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-excha nged zeolite A were characterized by different techniques such as X-ra y diffractometry, Fourier transform infrared spectroscopy, differentia l thermogravimetric analysis, differential scanning calorimetry, scann ing electron microscopy, determination of the particle size distributi on and determination of the specific surface area. Based on the result s of this characterization, it was found that controlled heating cause s 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, partic le size, particle size distribution, specific surface area) of the amo rphous aluminosilicate and the mixture of kalsilite and kaliophilite a re, curiously enough, similar, or even the same as the particulate pro perties of the starting crystalline material (potassium-exchanged zeol ite A). (C) 1997 Elsevier Science B.V.