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A summary of results obtained in Working Group 002 "Synthesis and Processing of Nanopowders"

Witold Łojkowski 

Polish Academy of Sciences, Institute of High Pressure Physics (UNIPRESS), Sokolowska 29/37, Warszawa 01-142, Poland


The area of research of the working group includes:

-       Methods of synthesis of nanopowders,

-       Development of high pressure reactors for nanopowders synthesis

-        Characterisation of nanopowders

-       Their applications

Nanopowders are powders with particle size below 100 nm. Nanopowders are produced in industrial scale since long time, e.g., carbon black, silica, titania etc. However, recently much interest is in nanopowders of high commercial value due to their specific optical and magnetic properties that result from nano-size.. Furthermore, from nanopowders, or using nanopowders, one can produce nanocrystalline materials or nanocomposites  of radically improved strength. Nanopowders do already play an important role in many industrial fields, and the field of their application will continuously increase in future.

1. One of major barriers in the science and technology of nanopowders is that high value nanopowders need to be produced with well controlled and narrow grain size distribution, and these parameters are difficult to control and measure.

2. Wet chemistry methods for their production are usually cheap, but after such synthesis processes nanoparticles are frequently coated with a layer of untreated reaction precursors. Therefore a major issue is to obtain nanoparticles of high degree of crystallinity.

3. It is worth developing technology of nanopowders with engineered magnetic or optical properties. An efficient method to add to nanopowders controlled magnetic or optical properties is to dope them with ions of metals which have themselves magnetic or optical properties. These ions are then protected from the environment since they are embedded in a stable oxide lattice, and at the same time this particle is so small, that it can be embedded in various materials like polymers, textiles, other ceramics, dispersed in fluids, or used  for imaging cells. Adding value to nanoparticles requites synthesis methods that permit to dope the nanoparticles to high level with such ions, without their segregation as clusters.

4. It is important to be able to coat the nanopowders with functional layers which enhance their sintering into usable mechanical parts or dispersion in fluids, or attaching to selected surfaces. . Such a process is impossible in high temperature production processes.

5. Therefore, there is a need for innovative synthesis methods that would permit to scale up production of nanopowders and at the same time meet all the above criteria, and for commonly agreed characterisation procedures to ensure delivery of quality nanopowders.

The above issues have been addressed by our working group and solutions found will be reported bellow.

  1. We have developed a method to estimate the grain (or crystallite) size distribution of nanopowders based solely on an analysis of the shape of XRD peaks. The peaks must be measured according to well defined procedures and can be analysed using an analytical formula.
  2. We introduced density measurements as an important tool for characterisation of nanopowders. Density tells us about the thickness of the layers on the powders surface. We could optimise the synthesis process so that such layers thickness is the minimum possible under given thermodynamic conditions.
  3. Competence we acquired in characterisation of nanopowders and nanoceramics nanostructure permitted us to edit a first Nanometrology report focussed on Nanoparticles and nanomaterials, published as a prestigious Nanoforum report at the European nanotechnology web page
  4. We have found that solvothermal and hydrothermal  synthesis, i.e., a method where reagents in solution are heated above the boiling point at atmospheric pressure (and this is made possible because the fluids are in a high pressure vessel) is a method that permits to incorporate in the lattice  of ZnO a relatively large amount of metal ions: Al3+, Mn2+, Ni2+¸Co2+¸Cr3+ without formation of measurable clusters or precipitates. It was found that addition of Al ions in the range 0f 0.4 mol %n is possible. And this leads to increase of luminescence by more than one order of magnitude. As far as magnetic ions, the material obtained was paramagnetic. Absence of ferromagnetism indicates that ZnO doped with Mn2+ is not a suitable material for spintronics, contrary to many claims. Probably the magnetic properties of material obtained by other methods is caused by segregation of Mn clusters.
    Also doping of Zirconia with rare earth ions was very successfully performed, and nanoparticles emitting under excitation by laser, UV or X-ray radiation emit a range of colours have been produced.
  5. We produced hydroxyapatite powders coated with collagen, which could be sintered into biocompatible material with very good mechanical properties; combined strength and ductility. Such material can be sued in tissue engineering.
  6. Our studies show a range of advantages of the solvothermal method, and in particular when microwaves are used for heating:
    - comparing to high temperature methods high levels of doping are possible, and non volatile ions can be doped.
    - comparing to precipitation/ calcination or sol-gel methods, no high temperature annealing is necessary for nanopowders production, and the powders can stay all the time in closed vessels.

    A drawback of solvothermal synthesises that high pressure vessels are slow to heat up and cool down due to high thermal inertia. Furthermore, contact with heating elements or  steel parts of the vessel should be avoided and highly pure products can be obtained. This can be achieved by heating the reagents using microwaves, which act across a Teflon vessel where the reagents are enclosed.  In addition to that, if microwaves are used, the process of synthesis is shortened about 5 times or more, because the thermal inertia of the vessel is not limiting hating rates. However, such Teflon lined reactors are not suitable for processes at temperatures above 300oC. 
  7. We compared all the methods available in our group, and based on a SWOT analysis, we have developed two production processes:
    Stopped – flow microwave – pressure reactor, capable of producing about 1 kg of zinc oxide nanopowders per day, at pressure up to 4 MPa and temperature up to 250oC. .

    Continuous synthesis of YAG nanopowders in supercrical water, at temperature about 450oC and pressure about 40 MPa. The process includes also a thermal annealing of the powders at 600oC to obtain a good density. Contrary to precipitation/calcination methods powders prepared in that way do not form aggregates. We have also shown several advantages of the present method over the claimed in the literature synthesis methods of YAG in continuous flow reactors.
    Both reactors are unique world wide, and give the opportunity of industrial production of nanopowders. There are some patents pending.

In summary, the results of our working group collaboration are as follows:

  1. Obtaining new information about synthesis of nanopowders with the use of  microwave and pressure reactors. It was found that these techniques are especially well suited to produce  doped nanopowders of ZnO and ZrO2 as well as hydroxyapatite powders coated with organic material.
  2. Scaling up of the nanopowders production using high pressure and/or microwave reactors. It was found that scaling up to industrial production is feasible. New concepts for such reactors have been developed.
  3. Developing procedures for characterisation of nanopowders. We developed two new procedures, but still a lot has to be done in this field.
  4. First steps towards understanding basic phenomena which take place during synthesis and sintering. This field of research is now a hot topic, since important data have been gathered and need to be explained.
  5. Ready for applications. The powders produced can now be tested in various applications. Prototype devices need to be developed to convince industry about advantages of nanopowders based nanotechnology.

The general conclusion is that: “High Pressure Technology for production and processing nanopowders is now a fact that needs to be taken into account by the scientific and industrial communities”

WG D30/003    Papers

1. Study of Grain Size Distribution in Nanocrystalline Iron Oxides Synthesized by Hydrothermal Method, Solid State Phenomena 94, 239 (2003),
R. Fedyk , T. Chudoba , A. Presz , W. Lojkowski and. K. Kurzydlowski

2. New hydroxyapatite based nanomaterials for potential use in medical field, Annals of Transplantation, 9, 20 (2004),  R. M. Piticescu, G.C. Chitanu. M.L. Popescu, W. Lojkowski, A. Opalinska, T. Strachowski,

3. Biocompatibility of hydroxyl-apatite thin films obtained by pulsed laser depositionReviews on Advanced Materials Science, 8,: 164,  (2004), M.L Popescu. R.M., Piticescu , S. Petrescu, L.Zdrentu, I.Mihailescu, G.Socol, W.Lojkowski

4. Hybrid HAp-maleic anhydride copolymer nanocomposites obtained by in-situ functionalisation, Solid State Phenomena:  6, 47  (2005), R.M. Piticescu, C.C. Chitanu, M.  Albulescu, M. M. Giurginca, L. Popescu, W. Lojkowski,

5. Application of image analysis for characterization of powdersMaterials Science - Poland, 23, 79, (2005), J. Michalski, T.Wejrzanowski, R.Pielaszek, K. Konopka, W.Lojkowski, K.J. Kurzydlowski.

6. Chemical Synthesis of nanostructured Powders and Films with controlled Properties, Proceedings of the International Conference on Materials Science and Engineering, Brasov, Romania, 24-26 February 2005, ISBN 973-635-454-7, R. M Piticescu., R. R.Piticescu, V.Badilita, C.Monty,  F.Sibieude  and W. Lojkowski

7. Quantitative methods for nanopowders characterization, T,. Wejrzanowski R, . Pielaszek  A. Opalinska, H. Matysiak, Lojkowski W,. K.J. Kurzydlowskx, APPLIED SURFACE SCIENCE,  253: 204-208 (2006)

8. Effect of Pressure on Synthesis of Pr-Doped Zirconia Powders Produced by Microwave-Driven Hydrothermal Reaction, Journal of Nanomaterials,  Volume 2006, Article ID 98769, Pages 1–8, A. Opalinska, C. Leonelli, W. Lojkowski, R. Pielaszek, E. Grzanka T. Chudoba, H. Matysiak, T.Wejrzanowski, and K. J. Kurzydlowski

9. Magnetic properties of ZnMnO nanopowders solvothermally grown at low temperature from zinc and manganese acetate, Applied Physics Letters 89, 242102 (2006), A. Tomaszewska-Grzeda, A. Opalińska, E. Grzanka, and W. Łojkowski, A. Gedanken, M. Godlewski, S. Yatsunenko V. Osinniy, and T. Story

10. Synthesis of nanoparticulate yttrium aluminum garnet in supercritical water–ethanol mixtures, J. of Supercritical Fluids 40, 284  (2007) , A Cabanas., Jun Li, P., Blond, T.Chudoba, W.Lojkowski, M. Poliakoff, E.Lester

11. Nanometrology. Editors Witold Łojkowski et al, Nanoforum report 2007,   www.nanoforum,org

12. Zirconia Based Nanomaterials for Oxygen Sensors – Generation, Characterisation and Optical Properties, J.D. Fidelus, W.Lojkowski, D. Millers, L. Grigorjeva, K. Smits, and R.R. Piticescu, Solid State Phenomena 141, Vol. 128, (2007)

13. Morphology and luminescence properties of zinc oxide nanopowders doped with aluminium ions obtained by hydrothermal and vapour condensation methods., J. Applied Physics, in Press., T. Strachowski, E. Grzanka, W. Lojkowski, A. Presz M. Godlewsk, S. Yatsunenko, H. Matysiak, R.R. Piticescu, C.J. Monty

14. Solvothermal synthesis of submicron zinc oxide doped with Mn2+, Ni2+, Co2+ and Cr2+ ions by means of a microwave reactor, A. Gedanken, W. Łojkowski, A. Tomaszewska Grzęda, A. Opalińska, E. Grzanka, M. Godlewski, J of Phys Chem of Solids, submitted


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Presentation: Invited at COST D30 Final Evaluation Meeting, by Witold Łojkowski
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Submitted: 2007-09-23 23:31
Revised:   2009-06-07 00:44