Ability of coverings to resist influencing of environment in which it will be used, very important. As coverings are maintained in various conditions, test methods are developed with the purpose of a prediction of their behavior in concrete environments. The most part of such tests provides definition of stability to influences of following factors:
- solvents (including spots formation);
- moisture;
- salt fog;
- atmospheres;
- ultraviolet irradiations;
- heat.
Test for stability to influence of solvents is of great importance, if the covering can be potentially influenced the certain solvents and other similar environments (gasoline, oils) during usage. Stability to influence of solvents usually is defined by means of immersing the test plate with the deposited covering on solvent environment, for example acetone.
Products from metals and alloys under action of various physical and chemical factors collapse or lose (reduce) the consumer qualities. Such destruction of products from metals at influence of an environment refers to as corrosion of metals.
Corrosion of metals - process spontaneous, almost always negative from the point of view of industrial practice (corrosion plays a positive role and it is purposely provoked at acid clearing a surface of metals).
The environment causing corrosion, refers to corrosion or aggressive. As a result of interaction of metal and the corrosion environment the chemical compounds named by products of corrosion are formed.
Protection of metals against corrosion is one of the major problems, as losses from corrosion in the industry, transport and other branches of economy congruent with expenses for development of the largest industries.
The Principal cause of corrosion of metals and alloys is their thermodynamic instability. The speed of corrosion process having crucial importance, depends on set of simultaneously operating factors: internal, describing the nature of metal; technology of its manufacturing; structure of an alloy; type of structure; an internal stress; the surface condition and external, describing structure of an excited environment and condition of process passing (temperature, pressure, hydrodynamical conditions).
Corrosion processes proceed on border of section of phases a prize interaction of firm substance with gas or a liquid; such mechanism of interaction name heterogeneous [13]. The elementary scheme of heterogeneous process can be presented in the form of following basic stages:
a) Transportation of reacting substances an interface of phases;
b) Chemical interaction;
c) Removal of reaction products from a reactionary zone.
Speed of corrosion is defined by speed of processes of slowest of consistently proceeding stages, or speed of fastest of parallel stages. The establishment of a limiting (defining) stage of process is the main kinetics issue of corrosion processes for, knowing a limiting stage, it is possible to influence its course, that to brake (to stop) corrosion destruction.
As corrosion process - system of the interconnected phenomena (electrochemical and chemical reactions and processes of carry) them classify to attributes which define corrosion processes and features of their course.
Distinguish corrosion processes:
a) On the mechanism of reactions of interaction of metal with Wednesday (chemical, electrochemical, microbiological, radiating);
b) By the form of the corrosion environment (gas, atmospheric, in solutions of electrolits, underground, corrosion in liquids-nonelectrolyte, etc.);
c) By the form of corrosion destructions on a surface or in volume of metal (the general; local: in the form of spots, ulcers, dot, undersurface, intercrystalline, knife-line; selective);
d) On character of additional influences, to which metal simultaneously with action of the corrosion environment (corrosion bursting, corrosion at friction, cavitation corrosion) is exposed.
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