cured and the most important accelerator has been found to be ethylene thiourea (ETU) which, although being an excellent and proven accelerator for polychloroprene, has been classified as reprotoxic. The European rubber industry has started a research project SafeRubber to develop a safer alternative to the use of ETU. Secondary Of the secondary or ultra-accelerators the main categories are the thiurams and the dithiocarbamates. In vulcanization of tire compounds they are used as small addition to sulfenamides to boost the speed and state of cure. They have a very fast vulcanization speed and therefore, next to boosters in tire compounds they are used as main accelerator in EPDM compounds and in latex compounds. EPDM compounds have much less cure sites than natural rubber or SBR, and therefore need a rapid vulcanization system to have sufficient cure speed. Latex is cured at relatively low temperature (100- 120 °C)and therefore need an inherently rapid accelerator. The major thiurams used are TMTD (tetramethylthiuram disulfide) and TETD(tetraethylthiuram disulfide), They are produced by the reaction between dimethylamine or diethylamine and carbon disulfide. The major dithiocarbamates are the zinc salts ZDEC (zinc diethyldithiocarbamate) and ZDBC (zinc dibutyldithiocarbamate). Cement and concrete accelerants Cement accelerators are available as admixtures for the use in concrete, mortar, rendering and screeds. The addition of an accelerator speeds the setting time and thus cure time starts earlier. This allows concrete to be placed in winter with reduced risk of frost damage. Concrete is damaged if it does not reach a strength of before freezing. Typical chemicals used for acceleration today are calcium nitrate (Ca(NO3)2), calcium formate (Ca(HCOO)2) and sodium nitrate (NaNO3). See also Catalyst Chemical kinetics Chemical reaction Rate law References Works cited General references Natural Rubber Science and Technology, editor: A.D. Roberts, Oxford University Press, Oxford 1988 A Pocket Guide to Accelerant Evidence Collection, 2nd edition, (1999) palimpsest.stanford.edu Firefighting Rubber