Accelerant
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Accelerants, or accelerators, are substances that increase the rate of a natural or artificial chemical process. They play a major role in chemistry, as most chemical reactions can be hastened with an accelerant. Understanding accelerants is crucial in forensic science, engineering, and other fields where controlled chemical reactions are essential. Accelerants function by either altering a chemical bond, speeding up a chemical process, or changing the reaction conditions. Unlike catalysts, accelerants may be consumed during the process.
They are commonly used in contexts such as fire investigation where they can indicate arson, in construction to speed the curing of building materials, and in sulfur vulcanization to produce rubber products such as tyres. In fire investigation, accelerants are often detected through laboratory analysis of fire debris. Various types of accelerants exist, including liquids, solids, and gases, each with specific properties and applications.
Applications
[edit]Vulcanization
[edit]Vulcanization of rubber can be categorized primarily into two types: sulfur and peroxide vulcanization. Both chemical processes are examples of using an accelerant.
Sulfur vulcanization, the more traditional method, uses sulfur to create cross-links between rubber polymer chains, enhancing flexibility and durability. Sulfur vulcanization is a chemical process crucial to the rubber industry, transforming raw rubber into a durable, elastic material. This process is suitable for a wide range of rubber products.
On the other hand, peroxide vulcanization uses organic peroxides to form cross-links, resulting in rubber that withstands higher temperatures and chemical exposure better than sulfur-vulcanized rubber. Each method offers distinct properties to the rubber, tailored to specific applications and performance requirements.
Cement and concrete
[edit]Cement accelerators are available as admixtures for use in concrete, mortar, render, and screed. The addition of an accelerator speeds the setting time and thus curing starts earlier.[1] This allows concrete to be placed in winter with reduced risk of frost damage.[2] Concrete is damaged if it does not reach a strength of 500 pounds per square inch (3.4 MPa) before freezing.[3] Typical cement accelerators are calcium nitrate (Ca(NO
3)
2), calcium formate (Ca(HCOO)
2), and sodium nitrate (NaNO
3).[4]
Fire
[edit]In fire protection, the term accelerant is used differently from its use in chemistry, to refer to any material that initiates and promotes the development of fire, including in cases of arson, whether a chemical or not. Chemists distinguish an accelerant from a fuel, such as gasoline.
A fire is a self-sustaining, exothermic oxidation reaction that emits heat and light. When accelerants such as oxygen-bearing liquids and gases (like NO
2) are used, fires produce more heat, consume fuel more quickly, and spread quicker. Fires involving liquid accelerants like gasoline burn quicker, but at the same temperature as fires involving ordinary fuels.
See also
[edit]References
[edit]- ^ Justnes, H. (2000): Accelerator Blends for Portland Cement. Proceedings of Cement and Concrete Technology in the 2000s, September 6–10, 2000, Istanbul, Turkey, Vol. 1, pp. 433–442
- ^ ACI 306R-88: Cold Weather Concreting. "Cold Weather Concreting" (PDF). Concrete Contractors Association of Greater Chicago. Archived from the original (PDF) on 2011-07-25. Retrieved 2011-03-05.
- ^ Korhonen, Cortez & Durning 1997, p. 19.
- ^ Korhonen, Charles J.; Cortez, Edel R.; Durning, Timothy A. (1997). "Antifreeze Admixtures for Concrete". Cold Regions Research and Engineering Laboratory. Special Report 97-26. ISBN 9781428913158.
