It was studied the effect of ultrasonic processing (22kHz) of the aqueous suspension of metakaolin, sodium hydroxide and alumina with a molar ratio 2Al2Si2O7:12NaOH:2Al2O3 on the low-modulus zeolite synthesis processes. To investigate the XRD, SEM, IR, EDS had been used. It was shown that after ultrasonic processing, sodium aluminates are formed, what leads to a change in process of further synthesis. It was found that without ultrasonic processing on the stage of thermal treatment at 650°C, SOD zeolite (|Na6|[Al6Si6O24]) and sodium aluminosilicate (Na6Al4Si4O17) are synthesized. In the sample after ultrasound during thermal treatment, only sodium aluminosilicates of cubic syngony (Na6Al4Si4O17 and Na8Al4Si4O18) are formed. It was demonstrated that sodium aluminosilicates are precursors for the formation of LTA zeolite (|Na12|[Al12Si12O48]). As a result zeolitization of sodium aluminosilicates after the hydrothermal crystallization in alkaline solution, the sonicated sample contained 97wt% LTA. Without ultrasonic processing, the product of synthesis contained 50wt% SOD and 40wt% LTA.
Nonisothermal kinetics of dehydration of gibbsite in a mixture with zinc oxide has been studied by Friedman analysis (differential method) and Flynn-Wall-Ozawa analysis (integral method). The values of the activation energy and preexponential factor depending on the decomposition extent of gibbsite to boehmite have been determined. It has been shown that both methods give similar results. It has been established that the activation energy has a maximum value of 150-170 kJ/mol in the start stages of thermolysis (for conversion extent of less than 0.3). During further dehydration, the activation energy is reduced to 100-110 kJ/mol. It has been found that comilling of the mixture results in decreasing activation energy to 40-50 kJ/mol for a conversion extent more than 0.8. This testifies to the transition of the dehydration process out of the kinetic mode to the diffusion mode. It was explained by the accumulation of mechanical energy in the form defects of crystal lattice of gibbsite at the comilling stage. C 2015 Wiley Periodicals, Inc. Int J Chem Kinet 47: 576-585, 2015
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