adout the opportunity to produce copper powder with smaller particles size by addition surfactant Ф-1 to solution
Darintceva A.B., Murashova I.B., Osipova M.L*., Saveliev A.M*., Lebed’* A.B.,ZaikovYu.P.
The Ural StateTechnicalUniversity,Yekaterinburg, Russia,
620002, Mira st., 19, Electrochemical Department, E-mail:
*PC «Uralelectromed’», V.Pyshma, Russia, E-mail:
The industry needs for copper powders of different brands. The powder of brand SA is in popular demand now. It contains the fractions of undersize particles more in compare with other heavy powders of other brands (for example of GG-brand). It is rather difficult to foresee the yield the powder of certain brand in all the powder mass because dendrytic deposit puts a lot of operations after electrolysis: transport from the cell, water rinsing, extraction, drying, miling, screening, classification [1]. It changes own properties on every of these stages. But still there is some opportunity to make clear the tendency of powder properties changing in new conditions of electrolysis.
It has been shown that cathode dendrite crystallysation runs under mixed control on growth front [2], to be more correct on dendrite tips [3]. The most of surfactants being carried in solution may be adsorbed on electrode surface and hence have influence on kinetics of electrode processes. The change of copper exchange current density and transfer factor in surfactant’s presence will result in another distribution of overpotential between activation and diffusion its parts. The surfactant Ф1 is known as the substance with the properties of flocculant. Really it has been mentioned its some decreasing effect on cathode overpotential (Fig.1)
Fig. 1. Potentiodynamic polarysation curves on copper electrode in pure electrolyte and in the presence of 1 mg/L of Ф1.
The curves have been obtained in solution with 40 g/L of (Cu2+) at 550C with the help of potentiostat IPC Pro at 4 mV/s velocity of potential arising. Transition to (Cu2+) concentration of 23 g/L (as it is necessary for powder production of SA brand) has been performed in accordance with the law of electrochemical kinetics [4]:
(1)
where - standard exchange current density, - transfer factor, cO – concentration of Ox-form,
cST – standard concentration (1000 mole/m3 for metal ions). Because of the large value of exchange current density in concentrated solution the anode component has been taken into account in cathode part of cathode current density.
, (2)
where ik and ia – are cathode and anode kinetic current densities. After devision by ik and abbreviation i0 in subtrahend it will be obtained after some transforms
, where . (3)
As a result the following kinetic parameters have been calculated for cathode processes (table).
Table. Kinetic parameters for cathode processes in solutions of different composition
Pure solution with Cu2+ concntration / Solution with Ф1 1mg/L and cCu 2+40 g/L / 23 g/L / 40 g/L / 23 g/L
io,A/m2 / 163,514 / 111,987 / 171,314 / 117,784
/ 0,316 / 0,323 / 0,316 / 0,323
ilim ,A/m2 / 1644 / 945,587 / 1632 / 938,4
Alteration the cathode kinetic parameters leads to change the structural characteristics of dendrite deposit [4].These characteristics may be estimated as a result of simulation in terms of dendrttic tip radii (rtip) distribution. The simulation of dendrite crystallization is based on consideration this process as consisting of two electrode reactions, one of which takes place under diffusion control (copper deposition) while another (hydrogen evolution) runs on all electrode surface under control of charge transfer. Four differential equations have been posed for description the crystallization of dendrite deposit (for dendrite length y, curvature radii of its tips rtip, metal kinetic current density ik , hydrogen current density iH). The initial conditions are calculated on the base of charge balance and on principle of electrode equipotentiality. Simulteneous equations have been decided computationally in mathematical packet by Runge-Kutta method. The received correlations y(t), rtip(t), ik(t) and iH(t) open the opportunity to describe the growth dendrite dynamics as well as the deposit structural change. The latter is described as the distribution the deposit accordingly to dendrite tip radii (rtip).
Search for initial conditions for differential system decision has led to different results for initial densities of dendrite-nuclei. There has been nucleated more nuclei with less curvature radii rtip in solution with Ф1 addition. It is very likely due to surface activity of flocculant Ф1.So the dynamics of dendrites growth have proved to be different too. (fig.2)
Fig.2. Dendrite tip radii changings and current densities on them during electrolysis. / Fig.3. Potential dynamics and current efficiencies in pure solution and in Ф1 presence.The dendrites with less tip curvature radii develop through all the period of their growth in solution with Ф1 addition. It calls for more quick their lengthening, higher current densities on the tips, quick increasing of growth front square and as a consequence the higher current efficiency (fig.3). Quick development of dendrites means the larger effective diameter of electrode with the deposit and decreasing of current density on growth front. These appearances are accompanied with potential shift to more positive region (fig.3).
The received information constitutes the base for calculation the structural characteristics of friable deposit after electrolysis: for example distribution the deposit in terms of dendrite tip radii. Certainly it is not just the same as the results of grain-size classification but still it gives information about future results of mechanical powder treatment. So let us divide all the region of radii changing on some parts and find the charge quantity for radii alteration from rj to rj+1 (Fig. 4).
Fig.4. Current on growth front and dendrites tip radii during electrolysis in pure electrolyte (a) and in the presence of Ф1 (b).
The area under the proper curve IM, t on the circuit between moments corresponding radii rj and r j+1 represents such the charge quantity with t in real scale. Therefore its quotient to all the area under the curve IM(t) is the share of the powder with dendrite radii 0,5(rj + r j+1 ). (fig.5)
The less tip radii of dendrites are accompanied by higher density of tips displacement on unit of growth front area. In turn, it means the more fork of dendrite side branches which provides them high stability of ready-made product. Simulated tip dendrite radii distribution has shown that distribution maximum shifts substantially to production of finer powder deposit in Ф-1 flocculant presence.The results of distribution analysis testifies that surfactant Ф1 may be rather useful for production the powder with the particles of less size in compare with the powder of GG brand.
Some practice of that direction took place in industrial conditions of PC «Uralelectromed’».
Fig. 5.Distribution the dendrite deposit in relation tо rtip in pure solution
and in presence of Ф1-surfactant.
Сommercial testing took place with electrolyte containing surfactant-analog of Ф-1. It showed that the yield of powder SA brand increased to 76-86% in compare with routine 66% without flocculant.
The test lasted for 22 days. Powder properties were measured periodically. The bulk density compiled from 1,4 to 1,92 g/sm3for thepowder taken off the cathode rod in electrolyte with 3,5 mg/L of flocculant and 1,4 to 1,85 g/sm3 when flocculant content was from raised to 5,0 mg/L. It wasn’t fixed the raised yield of cathode scrap.
Literature
1. Nichiporenko O.X., Pomosov A.V., Naboychenho S.S. The powders of copper and of its alloys (in Russian). Metullurgiya, Moscow, 1988
2. Despic A.A., Popov K.I. Тhe Modern Aspects of Electrochemistry N.Y.: Plenum-Press 1972 V.7 P.199-313.
3. Murashova I.B., Pomosov A.V.,Potapov O.A. // Powder metallurgy and ceramics, 1991, March, P.5.
4. Murashova I.B., Burchanova N.G. //Electrochimiya (Rus) 2001 V.37 #7 P.871-877.
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