Monte Carlo Simulation of Nanoparticle Encapsulation in Flames

摘要

Gas-phase combustion (flame) synthesis has been an essential industrial process for producing large quantities of powder materials such as carbon black, titanium dioxide, and silicon dioxide. The present interest in nanoparticles for advanced materials application has led to efforts to employ flames for the synthesis of unagglomerated nanoparticles (2 to 100 nm) of metals and non-oxide ceramics. Sodium-halide chemistry has proven to be viable for producing metals and non-oxide ceramics in flames. Materials that have been produced to date include Si, TiN, TiB2, TiC, TiSi2, SiC, B4C, Al, W, Ti, TiB2, AlN, and W-Ti and Al-AlN composites. The main challenge that faces application of flame synthesis for advanced materials is overcoming formation of agglomerates in flames. The high temperatures and high number densities in the flame environment favor the formation of agglomerates, which be avoided for many reasons. For example, when nanopowders are consolidated, agglomerates have a deleterious effect on compaction density, leading to voids in the final part. Another critical challenge that faces all synthesis routes for nanopowders is ensuring that the powders are high purity and that the process is scaleable. Though the containerless, high temperature environment of a flame is excellent for producing high-purity simple compounds, ultrafine metals and non-oxide ceramic powders are inherently reactive in the presence of oxygen and/or moisture. Thus, the handling of these powders after synthesis poses a challenging problem.