accelerator

/ak sel"euh ray'teuhr/, n.

1. a person or thing that accelerates.

2. Auto. a device, usually operated by the foot, for controlling the speed of an engine.

3. Brit. any two- or three-wheeled motor vehicle, as a motorcycle or motor scooter.

4. Photog. a chemical, usually an alkali, added to a developer to increase the rate of development.

5. Also called accelerant. Chem. any substance that increases the speed of a chemical change, as one that increases the rate of vulcanization of rubber or that hastens the setting of concrete, mortar, plaster, or the like.

6. Anat., Physiol. any muscle, nerve, or activating substance that quickens a movement.

7. Also called atom smasher, particle accelerator. Physics. an electrostatic or electromagnetic device, as a cyclotron, that produces high-energy particles and focuses them on a target.

8. Econ. See acceleration coefficient.

[1605-15; 1930-35 for def. 7; ACCELERATE + -OR²]

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▪ rubber manufacturing

      in the rubber industry, any of numerous chemical substances that cause vulcanization (q.v.) of rubber to occur more rapidly or at lower temperatures. Many classes of compounds act as accelerators, the most important being organic materials containing sulfur and nitrogen, especially derivatives of benzothiazole.

      The use of alkaline compounds of metals as vulcanization accelerators was cited in the original patent of the vulcanization process, granted to Charles Goodyear in 1844; magnesium oxide, zinc oxide, and basic lead carbonate were used until early in the 20th century, when the superiority of aniline, an organic compound, was discovered. Despite its toxicity, aniline was used as an accelerator for several years. Thiocarbanilide, less poisonous than aniline, succeeded it as the most important accelerator until it was displaced by mercaptobenzothiazole (MBT) about 1925. Compounds related to MBT have proved especially useful in vulcanizing synthetic rubbers.

      During vulcanization the accelerator apparently converts the sulfur into a compound that reacts more rapidly with rubber than does sulfur itself. An alternative possibility is that the accelerator reacts first with the rubber, changing it into a form that combines rapidly with sulfur.

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