Investigation of a synthetic aluminosilicate inorganic polymer

Abstract

A melt-quenched of mixture of alumina and silica (46 wt% Al2O3 or Al2O3(SiO2)2) was found to react with an alkaline silicate solution (Na2O)(SiO2)1.2(H2O)9.5) at low-temperatures to form a synthetic aluminosilicate inorganic polymer. The as-quenched material consisted of a mixture of amorphous and crystalline phases with a range of aluminium coordination environments. Upon reaction with the alkaline silicate solution, solid-state aluminium and silicon magic-angle spinning nuclear magnetic resonance (SS 27Al and 29Si MAS NMR) indicated that a conversion to four-fold aluminium coordination environments occurred, consistent with the formation of a three-dimensional cross-linked inorganic polymer comprised of NaAlO4 and SiO4 tetrahedra. Mechanical testing showed the compressive strength of the inorganic polymer increased as the Na2O/Al2O3 molar ratio decreased. Solution studies indicated that 73% of the aluminosilicate starting material was reactive. Scanning electron microscopy (SEM) showed the inorganic polymers had a porous nanoscale grain structure. Open porosity was confirmed by relatively high specific surface area values. Energy dispersive spectroscopy (EDS) and elemental x-ray composition mapping showed that the high-strength specimens had a composite microstructure consisting of 40% unreacted Al2O3(SiO2)2 and an inorganic polymer binder Na2O Al2O3(SiO2)3.4. The high compressive strengths have been rationalized by this in-situ particle reinforced composite structure, consisting of ~10 µm agglomerates of unreacted starting material bonded within a sub-micron aluminosilicate/inorganic polymer matrix.

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