| Popis: |
Procedures for making minerals include hydrothermal growth, pyrolysis, vapour phase deposition and pneumatolysis. In synthesis of porous crystals the hydrothermal method is standard, although the pyrolytic procedure yields water-swelling layered fluorsilicates and microporous felspathoid and zeolite frameworks in which salts replace zeolitic water. Pneumatolysis can also be important, not for synthesis but for zeolite modification, as in preparing USY from zeolite Y. Some physicochemical aspects of, and recent trends in, hydrothermal synthesis are considered. The many types of crystal which are, or can be made, permanently porous include 3-dimensional 4-, 6, 4- and 6-connected nets as host frameworks and, inter alia, layer structures such as clay minerals, hydrotalcites and certain phosphates, titanates and phosphonates. Even some organic crystals can display permanent microporosity. Molecule sieving and lock-and-key sorption are exemplified for several less familiar microporous crystals. |
