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
Substrate Gas and particle stream Powder Energy Melted particles form lamella structured coating Thermal spraying shortly • Plasma, HVOF and CJS spraying • Metals, ceramics, cermets in powder form • Wear and corrosion resistance, hardness, electrical properties etc.
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. • Nanosized alumina Al2O3 • High strength and toughness, electrical resistance • Use e.g. for electronics and high temperature applications • Silicon carbide SiC • High melting point, hardness, wear and chemical resistance, electrical properties • Used in electrical industry, high temperature applications, reinforcement for ceramic composites • Tungsten carbide WC • High melting point, hardness, oxidation resistance, electrical conductivity • Applications e.g. cutting tools and wear-resistant parts
Synthesis methods of ceramic NPs • WC • Direct carburization of W powder • Solid state metathesis • Reductions-caraburization • Mechanical / reaction milling • Polymeric precursor routes using metal alkoxides • SiC • Si metal direct carbonization • CVD (chemical vapor deposition) • Thermal plasma synthesis • Carbothermal reduction of silicon dioxide • Sol-gel 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–gel
Examples of synthesis methods Sol-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 Mirjalili 2010 Tong 2006
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
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
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 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 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 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) 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.
References • 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