Electron Accelerator to Help Producing Nanopowder
Russian physicists developed a new technique for making nanopowders with particles of a certain diameter – a property, which lack all other technologies of nanopowder production. High-energy electron flow knocks nickel atoms out of a sample, these atoms then deposit on a substrate – that is the way nanoparticles form.
Being components of various alloys, oils and lubricants, nanopowders are known to greatly improve technical characteristics of these materials. In order to introduce nanopowders into materials for getting excellent results, these powders should not contain any extraneous impurities, and their particles should have nearly the same size. Making nanopowders with such properties is not an easy task.
Russian researchers from the Institute of Theoretical and Applied Mechanics, Khakassia State University, the Institute of Nuclear Physics and Buryatiya State University have developed a highly effective technique for synthesizing nickel nanopowder without any impurities and with particles within one size range. Abovementioned technique for synthesis of nickel nanopowders is a precipitation method from a high-temperature phase. The process begins with a high-energy electron flow from a particle accelerator knocks nickel atoms from samples of technogenic origin. As a result, a nickel-containing gas forms. This gas can become as hot as several thousand degrees Celsius. The gas is then moved to a region with low temperature, where nickel deposits of specially prepared substrates. Layer by layers, nickel atoms form nanoparticles. Experiments showed that such kind of precipitation resulted in formation of two kinds of nanoparticles with average size of 100 and 200 nanometers.
The physicists have also developed a mathematical model, which describes a process of nanopowder formation. The models was designed to give answer to the question – is the result of the experiment a trend or an accident. The point is that theoretical prediction denied the possibility of simultaneous synthesis of two fractions of nanoparticles. Numerical modeling helped them answer the imposed question. A computer model consisted of 85 000 single nickel atoms and solved Newton motion equations for each of these atoms. Results of modeling have confirmed experimental results – after 7 nanoseconds the system reaches a stable state, and a plot, showing how particle size depended on their number, contained two clearly seen peaks, corresponding to 100 and 200 nanometer fractions.
Similar numerical modeling has been performed for other initial amounts of nickel atoms. Results were the same – two fractions of nanoparticles with size of 100 and 200 nanometers have formed. As can be seen from the above, direct evidence of nickel nanoparticles making two size fractions should have been a trend. Predictions didn’t show such a trend, because, researchers often make numerous simplification, when analyzing large molecular systems. Most important factors, influencing the size of nickel nanoparticles, are cooling speed and changes in atom spatial concentration.