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The Effect of La 2 O 3 Addition on Sol–Gel Derived Mullitization
Author(s) -
Mandić Vilko,
Tkalčec Emilija,
Kurajica Stanislav
Publication year - 2014
Publication title -
journal of the american ceramic society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.9
H-Index - 196
eISSN - 1551-2916
pISSN - 0002-7820
DOI - 10.1111/jace.12887
Subject(s) - mullite , spinel , materials science , calcination , crystallization , microstructure , sintering , sol gel , amorphous solid , rietveld refinement , phase (matter) , chemical engineering , thermal treatment , ceramic , mineralogy , scanning electron microscope , crystallography , chemistry , crystal structure , composite material , metallurgy , nanotechnology , catalysis , biochemistry , organic chemistry , engineering
Monophasic gel with stoichiometric 3 Al 2 O 3 ·2 SiO 2 composition and gels with 0.99, 1.96, and 2.91 mol% La 2 O 3 added were sol–gel derived. The crystallization path, structure evolution, microstructure, and morphology of calcined premullite powders and sintered ceramic bodies have been investigated as a function of La 2 O 3 content and sintering temperature. In addition to mullite, spinel phase at about 980°C, and α‐alumina at above 1000°C were determined; however, neither La 2 O 3 nor La ‐related compounds had crystallized. The La 2 O 3 predominately incorporated into the glassy phase, enhanced with La 2 O 3 level, which affected both mullite structure and composition, as confirmed by electron microscopy, Rietveld structure refinement, determination of unit cell parameters, electron microscopy, and achieved density of the sintered bodies. Increased thermal treatment changes the alumina/silica ratio in mullite (towards 3:2 below 1200°C, and toward 2:1 above), and decreases the mullite/amorphous ratio. Sintered dense ceramic bodies revealed a positive densification effect and increased sinterability as a result of the lanthanum‐induced increase in glassy phase.