Structural variability of high purity cordierite/steatite ceramics sintered from mixtures with various vermiculites

The cordierite/steatite ceramics were prepared from the pre-ceramic clay mineral mixtures containing talc, kaolinite and unconventionally used vermiculite. The aim was to characterize cordierite/steatite ceramics in relation to the vermiculites in the pre-ceramic mixtures and compare the influence of their sintering, loosely in crucibles and pressed into pellets. Quantitative X-ray diffraction (XRD) analysis revealed approximately a 5 vol% lower content of indialite (IND) sintered in pellets than in crucibles, and protoenstatite (PEN) slightly prevailing over orthoenstatite (OREN) at all ceramic samples. All ceramic samples showed linear dependency of porosity on the increasing content of potassium and sodium in structure of vermiculites. Highest porosity, 55%, was detected for sample in crucible made of vermiculite admixture from Letovice region (CR) and the smallest porosity 0.25% was in a sample in pellets made of vermiculite admixture from the Xinlong deposit (China).