Nov., 1956
REACTIONS BETWEEN CALCIUM HYDROXIDE AND AMORPHOUS SILICA
1559
HYDROTHERMAL REACTIONS BETWEEN CALCIUM HYDROXIDE AND AMORPHOUS SILICA IN ATMOSPHERES OF UNSATURATED STEAM BY GUNNAR 0. ASSARSSON Chemical Laboratory of Geological Survey of Sweden, Stockholm 60, Sweden Received June $8, I966
The study of the hydrothermal reaction between calcium hydroxide and amorphous silica was extended by investigations of the hydrothermal reactions under lowered va or pressure, Le., from saturation down to 1atmosphere within the temperature range 160-200" for periods of time up to 48 ir., in order to determine the conditions for a possible transformation boundary of the low temperature phase. It was established that there must be a transformation pressure boundary a t about 60% of the vapor saturation; at a pressure higher than the boundary pressure a transformation of the low temperature phase into high temperature phases takes place, a t lower pressure the low temperature phase remains unchanged even in the presence of an excess of uncombined calcium hydroxide. The high temperature phases are those shown in the earlier investigation. The pressure boundary is independent of the temperature within the range studied. The lowered pressure causes a decrease of the hydrate water of the low temperature compound. The X-ray photographs of the new-formed dehydrated compounds show only those diffraction lines which are characteristic for the low temperature phase indicating that the new, very minute elements are retained in their earlier arrangement, or/and that the repeating atterns of the elements have such a minute size that the composite crystals give a resulting pattern similar in character to t f a t of the low temperature phase.
In an earlier paper the present author and collaborators have given their results of the investigations on the hydrothermal reaction between calcium hydroxide and amorphous silica, in an atmosphere of saturated steam and within the temperature range 120-220O.1 The investigation has now been extended to include an examination of the influence on the react
