Mass Spectrometric Study on the Combustion of Tetramethylsilane and the Formation of Silicon Oxide Clusters in Premixed Laminar Low-Pressure Synthesis Flames

Abstract

This work investigates the decomposition of tetramethylsilane and the formation of silicon oxide clusters in a laminar premixed low-pressure hydrogen flame using molecular-beam mass spectrometry (MBMS). A comprehensive list of the species that exist in the gas phase was compiled and spatially resolved mole fraction profiles of species in the flame were obtained. Quantitative data in dependence of height above the burner were obtained for all major species and intermediates. The MBMS detection technique allowed to monitor Si-C-O-H, and Si-O-H-containing compounds as well as C-C species. The measured data show that the reaction of tetramethylsilane is initiated by H-abstraction from a methyl group and subsequent formation of oxygenated species. The measurements suggest that combustion of tetramethylsilane in a hydrogen flame proceeds mainly by a stepwise substitution of the methyl ligands by hydroxyl groups. Molecular and radical intermediates like Si(CH)OH, Si(OH), and Si(OH) are formed in the reaction zone. Significant amounts of Si(OH) are present at large distances above the burner. A repetitive growth pattern suggests that the monomer Si(OH) is a likely species initiating the formation and growth of larger silicon oxide clusters, e.g., SiOH, SiOH, and SiOH that can form nanoparticles in subsequent reactions.

A group additivity methodology for predicting the thermochemistry of oxygen‐containing organosilanes

“…Davidson et al 41 estimated the rate constants for the oxidation of sila‐isobutene ((CH 3 ) 2 Si=CH 2 ), producing (CH 3 ) 2 Si=O as a product. (CH 3 ) 2 Si=O was hypothesized to be an important intermediate for SiO production in TMS oxidation 3, 5 . Species with Si=O double bonds, such as O=Si(OC 2 H 5 ) 2 , O=Si(OH)(OC 2 H 5 ), and (OH) 2 Si=O were also considered in the TEOS oxidation mechanism of Nurkowski et al 7 .…”

“…The D2 derivatives are examples of such cases: it represents the cyc‐Si 2 O 2 (CH 3 ) 4 (tetramethyl‐cyclodisiloxane) species for which the experimental thermochemistry is unavailable because of difficulties in isolating and characterizing it, despite the fact that mass spectrometric experiments do suggest its existence 48 . Yet the GAVs of D2 derivatives would be useful for predicting the thermochemistry of larger silicon oxide clusters such as Si 4 O 10 H 4 or Si 5 O 12 H 4 3, 5 . As the molecular analogy of D2, these clusters comprise of Si atoms bridged by two O atoms 49 …”

“…(CH 3 ) 2 Si=O was hypothesized to be an important intermediate for SiO production in TMS oxidation. 3,5 Species with Si=O double bonds, such as O=Si(OC 2 H 5 ) 2 , O=Si(OH)(OC 2 H 5 ), and (OH) 2 Si=O were also considered in the TEOS oxidation mechanism of Nurkowski et al 7 We considered the possibilities of SiH 3 , CH 3 , H, and OH as ligands to the Si=O moiety and used the combinatorial approach (see Figure S1 in…”

“…48 Yet the GAVs of D2 derivatives would be useful for predicting the thermochemistry of larger silicon oxide clusters such as Si 4 O 10 H 4 or Si 5 O 12 H 4 . 3,5 As the molecular analogy of D2, these clusters comprise of Si atoms bridged by two O atoms. 49…”

“…Organic silicon-containing compounds like siloxanes are frequently used precursors for the synthesis of silica (SiO 2 ) nanoparticles, coatings, and SiO 2 -containing nanocomposites. The combustion chemistry of specific precursor compounds such as silane (SiH 4 ), 1,2 tetramethylsilane (Si(CH 3 ) 4 ; TMS), [3][4][5] and tetraethoxysilane (Si(OC 2 H 5 ) 4 ; TEOS) [6][7][8] was studied in detail. In these studies, the related thermochemical data were developed and usually estimated for the specific reaction systems, and a generalized, self-consistent thermochemical database for the precursor compounds and reaction intermediates is unavailable.…”