C ERAMIC NANOPARTICLES FOR THERMAL SPRAYING KE-31.5530 Nanoparticles Maria Oksa

CERAMIC NANOPARTICLES FOR THERMAL SPRAYING

KE-31.5530 Nanoparticles

Maria Oksa

CONTENTS

Background Thermal spraying Materials

Synthesis methods for ceramic NPs Drawbacks Analysis and characterization Case studies of ceramic nanoparticle synthesis Summary References

KE-31.5530 Nanoparticles / Oksa

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THERMAL SPRAYING SHORTLY

Plasma, HVOF and CJS spraying Metals, ceramics, cermets in powder form Wear and corrosion resistance, hardness, electrical properties etc.


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Energy

Powder

Substrate

Melted particles form lamella structured coating

Gas and particle stream

Silicon carbide SiCHigh melting point, hardness, wear

and chemical resistance, electrical properties

Used in electrical industry, high temperature applications, reinforcement for ceramic composites

CERAMICS FOR THERMAL SPRAYING Oxides: Al2O3 and TiO2

Carbides: WC and SiC


Nanosized titania TiO2

Unique structural, electrical, optical, magnetic and chemical properties

Use as white pigments, in photo catalysis, solar cells, water and air purification, etc.

Tungsten carbide WCHigh melting point, hardness,

oxidation resistance, electrical conductivity

Applications e.g. cutting tools and wear-resistant parts

Nanosized alumina Al2O3

High strength and toughness, electrical resistance

Use e.g. for electronics and high temperature applications

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SYNTHESIS METHODS OF CERAMIC NPS

TiO2

Wet-chemical synthesis by precipitation of hydroxides from salts

Sol–gel processes Microemulsion-mediated methods Gas phase (aerosol) synthesis

Al2O3

Mechanical synthesis (milling) Vapor phase reaction Precipitation Hydrothermal method Combustion Sol–gelKE-31.5530 Nanoparticles / Oksa

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WCDirect carburization of W powderSolid state metathesisReductions-caraburizationMechanical / reaction millingPolymeric precursor routes using

metal alkoxides

SiC• Si metal direct carbonization• CVD (chemical vapor deposition)• Thermal plasma synthesis• Carbothermal reduction of silicon

dioxide• Sol-gel

EXAMPLES OF SYNTHESIS METHODSSol-gel method Use of precursor, solvent, catalyst, surfactant Solution fabrication & evaporation amorphous

gel drying possible calcination High purity, high chemical activity

Thermal plasma synthesis Vapor-phase precursors with plasma rapid

quenching homogeneous nucleation High-purity particles, suitable especially for

carbides and nitrides

Flame aerosol synthesis Oxidation of vapor in atmospheric pressure

reactor ( metal oxides, e.g. TiO2) Safe and flexible, high purity particles with

different sizes and phase composition, commercial scale


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Tong 2006

Mirjalili 2010

DRAWBACKS IN NPS SYNTHESIS METHODS

Strong tendency to agglomerate during synthesis and/or subsequent processing

Expensive Raw material Complex technique High temperature and pressure

Time consuming Low efficiency Impurities to produced particles

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ANALYSIS AND CHARACTERIZATION X-ray diffraction

Phase structure Rheometry analysis Viscosity measurement Thermal analysis (TGA, DTA)

Evaporation, reactions and phase transformations Electron microscopes SEM, TEM

Microstructure, size and shape Surface area analyser Dynamic laser light scattering method

Particle size


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CASE 1SPRAY PYROLYSIS FOR TITANIA SYNTHESIS Low-pressure spray pyrolysis (LPSP)

Controlled composition and morphology Good crystallinity Uniform size distribution One-step method

Technique: Precursor solution is atomized and droplets poured into glass filter. Aerosol is heated and solvent evaporates in the reactor. Anatase-titania particles with nominal size of about 10 nm


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Wang 2004

CASE 2SOL-GEL METHOD FOR ALUMINA POWDER High purity solid particles with high specific surface

area High cost of alumiun alkoxides (e.g. Al isopopoxide) Aqueous sol-gel method

Low cost Al and AlCl36H2O powders and HCl Stirring at 95C for 4 hours transparent solution (sol) Drying at 85C for 48 hours (gel) Grinding and calcination at high temperature (600…1200 C) Spherical 32-100 nm -alumina particles


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Shojaie 2008

CASE 3SOLID-STATE SYNTHESIS FOR WC Solid-state carbothermic reduction of tungsten oxide

Calcining mechanically activated mixtures of WO3 and graphite

Planetary ball mill, Ar, 10 h Reduction by heating at 1215C in vacuum Mechanical milling increased homogeneity and enabled

production by decreasing the diffusion path WC particles via formation of intermediates, Magneli

phases WO2.72 and WO2


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Ma 2010

CASE 4SOL-GEL METHOD FOR SIC POWDER Benefits: high purity, high chemical activity, improvement of

powder sinterability, possibility for particles mixing at molecular scale

Materials: Tetraethyl orthosilicate (TEOS), chlorocidric acid and NaOH (catalysts solutions), phenolic resin, ethanol, acetone (resol solvent), distilled water and ammonium polycarboxylate (APC) (dispersant agent)

Method: Solution homogenisation hydrolysis reactions and gelation heating and drying pyrolyzation 700C 1 h (Ar) heat treatment 1500C 1 h cubic –SiC semi-spherical particles (agglomerates less than 100

nm)


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Najafi 2010

SUMMARY AND CONCLUSIONS Large variety of different methods for different materials Differences consist e.g. of

Temperature (TR… 1500C), pressure Wet, solid or sol-gel type Wide amount of different raw materials, precursors, surfactants

etc. One- or several steps Need for post treatment (calcination) Synthesis time Produced particle size, homogeneity, size distribution, purity

Influence on efficiency, cost and application As a conclusion: The possibilities for synthesizing ceramic

nanoparticles is in practice countless. Therefore thorough data acquisition and comparison is needed for finding the correct method for certain material and application need.


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REFERENCES

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Sahil Sahni, et al., Influence of process parameters on the synthesis of nano-titania by sol–gel route. Materials Science and Engineering A 452–453 (2007) 758–762

Kranthi K. Akurati, Andri Vital, Ulrich E. Klotz, Bastian Bommer, Thomas Graule, Markus Winterer, Synthesis of non-aggregated titania nanoparticles in atmospheric pressure diffusion flames. Powder Technology 165 (2006) 73–82

K.M. Parida, et al., Synthesis and characterization of nano-sized porous gamma-alumina by control precipitation method. Materials Chemistry and Physics 113 (2009) 244–248

M. Shojaie-Bahaabad, E. Taheri-Nassaj, Economical synthesis of nano alumina powder using an aqueous sol–gel method. Materials Letters 62 (2008) 3364–3366

F. Mirjalili, et al., Size-controlled synthesis of nano a-alumina particles through the sol–gel method. Ceramics International 36 (2010) 1253–1257

Lirong Tong, Ramana G. Reddy, Thermal plasma synthesis of SiC nano-powders/nano-fibers. Materials Research Bulletin 41 (2006) 2303–2310

J. Ma , S.G. Zhu, Direct solid-state synthesis of tungsten carbide nanoparticles from mechanically activated tungsten oxide and graphite. Int. Journal of Refractory Metals and Hard Materials 28 (2010) 623–627

A. Najafi, et al., Effect of APC addition on stability of nanosize precursors in sol–gel processing of SiC nanopowder. Journal of Alloys and Compounds 505 (2010) 692–697

Wei-Ning Wang, et al., One-step synthesis of titanium oxide nanoparticles by spray pyrolysis of organic precursors. Materials Science and Engineering B 123 (2005) 194–202

Wei-Ning Wang, Yoshifumi Itoh, I. Wuled Lenggoro, Kikuo Okuyama, Nickel and nickel oxide nanoparticles prepared from nickel nitrate hexahydrate by a low pressure spray pyrolysis. Materials Science and Engineering B 111 (2004) 69–76

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C ERAMIC NANOPARTICLES FOR THERMAL SPRAYING KE-31.5530 Nanoparticles Maria Oksa