Freezing experiments on clay gels

A three-component system consisting of butylammonium vermiculite, butylammo nium chloride, and water was studied by X-ray and neutron diffraction exper iments in freezing cycles between -5 and +5 degrees C. In liquid water, all the samples studied were in a colloidally swollen gel phase, with interlay er separations between the clay platelets of the order of hundreds of angst roms. Upon freezing gf the water, the colloidal state collapsed into a tact oid phase with an interlayer separation of d = 19.4 Angstrom. This phenomen on was observed throughout a wide range of clay concentrations r and salt c oncentrations c. The phase transition was observed to be reversible, the ge l phase always being recovered upon warming through the freezing point of w ater. Such a reversible phase transition between swollen and collapsed clay mineral phases may be important in the weathering of rocks in freezing cyc les.