**5. References**

Butkevich, G.V.; Belkin, G.S.; Vedeshenkov, N.A. & Javoronkov, M.A. (1978). *Electrical erosion of heavy-current contacts, Energy.* Moscow, 256 p. (in Russian)


One might estimate the range of coating thicknesses that could be obtained under the necessary restrictions for the number of superimposed layers. That is, substrates should be alloyed according to the condition given in Fig. 14. The average thickness of coating as a function of pulse energy was given in Fig. 18. For any chosen pulse amplitude, the coating thickness increases with increasing pulse energy, especially, for the low pulse energy range the rate of increase was the highest. Upon further increase of pulse energy, above 1 J, the growth of coating thickness levels off, that correlates in the course of mass loss of treating

The failure of coating during processing was observed for the entire range of pulse parameters that were employed. In order to save already deposited layer, it is necessary to

As mentioned previously, when chemical composition of the substrate surface becomes as same as that of treating electrode after some deposition, the mass transfer from treating electrode to substrate ceases down. This is a limitation on coating thickness in ESA technology. Therefore, pulse energy was increased in order to increase the mass loss of treating electrode and its transfer to the substrate. However, it was experimentally found out that the other limitation of mass transfer, in turn limitation on layer thickness is the destruction of already deposited layer during processing. This was due to local evaporation of materials underneath the outer surface of deposit. Evaporation was due to the heat

Most of the molten material at the tip of the treating electrode could not be ejected out. Part of the ejected molten mass could be transferred to substrate and the rest is wasted. The ejected mass, so the transferred mass, could be increased by the employment of pulse groups instead of employing individual pulses (Rybalko et al., 1998; Ribalko et al., 2006, 2008). Mass transferred to the substrate could also be increased by the choice of an optimum scanning rate of the treating electrode. Because cross-section of a single deposit has very big difference in thickness (if the mass transfer time is long), the spot has higher thickness in center. For a continuous coating, the subsequent spot should partially overlap with previous spot. But, continuity of coating essentially depends on the experience of the operator. Thus, a continuous coating with uniform thickness demands compulsory automated spot deposition system with pre-determined rate of speed to provide necessary level of spot overlapping. Consequently, the non uniformity in coating thickness could be lowered and

average coating thickness, that is mass transfer, would essentially be increased.

in Bulletin of Invention in USSR (in Russian)

Vanity press, Moscow (in Russian)

Butkevich, G.V.; Belkin, G.S.; Vedeshenkov, N.A. & Javoronkov, M.A. (1978). *Electrical* 

Lazarenko, B.R. (1951). *Method of metal surfaces deposition*. The USSR Patent №89933. Unveil

Lazarenko, N.I. (1976). Electrospark alloying of metal surfaces. In: *Mechanical Engineering*,

*erosion of heavy-current contacts, Energy.* Moscow, 256 p. (in Russian)

electrode as shown in Fig. 15.

limit the processing time by the beginning of its failure.

provided locally by spark discharges of high energy pulses.

**4. General conclusion** 

**5. References** 


**22** 

*México* 

**Mass Transfer in the Electro-Dissolution** 

Martínez-Meza E., Uruchurtu Chavarín J. and Genescá Llongueras J.

Copper is considered to be among the most important structural elements, just below iron and aluminum. Usually, the properties of this metal improve when combined with other elements (Kear et al., 2004b); the 90% Cu-10% Ni alloy has excellent physical, chemical and mechanical properties that allow it to adapt to different operating conditions (Kutz, 2002; Othmer, 2004). This metal is relatively inexpensive, as a structural element it is aesthetically attractive. It shows good thermal conductivity and a lower electrical resistivity than that observed both in the 70% Cu-30% Ni alloy and in steel; these characteristics make the 90% Cu-10% Ni alloy an efficient and competitive structural element in heat transfer processes

In the last few decades, while trying to establish the dissolution mechanism in the presence of chlorides (Cl¯), this alloy has been the subject of numerous studies (Lee & Nobe, 1984; Crundwell, 1991; Milosev & Metikos, 1997; Kear et al., 2004b), usually at low concentrations and operating conditions close to those in the environment. However, its behavior in the presence of other agents such as bromides (Br¯), has received little attention (Itzhak & Greenberg, 1999; Muñoz-Portero et al., 2005), especially under operating conditions similar to those found in a heat pump that uses the H2O-LiBr pair as a working fluid, which is very attractive because of its thermodynamic properties, however, it is very aggressive to the

The kinetics of dissolution of the 90% Cu-10% Ni alloy, in the presence of halides, shows marked similarities to the reaction mechanism of copper (Lee & Nobe, 1984; Crundwell,

In the Tafel region, in the vicinity of corrosion potential, three dissolution mechanisms have been proposed. Some researchers (Taylor 1971; Wagner et al., 1998; Kear et al., 2000, cited in Kear et al., 2004a) propose a two step mechanism; the first step consists in an electrochemical reaction, in which the cuprous ion (Cu +) is produced due to the anodic dissolution of metallic copper (Cu). Then, in a chemical process, this species is combined

due to thermodynamic matters, this is the least viable of the proposed mechanisms.

) to form the cuprous chloride complex ion (CuCl2-). However,

**1. Introduction** 

(Copper-Nickel Alloys in Marine Environment).

**1.2 Dissolution mechanism** 

1991; Kear et al., 2004a, 2004b).

with two chloride ions (Cl-

structural elements of the equipment (Muñoz-Portero et al., 2006).

**of 90% Copper-10% Nickel Alloy** 

**in a Solution of Lithium Bromide** 

*Universidad Nacional Autónoma de México* 

Zolotih, B.N. (1957). About the physical nature of electrospark metal processing. In: *Electrospark processing of current-carrying materials*, *Publication 1*. Vanity Press Аcademy of Science of the USSR, Moscow, pp.38-69 (in Russian)
