Search results for "Mullite"

Solubility and microstructural development of TiO2-containing 3Al2O3·2SiO2 and 2Al2O3·SiO2 mullites obtained from single-phase gels

2007

Abstract The interdependence of the titanium oxide amount and the anisotropic growth of mullites prepared from single-phase gels were investigated. Gels with stoichiometries 3(Al2−xTixO3)·2(SiO2) and 2(Al2−xTixO3)·(SiO2), with 0 ≤ x ≤ 0.15 were prepared by the semialkoxide method. Gels and specimens heated at temperatures between 1200 and 1600 °C were characterized by using infrared spectroscopy (IR), X-ray diffraction (XRD) and transmission and field emission scanning electron microscopies (TEM and FESEM). Al2TiO5 as minor impurity was detected in both series of mullites for gel precursor compositions x = 0.10 and x = 0.15, obtained at temperatures between 1200 and 1600 °C. Variations of l…

Phase evolution by thermal treatment of equimolar cobalt–magnesium cordierite glass powders

2004

Abstract The structural evolution with annealing time at temperatures between 900 and 1100 °C of loosely compacted equimolar cobalt–magnesium cordierite glass powder was reported. The glass, with composition MgCoAl4Si5O18, was prepared by melting a glass precursor, previously synthesized by a semiwet method, at 1650 °C. Field emission scanning electron microscopy (FESEM) of isothermally heated glasses at 900 and 950 °C revealed increased phase separation with thermal treatment. X-ray diffraction (XRD) results of these powders indicated that the first crystalline phase formed was μ cobalt-containing cordierite which transformed to α cordierite with longer annealing. At the beginning of the μ…

Sizes and Shapes of Crystallites in Mullites Produced by Thermal Treatment of Kaolin - Alumina Mixture

2001

Microstructural and magnetic characterization of fly ash from Kolaghat Thermal Power Plant in West Bengal, India

2011

Abstract This paper reports on the physical nature of the fly ash sample of the Kolaghat Thermal Power Plant, India with an emphasis on its ultrafine nature. This paper also deals with the measurement of the magnetic properties of the fine particles of the fly ash sample. Particle sizes of this fly ash sample estimated from the SEM images lie within 0.16–5.50 μm, and the EDX spectral analysis indicates the presence of O, Al, Si, C, Fe, Mg, Na, K and Ti in this sample. From the XRD study, it is found that physical nature of conglomeration in the fly ash is crystalline and the major components are mullite (Al 6 Si 2 O 13 ) and quartz (SiO 2 ). Additionally, the presence of hematite, microclin…

Low-temperature Ti-containing 3:2 and 2:1 mullite nanocrystals from single-phase gels

2007

Abstract TiO 2 -containig single-phase gels with (Al 2 O 3  + TiO 2 )/(SiO 2 ) molar ratios 3/2 and 2/1 were prepared by gelling mixtures of aluminium nitrate, tetraethylorthosilicate and titanium isopropoxide. Gels were fast heated at several temperatures up to 1100 °C. Dried and heated gels were characterized by differential thermal analysis (DTA), magic angle spinning nuclear magnetic resonance (MAS-NMR), X-ray powder diffraction (XRD), and scanning and transmission electron microscopies (SEM and TEM). Coupled DTA and XRD results of gels fast heated at 900 °C showed the crystallisation of two mullites as well as a small amount of alumina-silica spinel. 27 Al NMR spectra showed the format…

An X-ray powder diffraction study of the microstructural evolution on heating 3:2 and 2:1 mullite single-phase gels

2006

Single-phase gels with compositions 3Al2O3·2SiO2 and 2Al2O3·SiO2 were prepared by gelling mixtures of aluminium nitrate and tetraethylorthosilicate. Gels were fast heated at different temperatures between 900°C and 1600°C. The phase transformation and microstructural changes of both mullite precursor gels over the temperature range were followed by X-ray powder diffraction (XRD), lattice parameter determination (LP), and scanning and transmission electron microscopies (SEM and TEM). The distribution of crystallite sizes and strains were determined by linewidth refinements of X-ray diffraction patterns using the integral breadth method of Langford and the Warren-Averbach analysis. XRD of bot…

XRD Line Broadening Studies on Mullite

1996

An X-ray diffraction microstructural study on 110, 220, 001 and 111 peaks has been performed on mullite in the temperature range of primary mullite formation in order to monitor nucleation and growth process. Considering the crystallinity of the starting kaolinites, a greater disorder of the kaolinite has been found to enhance the mullite formation. Isothermal growth is related to a decrease in the Al 2 O 3 content of mullite.

Mechanism of Formation of TiO2-Doped Mullites from Heated Single-Phase Gels Investigated by Structural and Microstructural Parameters

2008

An analysis of the microstructure of TiO 2 -doped mullites prepared from monophasic gels thermally treated in the temperature range 900°-1600°C is reported. Two series of gels with nominal compositions 3(Al 2-x Ti x O 3 ) ·2(SiO 2 ) and 2(Al 2-x Ti x O 3 )·(SiO 2 ), in the range 0≤x≤0.15, were prepared. X-ray powder diffraction (XRD) and scanning electron microscopy (SEM) were used to follow the structural and textural evolution from gels to the final doped mullites. The crystallite sizes and microstrains were determined by linewidth refinements of XRD patterns using the integral breadth method of Langford and the Warren-Averbach analysis. XRD patterns showed the formation of Al 2 TiO 5 and…

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.

Effect of thermal treatment on the structural evolution of 3:2 and 2:1 mullite monophasic gels

2005

Abstract Single phase mullite gels with composition 3Al2O3 · 2SiO2 (3:2) and 2Al2O3 · SiO2 (2:1) were prepared by the semialkoxide method using aluminum nitrate nonahydrate and tetraethylorthosilicate as reagents. The influence of the thermal processing conditions on the reaction sequence was investigated. Both 3:2 and 2:1 mullite gels formed orthorhombic mullite under fast heating (40 °C/min) at 900 °C. Slow heatings delayed the formation of mullite in both gel compositions but no formation of spinel was detected between 1000 °C and 1100 °C. The slow transformation of pentacoordinated aluminum to octahedral and tetrahedral arrangements probably depends on the larger size and extent of the …