ceramic fibres

Vikas Singh IIT Delhi .

CONTENTS Introduction1. Ceramic vs glass2. Classification3. Need Basic terminology1. Porcelain2. Feldspar,kaolinite3. Clay4. Mullite5. Sintering & Pyrolisis

Fibre production Alumina fibre by sol gel process Recent developments Pros and cons Conclusion


INTRODUCTIONCeramic fibre is a collective term used for all the inorganic non-metallic fibres that are mostly crystalline.(Trade names- Nextel, Nicalon,Tyarnno,Sylramic etc)

Glass fibre is confined to those made from solidifying glass melts and mostly amorphous.

NEED- Polymeric fibres degrade before 400 0C Glass fibres before 700 0C Carbon fibre before 450 0C (oxidative conditions) Ceramic fibres upto 1500 0C or above !!!!!


# Key features stiffness, strength & high temperature performance– AEROSPACE application at earliest.

# commercial reality are Silicon carbide (SiC) and Alumina fibre (∝-Al2O3)

# SiC stable upto 700 0C Al2O3upto 1400 0C


FibresInorganic Organic

Carbon fibre

Polymeric

Metallic Non metallic

Ceramic Glass & mineral

OxideNon

oxide

Ceramic fibres under classification


TERMINOLOGYPorcelain- An aluminosilicate from clay. Similar in microstructure to brick, pottery etc.

Mullite- silicate mineral (a ceramic type) present in porcelain. 3Al2O32SiO2 or 2Al2O3 SiO2


Feldspar and Kaolinite- Feldspar is a mineral that gives Kaolinite (platelets) on weathering.

Source- wikipedia


Clay- mixture of kaolinite etc and pottery is made of it.

Common Ceramic- clay+water. Water helps in pliability so that kaolite pletelets can slide over. Its removal leads to crystalline structure.

Pyrolysis- pyr "fire" and lysis "separating“. Organic matter in absence of oxygen. Why CROSSLINKING important ?? (monomer,shape)


Sintering- process of producing objects from powders. Principle of atomic diffusion. Ice cubes in water !!!

(Powder compacting sintering cannot be in fibres)

Bulk ceramic Vs ceramic fibre (finer microstructure, less flaws and reduced large sized defects)


FIBRE PRODUCTIONDirect process – spun to form“green fibre” (intermediate).

Spinning dope based on1. Molecularly dispersed– molecular level

(ions)--additives2. Colloidally dispersed- sol gel3. Coarse ceramic powders- slurry process4. Inorganic polymers- precursor polymer

process


Precursor system

(brittle , flaws)

Solvent/melt spinning

Green fibre

Pyrolysis/SinteringCeramic fibre

Fibre before and after sinteringSource-Materials Letters 65 (2011) 2717–2720


Indirect process –

1. CVD- gas phase deposition of ceramic material

2. Relic process- cellulose in salt solution---burnt off---ceramic

percursor deposited on the surface or fibre is soaked in pre ceramic precursor-

pyrolysis


CVD & SOL GELCVD- Chemical vapour deposition Diameter and flexibility….. 10 micron vs 100 micron Oldest process for non oxide ceramic fibres Eg. SiC vapour deposition on Tungsten, Molybdenum or carbon fibre. Role of interface ??

Source-Composites Science andTechnology 32 (1988) 31-55


Vertical 2 m reactorTemperature 1400-1500 C1-2 min residence time ReactionCH3SiCl3 SiC + 3HCl

AdvantagesHigh deposition rateIsotropic and dense coating

DisadvantageHigh deposition temperatureGases may be corrosive or explosivesCostly process


Sol gel-used for Alumina

Advantages-Low temperature of processingHomogenity of productUniform diameter

Source- http://www.gitam.edu/

http://www.gitam.edu/eresource


OXIDE VS NON OXIDE FIBRES

OXIDE-Al2O3, SiO2, mullite

basedoxidisableProne to creep at 1100 0CLess complicated process

NON OXIDE- SiC, SiCN basedStable upto 1500 0CLess creepMainly amorphous

Source- Fibers for Ceramic Matrix CompositesBernd Clau ß


SiC and Alumina based commercial fibres


ALUMINA BY SOL GELAluminiumtrisopropoxide+water 1M solution100 ml taken added 10%,15%,20% hydroxyethylcellulose (HEC) for spinnability sol spun to gel in ammonia solution drying at room temp sintering at 1600 0C for 2 hoursCharacterizationDTA,TGA,Viscometry of dope


TGA analysisDTA analysis


Viscocity is high for thehigher organic content


ADDITIONAL Si gives flexibility but creep. So minimum Si (Zr,Ce)O2stablized zirconium fibre better than Y203 stablized. Melt spinning Vs sol gel. (Stiochiometry) Acetylacetone (acac)-chelating agent, drying control-DMF

Constant DMF-to-Zr ratio of 2.

Source-Materials Science and Engineering, A 189 (1994) 311-317


RECENT DEVELOPMENTS Green fibre morphology

Variable dia fibresSource- ICFT website


Si-B-N fibre – 1500-1800 0CPolymeric precursor-crosslinking problem…New route by condensation polymerisation of((CH3NH)4Si) and ((CH3NH)3B) Si/B ratio variation gives different performance

Electrospinning !!

Electrospun alumina fibre (SEM image)


DISADVANTAGES Most ceramic fibres only on laboratory scale Even sophesticated techniques cannot make 100% oxygen free fibres Carcinogenicity Dust problem


WHAT WE LEARNT...... Mainly used for high temperature applications (even upto 2000 0C) Silicon carbide and Alumina are used commercially Can be melt, dry or wet spun, former gives better economy and homogenity Sol gel and CVD techniques are still very useful Oxide containing ceramic fibres degrades early Ceramic fibre’s dust can be carcinogenic


REFERENCES1. X.Wang et l, Materials research bulletin 46 (2011)

2398-24022. H.Yu et al, Materials letter 74 (2012) 247-2493. X.Chen et al, Journal of Non-Crystalline Solids 355

(2009) 2415–24214. X. Zhao et al, Materials Letters 65 (2011) 2717–

27205. Bio-inorganic Hybrid Nanomaterials. Edited by E.

Ruiz-Hitzky, K. Ariga, Y. M. Lvov6. http://ntp.niehs.nih.gov/go/roc127. P.K. Chakrabarty et al. / Journal of the European

Ceramic Society 21 (2001) 355-3618. G. Emig et al. / Sol-gel process for spinning of

continuous (Zr, Ce) O2 fibers

http://ntp.niehs.nih.gov/go/roc12

http://ntp.niehs.nih.gov/go/roc12


9. M. Balasubramanian / Journal of Materials Processing Technology 173 (2006) 275–28010. Chem. Mater., Vol. 8, No. 8, 1996 205711. V.M.Kikko et al, Scripta mater. 44 (2001) 249–25512. www.wikipedia.org/sintering13. www.wikipedia.org/pyrolysis14. Xi Zhao, et al, Materials Letters 65 (2011) 2717–2720

http://www.wikipedia.org/sintering

http://www.wikipedia.org/pyrolysis


tHANK YOU(Queries…???)

ceramic fibres

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