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
  • C25D5/38—Pretreatment of metallic surfaces to be electroplated of refractory metals or nickel
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25F—PROCESSES FOR THE ELECTROLYTIC REMOVAL OF MATERIALS FROM OBJECTS; APPARATUS THEREFOR
  • C25F1/00—Electrolytic cleaning, degreasing, pickling or descaling
  • C25F1/02—Pickling; Descaling
  • C25F1/04—Pickling; Descaling in solution
  • C25F1/08—Refractory metals

Definitions

• the oxide proves difiicult to attack or to detach, it proves necessary to perform the attacking process for such lengths of time that, when the oxide layer has to be completely removed, the thickness of metal which is consequently removed is unpredictable or incompatible with the dimensional tolerances which have been laid down.
• the anodic oxide film which is formed prevents the flow of current with the result that, after a very short time, the oxidation rate becomes either very low or zero; such films can be etched only with great difiiculty above a certain thickness.
• the electrolytic bath is a mixture of nitric acid and hydrofluoric acid which may be diluted if necessary.
• the object of the present invention is therefore a method of electrolytic etching of zirconium and zirconiurn-base alloys which makes it possible to remove from the surface of these metals:
• Oxidation films which up to the present time could be removed only with difficulty by chemical process and then left a surface which was more or less modified geometrically and which was therefore unfit for many subsequent applications.
• the electrolytic etching process leaves a smooth surface and makes it possible to maintain geometrical dimensions within predictable tolerance ranges.
• One preferred form of embodiment of the invention consists in placing the parts to be etched as anode in an electrolytic bath containing from 7 to 70 volumes of nitric acid at 42 B., from 0.2 to 10 volumes of 40% hydrofluoric acid, the remainder being water, and in subjecting said parts at a temperature comprised between and C. to the following operations:
• the succession of two cycles can be repeated as many times as may be desired; the thickness of metal trans formed into oxide is approximately 0.436 per amp/dm. and per minute of the first oxidation stage.
• Example I A zirconium part which has been heated in air at 570 C. for a period of 5 minutes cannot be polished by chemical process in conventional baths such as, for example, a bath made up as follows:
• the film begins to break away from the part in fine particles which fall into the bottom of the tank.
• the complete break-away process lasts from 15 seconds to one minute. After withdrawal from the bath, the part is found to have a smooth surface.
• Example II A part formed of Zircaloy 2 which has been heated in air at 570 C. for a period of 5 minutes cannot be polished by chemical process in any conventional bath such as the following:
• the film begins to break away from the part in fine particles which fall to the bottom of the tank.
• the complete break-away process lasts from 15 seconds to one minute. After withdrawal from the bath, the surface of the part is found to be smooth.
• Example Ill An assembly formed of Zircaloy 2 was constructed by argon-shielded arc-welding process but with insufiicient shielding of the surfaces. The result thus achieved was the formation of a thermal oxide film on the weld bead and in the areas adjacent thereto.
• a first sample was processed in the chemical etching bath mentioned in Example I so as to remove 50 microns per face.
• the film was removed in an irregular manner and left local surface roughness.
• the anodic film breaks away and carries with it the thermal film. Break-away is complete in 15 seconds. The part has lost 10 microns per face approximately and can then be polished by chemical process for the purpose of removing the 50 microns per face prior to carrying out the corrosion resistance test.
• this sample had a practically uniform, black appearance, that is to say normally satisfactory for this type of exposure, the welding zone being little different from the remainder.
• the weight gain of this sample was 27.6 mg./dm.
• a process for the electrolytic etching of a workpiece composed of zirconium or zirconium alloys which comprises:
• the electrolytic bath consists of a mixture which contains between 7 and 70 volumes of nitric acid at 42 B., and between 0.2 and 10 volumes of 40% hydrofluoric acid, the remainder being water.
• step (b) is carried out until the oxide film reaches a thickness of the order of 10 microns.
• step 6 (c) is carried out at a voltage which is lower than that of step (b).
• step (c) wherein the voltage used in step (c) is maintained for a period of time of from 10 seconds to 20 minutes.
• step (c) is carried out at a voltage which is lower than that used in step (b) and in an electrolytic bath having concentrations of nitric acid and of hydrofluoric acid different from those concentrations used in the bath as recited in step (a).

Landscapes

• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Electrochemistry (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Electrolytic Production Of Non-Metals, Compounds, Apparatuses Therefor (AREA)
• ing And Chemical Polishing (AREA)
• Electrical Discharge Machining, Electrochemical Machining, And Combined Machining (AREA)

Applications Claiming Priority (1)

Publications (1)

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ID=8813409

Family Applications (1)

Country Status (8)

Cited By (1)

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Citations (3)

• 1963
  • 1963-10-01 FR FR949147A patent/FR1383839A/fr not_active Expired
• 1964
  • 1964-09-22 LU LU46993D patent/LU46993A1/xx unknown
  • 1964-09-22 US US398423A patent/US3371021A/en not_active Expired - Lifetime
  • 1964-09-23 GB GB38812/64A patent/GB1067911A/en not_active Expired
  • 1964-09-30 BE BE653789D patent/BE653789A/xx unknown
  • 1964-09-30 NL NL6411398A patent/NL6411398A/xx unknown
  • 1964-09-30 CH CH1271064A patent/CH433896A/fr unknown
  • 1964-09-30 ES ES0304523A patent/ES304523A1/es not_active Expired

Patent Citations (3)

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