Nepheline and Carnegieite Ceramics from A-Type Zeolites by Microwave Heating

The thermal disintegration processes of A-type zeolites and the properties of the materials that were formed after microwave heating (at 2.45 GHz) were studied. The thermal disintegration of 4A-type zeolite proceeded as follows: disintegration at ∼880°C, followed by transformations to high-carnegieite 1 at ∼920°C, nepheline (in nepheline(4A) form) at ∼990°C, and high-carnegieite 2 at ∼1254°C (further heating led to melting at ∼1526°C). High-carnegieite 1, nepheline(4A), and high-carnegieite 2 efficiently absorbed microwaves. Cooling of the molten material yielded low-carnegieite that contained some impurities. The change of 3A-type zeolite proceeded as follows: disintegration at ∼910°C and transformation to nepheline (in nepheline(3A) form) at ∼1006°C. In 3A-type zeolite, in contrast to 4A-type zeolite, carnegieite did not form before the crystallization of nepheline(3A). Nepheline of high purity and carnegieite with some impurities were synthesized easily by heating 3A- and 4A-type zeolites, respectively, using microwaves. These results suggest that the microwave heating of zeolites can be used to prepare some ceramic materials.