Classifications

• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
  • C23C18/00—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating
  • C23C18/16—Chemical coating by decomposition of either liquid compounds or solutions of the coating forming compounds, without leaving reaction products of surface material in the coating; Contact plating by reduction or substitution, e.g. electroless plating
  • C23C18/48—Coating with alloys

Definitions

• This invention relates to What is known in the art as chemical plating, i.e., to a plating process which does not employ electric current.
• This type of process when used to apply a binary alloy of copper and tin to the surface of a ferriferous metal substrate, is known in the industry as liquor finishing and this term will be employed in the following description and claims.
• a liquor finish has been described as a coppered or brass colored finish such as obtained from the coppertin coating mixture which is used to treat iron or steel articles. Descriptions of this process may be found on pages 685 and 713 of The Making, Shaping and Treating of Steel, 7th edition by United States Steel Corporation.
• Liquor finishing processes of the kind here involved have employed acid sulfate baths or solutions and have long been used on iron and steel surfaces, and particularly on wire surfaces, in order to facilitate subsequent cold drawing operations as well as, in some instances, to enhance the decorative appearance of the surface.
• Wire which has been coated with a copper-tin binary alloy is particularly suitable for use in manufacturing tires since the synthetic tire components adhere more tenaciously to the copper-tin or so-called liquor finish alloy than they do to bare or untreated wire surfaces or to wire surfaces which may have been treated by other chemical coating processes.
• the principal object of the present invention may be said to reside in the proice vision of a liquor finishing process of the general character described in which the plating bath employed can be utilized and maintained for long periods of time under conditions of heavy bath loading without frequent discard and replacement while at the same time making it possible to apply completely satisfactory and uniform binary alloy coatings of copper and tin on ferriferous metal surfaces with a consequent substantial reduction in the amount of chemicals consumed as well as in the cost of operation.
• the present invention is based upon the discovery that an acceptable, highly uniform copper-tin binary alloy coating can be obtained on a long sucession of steel surfaces if such surfaces are subjected to the action of an aqueous acid sulfate solution consisting essentially of:
• the treatment is to be continued until the desired coating is formed but the length of the treatment may vary greatly depending in large measure upon such factors as bath temperature, solution concentration and acidity within the ranges specified. Generally, for a given length of treatment, where a low solution temperature is employed, or where low chemical concentration is used, the coatings obtained will be light in weight so that longer treatment periods may be desirable. Conversely, Where higher temperatures and/ or solution concentrations are employed, the coating weights will be relatively heavier per unit of treatment time. Accordingly, the length of treatment is primarily dependent upon the processing factors of temperature and concentration. Suflice it to say, however, that treating periods of from 1 to 10 minutes have been found to be completely satisfactory when operating within the teachings of this invention.
• the stannous ion calculated as Sn, must be present in amounts of from 1 to 15 grams/liter of the coating solution. Where the stannous ion concentration falls below or rises above this range, the coatings obtained will not be uniformly acceptable, will lack the essential adhesion properties when utilized in tire manufacture, and will not display the customary brassy appearance which is desired for this type of coating.
• Dissolved copper ion must also be present in the chemi cal plating solutions of this invention and the amount of such copper ions which is to be employed will depend upon the level of stannous ion employed in accordance with the formula times in the operating solution, of a weight ratio of copper to stannous ion between 0.1 and 0.8.
• the coatings will be found to be very thin and of little commercial value, particularly so far as concerns utilization of the coatings in the tire manufacturing industry. Conversely, if the amount of copper ions dissolved in the solution is such as to cause the ratio of copper to stannous ions, as calculated from the formula to exceed the upper ratio of 0.8, then the coatings obtained will be appreciably heavier in weight and will be unacceptable from an appearance standpoint in that they will lack the customary brassy appearance.
• the stannous and copper ions are preferably supplied by utilization of their respective metal sulfate salts. Moreover, the utilization of stannous and copper sulfate salts provides a readily soluble form of the essential ionic constituents and these salts represent readily commercially available sources of these constituents.
• the acidity of the copper-stannous ion containing chemical plating bath is critical and, as noted hereinabove, must be maintained within the pH range of from 0.1 to 2.0. If the bath acidity is allowed to fall below the minimum pH value of 0.1, the bath will produce extremely thin coatings, if indeed any coatings are produced at all. Conversely, if the chemical plating solution acidity exceeds the pH value of 2.0 the coatings produced will be substantially non-adherent with respect to the base metal surface.
• acidic components such as sodium acid sulfate or sulfuric acid for the purpose of maintaining the pH within the essential range.
• acidic components must not include halide ions, particularly chloride ions, because it has been found that the presence of such ions in the chemical plating solutions of this invention will have an adverse effect upon the coating formation, and will result in totally unsatisfactory coatings having a predominantly copper content, if indeed any coating at all is produced on the metal surfaces being treated.
• aqueous sodium hydroxide solutions may be used to raise solution pH values. pH measurements are determined by standard glass electrode measurements in accordance with normal chemical procedures.
• While one or more of the required amino acids may be incorporated into the chemical plating solutions of this invention through utilization of essentially pure amino acids, it has been found that a desirable and economical source of such acids is commercial gelatin. Apparently as a result of acidic reaction on fibrous proteins, the gelatin molecule is hydrolyzed to yield one or more of the essential amino acid components. However, not all of the amino acids which may be derived from the hydrolysis of fibrous proteins have been found to be suitable for use in this invention. For example, use of either leucine or argenine failed to provide the uniform, high quality coatings obtained with the process of this invention. Where gelatin is employed the amount which should be utilized may range from 0.2 to 20 grams/liter and this will insure the provision of the required amount of amino acid constituent.
• the liquor finishing bath With respect to coating temperature, it is essential that the liquor finishing bath 'be operated between 15 C. and 66 C. If the bath falls below 15 C. the coatings subsequently obtained will be very light in weight and totally unsuitable for use either in subsequent drawing or deforming operations or in tire manufacture. Conversely, if the bath temperature is permitted to rise above 66 C., the coatings will become very heavy and the rate of loss of stannous ions through oxidation will increase with corresponding increases in the amount of sludge in the coating bath and a concomitant waste of essential stannous ions.
• Example I illustrates the bath which was employed:
• EXAMPLE -I 450 gallons (1703 liters) of an aqueous solution was prepared so as to contain:
• the solution just referred to had a pH of 1.3 and was heated to 60 C. Both cold and hot rolled steel wire, which previously had been pickled in sulfuric acid, were then subjected to the action of the above liquor finishing bath and the treatment was continued for periods of 5 minutes, following which the treated Wires were subjected to a waternnse. This procedure was continued over a long succession of wire surfaces and periodic replenishment of the bath was accomplished by utilizing suitable quantities of the following dry formulation:
• the titration of a bath sample with 0.1 N potassium permanganate solution to a permanent endpoint The amount (mls) of titrating solution required is Titration B.
• the desired tin titration value is then obtained by subtracting the Titration A value from this Titration B value.
• Example I falls within the relationship given as will be quickly apparent from examination of the last column of the example, the gelatin powder called for yielding from 0.05 to 5 grams/ liter of amino acid from the desired class of glutamic, aspartic and glycine acids.
• Formulation I has been found to be an exceedingly satisfactory dry admixture for use in effecting replenishment of the plating bath we have found that some reasonable variation in the proportionate relationship of the dry ingredients can be adopted in preparing a replenishment powder.
• dry admixtures which contain from 1% to amino acid from the class above described or of commercial gelatin; from 9% to 85% of sodium acid sulfate; and from 90% to of an admixture of SnSO and CuSO
• the amounts of stannous and copper sulfates employed in the dry formulations must be such as will yield the desired ratio of Cu Cu +Sn and this must lie between 0.1 and 0.8 when thedry replenishment material is dissolved in the coating bath.
• a liquor finishing aqueous acid sulfate solution consisting essentially of (a) from 1 to 15 grams/liter of dissolved stannous ion, calculated as Sn;
• a dry admixture for replenishing aqueous acid sulfate liquor finishing baths consisting ese-sntially of the following ingredients in the proportions indicated:

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• Chemical & Material Sciences (AREA)
• General Chemical & Material Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Chemically Coating (AREA)
• Electroplating And Plating Baths Therefor (AREA)

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Cited By (5)

Citations (5)

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• 1965
  • 1965-01-26 US US428241A patent/US3346404A/en not_active Expired - Lifetime
• 1966
  • 1966-01-26 BE BE675621D patent/BE675621A/xx not_active IP Right Cessation
  • 1966-01-26 ES ES0322277A patent/ES322277A1/es not_active Expired
  • 1966-01-26 NL NL6600984A patent/NL6600984A/xx unknown
  • 1966-01-26 GB GB3448/66A patent/GB1061248A/en not_active Expired
  • 1966-01-26 FR FR47293A patent/FR1465930A/fr not_active Expired
  • 1966-01-26 DE DEA51427A patent/DE1281220B/de active Pending
  • 1966-01-26 AT AT72166A patent/AT281536B/de not_active IP Right Cessation

Patent Citations (5)

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