Method for producing pre-shaped amp;agr;-silicon nitride whisker compacts and loose whiskers for composite material reinforcement

摘要

Method for producing &agr;-silicon nitride whiskers. Silicon is blended with composition particles able to sublime without leaving a residue, such as naphthalene particles. The blend is compacted to a desired shape, after which the composition particles are sublimed from the blend to form a porous silicon precursor compact having the desired shape. The silicon precursor is reacted with a substance that releases free nitrogen, such as nitrogen or dry ammonia. The reaction is carried out at a temperature sufficiently high to form an identically shaped porous compact of &agr;-silicon nitride whiskers but sufficiently low to avoid subliming substantially all of the formed whiskers. Preferably, the reaction is carried out in a range between about 2100° F. and 2750° F. The shaped porous compact of &agr;-silicon nitride whiskers may be impregnated with a resin binder, a liquid metal, a colloidal suspension, an ionic solution or a gaseous material to form an isotropic composite. Alternatively, the compact of &agr;-silicon nitride whiskers formed by the method described above may be broken down by crushing or grinding to form individual whiskers. Preferably, silicon particles in powder form are mixed with about 5 to 20 weight percent of composition particles, such as naphthalene particles, and treated so that the silicon particles are coated by the composition particles. The coated silicon particles are blended with more of the composition particles, followed by the steps outlined above to produce a loose compact of &agr; -silicon nitride whiskers. A loose compact so produced breaks down more easily into individual whiskers, which whiskers can be added as reinforcement to metal, ceramic or resin molding powders and then formed by conventional methods, such as compacting, to produce composite parts in which &agr;- silicon nitride is the reinforcing phase.