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Mechanism and Kinetics of the Carbothermal Nitridation Synthesis of α‐Silicon Nitride
Author(s) -
Weimer Alan W.,
Eisman Glenn A.,
Susnitzky David W.,
Beaman Donald R.,
McCoy Jeffrey W.
Publication year - 1997
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.1151-2916.1997.tb03203.x
Subject(s) - nucleation , carbothermic reaction , silicon nitride , activation energy , chemical engineering , silicon , materials science , reaction mechanism , carbon fibers , phase (matter) , kinetics , chemical kinetics , reaction rate , nitride , porous silicon , chemistry , layer (electronics) , nanotechnology , catalysis , composite material , metallurgy , composite number , organic chemistry , physics , quantum mechanics , engineering
The carbothermal nitridation synthesis of α‐Si 3 N 4 is studied using electron microscopy techniques(FEG/SEM and TEM) and chemical composition analysis to characterize the reaction at various degrees of conversion. The reaction follows a nucleation‐growth mechanism. Without “seed”α‐Si 3 N 4 in the precursor, the reaction rate is controlled by the formation of nuclei which are associated with a Si‐O‐C intermediate phase. In the presence of “seed,” the limiting step is growth of α‐Si 3 N 4 onto the “seed” nuclei. Growth appears to follow a gas‐phase route and is characterized by an irregular porous layer which grows onto the “seed.” The porous structure is the result of reaction around car‐bon particles which are consumed during the process. The presence of admixed “seed” Si 3 N 4 in the precursor formu‐lation increases the reaction rate since the nucleation step is eliminated. An activation energy of E = 457 ± 55 kJ/mol for the overall reaction closely approximates that previously reported for the formation of SiO. This result, along with the finding that residual crystalline SiO 2 is present at all stages of the reaction, indicates that the overall reactionrate is controlled by the reduction of SiO 2 . Since reaction at the carbon and SiO 2 contact points is fast, the rate‐limiting step is most likely the gas‐phase carbon reduction of SiO 2 with CO.