Rubidium is used in vacuum tubes as a getter, a material that combines with and removes trace gases from vacuum tubes.
ɹuːbˈɪdiəm ɪz jˈuːzd ɪn vˈækjuːm tˈuːbz æz ɐ ɡˈɛɾɚ, ɐ mətˈɪɹiəl ðæt kəmbˈaɪnz wɪð ænd ɹᵻmˈuːvz tɹˈeɪs ɡˈæsᵻz fɹʌm vˈækjuːm tˈuːbz.