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
  • C25D3/06—Electroplating: Baths therefor from solutions of chromium from solutions of trivalent chromium
• • 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
  • C25D3/56—Electroplating: Baths therefor from solutions of alloys

Definitions

• This invention is concerned with an electroplating solution of chromium, which allows obtaining very quickly a chromium coating of very good physical and mechanical properties.
• All the solutions so constituted have the known inconveniences of hexavalent chromium solutions, among others, the necessity that the surface to be plated be perfectly clean, and the necessity to operate at or about room emperature and with low current densities, generally no higher than 12 to 15 amperes per square decimeter.
• Plating solutions in which chromium is present in the hexavalent state are poisonous, are corrosive, and liberate toxic gaseous products during electrolysis. These poisonous characteristics do not exist in the solutions according to the present invention.
• the electro-plating solution according to the present invention is characterized in that it contains only at least one salt formed by a complex anion constituted by trivalent chromium and at least one organic acid and by a cation which is an amine base.
• the anion of such complex salt is thus constituted by an atom of trivalent chromium associated with six radicals of a monocarboxylic organic acid, or three radicals of a di-carboxylic organic acid, these acid radicals being identical or different.
• This anion is thus trivalent, as the chromium is itself trivalent, and is consequently neutralized by a cation having three radicals of an amine base, these radicals being identical or different.
• the organic acid has less than six atoms of carbon and the amine has at most six atoms of carbon.
• the salts as employed according to the present invention are represented by the general formula [Cr (acid radicals)] (amine) where acid radicals designate the radicals of at least one organic acid, having each less than six atoms of carbon and the number of which radicals being such that the sum of their valences is equal to six, and where amine designates the ammonium radical or the radicals of at least one amine having at most six atoms of carbon, the number of said amine basic radicals being such that the sum of their valences is equal to three.
• Ammonium is considered as an amine radical.
• the acids and amines which are suitable are those which produce a soluble complex salt, that is to say acids whose number of carbon atoms is lower than six and amines whose number of carbon atoms is lower than six.
• complex salt is employed in the present specification and claims to denote a salt of the kind indicated hereinbefore, in the molecule of which the organic acid radicals are identical, and the amine radicals are also identical. I make use of the terms mixed complex salt to designate a salt in the same molecule of which are included diiferent carboxylic organic acid radicals and/ or amine radicals.
• an amount of chromium hydroxide corresponding to a molecule of chromium is dissolved in an amount of molecules of at least one carboxylic organic acid, n being the number of carboxylic groups in the acid radical.
• the current density is about 200 amperes per square decimeter.
• the process according to the present invention is satisfactory for plating small work pieces under very high current densities.
• chromium is present only in a complex anion.
• the object to be plated being the cathode, there is first obtained the well known phenomenon according to which the complex anion is transferred to the anode and the amine radical to the cathode, which is always surrounded by an alkaline medium; as the complex anion cannot remain in this form, it is split down into a chromium ion and an acid ion which remains near the anode, the chromium being transported towards and plated on the cathode. As the latter is always alkaline, there is no need that the object to be plated be perfectly clean or scoured.
• the proportions of the components used to prepare the solutions must be about those theoretically t in accordance with the formula of the salt to be prepared.
• a solution according to the present invention may be'tibtaihedby'dire'ctlydissolving of water a complex salt 'd'fch'rcrfilufn df the kind 'a'bo've specified, with 'the'additionof a salt of an amine base if necessary.
• I can also dissolve the amine base in the total necessary amount of organic acid, and thenI dissolve in this solution'the proper amount of hydroxide or basic carbonate of chromium.
• I can also start from a solution of a mineral salt o f chromium such as t he violet sulphate of chromium, to whichI add the proper amounts of an organic salt of the selected amine and of an organic acid, and I treat the resulting solution by an amount oi": hydrated baryta correspondingto the amount'of sulphuric ion of the sulphate. -Barium sulphate being insoluble, the solution is free from mineral compounds.
• a mineral salt o f chromium such as t he violet sulphate of chromium
• the alkalinity or acidity of the raw solution obtained according to one or the other of the above mentioned processes may be corrected by a convenient addition of organic acid or amine base so as to bring the pH of the solution to a pH value of about 7.
• platings may be obtained which are constituted by chromium alloys.
• I add to the solution of a complex salt of trivalent chromium, a soluble salt of a metal such as iron, nickel, cobalt, etc., which is compatible therewith, as shown by a preliminary test; the eleetroplatings of the other metal and of chromium are efiected simultaneously.
• the "chromium coatings obtaine'd from a solution according to the present invention are more or less carburized, that is to say contain a part of the chromium in the form of chromium carbide. Ihis characteristic is particularly outstanding when'the solution contains a formic complex of trivalent chromium and/ or when theanode is constituted by a graphite piece.
• The'solutions according to the present invention are particularly useful when they are-employed in the socalled spot plating method in which an absorbent mass connected to the positive pole of a source of electric current is soaked in the solution and is applied to the object to be plated which-is connected to' the vnega'tive pole of the source or current.
• spot plating method in which an absorbent mass connected to the positive pole of a source of electric current is soaked in the solution and is applied to the object to be plated which-is connected to' the vnega'tive pole of the source or current.
• Example 1 For a final volume of 1000 cm. 700 grams of "the chromium oxalate known as ammonium Gregory 's'alt, having the formula [Cr(C2O4)3] (NI-14):;
• Example 2 The two following.industrialsolutionsare mixed in the proportion of:
• the chromium is present :duringwelectrolysis 'as trivalent chromium.
• Thesolution is partly neutralized by 60grams of ammonia of 26% by Weigh't'of NHs. After'it hasdissolvcd, there are ad'dd35 grams or hydrazine of 50% by weight and ,apprdximatelyifrom' 60 to 70 grams, of ammonia of 26% to attain neutrality(about-pI-I 7);'and-'the-volume bf'the solution is 'broli'ghttdlOOO cm witlr water.
• Example 5 To 500 cm. of an industrial solution of green (trivalent) chromium sulphate at approximately 30 Baum, containing 300 grams of the anhydrous salt for one liter, there are added at 70 C.: 500 cm. of a solution of ammonium formate at 16 Baum, containing 610 grams per liter of this salt, and 120 grams of formic acid of 90% by weight.
• This solution is then treated by 350 grams of hydrated baryta, heated, and the precipitate of barium sulphate thus formed is filtered away.
• the solution so obtained is brought to pH of about 7, and 100 cm. of methyl alcohol are added thereto.
• Example 6 An amount of moist chromium hydroxide corresponding to 100 grams of (trivalent) Cr2O3 is dissolved in the cold in 200 cm? of water by means of 200 grams of 90% by weight formic acid which has less than six atoms of carbon.
• the resulting solution is rapidly mixed with a solution of formate of methylamine, having a pH of about 7, which is obtained by the neutralization of 400 grams of an aqueous solution of 33% by weight methylamine by means of about 200 grams of 90% by Weight formic acid.
• the formic acid is an organic acid having less than six atoms of carbon
• the methylamine is an amine having at most six atoms of carbon.
• the solution is maintained during 15 to 30 minutes at a temperature of 7080 C. and is then alkalinized (pl-1:75) by the addition of a small calculated amount of the solution of the amine.
• a complex salt having the following formula:
• Example 7 An amount of moist chromium hydroxide corresponding to 100 grams of 01203 is dissolved in the cold in 200 cm. of water by means of 200 grams of 90% formic acid. The resulting solution is rapidly mixed with a solution of formate of dimethylamine (CH3)2NH, obtained by the neutralization of 850 grams of an aqueous solution of dimethylamine of 25% by weight by means of about 200 grams of 90% formic acid.
• CH32NH formate of dimethylamine
• Example 8 To 6 volumes of an industrial solution of (trivalent) chromium acetate at 20 Baum, containing 250 grams per liter of the anhydrous salt, there are added 7 volumes of a solution of ammonium acetate at 11 Baum containing 450 grams of this salt per liter.
• the resulting solution is maintained during six hours at a temperature of 70 C., then cooled and brought to a pH of about 7 by a careful addition of ammonia water.
• the complex salt so obtained has the following formula:
• Example 5 500 grams of Gregoryssalt of potassium as identified in Example 1 above, having the following formula:
• Example 11 750 grams of tertiary amylamine (dimethyl-ethyl carbylamine) having the formula:
• CH; CH;CH:--NH2 are added to 600 cc. of water and are neutralized by means of 250 grams of formic acid.
• the solution is heated to 80 C. and mixed with 500 cc. of a solution of violet sulphate of chromium (trivalent) at about 30 Baum, containing 300 grams per liter of the anhydrous CH; [C r (H-o 0,)[0 113-0 HFCZNHZ] I I CH: :4
• Example 12 A complex salt having the following formula:
• the chromium . is present asv trivalent chromium.
• Example 14 An amount of moist chromium hydroxide corresponding to 100 grams of C1'203 (trivalent) is dissolved in a hot solution of 270 grams of maleic acid, having the formula:
• Example 15 The same operations are madeas in Example 14 but the two amounts of 270 grams of maleic acid are replaced by two successive amounts of 325 grams of propionic acid: CH3--CHz-CQ2H. -The following complex salt is obtained:
• Example 16 If two.- successiveamounts.of.300 grams ofglutaric acid: CO2H,CH2-,CO2H. aresubstituted for. the 270 grams of maleic acid of Example 14, the following complex saltisobtained:
• the chromium plating solutions which have been here described can be used for special electrolyzing methods, such as those known as spot or plugging or pencilling galvanoplasty. These solutions can be electrolyzcd using high current densities such as 200 to 300 amperes per square decimeter, and at temperatures as high as the boiling temperature of the solution itself. This is an important advantage of the plating solution here described.
• Deposits can be obtained at temperatures going up to theboiling temperature of the solution.
• a chromium electroplating bath of a pH of about 7 consisting of an aqueous solution of at least one com- 9 plex salt of trivalent chromium corresponding to the formula:
• acid designates at least one organic carboxylic acid radical having less than six carbon atoms
• 11 designates the number of carboxylic groups in said acid radical
• amine designates at least one radical selected from the group consisting of amine and ammonium radicals, said amine radical having at most six carbon atoms.
• a method of electrodepositing chromium upon a cathodic base which comprises passing an electrolytic current from an anode to said cathodic base through a chromium electroplating bath of a pH of about 7 consisting of an aqueous solution of at least one complex salt of trivalent chromium corresponding to the formula:
• a method of electrodepositing chromium upon a cathodic base which comprises passing an electrolytic current from an anode to said cathodic base through a chromium electroplating bath of a pH of about 7 consisting of an aqueous solution of at least one complex salt of trivalent chromium corresponding to the formula:
• Acid 2 Amine a wherein acid designates at least one organic carboxylic acid radical having less than six carbon atoms, n designates the number of carboxylic groups in said acid radical, and amine designates at least one radical selected from the group consisting of amine and ammonium radicols, said amine radical having at most six carbon atoms, the current density on said anode and cathode exceeding one hundred and fifty amperes per square decimeter.
• a chromium electroplating bath of a pH of about 7 consisting of an aqueous solution of a complex salt of trivalent chromium corresponding to the formula:
• a chromium electroplating bath of a pH of about 7 consisting of an aqueous solution of a complex salt of trivalent chromium corresponding to the formula:
• a chromium electroplating bath of a pH of about 7 consisting of an aqueous solution of a complex salt of trivalent chromium corresponding to the formula:
• a chromium electroplating bath of a pH of about 10 7 consisting of an aqueous solution of a complex salt of trivalent chromium corresponding to the formula:
• a chromium electroplating bath of a pH of about 7 consisting of an aqueous solution of a complex salt of trivalent chromium corresponding to the formula:
• a method of electrodepositing chromium upon a cathodic base which comprises passing an electrolytic current from an anode to said cathodic base through a chromium electroplating bath of a pH of about 7 consisting of an aqueous solution of a complex salt of trivalent chromium corresponding to the formula:
• a method of electrodepositing chromium upon a cathodic base which comprises passing an electrolytic current from an anode to said cathodic base through a chromium electroplating bath of a pH of about 7 consisting of an aqueous solution of a complex salt of trivalent chromium corresponding to the formula:
• a method of electrodepositing chromium upon a cathodic base which comprises passing an electrolytic current from an anode to said cathodic base through a chromium electroplating bath of a pH of about 7 consisting of an aqueous solution of a complex salt of trivalent chromium corresponding to the formula:
• a method of electrodepositing chromium upon a cathodic base which comprises passing an electrolytic current from an anode to said cathodic base through a chromium electroplating bath of a pH of about 7 consisting of an aqueous solution of a complex salt of trivalent chromium corresponding to the formula:

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• 0
  • NL NL75772D patent/NL75772C/xx active
• 1948
  • 1948-03-20 FR FR1007691D patent/FR1007691A/fr not_active Expired
  • 1948-12-27 CH CH289705D patent/CH289705A/fr unknown
• 1949
  • 1949-03-21 GB GB7681/49A patent/GB697225A/en not_active Expired
• 1953
  • 1953-07-27 US US370640A patent/US2748069A/en not_active Expired - Lifetime

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