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Thermal Reaction of Cristobalite in Nano‐ SiO 2 /α‐ Al 2 O 3 Powder Systems for Mullite Synthesis
Author(s) -
Yu PeiChing,
Tsai YungWei,
Yen FuSu,
Huang ChengLiang
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.12989
Subject(s) - mullite , cristobalite , materials science , nucleation , powder diffraction , scanning electron microscope , differential thermal analysis , particle size , particle (ecology) , transmission electron microscopy , mineralogy , crystallography , chemical engineering , diffraction , chemistry , ceramic , metallurgy , composite material , nanotechnology , organic chemistry , quartz , physics , oceanography , geology , optics , engineering
Nanoscaled cristobalite and α‐ Al 2 O 3 powders were used as the starting materials for synthesizing mullite by solid‐state reaction. The thermal reaction of the cristobalite with α‐ Al 2 O 3 during the thermal treatment was examined. Cristobalite powder with a D 50 value of 430 nm was adopted to mix with α‐ Al 2 O 3 powders with a D 50 values of 230, 310, and 400 nm in a stoichiometric composition of 3 Al 2 O 3 ∙2 SiO 2 (71.8 wt% α‐ Al 2 O 3 and 28.2 wt% SiO 2 ). Samples for thermal reaction were prepared using uniaxial pressed from the three mixtures that showed various particle number ratios of SiO 2 / Al 2 O 3 due to the different particle sizes of α‐ Al 2 O 3. Examinations were performed by differential thermal analysis, X‐ray diffraction, scanning electron microscopy, energy‐dispersive X‐ray spectroscopy, and transmission electron microscopy techniques. The results showed that cristobalite particles amorphized during the thermal treatment, and then reacted with the α‐ Al 2 O 3 particle to form mullite via nucleation and growth. The amorphization temperature can be reduced by using finer‐sized α‐ Al 2 O 3 powders, thus leading to a lower temperature for mullite formation. Mullite crystals with a multidomain structure were observed in the α‐ Al 2 O 3 particle matrixes. The crystal orientation of the mullite was controlled by the α‐ Al 2 O 3 matrix, that is, [001] α‐ Al 2 O 3 → [001] mullite. These results indicate that the amorphization of cristobalite may trigger the reaction of SiO 2 with α‐ Al 2 O 3 , initiating the nucleation of mullite. The α‐ Al 2 O 3 particles act as the hosts for mullite formation and determine the size of the mullite particles.