Powder preparation aerosol technique

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 three major routes are (i) true liquid crystal templating at high surfactant concentrations, which is used for the formation of monoliths, thick layers or, via electrodeposition techniques, formation of thin films (ii) cooperative self assembly at surfactant concentrations where micelles are present in solution, which can be used to make powders (with either well-defined particle shapes or random structures), fibres and thin films grown at interfaces from solution and (iii) EISA at very low surfactant concentrations, where no micelles are initially present in solution, and solutions are in general prepared in nonaqueous solvents. This route is used to prepare thin films by dip or spin coating and powders via aerosol routes. The following sections will look at the current understanding of the mechanisms involved in each route to mesoporous materials. 

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... 

The diversity of sizes and shapes of ceramic powders prepared by homogeneous precipitation, phase transformation, or aerosol techniques are reviewed by Matijevic and Gherardi [163]. (See, e.g., Fig. 12.) The... 

In an extension of the spray-drying technique called spray roasting , evaporative decomposition of solutions (EDS) , spray pyrolysis , or aerosol pyrolysis , the temperature of the heated chamber is high enough to decompose the dried salts after the solvent has evaporated. Nitrate salts are used because of their low decomposition temperatures. The technique eliminates the problems of handling dried nitrate powders, which can be hydroscopic. These methods are used to prepare chalcogenide powders" and barium titanate . 

The effect of processing technique on the aerosol performance of insulin formulations prepared by DG antisolvent precipitation and spray drying has been investigated. Two types of insulin formulations were produced. They were 1 20 insulin-mannitol (IM) and 1 20 8 insulin-mannitol-citric acid (IMC). Mannitol is an excipient commonly used to improve aerodynamic performance of powders for inhalation delivery. Citric acid has been found effective in improving insulin absorption in the lungs. ... 

A third technique used to prepare both Gd-doped CeOi and NiO/YSZ powders is that of aerosol flame deposition [134, 135]. In the case of NiO/YSZ powders used for the anodes (see Chapter 12), nanosized spherical particles were obtained and the particle size distribution could be limited by controlling the processing parameters [135]. Subsequently, the electrical conductivity of 70% NiO/YSZ was found to be lO Scm at 700°C, with the material exhibiting typically metallic behavior. However, the use of such materials in fuel cells was not reported. 

To overcome these problems, another comminution technique—atomization—was developed. Atomization produces solid or aerosol particles with reduced sizes by spraying molten material or material solution or suspension under conditions such that it breaks down and then solidifies as fine powder [32]. In a typical atomization process, a molten material passing through a nozzle scatters into fine droplets by a highspeed medium (e.g., gas or water) and then the droplets solidify to powder. Obviously, the atomization technique is highly efficient for preparing micron and submicron powders at industrial scales and recent development has enabled atomization to produce nanoparticles of sizes down to 20nm [33]. 

During the preparation of medicines, steam, vapour, aerosols, dust and fumes can be released, which may pose a health risk for the operator. It is not always possible to change the process releasing these hazardous substances. As a consequence it can be necessary to protect operators in preparation or quality control areas from exposure to the product or the active substance. This can be done by active ventilation and exhaust and by filtration in order to protect the environment (see also Sect. 26.4.1). The appropriate equipment may be fume cupboards, moveable exhaust ducts, powder exhaust units, (bio)safety cabinets and isolators. Fumes, gas mixtures and volatiles might be absorbed by special filters, but in pharmacy practice only the technique of exhausting and screen filtration is usually used. 

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