Boron nitride fibers mechanical properties

Green fibers derived from melt-spinnable polymers have been cured in an ammonia atmosphere, then pyrolyzed in ammonia and nitrogen atmospheres to generate at 1800 °C boron nitride fibers with excellent mechanical properties. It was interesting to note that boron nitride fibers, with controlled mechanical properties and crystallinity, could be produced through simply changing the meltspinning conditions (Table 14.1) [35]. 

Fiber reinforced ceramic matrix composites (CMCs) are under active consideration for large, complex high temperature structural components in aerospace and automotive applications. The Blackglas resin system (a low cost polymer-derived ceramic [PDC] technology) was combined with the Nextel 312 ceramic fiber (with a boron nitride interface layer) to produce a sihcon oxycarbide CMC system that was extensively characterized for mechanical, thermal, and electronic properties and oxidation, creep mpture, and fatigue. A gas turbine tailcone was fabricated and showed excellent performance in a 1500-hour engine test. 

The fiber/matrix interfece is a key area of study since the interface controls if the CMC behaves as a composite or not [4]. To assure composite behavior a weak bond is desired and this is the reason Carbon or Boron Nitride is used as the fiber interface coating [S]. The interfacial shear stress is a key property since it controls (influences) the prevalent damage mechanism and the resulting non-linearity [6-7]. 

Support is one of the important factors affecting the performance of catalyst, which include its type, composition, pore structure, surface properties and mechanical strength etc. The supports used include activated carbon, nanocarbon tube, carbon molecular sieves and carbon fiber, oxide, zeolite molecular sieve, alkali metal exchanged X- and Y-type molecular sieve,carbon covered alumina and boron nitride etc. 

Metallized metal, polymer and carbon. Types la, lb, and Ic, are variants of the solid metal fibers and are distinguished therefrom by a metal layer upon the base fiber s periphery. They are fabricated by electrochemical deposition or grafting of a suitable metal, such as nickel, copper, aluminum, and their alloys, as a thin layer upon the fiber s surface. In general, these variants evolved in attempts to improve upon one, or more, properties of the Type 1 fibers. Applications of metal-on-metal. Type la, are typified by the structures described in 1972 by McNab(26) who used refractory, non conducting, base fibers for example, aluminum oxide and boron nitride, upon which were deposited films of noble metals. McNab s objective was to improve upon the strength and flexibility of Type 1 fibers by selecting a base fiber for its mechanical... 

---