Corrosion

Corrosion (from Latin corrodere, " decompose, corrode, gnaw " ) is technically the reaction of a material with its environment, which causes a detectable change in the material and can lead to impairment of the function of a component or system. Chemical corrosion occurs on metals (DIN EN ISO 8044, DIN 50900 formerly ). The best-known type of corrosion is the rusting, ie the oxidation of iron.

In geology is meant by the decomposition of rock corrosion by the action of water. Such weathering processes play a role in buildings. Yet another is the meaning in medicine (decomposition of tissue).

Chemistry

In the chemical corrosion refers to the chemical reaction or an electrochemical reaction of a usually metallic material with material from its surrounding in a corrosion element, and a measurable change in the material occurs, usually a change in color and often negatively affect the other surface properties. In certain cases there is an increase in mass on the metal.

Main types of corrosion are:

• Tarnishing of silver to form silver sulfide
• Bacterial anaerobic corrosion
• Glass corrosion
• Patina on copper
• Rust on iron or general oxygen corrosion
• Hydrogen corrosion ( acid corrosion)
• Hydrogen embrittlement

Technology

Definition

The DIN EN ISO 8044 defines corrosion as follows:

"Corrosion, the reaction of a metallic material with its environment, which causes a measurable change of the material and may lead to an impairment of the function of a metal component or of a whole system. In most cases, is the reaction of an electrochemical nature, in some cases it may be of chemical or physical nature of the metal. "

Types of corrosion

The standard also defines 37 different types of corrosion.

In addition to the art material- based corrosion other types of corrosion can be distinguished on the basis of the place of occurrence:

• Contact corrosion
• Pitting corrosion
• Trough corrosion
• Surface corrosion
• Stress corrosion cracking
• Corrosion fatigue
• Crevice corrosion
• Intergranular corrosion
• Knife line corrosion
• Erosion corrosion
• Infiltration corrosion

Other types of corrosion:

• High Temperature Corrosion

Corrosion protection

It is important therefore a corrosion protection.

• Sacrificial anode
• Impressed current anode
• Hot-dip galvanizing
• Zinc flake coating
• Polarization
• Low power
• Inhibitors
• Reduction of the oxygen content
• Promotion of the passive layer formation
• Homogenization of the microstructure
• Optimization of the surface

• Hot-dip galvanizing
• Protective coating or protective coating with appropriate pretreatment or using adhesion promoters
• Other organic transport protection: fats, waxes, fluorinated polyurethane ( FPU)
• Inorganic non-metallic protection: passivation oxides
• Inorganic metallic protection: hematite ( iron mica), zinc, aluminum
• Constructive measures: continuous welding etc.
• Do not obstruct the dissimilar metals in direct contact, for example, no chrome or aluminum trim directly on steel; Mount license plates with plastic liner
• Provide in exposed areas water flows (eg in car doors )
• Hohlraumversiegelung
• Relay with protective gas filling, reed relays
• Electrolytic plating, such as in dental technology
• Air filtration and positive pressure ventilation of enclosures and cabinets, for example, by chemosorptive filter for the elimination of corrosive gases such as H2S

Note: Hot dip galvanized coatings produced both a passive and an active corrosion protection.

Buildings: Corrosion of rock

In geology " corrosion" the decomposition of rocks by the action of water. Even in buildings such corrosion occurs, there usually called weathering or stone feeding. As the word implies, but the weather plays a big role. Design measures which can be reduced, eg by

• Heavy duty material
• Drip edges
• Overhanging eaves to protect the facades
• Care
• Avoid fouling
• Prevention of flooding, groundwater
• Trees do not have sewers

Medicine: Corrosion of tissue

In medicine, the term ' corrosion " the destruction of tissues, which is caused by inflammation or corrosive agents.

On the other hand, the metallic corrosion in implantology and dentistry plays a role. The versatile clinical presentation is called metallosis and is usually asymptomatic in the early stages.