Classifications

• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D15/00—Electrolytic or electrophoretic production of coatings containing embedded materials, e.g. particles, whiskers, wires
  • C25D15/02—Combined electrolytic and electrophoretic processes with charged materials

Definitions

• the invention relates to a process for the codeposition from an electroplating bath of a metal and solid inorganic particles on an object acting as cathode, which particles are kept suspended in the bath liquid.in the presence of a surfactant and have an average size of less than 300 ⁇ m and are used in a concentration of 10 to 150 grammes per litre of bath liquid, and relates to objects entirely or partially provided with a coating thus deposited.
• a disadvantage to the known process is that only a low percentage of particles can be incorporated into the composite layers. Mention is made of a weight percentage of silicium carbide of 3 to 5%. This percentage can only be obtained at a relatively high concentration (90 to 150 grammes per litre) of silicium carbide particles in the bath liquid. Other conditions are an exceptionally high electrolyte concentration and very vigorous agitation of the bath liquid. The latter requirement serves to inhibit sedimentation of the suspension and to obtain a sufficiently homogeneous distribution of the particles in the coating.
• particles of metals or metal alloys can in this way be included in composite metal coatings.
• the percentage of inorganic particles that may form part of composite coatings when use is made of the process according to the invention varies from a few per cent to the theoretically maximum volume percentage of around 70%. It has been found that the smaller the particles the more of them can be deposited fromrthe same amount'by weight per litre of bath liquid.
• the electroplating baths used in the process according to the invention may contain particles of some other inorganic or organic material.
• particles of some other inorganic or organic material As an example thereof may be mentioned a combination of SiC,MoS 2 and Pb-oxide + PTFE.
• the preparation of the dispersions to be employed in the present process may be carried out in any convenient manner. It may be effected by adding the calculated amount of cationic surfactant to the electroplating bath in which the envisaged particles have been taken up or, as is preferred, first adding the wetting agent to a very strongly agitated, concentrated suspension of the particles to be occluded and subsequently adding the resulting suspension to the electroplating bath.
• cationic surface active fluorocarbon compounds In the process according to the invention use should be made of cationic surface active fluorocarbon compounds.
• the structural formulae of some of these compounds are as follows: Of the above compounds the last-mentioned one is to be preferred in that it is a surfactant.that gives the most favourable results. In view of the possibility of electrochemical oxidation and precipitation it is preferred that the anion of said last-mentioned compound be replaced with a Cl - or SO 4 2- ion.
• the electroplating bath also to contain a stress reducing agent, such as p-toluene sulphonamide or saccharin.
• the zeta-potential of the solid inorganic particles to be incorporated by electrodeposition was measured as a function of the amount of surfactant. This was done in order to determine at what amount of surfactant the particle potential exceeded +40 mV. In the actual experiments in the electrolyte bath then a somewhat larger amount of surfactant was used than the amount thus determined. Moreover, in Example I experiments were carried out with the same surfactant in 2 concentrations that were lower than that of said determined amount. The measurement of the zeta-potential was so carried out that as far as possible the same concentrations of the solid inorganic particles in the aqueous dispersions were used as those that were to be employed in the electroplating bath.
• the contents of the beakers were homogenized for 2 minutes with an Ultra Turrax stirrer, type T 45/N of the German firm of Janke und Kunkel A.G., operating at a speed of 10 000 revolutions per minute. Subsequently, the dispersions were allowed to stand for 15 hours to permit the air to escape. Next, the dispersions were stirred with a magnetic stirrer for about 10 minutes without air occlusion and visually inspected then for stability, flocculation symptoms and sedimentation speed.
• Ultra Turrax stirrer type T 45/N of the German firm of Janke und Kunkel A.G.
• Example I the procedure used in the experiments will be further described. The same procedure, mutatis mutandis, is used in all the other examples. Differences, if any, between the examples will appear from the respective tables. In these tables are summarized the various conditions used in the experiments and the results obtained with the experiments.
• a 11 ⁇ 2 1-Watt's nickel plating bath was prepared employing the following composition ingredients: grammes/litre The pH was 4,2 and the temperature 52 C.
• surfactant i.e. 5 mg of surfactant per 1 gramme of SiC.
• the surfactant had the following structual formula: In a 200 ml-beaker this mixture was homogenized with an Ultra Turrax stirrer of the type mentioned before at a speed of 10 000 revolutions per minute. Subsequently, the resulting dispersion was gently stirred for half an hour at a temperature of 52 0 C with an IKA Com- bimag magnetic stirrer to allow the escape of air occluded in the preceding stirring operation.
• the current density was 10 A/dm 2 .
• the electrodepositing lasted 15 minutes, the bath being moderately stirred to prevent sedimentation of SiC particles.
• the cathode and the anode were removed from the beaker, rinsed with water and transferred to a beaker of the same dimensions containing a normal Watt's nickel plating bath (without SiC or surfactant).
• the cathode bar was subjected to a continued electroplating treatment lasting 30 minutes at a current density of 5 A/dm .
• a second, entirely nickel coating.. was deposited on the composite coating of nickel and silicium carbide formed in the first electroplating step.
• the uniformity of distribution of the SiC particles in the nickel could therefore be very well determined;visually.
• the volume percentage of incorporated SiC particles was determined with a Zeiss microvideomat. The experiment was carried out at 3 different concentrations of surfactant, based on the amount by weight of SiC particles:
• zeta-potential without surfactant used in this table and also in other tables is meant the zeta-potential which was measured with the dispersion which exclusively contained the respective inorganic particles and demineralized water.
• the material of the solid inorganic particles in this experiment was a diamond powder supplied by the Swiss firm of Rudolf Spring A.G. under the name Diamond grade 3. Use was made of a nickel sulfamate bath and the same type of surfactant as employed in Example III. Table 5 gives- further particulars about the conditions used in and the results obtained by the experiment. Considering the relatively small concentration of diamond powder (as little as 20 g/litre bath liquid) a remarkably high percentage of incorporated diamond powder was reached (28%) compared with the percentage obtained with the known electroplating process for deposition of metals and diamond powder .
• the solid inorganic substance consisted of chromium powder having a particle size of about 2 pm.
• the powder had been supplied by the American firm of Alfa Products at Danvers.
• the experiment was again carried out in a Watt's nickel plating bath, use being made of the same surfactant as in Example I.
• the conditions and the results of the experiment are given in Table 6.
• the composite layer contained 47 per cent by volume of chromium powder which was homogeneously distributed in it.
• Example I use was made, as in Example I, of a Watt's nickel plating bath containing dispersed silicium carbide particles referred to as SiC 1200 .
• the treatment was carried out in the presence of cationic hydrocarbon surfactants.
• the cationic surfactant used here had the following structural formula: Further data are mentioned in Table 8.
• Example VIII In the experiment according to this example use was made of a mixture of two inorganic substances.
• One substance was SiC 1200 , as employed in Example VIII.
• the other substance was molybdenum disulphide having a particle size of about 25 ⁇ m. It had been obtained from the Swiss firm of Fluka A.G.
• the experiment was again carried out in a Watt's nickelplating bath, use being made of the same surfactant as in Example I.
• tabel 10 the conditions used and the results obtained are summarized.
• the composite layer contained 27 per cent by volume of silicium carbide and 18 per cent by volume of molybdenum disulphide. Both substances were homogeneously distributed in the metal coating.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Electrochemistry (AREA)
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• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Electroplating And Plating Baths Therefor (AREA)
• Paints Or Removers (AREA)
• Compositions Of Macromolecular Compounds (AREA)
• Inorganic Compounds Of Heavy Metals (AREA)

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• 1979
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