Multicomponent Ceramic Powder Generation by Spray Pyrolysis

Abstract

We have examined methods for controlling the morphology and microstructure of ceramic particles produced by spray pyrolysis. A variety of materials were examined including SrTiO3and BaTiO3 and the oxides of Al, Mg, Zn, Pd, V, Mo, and Bi. The morphology of the particles was influenced by using colloidal precursors in combination with molecular precursors for particle generation. Slow drying rates obtained by using high relative humidities and controlled axial temperature gradients did not influence particle morphology for the systems and conditions studied. The microstructure of Al2O3, V2O5, and PdO particles was controlled by varying the temperature to provide nanocrystalline or single-crystal particles. Evaporation and condensation of volatile species such as MoO3 and V2O5 dramatically modified particle microstructure and morphology.

Aerosol Processing of Materials

“…Therefore, much investigation has been devoted to define the parameters controlling particle morphology, and many attempts to control these parameters to produce solid particles have been made (Leong, 1981(Leong, , 1987aOdier et al, 1990;Tohge et al, 1991;Lyons et al, 1992a;Ortega and Kodas, 1992).…”

“…Some control over particle morphology was possible by choosing the proper precursor (high-solubility, permeable crust), and controlling the temperature and humidity of the process. Ortega and Kodas (1992) and Lyons et al (1992a) attempted to alter particle morphology for systems which typically produce hollow particles by using colloidal precursors and slowing the drying rate by evaporating the droplets in a drying tube. The addition of colloidal seed particles coupled with a slower drying rate still produced hollow particles of ZnO and MgO from nitrate precursors.…”

“…Since droplets used in spray pyrolysis are usually micron-sized or less, densification is more favorable for this process than for solid-state processes which generally have larger particles. Examples of materials which were produced in the form of solid particles by aerosol-phase densification include: Pd and PdO Pluym et al, 1993a), Ag (Pluym et al, 1993b1, Ba,,,Ca,,,,TiO, (Ortega et al, 1991, BaTiO,, and SrTiO, (Lyons et al, 1992a).…”

“…These losses can have profound effects on the microstructure and morphology of the product particles (Lyons et al, 1992a). Moreover, evaporation of volatile metal oxides from multicomponent materials such as Pb-Bi-Sr-Ca-Cu-0 and PbTiO, leads to modified stoichiometries resulting in degraded properties of sintered ceramics.…”

Modeling of spray pyrolysis—why are the synthesized Y2O3 microparticles hollow?

“…Three main types of particle morphology can be obtained: (i) completely filled or “solid” nanoporous particles, (ii) microporous particles, and (iii) hollow (shell‐like) particles. For instance, Lyons et al5 obtained hollow MgO and ZnO particles and full Al 2 O 3 particles from nitrate salt precursors. No change in particle size or morphology was observed in nitrate‐derived ZnO or MgO by modifying the initial air humidity or the heating rate.…”