Ceramics for Sustainable Energy Technologies with a Focus on Polymer-Derived Ceramics - Novel Combustion Concepts for Sustainable Energy Development - page 504

electron beam irradiation in inert atmosphere. The use of lower electron beam doses
reduces signi cantly the cost of the processing of ceramic SiCN fibers. Ceramic

SiCN fibers from cured ABSE fibers are processed by continuous pyrolysis at a low

temperature of 1,100 ° C. The SiCN fibers have adjustable diameters from 15 up to

120 m, a tensile strength up to 1.2 GPa and an oxidation stability comparable to

that of the Hi-Nicalon

µ

fibers (Hacker et al. 2001b ; Motz et al. 2002a , b ; Motz 2006 ;
Kokott and Motz 2007 ). The fracture surfaces of a Hi-Nicalon ceramic SiC ber

and an ABSE-derived ceramic SiCN fiber are shown in Fig. 4 .

The rheological properties of ABSE and the mechanical stability of the green

fibers were further improved by adding dispersed multiwalled carbon nanotubes
(MWCNTs) to the polysilazane matrix. The addition of just 0.5 wt% carbon
nanotubes improves the viscoelasticity of the polymer melts, allowing the pro-
cessing of reinforced ceramic C/SiCN

fibers via melt spinning and curing via
electron beam (300 kGy). The ceramic C/SiCN C can

reach tensile strengths about 50 % higher than the ABSE-derived ceramic SiCN

fibers pyrolyzed at 1,100 °

fibers without carbon nanotubes (Kokott et al. 2008 ).
In a cooperation between the University of Bayreuth and the company Clariant
GmbH, a new method was developed to modify two types of commercially available
liquid oligosilazanes, ML33 and HTT1800 (Fig. 5 shows their chemical structures),
into solid meltable polysilazanes by a selective cross-linking via dehydrocoupling of
N - H and Si - H groups with tetra-n-butylammonium fluoride (TBAF) as a catalyst.
The termination of the reaction with calcium borohydride as inhibitor allows the

Fig. 4 Fracture surfaces of non-oxide ceramic fibers: a Hi-Nicalon and b ABSE-derived SiCN
fiber. Reprinted with permission from Flores et al. 2014 . Copyright 2014, John Wiley and Sons

Me H H

Si Si Si

Si
Me

N
H

N
H

N
H

N
H Me Me Me

0.33n 0.67n 0.2n 0.8n

ML33

HTT1800

Fig. 5 Chemical structures of liquid oligosilazanes ML33 and HTT1800. Reprinted with
permission from Flores et al. 2014 . Copyright 2014, John Wiley and Sons