Oxidation displacement deposition

This reaction is called displacement deposition, because the nickel ions in solution simply displace the silicon at the surface. The substrate. Si, acts here as a reducing agent, as discussed in Chapter 9. Copper may be deposited on Si from HF acid solutions (69). In the presence of HF, Si is oxidized into [SiF5] . 

Activation by Thermal Decomposition of Metallic Oxides. The surface of alumina, AI2O3, may be activated by employing laser or ultraviolet irradiation to decompose AI2O3 (68). Decomposition of AI2O3 results in the generation of aluminum particles that are catalytic for electroless deposition of Cu (the first reaction probably is displacement deposition). 

We described one example of this type of electrochemical deposition in Section 5.7 when we considered processes on a strip of Zn placed in a solution of CUSO4 (Fig. 5.11). In Chapter 5 we stated that there are two partial reactions in that system, as in an electroless system. In displacement deposition of Cu on Zn, electrons are supplied in the oxidation reaction of Zn ... 

This is obtained via combination of the two partial electrode reactions, oxidation and reduction, reaction (9.5) and (9.6), respectively. Thus, in the displacement deposition of Cu on a Zn substrate, a layer of metallic Cu is deposited on the zinc while Zn dissolves into solution (Fig. 5.11). We stated that this reaction is possible since the Zn/Zn system has an electrode potential lower than that of the Cu/Cu system (Table 5.1 and Fig. 5.10). The overall displacement deposition reaction according to Eq. (9.7) can be considered as the reaction of the electrochemical cell... 

Electroless plating should not be confused neither with the electrochemical (galvanic) displacement deposition - process involving the oxidation (dissolution) of the metallic substrate and concomitant reduction of metallic ions in solution - nor with the homogeneous chemical reduction process - indiscriminate deposition over all objects in contact with the solution. 

By the definition, the galvanic displacement deposition is a heterogeneous process in which the noble metal is deposited at the surface of an active metal [1]. The consequence is that the less noble (or active) metal is oxidized or dissolved in the appropriate solution. As a result, the ions of a more noble metal present in the solution are reduced leading to the deposition of the more noble metal. This situation can be described using the electrochemical half reactions in the following way. 

In the galvanic displacement deposition, the electrons produced due to oxidation or dissolution of the metal Mi, as shown by the reaction (9.1), are further used for the reduction of the metallic ions of the metal M2 (reaction (9.2)). Consequently, a combination of the reactions (9.1) and (9.2) leads to ... 

When a metal is immersed into the solution of salt of another metal farther to the right in the electromotive series, the first metal dissolves (is oxidized) while the second metal is deposited (its ions are reduced). Thus, the first metal displaces the second from its solution. 

Ligands of the NTA3" and EDTA4 type (complexones or sequestering agents, as they are sometimes called) are often able to dissolve deposits of metal oxides, hydroxides, sulfides, and carbonates because they displace solubility equilibria such as reaction 13.13 to the right by reducing the free... 

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