Thermal Behavior of Mixtures Based on Metakaolin and Sodium Hydroxide

The behavior of the mixtures 6Al2Si2O7: 12NaOH and 6Al2Si2O7: 12NaOH : 2Al2O3 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 Na6Al4Si4O17 is synthesized at temperatures up to 700°C. Sodium aluminum silicate Na8Al4Si4O18 , 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.