Processing Salt-encapsulated Tantalum Nanoparticles for High Purity, Ultra High Surface Area Applications


In this study a process for removing the protective encapsulate from salt encapsulated nanopowders has been developed and tested for tantalum nanopowder produced by sodium/halide gas-phase combustion synthesis. A sodium/halide flame can be used to produce salt-encapsulated nanoparticles for many metal and nonoxide ceramic materials. The salt encapsulate allows for control of size and morphology, and protects the core particles from oxygen contamination. Without a protective coating, non-oxide nanopowders can be pyrophoric or form a surface oxide. Despite the beneficial attributes of the NaCl encapsulate, it can also be a source of contamination. Thus, a method by which the encapsulate can be removed and the exposed particles subsequently processed without exposure to environmental contamination was developed. A two step process was developed, where the bulk of the salt is sublimed from the core particles at 880°C and directed out of the system with an inert gas flow followed by a vacuum sublimation at temperatures at or greater than 1200°C for 120 min. These conditions reduced Na and Cl concentrations to below detectable limits of their respective analyses (5 ppm Na and 20 ppm Cl). Heat treating the core particles for 120 min at 1200°C, 1400°C and 1600°C coarsened the particles from 30 nm to approximately 250 nm, 400 nm and 3µm, respectively. At 1600°C a fully dense Ta consolidate was produced by applying a uniaxial load of 45 MPa pressure for 210 min.

This is a preview of subscription content, log in to check access.


  1. Andrievski R.A. (1994). Compaction and sintering of ultrafine powders. Int. J. Powder Metall. 30(1): 59–66

    CAS  Google Scholar 

  2. Axelbaum R.L. (2000). Synthesis of stable metal and non-oxide ceramic nanoparticles in sodium/halide flames. Powder Metall. 43(4): 323–325

    CAS  Google Scholar 

  3. Axelbaum, R.L., DuFaux, D.P. & Rosen, L.J., 1995. Method and Apparatus for Producing High Purity and Unagglomerated Submicron Particles. U.S. Patent No. 5498446

  4. Axelbaum R.L., Lottes C.R., Huertas J.I. and Rosen L.J. (1996). Gas-phase combustion synthesis of aluminum nitride powders. Proc. Combust. Inst. 26: 1891–1897

    Google Scholar 

  5. Cho H., Waters M.A. and Hogg R. (1996). Investigation of the grind limit in stirred-media milling. Int. J. Mineral Proc. 44–45: 607–615

    Article  Google Scholar 

  6. Cox, D.M., 1999. WTEC Panel Report on Nanostructure Science and Technology: R & D Status and Trends in Nanoparticles, Nanostructured Materials, and Nanodevices: Final Report: December 1998. 49–66

  7. DuFaux D.P. and Axelbaum R.L. (1995). Nanoscale unagglomerated nonoxide particles from a sodium coflow flame. Combust. Flame 100: 350–358

    Article  CAS  Google Scholar 

  8. Gill J. (1996). Basic Tantalum Capacitor Technology. AVX Technical Information Articles. AVX Corporation, England

    Google Scholar 

  9. Groat E.A. and Mrox T.J. (1994). Aqueous slip casting of stabilized AIN powders. Am. Ceramic Soc. Bull. 73(11): 75–78

    CAS  Google Scholar 

  10. Groza J.R. and Dowding R.J. (1996). Nanoparticulate materials densification. Nanostruct. Mater. 7(7): 749–768

    Article  CAS  Google Scholar 

  11. Haber J.A. and Buhro W.E. (1998). Kinetic instability of nanocrystalline aluminum prepared by chemical synthesis; Facile room-temperature grain growth. J. Am. Chem. Soc. 120(42): 10847–10855

    Article  CAS  Google Scholar 

  12. Hirsch P.B., Howie A., Nicholson R.B., Pashley D.W. and Whelan M.J. (1965). Electron Microscopy of Thin Crystals. Butterworths, London

    Google Scholar 

  13. Jena P., Khanna S.N. and Rao B.K. (1996). Stability and electronic structure of cluster assembled materials. Mater. Sci. Forum 232: 1–25

    CAS  Article  Google Scholar 

  14. Kaufmann D.W. (1960). Sodium Chloride, The Production and Properties of Salt and Brine. Reinhold Publishing Corp, New York

    Google Scholar 

  15. Morris D.G. and Morris M.A. (1997). Hardness, strength, ductility and toughness of nanocrystalline materials. Mater. Sci. Forum 235–238: 861–872

    Google Scholar 

  16. Moser K.D. (1999). The manufacture and fabrication of tantalum. J. Minerals Metals Mater. Soc. 51(4): 29–31

    CAS  Google Scholar 

  17. Shriver D.F. and Drezdzon M.A. (1986.). The Manipulation of Air-Sensitive Compounds. , JohnWiley & Sons, New York

    Google Scholar 

  18. Suryanarayana, C. & Norton, M.G., 1998. X-Ray Difrraction: A Practical Approach. Plenum Publishing Corporation, pp. 207–221

  19. Weissmuller, J., 1996. Nanocrystalline Materials, an Overview. The Minerals Metals, and Materials Society, pp. 3–19

  20. Zhang H., Penn R.L., Hamers R.J. and Banfield J.F. (1999). Enhanced adsorption of molecules on surfaces of nanocrystalline particles. J. Phys. Chem. B 103(22): 4656–4662

    Article  CAS  Google Scholar 

Download references

Author information



Corresponding author

Correspondence to J. L. Barr.

Rights and permissions

Reprints and Permissions

About this article

Cite this article

Barr, J.L., Axelbaum, R.L. & Macias, M.E. Processing Salt-encapsulated Tantalum Nanoparticles for High Purity, Ultra High Surface Area Applications. J Nanopart Res 8, 11 (2006).

Download citation

Key words

  • aerosols
  • combustion synthesis
  • encapsulation
  • flame reactor
  • nanopowders