Experimental and numerical study on the influence of equivalence ratio on key intermediates and silica nanoparticles in flame synthesis

Abstract

Tetramethylsilane is a precursor often used for the production of flame-synthesized silica nanoparticles or coatings. This study investigates the chemical reaction mechanism of tetramethylsilane in a series of H2/O2/Ar low-pressure (p = 30 mbar) flames from fuel-lean to slightly fuel-rich flame conditions (φ=0.8, 1.0 and 1.2). Mole fraction profiles are obtained by molecular-beam mass spectrometry. The experimental data are compared to simulations using a recently published reaction mechanism. The present study reveals the influence of the flame composition on the depletion of the precursor TMS, the formation of its main carbon-containing products (e.g. CO2 and CO) and the main silicon-containing intermediates (e.g. Si(CH3)3(CH2)OO), Si(OH)4, SiO2, Si4O10H4) appearing along the routes of particle formation. TEM images of synthesized particles reveal that the nanoparticles obtained from the gas-phase synthesis are spheres with a low degree of agglomeration. The particle size distribution appears to be dependent on the equivalence ratio of the synthesis flames and the changes can tentatively be traced to different particle formation pathways. The data set provided in this work can serve a basis for improvements to the reaction mechanisms of the Si/C/H/O system that are urgently needed to improve particle synthesis processes.