Different Forms of Corrosion Classified on the Basis of Appearance 1) electrochemical corrosion is the only deterioration mechanism; 2) anodic and cathodic reactions take place all over the electrode surface, but not simultaneously at the same place, i.e. the anodic and cathodic reactions exchange places, constantly or frequently. Closely related to this dynamic behaviour it is assumed that: 3) there are no significant macroscopic concentration differences in the electrolyte along the metal surface, and the metal is fairly homogeneous. These three assumptions lead to uniform (general) corrosion. But this is only one of several corrosion forms that occur under different conditions. The other forms of corrosion depend on the deviations from the mentioned assumptions. Such deviations may be due to

The majority of metals are found in nature in the mineral state, that is, in their stable oxidised condition as oxides, chlorides, carbonates, sulphates, sulphides, etc. The extraction of a metal from the mineral involves a reduction process, which requires a great deal of energy. As a consequence of this large energy input the metal is in a high-energy condition and will endeavour to return to its former stable oxidised low Energy State, as quickly as environmental conditions will allow. It is this energy difference between the pure metal and its oxidised forms which is the driving force for corrosion of the metal. Many corrosion products show a chemical similarity to the corresponding minerals. Iron, for example, is extracted from its ores, mainly oxide and carbonate, by reduction with carbon in a blast furnace. In the presence of moisture and oxygen, the iron metal so obtained is oxidised to rust, which is chemically the same as its ore.

Corrosion [Working Title], 2021

This chapter describes the fundamentals of metal corrosion in relation to thermodynamics and kinetics. The chapter is so titled, because corrosion of metal is thermodynamically favourable. Moreover, it impacts negatively on economy and safety. Industries expend a substantial percentage of their budgets on corrosion control, and lose revenue due to corrosion damage. Effects of corrosion on industrial and public infrastructure cannot be overemphasized. Several accidents in the transportation and recreational industries have been linked to corrosion of metallic parts of respective gadgets. Some of these accidents are utterly catastrophic and fatal. Therefore, corrosion, albeit its thermodynamic favouability, is not desired by man. Metals corrode as a way of minimizing energy contents. Active metals are more stable in combined forms such as oxides, sulphides, and hydroxides, even though these forms are less useful to man. It appears the “price” to pay for extracting the pure forms of th...

Zastita materijala, 2016

In this paper, phenomena of chemical corrosion of metals and alloys in electrolyte solutions are analyzed. It is shown that iron, chromium and other metals and alloys dissolve much faster than is the corrosion rate determined by electrochemical methods. This means that the chemical dissolution takes place simultaneously with the electrochemical dissolution. The chemical dissolution does not depend on electrode potential. Under some conditions, chemical dissolution of metals is the dominant process of dissolution. Several mechanisms of chemical corrosion are described. Also, the consequences of chemical dissolution of various metals and alloys are discussed, as well as the hydrogen evolution during the chemical dissolution. The process of hydrogen evolution during the chemical corrosion is not subjected to the laws of electrochemical kinetics.

1. Uniform (general) corrosion 2. Galvanic (two–metal) corrosion 3. Thermogalvanic corrosion 4. Crevice corrosion (including deposit corrosion) 5. Pitting, pitting corrosion 6. Selective attack, selective leaching (de–alloying) 7. Intergranular corrosion (including exfoliation) 8. Erosion corrosion 9. Cavitation corrosion 10. Fretting corrosion 11. Stress corrosion cracking 12. Corrosion fatigue

References and Definitions Why Metals Corrode Nature of Corrosion Reaction Nature of Metals Effect of Electrolyte Composition Physical Variables Forms of Corrosion

InTech eBooks, 2012

Corrosion of metals or alloys occurs due to chemical or electrochemical reactions with their environment, which often results in drastic deterioration in the properties of metals or materials comprising thereof. Corrosion takes place on a steel surface, due to the development of anodic and cathodic areas, through oxidation and reduction reactions, forming of oxides of metals alloys. There are several corrosion causing agents or "corrodents" such as soot, sulphate salts, chloride ions, temperature, salinity, pH, dissolved gases, humidity, bacteria, sand, gravels, stones, mechanical stresses and also several protection methods employed for corrosion resistance such as the application of alloys, composites, inhibitors, cathodic and anodic protection, protective linings and coatings (

Corrosion may be defined as the destruction or deterioration in properties of materials by interaction with their environments. It is a natural phenomenon. Engineers generally consider corrosion when dealing with metallic materials. However, the process affects all sorts of materials, for example, ceramics, plastics, rubber etc. Rusting of iron and steel is the most common example of corrosion. Swelling in plastics, hardening of rubber, deterioration of paint, and fluxing of the ceramic lining of a furnace are all incidences of corrosion in non metallic materials. Metallurgists may think of corrosion as reverse extractive metallurgy. Metals are extracted from their compounds occurring in nature through extractive metallurgy processes involving considerable expenditure of energy, natural resources, time, and man power. Corrosion works to convert the metal I back into the same compounds.