Calculation and Experimental Studies of Systems of Dibasic Carboxylic Acids and Properties of Eutectics

The liquidus lines of binary systems of dibasic carboxylic acids HOOC-(CH2)(n)-COOH (n = 3, 4, 7, 8) and eutectic coordinates were calculated by the Schroder-Le Chatelier equation. The experimental studies were performed by differential thermal analysis on a DSC heat flux microcalorimeter. Five or six mixtures with different contents of components were studied in each system. The phase diagrams were constructed based on the set of DSC data. The experimental melting temperatures and the composition of binary eutectics were compared with the calculated values. All the systems were of the eutectic type. A theoretical analysis of the solubility of the acids was performed, and the equations of solubility of acids in water were obtained. The eutectic composition of the pentanedioic-hexanedioic acids system was chosen based on the analysis of the solubility data; it can be used to obtain anodic coatings on aluminum. For the eutectics of the system, the solubility in water was experimentally studied at temperatures from 20 to 60 degrees C. The composition of electrolyte for aluminum anodization was developed: eutectic mixture of pentadioic and hexanedioic acids, ethanedioic acid, and water. The temperature and time of aluminum anodization were recommended.