cathodic are in general not subject to chemical attack in the surroundings usually met with.
• the aim of the invention is to provide a method for pro- 7 3,011,9 5? Patented Dec. 5, 1961 tecting metals against corrosion, this method combining the special qualities of each kind of the adore-mentioned coverings.
• This method thus allows, under all circumstances, of obtaining a considerably greater resistance to corrosion, than is obtained by the known methods.
• the main feature of the invention consists in an electrolytic treatment, with high current density, of the cleaned metals in an aqueous bath which contains PO -ions, whereby the said metals one after the other form the cathode and then the anode in the electrolysis bath, by the reversing of the electrolysis current.
• this new, special treatment makes it possible to obtain in a very short time a phosphatizing which has a remarkable resistance against corrosion, as well as forming an excellent adhesive bases for other metallic protecting coverings.
• this bath contains also (ZN-dons, the pH- value of this bath being alkaline.
• this first dividing layer against corrosion can be improved by the electrolytic precipitation of a first protecting metal, which is preferably elec'tro-negative with respect to the basic metal that has to be protected, whereby this electrolytic precipitation is brought immediately onto the surface previously treated by means of the above-mentioned phosphatizing process.
• this protecting metal is cadmium.
• this second protecting metal is tin.
• the metals to be treated are first of all thoroughly degreased by some known method, for instance with trichlo-ro ethyl. If the metal parts have been appreciably attacked on their surface, it will be well to pickle them in the manner usual for electrolytic treatment, for example with diluted hydrochloric acid for iron and its alloys, or with diluted sulphuric acid. After rinsing in Water, the characteristic treatment by the method according to the invention can take place.
• a treatment-vat which contains 25 kg. cyanide of sodium, 22.5 kg. sodium hydroxide, 0.350 kg. phosphate of manganese, l lt.
• the utilized electrolysis vat consists of iron and its sides serve as electrodes.
• the clean metal parts, degreased and piclded, are placed into the bath Without the current being switched on and are left there for a certain time, for instance for five minutes, after which the pieces are connected for two to five minutes to the negative pole of a suitable source of direct current, and then the current is reversed, the pieces being then connected to the positive pole.
• the treatment is preferably carried out at a temperature of the order of 60 C., with a current density of the order of 10 amps.
• a zone influenced by the treatment can be determined.
• test plates of iron with a coating of the thickness of 5 to 12 microns obtained by successive treatment by the method according to the invention, by phosphatizing, cadmium plating and tinning, will prove resistant for 750 hours without showing a trace of corrosion, during a test in salt vapours of 21% .at 35 C. (French standard X41002). Similar plates, treated with the usual electrolytic methods, do not resist longer than 250 to 300 hours.
• the composite protecting layer obtained by the method according to the invention has also remarkable mechanical properties of resistance.
• cable protecting coverings of 4.8 to,3.2 and 2.4 mm. for airplane construction can be inserted and drawn after the treatment. They withstood the same test with salt vapour for more than 300 hours, whilst the cable protecting coverings treated with the usual electrolytic methods, showed traces of corrosion almost immediately under the same conditions.
• the composition of the phosphatizing bath may be altered'within fairly wide limits, depending on the to be protected in an alkaline, aqueous bath containing 25 kg. of sodium cyanide, 22.5 kg. of sodium hydroxide, 0.35 kg. of manganese phosphate and 1.0 litre of orthophosphoric acid for each 1000 litres of the bath, passing an electric current through the metal to be protected in said bath with a current density of approximately 10 amperes per square decimeter with the metal to be protected forming successively the cathode and then the anode so as to phosphatize the metal to be protected, rinsing-oft the phosphatized metal, electrolytically plating the phosphatized metal with a first protective metal which is electro-negative with respect to said .phosphatized metal, and then electrolytically plating the thus plated metal with a second protective metal which is electro-positive with respect to the metal to be protected and said first protective metal.

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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 Methods And Accessories (AREA)

Applications Claiming Priority (1)

Publications (1)

Family

ID=8705185

Family Applications (1)

Country Status (4)

Cited By (2)

Citations (4)

• 1957
  • 1957-11-29 FR FR1197696D patent/FR1197696A/fr not_active Expired
• 1958
  • 1958-11-26 CH CH6660658A patent/CH381046A/fr unknown
  • 1958-11-28 BE BE573430A patent/BE573430A/fr unknown
  • 1958-11-28 US US776688A patent/US3011957A/en not_active Expired - Lifetime

Patent Citations (4)

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