Classifications

• • C—CHEMISTRY; METALLURGY
  • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
  • C23G—CLEANING OR DE-GREASING OF METALLIC MATERIAL BY CHEMICAL METHODS OTHER THAN ELECTROLYSIS
  • C23G1/00—Cleaning or pickling metallic material with solutions or molten salts

Definitions

• these alloys which form, on annealing, A 1 0;, and related oxides are uniquely cleaned by a process which consists of a duplex treatment requiring a first immersion in a hot alkaline solution followed by a second immersion in a hot mineral acid solution.
• a copper alloy containing about 66 percent copper, 1.55 percent aluminum, 1.0 percent iron, balance essentially zinc forms a refractory thermal oxide during annealing that cannot be reliably removed using ordinary cleaning procedure.
• the metal cannot be reproducibly soldered or electroplated because of the residual annealing oxide.
• lt is another object of the present invention to remove those films within the confines of existing copper-base alloy cleaning equipment.
• the process of the present invention comprises: immersing the surface to be cleaned in an aqueous alkaline solution having apH above 10 for at least two (2) seconds, with the solution being at a temperature of from 100 F. to the boiling point; and then immersing the surface to be cleaned in an aqueous mineral acid solution at a temperature of from 75 to 200 F. for from two (2) seconds to minutes, said solution having an acid equivalent to an H 50, solution of 3 to 50 percent by volume.
• a conventional water rinse or air wipe is performed between steps and after the final step.
• the exact time and the exact bath temperature in each of these two steps is determined by the type of annealing operation and the character of the resulting oxide including its thickness and constitution.
• the process is suitable to both continuous cleaning of strip and to batch cleaning of fabricated parts.
• copper base alloys coated with complex oxides can be successfully soldered and electroplated because the residual oxide resulting from annealing has been removed.
• the process of the present invention is effective for any copper basc alloy.
• the present process is especially effective with copper alloys containing as alloying additions: aluminum, from 0.5 to 12 percent; and silicon, from 0.5 to 5 percent.
• the process of the present invention is particularly useful with respect to copper alloys bearing: complex oxides; alumina:
• spinel type oxides such as copper aluminate and zinc aluminate; nickel oxides; etc.
• the process of the present invention utilizes a duplex treatment requiring a first immersion in a hot alkaline solution followed by a second immersion in a hot mineral acid solution.
• any alkaline solution may be used which has a pH above and preferably a pH from 1 1 to 14.
• Preferred solutions which may be used depend, of course, upon the particular alloy and the results desired.
• caustic soda is the preferred alkaline solution, but others may be readily employed such a lithium or potassium hydroxide, for example.
• the alkaline solution should be maintained at a temperature of from 100 F. to the boiling point, and preferably at a temperature of from 160 F. to the boiling point.
• the copper alloy to be cleaned should be immersed in the solution for at least 2 seconds and preferably for from 5 seconds to 1 minute. Naturally, longer treatment times may be employed, but in general no advantage is obtained thereby. Generally, the treatment time should be under 10 minutes. Naturally, temperature and time are related and the exact treatment conditions are dependent upon the alloy used and the results desired.
• the second immersion in acid may employ any mineral acid solution having an acid equivalent to an H 80 solution of3 to 50 percent by volume.
• any mineral acid may be used with sulfuric acid being preferred. Others which may be used include nitric and hydrochloric, for example.
• the preferred solution has an acid equivalent to an H SO, solution of from 5 to 20 percent by volume.
• the mineral acid solution should be maintained at a temperature of from 75 to 200 F. and preferably at a temperature of from to 175 F.
• a treatment time of at least 2 seconds should be employed and preferably from 5 seconds to 1 minute.
• the mineral acid treatment should generallynot exceed 5 minutes as in-some cases there is obtained an undesirable blush color for treatment times in excess of about 5 minutes.
• the alloy is, of course, effectively cleaned; however, the color is undesirable commercially.
• both the first and second solutions should be aqueous solutions.
• a conventional water rinse or air wipe is preferred between the steps and after the final step.
• Air annealing was carried out as follows: The alloy sheet was brought to a temperature of about l,l00 F. in several minutes and held at that temperature for 2 hours. The alloy was then cooled to room temperature by removal from the furnace. Air had access to the interior of the furnace.
• Bell annealing refers to annealing in whichsheet material was placed in a closed furnace. Air was displaced with an atmosphere resulting from hydrocarbon combustion. The furnace was brought to a temperature of about l,l00 F. over a period of several hours. The furnace was held at temperature for a period of several hours, after which it was slowly cooled over several hours to a temperature at which the furnace could be opened without promoting excessive oxidation.
• a strip is continuously fed through a furnace heated, for example, by gas burners or resistance heat and continuously exits therefrom with a gas atmosphere in the furnace produced by burning propane to eliminate oxygen.
• the rate of travel is adjusted so that residence time in the furnace is sufficiently low that the strip reaches the desired temperature, l,100 F,, in this case.
• the alkaline immersion for air annealed alloy C for short treatment times should use lithium hydroxide.
• an acid bath composition modification was used for the bell annealed alloy C treatment.
• sodium dichromate should be added to the acid bath in the range of from 1 to 8 ounces per gallon in order that the last 25 Angstroms of A1 0 might be removed.
• This acid dichromate bath modification can be used with the other alloys; however, it produces an etched surface which appears hazy or frosty; an undesirable surface condition for the final product. This is not important in most instances since further cold rolling and strip annealing will produce a bright surface.
• EXAMPLE ll The efficacy of the foregoing cleaning procedure has been accurately demonstrated by utilizing surface capacitive measurements before and after cleaning. It has been found that the cleaning technique described effectively increases the surface capacitance, a parameter linked to the thermal oxide thickness and solution double layer thickness, to a value indicative of only the surface double layer capacitance produced by immersion of the test specimen in the electrolytic solution used in capacity measurement. For example, a specimen of alloy C before cleaning was covered by a film of oxide which capacitance measurements allowed to be calculated 88 Angstroms thick. After cleaning, the thickness of oxide and double layer equivalent was 4.8 Angstroms. Correction for the double layer reduces any total value less than 8 Angstroms to zero thickness of oxide. Effectively, the capacitance bridge showed that the surface was cleaned. This was confirmed by the solder test.
• a process for cleaning a copper base alloy surface having a thermally formed oxide thereon comprising: immersing the surface to be cleaned in an aqueous alkaline solution having a pH of from 1 1 to 14 at a temperature from 160 F. to the boiling point of said aqueous alkaline solution for a period of time of at least 2 seconds; and then immersing the surface to be cleaned in an aqueous mineral acid solution at a temperature of from 75 to 200 F. for from 2 seconds to 5 minutes, said acid solution having an acid equivalent to an H 50, of 3 to 50 percent by volume.
• a process for cleaning a copper base alloy surface having a thermally formed oxide thereon comprising: immersing the surface to be cleaned in an aqueous alkaline solution having a pH of from 1 1 to 14 at a temperature from F. to the boiling point of said aqueous alkaline solution for from 5 seconds to 1 minute; and then immersing the surface to be cleaned in an aqueous mineral acid solution at a temperature from 125 to F. for a period of from 5 seconds to 1 minute, said acid solution having an acid equivalent to an H 80 solution of5 to 20 percent by volume.

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• Chemical & Material Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• General Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Mechanical Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Cleaning And De-Greasing Of Metallic Materials By Chemical Methods (AREA)
• Electroplating Methods And Accessories (AREA)

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Citations (11)

• 1969
  • 1969-01-06 US US789417A patent/US3646946A/en not_active Expired - Lifetime
  • 1969-11-05 GB GB54269/69A patent/GB1247980A/en not_active Expired
  • 1969-12-16 FR FR6943537A patent/FR2027786A1/fr not_active Withdrawn
  • 1969-12-24 JP JP44104210A patent/JPS504185B1/ja active Pending

Patent Citations (11)

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