FR2545841A1 - ELECTROLYTE FOR THE DEPOSITION OF TRIVALENT CHROME AND METHOD OF USING SAME - Google Patents

Abstract

AN AQUEOUS ACID TRIVALENT CHROME ELECTROLYTE AND A PROCESS FOR THE ELECTROLYTIC DEPOSIT OF CHROME COATINGS, INCLUDING AN ELECTROLYTE CONTAINING TRIVALENT CHROME IONS, A COMPLEX TRANSFORMER, IONS HALOGENIDE OF AMMONIUM IONS AND AN ADDITIONAL AGENT. METAL CHOSEN FROM GROUP CONSISTING OF NEODYME, GOLD, SILVER, PLATINUM, PALLADIUM, RHODIUM, IRIDIUM, OSMIUM, RUTHENIUM, RHENIUM, GALLIUM, GERMANIUM, INDIUM , SAMARIUM, EUROPE, GADOLINIUM, TERBIUM, DYSPROSIUM, HOLMIUM, ERBIUM, THULIUM, YTTERBIUM, LUTETIUM, PRASEODYME, SCANDIUM, YTTRIUM, LANTHAN, TITANIUM , OF HAFNIUM, ARSENIC, SELENIUM, TELLURUS, CERIUM, URANIUM AND THEIR MIXTURES, PRESENT IN SUFFICIENT QUANTITY TO REDUCE THE CONCENTRATION OF HEXAVALENT CHROME IONS FORMED IN THE BATH TO A LEVEL FOR WHICH DEPOSITS SATISFACTORY CHROME ELECTROLYTICS ARE OBTAINED.

Description

Chromium electroplating baths are widely used

  industrially to apply protective and decorative coatings to metallic substrates For the most part, the commercial chromium coating solutions used up to now use hexavalent chromium coming from compounds such as chromic acid, for example, as source of

  constituent chrome These electrolyte coating solutions

  hexavalent chromium tick have long been characterized

  as having a limited recovery power and a gasified

  excessive fication especially around the openings

  in coated parts, which may cause

  incomplete coverage These hexavalent chromium coating solutions are also very sensitive to power interruptions resulting in what is called "white washing"

of the deposit.

  As a result of these and other problems including the relative toxicity of hexavalent chromium,

  and associated residue disposal problems, tra-

  important vail has been conducted in recent years 2.

  to develop chrome electrolytes incorporated

  rant of trivalent chromium providing numerous advantages

  According to the present invention, a new trivalent chromium electrolyte and its process for

  deposit chrome coatings have been discovered, se-

  where shiny chromium deposits are produced having a color equivalent to that obtained from hexavalent chromium baths The electrolyte and process of the present invention further provide a coating

  electrolytic by using current densities which will

  laugh in a wide range without producing the associated burn

  bonded to deposits coated with hexavalent chromium coating baths; o the electrolyte composition minimizes or

  eliminates the release of fog or harmful odors from the

  rant coating; the electrolyte and the process provide excellent covering of the substrate and good spraying power; power interruptions during the electrolytic coating cycle do not adversely affect

  the deposit of chromium allowing parts to be reti-

  of the electrolyte, inspected and then returned to the bath to continue the electrolytic coating cycle; the electrolyte uses low concentrations of chromium, thereby reducing the loss of chromium due to entrainment; and removal of chromium residues is facilitated by the fact that trivalent chromium can easily be precipitated at

  from the residual solutions by the addition of subs-

  alkaline tances to raise the p H to about 8 or above. The electrolyte of the present invention further incorporates one or more agents to prevent the formation of harmful concentrations of hexavalent chromium during operation of the bath which has hitherto interfered with the effective electrolytic deposition of chromium from coating baths. trivalent chromium including 3. reduction of efficiency and covering power

  bath In some cases, the accumulation of chromium hexa-

  are worth harmful has occurred to such an extent that a

  cessation of electrolytic chromium deposition has occurred

  pick requiring spillage and replacement of the electrolyte According to another discovery of the present invention, it has been found that the addition of one or more of the additive agents according to the electrolyte described here performs

  a rejuvenation of an electrolyte contaminated with chromium

  hexavalent me in excessive quantity by restoring the effi-

  cacity of the coating and the projection power of such a bath and avoiding the costly and time-consuming step

  electrolyte discharge and replacement time.

  The advantages of the present invention according to the composition aspects are achieved by the aqueous acid electrolyte containing, as essential constituents, controlled amounts of trivalent chromium, an agent

  transformation into a complex present in sufficient quantities

  health to form a chromium complex, halo ions

  genures, ammonium ions and an additive agent comprising metal ions chosen from the group consisting of neodymium, gold, silver, platinum, palladium, rhodium, iridium, osmium, ruthenium, rhenium,

  gallium, germanium, indium, samarium, euro-

  pium, gadolinium, terbiumi dysprosium, hol-

  mium, erbium, thulium, ytterbium, lutetium, praseodymium, scandium, yttrium, lanthanum, titanium, hafnium, arsenic, selenium, tellurium, cerium, d uranium and their mixtures, present in an amount effective to maintain the concentration of hexavalent chromium ions at a level below that for which an optimum continuous efficiency and a power of

  optimum continuous projection of the electrified coating bath

  trolytics are particularly maintained, the elect

  trolyte may contain roughly a concentration of about 254,584 ai 1 4. 0.2 to about 0.8 molar of trivalent chromium ion, a complexing agent formed from formate and / or

  acetate present in quantity in relation to the concentration

  tration of the constituent chrome and typically present following

  with a molar ratio of transformation agent to complete

  xe / chromium ions from about 1: 1 to about 3: 1, a salt

  soluble in the bath and compatible with the bath or a met

  lange of salts of the additive metal ions present at a concentration of at least about 0.001 gram per liter

  (g / l) up to about 30 g / l as a reducing agent.

  re the quantity of hexavalent chromium formed during the pro-

  ceded with electrolytic coating, ammonium ions as a secondary complex transformation agent

  present in an ammonium / chromium molar ratio of

  about 2.0: 1 to about 11: 1, halide ions,

  preferences of chloride ions and bromides present following

  with a halide / chromium ion molar ratio of from about 0.8: 1 to about 10: 1; one or a combination of salts soluble in the bath to increase the conductivity of the bath comprising simple acid compatible salts

  strong such as hydrochloric acid or sulfuric acid

  that and their alkali, alkaline earth metal and ammonium salts o U sodium fluoroborate comprises a salt of preferred conductivity, and hydrogen ions present to provide an acid electrolyte having a p H of about

2.5 to about 5.5.

  Optionally and preferably, electro-

  lyte may also contain a buffering agent such as boric acid typically present at a concentration of about 1 molar, a wetting agent present in small but effective amounts of the types conventionally used in nickel or chromium coating baths as well

  that controlled effective amounts of anti-foaming agents

  In addition, the bath can incorporate other metals available.

  as optional constituents including iron, cobalt, nickel, manganese, tungsten or the like

  in cases where a deposit of chromium alloy is desired.

  According to the process aspects of the present in-

  vention, the electrolytic deposition of chromium on a conductive substrate is carried out by using the electrolyte at a

  temperature ranging from about 15 to about 451 C The subs-

  trat is cathodically charged and chromium is deposited

  dried for current densities ranging from about 5.0 to

  about 25.0 amperes per square decimeter (A / dm 2), usually using insoluble anodes such as carbon,

  platinum titanium or platinum The substrate, before the

  chrome garment, is subject to standard pre-treatments

  preferably with a nickel coating

  on which the chromium deposit is applied.

  According to another process aspect of the present invention

  vention, electrolytes of the trivalent chromium type which have

  rendered inoperative or ineffective as a result of the accumulated

  lation of hexavalent chromium ions are rejuvenated by the ad-

  addition of controlled effective amounts of the metal ion additive to reduce the concentration of hexavalent chromium to levels below about 400 parts per million (ppm) and preferably below ppm for which the effective chrome coating can

be resumed.

  Additional advantages of the present in-

  vention will appear on reading the description of

  preferred embodiments and specific examples

what provided.

  According to the composition aspects of this

  invention, the trivalent chromium electrolyte con-

  holds, as one of its essential constituents, trivalent chromium ions whose concentration can range

  roughly from about 0.2 to about 0.8 molar, and preferably

  rence from about 0.4 to about 0.6 molar Trivalent chromium concentrations below 6. of about 0.2 molar have been found to provide poor projection and poor coverage in some cases

  while concentrations of more than about 0.8 molai-

  re have in some cases resulted in precipitation of the chromium component in the form of complex compounds. For this reason, we prefer to maintain the concentration

  trivalent chromium ion in a range of about 0.2 to about

  ron 0.8 molar, and preferably from about 0.4 to about

  0.6 molar Trivalent chromium ions can be in-

  products in the form of any simple salt solu-

  ble in water and compatible such as chromium chloride hexahydrate, chromium sulfate and the like Preferably, the chromium ions are introduced in the form

  chromium sulfate for economic considerations.

  A second essential constituent of electrolysis-

  te is a complex transformation agent for trans-

  form in complex the constituent chrome present in the-

  now in solution The transformation agent in com-

  plex employee must be sufficiently stable and linked to

  chromium ions to allow their electrolytic deposition as well

  if to allow precipitation of chromium during

  effluent residue treatment The processing agent

  tion in complex can include formate ions, acetate ions or mixtures of both of which the ion

  formate is preferred

  xe can be used in concentrations ranging from approx.

  ron 0.2 up to around 2.4 molars depending on the trivalent chromium ions present The transformation agent into

  complex is normally used in a molar-

  re transformation agent into complex / chromium ions of

  approximately 1: 1 to approximately 3: 1, ratios of approximately

  1.5: 1 to about 2: 1 being preferred The ex-

  cessation of the agent of transformation into complex such

  that the undesired formate ions are undesirable since we have

  vé that in certain cases these excesses provoked the 7.

  precipitation of the chromium component in the form of

its complex.

  A third essential constituent of electro-

  lyte comprises one or a combination of additive agents based on metal ion in the form of salts soluble in the bath and compatible with the bath present in an amount which varies somewhat depending on the specific metal ion or

  the combination of metal ions used The concentra-

  wide and preferred ions of specific metal ions

  which are presented in Table 1.

TABLE 1

METAL ION

  Scandium Yttrium Lanthanum Titanium Hafnium Arsenic Selenium Tellurium Cerium Uranium Gold Silver Platinum Rhodium Iridium Osmium Ruthenium Rhenium Gallium Germanium Indium Samarium Europium Gadolinium Terbium Dysprosium Holmium Erbium Thulium Ytterbium Lutetium Praseodymium

RANGE RANGE

LARGE PREFEREE

0.02-20

0.025-20

0.01-20

0.01-20

0.015-15

0.025-10

0.025-10

0.025-10

0.002-10

0.003-10

0.004-5

0.003-10

0.002-10

0.002-10

0.002-10

0.001-10

0.025-10

0.025-10

0.060-10

0.020-10

0.030-10

0.020-10

0.020-10

0.002-10

0.002-10

0.002-10

0.002-10

0.002-10

0.002-10

0.002-10

0.002-10

0.002-10

0.005-17

0.002-10

  _ I 0.1-1 0.1-1 0.1-1 0.1-1 0.1-1 0.1-1 0.1-1 0.1-1

0.05-1

0.05-1

0.025-2

0.025-2

0.025-1

0.025-1

0.025-1

0.02-1

0.1-1 0.1-1 0.1-1 0.1-1

0.05-1

0.05-1

0.05-1

0.05-1

0.05-1

0.05-1

0.05-1

0.05-1

0.05-1

0.05-1

0.05-1

0.05-1

0.05-5

0.025-1

i 8.

  Excess of additive agents based on metal ion-

  really seem to adversely affect the function

  electrolyte in some cases by causing

  dark streaks in the coating depot and a red

  coating rate reduction Typically and preferably, metal ion concentrations are controlled within the preferred ranges presented in Table 1 which are satisfactory for keeping the concentration of hexavalent chromium in the electrolyte below about 400 ppm, preferably below about 100 ppm, and more commonly from about 0 to about 50

  ppm for which the optimum efficiency of the bath is obtained.

  The metal ion additive is

  produced in the electrolyte by any of a large

  number of compatible and soluble salts in the compressed bath

  those having only a minimum solubility and in this case mixtures of these salts are used to obtain the

concentration required.

  For example, the neodymium additive agent is introduced into the electrolyte by any of one

  large number of neodymium salts which do not affect defa

  vorably the deposit of chromium and include for example-

  ple neodymium trichloride (Nd C 13), neodymium acetate

  me lNd (C 2 H 302) 3 H 20 l, neodymium bromate

  lNd (Br O 3) 3 9 H 20 l, neodymium tribromide (Nd Br 3), he-

  neodymium trichloride xahydrate (Nd C 13 6 H 20) and oc-

  neodymium sulfate tahydrate lNd 2 (504) 3 8 H 20 l, as well

than their mixtures.

  Since the trivalent chromium salts, the complexing agent and the salts

  metal additives do not provide conductivity

  Adequate lity of the bath in themselves, it is preferred to further incorporate into the electrolyte controlled amounts of conductivity salts which typically include salts of alkali or alkaline earth metals and acids 9.

  strong such as hydrochloric acid and sulfuric acid.

  The inclusion of these conductivity salts is well known

  in the art and their use minimizes the dissipation

  energy during electrolytic coating Typical conductivity salts include potassium and sodium sulfates and chlorides as well as ammonium chloride and ammonium sulfate A particularly satisfactory conductivity salt is fluoroboric acid and salts of metal fluoroborates

  alkali, alkaline earth metal and ammonium solu-

  bles in the bath which introduce the fluoroborate ion into the bath and which have been found to further enhance chromium deposition These fluoroborate-based additives are preferably used to provide a concentration of fluoroborate ion of about 4 to about 300 g / l It is

  also typical to use metal salts of sul-

  and methanesulfonic acid as conductive salts

  tibility alone or in combination with conductive salts

  mineral susceptibility These conductivity salts or their metals

  swaddles are commonly used in amounts up to

  only about 400 g / l or more to obtain conductivity

  electrolyte t required and optimum chromium deposition.

  It has also been observed that the ammonium ions in the electrolyte are advantageous for enhancing the effectiveness of the additive component based on metal ion in order to

  transform the hexavalent chromium formed into a trivalent state.

  Particularly satisfactory results are obtained for molar ratios of ammofium ion / chromium ion ranging from approximately 2.0: 1 to approximately 11: 1, and preferably from approximately 3: 1 to approximately 7: 1. amminium can be partly introduced as the ammonium salt of the agent

  for transformation into a complex such as ammonium formate

  nium, for example, as well as in the form of

additional ductility.

  The effectiveness of the ion-based additive agent 10.

  metallic to control the formation of hexava chromium-

  slow is also reinforced by the presence of halogen ions

  res in the bath among which the chloride and bromide ions are preferred The use of a combination of chloride and bromide ions also inhibits the release

  chlorine at the anode While iodine can also be em-

  folded in the form of a halide constituent, its relatively higher cost price and its low solubility

  make it less desirable than bromide and chloru-

  re Generally, halide concentrations of at least about 15 g / l have been found necessary to

  obtain an efficient maintained operation of the electro-

  lyte More specifically, the concentration of halogenu-

  re is controlled in relation to the chromium deposit present and is controlled in a molar ratio of approximately 0.8: 1 to approximately 10: 1, for halide / chromium a ratio

  about 2: 1 to about 4: 1 molar being preferred.

  In addition to the above constituents, the bath may also optionally but preferably contain a buffering agent in an amount of from about 0.15 mol to

  solubility in the bath, amounts ranging typically-

  preferably up to about 1 molar

* Tration of the buffering agent is controlled between approximately 0.45 and approximately 0.75 molar calculated in the form of boric acid The use of boric acid as well as its alkali metal and ammonium salts as buffering agent is also effective in introducing borate ions into

  the electrolyte which has been found to improve the

  see electrolyte recovery According to a preferred practice, the concentration of ionsborate in the bath is controlled at a level of at least about 10 g / l The upper level is not critical and concentrations amounting to 60 g / l or more can be used without

apparent harmful effect.

  The bath also incorporates as constituting it. optional but preferred, a wetting agent or

  mixture of wetting agent of any of the types

  pes conventionally used in electrolytes for the deposition of nickel and hexavalent chromium These wetting agents or these surfactants can be anionic or cationic and are chosen from those which are compatible with the electrolyte and which do not adversely affect the electrolytic deposition performance of the chromium component Typically, wetting agents

  i D which can be used satisfactorily

  are sulfosuccinates or sodium lauryl sulfate and

  alkyl ether sulfates alone or in combination with other

  very compatible anti-foaming agents such as octyl alcohol, for example It has been found that the presence of these wetting agents produces a deposit of light chromium eliminating the dark speckled deposits and providing an improved covering in the areas with low current density While relatively high concentrations of these wetting agents are not particularly harmful, it has been found that higher concentrations

  about 1 gram per liter in some cases produced

  know a veiled deposit As a result, the wetting agent

  when used is usually controlled at concentrations below about 1 g / l, amounts

  from about 0.05 to about O, 1 g / l being typical -

  It is also expected that the electrolyte may contain

  other metals including iron, manganese and

  analogous to concentrations from O to saturation

  ration or at levels below saturation for

  which have no harmful effect on the electrolyte

  duit in cases where it is desired to deposit coatings of chromium alloy When iron is used, it is generally preferred to maintain the concentration of iron at

  levels below about 0.5 g / l.

  The electrolyte further contains a concentration of hydrogen ion sufficient to make the electrolyte acid The concentration of the hydrogen ion is largely controlled to provide a p H of about 2.5 to about 5.5 then that a range of p H of about 2.8 to 3.5 is particularly satisfactory The setting

  initial electrolyte up to the range of p H desi-

  can be obtained by adding any acid

  of suitable base compatible with the constituents

  bath including hydrochloric or sulfuric acid

  that and / or ammonium or sodium carbonate or ammonium

  niac or soda are preferred During the use of

  the coating solution, the electrolyte tends to

  come more acidic and appropriate p H settings are ef-

  made by the addition of hydroxides and carbonates of

  alkaline and ammonium levels among which the ammonium salts

  nium are preferred because they restock if-

  simultaneously the ammonium component in the bath.

  According to the process aspects of this

  invention, the electrolyte as described above is em-

  bent at a working temperature ranging from about 15 to about 451 C, preferably from about 20 to about 301 C.

  The current densities during the electrolytic coating

  that can go from about 5.0 to 25.0 A / dm, densities

  from around 7.5 to around 15.0 A / dm 2 being more typical.

  The electrolyte can be used to coat chromium on conventional ferrous or nickel substrates and on stainless steel as well as non-ferrous substrates such as aluminum and zinc The electrolyte can also be used to coat chromium on plastic substrates which have been subjected to a suitable pretreatment according to well known techniques to provide an electrically conductive coating such as a layer

  nickel or copper These plastics include

  ABS, a polyolefin, PVC (polyvinyl chloride)

  nylon), and phenol-formaldehyde polymers The work pieces to be coated are subjected to conventional pre-treatments according to prior art practices and the method is particularly effective for depositing chromium coatings on conductive substrates which have been previously coated with nickel. During the electrolytic coating, the work pieces are cathodically charged and the bath incorporates a suitable anode of material which will not adversely affect the electrolyte composition and which is compatible with this composition.

  anodes of an inert material such as carbon, for example

  ple, are preferred although other inert anodes in

  platinum or platinum titanium can also be used.

  When a chromium-iron alloy is to be deposited, the anode can suitably be formed from iron which will serve itself

source of iron ions in the bath.

  According to another aspect of the process of the present invention, a rejuvenation of a chromium electrolyte

  which has been rendered ineffective or ineffective by-

  te of the high concentration of hexavalent chromium ions

  is obtained by adding an effective, controlled amount

  Additive agent based on metal ion According to the

  specific composition of the chrome electrolyte triva-

  slow, it may also be necessary to add or adjust other constituents in the bath in the wide usable or preferred ranges as previously specified for

  obtain optimum coating performance For example-

  ple, the rejuvenation product may comprise a concentrate containing a salt formed of an additive agent based on suitable metal ions in combination in addition

  with salts consisting of halides, ammonium salts

  nium, borates and conductivity salts as may be desired or required The addition of the additive agent based on metal ions can be carried out in the form of dry salt or in the form of an aqueous concentrate in the presence of agitation to obtain a mixture

  uniform The time required to restore the electroly-

  until effective operation will vary with the concentration of harmful hexavalent chromium present and will usually range from only 5 minutes to about 2 hours or more. Rejuvenation treatment may also advantageously employ a

  electrolytic treatment of the bath after the addition of the pro-

  lo rejuvenation product by subjecting the bath to a low current density of about 1.0 to about 5.0 A / dm 2

  for a period of approximately 30 minutes to approximately 24 hours

  res to perform a conditioning or what is called a "sham" of the bath before resuming the coatings

  The concentration of metal ions to obtain

  hold rejuvenation can be included in the same

  limits than those previously defined for the elect

trolyte in operation.

  To further illustrate the composition and process

  As of the present invention, the specific examples follow

  It is understood that the examples are given by way of illustration and are not intended to

limit the present invention.

EXAMPLE 1

  A trivalent chromium electrolyte is prepared having a composition as presented below INGREDIENT CONCENTRATION, g / l Cr + 3 22

NH 4 COOH 40

NH 4 Ci 150 Na BF 4 50

H 3 B 03 50

  Ions Nd 0.05 Surfactant 0.1 The specific sequence of addition of the 15. constituents of the bath during the constitution of the bath is not

  not critical to obtain satisfactory performance.

  The trivalent chromium ions are introduced in the form of chromium sulphate The neodymium ions are introduced in the form of neodymium trichloride The surfactant used comprises a mixture of dihexyl ester of

  sodium salt of sulfosuccinic acid and sulphate derivative

  2-ethyl-1-hexanol sodium fate The operating temperature of the electrolyte is 21-270 C for cathodic current densities of approximately 10.0 to approximately, 0 A / dm and an anodic current density about 0.0 A / dm The electrolyte is used using a graphite anode for an anode / cathode ratio of about 2: 1 The electrolytic coating bath is operated using moderate agitation by air and / or mechanical We found it advantageous to submit the bath

  electrolytic preconditioning for low den-

  current, for example about 1.0 to about 5.0 A / dm 2 for up to about 24 hours to achieve satisfactory coating performance for

  higher normal operating current densities

laughing.

  The electrolyte used under the pre-

  cédentes produced a deposit of completely shiny and uniform chromium having a good to excellent covering, the ranges of current densities employed including a good covering in the zones with deep recesses

  J-type panels used for the surface covering

rimental.

EXAMPLE 2

  This example clearly shows the effectiveness of the

  dried neodymium to rejuvenate trivalent chromium electrolytes that have been rendered unacceptable or ineffective as a result of increasing the concentration of hexavalent chromium to an undesirable level.

  experience that the progressive accumulation of concentra-

  tion of hexavalent chromium will eventually produce flax jump

  chrome coating and will ultimately prevent it from

  any deposit of chromium coating These tests using electrolytes typical of trivalent chromium

  to which hexavalent chromium is intentionally added

  have highlighted the fact that a concentration of

  about 0.47 g / l of hexavalent chromium results in a coating

  of deposits with large coating locations

  of dark chrome and smaller surfaces that are totally

  Uncoated When the concentration of chromium hexa-

  are also increased to approximately 0.55 g / l se-

  lon these tests, a subsequent deposit of chromium on the subs-

  trat is completely prevented The concentration of hexavalent chromium at which the coating ceases will vary

  little according to the specific composition of the electrolyte.

  To demonstrate rejuvenation of the electrolyte

  contaminated with hexavalent chromium, a tri-

  valent is prepared with the following composition: INGREDIENT CONCENTRATION, g / l Sodium fluoroborate 110 Ammonium chloride 90 Boric acid 50 Ammonium formate 50 Ions Cr + 3 26 Surfactant 0.1 The bath is adjusted to a p H between about 3.5 and 4.0 at a temperature of about 21 C to about 27 C S-shaped nickel coated experimental panels are coated in the bath for a current density of about 10.0 A / dm 2 After each experimental test, the concentration of hexavalent chromium ions is increased by substantially 0 in the original bath in increments

  about 0.1 g / l by the addition of chromic acid No ef-

  harmful in the chrome coating of the panels 17.

  have been observed across the range of con-

  hexavalent chromium centrations from 0.1 to 0.4 g / l.

  However, when the concentration of hexavalent chromium has been increased above 0.4 g / l, large deposits of chromium will darken with small areas devoid of any

  chromium deposits were observed on the experimental panels.

  When the concentration of hexavalent chromium has reached a level of 0.55 g / l, no other deposit of chromium

  could not be coated on the experimental panel.

  13 In these circumstances it has so far been

  common practice to pour out the bath containing chromium

  me hexavalent in high quantity requiring a cons-

  titution of a new bath, which provides an operation

expensive and time consuming.

  To clearly show the rejuvenation aspects of the present invention, neodymium ions were added in increments of approximately 0.55 g / l to the bath containing 0.55 g / l of hexavalent chromium ions, and a coating of the panels.

  was taken up under the conditions as de-

previously written.

  The initial addition of 0.55 g / l of neodymium ions to the bath contaminated with 0.55 g / l of hexavalent chromium ions resulted in a restoration of the efficiency of the chromium coating bath, producing a good deposit of chromium good color and good coverage although hexavalent chromium ions are still detected as

present in the bath.

EXAMPLE 3

  A basic trivalent chromium electrolyte is prepared having a composition as presented below: INGREDIENT CONCENTRATION, g / l Cr + 3 22

NH 4 COOH 40

NH 4 Cl 150 Na BFA 50 q TAJ 18.

H 3 BO 3 50

  Surfactant 0.1 Trivalent chromium ions are introduced

  in the form of chromium sulfate The tensio-

  active ingredient used comprises a mixture of dihexyl ester of sodium salt sulfosuccinic acid and sodium sulfate derivative of 2-ethyl-lhexanol A electrolyte at

  previous basic trivalent chromium, counter quantities 6-

  The reducing metal ions are added according to

examples 4 to 26 and 28 to 37.

EXAMPLE 4

  To the trivalent chromium electrolyte of the example-

  ple 3, 0.05 g / l of gold ions are added in the form of

  gold chloride (Au C 13) Gold ions can also be added

  electrolyte tees using gold compounds at half

  be of variant, satisfactory, soluble in the bath and compatible with the bath, comprising gold bromide (Au Br 3),

  gold iodide (Au I) and their mixtures.

EXAMPLE 5

  To the trivalent chromium electrolyte of Example 3, 0.05 g / l of silver ions are added in the form of silver acetate lAg (C 2 H 302) l The silver ions can

  also be added to the electrolyte using compounds

  silver seeds as a soluble and compatible satisfactory variant comprising silver tetraborate

  (Ag 2 B 407 2 H 20), silver chlorate (Ag C 103), perchlo-

  silver spleen (Ag Cl O 4), silver fluogallate

  lAg 3 (GAF 6) 10 H 20 l, silver fluoride (Ag F), fluosili-

  silver cate (Ag 2 Si F 6 4 H 20) as well as their mixtures.

33 EXAMPLE 6

  0.05 g / l of platinum ions in the form of platinum chloride (Pt C 14) are added to the trivalent chromium electrolyte of Example 3

  also be added to the electrolyte using compounds

  platinum seeds as a satisfactory variant, soluble in the bath and compatible with the bath comprising the

  platinum trichloride (Pt C 13), tetra pentahydrate

  platinum chloride (Pt C 14 5 H 20), plat tetrafluoride

  tine (Pt F 4), platinum sulfate lPt (SO 4) 2 4 H 20 l and their mixtures.

EXAMPLE 7

  0.05 g / l of palladium ions in the form of palladium chloride (Pd C 12) are added to the trivalent chromium electrolyte of Example 3

  also be added to the electrolyte using compounds

  palladium seeds as a satisfactory alternative, solu-

  in the bath and compatible with the bath including

  palladium chloride dihydrate (Pd C 12 2 H 20), di-

  2 2 palladium fluoride (Pd F 2), palladium sulfate

  (Pd 504 2 H 20) as well as their mixtures.

EXAMPLE 8

  To the trivalent chromium electrolyte of Example 3, 0.05 g / l of rhodium ions are added in the form of rhodium chloride trihydrate (Rh C 13 3 H 20) The ions

  rhodium can also be added to the electrolyte in em-

  bending rhodium compounds as a satis-

  making, soluble in the bath and compatible with the bath comprising rhodium sulfate hydrate lRh 2 (504) 3 XH 20 l, rhodium sulfite lRh 2 (503) 3 6 H 20 l

as well as their mixtures.

EXAMPLE 9

  To the trivalent chromium electrolyte of Example 3, 0.05 g / l of iridium ions are added in the form of iridium tetrachloride (Ir C 14) The iridium ions can

  also be added to the electrolyte using compounds

  iridium seeds as a satisfactory variant, soluble in the bath and compatible with the bath comprising

  iridium tribromide (Ir Br 3 4 H 20), iridium tetrabromide

  dium (Ir Br 4), iridium dichloride (Ir C 12), triiodu-

  re iridium ((Ir I 3), iridium sulfate 20.

  Ir 2 (504) 3 XH 20 l and their mixtures.

EXAMPLE 10

  To the trivalent chromium electrolyte of the example-

  ple 3, 0.05 g / l of osmium ions are added in the form of osmium trichloride (Os C 13) Osmium ions can

  also be added to the electrolyte using

  installed osmium as a satisfactory alternative, solu-

  in the bath and compatible with the bath comprising osmium trichloride trihydrate (Os C 13 3 H 20), osmium tetrachloride (Os C 14), osmium octafluoride (Os F 8), osmium tetraoxide (Os O 4) and their mixtures.

EXAMPLE 11

  To the trivalent chromium electrolyte of the example-

  ple 3, 0.05 g / l of ruthenium ions are added in the form of ruthenium chloride trihydrate (Ru C 13 3 H 20) The ruthenium ions can also be added to the electrolyte

  using ruthenium compounds as a varian-

  te satisfactory, soluble in the bath and compatible with the bath comprising ruthenium tetrachloride (Ru C 14 5 H 20), ruthenium hydroxide lRu (OH) 3 l,

  ruthenium tetroxide (Ru O 4) as well as their mixtures.

EXAMPLE 12

  To the trivalent chromium electrolyte of the example-

  ple 3, 0.05 g / l of rhenium ions are added in the form

  rhenium trichloride (Re C 13) Rhenium ions can

  can also be added to the electrolyte using alternatively satisfactory rhenium compounds,

  soluble in the bath and compatible with the compre-

  as rhenium heptoxide (Re 207), rhenium tetrachloride (Re C 14), rhenium hexachloride (Re C 16),

  rhenium hexafluoride (Re F 6) and their mixtures.

EXAMPLE 13

  To the trivalent chromium electrolyte of Example 3, 0.05 g / l of gallium ions are added in the form of gallium trichloride (Ga C 13). Gallium ions can also be added to the electrolyte by using the gallium compounds as a satisfactory variant,

  soluble in the bath and compatible with the compre-

  nant gallium acetate lGa (C 2 H 302) 3 l, gallium tribromide (Ga Br 3), gallium perchlorate lGa (C 104) 3 6 H 20 l,

  gallium oxalate lGa 2 (C 204) 3 4 H 20 l, gal selenate

  lium lGa 2 (Se O 4) 3 22 H 20 l, gallium sulfate lGa 2 (504) 3 l, gallium sulfate hydrate lGa 2 (504) 3 18 H 20 l as well

than their mixtures.

EXEMP 4 E 14

  To the trivalent chromium electrolyte of Example 3, 0.05 g / l of germanium ions are added in the form of

  germanium chloride (Ge C 14) Germanium ions can

  can also be added to the electrolyte using germanium compounds as a satisfactory variant,

  soluble in the bath and compatible with the compre-

  nant germanium difluoride (Ge F 2), germanium tetrafluoride (Ge F 4 3 H 20), germanium diiodide (Ge I 2),

  germanium tetraiodide (Ge I 4), geroxide

  manium (Ge O 2) and their mixtures.

EXAMPLE 15

  To the trivalent chromium electrolyte of the example

  3, 0.05 g / l of indium ions are added in the form of chlo-

  indium rure (In C 13) Indium ions can also be added to the electrolyte using satisfactory indium compounds, soluble in the bath and compatible with

  bath comprising indium tribromide (In Br 3), per-

  indium chlorate lIn (C 104) 3 8 H 20 l, indium fluoride (In F 3 XH 20), indium selenate lIn 2 (Se O 4) 3 10 H 20 l, sulphate of indium lIn 2 (504) 3 l, indium sulfate nonahydrate lIn 2 (504) 3 9 H 20 l, indium diacid sulfate

  lIn 2 (504) 3 H 12504 7 H 20 l and their mixtures.

EXAMPLE 16

  To the trivalent chromium electrolyte of Example 22.

  3, 0.05 g / l of samarium ions are added in the form of he-

  samarium chloride xahydrate (Sm C 13 6 H 20) Samarium ions can also be added to the electrolyte by using samarium compounds as a satisfactory variant, soluble in the bath and compatible with the bath comprising acetate of samariuxm lSm (C 2 H 302) 3 3 H 20 l, samarium bromate lSm (Br O 3) 3 9 H 20 l, samarium chloride (Sm C 13), samarium sulfate lSm 2 (504) 3 8:20 a.m.

as well as their mixtures.

EXAMPLE 17

  To the trivalent chromium electrolyte of the example-

  ple 3, 0.05 g / l of europium ions are added in the form of europium sulfate octahydrate lEu 2 (504) 3 8 H 20 l The europium ions can also be added to the electrolyte using alternatively satisfactory compounds of europium, soluble in the bath and compatible with

the bath and their mixtures.

EXAMPLE 18

  To the trivalent chromium electrolyte of the example-

  ple 3, 0.05 g / l of gadolinium ions are added in the form of gadolinium chloride hexahydrate (Gd C 13 6 H 20)

  gadolinium ions can also be added to the electrolyte

  using gadolinium compounds as a

  laughing, satisfying, soluble in the bath and sympathetic

  wheat with the bath comprising gadolinium acetate lGd (C 2 H 302) 3 4 H 20 l, gadolinium bromide lGd Br 3 6 H 20 l, gadolinium chloride (Gd C 13), gadolinium oxide (Gd 203), gadolinium selenate lGd 2 (Se O 4) 3 8 H 20 l, gadolinium sulfate lGd 2 (504) 3 l, gadolinium sulfate octahydrate lGd 2 (504) 3 8 H 20 l

as well as their mixtures.

EXAMPLE 19

* To the trivalent chromium electrolyte of the example-

  ple 3, 0.05 g / l of terbium ions are added in the form

  terbium trichloride hexahydrate (Tb C 13 6 H 20).

23.

  Terbium ions can also be added to the electrolyte.

  using terbium compounds as a satisfactory alternative, soluble in the bath and compatible with

  the bath comprising terbium chloride (Tb C 13), oxy-

  of terbium (Tb 203), terbium sulfate

  lTb 2 (504) 3 8 H 20 l and their mixtures.

EXAMPLE 20

  To the trivalent chromium electrolyte of the example-

  ple 3, 0.05 g / l of dysprosium ions are added in the form of dysprosium trichloride (Dy C 13) Dysprosium ions can also be added to the electrolyte using

  dysprosium compounds as a satisfactory variant

  sants, soluble in the bath and compatible with the bath, comprising dysprosium acetate lDy (C 2 H 302) 3 4 H 20 l, dysprosium bromate lDy (Br O 3) 3 9 H 20 l, oxide dysprosium (Dy 203), dysprosium selenate lDy 2 (Se O 4) 3 8 H 20 l, dysprosium sulfate lDy 2 (504) 3 8 H 20 l

as well as their mixtures.

EXAMPLE 21

  To the trivalent chromium electrolyte of the example-

  ple 3, 0.05 g / l of holmium ions are added in the form of holmium trichloride hexahydrate (Ho C 13 6 H 20) The holmium ions can also be added to the electrolyte using compounds d holmium as a satisfactory variant, soluble in the bath and compatible with

the bath and their mixtures.

EXAMPLE 22

  To the trivalent chromium electrolyte of the example-

  ple 3, 0.05 g / l of erhium ions are added in the form of erbium trichloride hexahydrate (Er C 13 6 H 20) The erbium ions can also be added to the electrolyte in

  employing erbium compounds as a suitable variant

  doable, soluble in the bath and compatible with

  bath comprising erbium sulphate lEr 2 (SO 04) 3 l, octa-

  erbium sulfate hydrate lEr 2 (504) 3 8 H 20 l as well as 24.

their mixtures.

EXAMPLE 23

  To the trivalent chromium electrolyte of Example 3, 0.05 g / l of thulium ions are added in the form of thulium trichloride (Tm C 13) The thulium ions can

  also be added to the electrolyte using compounds

  thulium seeds as a satisfactory variant, soluble in the bath and compatible with the bath as well as their mixtures.

EXAMPLE 24

  To the trivalent chromium electrolyte of Example 3, 0.05 g / l of ytterbium ions are added in the form of ytterbium trichloride hexahydrate (Yb C 13 61120) The ytterbium ions can also be added to the electrolyte using ytterbium compounds as a satisfactory variant, soluble in the bath and compatible with the bath, comprising ytterbium acetate lYb (C 2 H 302) 3 4 H 20 l,

  ytterbium sulfate lYb 2 (504) 3 l, sulfa octahydrate

  te d'ytterbium lYb 2 (SO 04) 3 8 H 20 la as well as their mixtures.

EXAMPLE 25

  To the trivalent chromium electrolyte of the example

  3, 0.05 g / l of lutetium ions are added in the form of oc-

  lutetium sulfate tahydrate lLu 2 (504) 3 8 H 20 l Lutetium ions can also be added to the electrolyte using alternatively lutetium compounds, satisfactory, soluble in the bath and compatible with

the bath and their mixtures.

EXAMPLE 26

  To the trivalent chromium electrolyte of Example 3, 0.05 g / l of praseodymium ions are added in the form

  of praseodymium sulfate octahydrate lPr 2 (504) 3 8 H 20 l.

  Praseodymium ions can also be added to the electro

  trolyte by using praseodymium compounds as

  alternatively satisfactory, soluble in the bath and

  patible with the bath, comprising praseodymium acetate 25. lPr (C 2 H 302) 3 3 H 20 l, praseodymium bromate lPr (Br O 3) 3 9 H 20 l, praseodynm chloride (Pr C 13 ), heptahydrate

  praseodymium chloride (Pr C 13 7 H 20), pra- selenate

  seodymium lPr 2 (Se O 4) 3 l, praseodymium sulfate lPr 2 (504) 3 l, praseodymium sulfate pentahydrate

  lPr 2 (504) 3 5 H 20 l and their mixtures.

EXAMPLE 27

  This example shows the effectiveness of the agents

  metallic ion reducers to rejuvenate electro

  trivalent chromium trolytes which have been made unacceptable

  harmless or inoperative as a result of increased

  centering of hexavalent chromium to an undesirable level

  maple We have found by experience that the accumulation

  progressive concentration of hexavalent chromium pro-

  will eventually cause a jump in the chrome coating and will ultimately prevent any deposit of

  chrome coating These tests employing electrolytes

  your typical trivalent chromium to which we add inten-

  tional hexavalent chromium have highlighted the

  fact that a concentration of about 0.47 g / l of chromium he-

  xavalent results in a coating of deposits with large

  dark chrome coating surfaces and surfaces

  these smaller ones which are completely uncoated

  that the concentration of hexavalent chromium is further increased

  lying down to about 0.55 g / l according to these tests, another

  deposit of chromium on the substrate is completely prevented.

  The concentration of hexavalent chromium for which the

  coating stops varying somewhat depending on the composition

specific electrolyte.

  To further demonstrate a rejuvenation of the electrolyte contaminated with hexavalent chromium, a

  trivalent chromium bath is prepared having the composition

  following concentrations: 26. CONCENTRATION INGREDIENT, g / l Sodium fluoroborate 110 Ammonium chloride 90 Boric acid 50 Ammonium formate 50 Ions Cr + 3 26 Surfactant 0.1 The bath is adjusted to p H between about

  3.5 and 4.0 at a temperature of about 21 C to about 27 C.

  S-shaped nickel coated test panels are coated in the bath at a current density of approximately 10.0 A / dm 2 After each experimental test, the concentration of hexavalent chromium ions is increased substantially by 0 in the bath original in increments of approximately 0.1 g / l by addition of chromic acid None

  harmful effect on the chrome coating of the panels

  have been observed in all ranges of concentrates

  hexavalent chromium trations from 0.1 to 0.4 g / 1 Cepen-

  in the case where the concentration of hexavalent chromium has been increased above 0.4 g / l, large deposits of dark chromium with small areas devoid of any deposit

  of chromium were observed on the experimental panels.

  When the concentration of hexavalent chromium reached a level of 0.55 g / l, no other chromium deposit could

  be coated on the experimental panel.

  In these circumstances, it was previously

  common practice to pour out the bath containing chromium

  me hexavalent in high quantity requiring a cons-

  titution of a new bath, which constitutes an operation

expensive and time consuming.

  To show the rejuvenating aspects well-

  ment of the present invention, metal ions reduce

  as described in Examples 4 to 26 have been added

  teas in increments of approximately 0.55 g / l in the container bath

  0.55 g / l of hexavalent chromium ions and a coating of -

  27. experimental panels was included in the conditions

as previously described.

  In each case, the initial addition of 0.55 g / l

  of individual reducing metal ions in the contaminated bath

  born with 0.55 g / l of hexavalent chromium ions led to a restoration of the efficiency of the chromium coating bath producing a good deposit of chromium with good color and good covering although the hexavalent chromium ions

  are still detected as being present in the bath.

EXAMPLE 28

  To the trivalent chromium electrolyte of the example-

  ple 3, 0.05 g / l of scandium ions are added in the form

  scandium trichloride hexahydrate (Sc C 13 6 H 20).

  Scandium ions can also be added to the electro-

  lyte using scandium compounds as a va-

  satisfactory, soluble in the bath and compatible

  wheat with the bath, including scandium chloride

  (Sc C 13), scandium sulfate lSc 2 (504) 3 l, pentahydra-

  te of scandium sulfate lSc 2 (504) 3 5 H 20 l, scandium sulfate hexahydrate lSc 2 (504) 3 6 H 20 l as well as their mixtures.

EXAMPLE 29

  To the trivalent chromium electrolyte of the example-

  ple 3, 0.05 g / l of yttrium ions are added in the form of yttrium trichloride hexahydrate (YC 13 6 H 20) The yttrium ions can also be added to the electrolyte using compounds of yttrium as a satisfactory variant, soluble in the bath and compatible with the bath comprising yttrium acetate lY (C 2 H 302) 3 4 H 20 l, yttrium bromate lY (Br O 3) 3 9 H 20 l, yttrium bromide (Y Br 3), yttrium bromide nonahydrate (Y Br 3 9 H 20), yttrium chloride (YC 13), chloride monohydrate

  yttrium (YC 13 H 20), yttrium iodide (YI 3), oxala-

  te of yttrium lY 2 (C 204) 3 9 H 20 l, yttrium oxide (Y 203), yttrium lY 2 sulfate (504) 3 l, sulfate octahydrate 28.

  yttrium lY 2 (504) 3 8 H 20 l as well as their mixtures.

EXAMPLE 30

  To the trivalent chromium electrolyte of the example

  3, 0.05 g / l of lanthanum ions are added in the form of hep-

  lanthanum trichloride tahydrate (La C 13 7 H 20) Ions

  lanthanum can also be added to the electrolyte by em-

  folding lanthanum compounds as an alternative

  making, soluble in the bath and compatible with the bath comprising lanthanum acetate lLa (C 2 H 302) 3 1/2 H 20 l,

  lanthanum bromate lLa (Br O 3) 3 9 H 2 OJ, lan bromide

  thane (La Br 3 7 H 20), lanthanum carbonate

  lLa 2 (C 03) 3 8 H 20 l, lanthanum chloride (La C 13), hydro-

  lanthanum xyde lLa (OH) 3 l, lanthanum iodate lLa (I 03) 3 l, lanthanum molybdate lLa (Mo O 4) 3 l, lanthanum oxide

  (La 203), lanthanum sulfate lLa 2 (504) 3 l, nonahydra-

  te of lanthanum sulfate lLa 2 (504) 3 9 H 20 l as well as their mixtures.

EXAMPLE 31

  To the trivalent chromium electrolyte of Example 3, 0.05 g / l of titanium ions are added in the form of titanium trichloride (Ti C 13). The titanium ions can

  also be added to the electrolyte using compounds

  titanium seeds as a satisfactory, soluble alternative

  in the bath and compatible with the bath including tri-

  titanium bromide (Ti Br 3 6 H 20), titanium tetrachloride (Ti C 14), titanium trifluoride (Ti F 3), titanium tetrafluoride (Ti F 4), titanium iodide (Ti I 4), titanium oxalate lTi 2 (C 204) 3 10 H 20 l, titanium dioxide

  (Ti O 2 XH 30) and their mixtures.

EXAMPLE 32

  To the trivalent chromium electrolyte of the example

  3, 0.05 g / l of hafnium ions are added in the form of octa-

  hafnium oxychloride hydrate (Hf OC 12 8 H 20) The hafnium ions can also be added to the electrolyte by using hafnium compounds as variant 29. satisfactory, soluble in the bath and compatible with

bath and mixtures thereof.

EXAMPLE 33

  To the trivalent chromium electrolyte of Example 3, 0.05 g / l of arsenic ions are added in the form of arsenic oxide (As 205) The arsenic ions can also be

  added to the electrolyte using assay compounds

  nic as a satisfactory variant, soluble in

  bath and compatible with the bath comprising pentafluo-

  arsenic rure (As F 5), arsenic trioxide (As 203) as well

if their mixtures.

EXAMPLE 34

  To the trivalent chromium electrolyte of Example 3, 0.05 g / l of selenium ions are added in the form of sodium selenate (Na 2 Se O 4) The selenium ions can

  also be added to the electrolyte using compounds

  selenium seeds as a satisfactory, soluble alternative

  in the bath and compatible with the bath comprising the hy-

  sodium selenate drate (Na 2 Se O 4 10 H 20), sodium selenite (Na 2 Se O 3 5 H 20), selenium dioxide (Se 02),

  potassium selenate (K 2 Se O 4), potassium selenite-

  sium (K 2 Se O 3) as well as their mixtures.

EXAMPLE 35

  To the trivalent chromium electrolyte of Example 3, 0.05 g / l of tellurium ions are added in the form of

  tellurium sodium dihydrate (Na 2 Te O 4 2 H 20).

  Tellurium ions can also be added to the electro-

  lyte by using tellurium compounds as alternatives, satisfactory, soluble in the bath and compatible

  wheat with bath including potassium orthotellurate-

  sium (K 2 H 4 Te O 6 3 H 20), potassium telluride (K 2 Te), potassium tellurite (K 2 Te O 3), sodium orthotellurate (Na 2 H 4 Te O 6) , sodium tellurite (Na 2 Te O 3)

as well as their mixtures.

30.

EXEIPLE 36

  To the trivalent chromium electrolyte of the example-

  ple 3, 0.05 g / l of cerium ions are added in the form of cerium sulphate (Ce 2 (504) Cerium ions can

  also be added to the electrolyte using compounds

  alternatively, satisfactory, soluble cerium seeds

  in the bath and compatible with the bath comprising the acé

  cerium tate lCe (C 2 H 302) 2 l, cerium bromate lCe (Br O 3) 3 9 H 20 l, cerium carbonate lCe 2 (C 03) 3 5 H 20 l, cerium chloride ( Ce Ci 3), cerium iodide

  lCe I 3 9 H 20) l, the cerium molybdate lCe 2 (Mo O 4) 31, the selec-

  cerium niate lCe 2 (Se 04) 3 l, cerium sulfate tetrahydrate lCe 2 (504) 3 4 H 20 l, octahydrate-cerium sulfate lCe 2 (SO 4) 3 8 H 201, nonahydrate sulfate

  cerium lCe 2 (504) 3 9 H 20 l as well as their mixtures.

EXAMPLE 37

  To the trivalent chromium electrolyte of the example-

  ple 3, 0.05 g / l of uranium ions are added in the form of uranium oxysulfate hydrate (U 02 (504) 3 1/2 H 20) Uranium ions can also be added to the electrolyte using alternative uranium compounds, satisfactory, soluble in the bath and compatible with the bath comprising uranium tribromide (U Br 3), uranium tetrabromide (U Br 5), trichloride d 'uranium (UC 13), uranium tetrachloride (UC 14), uranium tetraiodide (UI 4), uranyl acetate lU 02 (C 2 H 302) 2 2 H 20 l, bromide d 'uranyl (UO 2 Br 2), uranyl chloride

  (U 02 C 12), uranyl formate lU 02 (CHO 2) 2 H 20 l, ioda-

  te of uranyl lU 02 (IO 03) 2 H 20 l, uranyl oxalate lUO 2 C 204 3 H 20 l, uranyl sulfate heptahydrate

  (2 U 02504 7 H 20) as well as their mixtures.

  The electrolytes of Examples 4 to 26 and 28 to

  37 were used at a working temperature of approx.

  ron 21 at around 27 C for cathodic current densities

  dique from around 10.0 to around 25.0 A / dm 2 and for a 31.

  anodic current density of about 5.0 A / dm Electro-

  lyte is used using a graphite anode and

  an anode / cathode ratio of about 2: 1 The coating bath

  electrolytic system is put into operation when

  i y moderate agitation by air and / or mechanical In each case, it was found advantageous to subject the bath

  electrolytic preconditioning at low den-

  current rating, for example about 1.0 to about 5.0 A / dm for a period of up to about 24 hours for 1 D obtain satisfactory coating performance for

  higher normal working current densities.

  Electrolytes incorporating metal ions

  that additives according to examples 4-26 and 28-37 under the preceding operating conditions produce deposits

  totally shiny and uniform chromium having a re-

  good to excellent coverage in the current density ranges employed including good coverage in the deep recess surfaces of panels of the type

  J used for the experimental coating.

EXAMPLE 38

  This example shows the effectiveness of the agents

  additives based on metal ions to rejuvenate the elect

  trivalent chromium trolytes which have been made unacceptable

  injured or inoperative due to an increase in

  concentration of hexavalent chromium up to a low level

  desirable We have found by experience that the accumulation

  progressive concentration of hexavalent chromium pro-

  will eventually have to skip the chrome coating and

  will ultimately result in the prevention of any deposit of

  chrome garment These tests using typical electrolytes of trivalent chromium to which hexavalent chromium is intentionally added have demonstrated the fact

  that a concentration of about 0.47 g / l of hexava chromium-

  slow results in the coating of deposits with large areas of dark chrome coating and larger surfaces.

  which are completely uncoated When the con-

  hexavalent chromium centration is further increased up to

  that at around 0.55 g / l according to these tests, another deposit of

  chromium on the substrate is completely prevented The concen-

  hexavalent chromium tration for which the coating ceases will vary somewhat depending on the specific composition

of the electrolyte.

  To clearly show a rejuvenation of an electro-

  lyte contaminated with hexavalent chromium, a trivalent chromium bath is prepared having the following composition: INGREDIENT CONCENTRATION, g / 1 Sodium fluoroborate 110 Ammonium chloride 90 Boric acid 50 13 Ammonium formate 50 Ions Cr + 3 26 Surfactant active 0.1 The bath is adjusted to a p H between approximately 3.5 and 4.0

  at a temperature of about 21 C to about 27 C The pan-

  S-shaped nickel coated experimental cells are coated in the bath for a current density of approximately

  , 0 A / dm After each experimental test, the concentration

  tion of hexavalent chromium ions is appreciably increased by O in the original bath in increments of approximately 0.1 g / l by addition of chromic acid No harmful effect in the chromium coating of the experimental panels has been observed across the full range of hex chromium concentrations from 0.1 to 0.4 g / l However, when the

  concentration of hexavalent chromium has been increased

  39 above 0.4 g / l / large deposits of dark chromium with small areas devoid of any chromium deposit were observed on the experimental panels When the concentration of hexavalent chromium reached a level

  0.55 g / 1 no other chromium deposit could be re-

dressed on the experimental panel.

33.

  In these circumstances, it was until pre-

  it is common practice to pour out the bath containing

  high concentrations of hexavalent chromium require

  both a constitution of a new bath, which is an expensive and time-consuming operation.

  To show the rejuvenating aspects well-

  ment of the present invention, metal ions addi-

  As described in Examples 28 to 37 were added in increments of approximately 0.55 g / l to the bath containing 0.55 g / l of hexavalent chromium ions and a coating of the experimental panels was resumed under conditions as previously described In each case, the initial addition of 0.55 g / l of the individual additive metal ions to the bath

  contaminated with 0.55 g / l of hexavalent chromium ions entrained

  a re-establishment of the effectiveness of the coating bath is born

  chromium producing good chromium deposition with good color and good coverage although hexavalent chromium ions are still detected as being present

in the bath.

  The appreciation of some of the measurement values indicated above must take into account the fact

  that they come from the conversion of English units

Saxons in metric units.

  The present invention is not limited to the examples

  ples of realization which have just been described, it is on the contrary susceptible of modifications and variants

  which will appear to those skilled in the art.

34.

Claims (19)

  1 Aqueous acid trivalent chromium electrolyte, characterized in that it contains trivalent chromium ions, a complexing agent for keeping trivalent chromium ions in solution, halide ions, ammonium ions, hydrogen ions   to provide a p H on the acid side, and an additive agent   taking a metal ion chosen from the group consists   health of neodymium, gold, silver, platinum, palladium, 19 rhodium, iridium, osmium, ruthenium, rhenium,   gallium, germanium, indium, samarium, euro-   pium, gadolinium, terbium, dysprosium, holmium,   erbium, thulium, ytterbium, lutetium, praseo   dyme, scandium, yttrium, lanthanum, titanium, haf-   nium, arsenic, selenium, tellurium, cerium, ura-   nium and their mixtures, present in an amount effective to maintain the concentration of hexavalent chromium ions at a level for which electrolytic deposits of chromium satisfactory are obtained.   2 Electrolyte according to claim 1, charac-   terized in that the trivalent chromium ions are present   in an amount of about 0.2 to 0.8 molar.   3 Electrolyte according to claim 1, charac-   terized in that the trivalent chromium ions are present   in an amount of about 0.4 to about 0.6 molar.   4 -Electrolyte according to claim 1, charac-   terrified in that the complex transformation agent   is present in a molar ratio of transforming agent   complexation / chromium ions about 1: 1 up to viron-3 1.   Electrolyte according to claim 1, characterized in that the complexing agent is present in a molar ratio of processing agent   in complex / chromium ions - from about 1.5: 1 to about 2: 1.   6 -Electrolyte according to claim 1, 35. characterized in that the ammonium ions are present in quantity to provide a molar ratio of ammonium ions / ions   chromium ranging from about 2 jo, 0: 1 to about 11: 1.   7 electrolyte according to claim 1, charac-   terized in that the ammonium ions are present in quantity to provide a molar ratio of ammonium ions / ions   chromium ranging from about 3: 1 to about 7: 1.   8 Electrolyte according to claim 1, character-   laughed in that the halide ions are present in quan-   to provide a halide ion to ion molar ratio   chromium from about 0.8: 1 to about 10: 1.   9 Electrolyte according to claim 1, charac-   terized in that the halide ions are present in quantity to provide a halide ion / molar ratio   chromium ions from about 2: 1 to about 4: 1.   Electrolyte according to claim 1, character-   laughed at in that it also contains conductive salts lity.   11 Electrolyte according to claim 10, ca-   characterized in that the conductivity salts are pre-   smells in quantities of up to about 400 g / l.   12 Electrolyte according to claim 1, charac-   terized in that it additionally contains borate ions.   13 -Electrolyte according to claim 1, charac-   terized in that it additionally contains a tensio- active.   14 Electrolyte according to claim 1, charac-   terized in that hydrogen ions are present for   provide a p H of about 2.5 to about 5.5.   15 Electrolyte according to claim 1, charac-   terized in that the metal ion-based additive agent   includes a metal ion selected from the group   posing scandium present in an amount of about 0.02 to about 20 g / l, yttrium present in an amount of about 0.025 to about 20 g / l, lanthanum present in an amount 36.   from about 0.01 to about 20 g / l, of titanium present in quan-   tity of about 0.01 to about 20 g / l, of hafnium present in   amount of about 0.015 to about 15 g / l of arsenic pre-   smells in an amount of from about 0.025 to about 10 g / l, of selected   nium present in an amount from about 0.025 to about 10 g / l, tellurium present in an amount from about 0.025 to about g / l, cerium present in an amount from about 0.002 to about 10 g / l, uranium present in quantity of about   0.003 to about 10 g / 1 and their mixtures.   16 Electrolyte according to claim 1, charac-   terized in that the metal ion-based additive agent   includes a metal ion selected from the group consisting   health of scandium present in an amount of about 0.1 to about 1 g / l, of yttrium present in an amount of about   0.1 to about 1 g / l of lanthanum present in the amount of   about 0.1 to about 1 g / l, of titanium present in quantity   from about 0.1 to about 1 g / l, of hafnium present in quanti-   approximately 0.1 to approximately 1 g / l of arsenic present in quan-   amount of about 0.1 to about 1 g / l, of selenium present in an amount of about 0.1 to about l g / l, of tellurium present   in an amount of about 0.1 to about 1 g / l, of pre-cerium   smells in an amount of about 0.05 to about 1 g / l, of uranium present in an amount of about 0.05 to about 1 g / l and their mixtures.   17 Electrolyte according to claim 1, charac-   terized in that the additive agent based on metal ion comprises neodymium ions present in an amount of approximately 0.005 to about 17 g / l.   18 Electrolyte according to claim 1, charac-   terized in that the additive agent based on metal ion comprises neodymium ions present in an amount of approximately 0.05 to about 5 g / l.   19 Electrolyte according to claim 1, characterized in that the metallic additive agent comprises a metallic ion chosen from the group consisting of 37 gold. Present in an amount of approximately 0.004 to approximately 5 g / l, of silver present in about 0.003 to about g / l of platinum present in about 0.002 to   about 10 g / l, of palladium present in an amount of approx.   ron 0.002 to about 10 g / l, of rhodium present in quantity   from about 0.002 to about 10 g / l, of iridium present in quan-   tity of about 0.002 to about 10 g / l, of osmium present in an amount of about 0.001 to about 10 g / l, of ruthenium present in an amount of about 0.025 to about 10 g / l, of rhenium present in an amount from about 0.025 to about 10 g / l, gallium present in an amount from about 0.060 to about g / l, germanium present in an amount from about 0.020 to about 10 g / l, indium present in an amount of about 0.030 to about 10 g / l, samarium present in an amount from about 0.020 to about 10 g / l, europium present in an amount from about 0.020 to about 10 g / l, gadolinium present in an amount about 0.002 to approximately 10 g / l, terbium present in an amount of approximately 0.002 to approximately g / l, dysprosium present in an amount of approximately 0.002 2) to approximately 10 g / l, of holmium present in an amount of approximately   0.002 to about 10 g / l of erbium present in the amount of   about 0.002 to about 10 g / l, thulium present in an amount of about 0.002 to about 10 g / l, ytterbium present-in an amount of about 0.002 to about 10 g / l, lutetium 2 Z present in an amount of about 0.002 to about 10 g / l, of praseodymium present in an amount of about 0.002 to about g / l and their mixtures.   Electrolyte according to claim 1, charac-   terized in that the metal ion-based additive agent   includes a metal ion selected from the group consisting   health of gold present in an amount of about 0.025 to about   2 g / l of silver present in an amount of about 0.025 to about   about 2 g / l, of platinum present in an amount of approximately 0.025 to approximately 1 g / l, of palladium present in an amount 33 of approximately 0.025 to approximately 1 g / l, of rhodium present in 38.   amount of about 0.025 to about 1 g / l, pre-iridium   smells in the amount of about 0.025 to about 1 g / l, of osmium present in the amount of about 0.02 to about 1 g / l, of the ruthenium present in the amount of about 0.1 to about 1 g / l , rhenium present in an amount of about 0.1 to about 1 g / l, gallium present in an amount of about   0.1 to about 1 g / l, germanium present in amount of   about 0.1 to about 1 g / l, of indium present in an amount of about 0.05 to about 1 g / l, of samarium present in   amount of about 0.05 to about 1 g / l, of pre-   smells in an amount of about 0.05 to about 1 g / l, gado-   linium present in an amount from about 0.05 to about 1 g / l, terbium present in an amount from about 0.05 to about 1 g / l, dysprosium present in an amount from about 0.05 to about 1 g / l, of holmium present in an amount of approximately   0.05 to about 1 g / l of erbium present in an amount of approx.   ron 0.05 to about 1 g / l, of thulium present in an amount of about 0.05 to about 1 g / l, of ytterbium present in   amount of about 0.05 to about 1 g / l, of pre-lutetium   smells in an amount of about 0.05 to about 1 g / l, of praseo   dyme present in an amount of about 0.05 to about 1 g / l and their mixtures.   21 Electrolyte according to claim 1, ca-   characterized in that the trivalent chromium ions are pre-   smells in an amount of about 0.2 to about 0.8 molar, the complexing agent is present in a molar ratio of complexing agent / ions   chromium from about 1: 1 to about 3: 1, the halogen ions   are present in a molar ratio of halogen ions   res / chromium ions from approximately 0.8: 1 to approximately 10: 1, the ammonium ions are present in a molar ratio of ammonium ions / chromium ions from approximately 2.0: 1 to approximately 11: 1, the hydrogen ions are present in an amount to provide a p H of about 2.5 to about 5.5 and the metal ion-based additives are present in an amount 39. from about 0.001 to about 30 g / l.   22 Electrolyte according to claim 1, charac-   terized in that the trivalent chromium ions are present in an amount of about 0.4 to about 0.6 molar, the complexing agent is present in a molar ratio of complexing agent / chromium ions of approximately - 1.5: 1 to about 2: 1, the halide ions are selected from the group consisting of chloride, bromide and their mixtures present in quantity to provide a halide ion / chromium ion molar ratio of about 2: 1 to about 4: 1, the ammonium ions are present in quantity to provide an ammonium ion / chromium ion molar ratio of from about 3: 1 to about 7: 1, the   hydrogen ions are present to provide a p H of approxi-   from 2.8 to about 3.5, additive agents based on metal ion are present in an amount from about 0.02 to about 5 g / l.   23 Process for electrolytically coating   that a deposit of chromium on an electrically conductive substrate, characterized in that it consists in immersing the substrate in an aqueous acid trivalent chromium electrolyte according to claim 1, in applying a cathodic charge to the substrate to effect a progressive deposition   of an electrolytic deposit of chromium and to continue the de-   electrolytic deposit of chromium electroplating up to   until the desired thickness is obtained.   24 A method of rejuvenating an aqueous acidic trivalent chromium electrolyte which has been degraded from an efficiency point of view as a result of contamination by excessive amounts of trivalent chromium, the electrolyte comprising trivalent chromium ions, a transformation agent into   complex to maintain the trivalent chromium ions in so-   lution, halide ions, ammonium ions and   hydrogen ions to provide p H on the acid side, characteristic   laughed at in that it consists in adding an agent 40 to the electrolyte. additive comprising a metal ion chosen from the group consisting of neodymium, gold, silver, platinum, palladium, rhodium, iridium, osmium, ruthenium,   rhenium, gallium, germanium, indium, sama-   rium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium,   praseodymium, scandium, yttrium, lanthanum, ti-   tane, hafnium, arsenic, selenium, tellurium,   cerium, uranium and their mixtures, in sufficient quantity   to reduce the concentration of chromium hexava ions   slow to a level for which the efficiency of the electrolyte-   to deposit satisfactory chromium deposits is re-attained.