Chemical decomposition
Decomposition ( or degradation, demotion ) means the decomposition of a chemical compound into smaller molecules or even to elements by physical, chemical or biological effects in chemistry and biology. Therefore, we distinguish the physical decomposition or thermal decomposition, chemical decomposition and biological decomposition or biodegradation.
Types of decomposition
Physical decomposition
The breakdown of a chemical substance is often done by supplying energy in the form of heat ( see pyrolysis). Therefore it is referred to as thermal degradation. Other energy supplies like electric current ( electrolysis, lightning, arc ), ultraviolet radiation (photolysis ) or X-rays cause the splitting of bonds within molecules. This often arise radicals, which then react further as unstable, high-energy particles. In the absence of oxidizing agents such as oxygen in the air, this decomposition can be carried out up to the elements from which the connection is established (eg, formation of coal deposits ) or under the chosen conditions thermodynamically stable compounds. In the synthesis of chemical decomposition of the starting materials under low pressure and high temperature is used for a desired end product as a "Flash vacuum pyrolysis " technique.
Chemical decomposition
Are at a decomposition oxidant present, arising from combustibles combustion, the most stable compounds with the oxidant, some even without power supply. The oxidizing agent is oxygen ( for example from the air), as the case of organic compounds (including sulfur oxides, nitrogen oxides or nitrogen may be as a gas ), water H 2 O and carbon dioxide CO 2 formed with inorganic substances usually oxides or other oxygen-containing compounds such as sulfates, phosphates or silicates.
Some compounds also decompose on heating with elimination of stable compounds such as carbon dioxide ( decarboxylation) or water (dehydration, such as the release of crystal water from hydrates ). If metals are attacked in the decomposition, this is called corrosion, especially when iron is called the resultant product of various iron oxides and water grate. In the decomposition of biologically important polymeric biomolecules such as proteins and polysaccharides by enzymes, dilute acids or bases is called hydrolysis ( decomposition by water). The degradation products of a substance can give information about the composition of the starting materials. The thermal degradation plays therefore in analytical chemistry an important role.
Biological decomposition
Organisms that decompose organic substances, collectively referred Saprobionten or decomposers. These are animals such as mites, lice, and microorganisms such as bacteria (eg, actinomycetes ) and fungi. This organic substances, mostly high polymer proteins or carbohydrates are first mechanically by these creatures, then chemically either the absence of air ( anaerobic) or presence of air ( aerobic) decomposed. The Saprobionten taking advantage of the organic compounds as energy source.
With total mineralization caused by decomposition of the polymers on enzymes from the class of hydrolases first monomers such as amino acids, and monosaccharides. These are then broken down completely to carbon dioxide, water, ammonium compounds and nitrates. For non- optimal conditions only occur still high molecular weight humic substances.
Biodegradation
The decomposition of organic matter by Saprobionten or their enzymes, which supplies waste the natural cycle is also commonly called biodegradation. The biodegradability of Industrially -made chemicals, including based on renewable raw materials such as in oleochemicals, and materials ( ex. plastics) is investigated with ( partial) testing methodology. In particular, for biodegradable plastics exist marking systems. Often the terms or biodegradability biodegradability are used.
Substances are referred to as a degradation -resistant, if they are not subject to biodegradation. If they are not degraded by other chemical or physical processes, they are called persistent.