THERMAL BEHAVIOR OF THE METACAOLINE-BASED MIXTURE FOR THE SYNTHESIS OF LEA ZEOLITE: THE INFLUENCE OF ULTRASONIC TREATMENT
Abstract
A study of the influence of ultrasonic treatment on the kinetics of solid-phase interaction of metakaolin with the sodium hydroxide was performed.Reflections corresponding to the zeolite LTA were observed on X-ray patterns according to phase analysis before calcination at 500°C for the sample without pre-treatment.The appearance of a new phase of sodium alumosilicate (Na6Al4Si4O17) was observed with increasing temperature to 700°C.The reflections of sodium aluminosilicate (Na8Al4Si4O18) and nepheline were detected on the X-ray pattern when the temperature calcination 800°C besides to the characteristic reflections of the zeolite.Aluminosilicates were obtained by recrystallization of the zeolitepart.Also the process was accompanied by metakaolin decomposition in silica and mullite. Reflections corresponding to the zeolite was not discovered at 900°C.According to the X-ray analysis, it was found that ultrasonic treatment has no effect on the phase composition of the samples.Based on these data, it was determined the temperature range (500-800°C).There was recrystallization of zeolite in aluminosilicates for this temperature range.According to the thermal analysis, especially the data of mass loss in a given temperature interval, the exact temperature ranges were established for each heating rate of the samples without pre-treatment and the samples after ultrasonic treatment. The Ozawa-Flynn-Wall method was selected as an isoconversional analysis.The monotonous growth of apparent activation energy was found in all range of conversion extents after ultrasonic treatment. It smoothes the change of the transition regime (up to 200 kJ/mol) to kinetic one.The apparent activation energy for the sample without ultrasonic treatment gone approximately at one level (350 kJ/mol) upon reaching the conversion extent of 0.5-0.6.The apparent activation energy increases after ultrasonic treatment from 350 to 450 kJ/mol upon reaching the conversion extent above 0.9.
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