Ceramics for Sustainable Energy Technologies with a Focus on Polymer-Derived Ceramics - Novel Combustion Concepts for Sustainable Energy Development - page 500

2.1 Ceramic Fibers

Ceramic fibers, which combine high thermal and creep

resistance with structural stability. Their high tensile strength >2 GPa and stiffness
>200 GPa, together with the capacity to withstand temperatures >800

fibers are high-performance

°

C, make
them attractive materials to be used as reinforcement in metal (MMCs) and CMCs.
Ceramic fibers. Oxide

ceramic fibers are mainly Al 2 O 3 (e.g., Nextel 610) and Al 2 O 3 /SiO 2 (e.g., Nextel
720)-based

fibers can be classi ed into two groups: oxide and non-oxide

fibers are very stable against oxidation at high
temperatures. In spite of their high oxidation resistance, the creep resistance of
oxide

fibers. These types of

fibers is limited to temperatures up to 1,100 ° C due to the formation of larger

grains and, consequently, fibers are mostly based

on SiC(O) and SiCN(O) systems, but studies with SiBCN and BN are frequently
found in the literature. In contrast to oxide

fiber failure. Non-oxide ceramic

fibers, non-oxide fibers have higher

creep resistance at temperatures up to 1,450 ° C and their oxidation behavior

*

depends on the fiber processing conditions and the fiber microstructure.

2.1.1 Introduction to Processing, Structure, and Properties of Ceramic
Fibers

Ceramic fibers, which are currently commercially available, typically are processed

either using the solgel process and chemical vapor deposition (CVD), or using
preceramic polymer processing.
In preceramic polymer processing, organometallic polymers are used as pre-
cursors for

cally
organosilicon ones, dates back several decades when Fritz et al. ( 1965 ) and Yajima
et al. ( 1975 ) reported the

fiber spinning. The use of organometallic polymers, more speci

first SiC materials obtained from polycarbosilane pre-

cursors. These findings marked the beginning of extensive research on silicon-based

inorganic polymers, leading to the development of ceramic Si 3 N 4 and SiC fibers.
A recent review of the ceramic

fibers from preceramic precursors provides a good
overview of this approach and the original references for the work summarized
below (Flores et al. 2014 ).
A high molecular weight and adequate viscoelastic properties of the melt are
necessary properties of the organosilicon polymer to enable a stable spinning
process and stretching of the fibers without breaking of the filament. In a melt

spinning process, uncured green fibers are processed and subsequently cured

chemically, thermally, or by electron beam irradiation. This curing step is necessary
to avoid the remelting of fibers during the last stage, which is the conversion of the

polymer to a ceramic fiber by pyrolysis. Figure 3 shows the manufacturing process

of ceramic fibers employing the preceramic polymer route, as well as important

parameters for a controllable processing of ceramic bers.

fibers show a strong correlation between the micro-
structure, mechanical, and thermal properties, which in turn depends on the

Polymer-derived ceramic