Applications

Applications of Si/B/N/(C) ceramics

Ceramic coatings and infiltrations

Ceramic parts made from carbon containing materials, e.g. graphite, carbon fiber and CFC (carbon fiber-reinforced carbon), are already applied in many fields. However, low oxidation stability of carbon limits their suitability for many applications. Fortunately, SiBNC coating of carbon containing materials overcome these limitations.

Graphite cube coated with SiBN₃C in oxyhydrogen flame

Fibers

SiBN₃C ceramic fibers are spun from predensified N-methylpolyborsilazane, pyrolyzed at 1500 °C. They have a very smooth surface and very constant diameter. They keep the amorphous state at least up to 1800 °C without any significant microstructural changes, resulting in remarkably good high-temperature creep-resistance. Even better, the formation of only a thin and crack-free amorphous SiO₂ layer, when exposed to air at 1500 °C, causes considerably larger oxidation stability compared to those of the standard non-oxide materials, e.g. Si₃N₄ and SiC.

SiBN₃C fibers prepared at Fraunhofer Institute for Silicate Research, Würzburg

The SEM picture of SiBN₃C fibers

SiBN₃C fiber weavings for ceramic matrix composites

Movie: Example for the resistivity of

Si/B/N/(C)- Fibers.

Phosphors for LEDs

Thermally and chemically stable and highly pure amorphous Si₃B₃N₇ ceramic surprisingly serves as a host matrix for activators to be used as a new class of phosphors for LED applications^*. Unlike the crystalline hosts, there is no need to replace any ion from the host lattice with activators. This brings a significant advantage over conventional phosphors that more than one activator ions can easily be incorporated into amorphous matrix, which enables tuning the emission color. Even better, the synthesis method, i.e., the polymer route, may enables to coat LEDs without requiring any resin, which is impossible with conventional solid state routes.

Photoluminescence spectrum of Eu²⁺ doped amorphous Si₃B₃N₇ ceramic

^* H. Cakmak, M. Jansen, German Patent Application, DE 10 2006 051 757.1, 2006.