A two-step strategy for production of spherical non-aggregated multi-component particles by suspension-fed spray flame

For applications in optics, energy storage, and semiconductors etc., spherical non-aggregated particles are desired for better flowability , molding capability and homogeneous densification . Spray flame synthesis has attracted widespread attention with its excellent ability for atomic-level mixing/doping and good potential for scale-up production. However, spray flame synthesis usually produces aggregates due to the known collision-coalescence growth. In this paper, we propose a two-step strategy of suspension-fed spray-flame synthesis. The first step involves the synthesis of aggregated nanoparticles , followed by a second step where these aggregates are reconstructed into spherical non-aggregated particles while retaining the advantage of atomic-level homogeneous mixing. It is found that for aggregated Y 2 O 3 nanoparticles , the critical point for reconstructing into spherical particles occurs when the flame temperature exceeds the melting point. The spherical particle size increases with the solid concentration of the suspension by a power of about 0.28. Assuming that droplets do not undergo micro-explosions and instead follow a one droplet to one particle route results in an overestimation of particle size by a factor of 6 to 8. This discrepancy suggests that micro-explosions may play certain role in the new suspension-fed flame synthesis, and largely reduces the final particle size. Furthermore, the Al 2 O 3 -Y 2 O 3 and MgO-Y 2 O 3 particles are selected for the multicomponent suspension-fed synthesis, representing the miscible and immiscible systems, respectively. The results show that for the Al 2 O 3 -Y 2 O 3 system, uniformly mixed spherical non-aggregated particles are obtained. For the MgO-Y 2 O 3 system, both composite spherical particles with pinning structure and MgO nanoparticles are identified, indicating that for obtaining spherical multi-component non-aggregated particles, the flame temperature needs to be higher than not only the eutectic component's melting point but also any single component's melting point. Overall, suspension-fed spray flame synthesis opens up a new pathway for the low-cost industrial-scale production of spherical non-aggregated multi-component particles.