Nonmetallic and Composite Materials as Solid Superleaks

There are two types of superleaks, namely: the undesirable and the desirable. The former corresponds to, for instance, a crack in a Dewar containing He II and through which a super flow is established, ie, it leaks the so-called superfluid component of the He II. The latter is a device through which one needs, at given circumstances, a flow of superfluid He II. Summarising, the first is an accident and the second a device. This paper deals only with the devices, in general solid porous materials in which the so-called diameter of the pores, gaps, inter-crystalline spaces, or small channels, etc, are equal or smaller than 100 A. Of course, the type of slits and capillaries used by Kapitza1 and by Allen and Misener2 when they discovered the superfluidity are also superleaks. However, the small channels they considered differed by approximately two orders of magnitude to those considered in this paper.