Vapor condensation/deposition

Identify each phase change with the proper term vaporization, condensation (deposition), sublimation, melting (fusion), or freezing. 

Condensation Scrubbing The collection efficiency of scrubbing can be increased by the simultaneous condensation of water vapor from the gas stream. Water-vapor condensation assists in particle removal by two entirely different mechanisms. One is the deposition of particles on cold-water droplets or other surfaces as the result of... 

Figure 19. Schematic view of the ion assisted deposition technique. As the vapor condenses on the substrate, ions hammer the coating in formation to compress it.

Condensation Scrubbing The collection efficiency of scrubbing can be increased by the simultaneous condensation of water vapor from the gas stream. Water-vapor condensation assists in particle removal by two entirely different mechanisms. One is the deposition of particles on cold-water droplets or other surfaces as the result of Stefan flow. The other is the condensation of water vapor on particles as nuclei, which enlarges the particles and makes them more readily collected by inertial deposition on droplets. Both mechanisms can operate simultaneously. However, for the buildup of particles by condensation to be effective, there must be adequate time for the particles to grow substantially before the principal gas-liquid-contacting operation takes... 

In practice, a mixture of actinide dioxide and graphite powder is first pelletized and then heated to 2275 K in vacuum in a graphite crucible until a drop in the system pressure indicates the end of CO evolution. The resulting actinide carbide is then mixed with tantalum powder, and the mixture is pressed into pellets. The reduction occurs in a tantalum crucible under vacuum. At the reduction temperature, the actinide metal is vaporized and deposited on a tantalum or water-cooled copper condenser. 

Nanomaterials are also prepared by chemical vapor deposition (CVD) or chemical vapor condensation (CVC). In these processes, a chemical precursor is converted to the gas phase and then it undergoes decomposition to generate the nanoparticles. These products are then subjected to transport in a carrier gas and collected on a cold substrate, from where they are scraped and collected. The CVC method may be used to produce a variety of powders and fibers of metals, compounds, or composites. The CVD method has been employed to synthesize several ceramic metals, intermetallics, and composite materials. 

It is well established that in non-arid regions, precipitation is the primary means by which contaminating aerosols are removed from the atmosphere. Many chemical, physical, and meteorological parameters affect the micro, meso, and synoptic scale processes through which precipitation transports radioactive aerosols from atmosphere to ground. These parameters include the radioactivity component of the natural aerosols, the processes by which water vapor condenses and grows to raindrops, and the incorporation of the radioactive aerosol into the precipitation. Thus, the prediction of specific deposition from fundamental considerations has proved to be difficult because of the many uncertainties yet prevalent in these processes. Many attempts have been made to evaluate the deposition of these aerosols by empirical studies. 

As the size of species increases due to reactions in gas phase, the vapor pressure of the species decreases, enhancing the condensation (deposition of reactive species) on the surface. 

The dew point is the temperature at which a vapor condenses when cooled at constant pressure. If air of the condition denoted by point A in Fig. 4 is cooled, the relative humidity increases until the mixture is fully saturated. This condition is given by point B the temperature coordinator is the dew point, which can be measured rapidly by evaporating ether in a silvered bulb. The temperature at which dew deposits from the surrounding air is noted and the humidity is read directly from a psychrometric chart. 

Valmari, T, Lind, T.M., Kauppinen, E.I., 1998, Field study on ash behaviour during circulating fluidized>bed combustion of biomass. 2. Ash deposition and alkali vapor condensation. Energy Fuels 13 390-395. 

One of the most useful and convenient techniques for the purification of solids is sublimation. In this process, the solid is warmed (often under reduced pressure) until its vapor pressure becomes high enough for it to collect on a cooled surface placed above the solid. Sublimation is limited to compounds which have reasonably high vapor pressures and which pass directly from the solid state to the vapor. However, the process involving initial melting followed by vaporization and deposition on the condenser may be carried out in the same apparatus and is often loosely called sublimation. 

The basic structure of polycrystalline cadmium telluride (CdTe) thin-film cells has a glass superstrate and a layer of TCO as front contact, a near-transparent n-type cadmium sulfide (CdS) window layer, p-type CdTe, and a metallic rear contact. The CdTe is usually deposited by three families of techniques. In the first group (vapor transport deposition, close space sublimation, physical vapor deposition, and sputtering) elemental vapors of Cd and Te condense and react on the substrate. In the second (electrodeposition), Cd + and HTe02" ions in acidic electrolyte are galvanically reduced at the surface ... 

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