Structural characteristics of cordierite/steatite ceramics sintered from mixtures containing pore-forming organovermiculite

Abstract

The preceramic mixtures appropriate to the composition of cordierite are composed of talc, kaolinite and vermiculite (Ver), and/or organovermiculite (Ver-org) as a pore-forming agent. The preceramic mixtures for sintering at 1300 °C were prepared in two different ways, loosely in crucibles and compressed into pellets. Structural characterization of cordierite/steatite ceramic was performed using X-ray powder diffraction (XRD), FTIR spectroscopy, scanning electron microscopy analysis and porosity measurement. The ceramic samples showed (1) bimodal meso-macropore size distribution and unimodal macropore size distribution, when the preceramic mixtures included Ver and Ver-org, respectively, and (2) higher porosity when sintering mixtures occurred in crucibles in comparison with pellets. The XRD patterns and quantitative XRD phase analysis revealed cordierite/steatite ceramics in the composition of indialite (IND) and two orthorhombic forms of enstatite: protoenstatite (PEN) and orthoenstatite (OREN). All cordierite/steatite samples contained a greater amount of PEN than OREN and a slightly higher quantity of IND when sintered in crucibles compare to pellets. The ceramic samples prepared from the preceramic mixtures with twice the amount of Ver-org contained a high quantity of IND (91 vol%), PEN (about 9 vol%) and no OREN. The unit cell parameter c in comparison with the pure IND was about 0.001–0.003 nm shorter at all INDs. The pore-forming Ver-org supports structural substitution of cations during crystallization of IND with the substitution Ca0.50Mg1.50–Ca0.25Mg1.75. The IR spectra in the 400–1600 cm−1 region confirmed the presence of cordierite and steatit