Assertion: hafnium's compound | /r/ObjectUse | used by chemist
Facets:
value: for over two centuries
type: TEMPORAL
Source sentences:
text: The chemical similarity between zirconium and hafnium made a separation difficult and, without knowing what to look for, hafnium was left undiscovered, although all samples of zirconium, and all of its compounds, used by chemists for over two centuries contained significant amounts of hafnium.