Figure 1.

SEM images of a “clean” filter, in which it can be seen that it is made up of quartz fibers of different diameters. (a) Micrograph of the filter surface, in which the existence of points of contact between the quartz fibers can be appreciated; (b) micrograph of the transversal cross section of the filter in which voids can be observed surrounded by groups of quartz fibers, as well as several circumferences of variable radii between the fibers.