Invariability of the particulate properties during the thermal treatment of potassium-exchanged zeolite A: evidence for “amorphous crystals”

The products obtained during the controlled heating of potassium-exchanged zeolite A were characterized by different techniques such as X-ray diffractometry, Fourier transform infrared spectroscopy, differential thermogravimetric analysis, differential scanning calorimetry, scanning electron microscopy, determination of the particle size distribution and determination of the specific surface area. Based on the results of this characterization, it was found that controlled heating causes a phase transformation in the sequence (Na,K)-zeolite A→amorphous (Na,K)-aluminosilicate→kalsilite + kaliophilite. In contrast to the structural changes, the particulate properties (particle shape, particle size, particle size distribution, specific surface area) of the amorphous aluminosilicate and the mixture of kalsilite and kaliophilite are, curiously enough, similar, or even the same as the particulate properties of the starting crystalline material (potassium-exchanged zeolite A).