Thermal Behavior of Mixtures Based on Metakaolin and Sodium Hydroxide

• Published in: Glass and ceramics 2020-05, Vol.77 (1-2), p.9-14
• Main Authors: Gordina, N. E., Prokof’ev, V. Yu, Shamanaeva, N. V., Borisova, T. N., Konstantinova, E. M., Voinova, V. V.
• Format: Article
• Language: English
• Subjects: Activation energy; Aluminum; Aluminum compounds; Ceramics; Characterization and Evaluation of Materials; Chemistry and Materials Science; Composites; Diffraction; Glass; Granulation; Heat treatment; Hydroxides; Materials Science; Metakaolin; Mullite; Natural Materials; Nepheline; Reaction mechanisms; Silicates; Sodium aluminum silicates; Sodium hydroxide; Thermal analysis; Thermodynamic properties; Ultrasonic processing; X-rays; Zeolites
• ISSN: 0361-7610; 1573-8515
• DOI: 10.1007/s10717-020-00227-2

The behavior of the mixtures 6Al 2 Si 2 O 7 : 12NaOH and 6Al 2 Si 2 O 7 : 12NaOH : 2Al 2 O 3 during heat-treatment was studied by means of x-ray diffraction and simultaneous thermal analysis. It was shown that hydrated zeolite LTA forms after ultrasonic treatment and evaporation of a suspension, granulation of paste, and drying. It was determined that sodium aluminum silicate Na6Al 4 Si 4 O 17 is synthesized at temperatures up to 700°C. Sodium aluminum silicate Na 8 Al 4 Si 4 O 18 , mullite, and nepheline were found in the systems after heat-treatment at temperatures above 800°C. It is shown that the calculations performed by Friedman’s isoconversion method (differential) and the Kissinger–Akahir–Sunose (integral) method, for which the temperature interval 500 – 800°C is of interest, give close values of E . The growth of the apparent energy of activation with increasing degree of transformation attests a change in the reaction mechanism.