Gas-phase synthesis is a well-known chemical manufacturing technique for an extensive variety of nanoscale particles. Since the potential of ultrafine and, in particular, nanoscale particles in high-performance applications has been identified, scientific and commercial interest has increased immensely, thus identifying this field as a most important technology of the future. However, nanomaterials can perform their multifunctional tasks only if they are customized in terms of chemical composition, size, and morphology to suit the application at hand. Profound knowledge of the synthesis and precise process control is crucial in meeting the stringent specifications. Although the gas-phase synthesis of ultrafine materials has been known and commercially exploited for decades, existing knowledge is based almost exclusively on empirical know-how. Process simulation is a very suitable tool for expanding the understanding of the synthesis-relevant processes, particle formation mechanisms, and operating parameters. Based on the resulting expertise some special nanoscale gas-phase products of high innovative potential have been developed.
Gas-phase synthesis is a well-known chemical manufacturing technique for an extensive variety of nano-sized particles. Since the potential of ultra-fine and especially nano-sized particles in high-performance applications has been identified, the scientific and commercial interest has increased immensely, disclosing this field as a most important technology of the future.The paper will present the basics of the gas-phase synthesis and particle formation process including the relation between the principal process conditions and the product characteristics.Moreover, several reactor technologies such as f lame, hot-wall, plasma and laser reactors will be introduced and their specific advantages will be pointed out. Precise process control is crucial in order to meet stringent specifications regarding the particles ' chemical composition and morphology. In addition, the paper will deal with some special nanoscaled gas-phase products of high innovative potential and their functional contribution in various applications.Rodenbacher Chaussee 4, 63457 Hanau, Germany † Accepted: June 28, 2002The smaller the particles, the ...• higher the catalytic activity (Pt@Al 2 O 3 )• higher the mechanical reinforcement (carbon black in rubber)• higher the electrical conductivity of ceramics (CeO 2 )• lower the electrical conductivity of metals (Cu, Ni, Fe, Co, Cu alloys)• initially increasing and later decreasing magnetic coercivity, finally superparamagnetic behaviour (Fe 2 O 3 )• higher the hardness and strength of metals and alloys• higher the ductility, hardness and formability of ceramics; the lower the sintering and superplastic forming temperature of ceramics (TiO 2 )• higher the blue-shift of optical spectra of quantum dots (quantum confinement of Si)• higher the luminescence of semiconductors (Si, GaAs, ZnS:Mn 2ѿ ) silica, for which Degussa is the world market leader, is used in particular as a reinforcing filler in silicone rubber and to control the rheology of coatings and colorants. Industrial carbon black, in which Degussa ranks second in the world, is used particularly in the tyre industry and as a pigment in printing inks, coatings and plastics. In industrial products, primary nanoscale particles are normally not isolated but build up aggregates and agglomerates. In aggregates, the primary particles contact each other at surfaces or edges and Ҁ as a rule Ҁ they cannot be broken down further by shear forces applied in the application. Agglomerates are formed when aggregates and/or primary particles contact each other at points. If nanoparticles are dispersed in a liquid, the agglomerates are destroyed and the surface chemical groups of the aggregates interact with each other (see Fig. 1). In the case of fumed silica, this affinity is attributed to the hydrogen bridge linkages and results in a temporary, three-dimensional lattice structure becoming macroscopically "visible" in the form of thickening and thixotropy. To control the application behaviour often means to generate tailor-made aggregates with a ta...
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