boiling chip
tiny uneven-shaped particles added to liquids to avoid superheating by providing nucleation sites; often made of porous material (e.g. alumina, silicon carbide, calcium carbonate, calcium sulfate, porcelain or carbon) with nonreactive PTFE coating
en-US/ˈbɔɪliŋ ˈt͡ʃɪp/
en-GB/ˈbɔɪlɪŋ ˈt͡ʃɪp/