Nanopowders are produced by laser evaporation of the target followed by vapor condensation in the resulting laser plume, accompanied by its vortex mixing with the flow of the carrier gas. Since the bulk of nanoparticles are formed in the laser plume from the vapor phase, they have a spherical or faceted shape.
In addition to nanoparticles, the resulting nanopowder also contains micron-sized particles: droplets of solidified melt and shapeless fragments of the target. Droplets are the result of displacement of the melt from the crater under steam pressure, and the fragments are formed by cracking the crystallized melt. The use of cyclones reduces the content of the second particles in the collected nanopowders to 0.3 Ц 0.5 weight%. Droplet sizes are 0.2 Ц 5 microns, and shapeless fragments are 0.5 Ц 10 microns. Particles of this fraction can be removed from the nanopowder by sedimentation.
Due to the rapid formation and rapid cooling of nanoparticles(< 1 msec) in the laser plume during its vortex mixing with the buffer gas, the nanopowders obtained by the laser have the following advantages:
- The sizes of nanoparticles are in the range of 2 Ц 60 nm, and their average arithmetic size is 10 Ц 23 nm. In this case, the average size of nanoparticles of fusible oxides is slightly higher than that of nanoparticles of refractory oxides.
- They contain individual nanoparticles weakly interconnected by van der Waals forces.
Other advantages of the laser method for producing nanopowders are:
- Easy to obtain nanoparticles of complex oxides by evaporation of the target from mechanically mixed in the appropriate proportion of simple oxides;
- There is no need to remove the products of chemical reactions from the resulting nanopowder;
- Good sintering of nanopowder in the manufacture of ceramic products;
- Sufficiently high productivity of nanopowder (3 Ц 300 g/h).
The peculiarity of the laser method is that the obtained nanopowders, as a rule, have a metastable crystal lattice, which is also explained by the rapid cooling of nanoparticles during their synthesis.
Was obtained nanopowders quite a wide range of simple and complex oxides YSZ, Nd(Yb):Y2O3, Fe:MgAl2O4, Al2O3, FexOy, Yb2O3, WO3 и etc. This is an incomplete list, because the range of the obtained nanopowders is expanding all the time. In particular, experiments for obtaining in a stream of argon nano-powders of non-volatile fluorides such types as CaF2, YbF3.
- Creation of fuel cells based on solid oxides.
- Synthesis of high-transparent ceramics for creation of solid-state lasers, scintillators, light modulators, hot-and mechano - strong windows, wide-angle optics.
- Synthesis of structural ceramics.
- In medicine, for targeted drug delivery to the facility.