فارسی 
Corrosive environments
Corrosion and corrosive environments:
In most chemical environments, metals are exposed to corrosion, for example, they are corroded in contact with water, moisture, acids, bases, salts, oils, gases and other chemicals.
In general, compared to organic materials, minerals are more corrosive. For instance, in the oil, gas and petrochemical industries corrosion is often caused by mineral substances such as chlorine, sulfur, etc. rather than organic substances such as, petroleum, diesel, and oil.
Corrosion reacts in different environments, which will be explained briefly as follows:
1) Acidic environment
2) Neutral environment
3) Alkaline environment
4) other environments
Corrosion in acidic environments:
Among the common ways to produce hydrogen in the laboratory, one is to place zinc in a dilute acidic solution such as hydrochloric acid or sulfuric acid. In this way, through occurring a rapid reaction, zinc metal is attacked (dissolution of zinc metal) and hydrogen is released as a gas:
ZnCl2 + H2(g)=> Zn + 2HCl
In the same way, zinc metal reacts with sulfuric acid as follows and the result is zinc sulfate (salt) and hydrogen gas:
ZnSO4 + H2(g) => Zn + H2SO4
It is true for other metals as well, which are corroded or dissolved by acids, and the result is a soluble salt and hydrogen gas:
FeCl2 + H2(g) => Fe + 2HCl
2AlCl3 + 3H2(g) => 2Al + 6HCl
The two reactions mentioned above show that both iron and aluminum metals are corroded by hydrochloric acid.
Corrosion in neutral and alkaline solutions:
Corrosion reactions mostly take place in environments such as freshwater, sea water, saline and alkaline solutions, of course, to carry out such reactions, the presence of oxygen is necessary, which is usually provided from the air in aquatic environments. As an example, rusting of iron in a humid environment can be mentioned, which actually takes place in the reaction below:
Anodic reaction: Fe→Fe2++2e–
Since the desired environment is in contact with the atmosphere, it contains dissolved oxygen. Water and sea water are almost neutral, so the cathodic reaction will be:
Cathodic reaction: O2+ 2H2O 4e–→4OH–
With due attention to the fact that sodium and chlorine ions of salt solutions do not take part in the reaction, the whole reaction is obtained from the sum of both anodic and cathodic reactions:
2Fe+2H2O+O2→2Fe2++4OH–→2Fe(OH)2
Precipitates of ferrous hydroxide are separated from the solution. This compound cannot be stable in solutions containing oxygen and the result is ferric oxide salts.
2Fe(OH)2+H2O+1/2 O2→2Fe(OH)3
The obtained ferric hydroxide loses its water and turns into a rust and brownish-red color:
2Fe(OH)3→Fe2O3+3H2O
Also, zinc metal reacts in the presence of oxygen and humid environment as follows:
2Zn+2H2O+O2→2Zn(OH)2
Zn(OH)2→ZnO+H2O
Zinc oxide is obtained from a white precipitate that can be seen on galvanized buckets, rainwater channels, etc.
Note: Compared to soft water, hard water usually has less corrosive properties, the reason is the tendency of hard water to precipitate and form a protective layer of calcium carbonate.
Corrosion in other environments:
Corrosion may also take place in non-acidic and oxygen-free environments, for example, the reaction of zinc metal in chloroferric and copper sulfate environments can be mentioned:
ZnCI2 + 2FeCl2 =>Zn + 2FeCl3
ZnSO4 + Cu => Zn + CuSO4
share :
Related Articles
Corrosion process
Corrosion of metals is the process in which metals reach their original oxidation numbers. In fact, corrosion of metals is an oxidation-reduction reaction in which the metal is oxidized by its surroundings. Typically, oxygen from the air acts as the oxidant in these processes.
Copper anti-corrosion
Copper anti-corrosion is an extremely effective product that ensures the health and longevity of the system, given the use of copper in various industries.
Corrosion engineering (general factors affecting damage caused by corrosion)
The impact of various factors on corrosion damage are: 1_ Design, material selection and process 2_ Lack of necessary instructions 3_ Human error 4_ Poor inspection 5_ Poor layout, installation and coordination 6_ Failure to anticipate unwanted events 7_ Other cases
Corrosion engineering (damages and costs due to corrosion)
Investing in corrosion control is a form of profitability. Ignoring corrosion problems in any industrial and manufacturing unit leads to hidden costs that are impossible to avoid. The first step in corrosion economics is to choose an appropriate method to minimize corrosion costs. These costs can include: production and equipment costs, loss of valuable products, undesirable product appearance, environmental costs, and so on.
Corrosion management
Corrosion management is an action to organize corrosion activities and its control methods that has gained a special place in various industries in recent years. With the increasing development of corrosion prevention technologies, the selection of appropriate methods for corrosion control in a specific unit, the need to implement a comprehensive and well-written program called corrosion management, seems essential. Corrosion management is a set of methods and solutions that are applied in a system to prevent corrosion in order to optimize corrosion control methods economically.
What is corrosion?
The gradual reduction (decomposition) of metals due to chemical and electrochemical interactions is called corrosion, which causes significant financial losses to industries every year. For example, in water systems, various types of corrosion are defined as an electrochemical process.
Ways to prevent corrosion
Any process that delays corrosion is called corrosion inhibition (prevention of corrosion). In general, corrosion inhibition means reducing the rate of oxidation of a metal or adding a chemical compound that will be in contact with the solution in the system. The corrosion inhibitor may be added in liquid, vapor, or both. Specifically, a corrosion inhibitor is a chemical compound that is added to the liquid phase in such a way that it affects the metal surface.
Sedimentation and corrosion in refinery and petrochemical water systems
Just as living organisms cannot survive without water, oil refineries and petrochemical plants cannot function without water. Water is used in water cooling systems, to provide steam and fire extinguishing systems. Petroleum products and fuels produced after distillation and various catalytic and cracking processes must be cooled. Water is the best fluid for this.
Submit your opinion
Your email address will not be published.