Partial flocculation for spray drying of spherical mixed metal oxide particles

Abstract

Particles are an important design consideration for many proposed solar thermochemical water splitting reactor concepts. These particles must maintain physical integrity and chemical performance at very high temperatures (>900°C) while flowing within a system. Spray drying is a commonly used, scalable method to produce solid spherical particles that have the best opportunity to meet these requirements. Spray drying is used to produce hercynite (FeAl2O4) particles using pH‐modification of a charge‐stabilized sol. This process involves inducing partial flocculation in nanoparticle suspensions to yield larger particles that are spherical and structurally robust. A commercial boehmite suspension is characterized along with a mixture of the boehmite suspension with an iron oxide suspension. Zeta potential near zero and peak yield stress measurements at the same pH indicate flocculation, but associated sedimentation behavior is not observed. The behavior of both the boehmite‐only and mixed suspensions both seem to be driven by the behavior of the boehmite suspension alone. Spray dried particles from the mixed suspension at the critical pH gave significantly larger and more spherical particles, which also indicates flocculation. This relatively simple technique shows promise for new mixed‐metal material formulations and scalable applications.

Spray-Dried Hierarchical Aggregates of Iron Oxide Nanoparticles and Their Functionalization for Downstream Processing in Biotechnology

“…The small iron oxide particles will form a shell of the droplet with a thin, closely packed wall that remains stable during most of the drying process and leads to the formation of a hollow sphere that ultimately collapses, resulting in the buckling of the aggregates similar to the observation described by Sen et al 34 The introduction of bigger silica particles into the suspension changes the processes during the drying of the droplet, with the iron oxide wall being thinner and the particles able to reorganize while the droplet shrinks, thus leading to spherical aggregates. 23,33 Additionally, the surface of the aggregates shows increasing roughness with a higher content of the silica particles.…”

“…By SD of colloidal suspensions, structures containing multiple (iron oxide) cores can be prepared and the morphology of the produced aggregates can be controlled . However, while iron oxide nanoparticles have been spray-dried in mixed materials, − to the best of our knowledge, we present for the first time a systematic study on the SD of SPIONs and the resulting magnetic characteristics. Furthermore, spray-drying of a bimodal nanoparticle population in one suspension leads to the segregation of the particle classes during the drying process and results in core–shell-like aggregates with the smaller particles forming the shell and the bigger particle fraction being in the core based on a segregation process. − The formation of a shell of small particles is only avoided when the drying time is drastically increased .…”