US3088886A - Process of electropolishing zinc - Google Patents

Process of electropolishing zinc Download PDF

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Publication number
US3088886A
US3088886A US771507A US77150758A US3088886A US 3088886 A US3088886 A US 3088886A US 771507 A US771507 A US 771507A US 77150758 A US77150758 A US 77150758A US 3088886 A US3088886 A US 3088886A
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zinc
electrolyte
cathode
anode
electropolishing
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Expired - Lifetime
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US771507A
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English (en)
Inventor
Duc Joseph Adrien M Le
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Diamond Shamrock Corp
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Diamond Alkali Co
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Priority to NL239247D priority Critical patent/NL239247A/xx
Application filed by Diamond Alkali Co filed Critical Diamond Alkali Co
Priority to US771507A priority patent/US3088886A/en
Priority to US791840A priority patent/US3088887A/en
Priority to DED30300A priority patent/DE1118562B/de
Priority to GB16091/59A priority patent/GB869481A/en
Priority to CH7522959A priority patent/CH396562A/fr
Priority to FR799584A priority patent/FR1233745A/fr
Priority to GB4226/60D priority patent/GB899052A/en
Priority to FR817878A priority patent/FR77123E/fr
Priority to BE587387A priority patent/BE587387A/fr
Application granted granted Critical
Publication of US3088886A publication Critical patent/US3088886A/en
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    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25F—PROCESSES FOR THE ELECTROLYTIC REMOVAL OF MATERIALS FROM OBJECTS; APPARATUS THEREFOR
    • C25F3/00—Electrolytic etching or polishing
    • C25F3/16—Polishing
    • C25F3/22—Polishing of heavy metals

Definitions

  • This invention relates to the electropolishing of zinc and zinc alloys and, more particularly, to a process for the anodic polishing of zinc and zinc alloys and to an electrolyte composition for use in such a process.
  • Zinc and zinc alloys are presently widely used as the base material for making plated articles, particularly chromium plated articles.
  • a casting is made of the zinc or zinc alloy, which casting is customarily then trimmed, strapped and boiled. generally in an automatic bufling machine, to smooth the surface and to eliminate, as much as possible, any pits therein.
  • the surface of the casting is then degreased and cleaned, after which it is plated, first with copper, then nickel and finally chromium, to give the finished plated article.
  • the primary cause for the unsatisfactory characteristics of this method is that considerable quantities of spongy zinc are deposited on the cathodes of the electropolishing apparatus during its use.
  • This spongy deposit of zinc on the cathode becomes larger as the electropolishing is continued, loosens itself from the cathode, floats on the electrolyte and becomes mixed therewith.
  • This floating spongy mass comes in contact with the anode work, thereby short-circuiting above the solution, in a hydrogenoxygen atmosphere, often resulting in an explosion.
  • an oxidizing agent or compound having available oxygen can be added to the electrolyte to prevent the plating of zinc on the cathode. It has been found, that contrary to the prior beliefs, the inclusion of zinc oxide in the alkali metal hydroxide electrolyte is not essential, and additionally, that certain materials, which will prevent the foaming of the alkali metal hydroxide electrolyte during electropolishing, can be included in the electrolyte, without any detrimental effect thereto.
  • Another object of this invention is to provide such a process, whereby the electropolishing takes place in an alkali metal hydroxide electrolyte.
  • a further object of this invention is to provide a suitable alkali metal hydroxide electrolyte for use in the above process.
  • alkali metal hydroxide is meant to refer to the hydroxides of lithium, sodium, potassium, cesium and rubidium.
  • sodium hydroxide is preferred, and for this reason, primary reference will be made hereinafter to sodium hydroxide.
  • FIGS. I to XXIV are reproduced from actual photographs of cathodes, of various materials made before and after the cathodes were used in the electropolishing of zinc in alkali metal hydroxide solutions.
  • FIGS. XXV and XXVI are graphs illustrating the electrode potentials for some of these cathode metals.
  • the method of the present invention envisions the following operative conditions, within the broad range of operating conditions disclosed in the prior art.
  • concentration of the alkali metal hydroxide, preferably sodium hydroxide, electrolyte should be within the range of about 450 to 900 g./liter, with the preferred range being 572 to 763 g./liter, i.e., about a to aqueous sodium hydroxide solution.
  • the temperature of the electrolyte may be varied within the range of to 220 F., depending upon the concentration of the electrolyte which is used.
  • the preferred temperature range is 125 to 162 F.
  • these high temperatures will not produce the most effective electropolishing of zinc and zinc alloys, while temperatures within the range of to F. give the best electropolishing and hence are the preferred temperatures for this concentration range.
  • the solution current density which may be defined as the total applied current divided by the total effective volume of electrolyte, should not be in excess of about 2.5 amps/liter. Where this value is exceeded, the zinc or zinc alloy castings are polished but zinc is plated on the cathode.
  • cathode having a surface which contains Fe O it is meant to include cast iron, which has likewise been found to exhibit the same desirable qualities as the materials mentioned above.
  • Preferred among such cathodes is one of hot-rolled steel or black oxide coated steel.
  • Such a cathode may be in the form of one or several plates or if desired may be the tank which contains the electrolyte.
  • the cathode When such a cathode is used, there is no deposition of a spongy, porous zinc plate thereon, the zinc remains in solution as zincate and considerable quantities of hydrogen gas are discharged at the cathode.
  • the area of the cathode should be of the order of 10-40 times the area of the anode.
  • an oxidizing agent may be added to the electrolyte.
  • examples of such materials are perborates, peroxydisulfates, oxychlorides, permanganates, bichromates, chlorates, bromates, iodates, nitrates, peroxides, and chlorine.
  • Particularly good results have been obtained using the alkali metal perborates, peroxydisulfates, peroxides and nitrates and the alkaline earth metal oxychlorides, specifically, sodium nitrate, sodium perborate, potassium peroxydisulfate, and sodium peroxide and calcium oxychloride.
  • the hydrogen overvoltage value of the Fe O coated cathode has greatly changed the characteristics of the system, so that the current does not plate zinc on the cathode, but rather electrolyzes the contents of the electrolyte, hydrogen being given off at the cathode and the oxygen combining with the zinc and the alkali to form a zincate, which gradually builds up in concentration during electropolishing.
  • the alkali metal hydroxide electrolyte such as sodium hydroxide
  • the addition of zinc oxide to the electrolyte is undesirable, in that as the electropolishing continues, there is a gradual build-up of zinc oxide in the electrolyte until a point is reached at which electropolishing no longer takes place. This point, that is, the concentration of zinc oxide which can be tolerated in the electrolyte, has been found to be about g./liter.
  • an electrolyte bath consisting essentially of a 40 to 50% solution of sodium hydroxide may be used for a period of about 2 to 3 weeks before the zinc oxide concentration therein builds-up to the toleration point of 175 g./liter, whereupon the entire bath may be renewed or any portion thereof may be replenished, which is necessary to reduce the zinc oxide concentration to below the toleration point.
  • the bath may be dragged out every day either by removal or loss of solution and the caustic soda electrolyte replenished by the addition of about 5%, by volume of the total bath, caustic soda, thereby maintaining the zinc oxide concentration in the bath below the toleration point for a period of 6 months or more, after which time the entire bath, generally, will have to be replaced.
  • FIG. I to FIG. III and FIG. VII are Fe O surfaced cathodes.
  • the before and after pictures show that there is no zinc plating where such cathodes are used.
  • FIG. IV to FIG. VI and FIG. VIII to FIG. XXIV show that where the cathode surface does not contain Fe t) there is a considerable build-up of zinc on the cathode.
  • the conditions under which electropolishing was carried out with these various cathodes will be shown in the specific examples which are included hereinafter.
  • an open tank is made of hot-rolled steel or heat treated steel, which tank serves as the cathode.
  • aqueous caustic soda solution containing from 572 to 763 g./liter of caustic soda are placed in the cathode tank.
  • This quantity of electrolyte gives a solution density not in excess of 2.5 amps/liter.
  • the temperature of this solution is maintained within the range of 70 to 90 F.
  • To this solution is added one of the defoaming agents disclosed above, in the amount of .2 g./liter.
  • the size of the cathode tank is about 20-25 times that of the workpiece anode, i.e., for an anode workpiece having an area of 1 square foot, the cathode tank has an area of 20-25 square feet.
  • the work piece of zinc or zinc alloy which is the anode is placed in the electrolyte solution and using a current of 200 ampcres for each square foot of workpiece area, thereby giving a current density of 200 amperes/square foot, electropolishing is carried out for a period of about 4 minutes. At the expiration of this time, the workpiece is removed from the electrolyte and is found to have a smooth, bright, lustrous surface, free of pitting.
  • the cathode tank is completely free of any zinc plate or spongy deposit and there is little if any foam or froth in the electrolyte, thus showing the efiectiveness of the defoaming agent as well as the cathode having a surface containing Fe O in preventing the plating of zinc.
  • the electropolishing is carried out in a 2000 ml. glass beaker, equipped with cooling coils and a hot plate.
  • a 6" x 12" sheet of heat treated steel is formed into a cylindrical cathode and placed into the beaker and 1700 ml. of electrolyte are added to the beaker.
  • the effective volume of electrolyte contained within the cylindrical cathode is about 1115 ml.
  • a x 1" workpiece having a total surface area of about .01 square foot, is secured to a work bar which is lowered into the electrolyte.
  • This workpiece is a zinc alloy known by the trade name Zamak-3 (trademark of The New Jersey Zinc Company) and having the following composition as specified in the 1957 ASTM Supplement, Part 2, page 115:
  • the electrolyte is agitated by means of work bar agitation, the work bar having a two inch displacement/one second stroke.
  • a source of DC. current is connected to the workpiece and electropolishing is carried out for the desired length of time.
  • Examples 1 through 14 illustrates the effect of varying the electrolyte concentration.
  • the voltage range is 5.0-7.8 volts and the applied current is 2.5 amperes.
  • 46B 550 200 2. 5 7345 Clean and bright.
  • 46C 550 400 4. 5 73-75 D0.
  • 47A 600 100 1. 5 73-75 D0.
  • 47B 609 200 2. 5 73-75 Clean and very bright.
  • 47C 600 400 4. 5 73-75 Do. 17.
  • 60A 665 100 1. 73-75 Clean and bright.
  • the effect of varying the temperature of the electrolyte can be seen.
  • the voltage is 4.8 volts
  • the applied current is 2.5 amperes
  • the anode current density is 200 amps/square foot
  • the contact time is 4 minutes.
  • 013-2 800 129 Clean and bright, slightly pitted. 9D-2 800 154 Dark grey oxide coating.
  • the following table incorporating Examples 46-62, illustrates the effects obtained by incorporating zinc oxide and other metallic oxides in the caustic soda electrolyte composition.
  • the voltage range is 4.8-6.2 volts
  • the temperature varied between 73-75 F. and the contact time is 4 minutes.
  • 53B 625 200 2. 5 Clean and very bright.
  • 53C 625 400 4. 5 Do. 58.. 54A 665 100 1. 25 Clean and bright.
  • MB 665 200 2. 5 Clean and very bright. 54C 665 400 4. 5 Do.
  • 70B 665 200 2. Clean and very bright. 70C 665 400 4.5 Do.
  • IZOD-2 665 100 15 81 Clean and slightly polished. 120D-3 065 6O s0 81 Do. D-4 665 100 60 45 81 Clean and bright. 67 120E-1 655 100 100 5 82 Clean but not poliShBd.
  • HOE-2 665 100 100 15 82 (lean and slightly polished. HOE-3 665 104) 30 82 Clean and bright.
  • l20E-4 6G5 100 100 45 82 Clean and very bright.
  • Example 75 To illustrate the build-up of zinc oxide concentration during electropolishing, a life test is made using as the electrolyte liters of caustic soda solution in a hard rubber tank containing 668 g. of caustic soda/liter and 0.2 g./liter polyoxyethylene ester of mixed fatty and rosin acid (Renex 20) as a defoamer. During this test the anode current density is 200 amps/square foot, the cathode current density is 13.8 amps/square foot and 12 oxide, electropolishing is carried out in 31.5 liters of electrolyte containing 665 g. of sodium hydroxide/liter, 100 g. of zinc oxide/liter, 0.2 g.
  • the electropolishing is carried out in a 32 liter tank of heat-treated steel, which tank forms the cathode and has a surface area of 5.4 square foot.
  • the solution densit is 1.6 am s./liter.
  • the anodes used are 1/2 inch Stripsyof alloy having a total sub the anode, .2 strips of Zamak-3 are used, having a total face area of .04/square foot, while the cathode is two surface area of sqllare AS m
  • Example the sheets, 7 inches x 7 inches of heat-treated iron having anodes are electropohshed they are about a surface area of 0.58/ square foot.
  • the temperature of consumed, whereupon they l replaced The condltlons the electrolyte is maintained within the range of about 15 of operation and results Obtamed are reported below in 7595 F., the average temperature being about F.
  • the anode is electropolished continuously until it is about 75% consumed whereupon it is replaced with a new anode.
  • the following table is a summary of tabular summary, the results being reported every 1020 hours. It should be noted that observations made during the intervals between the reported data indicate no significant deviation from the general trend.
  • Example 76 In order to show the zinc oxide build-up during elec- To show the effect of daily replenishment of electrolyte tropolishing in an electrolyte which initially contains zinc 75 to simulate drag-out with regard to the zinc oxide builds,oss,sse
  • a life test is made using liters of electrolyte containing 669.8 g. of sodium hydroxide/liter, 93.6 g. of zinc oxide/liter and 0.2 g./liter defoamer (Renex).
  • the anode current density is 200 amps./ square foot, the cathode current density 13.8 amps./ square foot and the solution density is 1.6 amps/liter.
  • the temperature is maintained within the range of about 70-90 F. with the average temperature being about 80 F.
  • the cathode is formed from two 7 inch x 7 inch sheets of heat-treated steel having a total surface area of .58 square foot.
  • the anode is a /2 inch strip of Zamak-3 alloy having a total surface area of .04 square foot.
  • the following examples show the results obtained in testing different materials as cathodes for use in the present process.
  • the half-tones which form the illustrative figures of the present invention were made of the cathode before and after electropolishin
  • electropolishing is carried out in a one liter beaker containing 784 ml. of electrolyte, containing 632 g./liter sodium hydroxide and 1 01 g./liter zinc oxide.
  • the anode is of Zamak-3 and has an area of 0.052 square foot.
  • the anode current density is 200 amps/square foot and the solution density isl.
  • the following examples which are carried out separately, are given in which the oxygen and hydrogen efilciencies during electropolishing using various cathode materials are measured.
  • the anode is Zamak-S and has an area of 0.65 square inch.
  • the anode current density is 200 amps/ square foot.
  • the electrolyte is 750 ml. containing 632 g. sodiiun hydroxide/liter and 101 g. zinc oxide/liter.
  • the applied current is 1 amp. and the solution density is 1.25 amps/liter.
  • cathodes having a surface of l e- 0 potential measurements are carried out with several cathode materials in both 45% caustic soda solution and sodium zincate (665 g./liter NaOH, 100 g./liter ZnO) media.
  • the measurements are made using the conventional direct method" for electrode potential and over potentials under continuous electrolysis in a 1000 ml. solution with constant stirring.
  • Both the reference and the elccti'opolisliing cells are kept at a constant temperature of C.-* :O.1.
  • the anode area is kept constant at 3.9 cm. while the cathode area varies from 50-100 cm.
  • the anode material is Zamak-3 alloy. Because of the alkali medium, the reference electrode selected is mercury-mercuric oxide; it is checked with a standard saturated calomel electrode (0.2415 v.).
  • Table XIIA gives the reference electrode potentials for various sodium hydroxide concentrations. The values (unknown in literature) are reported to serve as the basis for the measurements. The E.M.F. of the mercurymercuric oxide electrode with the zincate solution is determined to be 0.065 v. (not included in Table XII-A).
  • Table XII-B gives the values obtained with various cathodes under various current densities in both the 45% caustic soda and zincate media.
  • FIGS. 25 and 26 give a graphic comparison of these potentials.
  • the oxide film is formed by the F o I I T8322 electrochemical oxidation of the anodes until the point 10.30 +0.1749 -0.006e where a break-through occurs and thereafter electropol- V0 u I v 23 1811233 $1835: ishing 15 produced.
  • the point on the anodic potential 9- +0.18% 53 curve is at about 40-50 amps/square foot which is in agreement with the result obtained by varying the cur- TABLE XII-B Electrode potential in 45% NaOH Electrode potential in the zineiite solution Current density, Stainless Steel Stainless Nickel Steel Steel 7 malcm.
  • a method of anodically electropolishing an article having a surface of metal selected from the group consisting of zinc and zinc base alloys which comprises making the article to be polished the anode in an electrolytic cell, the electrolyte of which is comprised of an alkali metal hydroxide in the amount between about 450 and 900 grams/liter, maintained at a temperature between about 60 and 220 F.
  • a method of anodically electropolishing an article having a surface of metal selected from the group consisting of zinc and zinc base alloys which comprises making the article to be polished the anode in an electrolytic cell, the electrolyte of which is comprised of an alkali metal hydroxide in the amount between 572 and 763 grams/ liter, maintaining said electrolyte at a temperature between about 70 and 90 F., passing an electric current through said electrolyte between said anode and a cathode at an anode current density of about 200 amps/square foot, said cathode having a surface of Fe the passage of current being for a period of time sufficient to electropolish said anode, and using a voltage sufficient to provide the above current density, said voltage being below that at which zinc will be electrodeposited on said cathode having a surface of Fe O 3.
  • the alkali metal hydroxide in the electrolyte is sodium hydroxide.
  • a method of anodically electropolishing an article having a surface of metal selected from the group consisting of zinc and zinc base alloys which comprises making the article to be polished the anode in an electrolytic cell, the electrolyte of which is comprised of sodium hydroxide in the amount of about 665 grams/liter, maintained at a temperature of about 76 F.

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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)
  • Electrical Discharge Machining, Electrochemical Machining, And Combined Machining (AREA)
  • Electroplating Methods And Accessories (AREA)
US771507A 1958-11-03 1958-11-03 Process of electropolishing zinc Expired - Lifetime US3088886A (en)

Priority Applications (10)

Application Number Priority Date Filing Date Title
NL239247D NL239247A (fr) 1958-11-03
US771507A US3088886A (en) 1958-11-03 1958-11-03 Process of electropolishing zinc
US791840A US3088887A (en) 1958-11-03 1959-02-09 Electropolishing of zinc-copper alloys
DED30300A DE1118562B (de) 1958-11-03 1959-03-26 Verfahren zum anodischen Glaenzen von Zink und Zinklegierungen
GB16091/59A GB869481A (en) 1958-11-03 1959-05-11 Improvements in or relating to the electro-polishing of zinc and zinc alloys
CH7522959A CH396562A (fr) 1958-11-03 1959-07-02 Procédé d'électropolissage anodique
FR799584A FR1233745A (fr) 1958-11-03 1959-07-07 Procédé d'électropolissage anodique
GB4226/60D GB899052A (en) 1958-11-03 1960-02-05 Improvements in or relating to electropolishing of zinc and zinc alloys
FR817878A FR77123E (fr) 1958-11-03 1960-02-08 Procédé d'électropolissage anodique
BE587387A BE587387A (fr) 1958-11-03 1960-02-08 Procédé d'électropolissage anodique.

Applications Claiming Priority (2)

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US771507A US3088886A (en) 1958-11-03 1958-11-03 Process of electropolishing zinc
US791840A US3088887A (en) 1958-11-03 1959-02-09 Electropolishing of zinc-copper alloys

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US791840A Expired - Lifetime US3088887A (en) 1958-11-03 1959-02-09 Electropolishing of zinc-copper alloys

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BE (1) BE587387A (fr)
CH (1) CH396562A (fr)
DE (1) DE1118562B (fr)
FR (2) FR1233745A (fr)
GB (2) GB869481A (fr)
NL (1) NL239247A (fr)

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Publication number Priority date Publication date Assignee Title
ES2343298B1 (es) * 2009-01-26 2011-06-06 Metal Finishing Development, S.L. "medio, procedimiento y dispositivo para el tratamiento superficial de superficies de piezas de oro o sus aleaciones".
CN106637377B (zh) * 2016-12-19 2019-03-19 二重（德阳）重型装备有限公司 镍基合金电解抛光液及其抛光方法

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US670201A (en) * 1900-10-11 1901-03-19 Ferdinand F Cimiotti Process of producing zinc oxid and nitrites.
US931513A (en) * 1907-03-21 1909-08-17 Chem Fab Griesheim Electron Electrode.
US2655472A (en) * 1949-12-16 1953-10-13 Robert V Hilliard Process of extracting and recovering metals by leaching and electrolysis

Family Cites Families (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2075623A (en) * 1934-11-12 1937-03-30 Du Pont Zinc plating
US2154469A (en) * 1934-12-17 1939-04-18 Du Pont Bright dip
US2101580A (en) * 1936-05-02 1937-12-07 Udylite Company Process for obtaining bright zinc coating
US2384660A (en) * 1940-03-11 1945-09-11 Bethlehem Steel Corp Apparatus for electrolytic galvanizing of sheets
NL69965C (fr) * 1945-08-10
GB626244A (en) * 1946-04-17 1949-07-12 Du Pont Production of smooth electrodeposits
US2610144A (en) * 1947-02-08 1952-09-09 Oneida Ltd Method of electropolishing
GB724829A (en) * 1953-04-01 1955-02-23 Siemens & Halske G M B H A process for electrolytically polishing articles made of, or substantially of, gold
NL90899C (fr) * 1953-04-28
US2799636A (en) * 1954-03-03 1957-07-16 Coats & Clark Processing of separable fastener stringers

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US670201A (en) * 1900-10-11 1901-03-19 Ferdinand F Cimiotti Process of producing zinc oxid and nitrites.
US931513A (en) * 1907-03-21 1909-08-17 Chem Fab Griesheim Electron Electrode.
US2655472A (en) * 1949-12-16 1953-10-13 Robert V Hilliard Process of extracting and recovering metals by leaching and electrolysis

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US3088887A (en) 1963-05-07
FR77123E (fr) 1962-01-19
GB869481A (en) 1961-05-31
FR1233745A (fr) 1960-10-12
NL239247A (fr)
GB899052A (en) 1962-06-20
BE587387A (fr) 1960-05-30
CH396562A (fr) 1965-07-31
DE1118562B (de) 1961-11-30

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