Classification of corrosive environments

Methods of protection against corrosion of metals and alloys

Individual project

Head: Mukhametdinova Guzel Mansurovna

Grade : ______________________________________ ( )

In numbers and words Signature of the head

Magnitogorsk, 2017

Content

INTRODUCTION 3

1. The concept of corrosion. 4

2. Characteristics and essence of corrosion processes. 4

2.1 Classification of corrosive environments. 4

2.1 Corrosion rate. 5

2.2 Fundamentals of the theory of corrosion. 6

2.3 Classification of corrosion processes. 6

3. Corrosion protection methods. eleven

3.1 Doping. eleven

3.2 Protective films. eleven

3.3 Primers and phosphating. 12

3.4 Electrochemical protection. thirteen

3.5 Silicate coatings. thirteen

3.6 Cement coatings. fourteen

3.7 Plating with metals. fourteen

3.8 Inhibitors.. 16

CONCLUSION. eighteen

LIST OF USED SOURCES.. 19

INTRODUCTION

Metals are one of the foundations of civilization on our planet. Their widespread introduction into industrial construction and transport occurred at the turn of the XVIII-XIX. At this time, the first cast-iron bridge appeared, the first ship was launched, the hull of which was made of steel, and the first railways were created. The beginning of the practical use of iron by man dates back to the 9th century BC. It was during this period that humanity moved from the Bronze Age to the Iron Age.

In the modern world of corrosion of metals and their protection against corrosion is one of the most important scientific and economic problems. [5]

Technological progress in many industries is hampered by a number of unresolved problems of corrosion control. This is most relevant in industrialized countries with a large metal fund (especially in recent years) due to the increasing use in industry of not only high-strength materials, but also especially aggressive media, high temperatures and pressures. Under these conditions, the specific weight of losses caused by such dangerous forms of corrosion as corrosion cracking, intergranular corrosion, pitting, etc., increased significantly.

The economic losses from metal corrosion are enormous. At the same time, metal losses, including the mass of failed metal structures, products, equipment, range from 10 to 20% of the annual steel production.

The purpose of the presented work is to give general information about the corrosion of metals, its types and types, to derive the main methods of protection against corrosion processes.

Tasks:

1) Get acquainted with the concept of corrosion and its types;

2) Analyze the characteristics and essence of corrosion processes;

3) Learn methods of corrosion protection.

The concept of corrosion

The term corrosion comes from the Latin word corrodere, which means to corrode, destroy.

Corrosion is a spontaneous process of destruction of materials and products from them under the chemical influence of the environment.

Corrosion of metals is the destruction of metals due to the physical and chemical effects of the external environment, in which the metal passes into an oxidized (ionic) state and loses its inherent properties. (Picture 1).

Picture 1 – Corrosion of metal

In cases where the oxidation of the metal is necessary for the implementation of any technological process, the term “corrosion” should not be used. For example, one cannot speak of corrosion of a soluble anode in a plating bath, since the anode must oxidize, sending its ions into solution, in order for the desired process to proceed. It is also impossible to talk about the corrosion of aluminum in the implementation of the aluminothermic process. But the physicochemical essence of the changes that occur with the metal in all such cases is the same: the metal oxidizes.[3]

Characteristics and essence of corrosion processes

Classification of corrosive environments

The environment in which the metal corrodes (corrodes) is called a corrosive or aggressive environment. According to the degree of impact on metals, it is advisable to divide corrosive media into:

  • non-aggressive;
  • slightly aggressive;
  • medium aggressive;
  • highly aggressive.

To determine the degree of aggressiveness of the environment during atmospheric corrosion, it is necessary to take into account the operating conditions of metal structures of buildings and structures. The degree of aggressiveness of the environment in relation to structures inside heated and unheated buildings, buildings without walls and permanently aerated buildings is determined by the possibility of moisture condensation, as well as the temperature and humidity conditions and the concentration of gases and dust inside the building. The degree of aggressiveness of the environment in relation to structures in the open air, not protected from direct ingress of precipitation, is determined by the climatic zone and the concentration of gases and dust in the air. Taking into account the influence of meteorological factors and the aggressiveness of gases, a classification of the degree of aggressiveness of media in relation to building metal structures has been developed. [ten]

Thus, the protection of metal structures from corrosion is determined by the aggressiveness of their operating conditions. The most reliable protective systems for metal structures are aluminum and zinc coatings.

Corrosion rate

The rate of corrosion of metals and metal coatings in atmospheric conditions is determined by the complex effect of a number of factors: the presence of phase and adsorption moisture films on the surface, air pollution with corrosive substances, changes in air and metal temperature, the formation of corrosion products, and so on.

Evaluation and calculation of the corrosion rate should be based on taking into account the duration and material corrosive effect of the most aggressive factors on the metal. [4]

Depending on the factors affecting the corrosion rate, it is advisable to subdivide the operating conditions of metals subjected to atmospheric corrosion as follows:

1. Enclosed premises with internal sources of heat and moisture (heated premises);

2. Enclosed premises without internal sources of heat and moisture (unheated premises);

3. Open atmosphere.[8]

Fundamentals of the theory of corrosion

Any corrosion process is multistage.

1. Supply of a corrosive medium or its individual components to the metal surface.

2. Interaction of the medium with the metal.

3. Complete or partial removal of products from the metal surface (into the liquid volume, if the medium is liquid).

Most metals (except gold, silver, platinum, copper) occur in nature in the ionic state: oxides, sulfides, carbonates, and so on, and are usually called ores. The ionic state is more favorable, it is characterized by lower internal energy. This is noticeable when obtaining metals from ores and their corrosion. The energy absorbed during the reduction of metal from compounds indicates that the free metal has a higher energy than the metal compound. This leads to the fact that the metal in contact with the corrosive medium tends to move into an energetically favorable state with a lower energy reserve. The root cause of metal corrosion is the thermodynamic instability of metals in a given environment. [nine]

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