ISSN:
1573-4803
Source:
Springer Online Journal Archives 1860-2000
Topics:
Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
Notes:
Abstract Monophasic and diphasic xerogels have been prepared as precursors for mullite (3Al2O3-2SiO2). Monophasic xerogel was synthesized from tetraethyl orthosilicate and aluminium nitrate nanohydrate and the diphasic xerogel from colloidal suspension of silica and boehmite. The chemical and structural evolutions, as a function of thermal treatment in these two types of sol-gel-derived mullite precursor powders, have been characterized by differential thermal analysis (DTA), thermogravimetric analysis (TGA), X-ray diffraction (XRD), scanning electron microscopy (SEM), and infrared spectroscopy (IRS). Monophasic xerogel transforms to an aluminium-silicon spinel from an amorphous structure at ∼980 ° C. The spinel then changes into mullite on further heating. Diphasic xerogel forms mullite at ∼1360 ° C. The components of the diphasic powder react independently up to the point of mullite formation. The transformation in the monophasic powder occurs rapidly and yields strongly crystalline mullite with no other phases present. The diphasic powder, however, transforms rather slowly and contains remnants of the starting materials (α-Al2O3, cristobalite) even after heating at high temperatures for long periods (1600 ° C, 6 h). The diphasic powder could be sintered to high density but not the monophasic powder, in spite of its molecular-level homogeneity.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00584886
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