A perspective on gas-phase synthesis of nanomaterials: Process design, impact and outlook

Abstract

For over a century, gas-phase (aerosol) technology has enabled manufacture of nanostructured commodities (i.e. carbon black, fumed oxides and metals) at high temperatures. As such this technology impacts consumer products like tires, paints, optical fibers, photocatalysts, pharmaceutics and microelectronics. Even though its early development was largely Edisonian, today is on a firm scientific basis through multiscale process design and sophisticated diagnostics. As a result, it’s attractive for its undisputable scale-up to tons/h and, most importantly, for its capacity to form novel materials with closely controlled size, morphology and composition that are inaccessible by solid state or wet chemistry processes. Coagulation, sintering and surface reactions largely determine material characteristics through the high temperature particle residence time, in sync with classical reaction engineering. The inevitable high particle concentrations during manufacturing lead to rapid attainment of asymptotic particle size distributions (self-preserving) and structures (fractal-like) following power laws for agglomerate, aggregate and primary particle sizes. As a result, particle dynamics are described by particle number, area and mass (volume) balances that can be readily interfaced with fluid mechanics without always involving cumbersome population balances. These facilitate process design and inspire research for the development of flexible processes (i.e. flame spray pyrolysis) for synthesis of unique particle compositions and morphologies that exhibit superior performance in catalysis, gas sensing and a spectrum of biomedical applications. Such advances motivate the development of new products that lead to creation of spinoffs blossoming in niche markets.