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The corrosion behaviour of monophasic and diphasic gel derived mullite ceramics in nitric acid

Two types of premullite gels, monophasic and diphasic, have been prepared by sol-gel process. Thermal evolution of gels has been evaluated using differential thermal analysis (DTA) while thermally treated crystalline phases were characterized by powder X-ray diffraction (XRD), confirming gels monophasic and diphasic nature. Prepared gels were dried, grinded, calcined, pressed into pellets and sintered at temperature of 1600 °C for 4 h. Morphology of sintered bodies has been investigated using transmission electron microscopy (TEM). TEM revealed the presence of glassy phase while its chemical composition has been determined using energy dispersive X-ray spectroscopy (EDS). Microstructure of the samples has been observed using scanning electron microscopy (SEM) where monophasic gel derived sample yield greater porosity. The ceramics corrosion behaviour was explored in nitric acid aqueous solutions with various concentrations by measuring the amount of eluted ions using inductively coupled plasma- optical emission spectrometry (ICP-OES). Both samples are characterized with low corrosion rates, parabolic corrosion kinetics and higher Si4+/Al3+ ratio in eluate in comparison with nominal composition. Such corrosion behaviour was attributed to the leaching of the glassy phase in corrodent media. Higher corrosion rate constants of monophasic gel derived samples were attributed to greater porosity of those samples.

Mullite; corrosion; nitric acid

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