Flame synthesis of functional materials brings new challenges to aerosol science

摘要

Aerosol routes are attractive for materials manufacture as they offer unique advantages over classic wet chemistry routes. Today a number of particulate commodities such as carbon blacks, fumed silica and titania are made by flame aerosol processes that had been developed largely by evolutionary research. Recent breakthroughs, however, in aerosol and combustion science allow now scalable flame synthesis of mixed oxides, metal salts and even pure metals as nanostructured, layered particles and highly porous but well-adhering films with unique functionality contribute decisively to manufacturing of novel catalysts, sensors, biomaterials, phosphors and even nutritional supplements. This essentially new aerosol discipline creates a wealth of new challenges to aerosol science. Distinguishing between aggregates and agglomerates of nanoparticles is most intriguing for both engineering applications and health effects. These fractal-like particles occupy far more volume than their equivalent solid mass. Such particles may grow initially by surface growth and/or Brownian coagulation but quickly their collision volume fraction becomes much larger than their particle volume fraction, e.g. there is less "free gas" volume per agglomerate. As their collision volume fraction continuously increases by coagulation (that cannot be described by classic Smoluchowski theory), particle restructuring, fragmentation and even gelation take place.