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
  • C25D3/02—Electroplating: Baths therefor from solutions
  • C25D3/04—Electroplating: Baths therefor from solutions of chromium

Definitions

• the present invention is based on methodical researches which have resulted in the establishment of the fact that considerable modifications of current density conditions may be rendered possible by adding to the chromic acid (between very close limits the reason for which will be given below) ions of Na (in the form of Na: Cr: 01, or of an equivalent quantity of neutral sodium chromate or sodium hydroxide).
• the maximum admissible current density can be raised to a value ten times greater than the known value.
• the quality of the layer of chromium obtained is, moreover, notably improved; it has an almost yellowish coloration, a remarkable ductility and a total absence of structure.
• the meanratio is thus: 2 mol. NaOH to 5 mol.
• composition of the tetrachromate is: 2 mol. NaOH to 4 mol. 'C1O3.
• I can proceed either by adding to 131 grams of caustic soda, 660 grams of. chromic acid and 210 cc. of water; or by mixing 490 grams of crystallized dichromate of sodium (2H2O) with 330 grams of chromic acid and 180 495 grams of chromic acid and evaporating until 57 grams of water have disappeared.
• I can proceed either by adding to 40 grams of caustic soda, 264 grams of chromic acid and 696 grams of water; or by adding to 163 grams of neutral chromate of sodium 10H2O), 210 grams of chromic acid and 627 cc. of water; or finally by mixing 123 grams of dichromate of sodium (2H2O), grams of chromic acid and 712 cc. of water.
• the solutions are to be maintained at a temperature below 40 C.
• the reaction differs according to the current density. It only attains its typical qualities lhigh yield, yellow coloration of the chromium) for the most elevated current densities while, for medium or weak current densities, the yield and also the coloration of the chromium rather approach the known conditions.
• Ah signifies ampere hours.
• the formation of the intermediate chromium range (chromates of chromium) is prevented the more, the higher is the cathodic pressure of hydrogen; the reduction of ClOs to Cr is in this case preferably produced directly.
• the deposited chromium then automatically takes the molecular structure of ClOa which determines among other things the coloration of the deposit.
• the reduction takes place principally on the chromic range.
• the bluish coloration of the chromium which is deposited in this case is due to the molecular structure of the chromium hydroxide.
• the hardness of the chromium moreover, varies in a corresponding manner to the coloration.
• the yellow chromium is more ductile than the blue chromium, the chromate structure being less dense than the chromic structure. Certain peculiarities are directly due to this fact.
• the chromic chromium With the exception of its tendency to the adsorption of hydrogen, the chromic chromium is definitely more inactive from the chemical point of view than, the chromate chromium, this latter being inactive as regards the adsorption of hydrogen but more sensitive to other influences and.
• the chromic chromium is superior to the other, which in its turn is'to be preferred when there is desired a certain ductility and chemical reactivity. This latter thus serves for chromium plating intended subsequently to be machined (rolling and cutting) or for objects subjected to considerable bending (wires).
• the chromate chromium has retained the tendency which chromic acid likewise possesses, that is to say, the tendency to attack metals, i. e. in the metallographic sense, that is to say, of the formation of alloys with the support.
• the layers of chromium deposited in baths of tetrachromate adhere atomically to the metals of the base, above all in the case in which the structure of these latter is favourable.
• a process of rapid electrolytic chromium plating which consists in: rendering the bath of chromic acid effectively responsive to a high amperage current by adding to the bath a substance of the group comprising sodium dichromate, neutral sodium chromate and sodium hydroxide in such quantity as to form sodium tetrachromate, maintaining said bath below 40 0.,

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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)

Applications Claiming Priority (1)

Publications (1)

Family

ID=8897621

Family Applications (1)

Country Status (4)

Cited By (6)

• 0
  • FR FR754299D patent/FR754299A/fr not_active Expired
• 1933
  • 1933-07-28 US US682707A patent/US1985308A/en not_active Expired - Lifetime
  • 1933-07-28 GB GB21303/33A patent/GB410645A/en not_active Expired
  • 1933-07-28 DE DES110357D patent/DE608757C/de not_active Expired

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