Suspended-particle devices

Figure 2.52. Cross-section schematic of an (a) electrochromic device and (b) suspended-particle device.

Conductive polymers have been produced to develop smart windows by electrodeposition of various high conductivity polymers on transparent conductive substrate. A suspended particle device that enables users to control the passage of light through glass or plastic windows has been commercialised. The specially treated panes can also be used to shield instrumentation. In such systems a polymer film between two panes of glass or plastic is... 

One of SACHEM s products is tetramethylammonium hydroxide (TMAH), which is sold to semiconductor industries. Suspended particles in TMAH solutions could cause severe mechanical damage to the electronic devices manufactured by their customers. The determination of the particle content in such solutions is therefore critical. It is performed with a laser-equipped particle counter, which provides 70% detection efficiency. The counting must take place in a clean room because tiny airborne particles can land in the solutions and give them a false high reading. A class 1000 environment is required in this case, which means that the count of particles in the air that are greater than or equal to 0.5 jrm in diameter must be less than 1000 per cubic foot. Typically, a customer s specification for TMAH solutions is less than 100 particles per milliliter for particles greater than or equal to 0.5 fim in diameter. 

An acid-leached polyethylene terephthalate (Mylar) sheet was placed inside the circumference of the centrifuge bowl to enable rapid recovery of trapped particles. Particles and lake water (4 L), retained in the centrifuge bowl after the selfsealing device isolated the bowl, were recovered and kept at 4 °C for transport to the laboratory. Time delay from the collection to laboratory processing varied from 24 to 36 h. At typical lake-water particle concentrations of 1 mg/L, more than 0.5 g of suspended particles could be collected in 1 h. On-station time limited the number of large-volume depths sampled per cruise to six or seven. The depths chosen were selected to be representative of distinct layers of the water column and also to correspond to depths at which sediment traps were deployed. 

Fibrous filters are the most economical and effective devices for the purification of air from suspended particles. This purification is achieved with minimal loss of pumping energy associated with flow resistance, compared with other types of filters. The porosity of such materials is 85-99%, and fiber diameter varies from 102 to 10 2 /um. 

The principle on which inertial impactors operate is based on the aerodynamic behavior of aerosol particles. Fig. 6 shows a schematic diagram of particle collection by an inertial collection device. When the direction of a gas flow changes, the suspended particles continue to move in the original direction of... 

Other materials being investigated include ferrocene with a bipyridinium salt,234 niobium oxide,235 nickel oxo-hydroxide,236 and cobalt oxohydroxide.237 The last is pale yellow in the reduced state and dark gray in the oxidized state. A typical electrolyte is lithium perchlorate in propylene carbonate. Solid electrolytes, such as a lithium salt (perchlorate, tetrafluoroborate, or triflate), in a polyepoxide238 or in a polyvinyl chloride gel in ethylene carbonate-propylene carbonate,239 lithium iodide in polyvinyl bu-tyral,240 and Naflon H (a polymeric perfluorocarbon-sulfonic acid),241 have also been tested. Some other systems use suspended particles between two panes of glass.242 When the particles are aligned by an electric field, the window becomes transparent. Combination photo-voltaic-electrochromic devices are under study.243... 

Suspended atmospheric particles vary in size and composition. " Smaller particles (<0.08 pm) arise from condensation from the vapor phase while the larger particles (>2.5 pm) are produced by processes such as the weathering of soils, volcanic activity, and so on. Composition of the particles will vary with location and total carbon comprises 10-20% of the total suspended particles (TSP)." The average urban TSP load has been reported to be 98 pg m of air." The vapor-particle distribution under held conditions is evaluated using a device" in which air is drawn through the sampler such that particles will be trapped hrst on a hlter while compounds in the vapor phase will be absorbed on the absorbent plug. Each phase... 

Precipitation Precipitation of aerosols is achieved using thermal or electrostatic precipitators. Thermal precipitation is effected through a sharp temperature gradient by suspending a wire across a cylindrical collection chamber. This device is especially effective for collection of particles smaller than 5 pm. The suspended particles migrate from a zone of high temperature to a low-temperature one. The thermal force is negligible for a less than 750°Ccm ... 

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