This PhD-thesis contain two separate topics. The first focuses on the co-pyrolysis of silane at IFE, whereas the second activity of this work includes gas-phase reactions of siloxanes at the University of Oslo.
1. Gas Phase Chemistry of Silane Pyrolysis and Co-pyrolysis; it's Application in Energy Material Production
Silane pyrolysis is an important reaction in the production of silicon and silicon-containing compounds. Silicon is widely used in solar cells and the semiconductor industry. Silicon-containing materials such as silicon nitride are used as anode material in Li-ion batteries. Studying the reactions in silicon pyrolysis is useful in understanding the production process of silicon, silicon nitride, or similar materials.
Pyrolysis of silanes is a complex cascade of reactions. Silane converts to a series of higher-order silanes before particle production. This study uses a simplified pyrolysis reactor to study the intermediate gas-phase reaction. Additionally, ammonia is added to the existing setup and the instrument is modified for the detection of the new products. The formation of higher-order silane during monosilane pyrolysis is reported. Addition of ammonia results in the formation of amino silanes. The work on phase 1 was mainly conduced from 2018-2020.
2. Measuring rate constants for gas-phase reactions of linear and cyclic siloxanes with OH radicals using PTR-TOF-MS
Siloxanes are compounds with Si-O-Si bonds. They have industrial applications such as in the production of additives, cleaners, and foam suppressants. Siloxanes are also found in consumer products such as detergents, lotions, and shampoos. In a 2010 study, NIVA and Stockholm University found accumulated D5 siloxane in aquatic species in Lake Mjøsa and in Randsfjorden, Norway. D4 siloxane is associated with adverse effects on the reproductive health of humans. In 2020, the European Chemical Agency (ECHA) limited the concentration of D4, D5, and D6 in consumer products to 0.1%.
Most siloxanes emitted to the environment remain in the atmosphere, where they are slowly broken down by OH radicals. The rate at which these OH reactions occur have been studied since the 1990ies, but some of the measurements disagree beyond their uncertainty bounds. Additional studies are thus needed for better constraining the atmospheric lifetimes of siloxanes. We have carried out extensive kinetic studies on the reaction of linear (L3, L4, L5) and cyclic (D4, D5, D6) siloxanes with OH radicals using proton-transfer-reaction time-of-flight mass spectrometry (PTR-ToF-MS) as a method for sensitive detection of siloxanes in air. The work on phase 2 was mainly conducted from 2020-2022.
The PhD work has resulted in a more detailed knowledge on the pyrolysis processes of silane decomposition, and in particular that of co-pyrolysis. The co-pyrolysis of silicon with ammonia gas has been relevant to the development of silicon nitride material, which IFE has developed internally since 2014 and has an extensive patent portfolio on.
Additional understanding about how this material forms, and especially the sub-stoichiometric material can be very relevant to both research and industry actors that are working within production of battery material anodes.
The second part of the PhD thesis can be very useful to better understand the decomposition of siloxanes in the atmosphere, which currently poses a potential health hazard. Additional information is needed to reduce the reproductive health risks of atmospheric siloxanes, and the results of the PhD thesis can hopefully shed some light on this.