Heat Resistant Fibers

By:Haider Ali (15-NTU-0049)Haseeb-ur-Rehman (15-NTU-0051)Mohsin Ali (15-NTU-0066)Khalid Mehmood (15-NTU-0189)

Saqib

Outline:IntroductionExamples of heat resistance fibresCeramic materialsCeramic fibersCeramic raw materialsProductionClassification of ceramic fibersProperties of ceramic fibersUses of ceramic fibers

Introduction:Heat resistant fibers are all man made

fibers when we talk about very high temperatures e.g. above 500 ° C.

These are all high performance fibers.

Examples of Heat Resistance Fibers:

NomexCeramic fibersGlass fibersCarbon fibers

Ceramic Materials:The word ceramic is derived from the Greek words

kéramos.kéramos - ground, clay; kerameoús - made of clay. The term covers inorganic non-metallic materials that

have been permanently hardened by firing at a high temperature.

The structural ceramic matrix composites (CMC) are used in reinforcements at temperatures above 1000°C.

Ceramic Fibers:

The definition of ceramic is often restricted to inorganic non-metallic polycrystalline solids, as opposed to the noncrystalline glasses.

The distinction between ceramic and glass has become difficult now, because ceramics produced from new precursors or sol – gel routes can be amorphous.

Ceramic Raw MaterialsCeramic raw materials (ceramic powders) can be divided into two groups

Production:The ceramic fibers can be produced by either:

direct process

or indirect process.

Direct process:

• The pre-treated fibers are spun through melt spinning.

• The spun fiber is then treated to form actual ceramic fibers.

Transition of pores during treatment

Heat treating:• Organosilicon polymers such as

polydimethyl silane are used.• The melt spun filament is heated in the

air to 190 °C to crosslink the polydimethyl silane molecules by oxygen

• Then heat treated at 800-1500 °C in nitrogen or vacuum to form crystalline structure.

• The conversion to ceramic fibers occurs by pyrolysis above 1200 °C.

Indirect method: In the indirect process, ceramic fibers are not obtained by spinning process,

but by using some other approach. The process involves two steps

• Step 1: Organic substrate fibers are soaked with the precursor material or precursor material is deposited on the surface.

• Step 2: The inorganic fibre is then

formed by pyrolysis of the organic template fibre.

By Chemical vapor deposition• Both tungsten and carbon cores are

used as templates for making silicon carbide fibres by CVD route.

• Various carbon-containing silanes have been used as reactants.

• In a typical process, with CH3SiCl3 as the reactant, SiC is deposited on the core as follows:

During fabrication of ceramic products significant structural changes are observed

Classification of Ceramic Fibers:

Chemically these fibers have different compositions and thus these fibers can be broadly divided into following two categories: Oxide fibres : Silica fibres, alumina fibres, alumina-silica fibres, alumina zirconia fibres

Non-oxide fibres: Silicon carbide(SiC), silicon carbon nitride, silicon nitride(SiN)

Ceramic fibers are • hard, • have low densities (compared to metals) • high compressive strength• very good thermal resistance• strength at higher temperature.

Properties of Ceramic Fibers:

Working Temperature :      1,800 °F. for Continuous Use, 2300 °F Maximum

Specific Heat (@2000°F):     0.27 Btu/lb °F pH Range: 2-12

• Due to their notable high temperature performance, these are useful as reinforcement in metal and ceramic matrix composites, where the structures are required to operate at high temperature.

Uses of Ceramic Fibers:

• Ceramic fibers are used in various applications which include high temperature insulating material in the form of mats, blankets and boards, fire protection.

•High temperature insulation seals and gaskets•Protective blankets, curtains, covers, pads and wrapping•Expansion joint fabric, safety clothing

Thank you