Hydrothermal chemistry of silicates. Part XVI. Replacement of aluminium by boron during zeolite growth
Abstract
The possibility of isomorphous replacement of Al by B during crystallisation of some zeolites has been investigated in the system Na2O–Al2O3–B2O3–SiO2–H2O. Of the zeolites grown the compact analcite structure is essentially free of boron even when the borate concentration is very high. Zeolite A and the gismondite-type zeolite Na-P1 crystallise with significant amounts of boron, which however can readily be washed out again leaving the compounds with only minimal boron content. The faujasite-type zeolite X retains a significant amount of boron after thorough washing, while in sodalite hydrate this boron content is substantial. Various properties have been examined and it is probable that in zeolite X and sodalite hydrate boron is nearly all present as borate in the tetra-decahedra1 sodalite cages which occur in each. Thus substitution of Al by B in the above zeolite frameworks is considered to be insignificant during synthesis in alkaline aqueous media.