Ceramics-Silikáty 60, (4) 308 - 316 (2016)

The preparation and characterization of cordierites based on the commercial vermiculites obtained from the powder mixtures containing talc, kaolinite and vermiculite in the composition close to the cordierite 2MgO∙2Al₂O₃∙5SiO₂ has been reported since 2009. The aim of this paper was to characterize the structural properties of the nine synthetic cordierites sintered from the pre-ceramic mixtures containing commercial vermiculites at 1300° C in comparison with the orthorhombic natural and synthetic hexagonal cordierites (indialites) selected from literature. The orthorhombic natural cordierites showed the elements Fe and Mn replacing Mg in an appropriate correlation F = (Fe+Mn)/(Fe+Mn+Mg) with the unit cell parameter a, and an inverse correlation with parameter c. The unit cell parameters c calculated for the nine synthetic cordierites based on vermiculites (Ver) were in good linear relation with the F_Ver = (Fe/(Fe+Mg)_oct + (K+Na+Ca)_int) per formula unit of the corresponding vermiculites in the pre-ceramic mixtures. The structural disorder of cordierites based on vermiculites was determined higher, according to the wide index W1/3 of (211) reflection varying in a narrow range W1/3₍₂₁₁₎ from 0.290° to 0.299° 2Θ, in comparison with the W1/3₍₂₁₁₎ = 0.324° 2Θ of the cordierites based on the alumina.