Glass aerosols

Figure 7.11. Photo of a glass aerosol delivery system used to spray solvent-suspended particulates onto a TEM grid.

Glass aerosols inevitably cost more than metal cans but offer plus features on appearance, which is highly desirable for toiletries and cosmetics. 

It is in the field of aerosols that metal containers have predominantly established themselves. Although glass, plastic and plastic-coated glass aerosols are finding their own specialised applications, metal aerosols are likely to retain the bulk of the market as long as cost advantages are offered. 

Most products are assessed directly from the bottle or jar, soap wrapper or box. However, some products, the true odour characteristics of which show up better in solution, are dissolved in warm water in an assessment cup. Aerosols are assessed on test pads, with time allowed for the propellant to evaporate. Testing in special, plastic-coated, clear, glass aerosols may be required in cases where solubility or discolouration reactions need to be observed inside the product. 

Both aluminum and glass aerosol containers are available. Aluminum aerosol canisters are light, impervious to light, robust, and cheap to make. Glass containers are now very rare. Typically they are laminated or plastic-coated so they can withstand pressures of up to 150 psig. Occasionally the inert nature of glass containers makes them a more suitable choice for some solution formulations. 

A wide variety of colloids are foimd in everyday life forming silver-centers in photographic films, the red color of glass, aerosols, exhausts, precipitates or just dust and dirt. Thus, the discovery of the colloidal state of matter alre y dates back hundreds of years based on inventions and theories from Faraday, Mie, Ostwald, Seitz, Svedberg and Zsigmondy. Since 1986 clusters as a base for nanotechnology, nano-engineering or nano-... 

The aim of breaking up a thin film of liquid into an aerosol by a cross flow of gas has been developed with frits, which are essentially a means of supporting a film of liquid on a porous surface. As the liquid flows onto one surface of the frit (frequently made from glass), argon gas is forced through from the undersurface (Figure 19.16). Where the gas meets the liquid film, the latter is dispersed into an aerosol and is carried as usual toward the plasma flame. There have been several designs of frit nebulizers, but all work in a similar fashion. Mean droplet diameters are approximately 100 nm, and over 90% of the liquid sample can be transported to the flame. 

The sample solution flows onto a piece of fritted glass through which argon gas flows. The flow of argon is broken down into narrow parallel streams of high linear velocity, which meet the thin film of liquid percolating into the pores of the frit. At the interfaces, an aerosol is formed and is blown from the top of the frit. 

Some solid materials are very intractable to analysis by standard methods and cannot be easily vaporized or dissolved in common solvents. Glass, bone, dried paint, and archaeological samples are common examples. These materials would now be examined by laser ablation, a technique that produces an aerosol of particulate matter. The laser can be used in its defocused mode for surface profiling or in its focused mode for depth profiling. Interestingly, lasers can be used to vaporize even thermally labile materials through use of the matrix-assisted laser desorption ionization (MALDI) method variant. 

The previous discussion has centered on how to obtain as much molecular mass and chemical structure information as possible from a given sample. However, there are many uses of mass spectrometry where precise isotope ratios are needed and total molecular mass information is unimportant. For accurate measurement of isotope ratio, the sample can be vaporized and then directed into a plasma torch. The sample can be a gas or a solution that is vaporized to form an aerosol, or it can be a solid that is vaporized to an aerosol by laser ablation. Whatever method is used to vaporize the sample, it is then swept into the flame of a plasma torch. Operating at temperatures of about 5000 K and containing large numbers of gas ions and electrons, the plasma completely fragments all substances into ionized atoms within a few milliseconds. The ionized atoms are then passed into a mass analyzer for measurement of their atomic mass and abundance of isotopes. Even intractable substances such as glass, ceramics, rock, and bone can be examined directly by this technique. 

Containers. Aerosol containers, made to withstand a certain amount of pressure, vary in both size and materials of constmction. They are manufactured from tin-plated steel, aluminum, and glass. The most popular aerosol container is the three-piece tin-plated steel container. Glass containers, which are usually plastic coated, generally have thicker walls than conventional glass jars. They are limited to a maximum size of 120 mL and are used for pharmaceutical and cosmetic aerosols. 

The DEP of numerous particle types has been studied, and many apphcations have been developed. Particles studied have included aerosols, glass, minerals, polymer molecules, hving cells, and cell organelles. Apphcations developed include filtration, orientation, sorting or separation, characterization, and levitation and materials handhng. Effects of DEP are easily exhibited, especially by large particles, and can be apphed in many useful and desirable ways. DEP effects can, however, be observed on particles ranging in size even down to the molecular level in special cases. Since thermal effects tend to disrupt DEP with molecular-sized particles, they can be controlled only under special conditions such as in molecular beams. 

FIG. 22-36 Efficiency of an electrofilter as a function of gas flow rate at 5 different voltages. Experimental materials l- im aerosol of dioctyl phthalate glass-fiher filter. Symbols O, no voltage applied A, 2 kV , 3.5 kV , 5 kV , 7 kV. After Fielting et ah, Dielectrophoretic Filtration of Solid and Liquid Aerosol Particulates, Prepr. 75-32.2, 68th ann. meet., AirPollut. Conttol Assoc., Boston, June 1975.)... 

Recent applications of e-beam and HF-plasma SNMS have been published in the following areas aerosol particles [3.77], X-ray mirrors [3.78, 3.79], ceramics and hard coatings [3.80-3.84], glasses [3.85], interface reactions [3.86], ion implantations [3.87], molecular beam epitaxy (MBE) layers [3.88], multilayer systems [3.89], ohmic contacts [3.90], organic additives [3.91], perovskite-type and superconducting layers [3.92], steel [3.93, 3.94], surface deposition [3.95], sub-surface diffusion [3.96], sensors [3.97-3.99], soil [3.100], and thermal barrier coatings [3.101]. 

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