A platinum wire can easily be sealed to a glass bulb while a copper wire wire cannot. Why?

Explanation

A copper wire cannot be sealed to glass as their coefficients of thermal expansion are different. After being sealed at a high temperature, and then being cooled, glass cracks or a gap develops between the wire and the glass because of unequal contraction. Glass and platinum, having almost the same coefficients of expansion, contract or expand equally on cooling or heating, keeping the seal intact.