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An X‐ray powder diffraction study of the microstructural evolution on heating 3:2 and 2:1 mullite single‐phase gels
Author(s) -
Ruiz de Sola E.,
Serrano F. J.,
Torres F. J.,
Reventós M. M.,
Esteve V. J.,
Kojdecki M. A.,
Amigó J. M.,
Alarcón J.
Publication year - 2006
Publication title -
crystal research and technology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.377
H-Index - 64
eISSN - 1521-4079
pISSN - 0232-1300
DOI - 10.1002/crat.200610717
Subject(s) - crystallite , materials science , mullite , phase (matter) , transmission electron microscopy , diffraction , powder diffraction , x ray crystallography , analytical chemistry (journal) , aluminium nitrate , scanning electron microscope , atmospheric temperature range , nanocrystal , microstructure , crystallography , orthorhombic crystal system , mineralogy , aluminium , composite material , crystal structure , ceramic , chemistry , nanotechnology , optics , chromatography , metallurgy , physics , organic chemistry , meteorology
Single‐phase gels with compositions 3Al 2 O 3 ·2SiO 2 and 2Al 2 O 3 ·SiO 2 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 both heated gels showed the formation of crystalline mullite single phase. Some amount of glassy phase coexisted with mullites at low temperatures, i. e. below 900°C. The compositional range of mullites formed on heating gels at temperatures between 900°C and 1600°C was dependent on the starting nominal composition of gels. SEM and TEM micrographs of both heated gels below 1200°C showed the formation of small, discrete, prismatic, well‐shaped nanocrystals in a very ordered arrangement. The size of these nanocrystals was dependant on the nominal composition of gels and increased on rising the heating temperature of gel precursors. The microstructural features obtained from linewidth refinement results of X‐ray diffraction patterns also allowed to suggest the formation of prismatic a little elongated nanocrystals at temperatures below 1200°C. Microstrain values were small and only displayed a relatively significant value for mullites processed at 900°C. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)