Computational Study of Surface Deposition and Gas Phase Powder Formation during Spinel Chemical Vapor Deposition Processes
MetadataShow full item record
Chemical vapor deposition (CVD) processes are often employed to produce high quality materials. In some applications, a relatively fast deposition rate is required to produce thick pieces of material, e.g., on the order of centimeter, in an economical manner. However, in some processes the formation of solid nuclei or powder in the gas phase can be a major obstacle to increasing the deposition rate. The homogeneous powder formation reaction can compete with the surface deposition reaction and consume the gas phase reactants, thus reducing the available material to grow on the substrate surface. Understanding the thermodynamics as well as kinetics of these two competing reactions helps elucidate the reaction conditions that best reduce powder formation and increase deposition rate. As an example where gas phase powder formation can significantly limit the surface deposition rate CVD growth of spinel (MgAl2O4) is investigated. In this CVD process, reverse water gas shift (rWGS) is employed to generate water, which reacts with either chlorides or fluorides of magnesium and aluminum to produce spinel. Density functional theory (DFT) was used to study the thermodynamics of surface reactions of spinel deposition. This study shows that the surface reaction to form spinel is thermodynamically favorable. However, the spinel deposition could be limited by its surface kinetics and/or competition for reactants with gas phase powder formation. We have employed molecular dynamics (MD) with a reactive force field (ReaxFF) to simulate gas phase rWGS and powder formation. These simulations show that the reactants’ residence time should be minimized to reduce powder formation. A comparison of magnesium and aluminum chlorides with their corresponding fluorides indicates that fluorides are better in reducing powder formation.
Showing items related by title, author, creator and subject.
Veder, Jean-Pierre M. (2010)This thesis reports on a methodology for the nanocharacterization of complex electrochemical systems. A series of powerful techniques have been adapted and applied to studies of two scientifically important electrochemical ...
Muryanto, Stefanus (2002)Scale formation is one of the persistent problems in mineral processing and related industries. One of the main components of the scale is frequently gypsum or calcium sulphate dihydrate (= CaS04.2H20). Gypsum is formed ...
Cai, R.; Yuan, T.; Ran, R.; Liu, X.; Shao, Zongping (2011)Spinel-type Al3+-doped Li4Ti5O12 oxide with the nominal composition of Li4Ti4.85Al0.15O12 was synthesized by a cellulose-assisted glycine–nitrate combustion process at reduced temperatures. X-ray diffraction characterization ...