Search results for "Mullite"
showing 4 items of 24 documents
Cobalt aluminate spinel-mullite composites synthesized by sol-gel method
1997
Abstract CoAl 2 O 4 spinel-mullite composites were prepared by double substitution of Al by Ti and Ni in stoichiometric 3:2 mullite. Gels with compositions 3(Al 2 − 2 x Co x Ti x O 3 )·2SiO 2 (x = 0.025, 0.05 and 0.2) and 3(Al 2 − 2 x M x O 3 )·2SiO 2 (x = 0.05; M = Co 2+ or Ti 4+ ) were synthesized by sol-gel techniques. The structure of the gels was investigated by infra-red spectroscopy. Heating gels at 750 °C produced an amorphous silicoaluminate network. The reaction sequence was investigated by differential thermal analysis, X-ray diffraction and ultraviolet-visible spectroscopy. All samples crystallized at temperatures lower than 1000 °C from the amorphous state. Al-Si spinel and/or …
Reaction Sequence in the Preparation of NiAl2O4 Spinel-Mullite Composites by Sol-Gel
2005
NiAl 2 O 4 spinel-mullite composites were prepared by simultaneous replacement of Al by Ti and/or Ni in 3:2 stoichiometric mullite. Specimens having nominal compositions 3(Al 2-2x Ni x Ti x O 3 ).2SiO 2 (x = 0, 0.025, 0.05, 0.2) and 3(Al 2-x M x O 3) .2SiO 2 (M = Ni 2+ or Ti 4+ and x = 0.05) were synthesized by sol-gel techniques, which provide homogeneous gels in the SiO 2 -Al 2 O 3 system. Gel structures investigated by infrared (IR) spectroscopy revealed the formation of Al-O-Si bonds in dried gels. The reaction sequence of gel-derived glasses, previously obtained by preheating gels at 750°C for 3 h, was evaluated by X-ray powder diffraction (XRD) and ultraviolet-visible (UV-vis) spectro…
Microstructural evolution and growth of crystallite size of mullite during thermal transformation of kyanite
1997
Abstract The microstructural evolution of mullite during the thermal transformation of kyanite has been studied in the temperature range 1200–1600 °C. The shape and size of the grains were analysed by means of SEM-EDS while crystallite size evolution was studied by X-ray line profile analyses. The results obtained showed that total transformation of kyanite to mullite takes place between 1350 and 1400 °C. At temperatures below 1350 °C needle-like mullite grains are always produced. At higher temperatures the mullite grains reveal rounded end platelet morphology. Evolution from needle-like to platelet shape was correlated with the X-ray data.
Effect of TiO2 on the mullite formation and mechanical properties of alumina porcelain
2010
Abstract The effect of adding TiO 2 to standard alumina porcelain on its microstructure and flexural strength was investigated. A series of alumina porcelain bodies containing increasing amounts of TiO 2 were prepared by extruding mixtures of raw materials and TiO 2 . Porcelain rods were fired under industrial scheduling in a manufacturing kiln. The overall degree of crystalline and amorphous phase content within the porcelain bodies was quantitatively determined using a Rietveld analysis. Results indicated a higher amount of mullite formation in porcelain bodies containing TiO 2 . Examination of the product materials using field emission scanning electron microscopy showed a high density o…