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

Abstract

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 Y2O3 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 Al2O3-Y2O3 and MgO-Y2O3 particles are selected for the multicomponent suspension-fed synthesis, representing the miscible and immiscible systems, respectively. The results show that for the Al2O3-Y2O3 system, uniformly mixed spherical non-aggregated particles are obtained. For the MgO-Y2O3 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.