Structural and Chemical Analysis of Micro-sized Particles Found in Aluminous Electrical Porcelains

Abstract

Uncommon, micro-sized particles with different morphologies were found in sintered aluminous electrical porcelains. The presence of these particles seems to be relatively insensitive to changes in composition of the porcelain system as well as in firing temperatures. X-ray energy-dispersive spectrometry (EDS) microanalysis showed that some particles, those with very well–defined geometries, were composed of K, Si, Al, and O with empirical formula KAlSi2O6—that is, leucite particles. Other particles showed less well–defined geometries, including some composed of Na, Si, Al, and O, corresponding to a sodium aluminum silicate structure, and others of K, Si, Na, Al, and O, corresponding to the leucite composition, where some K has been substituted for Na. The well–defined geometry particles were detected most often, and diffraction analysis with backscattering electrons showed that their unit cell was cubic, with unit cell parameter a = 1.343 nm. The formation of these particles may be the result of the relatively high concentration of K2O and/or Na2O in some very localized zones of the glassy phase due to weak coupling (e.g., alkali-enriched or -depleted melts) during diffusion at a slow cooling rate in the presence of catalytic agents such as TiO2.