Liquid-feed flame spray pyrolysis
Liquid–feed flame spray pyrolysis (LF-FSP) is one of the most recent iterations in flame spray pyrolysis (FSP) powder production technology. FSP produces metal oxide powders from highly volatile gaseous metal chlorides that are decomposed/oxidized in hydrogen-oxygen flames to form nano-oxide powders. However, products made from FSP's vapor-phase process are limited to Al-, Ti-, Zr-, and Si-based oxides from their metal chlorides. Thus, interest in producing more complex materials required a new methodology, LF-FSP.LF-FSP, as invented at the University of Michigan, uses metalloorganic precursors such as metal carboxylates or alkoxides, not metal chlorides. Briefly, alcohol (typically ethanol) solutions containing 1–10 wt % loading of the target ceramic components as precursors are aerosolized with O2 into a quartz chamber and ignited with methane pilot torches. Initial combustion temperatures run 1500–2000 °C, depending on the processing conditions, generating nanopowder ""soot"". Temperatures drop to 300–500 °C over 1.5 m, equivalent to a 1000 °C quench in 100 ms leading to kinetic products and nanopowders that are unaggregated. Production rates can be 200 g/h when using wire-in-tube electrostatic precipitators operating at 10 kV. Typical powders have 15–100 nm average particle sizes (APS) with specific surface areas of 30–100 m2/g. LF-FSP technology can be used to produce mixed and single metal oxides easily from low cost starting materials in a single step without forming harmful byproducts like HCl, which forms when metal chlorides are used as precursors.