Spray pyrolysis nanoparticles production

Mueller R, Madler L, et al (2003) Nanoparticle synthesis at high production rates by flame spray pyrolysis. Chemical Engineering Science 58(10), 1969-1976... 

There are also other methods such as spray pyrolysis and electrospray pyrolysis besides the above method [26]. To prepare nanoparticles by spray pyrolysis, a starting solution is prepared by dissolving, usually, the metal salt of the product in the solvent. The droplets atomized from a starting solution are introduced to furnace. Drying, evaporation of solvent, diffusion of solute, precipitation, reaction of precursor, and surrounding gas, pyrolysis may occur inside the furnace before the formation of product. It is similar to spray drying except the type of precursor. For this, colloidal particles are typically used as precursors. Some products prepared by spray pyrolysis are listed in Table 34.1. 

Flame spray pyrolysis involves the ultrafine droplets of the solution of precursor materials (often salt) to be sprayed into a high-temperature chamber. On evaporation of the solvent, the dissolved precursors are converted into nanoparticles after reaction with oxygen. Each droplet contains the stoichiometric amount of precursors required in the final nanopowder product. This ensures the uniform composition in each nanoparticle and is a distinctive advantage over the chemical vapor reaction technique mentioned above. Highly uniform nanoparticles are produced in a commercial quantity using this method. The size distribution is controlled by the droplet size, concentration of the precursor salt in the solvent, and the velocity of the droplets in the furnace. 

Mueller R., Madler L., Pratsinis S.E., Nanoparticle synthesis at high production rates by flame spray pyrolysis. Chem. Engng Sci. 2003 58(10) 1969-1976 Murphy, P.J., Posner A.M., Quirk J.P. Characterization ofpartially neutralized ferric nitrate solutions. J. Colloid Interface Sci. 1976a 56(2) 270-283... 

Figure 8.8 Transmission electron microscopy images of YSZ nanoparticles (containing 10mol% yttria) by flame spray pyrolysis at (a) low and (b) high production rates [102]. Reproduced from Ref [37] Institute of Physics Publishing.

Many different methods have been reported for the production of metal oxide nanoparticles. The most common processes have been developed to synthesize oxide are chemical solution decomposition (CSD) [97], spray pyrolysis [98], CVD [99-101], two-step wet chemical method [102], sol-gel [103], ultrasonic irradiation [104,105], and ethanol thermal and hydrothermal method [106], Literature revealed that sol-gel is the most commonly used method for the preparation of metal oxide nanoparticles. It facilitates the synthesis of nanometer-sized crystallized metal oxide powder of high purity at a relatively low temperature [103]. 

Widely used methods in the synthesis of silica nanoparticles are the sol-gel process and flame synthesis [5]. The latter is an effective synthetic route to continuously produce extremely pure nanoparticles, but in many cases the final products are agglomerated or show low reactive surfaces that make them difficult to functionalize. Nevertheless, flame synthesis is a prominent method to commercially produce silica nanopartides in powder form [6]. It is being used since decades for the production of the so-called fumed siUca, which is a filler in many applications, for example, in the pharmaceutical or polymeric business [7]. The extension of this preparation route is the so-called flame spray pyrolysis that has expanded in the last two decades to many other material compositions and is a promising rapid technique for the production of nanopowders [8]. 

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