Optically clear, homogeneous aluminosilicate gel can be prepared by sol-gel method in wide range of Al-Si compositions, with bonded Al-containing of 0-70%. Only 10 % Al-content can be achieved by traditional melting process in the silicate glasses. The precursors are Al nitrate and TEOS, the solvent is n-propanol. The synthesis is carried out at 80 °C without of time-consuming sol formation. The SANS and SAXS measurements verify the fractal structure of aluminosilicate gels.
► Very hard solid sample can be produced with molar ratio of Al / Si = 2 – 4 from Al acetate and water glass The hardness of monolith samples with molar ratio of Al / Si = 2 – 4 is multiple harder than other aluminosilicate monolith prepared from other molar ratios and from other precursors. This hardness is remained after drying at 100 °C, however, the samples with smaller density and larger porosity are obtained.
► The extra mechanical strength can be attributed to a nanocomposite system, formation of a Al-containing nanocrytalline reinforcing phase. The aluminosilicate nanocomposites are composed of an amorphous aluminosilicate network and Al-containing nanocrystallites.
► Development of sol-gel technique is motivated by decrease of the energy demand of melting process; the synthesis of ceramics with special chemical composition, which cannot be produced by melting; formation of porous structure required by the bioactivity; modest introduction of carbonate anions, which can be found in the natural bonds.
► Calcium silicate samples prepared in the presence of ammonia proved to be the most suitable material as bioceramics. The use of ammonia supports the development of Q2 (SiO)2Si(O−)2 or (SiO)2Si(OH)2 units. The calcium ions connect easily to Q2 units. The number of calcium ions, which are bonded in the silicate network, increases parallel with the number of Q2 units. More compact aggregate structure forms in basic medium.
Iron phosphate glass
Fe2O3-Al2O3-SiO2
Iron(III) silicate