Chemistry and chemical technologies/6. Organic chemistry

 

 

Candidate of Chemistry A.K. Mamyrbekova

M. Auezov South Kazakhstan state university, Kazakhstan

Electrodeposition of copper

from water-dimethylsulphoxide electrolytes

 

DMSO thoroughly dissolves inorganic salts, particularly nitrates [1]. The solubility of copper(II) nitrate in DMSO has not been studied. Water and DMSO are completely miscible. The excess negative charge on the oxygen atom of the (ÑÍ3)2SO molecule causes hydrogen bonding with both the hydrogen-containing molecules dissolved in DMSO and the H atoms of the methyl groups in DMSO. Liquid DMSO is therefore characterized by a definite level of structure [2] that is destroyed easily at about 30°Ñ [3]. Since DMSO molecules are cationotropic, they form quite strong complexes with copper(II) ions that have coordination numbers from 2 to 4. There are data on the formation of stable [(ÑÍ3)2SO · NO3]– complexes in the presence of water [4] when the nitrogen atom is linked directly with the sulfur atom, although the possibility of such bonding was denied in [5]. The existence of Cu(NO3)2 · mDMSO complexes where m is 2–4 was mentioned in [6].

The physic-chemical properties of Cu(NO3)2.3H2O in dimethylsulphoxide (DMSO), and also the cathodic deposition of electroplatings copper in dependence from concentration (0.1-0.6 Ì), temperature (283-343 K) and current density          (1-60 mÀ/sm2) have been investigated.

The new electrolyte of copper on the basis of aprotonic polar solvent – dimethylsulphoxide was elaborated and the optimum conditions permiting to obtain light, petty-crystal, well cohesioned with basis deposits of high cleanliness were determined (Fig.1):

                                       Cu(NO3)2.3H2O, M – 0.1-0.4

                                        jk, mÀ/sm2              – 1-22

                                        T, K                         - 283-298

                                     a                                                        b

                                      c                                                       d

 

Fig.1.  Morphology of deposits of the copper received from 0,1 M of  Cu(NO3)2.3H2O  in DMSO  at  jk = 5 mÀ/sm2 and  different temperatures, K:

a – 288; b – 308; c – 318; d – 328  (increase in 2000 times).

The dependence yield of copper from density of current about all investigated concentrations expresses characteristic  curve analogous overturned parabola. From 0.1 M solutions curve was obtained at jk=1-10 mÀ/sm2. Increasing of concentration to 0.25 and 0.4 M stipulate for increasing of maximum and widening of foundation parabols to 0.3-17 and 0.5-40 mÀ/sm2 respectively.

At the high densities of current and temperatures the electroplatings soil with  oxides, sulphides, that confirm  dates roentgenographical analysis and aggravation of appearance of plating. From 0.6 M solutions the yield current of copper and quality  obtained electroplatings appreciablely decrease in all range of current densites.

The electroreduction of the complex ions of copper(II) the composition [Cu(DMSO)4(H2O)2]2+ is proceeding in two-stage on the adsorbate molecules of organic solvent electrode.

The main kinetic parameters (coefficients of transfer a, heterogeneous constant of velosity ks and effective energy of activation Aef) of process electroreduction of the ions copper(II) in dimethylsulphoxide, witnessing  about reversible of process were determined. The general velosity of cathodic process brakes of more slow second stage, probably, having the mixed nature of control, as compared with stage transfer of first electron was showed.

The analysis of partial termodinamical parameters and physic-chemical properties of investigated solutions and described results of experiment in electrodeposition of galvanoplatings allows to make the following conclusion about dependence of  conditions electroreduction of metall ions and formation of the cathodic deposit from  condition the ions in solution: the delivery electroactive ions to cathode, their  discharge and inclusion the atoms in cathodic deposit favourablely proceeding in certain ranges of concentration, which coincides with maximum of mobility ions in electrolyte. The conditions of maximum of mobility of the ions are determined with conductometric method.                              

REFERENCES

1. A. V. Kolomiets and N. D. Chkanikov, Chemical Encyclopedy (Sov. ntsiklopediya, Moscow, 1990), Vol. 2, p. 64 [in Russian].

2. V. I. Skomorokhov and A. F. Dregalin, Zh. Fiz. Khim. 66, 2947 (1992).

3. D. Martin and H. Hauthal, Dimethylsulfoxid (Academic_Verlag, Berlin, 1971).

4. H. L. Schlafer and W. Schaffernicht, Angew. Chem. 72, 618 (1960).

5. F. Whitmore, Organic Chemistry (van Nostrand, New York, 1987), p. 164.

6. Yu. N. Kukushkin, Achievements of the Chemistry of Coordination Compounds (Naukova Dumka, Kiev, 1975) [in Russian].