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Synthesis of Nanocrystalline α‐Al 2 O 3 Powders from Nanometric Ammonium Aluminum Carbonate Hydroxide
Author(s) -
Sun Xudong,
Li Jiguang,
Zhang Fang,
Qin Xiaomei,
Xiu Zhimeng,
Ru Hongqiang,
You Jian
Publication year - 2003
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/j.1151-2916.2003.tb03469.x
Subject(s) - nanocrystalline material , hydroxide , materials science , amorphous solid , sintering , calcination , phase (matter) , particle size , particle (ecology) , ammonium hydroxide , chemical engineering , mineralogy , crystallography , metallurgy , chemistry , nanotechnology , catalysis , biochemistry , oceanography , organic chemistry , geology , engineering
Nanometric ammonium aluminum carbonate hydroxide (AACH) with a particle size less than 5 nm was produced from ammonium aluminum sulfate and ammonium hydrocarbonate under an optimized adding condition, and phase transformations of the AACH on heating and the effect of α‐Al 2 O 3 seeding on the transformation kinetics were investigated. The phase transformation sequence of AACH on heating was found to be AACH → amorphous Al 2 O 3 →γ‐Al 2 O 3 →θ‐Al 2 O 3 →α‐Al 2 O 3 , where the formation temperatures of θ‐Al 2 O 3 and α‐Al 2 O 3 are 850° and 1050°C, respectively. The phase transformation sequence on heating of the AACH seeded with 5 wt%α‐Al 2 O 3 seed crystals 100 nm in diameter was found to be AACH → amorphous Al 2 O 3 →θ‐Al 2 O 3 →α‐Al 2 O 3 . γ‐Al 2 O 3 was not observed, and the θ‐Al 2 O 3 →α‐Al 2 O 3 transformation temperature was reduced to 900°C by the seeding. By calcining the γ‐AlOOH, the AACH, and the seeded AACH at their lowest temperatures to transform completely to α‐Al 2 O 3 (i.e., about 1200°, 1100°, and 900°C, respectively), α‐Al 2 O 3 powders have been obtained with mean particle sizes of about 150, 70, and 30 nm, respectively. The α‐Al 2 O 3 powder produced from the seeded AACH has the highest sintering reactivity. After sintering at 1400°C for 2 h, relative densities of the powder compacts of α‐Al 2 O 3 obtained by calcining γ‐AlOOH, AACH, and the seeded AACH are 74.3%, 95.0%, and 98.5%, respectively.