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 11 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.
• the present invention provides a process which makes it possible to incorporate far higher percentages of solid particles into the coatings with the use of an electroplating bath having a far lower concentration of solid particles and electrolyte and far less vigorous agitation of the bath.
• the invention consists in that in a process of the known type indicated above use is made of a surfactant in the form of a cationic fluorocarbon compound in at least the same weight ratio to the particles in the bath liquid as would be needed, in an 0,005 M KNO 3 -solution for the particles to assume a zeta-potential of at least +40 mV with the exclusive use of said cationic fluorocarbon compound. It should be added that the use of a cationic compound for the codeposition from an electroplating bath of a metal and solid inorganic particles on an object acting as cathode has been proposed before in the United States Patent Specification 3 844 910.
• An amino-organosilicium compound for instance gamma-propyltriethoxysilane is employed then to promote the incorporation into a matrix of metal of non-metallic particles such as silicium carbide.
• solid inorganic particles that can be incorporated when use is made of the present process according to the invention are to be understood here not only all particles that are of solid inorganic compounds which are inert relative to the bath conditions, such as the carbides, borides, silicides or nitrides of titanium, zirconium, wolfram, hafnium, niobium, tantalum, chromium, molybdenum, vanadium and thorium, but also particles of simple or composite metal oxides such as Al 2 O 3 ; SiO 2 ; IrO 2 ; Cr 2 O 3 ; ZrO 2 ; PbO 2 ; Pb 3 O 4 ; Al 2 O 3 -2TiO 2 ; BeO.SiO 2 and ZrO 2 Si.
• BET Brunauer, Emmett and Teller
• an abrasion-resistant coating especially the incorporation of SiC or B 4 C particles is mentioned.
• 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 an 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 from the same amount by weight per litre of bath liquid.
• metals that may be used the same limitation holds as for the number that can be deposited from an electroplating bath in the known manner.
• these metals may be mentioned silver, iron, lead, nickel, cobalt, cadmium, copper, zinc and metallic alloys such as bronze, brass and the like.
• 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.
• the last-mentioned one is to be preferred in that it is a surfactant that gives the most favourable results.
• the anion of said last-mentioned compound be replaced with a CI- or SO 4 z - 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 large amount of surfactant was used that 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.
• the dispersions were stirred with the magnetic stirrer for about 5 minutes, after which from each beaker 1 ml of the dispersion was taken, which was diluted with 50 ml of an aqueous 0,05%-solution of KN0 3 (0,005 M KN0 3- solution).
• 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 1 1 1-Watt's nickel plating bath was prepared employing the following composition ingredients:
• the pH was 4,2 and the temperature 52°C.
• the anode hanging in the beaker consisted of a nickel plate 1 mm thick, 8 cm high, and 15 cm long and was so bent that it was just touching the inside wall of the beaker.
• the anode and the cathode were then connected to a current source supplying a direct current of 0,75 A.
• 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 2 .
• 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 well determined visually.
• the volume percentage of incorporated SiC particles was determined with a Zeiss micro- videomat. 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 containing the respective inorganic particles and demineralized water.
• Example 2 The procedure used in Example 1 was repeated with SiC particles having a size of about 15 fl m and supplied by the Dutch firm of Norton at Rotterdam under the name SiC 500. The conditions and the results are given in Table 2.
• the solid inorganic particles were of B 4 C.
• Particles of this boron carbide having a particle size of about 2 ⁇ m, known under the name B 4 C, 5oo had been obtained from the German firm of Kempten GmbH, Kunststoff.
• Use was made of a nickel sulfamate bath and a different cationic fluorocarbon surfactant from the one used in the Examples I and II.
• the surfactant now has as structural formula
• Table 3 shows that under the given conditions the particles were quite satisfactorily incorporated, both quantitively and qualitatively, also when use was made of boron carbide.
• 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 jM m.
• 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.
• the resulting coating was black and had a poor appearance.
• 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:
• Example II The experiment was again carried out in a Watt's nickelplating bath, use being made of the same surfactant as in Example I.
• table 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)
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• Organic Chemistry (AREA)
• Electroplating And Plating Baths Therefor (AREA)
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• Compositions Of Macromolecular Compounds (AREA)
• Inorganic Compounds Of Heavy Metals (AREA)

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• 1979
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