Synthesis of nanopowders at elevated pressure and their characterisation - summary of work of the WG-002

The first two years of cooperative research of the working group "High Pressure Synthesis and Processing of Nanopowders" was focused on:

a) comparison of the various reactors used by the project partners

b) development of characterization method to assess the quality of the nanopowders

c) synthesis of a nanopowders doped with a range of elements and investigation of their optical and magnetic properties.

Ad a.

A SWOT (Strength-Weakness-Opportunity-Threats) analysis of 5 reactors developed by each of the project partners was carried out, and recommendations for their optimal applications were prepared. This work permitted also to select the most promising research direction of our group: synthesis of stoichiometric powders like YAG, and first of all doped nanopowders. These research directions best exploit the strengths of the hydro and solvothermal reactors we are using in our research and are also very prospective in terms of the applications of nanopowders.

Ad b.

Two new methods for characterization of nanopowders have been extensively tested:

i) Use of fine analysis of X-ray diffraction peaks to determine grain size distribution of nanopowders. Narrow distribution of grain sizes of nanopowders is an equally important parameter for their characterization as the average grain size. Although there are many methods to determine the average grain size, few methods exist to assess grain size distribution. By comparing grain size distribution evaluated using Transmission Electron Microscopy and the newly developed fine analysis of X-ray diffraction profiles, we have shown the later one to be a powerful and reliable method.

ii) Use of picnometric measurement of density of nanopowders as their quality test. We have found that with increase of pressure of synthesis the density of nanopowders increased and approached that of conventional powders. That means for too small synthesis pressure (what is equivalent to too small temperature) the reaction substrates did not fully convert in the oxide phase. Based on that we introduced density measurement as a simple and cheap quality test for powders.

Ad. c.