NANOSIZED OXIDES AND OXYNITRIDES BY FLAME AEROSOL PROCESSES

1
NANOSIZED OXIDES AND OXY-NITRIDESBY FLAME
AEROSOL PROCESSES
T.Sushil Kumar Rajan Cabot Materials
Research Port Dickson
2
CLASSIFICATION OF FINE PARTICLES
3
NANOSIZED PROCESSING
The Building-up processes can be divided into
three broad categories of phase
transformations Type-I) Solid-vapor-solid, such
as Inert gas condensation, laser ablation,
sputtering and plasma-CVD Type-II) Liquid-vapor-
solid, such as vapor and aerosol precursor
processes such as flame and aerosol
synthesis Type-III) Liquid-solid, such as
aqueous and non- aqueous solution precipitation
processes Type I and II are gas phase
processes, while Type-III fall under wet chemical
routes.

4
GAS PHASE PROCESSES (Vapor and Aerosol Synthesis)

• ADVANTAGES
• Complex oxide formation possible
• Molecular level mixing of constituents
• Direct formation of particulate
• Suitable for continuous production
• High product purity is possible
• Precise and reproducible particle size
  distribution and phase purity control
• Metastable phases can be produced
• Vapor / Aerosol methods differ in
• Method of Thermal Energy transfer to precursor
  species
• Mode of delivery of precursor species to reaction
  site
• Product properties for specific applications
• Permits better stoichiometry retention than gas
  to particle conversion processes particularly
  advantageous for mixed metal oxides.

5
SPRAY PROCESS FOR NANOPARTICLE PRODUCTION
6
FLAME PROCESS FOR MAKING NANOSIZE-OXIDES
Burner and cooling system
Product separation and calcination
PRODUCT
World capacity 1.6-1.7 lakh tonnes per annum
Flue gases with Cl2 and HCl
Fuel - H2 or upon combustion water forming gas
Oxidant Air or Oxygen
Acid recovery and desorption system
Precursor A volatile halide such as SiCl4 ,
AlCl3 , TiCl4 etc.
HCl Cl2 to recycle and reuse in making volatile
precursors
CHEMICAL EQUATIONS SiCl4 2H2 O2 ? SiO2
4HCl 4AlCl3 6H2 3O2 ? 2Al2O3 12HCl TiCl4
2H2 O2 ? TiO2 4HCl SiCl4 O2 ? SiO2
Cl2 4AlCl3 3O2 ? 2Al2O3 6Cl2 TiCl4
O2 ? TiO2 Cl2 CH3SiCl3 2O2 ? SiO2 CO2
3HCl
7
DIRECT PROCESS FOR ALKOXY SILANES

• With the introduction of a patented process in
  2003 for the direct production of alkoxysilanes
  and alkoxy orthosilicates from silicon metal and
  alcohol in the presence of copper salt of
  diethylphosphoric acid as catalyst,
• Si 3ROH catalyst ? HSi(OR)3 H2, and
• Si 4ROH catalyst ? Si(OR)4 2H2
• A commercial process for making nanosized metal
  oxides from alkoxides is worth investigating.
• Some advantages envisaged are
• Simple equipment and inexpensive materials of
  construction can be used
• Expensive acid recovery / reuse unit operation
  is avoided
• Expensive equipment for product after-treatment
  can be avoided
• Chloride free product can be produced
• Small plants would become commercially feasible
• Disadvantages
• Process evolves green house gas CO2
• The in-flame-reaction method for Al2O3 aerosol
  formation from aluminium acetylacetonate in
  hydrocarbon-oxygen flame was investigated in 1977
  by Sokolowski et. Al (J. Aerosol Sci. 1977, Vol.
  8, pp 219-230).

8
FLAME AEROSOL SYNTHESIS
THE AEROSOL FLAME REACTOR
9
PRECURSORS USED AND OPTIMISED FLOWRATES
 
 
 
     
10
PROPERTIES OF NANO-PARTICLES
 
11
TEM PHOTOMICROGRAPHS OF AEROSOL DERIVED
NANOPARTICLES
SILICA PARTICLES
TITANIA PARTICLES
ALUMINA PARTICLES
12
TEM PHOTOMICROGRAPH OF AEROSOL DERIVED MULLITE
100 nm
MULLITE PARTICLES
13
EFFECT OF RAPID PARTICLE QUENCH ON SSA
Quench varied by increasing or decreasing blower
by-pass Variation in BET SA of SiO2 with TEOS
aerosol
14
RAPIDLY QUENCHED NANOSIZED SILICA OF HIGH SURFACE
AREA
AGGREGATE
AGGLOMERATE
15
PARTICLE GROWTH IN FLAMES
Ref G.D.Ulrich, Combust. Sci. Tech., 4 (1971) 47
16
OXY-NITRIDE MATERIALS BY AEROSOL PROCESS
17
PROPERTIES OF SILICON NITRIDE MADE
Results of Imide precipitation-pyrolysis
Comparison of powder properties obtained by the
three routes
18
IMIDE PRECIPITATION PYROLYSIS ROUTE FOR Si3N4
Flame Aerosol derived SiAlON
Reactor for Si3N4
19
AEROSOL SYNTHESIS USING NITRIDES
Synthesis optimized at a solution spray rate of
1.1 l/h Solution composition per 100 mL
DFH Diformylhydrazide The powder obtained in
both cases was a-Si3N4 which converted upon
calcination at 1600oC in N2, 2h to single phase
ß-SiAlON.
20
SINTERNG OF ß-SIALON COMPACTS
Sintered compacts of SiAlON
Powder XRD pattern showing ß-SiAlON formation
21
CONCLUSIONS

• High purity material can be synthesized by
  aerosol processes.
• Lower volatility precursors have been used.
• Particle size has been varied over a fairly wide
  range by controlling flame temperature.
• Spherical, sinter-active particles with
  controlled phase purity and aspect ratios have
  been prepared.
• The process is simple, reproducible, easily
  scaled-up with high production rates.
• Such processes produce dry materials in a
  continuous manner.
• An environmentally acceptable, lower capital cost
  intensive process has been investigated
  advantageously in a lab reactor.
• The aerosol reactor can also be used for the
  solution combustion process.

22
BIBLIOGRAPHY

• Kodas, T.T., and Hampden-Smith, M.J. (1999),
  Aerosol Processing of Materials. New York
  Wiley-VCH
• Pratsinis, S.E., Flame Aerosol synthesis of
  ceramic powders, Progess in Energy and Combustion
  Science, 24(3) 197-219, 1999.
• Mädler, L., Liquid fed reactors for one-step
  synthesis of nano-structured particles. KONA.
  22107-120, 2004.
• Stark, W.J. and Pratsinis, S.E., Aerosol flame
  reactors for manufacture of nanoparticles. Powder
  Technol., 126 103-108, 2002.
• Patil, K.C., Advanced ceramics combustion
  synthesis and properties. Bull Mater Sci., 16
  533-541, 1993.
• Calcote, H.F., and Felder, W. A New Gas-Phase
  Combustion Synthesis process for pure metals,
  alloys and ceramics, 24th Symposium (Intl) on
  Combustion / The Combustion Institute, 1869-1876,
  1992.
• Rajan, T.S.K., Studies on Oxide, nitride and
  oxy-nitride ceramics. PhD thesis, Indian
  Institute of Science, Bangalore, 1997.