Effect of ultrasound on the thermal behavior of the mixtures for the LTA zeolite synthesis based on metakaolin

The effect of ultrasonic treatment on the thermal behavior of the mixtures from metakaolin, sodium hydroxide and alumina designed for LTA zeolites synthesis was studied. X-ray diffraction analysis, infrared spectroscopy, scanning electron microscopy and synchronous thermal analysis have been used. It was shown that after evaporation of the suspension, LTA zeolite (24 mass%) is contained in the samples. It was established that the new phase (sodium aluminum silicate) is formed at a calcination temperature of about 600 °C. It was demonstrated that at a calcination temperature over 800 °C, nepheline is synthesized. The reaction of nepheline formation has been described by the topochemical equation of four-dimensional nucleation/nucleus growth according to Avrami/Erofeev. Using the Ozawa–Flynn–Wall analysis for non-isothermal data, the values of the activation energy and the pre-exponential factor have been calculated. It is shown that after the ultrasonic treatment the activation energy of the nepheline synthesis reaction has smaller values than in the sample without pretreatment. These phenomena have been explained by differences between the structural parameters of the particles (dimension of the coherent scattering region, the value of microdeformations).