CHROMIUM PLATING FROM BATHS CATALYZED WITH ALKANEDISULFONIC-ALKANESULFONIC COMPOUNDS WITH INHIBITORS SUCH AS AMINEALKANESULFONIC AND HETEROCYCLIC BASES

Abstract: C1-C12 Alkanesulfonic or Alkanedisulfonic compounds and Aminoalkanesulfonic acids or salts thereof, are used as additives in chromium plating baths to reduce anodic corrosion, improve the covering and penetrating power of the bath, reduce the surface-tension and give a bright deposit.

Description: "CHROMIUM PLATING FROM BATHS CATALYZED WITH ALKANEDISULFONIC- ALKANESULFONIC COMPOUNDS WITH INHIBITORS SUCH AS AMINEALKANESULFONIC AND HETEROCYCLIC BASES". Technical Field The present invention relates to chromium plating baths with organic additives, resistant in solutions of chromium, to obtain electrodeposition of penetrating and covering chromium while avoiding anodic corrosion. Background Of The Invention Alkane sulfonic and disulfonic acids were first used as additives for electrolytic baths in 1930, at the Politecnico of Milan. After the Second World War American, French, German, Polish and Soviet researchers reported and claimed disulfonic acids and their salts as improvers of cathode efficiency in chromium plating baths. However, application of these types of baths on a large scale over a period of time revealed inferior properties compared to traditional baths, in that they cause accelerated corrosion of the anode (an alloy of lead). The mechanism that leads to these drawbacks is described as follows: Acidic dissolution of Pbθ2 due to the polarization of acid concentration: Pb0 2 +2H + = Pb0 2+ +H 2 0 Reaction of the lead oxide favored by the excess of acidity with H2O2 formed at the anode Pb0 2 +H 2 0 2 +2H + = Pb 2+ +0 2 +2H 2 0 (the reformation and the stabilization of the Pbθ2 is, on the contrary, favored by a deficit of free acid: Pb 2+ + O2+ H 2 0= Pb0 2 + H2O2+ 2H + ). The anode degradation rate is further increased by the fact that the Pb 2+ ions formed are removed from the equilibrium by the formation of stable complexes with ions in solution - for instance traces of halides and degradation products of the organic acids. Many proposals have been suggested to eliminate the drawbacks described above, by chemical and electrical means, but with unsatisfactory results. Disclosure Of The Invention This patent claims the use of certain additives in specific concentrations, to improve the covering and penetration power of the chromium plating baths while avoiding anodic corrosion. Anodic corrosion can be drastically reduced or eliminated by adding appropriate concentrations of aminoalkanesulfonic compounds or heterocyclic nitrogen containing bases to the chromium plating baths containing Alkanedisulfonic or Alkanesulfonic acids or salts. These substances in elevated concentrations can lead to a cathode efficiency below that of a traditional chromium plating bath . a) The aminoalkanesulfonic and the heterocyclic bases are added to the chromium plating baths containing Alkanedisulfonic and Alkanesulfonic acids and salts, in such concentrations as to give a Faraday output of 15-16% constant (not of interest in this patent which claims other parameters). b) The corrosion inhibitors, chemical compounds, added to the chromic solutions containing Alkanesulfonic and Alkanedisulfonic acids and salts, drastically reduce the corrosion rate of anodes immersed in them, shifting the corrosion potential to values nobler than the primary potential, or increasing the overload of the anodic or cathode process or of both simultaneously according to their chemical nature. Such purpose is achieved by the present invention, which relates to chromium plating baths comprising one or more compounds selected from compounds having general formula: X - (CH 2 )n- S0 3 H [1] where: n= integer from 1 to 12 X= NH 2 and salts thereof, and nitrogen containing heterocyclic bases and/or their complexes with Cr0 3 . Preferred compounds of formula [1] are aminoalkanesulfonic acids and salts C2-C6 and most preferably C2 and C3 compounds. Preferably, nitrogen containing heterocyclic bases are provided as complexes with chromium, namely with Crθ3. An example of such complexes is the complex between pyridine and Crθ3, as shown by the following formula: Further preferred complexes are those of pyridine homologues,, optionally with ring substituents, such as e.g. nicotinic acid, picolinic acid, 4-pyridinethanesulfonic acid, etc.. In presence of these compounds the anodic corrosion is drastically reduced even in the presence of high concentrations of compounds of general formula: Y - (CH 2 )n- S0 3 H [ 2] where: n= integer from 1 to 12 and salts thereof. These additives are employed in chromium plating baths, in combination with the previously disclosed compounds in order to give penetrating and covering chromium deposits without corrosion of the lead alloy anode. The invention therefore also relates to chromium plating baths according to Claim 8. Preferred aspects of the invention are claimed in Claims 9- 11. The additives object of the invention are provided within the range of 0.1-40 g/l, preferably within 1-20 g/l and most preferably within the range of 2-3 g/l. Another object of the invention is a concentrated formulation containing Crθ3 and one or more additives of formula [1], and/or one or more nitrogen containing heterocyclic bases and their complexes with chromium, and/or compounds of formula [2] for the preparation of chromium plating baths, according to Claim 12. Further objects of the invention are the uses of the compounds of formula [1] and [2], including nitrogen containing heterocyclic bases and chromium complexes thereof, according to Claims 13, 14 and 15. A further advantage of the present invention is given by the fact that the addition to a chromium plating bath of compounds of general formula [1] and [2j with 6-12 atoms of carbon, leads to a reduction of the surface tension of the bath with the advantage of eliminating splashing, reducing the losses to transport with notable saving of chromic acid, so much so that their employment is cost-reducing and improves the work environment (TLV-TWA values). Another object of the invention is the use of the compounds of formula [1] and [2] according to Claim 16. Preferred compounds are those of formula [2]. Penetrating power is a grading of the metal in function of the electric current, where chromium plating baths have scarce penetrating power. Various methods for the measurement of the penetrating power of the electrolytic baths exist as for instance: a) the technique of E.Haring and W.Blum; b) Method of C.Pam. Best Mode for Carrying Out The Invention The invention will now be disclosed by way of non-limitative reference to the following examples and to the enclosed drawings, where: Figure 1 is the schematic representation of a test-plate of the penetrating power of a traditional bath; Figure 2 is the schematic representation of a test-plate of the penetrating power of a traditional bath in the presence of additives; and Figures 3 and 4 are a schematic representation of the covering power of a V-shaped plate. We have established the penetrating power of the chromium plating bath through a Hull cell. For this purpose it is sufficient to observe the presence and degree of deposition of chromium which is obtained on the test-plates in zones of least density of current. EXAMPLE 1 A chromium plating bath of the traditional type was prepared : 250 gr/ It CrOs 2.5 gr/ It H 2 S0 4 The chromium was deposited in Hull cell, for 8' on an iron cathode of length of 10 cm, at a temperature of 60°C with current of 10 Amp. The bare part was 6 cm. EXAMPLE 2 The test was repeated, in similar conditions to Example 1 , in the presence of non-limiting additives: 250 g/lt Cr0 3 2.5 g/lt H S0 4 6 g/lt Ethαnedisulfonic sodium salt 1 g/lt Aminoethanesulfonic acid The bare part was 2 cm. Covering power of a chromium plgting bgth is the minimum current gt which the chromium deposit begins to form. EXAMPLE 3 A chromium both of the troditionol type wgs prepgred: 250 g/lt CrOs The ccthode used was a V-shaped panel. Temperature was 60°C. The chromium was deposited on the cathode for 8' with a current of 10 Amp. The part not electroplated was 6 cm. (fig. 3). EXAMPLE 4 The test is repeated with a catalyzed chromium plating bath in the following concentrations: 250 g/lt CrOs 2.5 g/lt H 2 S0 4 6 g/lt Ethanedisulfonic sodium salt 1 g/lt Aminoethanesulfonic The part not electroplated was 3 cm. (fig. 4). The chromium plating baths were re-tested in the presence of nitrogen containing heterocyclic base-type inhibitors; the results were similar to the preceding examples. Figure 3 is a scheme of "V"-shaped cathode after deposition in a traditional bath for evaluation of the covering power . Figure 4 is an gnglogous scheme to thot of figure 3 offer deposition in o bath containing the odditives according to the invention. The solts of the olkyldisulfonic ocid can be prepared by reaction of an Alkyl dihalide with a sulphite, through a nucleophilic substitution reoction with the hologens, the leoving groups, thot gre replgced by SO3 groups. The olkyl dihglides thgt cgn be employed in this process hove genergl formulo: where n = integer from 1 to 12 X= Cl, Br, I e.g. 1 ,2-dibromoethone, 1,3-dibromopropone, l-chloro-3- bromopropone etc. The regctivity order is I > Br > Cl; the more convenient compounds are the Alkyl dibromides, e.g. 1-2 dibromoethane - a good compromise between reagent cost and reactivity. Water-soluble sulphites e.g. Na 2 S0 3 , K2SO3, (NH 4 ) 2 S0 3 , ZnSOs, MgSOs etc. can be used as reactive sulphites, or the corresponding soluble metabisulphite could be used, treated with an equimolar quantity of the corresponding hydroxide. Water or H2θ-ethanol, H∑O-methanol mixtures can be used as solvents. The reaction proceeds very slowly at ambient temperature and T > 80°C is preferable to give an acceptable reaction. The reaction can be represented by the following general equation CnH 2 nX 2 + 2Me 2 S0 3 — > CnH 2n (S0 3 Me) 2 + 2 MeX where n = number from 1 to 12, X = Cl, Br, I. The reaction must take place with sulphite in excess of the stoichiometric quantity to guarantee the maximum yield of alkyldisulphonate and minimize the secondary reactions of hydrolysis of the halide, with formation of glycols and hydroxyalkylsulphonates. The reaction can be performed with a sulphite : dibromoethane molar ratio of from 1.1/1 to 1.5/1. Example 5 (not limiting) A solution formed of: 1 liter H2O is plgced in g 2 liter regctor provided with refrigerant, thermometer, stirrer ond drip-funnel. This solution is heoted to o temperature of 80°C; thereafter, 200 g of dibromoethane was added over 40 minutes; the molar ratio of sulphite/dibromoethane is 1.4 compared to the stoichiometric equivalent. The reactor was left to reflux for 6 hours. The yield of the reaction is 95%. Example 6 The procedure is the same as in the preceding example; the reagent proportions are the following: 161 g. Na 2 S0 3 100 g. dibromoethane The molar ratio sulphite/ dibromoethane is 1.2 compared to the stoichiometry. The yield of the reaction is 91% of the theoretical. The reaction product can be separated from the sodium bromide, the unreacted sulphite and the by-products by means of recrystalization in water or in aqueous-methanol. The methodology is also similar for dihalides or Alkyl halides, but, obviously, the molar ratios must be adjusted accordingly.

Claims: CLAIMS 1. An electrolytic chromium plating process containing the additives specified in concentrations from 1 to 20 g./lt. 2. An electrolytic chromium plating process containing the odditives specified to prevent onodic corrosion in concentrations from 1 tolO g./ It. 3. An electrolytic chromium ploting process containing the additives specified to reduce the surface-tension of the chromium solution . 4. An electrolytic chromium plating process containing the additives specified to improve the covering power . 5. An electrolytic chromium plating process containing the additives specified to improve the penetrating power. 6. A method of preparation and production of the compounds cited in general formula in this Patent. 7. The application in chromium plating baths of the compounds cited by the Patent in general formula and also their method of production. 8. A chromium plating bath, characterized by comprising one or more compounds selected from compounds of general formula: X-(CH 2 )rrS0 3 H []] where: n = integer from 1 to 12 x = NH 2 and the salts thereof; and from heterocyclic nitrogen containing bases and/or their complexes with chromium. 9. A chromium plating bath according to claim 8, further comprising one or more compounds of general formula: Y-(CH 2 ) n -S0 3 H [2] where: n = integer from 1 to 12 Y = H orS0 3 H and the salts thereof. 10. A chromium plating bath according to claim 8 or 9, comprising one or more compounds of formula [1] and/or [2] having from 6 to 12 atoms of carbon, or the salts thereof. 11. A chromium plating bath according to any previous claim, wherein said additives are present in total concentration whitin the range of 1 to 20 g/lt. 12. A formulation for the preparation of a chromium plating bath according to any Claim 8 to 1 1. 13. The use of compounds having general formula: X-(CH 2 )n-S0 3 H [1] where: n = integer from 1 to 12 X = NH 2 or salts thereof, and of heterocyclic nitrogen-containing bases and their complexes with chromium, to reduce or prevent anodic corrosion in chromium plating baths. 14. The use of compounds having general formula: Y-(CH 2 )n-S0 3 H [2] where: n = integer from 1 to 12 Y = H or SOsH or salts thereof, to improve the penetrating and covering power in a chromium plating baths. 15. The use of compounds hoving general formulo X-(CH 2 )n-S0 3 H [1] where: n = integer from 1 to 12 X = NH 2 or of the solts thereof, ond of heterocyclic nitrogen-contoining bgses gnd their complexes with chromium, in combinotion with compounds of general formula Y-(CH 2 )π-S0 3 H [2] where: n = integer from 1 to 12 Y = H or SOsH, or salts thereof, to improve the penetrating and covering power of a chromium plating bath. 16. The use according to the Claim 14 or 15, wherein Y is a sulfonic acid group or a salt thereof. 17. The use of compounds having general formula: where: n = integer from 6 to 12 X = NH and salts thereof, and of compounds having general formula: Y-(CH 2 )n-S0 3 H [2] where: n = integer from 6 to 12 Y = H or SOsH and salts thereof, to lower the surface-tension in chromium plating baths.

Inventors: FREDIANI LIDO, MERELLO GIOVANNI, FREDIANI, LIDO, MERELLO, GIOVANNI
Applicants: FREDIANI LIDO, MERELLO GIOVANNI, STOPPANI LUIGI SPA, FREDIANI, LIDO, LUIGI STOPPANI S.P.A., MERELLO, GIOVANNI
Application year: 1998
Main classification: C25D3
IPC codes: C25D3