(190a) A Novel Flame Assisted Spray Pyrolysis Reactor for Synthesis of Nanoparticles From Low Enthalpy Precursor Solutions

A new flame assisted spray pyrolysis (FASP) reactor design is presented, which allows manipulating the enthalpy content of the flame independently of the precursor solution chemistry. In this reactor design, a gas-assisted atomizer generates the precursor solution/oxygen spray. The spray is mixed and combusted with externally-fed acetylene or premixed methane/oxygen fuel gases at a defined height above the atomizing nozzle. The gaseous fuel feed can be varied to control the enthalpy content of the flame, where particle formation takes place. This way, the enthalpy density of the flame is decoupled from the precursor solution composition. Precursor solution compositions with low internal energy contents were shown to be prone for production of inhomogeneous product particles of a bimodal size distribution in the related flame spray pyrolysis (FSP) process. For example precursor compositions of various metal nitrates in ethanol were shown to produce inhomogeneous products consisting of nanosized particles from gas-to-particle conversion along with a fraction of large particles from droplet-to-particle conversion. A typical route to avoid this product inhomogeneity in FSP is to increase the flame enthalpy by the precursor chemistry, resulting in more complex and costly precursors. The FASP design facilitates the use of the low enthalpy precursor solutions for the production of homogeneous product powders by increasing the enthalpy density of the flame with low cost gaseous fuels. The effect of the flame enthalpy density on product properties in FASP configuration is explored on the example of various nanoparticle materials produced from nitrate in ethanol precursor solutions. Product powders were characterized by nitrogen adsorption, X-ray diffraction and transmission electron microscopy. Homogeneous product powders from nitrate precursor in ethanol were produced by the new FASP design.