Chapter 37. Prototype Reactor for Scale-Up of Si-N-O Fiber Production

Summary

A mat of amorphous silicon oxynitride (Si-N-0) can be grown at 1723 K under flowing ammonia on a precursor powder mixture consisting of fine silica, silicon carbide and titanium particles spread on a SiC substrate plate. Single fibers sampled from the mat surface were found to possess outstanding high- performance properties with respect to chemical, mechanical as well as structural stability. The fibers are therefore promising candidates for use as reinforcement in CMC's for high-temperature applications. In the laboratory reactor, however, the production rate is a mere 3 g of fibers per batch run. In order to allow the manufacture of preforms and test bodies, an increase in the production rate to 50g of fibers per batch run was desired. This aim has been achieved by the scale-up of the laboratory furnace to a high-temperature prototype reactor.

Based on the knowledge obtained from the laboratory reactor, it could be concluded that an increase in the fiber production rate could be achieved by increasing the reaction area between the precursor powder and the flowing ammonia. The results of previous experiments also suggested that extending the dwell time at reaction temperature may further improve the production rate. The fiber growth area was therefore enlarged by a factor of 30 from the laboratory reactor to the prototype reactor. Experiments have proven that Si-N-0 fibers can be grown in the new reactor and at present up to 62 g of fibers can be produced per batch run. However, the fibers from the prototype reactor are smaller in diameter and possess a higher oxygen content then those grown in the laboratory tube furnace. These differences are assumed to be due to variations in gas flow conditions. To facilitate the control of the gas phase in the reaction zone, an IR-spectrometer which allows in-situ analysis of the gas atmosphere has been adapted to the prototype reactor.