Mechanical & Industrial Engineering

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The mission of the Mechanical & Industrial Engineering Department is to serve the State of Montana, the region, and the nation by providing outstanding leadership and contributions in knowledge discovery, student learning, innovation and entrepreneurship, and service to community and profession.

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Author: search.filters.author.Aller, Josh

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    Influence of silicon on high-temperature (600 degrees C) chlorosilane interactions with iron
    (2017-02) Aller, Josh; Swain, Nolan; Baber, Michael; Tatar, Greg; Jacobson, Nathan; Gannon, Paul E.
    High-temperature (>500 °C) chlorosilane gas streams are prevalent in the manufacture of polycrystalline silicon, the feedstock for silicon-based solar panels and electronics. This study investigated the influence of metallurgical grade silicon on the corrosion behavior of pure iron in these types of environments. The experiment included exposing pure iron samples at 600 °C to a silicon tetrachloride/hydrogen input gas mixture with and without embedding the samples in silicon. The samples in a packed bed of silicon had significantly higher mass gains compared to samples not in a packed bed. Comparison to diffusion studies suggest that the increase in mass gain of embedded samples is due to a higher silicon activity from the gas phase reaction with silicon. The experimental results were supported by chemical equilibrium calculations which showed that more-active trichlorosilane and dichlorosilane species are formed from silicon tetrachloride in silicon packed bed conditions.
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    High-Temperature (550-700 degrees C) Chlorosilane Interactions with Iron
    (2016-08) Aller, Josh; Mason, Ryan; Walls, Kelly; Tatar, Greg; Jacobson, Nathan; Gannon, Paul
    Chlorosilane species are commonly used at high temperatures in the manufacture and refinement of ultra-high purity silicon and silicon materials. The chlorosilane species are often highly corrosive in these processes, necessitating the use of expensive, corrosion resistant alloys for the construction of reactors, pipes, and vessels required to handle and produce them. In this study, iron, the primary alloying component of low cost metals, was exposed to a silicon tetrachloride-hydrogen vapor stream at industrially-relevant times (0-100 hours), temperatures (550-700 degrees C), and vapor stream compositions. Post exposure analyses including FE-SEM, EDS, XRD, and gravimetric analysis revealed formation and growth of stratified iron silicide surface layers, which vary as a function of time and temperature. The most common stratification after exposure was a thin FeSi layer on the surface followed by a thick stoichiometric Fe3Si layer, a silicon activity gradient in an iron lattice, and finally, unreacted iron. Speculated mechanisms to explain these observations were supported by thermodynamic equilibrium simulations of experimental conditions. This study furthers the understanding of metals in chlorosilane environments, which is critically important for manufacturing the high purity silicon required for silicon-based electronic and photovoltaic devices.
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