Silicon Nitride Fibers by Laser Chemical Vapor Deposition

Laser chemical vapor deposition (LCVD) silicon nitride fiber growth is proposed, to make fibers which have the strength and oxidative stability required for advanced high temperature structural applications. This method has been demonstrated to yield continuous, high strength fibers of materials such as boron, silicon, and others, with diameters in the range 10-30 microns, tensile strengths up to 7 GPa (10 6 psi), and high modulus. Preliminary experiments have demonstrated silicon nitride fiber growth but further research is required to determine conditions for making the fibers with superior properties. The LCVD process grows fibers by deposition at the hot spot created by a focussed laser beam. It can yield fibers with extremely uniform properties, e.g., +/- 5% in tensile strength, which result in part from an unique control mechanism. The fiber automatically grows to a position near the laser focal point where the growth rate equals the fiber pulling rate, maintaining a reproducible and constant fiber growth temperature if the fiber pulling rate is kept constant. The same mechanism supports economical design and operation of fiber production reactors. LCVD growth of continuous, small diameter (10-40 microns), high stength ( > 7 GPa = 10 6 psi tensile strength), stoichiometric and/or chemical composition-controlled silicon nitride fibers will be developed and optimized.