**4. Summary**

418 Corrosion Resistance

**200 μm 10 μm** 

Fig. 24. SEM images of the surface of Nim, Nin, and NiP alloy after corrosion tests in an

**200 μm 10 μm** 

environment of 0.5M NaCl solution.

**R**

 **200 μm**

**Nin** 

**Nim** 

**NiP**

The rate of corrosion processes of metallic materials in a corrosive environment depends on the chemical activity of the metal and the additional components, the structure of the material as well as the degree of development of their surfaces.

Electrochemical methods for the study of corrosion processes are based on the relationships between electrical, chemical and physical properties, which are used to identify phenomena and processes at the interface metal-corrosive environment. Electrochemical potentiodynamic polarization method allows determining the corrosion potential and corrosion current density of the metallic material in a corrosive environment. Additionally, the precise measurement method using electrochemical impedance spectroscopy (EIS) generates frequency characteristics of corrosion systems and forms the solid basis to design models based on equivalent electrical circuits, which maps the processes occurring in the corrosion system under investigation. Such an equivalent electrical circuit that meets the criteria of a mathematical (and metrological) model can also be considered as a physical model describing the phenomena and the processes occurring in a given system undergoing electrochemical corrosion.

The current research of corrosion phenomena appearing at the interface metal-natural environment showed that chemical re-combination of the metals to form ore-like compounds is a natural process, because the energy content of the metals and alloys is higher than that of their ores. It has to be emphasized that there are number of means of controlling corrosion. The choice of a means of corrosion control depends on economics, safety requirements, and a number of technical considerations. However, it is necessary to learn and recognize the forms of corrosion and the parameters that must be controlled to avoid or mitigate corrosion.

Through the understanding of the electrochemical processes and how they can act to cause the various forms of corrosion, the natural tendency of metals to suffer corrosion can be overcome and equipment that is resistant to failure by corrosion can be designed. In this study we have shown that the measuring methods based on the electrochemical impedance spectroscopy are able to detect the potential corrosion spots in very early stages.
