Preparation of Aerosols

There are four common approaches to the preparation of aerosol dispersions  

In the condensation method, a sample of vapour-saturated gas is subjected to a rapid volume expansion. This lowers the temperature and causes a state of supersaturation. Condensation of the vapour will then take place on any particles or ions present in the sample. If the sample is free of particles and ions, there will still be collisions of vapour molecules that create clusters, called embryos, which can serve as nuclei for condensation. Although the seeding nuclei maybe of different sizes, they grow by diffusion of the condensable vapour to ultimate diameters that are almost independent of the original nuclei sizes. The condensation method can be used to make aerosols having diameters from about 36 nm to just over 1 pm and concentrations from about 10 to 10 particles/cm [64]. 

Example 7.2 The Wilson cloud chamber is a device that allows one to rapidly expand and cool a sample of gas adiabatically. This can be used to induce supersaturation in the gas, which in turn causes aerosol droplet formation by nucleation on particles in the chamber. The paths of ionized particles travelling in a gas are made visible since the particles, such as alpha or beta particles, leave a noticeable trail of the larger aerosol mist droplets as they move through the chamber. When this experiment is done using regular air, the ions are those that result naturally in the air from interaction with cosmic rays and from the decay of radioactive gases from soil emissions. The Wilson cloud chamber is named for Charles T.R. Wilson, who developed it in the late 1800s, and received the Nobel Prize for physics in 1927 (see Reference [65]). 

Example 7.3 The Sinclair-La Mer Aerosol Generator uses a superheater to form a supersaturated vapour, which is then cooled to produce aerosol nucleation and 

Evaporation/condensation reactors involve evaporating a solid, such as a metal, and then mixing it with a cool gas to induce condensation as an aerosol of metal particles. 

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Evans and Farr [314] patented a process for preparation of aerosol inhalants containing proteins and peptides (with particular reference to insulin) solubilized in RMs. 

Cool to room temperature when homogeneous. Preparation of Aerosol ... 

Practical aerosols exhibit size ranges from molecular clusters in the nanoscale (1 nm and larger) to dusts and clouds containing aerosol droplets that exceed the classical colloidal size range limits given earlier, easily ranging to about 100 pm (see Tables 1.5,9.4 and 9.5). Section 7.1 describes the preparation of aerosols. Subsequent chapters (especially Chapters 8, 9,13, and 15) provide many examples of aerosols in industry and everyday life. 

CH3CH2OHCH3. B.p. 82 C. Manufactured by hydrolysis of propene. Used in the production of acetone (propanone) by oxidation, for the preparation of esters (e.g. the ethanoate used as a solvent), amines (diisopropylamines, etc.), glycerol, hydrogen peroxide. The alcohol is used as an important solvent for many resins, aerosols, anti-freezes. U.S. production 1978 775 000 tonnes. 

Aerosol products are hermetically sealed, ensuring that the contents caimot leak, spill, or be contaminated. The packages can be considered to be tamper-proof. They deUver the product in an efficient manner generating Httie waste, often to sites of difficult access. By control of particle size, spray pattern, and volume deUvered per second, the product can be appHed directiy without contact by the user. For example, use of aerosol pesticides can minimize user exposure and aerosol first-aid products can soothe without applying painful pressure to a wound. Spray contact lens solutions can be appHed directiy and aerosol lubricants (qv) can be used on machinery in operation. Some preparations, such as stable foams, can only be packaged as aerosols. 

Other minor uses of ethyl chloride iaclude blowiag agents for thermoplastic foam (51) and styrene polymer foam (52), the manufacture of polymeric ketones used as lube oil detergents (53), the manufacture of acetaldehyde (qv) (54), as an aerosol propellent (55), as a refrigerant (R-160), ia the preparation of acid dyes (56), and as a local or general anesthetic (57,58). 

Specific advancements ia the chemical synthesis of coUoidal materials are noteworthy. Many types of genera ting devices have been used to produce coUoidal Hquid aerosols (qv) and emulsions (qv) (39—43) among them are atomizers and nebulizers of various designs (30,44—50). A unique feature of produciag Hquid or soHd coUoids via aerosol processes (Table 3) is that material with a relatively narrow size distribution can be routinely prepared. These monosized coUoids are often produced by relying on an electrostatic classifier to select desired particle sizes ia the final stage of aerosol production. 

Enzyme manufacturers have developed formulations that minimize the release of enzyme dust. In the case of Hquid preparations, handling precautions recommend users to avoid the formation of aerosol sprays. In all cases, direct contact with the skin or eyes should be avoided. Enzymes have a good record of occupational health and safety. 

The patent of Russia No. 2239170. A method of the preparation of standard samples of the atmospherie aerosols loaded on the filter / Korzhova E.N., Smagunova A.N., Kuznetsova O.V., Kozlov V.A. 

Other natural materials with expected intrinsic homogeneity properties that could be produced as CRMs include fractionated aerosols, conifer pollen, egg yolk or albumen, plankton of defined origin and size, and certain sediments. However, there are particular problems related to the collection and preparation, of large enough quantities of such matrices for their preparation as RMs. RM producers might initiate research and development to provide technical solutions to handle some of these problems. 

C Sirand, J-P Yarlet, AJ Hickey. Aerosol-filling equipment for the preparation of pressurized pack pharmaceutical formulations. In AJ Hickey, ed. Pharmaceutical Inhalation Aerosol Technology. New York Marcel Dekker, Inc., 1992, pp. 187-217. 

Some of the reports are as follows. Mizukoshi et al. [31] reported ultrasound assisted reduction processes of Pt(IV) ions in the presence of anionic, cationic and non-ionic surfactant. They found that radicals formed from the reaction of the surfactants with primary radicals sonolysis of water and direct thermal decomposition of surfactants during collapsing of cavities contribute to reduction of metal ions. Fujimoto et al. [32] reported metal and alloy nanoparticles of Au, Pd and ft, and Mn02 prepared by reduction method in presence of surfactant and sonication environment. They found that surfactant shows stabilization of metal particles and has impact on narrow particle size distribution during sonication process. Abbas et al. [33] carried out the effects of different operational parameters in sodium chloride sonocrystallisation, namely temperature, ultrasonic power and concentration sodium. They found that the sonocrystallization is effective method for preparation of small NaCl crystals for pharmaceutical aerosol preparation. The crystal growth then occurs in supersaturated solution. Mersmann et al. (2001) [21] and Guo et al. [34] reported that the relative supersaturation in reactive crystallization is decisive for the crystal size and depends on the following factors. 

Chan, H.-K., and Gonda, L, Preparation of radiolabeled materials for studies of deposition of fibers in human respiratory tract, J. Aerosol Med., 6 241-249 (1993). 

Hidy, G. M. Characterization of Aerosols in California (ACHEX). Vol. 1. Summary. Final Report. (Prepared for California Air Resources Board) Thousand Oaks, Calif. Rockwell International, 1974. 33 pp. 

Upeles, M., D. A. Landis, and G. M. Hidy. The Formation of Aerosols in a Photochemical Fast Flow Reactor. EPA-68-02-0771. Prepared for the Environmental Protection Agency and the Coordinating Research Council. Thousand Oaks, Calif. Rockwell International Science Center, 1975. 67 pp. 

The Yellow Card Scheme was soon beginning to pay dividends. In early 1966, the YeUow Card Scheme had identified methyldopa as a cause of haemolytic anaemia and an appropriate advice was issued. Another success was the detection of a faulty batch of a particular product, which the manufacturer immediately withdrew, underlining the value of an efficient procedure for tracing a batch. During June 1967, the Committee distributed a leaflet on the use of aerosols in asthma. This was prompted by the death rate amongst asthmatic patients aged 5 to 34 years that had risen some 300% above the level in 1959-60 when such preparations were introduced. By September 1968, the rate had dropped to only 50% above that seen in 1959-60 despite sales having dropped only 20%. 

Figure 1. Aerosol process configuration for the continuous preparation of metal oxides by the High Temperature Aerosol Decomposition (HTAD) Process.

Figure 2. Compositional diagram for the preparation of bismuth molybdate catalysts using the HI AD process configuration shown in Figure 1 at 900°C using air as make up gas. Plot is of concentrations of bismuth used in the reacting solution vs arc plasma analyzed concentrations of the finished catalysts directly fi-om HTAD reactor Circles Co-precipitation prepared materials. Triangles Up flow prepared aerosol materials. Squares. Down flow prepared aerosol materials.

The preparation of precious metal supported catalysts by the HTAD process is illustrated by the synthesis of a wide range of silver on alumina materials, and Pt-, Pt-Ir, Ir-alumina catalysts. It is interesting to note that the aerosol synthesis of alumina without any metal loading results in a material showing only broad reflections by XRD. When the alumina sample was calcined to 900°C, only reflections for a-alumina were evident. The low temperature required for calcination to the alpha-phase along with TEM results suggest that this material was formed as nano-phase, a-alumina. Furthermore, the use of this material for hexane conversions at 450°C indicated that it has an exceptionally low surface acidity as evidenced by the lack of any detectable cracking or isomerization. 

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. 

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