Spray pyrolysis particle size

Various methods are applied to the synthesis of titania particles including sol-gel method, hydrothermal method [2], citrate gel method, flame processing and spray pyrolysis [1]. To utilize titania as a photocatalyst, the formation of ultrafme anatase titania particles with large crystallite size and large surface area by various ways has been studied [4]. 

In this work, flame spray pyrolysis was applied to the synthesis of titania particles to control the crystal structure and crystallite size and compared with the particle prepared by the conventional spray pyrolysis... 

Another distinguishing feature of titania prepared by flame spray pyrolysis is the draar e of anatase crystallite size with the increase of flame temperature. Generally, the increase of preparation temperature increases the crystallite size in other processes such as sol-gel method, hydrothermal method [2, 3], flame processing and conventional spray pyrolysis. The decrease of crystallite size was directly related to the decrease of particle size. Fig. 5 shows SEM and TEM images of titania particles prepared by flame spray pyrolysis. 

Spray pyrolysis routes have been extensively investigated to prepare Pt-based catalysts. Typically, a liquid feed of metal precursor and carbon is atomized into an aerosol and fed into a continuous furnace to evaporate and heat-treat to form a collectable powder. The method has good control over final aggregate particle size and metal particle size distributions, as well as producing powder without further isolation or separation. Hampton-Smith et al. have reviewed efforts of Superior MicroPowder (now Cabot Fuel Cells) in this area. ... 

A method for the preparation of undoped ZnO films is by spray pyrolysis, using Zn(acac)2 H20 between 100 and 400 °C either with a dry solvent or in the presence of excess water. Above 200 °C, a change in the decomposition mechanism occurs and the films became more consolidated, transparent, have larger grains and are more conductive. Ultrafine ZnO particles of size less than 9 nm with a narrow size distribution were prepared by Zn(acac)2 and NaOH in ethanolic solution . The formation of stable ZnO nanoparticles is attributed to the stabilization of surface Zn + ions chelated by acac ligands and the presence of only a small amount of H2O. 

The adsoqjtion of NO on metal loaded ceria has been examined for Pt, and Pd, As known from work on single crystals, NO dissociates to some extent on each of these metals. The amount of dissociation is dependent upon the structure of the metal surface. Gorte considered Pt and Pd particles deposited on rough, poly crystal line ceria films grown by spray pyrolysis.For Pt they found variation in the TPD results (amount of NO uptake and shape of N2 desorption profile) that varied with the size of the Pt particles. However, the results were comparable to NO TPD results from Pt grown on sapphire. It was concluded that no unusual interaction existed between Pt and the (oxidized) ceria. For Pd it was found that a pronounced difference in the TPD product ratio, NO/N2, occurred for Pd on ceria compared to Pd on sapphire. They attributed the difference to NO adsorption on reduced ceria. 

Osaka A, Mima Y, Takeuchi K, Asada M, Takahashi K (1991) Calcium apatite prepared from calcium hydroxide and orthophosphoric acid. J Mater Sci Mater in Med 2 51-55 Osaka A, Tsura K, lida H, Ohtsnki C, Hayakawa S, Miura Y (1997) Spray pyrolysis preparation of apatite-composite particles for biological application. J Sol-Gel Sci Technol 8 655-61 Otsuka M, Matsuda Y, Suwa Y, Fox JL, Higuchi W1 (1995) Effect of particle size of metastable calcium phosphates on mechanical strength of a novel self-setting bioactive calcium phosphate cement. J Biomed Mater Res 29 25-32... 

Precipitation from a concentrated solution of cations can be performed by solvent evaporation. To ensure that the particle size remains small, the concentrated solution may be atomised at high pressure into fine droplets of 100-500 pm diameter the solvent is rapidly evaporated by an upward stream of hot gas. The particles obtained, which can be as small as 100 nm, are compacted and calcined to produce the ceramic. A schematic representation of the spray-drying process is shown in Fig. 3.4. Several alternative methods are currently under development they are known as aerosol synthesis, aerosol pyrolysis or mist pyrolysis, depending on the specific technique to produce the gaseous suspension of fine particles aerosols are produced in high pressure nozzles and mists are obtained by means of nebulisers. YIG particles (0.25 pm) have been obtained by mist pyrolysis (Matsumoto et ai, 1991) by nebulising an aqueous solution of... 

As explained in Sect. 38.2, to produce particles using a conventional spray pyrolysis (CSP) process, the precursor is first atomized into a reactor where the aerosol droplets undergo evaporation and solute condensation drying and thermolysis of the precipitate particles at higher temperature forms micro- or meso-porous particles, and, finally, sintering of these porous particles forms dense particles. However, sub-micrometer to micrometer-sized particles traditionally are formed using the CSP process based on the one-droplet-to-one-particle (ODOP) principle due to the difficulty of generating very fine droplets (below 1 pm) [1-3]. 

The morphology and size of particles prepared by the LPSP process are different from those produced by CSP using either an ultrasonic nebulizer or a two-fluid nozzle as atomizers under an atmospheric environment. For example, nickel oxide (NiO) nanoparticles can be formed via the LPSP route whereas, only submicronsized NiO particles are produced by ultrasonic spray pyrolysis [9]. It is evident that the nanoparticle formation mechanism in the LPSP process is different from that in the CSP process. The calculated particle size based on the ODOP principle is much larger than 100 nm, indicating that the nanoparticles are formed based on one-droplet-to-multiple-particles (ODMP). The reason can be attributed to the difference in operating pressures and aerosol formation mechanisms between the two types of aerosol generators. 

I. W. Lenggoro, Y. Itoh, N. lida, K. Okuyama Control of size and morphology in NiO particles prepared by a low-pressure spray pyrolysis. Mater. Res. Bull. 38 (14), 1819-1827 (2003). 

Purwanto, A. Lenggoro, I. W. Chang, H. W. Okuyama, K. Preparatirai of submicron- and nanometer-sized particles of Y2O3 Eu by flame spray pyrolysis using ultrasonic and two-fluid atomizers. Journal of Chemical Engineering of Japan 2006, 39, 68-76. 

The basic approach to classify powder production methods is based on whether a method is top-down or bottom-up. In a top-down method, micro- and nano-particles are produced due to the stracture and size refinement through the breakdown of the larger particles in a bottom-up method, the mechanism of particle formation is usually by means of nucleatimi, growth and aggregation of atoms and molecules. In a more practical approach, one may divide the powder synthesis methods as follows (1) wet chemistry, such as the chemical precipitation, sol-gel, microemulsion, sonochemistry, and hydrothermal synthesis methods (2) mechanical attrition, grinding and milling (3) gas phase methods, such as the chemical and physical vapor deposition (4) liquid phase spray methods, such as the molten metal spray atomization, spray pyrolysis, and spray drying, and (5) liquid/gas phase methods. 

Nano-sized MgO particles with weU-crystaUized structures have been prepared by using spray pyrolysis method with solutions of citric acid [219]. The optimum concentration of citric acid was 0.4 M, in order to obtain micrometer-sized MgO particles. The function of citric acid in the spray solution was to alter the thermal properties of the solution and thus to control the morphologies of the particles. The micrometer-sized precursor particles with hollow porous structures which were... 

A series of works have been reported on preparation of YAG based phosphor powders by using spray pyrolysis method, with spray solutions of different fluxes [226-229]. It has been demonstrated that spray pyrolysis method can be used to control the morphologies and sizes of the YAG based phosphor powders in a very feasible way. Highly spherical particles with well controlled size distribution can be readily synthesized by optimizing the processing parameters. 

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