CAUSE AND EFFECT CHEMICAL REACTION

CAUSE AND EFFECT OF CORROSION

 

Corrosion is the destruction or degradation of metals due to a redox reaction between a metal and various substances in the environment that produce undesirable compounds. In ordinary language, corrosion is called kararatan. The most common example of corrosion is iron fi gure.

In corrosion events, the metal undergoes oxidation, while oxygen (air) is reduced. The metal rust is generally oxide or carbonate. The chemical rust formula is Fe2O3.nH2O, a solid brown-red substance.

Corrosion is an electrochemical process. In iron corrosion, certain parts of the iron act as anodes, in which iron oxidizes.

Fe (s) <-> Fe2 + (aq) + 2e

The freed electrons in the anode flow to another part of the iron which is the cathode, where the oxygen is reduced.

O2 (g) + 4H + (aq) + 4e <-> 2H2O (l)

Or

O2 (g) + 2H2O (l) + 4e <-> 4OH- (aq)

The iron ions (II) formed on the anode subsequently oxidized to form iron (III) ions which then form hydrated oxide compounds, ie rust of iron. Regarding which part of the iron is the anode and which part is the cathode, depends on various factors, such as impurities, or the density of the metal.

Corrosion can also be interpreted as an attack that destroys metal because metal or electrochemical with the environment. There is another definition that says corrosion is in terms of metal extraction from its mineral ore. For example, iron ore minerals in the wild are present in the form of iron oxide or iron sulphide, after extracting and treating, an iron will be produced which is used for the manufacture of steel or alloy steel. During use, the steel will ignite with an environment that causes corrosion (back into iron oxide compounds).

Volta series and Nernst's law will help to know the possibility of corrosion. The speed of corrosion is highly dependent on many factors, such as the presence or absence of oxide layers, because the oxide layer can be potentially different to other electrodes that will be very different when it is clean from the oxide.

A. Cause of corrosion

Corrosion on the surface of a metal can be caused by several factors, including:

1.     Direct contact metal with H2O and O2

Corrosion on metal surfaces is a process that contains redox reactions. This reaction is a mini Volta cell. For example, iron corrosion occurs when there is oxygen (O2) and water (H2O). Iron metal is not pure, but contains a mixture of carbon that spreads unevenly in the metal. Consequently, there is a difference in electrical potential between metal atoms and carbon atoms (C). The iron metal atom (Fe) acts as anode and C atom as a cathode. The oxygen from the water-soluble air will be reduced, while the water itself serves as a medium where the redox reaction in the corrosion event occurs. The more the amount of O2 and H2O are in contact with the metal surface, the faster the corrosion occurs on the metal surface. Watch the animation. Following: iron corrosion animation.

2.    The existence of impurities

Impurities on metal surfaces may cause additional reduction reactions to cause more oxidized metal atoms. For example, the presence of carbon dust from the combustion of fuel on the metal surface can accelerate the oxygen gas reduction reaction on the metal surface. Corrosion events are thus accelerated.

3.    Contact with Electrolyte

The presence of electrolytes, such as salt in seawater can accelerate the rate of corrosion by increasing the occurrence of additional reactions. While large electrolyte concentrations can perform the rate of electron flow so that corrosion increases.

Shipwrecks on the seabed that have been corroded by a high salt content.

4.    Temperature

Temperature affects the speed of the redox reaction in corrosion events. In general, the higher the temperature the faster the corrosion occurs. This is due to the increase in temperature, so the kinetic energy of the particles increases, so the possibility of effective collision in the redox reaction is greater. Thus the rate of corrosion in the metal increases.

5.    Ph

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2H + (aq) + 2e- → H2

The presence of additional reduction reactions at the cathode causes more metal atoms to oxidize so that the corrosion rate on the metal surface is greater.

6.    Metallurgy

• Metal surface
Rougher metal surfaces will give rise to potential differences and have a tendency to become corroded anodes.
• Galvanic Coupling Effect
The low purity of the metal indicates the number of other elemental atoms present in the metal, thus triggering the Galvanic Coupling effect, ie, the potential difference in the metal surface due to the difference of E ° between different metal atomic atoms and present on the surface of the metal with low purity . This effect triggers corrosion on the metal surface by increasing the oxidation reaction in the anode region.
7. Microbes
The presence of microbial colonies on metal surfaces can lead to increased corrosion in metals. This is because the microbes are able to degrade the metal through redox reactions to obtain energy for its survival. Microbes that can cause corrosion, among others: protozoa, iron bacteria manganese oxide, sulfate reduction bacteria, and sulfur-sulphide oxidation bacteria.

B.  Effect of corrosion

Carcass (corrosion) is a term given to the corrosion-damaged metal. While the metal parts are damaged and brownish black on steel is called Rust. Theoretically, rust is a term given to only one type of metal that is steel, whereas in general the term rust is more accurately called corrosion. Corrosion is defined as material degradation (especially metals and alloys) or by interacting with the environment. Corrosion is an electrochemical process or reaction that is natural and takes place by itself, therefore corrosion can not be prevented or stopped completely. Corrosion can only be controlled or slowed down so that it slows down the process of destruction. Viewed from the electrochemical aspect, corrosion is the process of electron transfer from metal to its environment. The metal acts as a cell that delivers electrons (anodes) and its environment as an electron receiver (cathode). The reaction that occurs in corrosive metal is the oxidation reaction, in which metal atoms dissolve into their environment by releasing electrons in the metal. While the cathode from the reaction occurs, where the ions from the environment close to the metal and capture the electrons left on the metal. The corrosion-generated impact is remarkable.

In Indonesia, twenty years ago the costs incurred due to corrosion in the field of industry reached 5 trillion rupiah. This value gives us an idea how big the impact of corrosion and value is increasing every year because of the lack of proper corrosion control in the field of industry. Corrosion-induced impacts may include direct and indirect losses. Direct losses are in the form of damage to equipment, machinery or building structures. While the indirect losses are the cessation of production activities due to the replacement of equipment damaged by corrosion, the loss of the product resulting from damage to the container, fuel tank or piping network of clean water or crude oil, the accumulation of corrosion products on heat exchangers and piping networks will decrease Its heat transfer efficiency, and so on.