engleski

The influences of the way of preparation of Me-aluminosilicates (Me = Li, Na, K, Rb and Cs) on the products

X-ray amorphous Me-aluminosilicates (gels ; Me = Li, K, Na, Rb and Cs) were prepared in two ways: (A) By exchange of original (sodium) ions from Na-aluminosilicate with other alkaline cations (Li, K, Rb and Cs) and (B) by direct precipitation from the corresponding Me-aluminate and Me-silicate solutions. The Me-aluminosilicates prepared by both the mentioned methods as well as the products of their solid-state, high-temperature transformations were analyzed/characterized by different methods such as X-ray diffraction (XRD), X-ray dispersive analysis (EDAX), differential thermal analysis (DTA), differential scanning calorimetry (DSC) and nitrogen absorption (BET). Chemical analysis of the gels have shown that the exchange of original sodium ions from the gel prepared by procedure (A) [Na-gel(A)] does not considerably change the chemical composition, structural (XRD and DTG profiles), and physical properties (specific surface area). On the other hand, the type of cation Me+ considerably influences the aluminosilicate composition of the gels prepared by procedure B [Me-gels (B)], and thus their “ framework structure” as revealed by XRD analysis. Thermal treatment of all, the gels (isothermal heating at 925 – 1250o C for 3 h) resulted in their transformation into appropriate crystalline aluminosilicate phases having chemical composition MeAlSiO4 or MeAlSi2O6, respectively. All the transformations are accompanied with drastic decrease in the BET specific surface area caused by transition of (micro/meso)-porous amorphous Me-aluminosilicates into more dense, non-porous crystalline phases.

Amorphous aluminosilicates ; Thermal transformations ; Ceramics

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