Measurements of high-temperature silane pyrolysis using SiH4IR emission and SiH2 laser absorption
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abstract
The thermal decomposition of silane highly diluted in argon was observed behind reflected shock waves over the temperature range from 1060 to 1730 K and pressures between 0.6 and 5.0 atm, making this the first SiH 4 decomposition study to thoroughly investigate pressures above 1 atm. Silane and silylene time histories were monitored using the infrared emission of SiH 4 near 4.7 m and laser absorption of a SiH 2 -X transition near 579 nm. Reaction rate coefficients for the first- and second-order forms of the decomposition reaction SiH 4 + M = SiH 2 + H 2 + M were determined from the species measurements for M = Ar. The effects of competing reactions were considered using a detailed reaction mechanism. The bimolecular rate constant over the pressure range considered herein was determined to be k 1a = 7.2 10 15 exp(-E/RT), with k 1a in cm 3/mol s and E = 45.1 1.2 kcal/mol. This second-order rate coefficient describes the silane decomposition reaction over the entire range of temperatures and pressures herein and shows good agreement with the results of previous studies at similar temperatures as well as those at lower pressures and at temperatures above and below the values herein. The implication of the second-order reaction rate is that the silane decomposition is still in the low-pressure limit at total mixture pressures as high as 5 atm. A pressure-dependent rate is therefore not needed for SiH 4 decomposition over a wide range of conditions of practical interest when the reaction is simply expressed in the bimolecular form.
