单语范例（未经PONS编辑处理）
Because of the chemical similarity, up to 5% of the zirconium in zircon is replaced by hafnium.
en.wikipedia.org Due to the lanthanide contraction of the elements in the sixth period, zirconium and hafnium have nearly identical ionic radii.
en.wikipedia.org After zirconium was chosen as material for nuclear reactor programs in the 1940s, a separation method had to be developed.
en.wikipedia.org Furthermore, reports of zirconium-related adverse reactions are rare and, and in general, rigorous cause-and-effect relationships have not been established.
en.wikipedia.org It is mostly composed of iron, oxygen, silicon, zirconium and titanium with smaller fractions of yttrium and calcium.
en.wikipedia.org