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
  • C25D5/36—Pretreatment of metallic surfaces to be electroplated of iron or steel

Definitions

• This invention relates to electrodeposition of chromium on basis metals, and, more particularly, it is concerned with an activation process by which an adherent chromium electrodeposit is formed on metal substrates, such as ferrous metals, stainless steel or cast iron, using a high energy e ⁇ ticient chromium plating bath.
• metal substrates such as ferrous metals, stainless steel or cast iron.
• Such baths are o£ the types disclosed Dillenberg U.S. Patent No. 4,093,522; Perakh et al. , U.S. Patent No. 4,2134,396; and Chessin, U.S. Patent 4,450,050 and 4,472,249.
• the problem has been • attributed to the presence of the halide ion in the bath, which may intertere with initiation ot chromium deposition.
• An adequate bond with conventional chromium plating solutions such as those using a solution ot chromic acid and catalysts, such as sulfate, or sulfate m combination with various fluorides, can be obtained by reverse or anodically etching the substrate m the plating solution or in a separate chromium acid containing solution at a prede ⁇ termined current density for a predetermined time.
• a table which lists the time lengths for such an etching process is found in "Metal Finishing" 80 (5) 65-8 (1982) by C. H. Peger.
• the use of certain sulfuric acid and hydrofluoric acid etches for specific stainless steels is also suggested in the publication.
• Anodic chromic acid treatments for 400 stainless steel alloys and for low and high carbon steels is disclosed in "48th Metal Finishing Guidebook-Directory" /8, 188-202 (1980) by A. logozzo. Also recommended are cathod c treat- ments in sulfuric-tluoride solutions for 300 stainless, for nickel alloys and for cast iron.
• a further alternative which is found in the prior art is the use of a Woods nickel strike for certain special nickel and cobalt-based alloys.
• the use of a ferric chloride-hydrochloric acid solution as a clearing agent tor the smut produced by anodic sulfuric etches is disclosed at page 137 of "Hard Chromium Plating" Robert Draper Ltd., Teddington, 1964 by J. D. Greenwood. Brune and McEnally in "Plating” 42., 1127-32 (1955) describe the use ot a magnesium sulfate sulfuric acid anodic etch solution for preparing ferrous parts for plating.
• ASTM Specification B-242-49T suggests the appli ⁇ cation of an anodic etch using a sulfuric acid solution containing sodium sulfate.
• ASTM B1//-68 described the use of sulfuric acid or chromic acid as activators for chromium electroplating on steel tor engineering use.
• Chessin in U.S. Patent 4,450,050 described an activa ⁇ tion pretreatment for bonding high efficiency chromium electrodeposits on a metal substrate which is characterized by the step ot first plating the substrate metal with iron or an iron alloy from an iron salt containing bath.
• Cast iron substrates present a particular problem with respect to forming adherent chromium deposits.
• Several references describe pretreatments for case iron but neither recommends them for use in chromium plating.
• Canning Handbook on Electroplating W. Canning, Ltd., Birmingham, England) 1973, p. 338 and 345.
• Graham Electroplating and Engineering Handbook (Reinhold) 1955, p. 167. Graham's method is a pickling or immersion process and does not use electrolysis.
• Canning proposes a solution which contains chromium acid, which is disadvantageous because it creates a waste treatment problem. Chen and Baldauf, in U.S. Patent 4,412,892, uses an anodic treatment in a sulfuric acid-hydrochloric acid solution.
• an activation solution (1) which is a substantially neutral (pH 5-10) alkali metal sulfate solution.
• the activation solution does not require sulfuric or chromic acids to perform its activating function.
• an activation solution (2) which in ⁇ cludes sulfuric acid, added sulfate ion, and an inorganic oxidizing agent, may be used.
• the activation solution contains 10 to S Q7, by volume of concentrated sulturic acid, 0.25 to 2 moles/1 of added sulfate ion, and
• An activation solution also may consist of chromic acid and chloride ion, optionally with bromide ion, parti ⁇ cularly for stainless steel substrates.
• the process of the invention can be utilized for electrodepositing chromium from any chromium bath, it can be used advantageously tor forming adherent chromium on a metal substrate from a high energy efficient chromium bath which includes a hal-ide ion as an essential constituent.
• a hal-ide ion as an essential constituent.
• The. presence of the halide ion can cause problems with adherence of the chromium deposit unless the metal substrate is given the pretreatment of the invention.
• the process comprises subjecting the metal substrate to electrolytic etching, preferably anodic etching, in a substantially neutral (pH 5-10) solution of an alkali metal sulfate, and electrodepositing chromium thereon.
• the electrolytic etching step is carried out for about 10 seconds to 10 minutes at a current density of about 0.1 asi to 10 asi, and at a temperature from about room tempera ⁇ ture to 50°C.
• the metal substrate is placed in the chromium electro ⁇ plating bath and chromium metal is deposited thereon.
• a reverse i.e. the workpiece is made the anode
• a chromic acid-containing solution for example, the chromium plating solution itself, may be used preceding the actual chromium plating operation.
• the activation solution while free of added sulfuric acid or chromic acid, may contain one or more of the follow ⁇ ing additives: a buffer, such as borax, to maintain the pH of the solution at the desired level; an oxidizing salt, such as sodium molybdate or sodium chromate, for faster polarization; an attack metal compound, such as sodium chloride or sodium nitrate, to aid in attacking the surface of the substrate; a complexor such as citrate or gluconate, to stabilize the products of the electrolytic reaction; and a surfactant to reduce surface tension between solution and substrate.
• a buffer such as borax
• an oxidizing salt such as sodium molybdate or sodium chromate
• an attack metal compound such as sodium chloride or sodium nitrate
• a complexor such as citrate or gluconate
• This activating solution is particularly useful tor ferrous metals such as cast irons and alloy and high carbon steels.
• An activation solution was prepared from 45 g/1 of sodium sulfate and 20 g/1 of sodium molybdate hexahydrate. The pH was 7. A cast iron substrate was placed in the solution at room temperature and the substrate was anodi ⁇ cally etched at 0.5 asi for 30 seconds. After transfer to a rinsing bath, the activated metal was chromium plated in a high energy efficient bath containing iodide ion at 5 asi for 60 minutes. The chromium deposit exhibited excellent adherence to the substrate and was smooth.
• the activation solution consisted ot 120 g/1 sodium sulfate and 40 g/1 of sodium nitrate.
• the pH was 6 ' .
• the substrate was strut steel, 1024, an induction hardened steel. Activation was carried out at 23 ⁇ C at 1 asi for 3 minutes, followed by rinsing and high energy chromium reverse at 5 asi for 3 minutes, and high energy chromium plating at 5 asi for 15 minutes.
• the adherence of the chromium to the substrate was excellent and the deposit was quite smooth.
• Example 2 The process of Example 2 was repeated using addi ⁇ tionally 10 g/1 ot boric acid in the activation solution, a pH of 7, and anodic etching at.2 asi for- 2 minutes. A similar excellent adhering deposit was obtained.
• Example 2 The process of Example 2 was repeated using an activa ⁇ tion solution comprising 40 g/I sodium sulfate, 20 g/i sodium nitrate, 20 g/1 sodium citrate dihydr de, 5 g/1 sodium chloride, and 20 g/1 sodium tetraborate hexahydrate.
• the pH was 8.
• Activation was carried out at 1 asi tor 4 minutes , reverse etching in a high energy bath at 5 asi for 3 minutes and chromium plating at 5 asi for 15 minutes. An adherent, smooth chromium deposit was obtained.
• Example 2 The process of Example 2 may be repeated using addi ⁇ tionally 10 g/I of boric acid in the activation solution, a pH .of 7 and etching employing alternating current at 2 asi for 2 minutes. A similar excellent adhering deposit will result.
• the process of the present invention may consist of subjecting the metal substrate to -electrolytic etching, preferably anodic etching, in a solution of sulfuric acid, added sulfate ion, and an oxidizing agent, rinsing the activated substrate, and electrodepositing chromium thereon, preferably from a high energy efficient chromium bath.
• the activation solution consists essentially of 10 to 50% by volume of concentrated sulfuric acid, 0.25 to 2 moles/1, of added sulfate ion, and 3.5 x 10 " to 14U x iU -3 moles/1 of an inorganic oxidizing agent.
• the activation solution consists essen ⁇ tially of 20 to 0% by volume concentrated sulfuric acid, -8-
• the activation solution consists essentially of 20 to 40% by volume of concentrated sulfuric acid, 100 to 200 g/1 of magnesium sulfate and 1 to 2 g/1 of sodium nitrate.
• Suitable inorganic oxidizing agents for use in the activation solution of the invention include oxygenated inorganic oxidizing agents, such as nitrate, permanganate, perchlorate, persulfate and molybdate ions, usually added as the sodium or potassium salts. Chromate is not as useful since it gives a rough deposit.
• the added sulfate ion usually is present as magnesium sulfate heptahydrate which is very soluble m the activation solution.
• the electrolytic etching step is carried out for about
• the current is turned off and the activated metal substrate is transferred to a rinsing vessel where t is rinsed free of the activation solution, preferably within 1 minute after activation. Then the metal substrate is placed in the chromium electroplating bath and chromium metal is deposited thereon.
• a reverse i.e. the workpiece is made the anode
• a chromic acid-containing solution for example, the chromium plating solution itself, may be used preceding the actual chromium plating operation.
• Typical metal substrates include ferrous metals such as cast irons and alloy and high carbon steels.
• An activation solution was prepared from 40% by volume of concentrated sulfuric acid, 100 g/1 magnesium sulfate heptahydrate, and 0.5 g/1 of sodium nitrate.
• a cast iron substrate was placed in the solution and the substrate was anodically etched at 15.5 asd for 1 minute at 16°C.
• the activated metal was chromium plated in a high energy efficient bath contain ⁇ ing iodide ion at 77.5 asd for 60 minutes. The chromium deposit exhibited excellent adherence to the substrate and was bright, smooth and hard.
• the activation solution consisted of 40% by volume of concentrated sulfuric acid, 100 g/1 of magnesium sulfate heptahydrate and 2 g/1 ot sodium nitrate.
• the substrate was cast iron.
• Activation was carried out at 21 U C at 1 1 . _ asd for 20 seconds, followed by rinsing and h gh energy chromium plating at 77.5 for 15 minutes.
• the adherence of the chromium to the substrate was excellent, the deposit was quite smooth, bright and hard.
• Example 2 The process of Example 2 was repeated using 40% by volume of concentrated sulfuric acid, 100 g/1 of magnesium sulfate heptahydrate, and 5 g/1 of sodium nitrate as the activation solution, and anodically etching at 77.5 asd for 15 seconds at 12°C. An excellent adhering deposit was obtained.
• EXAMPLE 10 The process of Example 2 was repeated using 40% by volume of concentrated sulfuric acid, 100 g/1 of magnesium sulfate heptahydrate, and 5 g/1 of sodium nitrate as the activation solution, and anodically etching at 77.5 asd for 15 seconds at 12°C. An excellent adhering deposit was obtained.
• Example 2 The process ot Example 2 was repeated using an activa ⁇ tion solution of 40% by volume of concentrated sulfuric acid, 100 g/1 of magnesium sulfate heptahydrate, and 1 g/1 sodium perchlorate. Activation was carried out at 77.5 asd tor 15 seconds. An adherent, smooth chromium deposit was obtained.
• a stainless steel substrate is subjected to electrolytic etching, preferably anodic etch ⁇ ing, m a solution of chromic acid and chloride ion, or w th a mixture of chloride and bromide ions, and then electro ⁇ depositing chromium thereon from a " high energy efficient chromium bath.
• electrolytic etching preferably anodic etch ⁇ ing, m a solution of chromic acid and chloride ion, or w th a mixture of chloride and bromide ions
• the chloride ion should not exceed about 0.3M.
• the electrolytic etching step is carried out for about 10 seconds to 10 minutes, suitably 15 seconds to 1 minute, at a current density of about 0.5 to 155 amps/dm (asd), preferably 1-8 asd, and at a suitable temperature, prefer ⁇ ably at least about 40°C, and most preferably at about 55°- 60°C.
• the current is turned off and the activated metal substrate is transferred to a rinsing vessel where it can be rinsed free of the activation solution, if desired. Then the activated substrate s placed in the chromium electroplating bath and chromium metal is deposited thereon.
• a cathodic or reverse etching step may follow the anodic etching as part of the activation process.
• Typical stainless steels include stainless steels numbers 304, 316, 316L and 410.
• An activation solution was prepared comprising 0.15 M chromic acid containing 0.14M chloride ion.
• a 304 stainless steel substrate was placed in the solution and the substrate was anodically etched at 2.5- asi for 1 minute at 57°C.
• the activated metal was chromium plated in a high energy efficient bath containing iodide ion at 77.5 asd for 60 minutes.
• the chromium deposit exhibited excellent adherence to the substrate and was bright, smooth and hard.
• the activation solution consisted of 0.15 M chromic acid, 0.14M chloride ion and 0.025M bromide ion.
• the substrate was 304 stainless steel. Activation was carried out at 5 U C at 2.5 asi for 1 minute, followed by rinsing and high energy chromium plating at 77.5 asd for 15 minutes. Adherence ot the chromium deposit to the substrate was excellent, and it was smooth, bright and hard.
• Example 2 The process of Example 2 was repeated without the rinsing step. An excellent adhering deposit also was obtained.
• Example 2 The activation step of Example 2 was repeated at a temperature of 26 ⁇ C. The chromium deposit did not adhere well to the substrate.
• Example 2 The process of Example 2 was repeated using an activa ⁇ tion solution containing 0.34M chloride ion. The chromium deposit did not adhere well.
• the anodic step is carried out in a polarizing solution in which the surface of the cast iron substrate is dissolved without causing surface roughness.
• Suitable polarizing solutions include oxidizing agents, such as a concentrated sulfuric acid solution, chromic acid, dichromate, disulfate and the like, preferably in a medium of high ionic strength, such as is provided by electrolyte salts such as sodium sulfate, potassium sulfate and magnesium sulfate.
• the anodic step is carried out for a period of time sufficient to effect polarization in the solution, whereupon passivation sets in, and is terminated before surface roughness ensues.
• this period is 15 seconds to 10
• the step is preferably carried out at a lower operating temperature than with other oxidizing agents.
• the temperature of the bath preferably should be less than 20"C.
• concentrations of sulfuric acid higher than 30% can be 20 U C. and higher.
• the cathodic treatment step is effective to reduce the passive layer (oxide layer) formed on the substrate during the anodic step.
• nascent hydrogen is produced which interacts with the oxide layer to condition it to receive the chromium electrodeposit as an adherent film.
• the cathodic activation solution is an elec ⁇ trolyte, such as is provided by the anodic solution itself, or an acid or alkaline medium.
• An alkaline solution is preferred.
• a typical anodic activation solution comprises about 10 to 50% sulfuric acid, optionally with about 20 g/1 or more ot dichromate, and 180 g/1 or more " of magnesium sulfate.
• a typical cathodic solution comprises a strong sodium hydroxide solution.
• the current is turned off and the activated metal substrate is transferred to a rinsing vessel where it is rinsed free of the activation solution.
• the thus-activated sub ⁇ strate is placed in the chromium electroplating bath and chromium metal is deposited thereon. While the process of the invention can be utilized for electrodepositing chromium -14-
• Typical cast irons for use herein include nodular, grey and malleable cast irons.
• An anodic polarizing solution was prepared from a 30% sulfuric acid solution to which was added 24 g/1 of sodium dichromate and 216 g/1 of magnesium sulfate.
• a nodular cast iron substrate was placed in this solution and the substrate was treated anodically at 15 asd for 2 minutes at lb u .
• the substrate was subjected to a cathodic treatment in a strongly allcaline solution (50 g/I caustic) at 15 asd for 1 minute at 64°C. , and rinsed again.
• the thus-activated substrate then was placed m a high energy efficient chromium bath containing iodide ion and chromium was deposited thereon at 77.5 asd for 60 minutes.
• the chromium layer which formed exhibited excellent adherence to the activated cast iron and was bright, smooth and hard. In contrast, when only either one of the activation steps was used, very poor adhesion was obtained.
• the anodic polarizing solution consisted ot a 30% sulfuric acid solution containing 100 g/1 of chromic acid.
• the substrate was grey cast iron.
• the anodic treatment was carried out at 15 asd for 2 minutes at 16°C. , followed by rinsing.
• the cathodic treatment was performed in the strongly alkaline solution of Example 1 at 15 asd for 1 minute at 40°C. After rinsing, chromium was deposited at 77.5 asd for 15 minutes. Adherence of the chromium deposit to the activated substrate was excellent, and it was smooth, bright and hard.

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• 1986
  • 1986-06-24 WO PCT/US1986/001351 patent/WO1987000869A1/en not_active Application Discontinuation
  • 1986-06-24 EP EP86904565A patent/EP0235173A1/de not_active Withdrawn
  • 1986-06-24 BR BR8606816A patent/BR8606816A/pt unknown
  • 1986-06-24 AU AU61274/86A patent/AU6127486A/en not_active Abandoned
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• 1987
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