Pressure-induced hydration (PIH), also known as “super-hydration”, is a special case of pressure-induced insertion whereby water molecules are injected into the pores of microporous materials.
In PIH, a microporous material is placed under pressure in the presence of water in the pressure-transmitting fluid of a diamond anvil cell.
[1][2] Early physical characterization[3] and initial diffraction experiments[4] in zeolites were followed by the first unequivocal structural characterization of PIH in the small-pore zeolite natrolite (Na16Al16Si24O80·16H2O), which in its fully super-hydrated form, Na16Al16Si24O80·32H2O, doubles[5] the amount of water it contains in its pores.
PIH has now been demonstrated in natrolites containing Li, K, Rb and Ag as monovalent cations[6][7] as well as in large-pore zeolites,[8] pyrochlores,[9] clays[10] and graphite oxide.
[11] Using the noble gases Ar, Kr, and Xe as well as CO2 as pressure-transmitting fluids, researchers have prepared and structurally characterized the products of reversible, pressure-induced insertion of Ar[12] Kr,[13] and CO2[14] as well as the irreversible insertion of Xe[13] and water.