Coating of fibrous substrates by CVD; analysis of the fiber evolution

In this work the application of CVD technologies for inorganic coating of fibrous substrates is addressed. In analyzing this reaction system it is important not only to consider the transport phenomena in the gas phase but also to take the fiber evolution into account. In CVD applications to the synthesis of inorganic fibers, as in a host of others, deposited layers can reach space scales comparable to the substrate dimensions. In such cases deposit-substrate interaction processes (such as corrosion of the core) might become important and cause the fibers to evolve in space and time. In this study the authors want to stress the importance of the fiber evolution. Based on boundary layer assumptions for the gas phase, a one-dimensional "moving boundary" model for the deposition surface is formulated. The governing equations are solved numerically and analyzed for operating conditions in the actual experimental range. The results serve to identify possible causes for fiber failure under load as well as motivate alternate reactor configurations to optimize the process.