Aerosol techniques

Aerosol-Based Direct Fluorination. A technology that works on Hter and half-Hter quantities has been introduced (40—42). This new aerosol technique, which functions on principles similar to LaMar direct fluorination (Fig. 5), uses fine aerosol particle surfaces rather than copper filings to maintain a high surface area for direct fluorination. The aerosol direct fluorination technique has been shown to be effective for the synthesis of bicycHc perfluorocarbon such as perfluoroadamantane, perfluoroketones, perfluoroethers, and highly branched perfluorocarbons. 

SAMUEL PRUSSIN, Aerosol Techniques, Inc., Bridgeport, Conn. GEORGE LIEBERMAN, Rexall Drug Co., Los Angeles, Calif. 

Another application of microparticle technology is the production of polymeric microspheres, which are usually produced by emulsion polymerization techniques. But a variety of polymer colloids can be made by aerosol techniques (Partch et al, 1983 Nakamura et al, 1984 Partch et al, 1985). One advantage of the aerosol route is that larger sizes can be attained... 

In support of the conclusion based on silver, series of 0.2, 0.5, 1.0, 2.0, and 5.0 % w/w of platinum, iridium, and Pt-Ir bimetallic catalysts were prepared on alumina by the HTAD process. XRD analysis of these materials showed no reflections for the metals or their oxides. These data suggest that compositions of this type may be generally useful for the preparation of metal supported oxidation catalysts where dispersion and dispersion maintenance is important. That the metal component is accessible for catalysis was demonstrated by the observation that they were all facile dehydrogenation catalysts for methylcyclohexane, without hydrogenolysis. It is speculated that the aerosol technique may permit the direct, general synthesis of bimetallic, alloy catalysts not otherwise possible to synthesize. This is due to the fact that the precursors are ideal solutions and the synthesis time is around 3 seconds in the heated zone. 

To illustrate the capabilities of the aerosol process for the synthesis of solid state oxidation catalysts not normally obtained from classical synthesis, the preparation of a series of P-V-0 catalysts was examined. The original objective was to determine whether the synthesis of the reported (4) active phase, P-(VO)2P207, of the catalyst responsible for the selective oxidation of butane to maleic anhydride could be synthesized by the aerosol technique. 

Two series of catalysts were synthesized for subsequent evaluation as methane dimerization catalysts. The first series was alkali modified zinc oxide (6) and magnesium oxide catalysts (7), which were reported to be active for methane activation, while the second series was ion modified perovskites described by Machida and Enyo (8). The objective of the present study was to determine whether the aerosol technique could provide a wide range of ion substitutions as homogeneous solid solutions, and to determine whether moderately high surface area catalysts could... 

Figure 4. X-Ray diffraction patterns for phosphorous-vanadium oxide catalysts prepared by aerosol technique at 600 C, 8 seconds residence time, and 0.8 M V in feed a. Catalyst analyzed by XRD immediately after synthesis, b. catalyst calcined at 450°C in nitrogen for 3 hrs immediately after synthesis, c. Catalyst allowed to stand for 14 days in an air tight container at ambient temperature without calcining.

Finally, it is possible to produce aerosols by vaporization of solids and subsequent condensation, which under certain conditions may yield uniform spherical particles as shown on examples of NaCl (19-23), AgCl (24-26), V2Os (27), etc. It is quite apparent that all these techniques are based on physical changes of the matter that do not involve chemical reactions, while the emphasis in this chapter is on using the described aerosol technique to produce inorganic materials, in particular metal oxides and polymers, by chemical processes. 

Various metal alkoxides are ideal starting materials for the preparation of metal (hydrous) oxides by the described aerosol techniques, because many of these compounds are in the liquid state at room temperature, easily vaporized, and exceedingly reactive with water vapor. Additional advantage is the purity of the resulting powders, because the only products of the chemical reactions are the metal (hydrous) oxide and alcohol. The particles are, therefore, free of impurities, such as various ions, normally present in solids prepared from different salts. 

The aerosol technique can also be used to produce polymer colloids by addition polymerization. Thus, when droplets of toluene-2,4-diisocyanate (TD1) or 1,6-hexa-methylene diisocyanate (HDI) were brought into contact with ethylenediamine (EDA) vapor (in the apparatus shown in Fig. 1.5.3) spherical polyurea particles with modal diameters of 1-3 p,m were formed. The entire process, i.e., the formation of droplets and the polymerization, was carried out at moderate temperatures (<80°C)... 

The polydivinybenzene colloids prepared by the aerosol technique were carbonized to yield uniform porous spheres of carbon of relative high specific surface areas (69). 

In summary, the described aerosol technique offers a new way to produce exceedingly pure and morphologically predictable colloids. The products should especially find applications in areas of high value materials. While the principles of the procedure have been well established, it is now necessary to concentrate efforts on equipment designs that will yield large amounts of uniform droplets. 

In this chapter, we treat metallic fine particles whose size is less than micrometers in many cases down to nanometers, produced by physical methods in the gas phase (aerosol technique). Physical methods have a great advantage for producing fine particles because of their versatility and universality for application to many sorts of substances, rather than chemical methods, although they have a weak point in size control and mass production. It should be emphasized that chemically clean surfaces can be obtained by a physical method without any sophisticated techniques. If chemical reaction takes place, the surfaces of metallic particles are generally covered with unknown by-products. It is difficult to remove these contaminating species, once they have occurred, to reach the desired purity level. 

Fig. 9.4.1 Schematic diagram of a particle growth in the aerosol technique. Nucleation proceeds in between two substrates with high and low temperature, the difference of which is several thousands of kelvins, High-temperature substrate is a heating element and low-temperature substrate is a kind of coolant such as gas, liquid, or solid substrate, depending on the operation mode. (From Ref. 1,)...

Lead, tellurium, and selenium aerosols in 0.01 to 1 micrometer size range could be generated using a condensation aerosol technique. The particle size is dependent on the generation temperature. The aerosol output is dependent on both the generation temperature and the carrier gas flow rate. 

Messina MS, Smaldone GC. Evaluation of quantitative aerosol techniques for use in bronchoprovocation studies. J Allergy Clin Immunol 1985 75(2) 252-257. 

Aerosol Technique Aerosol of TiC was hydrolyzed in a home-made apparatus. AgCl was used as nucleating material. Similar syntheses were carried out with Ti(iv) alkoxides as the TiO, precursors. 

Generation of solid colloidal particles in aerosols has certain advantages over precipitation from homogeneous solutions described in Chapter IV. During precipitation from solutions it is usually impossible to predict a priori the shape of the resulting particles, while particles prepared by the aerosol methods are usually spherical because of the natural shape of liquid droplets dispersed in gas. Also, it was pointed out earlier (see Chapter IV) that in the case of particles of internally mixed composition, the molar ratio of constituents in the solid phase differs from that in solution [13], while in the case of aerosol technique the content of resulting solid particles is determined by the molar ratio of components in solution that is dispersed in the gas phase to form aerosol droplets. ... 

For more practical purposes, therefore, one should take recourse to metal particles as produced by other means, in particular on supports or in matrices. The advantage is the availability of macroscopic amounts of sample the disadvantage is that interaction with the supporting medium must be assessed. A great variety of synthetic methods exists, of which we can mention only a few. Metal clusters can be produced by aerosol techniques, by vapor deposition, by condensation in rare-gas matrices, by chemical reactions in various supports, e.g. zeolites, SiOi, AI2O3, or polymer matrices. Many different metal-nonmetal composites, such as the ceramic metals (cermets) have been obtained with metal particles with sizes varying from nanometers upward. In alternative approaches, metal particles are stabilized by chemical coordination with ligand molecules, as in metal colloids and metal cluster compounds. 

Lawford P, MacKenzie F. Pressurised bronchodilator aerosol technique influence of breath holding, time and relationship of inhaler to the mouth. Br J Dis Chest 1982 76 229-233. 

Lawford P, MacKenzie D. Pressurised aerosol technique. Lancet 1981 1 1003-1004. 

Pedersen 8, Ostergaard PA. Nasal inhalation as cause of inefficient pulmonary aerosol technique in children. Allergy 1983 38 191-194. 

Well-ordered and largely extended (up to 1 pm) 2-D superlattices by the selforganization of silver and gold nanopartides, protected by alkylthiolates, were identified by Whetten et al. in connection with the formation of 3-D assemblies (see Section 4.2.1) [6, 7]. The Ag particles were produced using a special aerosol technique in which elementary silver was evaporated at 1200-1500 K into an atmosphere of helium, followed by a cooling step to produce 4-5 nm Ag particles that were finally co-condensed with an excess of alkylthiols (C12 chains) [7]. 

We performed gas phase photocatalytic oxidation reactions of hydrocarbons by flowing a known mixture of heated humid air with organic vapor through an annular reactor (25). We used nanostructured TiOj coated using flame aerosol technique at optimized process conditions, which enabled us to achieve higher conversions and selectivities dian obtained by coating prepared by other methods. 

On-line Sizing of Colloidal Nanoparticles via Electrospray and Aerosol Techniques... 

Once the colloid has been transferred into the gas, its size distribution may be found by aerosol techniques.However, the high particle charge and the accompanying aerosol of involatile residues call for a number of modifications to available sizing procedures. 

Aerosol techniques on-line sizing of colloidal nanoparticles, 20-40 ultrafine powder synthesis, 64 Ag particles, synthesis method, 128 Aluminum nitride powder prepared via chemical synthesis, characterization using Fourier-transform IR spectroscopy, 312-332... 

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