0000000000291895
AUTHOR
Carla Valentín
showing 4 related works from this author
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 …
Spinel-mullite composites with optical properties
1997
The aim of this paper was to study the synthesis and characterization of spinel-containing mullite based materials, using sol-gel techniques. Several gels were prepared, with nominal compositions 3(Al2−2xMx TixO3)·2SiO2 and 3(Al2−xMxO3)·2SiO2, with M=Ni+2 or Co+2 and 0.0≤x≤0.2, by hydrolysis and condensation of mixtures of aluminum, silicon and titanium alkoxides and nickel chloride. Dried gels were homogeneous and displayed a glass transition at around 750°C, which indicated that the system could be described as an amorphous silicoaluminate network.
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…
Low-temperature metastabilization of tetragonal V+4-containing ZrO2 solid solutions
2001
Abstract The formation and characterization of tetragonal vanadium–zirconia solid solutions with different vanadium contents have been investigated. Vanadium–zirconia precursors were prepared by gelling mixtures of zirconium n-propoxide and vanadyl acetylacetonate, and studied over the range of temperature up to the tetragonal–monoclinic phase transformation. The formation of the tetragonal phase has been investigated by X-ray powder diffraction (XRD). It was found that it took place after annealing around 450°C for all specimens independently of the vanadium loading. In contrast, the temperature for the subsequent tetragonal to monoclinic transformation was dependent on the nominal vanadiu…