chimica oggi • Chemistry Today • Vol 25 nr 3 • May/June 2007 34 Microwave synthesis Main development directions in the application of microwave irradiation to the synthesis of nanopowders CRISTINA LEONELLI WITOLD LOJKOWSKI ABSTRACT Microwaves, MW, applications in synthesis of nanoparticles is a large and dynamically growing research field. The driving force is search for methods that permit production of nanoparticles with well controlled and tailored properties: degree of crystallinity and/or defect free crystalline lattice, dopped or alloyed with optically or magnetically active ions, crystals size and crystal size distribution, shape, capping with functional layers, etc. Although Europe was pioneering in research on microwave technology applied to chemical synthesis, recently the number of papers coming from Asia, and particularly China, has outnumbered these produced in Europe and in USA. This is mainly due to relatively low cost of experiments where modified commercially available microwave ovens or even kitchens can be used to make MW-assisted chemical synthesis. It has been proved worldwide that MW driven reactions provide fast heating of the reactants, in some conditions accelerated reaction rate, and high purity conditions. Microwave heating is particularly useful for reactions carried out under elevated pressures, because of contactless delivery of energy to the reading fluids, high energy density possible, and short heating times leading to nanoparticles weakly agglomerated, with high crystallinity and narrow grain size distribution. This progress was possible with the use of specially designed reactors, permitting pressure and temperature control and high purity conditions. Prospective research directions are development of continuous MW&HP reactors, increase of MW field strength, in situ preparation of functionalised nanopowders, investigation of the possible level of doping with functional ions, structure and properties of the nanoparticles, as well as extension of the range of fluids used as solvents. It is needed that laboratories working on nanopowders synthesis work closely together with the producers of the final commercial products and tailor the particles to their needs, while in parallel scaling up the production capacities. INTRODUCTION Nanosynthesis is still a hot topic for fully industrialize as well as emerging countries as indicated by hundred of millions dollar funding all over the globe (1). Their application fields is incredibly increasing, an updated list of them can be the following: 1. Anti-Microbial 2. Catalysts 3. Performance Coatings 4. Personal Care 5. Polishing 6. Abrasion-Resistant Coatings 7. Charge Dissipating Materials 8. Deodorant/Antiperspirant 9. Environmental Catalysts 10. Foot Powder 11. Fuel Cells 12. Glass Polishing 13. Marine Antifouling 14. Oral Care 15. Permanent Coatings 16. Semiconductor Polishing 17. Shaving/Depilatory Products 18. Sunscreen Formulations 19. Textile Fibers 20. Thermoplastics 21. UV-Attenuating Coatings 22. Wood Preservation An increasing number of researchers is preparing nanoparticles with microwave assisted methods. As showed in Table I starting from the year 1996, when equipment dedicated to microwave-mediated syntheses has been developed and worldwide commercialized, more and more interest was directed to dielectric heating of reagents in order to produce nanoparticles, intended as particles of 5-100 nm in diameter. Nanoparticles tend naturally to be aggregated and the agglomerate size is larger than the particle size. The dispersion/aggregation degree, even though of primary importance in their use, is not discussed hereafter. Europe was leading the research in this new synthetic field at the very beginning, but was recently surpassed in the number of publications by Asia, with People Republic of China in first position (Figure 1). Much of European research in this field is coordinated in European network COST. In this paper we report our experience in the field of microwave driven synthesis of nanoparticles that we gathered coordinating research networks COST D30/W002 (2): “High pressure synthesis and processing of nanoparticles” and COST D32/W003 (3): “Synthesis