US2704273A - Process for chromium electrodeposition - Google Patents

Process for chromium electrodeposition Download PDF

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US2704273A
US2704273A US255857A US25585751A US2704273A US 2704273 A US2704273 A US 2704273A US 255857 A US255857 A US 255857A US 25585751 A US25585751 A US 25585751A US 2704273 A US2704273 A US 2704273A
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chromium
bath
urea
ammonium
grams
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Yoshida Tadashi
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    • 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
    • C25D3/02—Electroplating: Baths therefor from solutions
    • C25D3/04—Electroplating: Baths therefor from solutions of chromium
    • C25D3/06—Electroplating: Baths therefor from solutions of chromium from solutions of trivalent chromium

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  • PROCESS FOR CHROMIUM ELECTRODEPOSITION I Filed liov. 10, 1951 40 5'0 7///. 51/4/ 5 4/75/5 PFE APAT/FA Haw- #9 Jim/19mm yum/5 IN VENTOR.
  • the present invention relates to a process for the electrodeposition of metallic chromium, wherein an aqueous solution containing chromic sulfate and free urea, with complex ions having reached an equilibrium at the temperature of electrolysis, is used as an electrolytic bath and at the same time a lead alloy containing relatively small quantities of tin, silver and cobalt is used as the anode.
  • the primary object of the present invention lies in establishing industrially valuable process for the electrodeposition of high quality metallic chromium at high efiiciency and without the evolution of poisonous gas during the operation using a chromic sulphate bath.
  • An additional object of the invention is to obtain the further industrial advantages as follows:
  • the advantages of the present invention are set forth as follows:
  • the chromic sulfate bath should be kept at a constant electrolytic temperature for a relatively long interval of time, so that the complex ions in the bath may be given time enough to reach an equilibrium for the temperature of electrolysis, before it is used for the plating operation.
  • the former workers conducted merely a macroscopical observation, on the state of complex ions in the aqueous solution of chromic sulfate, for instance, if it is purple or green.
  • a diagram as shown in the figure has been obtained by plotting the time elapsed after the preparation on the abscissa and the specific conductivity of each solution on the ordinate axes respectively.
  • the time needed for curve (A) and curve (B), in the figure, converting in straight lines parallel to the abscissa is dilferent.
  • the two curves, however, are converted finally in one straight line which is parallel to the abscissa.
  • the fact mentioned above proves that a state of complex ion, in a chromic sulfate bath of the same chemical composition, will reach a definite equilibrium at a given temperature in a certain period of time, despite of the initial state of the complex ion.
  • both curve (A) and curve (C) become parallel to the abscissa in about 45 hours after they have been prepared. Namely, it has been shown that aging for about 45 hours is necessary for the state of complex ion in the electrolytic bath of above-mentioned composition, which has once been boiled, to come to an equilibrium at about 40 C.
  • the optimum temperature for the electrolytic bath is found, according to the present invention, at a temperature between 25 and 55 C. At this temperature, the time for aging, needed by the complex ions of an electrolytic bath, which has once been subjected to boiling during its preparation, for attaining an equilibrium at the given temperature, can be obtained by a similar method as adopted in the above mentioned experiment.
  • the process according to the present invention employs an electrolytic bath containing 41 to 73 grams of trivalent chromium, to 264 grams of free urea in one liter of aqueous solution.
  • the free urea comprising 2.46 to 6.44 times the weight of trivalent chromium is added to the electrolytic bath.
  • the present inventor has deduced, from the molecular constitution, that the urea molecules existing in a free state in the electrolytic bath should demonstrate a strong buffer action. As a matter of fact, an atmosphere of extremely low hydrogen ion concentration taking place locally in the vicinity of the cathode is considerably weakened by the strong buffer action of free urea in the bath.
  • the electrolytic bath according to the invention when used, it is possible to obtain a satisfactory electrodeposition, in an electrolysis carried out with an anode of a material such as magnetite or graphite, etc., which shows a low oxidising power against chromium during electrolysis and is insoluble.
  • a lead alloy containing by weight 4 to 12% Sn, 1 to Ag, 0.1 to 2.5% Co and balance Pb as a most optimum anode material.
  • the lead alloy is high in electrical conductivity; the terminal voltage is relatively low in the course of electrolysis; forming and fabrication in desirable shapes being easy, it is convenient for electrodeposition on a cathode of relatively intricated shape; preparation from commercial raw material at relatively lower cost.
  • a lead alloy with 30 to 40% Sn and 0.1 to 0.5% Co has already been proposed by C. G. Fink and others (Transactions of The Electrochemical Society, volume 76, 1939, p. 401) as anode material for electrowinning of manganese. Also, C. G. Fink and others (Transactions of The Electrochemical Society, vol. 46, 1924, p. 349, and ibid.. vol. 49, 1926, p. have introduced as anode material for electrolysis of brine another lead alloy containing Ag as high as 50 to 60%, and described that Ag is extremely useful for protecting an anode from corrosion by chlorine.
  • the cathode When an aqueous solution containing trivalent chromium and hexavalent chromium is subjected to electrolysis, the cathode is covered with a membrane-like diaphragm consisting of chromic chromate as indicated by Miller et al. (E. Miller: Zeitschrift fiir Elektrochemie, Bd. 32, 8.399, 1926).
  • Miller et al. E. Miller: Zeitschrift fiir Elektrochemie, Bd. 32, 8.399, 1926.
  • the membrane of chromic chromate then formed is favorable for the electrolysis. Divalent chromium accumulates within this membrane discharges at the cathode to deposit fine metal.
  • the free urea molecule develops the aforementioned effect in the diaphragm.
  • the electrolytic bath of the present invention when the content of hexavalent chromium is excessively high, a smooth progress of electrolytic deposition seems to be hampered, because the chromic chromate diaphragm covering the cathode during electrolysis is then too thick and too hard.
  • hexavalent chromium which forms gradually in the electrolytic bath in an extremely small quantity during operation, does not show any obstacle in prac tice.
  • the small quantity of hexavalent chromium can readily be removed by suitable means, for instance, by addition of hydrogen peroxide solution of an appropriate quantity which reduce and remove it.
  • the anode made thereof is readily subject to corrosion, while, if those components are less than the above limits, the oxidising power of the anode made thereof will be high. In both cases, the alloy is no longer suitable for anode construction.
  • the most advantageous electrolytic bath from the point of industrial practice is one that contains chromic sulfate as the principal constituent with free urea and ammonium sulfate as secondary constituents.
  • chromic sulfate as the principal constituent with free urea and ammonium sulfate as secondary constituents.
  • a part of the ammonium sulfate can be substituted by either sodium sulfate or potassium sulfate within the limit given below.
  • the advantages furnished by those sulfates of ammonium, sodium and potassium added to the electrolytic bath are in the first place that the electrical conductivity of the path is improved thereby, and in the second place, they show buffer characteristics to some extent.
  • the optimum range for the amount of addition of ammonium, sodium and potassium sulfates are as in the following, and whenever the content of those sulfates in the bath may be less or more than those limits, the conductivity will become poor and inconvenient.
  • the layer of electrolytic deposition formed When the content of trivalent chromium in a liter of the solution is less than 41 g., the layer of electrolytic deposition formed will be scaly and easy to strip, and if it is more than 73 g., the viscosity and resistivity of the electrolytic bath will become exceedingly high, and inconvenient in both cases.
  • Electrolytic bath contains in a liter: 41 to 73 g. of trivalent chromium; 180 to 264 g. of free urea; 90 to 123 g. of ammonium radical, which can be substituted, to the extent of 55 g. maximum, of either sodium or potassium; sulfate radical stoichiometrically at least equivalent to the content of ammonium radical, sodium, potassium and trivalent chromium.
  • any one of the following solutions can be chosen: a solution obtained by reducing the hexavalent chromium solution; a solution of chrome-alum dissolved in the water; a solution of commercial chromic sulfate dissolved in the water. And in any of the above solutions, first the theoretical quantities of chemicals necessary are dissolved excepting urea. The solution thus obtained is boiled for several minutes and the theoretical quantity of urea is dissolved therein after being cooled down below 60 C. The procedure of boiling the solution in such a manner as above is not always necessary.
  • each necessary aging time is roughly as follows: over about 500 hours for 25 C., over about 100 hours for 35 C., over about 12 hours for C., and over about 4 hours for C.
  • the solution is used for the electrodeposition after it has been affirmed that the complex-ion state in the bath has reached an equilibrium for the temperature of electrolysis and that the hydrogen ion concentration. shows a pH- value ranging from 1.8 to 3.0.
  • the electrolytic bath affords no obstacle in the operation, even when it contains up to 1.5 g. maximum per liter of hexavalent chromium, in accordance with the operation.
  • the electrolytic bath always contains a small quantity of divalent chromium, during or immediately after the electrolysis.
  • Equipment-An acid-proof, open cell with a cathode consisting of a conductor to be electrodeposited hanging therein and an anode made of a lead alloy containing by weight 4 to 12% Sn, 1 to.10% Ag, 0.1 to 2.5% Co and balance Pb, is used.
  • the working temperature of the electrolytic bath is held at a definite temperature between 25 and 55 C.
  • the cathode current density to be applied ranges appropriately as follows: from 8 to 28 ampere/dm for temperatures of electrolysis of 25 C.; from 14 to 36 ampere/dm. for 35 C.; from 24 to 42 ampere/dm. for 45" C.; from 36 to 46 ampcre/dm. for 55 C. Stirring of the bath during the operation is favorable.
  • the hexavalent chromium formed due to the anodic oxidation accumulated gradually in the bath.
  • an appropriate quantity of hydrogen peroxide solution is added in order to reduce the said hexavalent chromium, and thus to assure that the content of hexavalent chromium does not exceed 1.5 grams per liter of the electrolytic bath.
  • the supply of chromium in the bath is maintained by dissolving the required quantity of chromic acid in the bath, then an appropriate reducing agent, for instance, hydrogen peroxide solution is added in an amount equivalent to the said chromic acid, in order to reduce the hexavalent chromium.
  • an appropriate reducing agent for instance, hydrogen peroxide solution
  • Example 1 An aqueous solution is used which contains per liter the following constituents as follows: 196 g. of chromic sulfate; 423 g. of ammonium sulfate; 240 g. of urea. A concentrated aqueous solution of chromic acid is first completely reduced with sulfur dioxide, then the excess sulfur dioxide absorbed is removed with chromic acid added in an equivalent quantity to it, and thus a green aqueous solution containing per liter about 392 g. of chromic sulfate is obtained. A theoretical amount of ammonium sulfate is added to the required quantity of the said solution and stirred thoroughly, while heating above 90 C.
  • a theoretical amount of urea is dissolved therein after it has been cooled down below C. Finally, an appropriate quantity of water is added. Then, an aqueous solution of the above-mentioned chemical composition is obtained. The solution obtained is filtered and held at about 40 C. in an open cell and is subjected to an aging treatment for about 40 hours. Then, the hydrogen ion concentration is adjusted to about 2.1 pH- value. This is used for the electrodeposition.
  • a lead-lined open cell is employed; the total quantity of the electrolytic bath is 200 liters.
  • a cathode a nickel plated copper sheet of 2 dm. per one surface is used, while an anode, which consists of a lead alloy sheet of which the effective area is 8 dm. containing 8% of tin, 4% of silver, 2% of cobalt and 86% of lead, is used by providing them on both sides of the cathode at a distance of 20 cm. from the cathode respectively.
  • the terminal voltage of about 10.5 volt is shown.
  • the agitation of the bath is appropriately conducted by means of the compressed air blown in the bath during the operation.
  • the electrolytic bath of 200 liter has been altered at the end of the operation carried out under a current input of net 540 amp-hour for one day, as follows:
  • the pH value of bath is then 2.4;
  • the decrease of chromium due to the electro-deposition and drug-out is 35 g.;
  • hexavalent chromium accumulated in the bath becomes 50 g.
  • 100 cc. of 96% concentrated sulfuric acid is added to the bath to adjust the pH value of bath, and at the same time 108 g. of urea is also supplemented.
  • 68 g. of chromic acid is dissolved and subsequently 340 cc. of 30% of hydrogen peroxide solution is gradually added in the bath under stirring. Thereby, the hexavalent chromium in the bath could then be reduced completely.
  • Example 2 An aqueous solution containing the following constituents per liter is used as the electrolytic bath: 196 g. of chromic sulfate; 271 g. of ammonium sul fate; 87 g. of potassium sulfate; 30 g. of sodium sulfate; and 240 g. of urea.
  • aqueous solution containing the following constituents per liter is used as the electrolytic bath: 196 g. of chromic sulfate; 271 g. of ammonium sul fate; 87 g. of potassium sulfate; 30 g. of sodium sulfate; and 240 g. of urea.
  • chrome-potassium alum is dissolved completely by heating in a small amount of added water.
  • the subsequent procedures in'the preparation are conducted almost similarly as in Example 1, and the aging is also the same as in the preceding case.
  • Example 1 When the electrolysis is carried out under perfectly the same condition as in Example 1 in except of what has been described above, a satisfactory result nearly the same as Example 1 is obtained.
  • the electrolytic bath as shown in this example, shows a terminal voltage of about 12 volts, on account of its somewhat low electrical conductivity.
  • a process for the electrodeposition of metallic chromium which comprises causing electrodeposition of metallic chromium from an electrolytic bath consisting of an aqueous solution containing per liter 41 to 73 grams trivalent chromium, 180 to 264 grams free urea, 90 to 123 grams of a substance selected from the group consisting of ammonium, ammonium and potassium, ammonium and sodium, and ammonium, potassium and sodium, the amount of potassium and sodium, when included, not exceeding 55 grams, and sulphate radical in an amount at least stoichiometrically equivalent to the amount of ammonium radical, potassium and sodium when included, and trivalent chromium, said solution having been aged at a.
  • a process for the electrodeposition of metallic chromium which comprises causing electrodeposition of metallic chromium from an electrolytic bath consisting of an aqueous solution containing per liter 41 to 73 grams trivalent chromium, 180 to 264 grams free urea, to 123 grams of ammonium radical, and sulphate radical in an amount at least stoichiometrically equivalent to the amount of ammonium radical, and trivalent chromium, said solution having been aged at a constant electrolytic temperature to cause an equilibrium in the state of the complex ions in the solution at the temperature of electrolysis, said temperature being between 25 and 55 C., with an anode consisting of 4 to 12% tin, 1 to 10% silver, 0.1 to 2.5% cobalt and the balance lead.
  • a process for the electrodeposition of metallic chromium which comprises causing electrodeposition of metallic chromium from an electrolytic bath consisting of an aqueous solution containing per liter 41 to 73 grams trivalent chromium, to 264 grams free urea, a combined weight of 90 to 123 grams of ammonium radical and sodium, the amount of sodium not exceeding 55 grams and sulphate radical in an amount at least stoichiometrically equivalent to the amount of ammonium radical, sodium and trivalent chromium, said solution having been aged at a constant electrolytic temperature to cause an equilibrium in the state of the complex ions in the solution at the temperature of electrolysis, said temperature being between 25 and 55 C., with an anode consisting of 4 to 12% tin, 1 to 10% silver, 0.1 to 2.5% cobalt and the balance lead.
  • a process for the electrodeposition of metallic chromium which comprises causing electrodeposition of metallic chromium from an electrolytic bath consisting of an aqueous solution containing per liter 41 to 73 grams trivalent chromium, 180 to 264 grams free urea, a combined weight of 90 to 123 grams of ammonium radical and potassium, the amount of potassium not exceeding 55 grams, and sulphate radical in an amount at least stoichiometrically equivalent to the amount of ammonium radical, potassium and trivalent chromium, said solution having been aged at a constant electrolytic temperature to cause an equilibrium in the state of the complex ions in the solution at the temperature of electrolysis, said temperature being between 25 and 55 C., with an anode consisting of 4 to 12% tin, 1 to 10% silver, 0.1 to 2.5% cobalt and the balance lead.
  • a process for the electrodeposition of metallic chromium which comprises causing electrodeposition of metal lic chromium from an electrolytic bath consisting of an aqueous solution containing per liter 41 to 73 grams trivalent chromium, 180 to 264 grams free urea, a combined weight of 90 to 123 grams of ammonium radical, potassium and sodium, the amount of potassium and sodium not exceeding 55 grams and sulphate radical in an amount at least stoichiometrically equivalent to the amount of ammonium radical, potassium and sodium and trivalent chromium, said solution having been aged at a constant electrolytic temperature to cause an equilibrium in the state of the complex ions in the solution at the temperature of electrolysis, said temperature being between 25 and 55 C., with an anode consisting of 4 to 12% tin, 11 t) 10% silver, 0.1 to 2.5% cobalt and the balance 6.

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US255857A 1951-09-28 1951-11-10 Process for chromium electrodeposition Expired - Lifetime US2704273A (en)

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GB858752A GB715225A (en) 1952-04-03 1952-04-03 Process for chromium electro-deposition

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Cited By (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2766196A (en) * 1953-11-09 1956-10-09 Yoshida Tadashi Process for the electrodeposition of iron-chromium alloys
US2801214A (en) * 1956-03-23 1957-07-30 Melvin R Zell Chromium plating bath
US2822326A (en) * 1955-03-22 1958-02-04 Rockwell Spring & Axle Co Bright chromium alloy plating
US3259560A (en) * 1961-07-26 1966-07-05 Nat Res Dev Process for the electrolytic production of cromium of a high degree of purity
US3268353A (en) * 1960-11-18 1966-08-23 Electrada Corp Electroless deposition and method of producing such electroless deposition
US3282723A (en) * 1960-11-18 1966-11-01 Electrada Corp Electroless deposition and method of producing such electroless deposition
WO2014202316A1 (fr) * 2013-06-20 2014-12-24 Tata Steel Ijmuiden B.V. Procédé permettant de fabriquer des substrats recouverts de chrome-d'oxyde de chrome
US10000861B2 (en) 2012-03-30 2018-06-19 Tata Steel Ijmuiden Bv Coated substrate for packaging applications and a method for producing said coated substrate

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
AU2348470A (en) * 1969-12-29 1972-07-06 International Lead Zinc Research Organization Aqueous chromium plating baths

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2340400A (en) * 1943-01-16 1944-02-01 Electro Manganese Corp Anode
US2419722A (en) * 1941-08-07 1947-04-29 Hudson Bay Mining & Smelting Alloy anode for electrodeposition of zinc

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2419722A (en) * 1941-08-07 1947-04-29 Hudson Bay Mining & Smelting Alloy anode for electrodeposition of zinc
US2340400A (en) * 1943-01-16 1944-02-01 Electro Manganese Corp Anode

Cited By (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2766196A (en) * 1953-11-09 1956-10-09 Yoshida Tadashi Process for the electrodeposition of iron-chromium alloys
US2822326A (en) * 1955-03-22 1958-02-04 Rockwell Spring & Axle Co Bright chromium alloy plating
US2801214A (en) * 1956-03-23 1957-07-30 Melvin R Zell Chromium plating bath
US3268353A (en) * 1960-11-18 1966-08-23 Electrada Corp Electroless deposition and method of producing such electroless deposition
US3282723A (en) * 1960-11-18 1966-11-01 Electrada Corp Electroless deposition and method of producing such electroless deposition
US3259560A (en) * 1961-07-26 1966-07-05 Nat Res Dev Process for the electrolytic production of cromium of a high degree of purity
US10000861B2 (en) 2012-03-30 2018-06-19 Tata Steel Ijmuiden Bv Coated substrate for packaging applications and a method for producing said coated substrate
WO2014202316A1 (fr) * 2013-06-20 2014-12-24 Tata Steel Ijmuiden B.V. Procédé permettant de fabriquer des substrats recouverts de chrome-d'oxyde de chrome

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