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Tellurium
Tellurium is in the same element family as oxygen and sulfur, but has more properties that are metallic. As early as 1968, the United States was using 10 percent of its total output of tellurium in vulcanizing natural and synthetic rubbers. The addition of tellurium diethyldithiocarbamate increases rubber̵7;s resistance to abrasion and heat, improve the elastomer̵7;s aging properties and increases the rate of vulcanization.
Selenium
Selenium and sulfur are in the same group in the periodic table, the chalcogens. Like sulfur, selenium is a solid with some metallic properties. It offers enhanced heat and abrasion resistance to rubber when used in vulcanization, but it is expensive, has an unpleasant odor and is toxic.
Selenium diethyldithiocarbonate has a low melting point and is an ultra-fast accelerator if zinc oxide is included. Another fast accelerator for use in vulcanized rubber is selenium dimethyl dithiocarbonate.
Additives Used in Butyl Processing
The first use of butyl rubber was in tire inner tubes. Processing it requires the use of thiuram, quinonedioxime or phenolic resins in the vulcanization process.
Peroxide Vulcanization
Organic peroxide vulcanization for natural, ethylene-propylene and silicone rubber does not require any foreign substances such as accelerators or metallic oxides. The addition of benzoyl peroxide to the process leads to completion in a short time and at low temperatures.
Additives for Polychioroprene Vulcanization
Polychioroprene is rubber that contains a synthetic elastomer with good mechanical strength, high weather and ozone resistance, aging resistance and low flammability. This additive cannot vulcanize with sulphur, so thiourea or zinc oxide is used instead.