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

Abstract

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.