Morphology of Single-Component Particles Produced by Spray Pyrolysis

Abstract

ABSTRACT. This work is a review of the experimental results from the literature for single-component metal and simple metal-oxide particles. Criteria for correlating particle morphology, i.e., whether the particles are solid or hollow, with process parameters and material properties during spray pyrolysis are presented and compared with the data available in the literature. The materials were classified into two categories for which the precursor: (1) melts and (2) does not melt before chemical reaction takes place, and separate criteria were used for each category based on the work of Jayanthi et al. (1993) J. Aerosol Sci. 19:478. In systems where the precursor melts before chemical reaction occurs, eg., decomposition of nitrates of Mg, Al, Fe, Zn, Pb, Ni, Co, Pd, Mn, Cu, Sr, and Ag, the particle morphology is determined primarily by the densities and formula weights of the reactant and product compounds unless high temperature densification or puffingup of the particles due to gases evolved during the chemical reaction alter the morphology. In systems where the precursor undergoes nucleation to form a solid crust which does not melt before chemical reaction takes place, e.g., Ba(C,H,O,),, A12(S04), , Zr(C,H3O2),, and Zn(C2H3O2),, solubility and density of the precursor as well as the operating temperature are the main factors that affect the product particle morphology. Overall, particle morphologies predicted by the criteria were in agreement with experimental observations reported in the literature.

Preparation of nanocrystalline titania powder via aerosol pyrolysis of titanium tetrabutoxide

“…The water that was formed in the bu- tanol combustion mainly supplied the hydrolysis water. In a recent review by Jain et al 45 solid particles were proposed to be formed if a chemical reaction occurred on a liquid (or melted) precursor droplet and the percolation criterion was fulfilled. We were using liquid precursor in our study, but according to the percolation criterion of Jain et al 45 hollow spheres should have been produced.…”

Preparation of Silica Nanostructured Spheres by Sol Spray Drying

“…There are two theories on the formation of the hollow particles by spray pyrolysis: One is nucleation based [13] and the other is density based. [14] In the former, the particles will become hollow if the droplet core is unsaturated when the surface is critically supersaturated during evaporation of solvent. In the latter, the particles will be hollow if the volume of the solid product contained in a single droplet is less than 0.16 times as large as the droplet volume at the onset of surface nucleation.…”

Morphologies and properties of NiO particles prepared from NiCl2·6H2O by spray pyrolysis

“…Their approach was extended by Yu et al [7] and Lenggoro et al [8] with little modification. On the other hand, Jain et al [9] emphasized the importance of salt(A)-to-product(B) transformation rather than salt precipitation, focusing the effect of density increase or volume contraction during the transformation. They proposed that hollow particle of B would form if the theoretical volume of B calculated from A in a droplet is below 0.16 times that of the primitive particles.…”

“…They proposed that hollow particle of B would form if the theoretical volume of B calculated from A in a droplet is below 0.16 times that of the primitive particles. The numerical value of 0.16 was given by the percolation theory [9]. Che et al [4] proposed a qualitative model for particle morphologies but they advanced considering intraparticle sintering and phase separation as well as a variety of intraparticle reaction.…”