Gas phase (aerosol) synthesis of ceramic nanoparticles is attractive as it does not require the multiple steps of wet chemistry processes and cleaning of liquid by-products resulting high purity products (e.g. optical fibers) while particle collection is easier from gas than liquid streams. As a result, the aerosol route is preferred in materials manufacture (pigmentary TiO₂ by the chloride versus the sulfate process) or in cleaning of process streams (gas versus wet scrubbing). Today flame aerosol technology, in particular, is used in large scale manufacture of fumed SiO₂, TiO₂ and Al₂O₃ nanoparticles up to several tons/hour.

It will be shown how characteristics (size, morphology and crystallinity) of metal oxide nanoparticles (e.g. SiO₂, TiO₂) can be controlled by flame variables (reactant mixing, composition and flowrate as well as external electric fields). Such understanding guides rational design and operation of aerosol reactors for the above commodities and enables now aerosol technology to develop new processes and products for catalysts, sensors, biomaterials, photonics and even nutritional supplements!

For example, noble metal bearing catalysts (e.g. Pt/Al₂O₃) that were made for eons by multi-step wet impregnation and costly effluent treatment are made now by one-step liquid-fed flame aerosol reactors. Likewise biomaterials for bone replacement and dental prosthetics are made such as transparent but radioopaque Ta₂O₅/SiO₂ nanocomposites. Highly efficient NOx storage-reduction Pt/Ba/Al₂O₃ catalysts are made by stereoscopically arranged twin flame reactors promoting component mixing at the nano rather than at the atomic level. Very recently, it was demonstrated gas-phase synthesis of sensors for organic vapors by one step synthesis of TiO₂ or Pt/SnO₂ nanoparticles and their direct deposition on Pt electrodes resulting in highly porous films. Hence all the demanding, impurity-prone steps of conventional sensor manufacture by wet processes are bypassed .

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