A series of small-angle neutron-scattering measurements was carried out to examine the nature of the changes in the density of water in a range of porous solids, namely Vycor, Ludox, and a montmorillonite clay, as a function of temperature through the freezing-defreezing transition. Comparison of the measurements for various types of porous solids show differences in the transition behavior, not only with regard to the temperature range, but also in the shape of the hysteresis loop. This behavior may result from differences in the geometry or connectivity of the pores, but the precise mechanism is not yet clear and further studies are in progress.

• Received 2 February 1993

DOI:https://doi.org/10.1103/PhysRevB.48.6716