BN coating

Fig. 5.33. Load-displaccmcnt records of monolithic mullitc, and SiC fiber reinforced mullitc composites with and without BN coating. After Singh (1988).

TiOi) result in substantial improvement in strength and toughness of the composites. The BN coating reduces the interface bond strength between the SiC reaction layer ind the mtitrix. A duplex coating of SiC/BN applied to the Nicalon... 

SEM micrograph of BN-coated Hi-Nicalon fiber for use as a reinforcement of a SiC/SiC-composite. (Source Nippon Carbon Co Ltd Japan). 

Coatings of h-BN are used in a wide range of applications due to the extraordinary properties of BN. BN coatings are used in the steel and iron... 

BN coating on SiC fibers or Al203 fibers reduces the thermal mismatch between fiber and matrix and also reduces fiber-matrix interfacial shear strength in ceramic matrix composites leading to higher overall strength and toughness. 

The excellent insulating and dielectric properties of BN combined with the high thermal conductivity make this material suitable for a huge variety of applications in the electronic industry [142]. BN is used as substrate for semiconductor parts, as windows in microwave apparatus, as insulator layers for MISFET semiconductors, for optical and magneto-optical recording media, and for optical disc memories. BN is often used as a boron dopant source for semiconductors. Electrochemical applications include the use as a carrier material for catalysts in fuel cells, electrodes in molten salt fuel cells, seals in batteries, and BN coated membranes in electrolysis cells for manufacture of rare earth metals [143-145]. 

Borazine is isoelectronic and isostructural with benzene. Poly(borazylene), a polymer of borazine and its derivatives, is reported extensively as a precursor of BN-coated ceramic libers.86 Polymeric borazine oxide derivative is claimed to be flame resistant (Figure 9.10).87... 

Fig. 8.15 Changes in interface microstructure in SiC fiber-reinforced BMAS glass-ceramic composites induced by exposure to high temperature oxidizing environments, (a) After tensile stress-rupture experiment at 1100°C, the 90° fibers show a distinct dual layer at the BN coating-fiber interface, (b) After thermal aging for 500 h at 1200°C, a subtle double layer appears at the same site, (c) Near the composite surface, the effects of thermal aging (and oxidation) are more pronounced.24...

R. W. Rice, BN Coating of Ceramic Fibers for Ceramic Fiber Composites, U.S. Patent 4,642,271, February 10,1987. 

Figure 3 Optical micrographs of fa) a cross section of a BN coated carbon fibres and (b) SEM image of the C/BN microcomposite. BN was obtained from (5)...

Figure 4 SEM image of a cross section of (5)-derived BN coated graphite sample...

A tetragonal form of BN can be prepared by vapor deposition on BN-coated Ta or graphite substrates at 1200-1600°C. The composition is close to BsoNx.g the density is 2.46 g/cm, and the lattice constants are a = 864.6 pm and c = 512.7 pmk Shock loading of diamond/BN mixtures produced several phases, including a tetragonal phase with the composition B2sN. ... 

Hollow BN fibers are made by depositing a coating of BN on carbon fibers, heating in an oxidizing atmosphere to form CO or CO2, and leaving a BN coating. The reaction between BF3 and NH3 at 1200-1400°C may be used . Yarn and BN/BN composites can be made with similar techniques (see 17.3.5.6). 

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