New materials obtained from high temperature phase transformations of natural zeolites

Abstract

Instituto de Technologia Quimica UPV-CSIC, Avenida de los Naranjos s/n, 46021 Valencia, Spain Natural zeolites are abundant raw materials used in several applications [1-3], such as animal nourish- ment [4, 5], agronomic and horticultural applications [6], slow release fertilizers [6], aquaculture [7, 8], adsorption of gases [9, 10], catalysis [11, 12] and as construction materials [2,13]. Nevertheless, the development of materials with interesting electrical, mechanical or other properties from natural zeolites has not often been reported in the literature. The aim of this letter is to show how it is possible, with the help of high temperature phase transforma- tions, to obtain materials with high resistivity, low dielectric loss and high hardness, which have potential for electronic and mechanical applications. The materials used were natural zeolites from the deposits of Castillas, Havana, Cuba (HC), San Andres, Holguin, Cuba (SA) and Palmarito, Santiago de Cuba, Cuba (MP). The chemical and mineralogi- cal analyses of the samples are listed in Table I and Table II. The characterization methods are reported elsewhere [14-16]. Zeolite HC was used for the preparation of ceramic materials. It was ground in an agate ball mill then sieved to obtain particles of grain size less than 100 gm. Cylindrical wafers (20 mm× 1 ram) were prepared from the powders by pressing at 100 MPa, after first agglomerating the powders with polyvinyl alcohol. The wafers were then thermally treated at 500, 600, 700, 800, 900, 1000, 1100 and 1150 °C. Zeolites MP and SA were used for the preparation E