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
• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D17/00—Constructional parts, or assemblies thereof, of cells for electrolytic coating
  • C25D17/10—Electrodes, e.g. composition, counter electrode
• • D—TEXTILES; PAPER
  • D06—TREATMENT OF TEXTILES OR THE LIKE; LAUNDERING; FLEXIBLE MATERIALS NOT OTHERWISE PROVIDED FOR
  • D06C—FINISHING, DRESSING, TENTERING OR STRETCHING TEXTILE FABRICS
  • D06C3/00—Stretching, tentering or spreading textile fabrics; Producing elasticity in textile fabrics
• • D—TEXTILES; PAPER
  • D06—TREATMENT OF TEXTILES OR THE LIKE; LAUNDERING; FLEXIBLE MATERIALS NOT OTHERWISE PROVIDED FOR
  • D06C—FINISHING, DRESSING, TENTERING OR STRETCHING TEXTILE FABRICS
  • D06C2700/00—Finishing or decoration of textile materials, except for bleaching, dyeing, printing, mercerising, washing or fulling
  • D06C2700/10—Guides or expanders for finishing

Definitions

• This invention relates to anodes for use in the electrodeposition of metals and is particularly directed to anodes which have a desired predetermined rate of solubility in an alkaline plating bath.
• plating baths remain as near as possible to a definite formula and changes in bath composition resulting from too rapid solution of metal anodes cause considerable difflculty.
• the bath composition be held rigidly within limits if the best possible results are consistently to be obtained.
• the best results can be ob tained only if the bath composition is maintained within some predetermined optimum range.
• Zinc anodes used in cyanide plating baths ordinarily dissolve quite unevenly and a black sludge is formed which floats in the bath and on the surface of the bath.
• the presence of black sludge is particularly disadvantageous in processes for the deposition of bright zinc from cyanide baths since this black sludge interferes with the production of a smooth and bright plate.
• Cadmium anodes similarly dissolve unevenly they are used in cyanide plating baths. Copper anodes likewise dissolve unevenly as well as dissolving more rapidly than is desired.
• the objects of my invention are accomplished by including in a soluble anode a small, predetermined amount of a metal which instead of dissolving forms a bath-insoluble compound.
• a small amount of magnesium is alloyed with a zinc, cadmium, or copper anode to control the solubility of the anode in alkaline baths.
• anodes having an eificiency corresponding closely to the cathode eificiency of the baths in which they are to be used may readily be produced.
• anodes it is possible to maintain the balance of bath constituents for a much longer period than has heretofore been practicable, particularly with cyanide baths.
• anodes of our invention advantageous by reason of their maintaining a bath composition accurately but additionally the anodes dissolve uniformly and with the production of a minimum amount of sludge.
• a metal which forms bath-insoluble compounds is entirely'difierent from the action of metals which have heretofore been included in soluble anodes to decrease their solubility.
• the metals heretofore used such as aluminum, are themselves soluble in cyanide plating baths and soluble metal anodes such as zinc alloys including such added metals are likewise soluble though they dissolve slightly less rapidly than pure soluble anodes.
• the effectiveness of such alloying metals as have heretofore been used depends upon the formation of an alloy of somewhat decreased solubility.
• Metals added to soluble anodes according to our invention apparently cause the formation of a film of an alkali insoluble compound on the surface of the anode when it is in use.
• This film polarizes the anode, in a measure resisting the passage of current between the anode and the bath.
• the film of insoluble compound has the further effects of making anode corrosion more uniform and of preventing objectionable sludge formation and distribution in the bath. Any sludge which forms is carried to the bottom of the bath by the insoluble compound and is thus rendered innocuous.
• the efiect of a metal which forms bath-insoluble compounds in alkaline solution is directly proportional to the amount of such metals present in an anode.
• Our invention will be found particularly advantageous in connection with the plating of metals from alkaline solutions and more specifically to the plating of zinc, cadmium, copper, and brass from cyanide baths.
• Electrolytic zinc anodes for use in cyanidezinc plating baths normally have an anode efflciency'of one hundred to one hundred and five per cent while the normal cathode efilciency in similar baths is around eighty to ninety-five per cent.
• the anode efiiclency of such electrolytic zinc anodes may be reduced to fall within the range of cathode efliciencies by the addition of a metal which instead of dissolving forms a bathinsoluble compound.
• magnesium is sufiicient to give a zinc-magnesium anode having an eficiency of eighty-five per cent when the zinc was of a commercial grade obtained by distillation.
• magnesium i particularly advantageous with the use of anodes which are less pure than the electrolytic zinc because the magnesium tends to reduce the amount of black sludge formed and further causes this sludge to drop to the bottom of the tank where it cannot interfere with the bright plates.
• Example I Molten zinc obtained in a zinc distillation process was transferred in the molten state to a gasfired graphite crucible and the temperature raised from about 450 C. up to a temperature of about 600 0. Eight hundreths per cent of magnesium was then added to the zinc by introducing finely divided magnesium into the molten zinc and maintaining it below the surface until it was dissolved in the zinc. After the magnesium was alloyed with the zinc, the mixture was further heated and the alloy was then cast into a form suitable for use as anodes. 20
• the zinc used was of commercial grade frequently employed for the manufacture of zinc anodes.
• the zinc contained about 0.07 per cent of cadmium and 0.005 per cent of iron. It also contained 0.10 per cent of lead and the cast anodes, accordingly, contained these impurities in addition to the added magnesium.
• a cyanide-zinc plating bath of the type recently developed for the deposition of brilliant zinc was made up as follows: 30
• Zinc cyanide Zn(CN)2 60 Sodium cyanide (NaCN) 52.5 Sodium hydroxide (NaOH) 78 Molybdic acid.(MOa) 7.5
• the anode efliciency was determined and it was found that the anodes made as above described and containing 0.08 per cent magnesium had an efliciency of about eighty-nine per cent in the above bath.
• a ZOO-gallon plating installation using such anodes was operated commercially for a period of four weeks and the zinc content of the the bath was substantially unchanged.
• the zinc metal content of a similar bath increased by thirty grams per liter of zinc metals.
• Example II A zinc-magnesium alloy anode was made up according to the procedure described in the above Example I, but using 0.11 per cent of magnesium. The zinc used was somewhat purer than that of the above example, containing only 0.05 per cent of lead. In making the alloy 0.05 per cent of lead was added to decrease the solubility of the anodes.
• the anodes were tested in a bath such as that shown in Example I and were found to have an anode efliciency of about eighty-six per cent.
• the magnesium probably acts by forming an alkali-insoluble magnesium hydrate or cyanide film which surrounds the particles of lead and drags them to the bottom of the bath where they can do no harm. It will be observed, of course, that there must be sufficient magnesium present since otherwise the lead would be free to exercise a deleterious influence.
• Example III made up with electrolytic zinc and containing the below indicated amounts of magnesium:
• the specific temperature required to effect the required change in alloy properties can readily be determined in each specific instance by a few simple trials.
• the electrolytic zinc alloy anodes mentioned were re-melted and heated to a temperature of 700 C. and it was then found that the magnesium exercised its usual profound effect upon the anode efficiency.
• magnesium may be used in zinc anodes depending upon the effect desired and upon the character of the zinc which it is desired to modify.
• suitable amounts of magnesium it is entirely possible to adjust the anode efficiency to correspond to the cathode efiiciency of substantially any commercial cyanide-zinc electroplating bath and it is principally in this connection that the invention will be found valuable.
• the beneficial effects of magnesium may be obtained by the use of small amounts of magnesium which will prevent the deleterious influence of metal impurities in the anode even without obtaining a very great reduction in the anode efiicienoy. Very small amounts of magnesium may therefore be used to advantage.
• magnesium may of course be used, though it will be understood that it will not be commercial to use excessively large amounts.
• the upper limit on the amount of magnesium used is determined by the cathode efiiciency of the baths in which the anodes are to be employed.
• magnesium While, as above indicated, widely varying amounts of magnesium may be used, it will generally be found desirable to use from .01 per cent to about 1.0 per cent of magnesium. More specifically. it will usuall be found that the desired anode eificienoy and character can be obtained using from about .05 per cent to 0.3 per cent of magnesium with electrolytic zinc or about .05 per cent to 0.2 per cent of magnesium with commercial zinc such as that shown in Examples I and II and obtained by distillation processes.
• Example IV Molten zinc obtained in a zinc distillation process was transferred in the molten state to a gasfired graphite crucible and the temperature raised from about 450 C. up to a temperature of about 600 C. Five-tenths per cent of calcium was then added to the zinc by introducing calcium turnings into the molten zinc and maintaining them belowrthesurface until they were dissolved in the zinc. After the calcium was alloyed with the zinc, the mixture was further heated to about 800 C. and the alloy was then cast into a form suitable for use as anodes.
• the zinc used was of commercial grade frequently employed for the manufacture of zinc anodes.
• the zinc contained about 0.07 per cent of cadmium and 0.005 per cent of iron. It also iii) aangeov contained 0.10 per cent of lead and the cast anodes, accordingly, contained these impurities in addition to the added calcium.
• a cyanide-zinc plating bath of the type recently developed for the deposition of brilliant zinc was made up as follows:
• Zinc cyanide Zn(CN)2 60 Sodium cyanide (NaCN) 52.5 Sodium hydroxide (NaOH) '78 Molybdic acid (M003) 7.5
• the anode efficiency was determined and it was found that the anodes made as above described and containing 0.5 per cent of calcium had an efficiency of about eighty-five per cent in the above bath.
• Example V A zinc-calcium alloy anode was made up according to the procedure described in the above Example IV, but using 0.6 per cent of calcium. The zinc used was somewhat purer than that of the above example, containing only 0.05 per cent of lead. In making the alloy 0.05 per cent of lead was added to decrease the solubility of the anodes.
• the anodes were tested in a bath such as that shown in Example IV and were found to have an anode eficiency of about eighty-four per cent,-
• the calcium probably acts by forming an alkali-insoluble calcium hydrate or carbonate film which surrounds the particles of lead and drags them to the bottom of the bath where they can do no harm. It will be observed, of course, that there must be sufiicient calcium present since otherwise the lead would be free to exercise a deleterious influence.
• Example VI A zinc-calcium alloy anode was made up using electrolytic zinc and 1.07 per cent of calcium. The alloy was made following the procedure used in the above Example IV, the electrolytic zinc being melted directly in the graphite crucible. The zinc-calcium alloy anodes so produced were tested in a bright zinc bath such as that shown above in Example IV and it was found that the anode efficiency was about eightytwo per cent.
• Cadmium anodes of decreased solubility for use in alkaline plating baths may be prepared in the manners above described with reference to zinc anodes. Employing magnesium for instance, as a metal according to our invention which does not dissolve but forms a bath-insoluble compound. a cadmium anode of decreased solubility may be prepared.
• the amount of an alloying metal according to our invention required to impart the desired characteristics to a cadmium anode can be determined following the considerations above discussed with reference to zinc anodesj
• the effects of these metals on cadmium seem approximately the same as for zinc and the ranges of magnesium. for instance. given for zinc are equally applicable for cadmium.
• Example VII To molten cadmium there was added magnesium in sufiicient quantity that the final alloy contained 0.15 per cent Mg. The cadmium-magnesium alloy was cast into a iorm suitable for use as an anode.
• the cadmium-magnesium alloy of this example was tried in a cyanide-cadmium plating solution and the anode efliciency was found to be about sium or calcium which form compounds insoluble in the bath is much greater in copper anodes than in zinc or cadmium anodes and much smaller quantities of such metals suffice to effect a desired reduction in anode solubility.
• the anode efliciency was found to be about sium or calcium which form compounds insoluble in the bath is much greater in copper anodes than in zinc or cadmium anodes and much smaller quantities of such metals suffice to effect a desired reduction in anode solubility.
• Example VIII Magnesium was dissolved in molten copper in such amounts that a final alloy containing 0.13 per cent of magnesium was obtained. The copper was cast into a form suitable for use as an anode.
• the copper-magnesium alloy thus prepared was used in a cyanide-copper plating solution and it was found that it had an anode efficiency of 23.8 per cent. Pure copper in the same solution had an efiiciency of 78.5 per cent.
• Such anodes could advantageously be used, of course, instead of iron anodes when it is desired to lower the metal content of a copper bath.
• a copper-magnesium alloy was made up containing 0.0012 per cent magnesium and this was found to have an anode efllciency of sixty-three per cent.
• a pure copper anode in the same bath had an anode efficiency of ninety per cent.
• the anode efiiciency of this copper-magnesium anode is about that required in the copper cyanide solution used to maintain the copper content of the solution at a fairly constant value.
• copper anodes as with cadmium and zinc anodes, the amount of an alloying metal used will need to be adjusted for the specific type of bath in which they are to be used.
• the anodes of this example were used with the greatest of success in a Rochelle salts-cyanide copper solution. This use is particularly advantageous because iron anodes cannot satisfactorily be used in such solutions.
• alloyanodes of this invention may be fabricated in any desired way to make anodes.
• alloys of our invention will be cast on a metal spine as in the Blouch Patent 2,097,508 or in the form of balls.
• the metals employed for anodes according to our invention are preferably as pure as possible in accordance with prior art practices.
• the inclusion of metals which do not dissolve but form insoluble compounds increases the deleterious effects of impurities. and metals of somewhat lower purity can successfully be used for the anodes of our invention.
• Patent 2,243,696 of coapplicant Farm and to Patent 2,214,331 of coapplicant Hull.
• a cast copper anode for use in a cyanide plating bath the anode containing from about 0.0005 to 0.5 per cent of magnesium, the coppermagnesium alloy having been heated prior to casting to a temperature not substantially lower than 700 C.
• a soluble metal anode cast of a metal selected from the group consisting of brass and copper for use in a cyanide plating bath the anode containing a metal selected from the group consisting of 0.05 to 5.0 per cent calcium and 0.0005 to 0.5 per cent magnesium and the alloy having been heated prior to casting to a temperature not substantially lowe than about 800 C. for calcium and not lower than about 700 C. for magnesium whereby the rate of solution of the anode is decreased by reason of the formation of a bath-insoluble film on the surface 01 the anode.

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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)
• Textile Engineering (AREA)
• Electroplating And Plating Baths Therefor (AREA)

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• 1938
  • 1938-03-30 US US198830A patent/US2315607A/en not_active Expired - Lifetime
• 1939
  • 1939-03-10 DE DEP78811D patent/DE706591C/de not_active Expired

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