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Crystallization of zeolite X coatings on stainless steel by microwave heating
The possibility of crystallization of zeolite X coatings on metal plates in a microwave oven was investigated. Characterizations were performed by X-ray diffraction, scanning electron microscopy, laser microscopy and gas adsorption. Crystalline zeolite X coatings with mass equivalent thicknesses of up to about 100 mu m could be obtained on stainless steel plates. Heating the reaction mixture by microwaves instead of conventionally resulted in faster crystallization of zeolite X coatings on metal. The yield of zeolite was about 2.5-4.7 fold higher during different earlier periods of synthesis in the presence of microwave irradiation. The utilization of a device, containing graphite having good absorbance of microwaves, which was brought into firm contact with the metal plate, resulted in an increase of the zeolite yield by about 20 %. This indicated that the metal substrate profited from being heated conductively by the mentioned device, rather than being convectively heated by the reaction mixture.