The sol-gel synthesis of calcium aluminate using various polymerizing agents

Rhombic calcium aluminate composition CaAhO4 was obtained by a sol-gel method using various organic acids as polymerizing agents. Using acids containing an ОН' group allows obtaining products with a high degree of homogenization. Based on the thermal data, X-ray diffraction, and infrared spectroscopy, a conclusion was made about the multistep process offorming the structure of rhombic calcium aluminate. The polymerization agent affects the temperature of formation of the desired product and the mechanism offormation of rhombic calcium aluminate. Thus, the lactic acid containing the two functional groups did not form a chelate complex with calcium, because the calcium aluminate was formed via the formation of calcium oxide. This led to obtaining a cubic structure. When using malic acid as a polymerizing agent, the desired product was formed at 860°C. Calcium aluminate with tartaric acid is obtained at 910°C and citric acid at 900°C. All samples obtained at temperatures above 800°C contained an admixture of cubic calcium aluminate CaAhOe, the proportion of which decreased with increasing temperature and almost disappeared in the range 1100-1200°C. We found that the least amount of impurities contains a sample for the synthesis by a polymerizing agent using tartaric acid. All final products of the synthesis are presented by orthorhombic modification of calcium aluminate with unit cell parameters: the sample that was used in the synthesis of tartaric acid, a = 0.866 nm, b = 0.807 nm, c = 1.516 nm; citric acid, a = 8.72 A, b = 8.07 A, c = 15.23 A; and malic acid, a = 8.72 A, b = 8.04 A, c = 15.02 A.

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