Tellurium

Tellurium is a semiconductor and is frequently doped with copper, tin, gold or silver. Tellurium is also used to colour glass and ceramics and is one of the primary ingredients in blasting caps. Tellurium is primarily used as an alloying agent. Small amounts of tellurium are added to copper and stainless steel to make them easier to machine and mill. Tellurium is also added to lead to increase its strength and resistance to sulfuric acid (H2SO4). Tellurium is considered a technology-critical element.