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Synthesis of Oxynitride Powders via Fluidized‐Bed Ammonolysis, Part I: Large, Porous, Silica Particles
Author(s) -
Bickmore Clint R.,
Laine Richard M.
Publication year - 1996
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.1151-2916.1996.tb08720.x
Subject(s) - nitriding , nitrogen , x ray photoelectron spectroscopy , chemical engineering , porosity , chemistry , pyrolysis , fluidized bed , triethanolamine , ethylene glycol , ceramic , activation energy , materials science , inorganic chemistry , analytical chemistry (journal) , mineralogy , organic chemistry , engineering
Reaction of silica (SiO 2 ) with triethanolamine (TEA, N(CH 2 CH 2 OH) 3 ) and ethylene glycol (EG) under conditions (∼200°C) where byproduct water is removed resulted in the formation of the neutral silatrane glycolate complex, N(CH 2 CH 2 O) 3 SiOCH 2 CH 2 OH (or TEASiOCH 2 CH 2 OH) in essentially quantitative yield. Solutions of this neutral precursor in EG, when rapidly pyrolyzed and then oxidized at 500°C, formed porous ceramic powders with high specific surface areas (>500 m 2 /g). These powders were nitrided via ammonolysis in a fluidized‐bed reactor at temperatures of 700°‐1000°C. The resulting nitrided powders were characterized by thermal and chemical analyses, diffuse reflectance infrared spectroscopy, gas sorption, and X‐ray photoelectron spectroscopy. The apparent activation energy for the nitridation process was determined to be 54 kJ/mol. Following nitridation, the powders were amorphous and had nitrogen contents as high as 21 wt% with retained surface areas >300 m 2 /g at 1000°C. Under the nitridation conditions used, the extent of nitrogen incorporation correlated linearly with increases in material density. This linearity suggested that the change in density occurred primarily because of changes in coordination that occurred as trivalent nitrogen replaced divalent oxygen in the glass structure and nominally because of viscous flow. The linear density increase also suggested that pore trapping did not occur under these processing conditions. This work serves as a model for ongoing studies on the nitridation of high‐surface‐area ceramic powders produced by the rapid pyrolysis of mixed‐metal TEA alkoxides.