Generation using aerosol processes

Finally the aerosol process could be used to coat particles, as exemplified in the system of titania cores and polyurea shells (39). In this case the titania particles were generated from Ti(IV) ethoxidc as described earlier, then contacted with dried... 

Most filtration processes used in large-scale biotechnology should not have the potential to generate microbial aerosols. Filtration columns normally use gravitational forces to separate products from impurities and so are low energy processes. The only potential problem can come in either rotary vacuum filtration or with filter presses if a violent method of biomass removal from the filter is used. Wickramanayake has reported that it is often the practice with filter presses to knock the cell mat of the filter with hammers. This practice has been shown to generate microbial aerosols. 

It is known that health hazards are caused by inhalation of sub-micron aerosol particles. Drinker and Hatch (1936) stated that vast numbers of particles below 0.25-pm radius are generated by industrial processes and they considered this sub-micron aerosol to be quite dangerous. Particles below 0.1-pm radius are too small for direct microscopic observation. Likewise, the standard light scattering techniques cannot be used. Consequently, the methods in use depend on observation of the particles with the ultramlcroscope or electron microscope. 

Ultrasonic devices have been extensively used to process sol-gel precursor solutions, e.g. precursor dispersion in liquid solution. Besides, several works report on the fabrication of calibrated powders from ultrasonically sprayed sol-gel precursors (process D, according to classification by Vigui6 and Spitz). The sol-gel fabrication of micro-lenses from a drop-on-demand ultrasonic nozzle (ink-jet type) was also studied in details (Biehl, 1998 Danzebrink, 1999, 2001). However, in this latter case, no aerosol was formed. When considering the use of an ultrasonically generated aerosol, it appears that very few works... 

Figure 6.17. Typical data generated by the Amherst Process Instruments Inc. Aerosizer for aerosol systems, and powders aerosolized prior to characterization smdies. a) Calibration using aerosols of standard latex spheres of known size, b) Characterization of a mixture standard of polystyrene latex spheres, c) Characterization of a sample of 5 micron silica microspheres mixed with a small number of 10 micron microspheres. D) Glass spheres used in reflective paint (ballotini). E) Two oil mists diatacterized by direct injection into the Aerosizer .

Capture efficiency is the fraction of generated contaminant that is directly captured by the hood. Measurement of capture efficiency involves measuring concentration of process-generated contaminant or a tracer material. Using process-generated contaminant requires use of instruments suited to each specific contaminant and its conditions (temperature, pressure, concentration, form, etc.). In order to facilitate these measurements, a tracer is often substituted for the process-generated contaminant. The tracer is usually a gas (sulfur hexafluoride, nitrous oxide, helium, or similar), but an aerosol (particles) can also be used (potassium iodide, polystyrene particles, microbiological particles, etc.). The chosen tracer should be as similar to the real contaminant as possible, but at the same time should... 

For non-volatile sample molecules, other ionisation methods must be used, namely desorption/ionisation (DI) and nebulisation ionisation methods. In DI, the unifying aspect is the rapid addition of energy into a condensed-phase sample, with subsequent generation and release of ions into the mass analyser. In El and Cl, the processes of volatilisation and ionisation are distinct and separable in DI, they are intimately associated. In nebulisation ionisation, such as ESP or TSP, an aerosol spray is used at some stage to separate sample molecules and/or ions from the solvent liquid that carries them into the source of the mass spectrometer. Less volatile but thermally stable compounds can be thermally vaporised in the direct inlet probe (DIP) situated close to the ionising molecular beam. This DIP is standard equipment on most instruments an El spectrum results. Techniques that extend the utility of mass spectrometry to the least volatile and more labile organic molecules include FD, EHD, surface ionisation (SIMS, FAB) and matrix-assisted laser desorption (MALD) as the last... 

In ICP-AES and ICP-MS, sample mineralisation is the Achilles heel. Sample introduction systems for ICP-AES are numerous gas-phase introduction, pneumatic nebulisation (PN), direct-injection nebulisation (DIN), thermal spray, ultrasonic nebulisation (USN), electrothermal vaporisation (ETV) (furnace, cup, filament), hydride generation, electroerosion, laser ablation and direct sample insertion. Atomisation is an essential process in many fields where a dispersion of liquid particles in a gas is required. Pneumatic nebulisation is most commonly used in conjunction with a spray chamber that serves as a droplet separator, allowing droplets with average diameters of typically <10 xm to pass and enter the ICP. Spray chambers, which reduce solvent load and deal with coarse aerosols, should be as small as possible (micro-nebulisation [177]). Direct injection in the plasma torch is feasible [178]. Ultrasonic atomisers are designed to specifically operate from a vibrational energy source [179]. 

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