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Alkaline earth metal aluminates activated by rare-earth ions (REn+) possess intensive luminescence upon UV excitation. The paper studies phase formation of calcium aluminate prepared by the sol-gel method. The stages of the end products’ formation using methods of the thermal and the infrared spectrometric analysis and X-ray diffraction are proposed. Dependence of phase composition, the surface morphology and luminescence properties on the annealing temperature of the precursor is investigated.

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Method for synthesis of calcium aluminate and sorbents based on this compound was developed on its basis of the sol-gel technology. The method makes it possible to obtain the target product with specifi c surface areas in the range from 7 to 120 m 2 g -1 . The compounds obtained were characterized by scanning electron microscopy, X-ray phase analysis, and X-ray fl uorescence microanalysis. It was found that the main phase of the sorbents is rhombohedral calcium monoaluminate CaAl 2 O 4 . The method of Hammett indicator adsorption was used to determine the content of active centers on the surface of the sorbents and the distribution of these centers over ionization constants. It was shown that the surface characteristics of the sorbents depend on their synthesis method. The retention parameters, polarities, and thermodynamic characteristics were determined for organic compounds of various classes. The possibility of using calcium aluminate modifi ed with sodium chloride for gas-chromatographic separation of aliphatic and aromatic hydrocarbons and carbonyl compounds was demonstrated.The synthesis of calcium aluminate-based materials with prescribed structure and surface morphology attracts researchers' attention owing to the high thermal stability, mechanical strength, resistance to solvents of varied nature, and hydrolytic stability of these materials [1][2][3][4][5]. The sol-gel technique is one of promising ways to obtain oxide materials with certain size and shape of particles, with this method capable of varying the specifi c surface area and porosity of the substances being synthesized [6][7][8]. The possibility of forming porous substances with certain surface characteristics enables development of new promising functional materials with various properties and, in particular, sorbents for gas chromatography and supports modifi ed with inorganic substances.The goal of our study was to examine the structural and acid-base characteristics of the surface of calcium aluminate synthesized by the sol-gel method and the possibility of its application as a sorbent for gaschromatographic separation. EXPERIMENTALBased on an analysis of the experimental and published data [9, 10], we synthesized calcium aluminate of composition CaAl 2 O 4 by the sol-gel method with aluminum (Al 3+ ) nitrate nonahydrate, calcium (Ca 2+ ) nitrate tetrahydrate, and citric acid (H 4 Cit) monohydrate as starting substances. The amount of the reagents was calculated on the basis of the stoichiometric ratio Ca 2+ : Al 3+ : H 4 Cit = 1 : 2 : 3; all the components were of chemically pure grade. The starting substances were dissolved in the minimum amount of twice-distilled water and the solution was agitated for 1.5 for the complexation reaction to be complete. The resulting solution was heated until a gel was formed, and the gel was thermally treated at 130°C (SNOL 58/350 drying box) to remove the liquid phase and to form a xerogel. The fi nal stage of this synthesis consisted in calcination of the resulting precursor in an SNOL 6/1300 muffl e ...

The paper studies phase formation of calcium aluminate prepared by the sol-gel method. The stages of the end products’ formation were proposed using methods of gas chromatography, the thermal and the infrared spectrometric analysis. Dependence of phase composition and the crystalline structure on the annealing temperature of the precursor was revealed.