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
  • C25D3/66—Electroplating: Baths therefor from melts
• • 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
  • Y10S428/00—Stock material or miscellaneous articles
  • Y10S428/922—Static electricity metal bleed-off metallic stock
  • Y10S428/9335—Product by special process
  • Y10S428/939—Molten or fused coating
• • 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
  • Y10T428/12778—Alternative base metals from diverse categories
• • 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
  • Y10T428/12861—Group VIII or IB metal-base component
  • Y10T428/12931—Co-, Fe-, or Ni-base components, alternative to each other

Definitions

• Nickelide, cobaltide or ironide coatings are formed on specified metal compositions by forming an electric cell containing said metal composition as the cathode joined through an external electrical circuit to a nickel, iron or cobalt anode using a specified fused salt electrolyte maintained at a temperature of at least 700 C., but below the melting point of said metal composition in the substantial absence of oxygen.
• This cell generates electricity, but, if desired, and may be impressed on the circuit providing a cathode current density does not exceed 10 amperes/dmf
• This deposited metal diffuses into the base metal to form a tight adherent coating on the substrate composed of nickel, cobalt or iron and the substrate metal. This process is useful in the making of such coatings on the substrate metals.
• This invention relates to a method for metalliding a base metal composition. More particularly, this invention is concerned with a process for nickeliding, cobaltiding or ironiding a 'base metal composition in a fused salt bath.
• the metal is employed as the anode and is immersed in a fused salt bath composed essentially of a member of the class consisting of the alkali metal fluorides, mixtures thereof and mixtures of the alkali metal fluorides with calcium fluoride, strontium fluoride or barium fluoride and containing from 0.015 mole percent of nickel fluoride, cobalt fluoride or iron fluoride.
• the cathode employed is the base metal upon which deposit is to be made. I have found that such a combination is an electric cell in which an electric current is generated when an electrical connection, which is external to the fused bath, is made between the base metal cathode and the nickel, cobalt or iron anode.
• the iron, nickel or cobalt dissolves in the fused salt bath and nickel, cobalt and iron ions are discharged at the surface of the base metal cathode where they form a deposit of nickel, cobalt or iron which immediately diffuses into and reacts with the base metal to form a nickelide, cobaltide or ironide coating.
• nickelide, cobaltide, ironide and metallide to designate any solid solution or alloy of nickel, cobalt or iron and the base metal regardless of whether the base metal does or does not form an intermetallic compound with nickel, cobalt or iron in definite stoichiometric proportions which can be represented by a chemical formula.
• the rate of dissolution and deposition of the nickel, cobalt or iron is self regulating in that the rate of deposition is equal to the rate of diffusion of the nickel, cobalt or iron into the base metal cathode.
• the deposition rate can be decreased by inserting some resistance in the circuit. A faster rate can be obtained by impressing a limited amount of voltage into the circuit to supply additional direct current.
• the alkali metal fluorides which can be used in accordance with the process of this invention include the fluo rides 'of lithium, sodium, potassium, rubidium and cesium. However, it is preferred to employ an eutectic mixture of sodium fluoride and lithium fluoride because some free alkali metal is produced by a displacement reaction and potassium, rubidium and cesium are volatilized with the obvious disadvantages. It is particularly preferred to employ lithium fluoride as the fused salt bath in which the nickel, cobalt or iron fluoride is dissolved, because at the temperatures at which the cell is operated, lithium metal is not volatilized to any appreciable extent. Mixtures of the alkali metal fluorides with calcium fluoride, strontium fluoride or barium fluoride can also be employed as a fused salt in the process of this invention.
• the chemical composition of the fused salt bath is critical if good metallide coatings are to be obtained.
• the starting salt should be as anhydrous and as free of all impurities as is possible or should be easily dried or purified by simply heating during the fusion step.
• the process must be carried out in the substantial absence of oxygen since oxygen interferes with the process.
• the process can be carried out in an inert gas atmosphere or in a vacuum.
• substantial absence of oxygen it is meant that neither atmospheric oxygen nor oxides of metals are present in the fused salt bath.
• the best results are obtained by starting with reagent grade salts and by carrying out the process under vacuum or an inert gas atmosphere, for example, in an atmosphere of nitrogen, argon, helium, neon, krypton or xenon.
• the base metals which can be metallided in accordance with the process of this invention included the metals having atomic numbers of from 27-29, 42-47 and 74-79 inclusive. These metals are, for example, cobalt, nickel, copper, molybdenum, technetium, ruthenium, rhodium, palladium, silver, tungsten, rhenium, osmium, iridium, platinum and gold.
• Alloys of these metals with each other or alloys containing these metals as the major constituent, that is, over 50 mole percent, alloyed with other metals as a minor constituent, that is, less than 50 mole percent, can also be metallided in accordance with my process, providing the melting point of the resulting alloy is not lower than the temperature at which the fused salt bath is being operated. It is preferred that the alloy contain at least 75 mole percent of the base metal and even more preferred, that the alloy contain mole percent of the base metal with correspondingly less of the alloying constituent.
• Tungsten and molybdenum especially, form carbides which interfere with the diffusion of the iding agent, and the iding agents themeselves, especially iron, by their over-absorption of carbon, interfere with their own diffusion into other metals.
• carbon can be removed from the fused salt by operating it as a cell until the carbide coatings are no longer formed on the surfaces of the base metal.
• nickel and cobalt can eb ironided and nickel can be cobaltided within the scope and teachings of this disclosure, nickel and cobalt and alloys of these metals are also included as materials which can be metallided by this process.
• the form of the anode is not critical.
• I can employ as the anode pure nickel, cobalt, or iron metal in the form of a rod or the iding agent can be employed in the form of chips in a porous copper or graphite basket.
• a graphite basket is used to hold anode material, it is advantageous to shield the basket with a tightly woven metal cloth to prevent carbon fragments from getting to the cathodes.
• the temperature at which the process of this invention is conducted is dependent to some extent upon the particular fused salt bath employed.
• an eutectic of sodium and lithium fluoride can be employed.
• the preferred operating range is from 900 C. to 1100 C., I prefer to employ lithium fluoride or a mixture of calcium and sodium fluorides as the fused salt.
• an electric current will flow through the circuit without any applied electromotive force.
• the anode acts by dissolving in the fused salt bath to produce electrons and ions.
• the electrons flow through the external circuit formed by the conductor and the metalliding ions migrate through the fused salt bath to the base metal cathode to be metallided, where the electrons discharge the metalliding ions and a nickelide, cobaltide or ironide coating is formed.
• the amount of current can be measured with an ammeter which enables one to readily calculate the amount of metal being deposited on the base metal cathode and being converted to the metallide layer. Knowing the area of the article. being plated, it is possible to calculate the thickness of the metallide coating formed, thereby permitting accurate control of the process to obtain any desired thickness of the metallide layer.
• the deposition rate of the iding agent must always be adjusted so as not to exceed the diffusion rate of the iding agent into the substrate material if high efficiency and high quality diffusion coatings are to be obtained.
• the maximum current density for good nickeliding, cobaltiding or ironiding is amperes/dm. when operating within the preferred temperature ranges of this disclosure. Higher current densities can sometimes be used to form coatings with these iding agents, but in addition to the formation of a metallide coating, plating of the iding occurs over the diffusion layer.
• Very low current densities (0.0l0.1 amperes/dm. are often employed when dilfusion rates are correspondingly low, and when very dilute surface solutions or very thin coatings are desired.
• the composition of the diffusion coating can be changed by varying the current density, producing under one condition a composition suitable for one application and under another condition a composition suitable for another application.
• the source for example, a battery or other source of direct current
• the source should be connected in series with the external circuit so that the negative terminal is connected to the external circuit, terminating at the base metal being metallided and the positive terminal is connected to the external circuit terminating at the metal anode. In this way, the voltages of both sources are algebraically additive.
• measuring instruments such as voltmeters, ammeters, resistances, timers, etc., may be included in the external circuit to aid in the control of the process.
• the coated metal compositions prepared by my .process have a wide variety of uses. They can be used to fabricate reaction vessels for chemical reactions, to make gears, bearings and other articles requiring hard,- wear-resistant surfaces. Other uses will be readily apparent to those skilled in the art as well as other modifications and variations of the present invention in light of the above teachings.
• Example 1 Twenty-three pounds of a mixture of 60 mole percent lithium fluoride and 40 mole percent sodium fluoride was placed in a monel liner (6" diameter x 17%" deep) fitted into a mild steel pot (6%" diameter x 18" deep). The pot was sealed with a cover plate of nickel plated steel (11" x 1") containing a water channel for cooling, two ports (2%.” in diameter) for glass electrode towers, and two 1'' holes for a thermocouple probe and a gas bubbler. The steel pot was placed in an electric furnace for heating and the electrode towers attached and the mixed salt melted (M.P. 650 C.) under vacuum (less than 0.1 mm.).
• the sample had a silvery mat finish, was very clean and had gamed 0.112 gram compared to a theoretical 0.073 gram.
• the bath temperature was raised to 800 C. and anproximately 0.5 mil thick and X-ray emission showed high other sample of copper strip of the same dimensions was concentrations of cobalt on the surface.
• nickelided in accordance with the data in the following Other metals were cobaltided and are summarized betable. low, Table V.
• Example 3 Volts Current The nickel fluoride dissolved in the sodiumlithium fluo- 45 523?; 39 7323 ride eutectic bath of Example 2 was displaced by adding lithium metal slowly to the salt at 900 C. Cobaltous o fluoride (60 gram) was then added to the salt and a cobalt 0. 5 Current on. anode (4%" x /2" x immersed 4" into the salt. '3 Current The bath temperature was raised to 960 and a 'strip of 8 copper 3" x x cobaltided as follows:
• the sample came from the bath bright and smooth and Further electrolytic clean-up was performed on the salt had gained 50 mg, the theoretical amount for the cathode and then a series of other metals ironided as shown in reaction of Co+++2e- Co.
• the diffusion coating was ap- Table VI.
• Tungsten 1 000 30 0 4 0.012 11 0.1 mil coat: mat finish, smooth, very hard ,slightly magnetic.
• Nickel 1 000 500 0 1 0. 770 48 2.0 mil coat; bright, smooth, very soft, all diflusion.
• fused salt electrolyte consists essentially of lithium fluoride and the fluoride of the metal being deposited as the metallide coating.

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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)
• Electrolytic Production Of Metals (AREA)

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Cited By (6)

Citations (6)

• 1966
  • 1966-11-10 US US593270A patent/US3489540A/en not_active Expired - Lifetime
• 1967
  • 1967-10-27 GB GB48887/67A patent/GB1199038A/en not_active Expired
  • 1967-11-10 DE DE19671621049 patent/DE1621049A1/de active Pending

Patent Citations (6)

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