  We investigate the minimal size of small superconducting grains by means of a
Ginzburg-Landau model confined to a sphere of radius $R$. This model is
supposed to describe a material in the form of a ball, whose transition
temperature when presented in bulk form, $T_{0}$, is known. We obtain an
equation for the critical temperature as a function of $R$ and of $T_{0}$,
allowing us to arrive at the minimal radius of the sphere below which no
superconducting transition exists.
