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Synthesis of a Mullite Precursor from Aluminum Nitrate and Tetraethoxysilane via Aqueous Homogeneous Precipitation: An 27 Al and 29 Si Liquid‐ and Solid‐State NMR Spectroscopic Study
Author(s) -
Jaymes Isabelle,
Douy André,
Massiot Dominique,
Busnel JeanPierre
Publication year - 1995
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.1151-2916.1995.tb08035.x
Subject(s) - aluminosilicate , mullite , aluminium nitrate , inorganic chemistry , aqueous solution , colloid , silicic acid , precipitation , solid state nuclear magnetic resonance , sol gel , hydrolysis , colloidal silica , chemical engineering , materials science , chemistry , aluminium , catalysis , ceramic , organic chemistry , nanotechnology , coating , physics , nuclear magnetic resonance , meteorology , engineering
A simple aqueous process is described for the preparation of aluminosilicate colloids and chemically homogeneous mullite precursor gel. Starting from a solution of aluminum nitrate and silicic acid, aluminum is slowly hydrolyzed at 80–100°C by in situ generation of ammonia. A silica gel is rapidly made, probably by a catalytic effect of urea, the base generator. This gel is then slowly digested by partially hydrolyzed aluminum species which break the Si‐O‐Si bonds and link to the gel by Si‐O‐Al bonds. Progressively a clear colloidal sol is obtained and the colloidal particle size continues to decrease toward aluminosilicate species where the silicon atoms are in a single environment and may be linked to three hexacoordinated aluminum atoms and a hydroxyl group, by reference to natural imogolite. When the hydrolysis of aluminum is nearly complete, these particles are cross‐linked and a final gel precursor of mullite is obtained. This gel is chemically very homogeneous and crystallizes to mullite at 980°C. The structural evolution, from the first gel to the ceramic, has been followed by 27 Al and 29 Si liquid‐ and solid‐state MAS NMR spectroscopy.