Aluminum, vapor transport

Growth of single crystals. Crystals of the aluminum selenide halides (needles, maximum length 15 mm) were grown by vapor transport in sealed ampoules between two temperatures (380 and 320°C for Al-SeCl, and 350 and 300°C for AlSeBr and AlSel) over a period of two months. A large excess of the halogenide was used (266). 

Recently one of the solutions to overcome this problem has been proposed.This does concern surface modification of the pyrochlore-based oxide.s. It is known that cerium and zirconium chlorides provide vapor phase complexes with aluminum chloride at elevated temperatures.The new surface modification technique utilizes the formation of these vapor complexes to remove and modify the top surface of the pyrochlore ceria-zirconia solid solution. This method is named "chemical filing". Application of the above complexes formation has already been demonstrated for the vapor phase extraction and mutual separation of rare earths based on the so-called chemical vapor transport (CVT). ... 

As a pyrometallurgical approach, Ozaki et al. (1999) studied the appUcatimi of the chemical vapor transport method described in Section 2.3.1. Used polishing powder was chlorinated by chlorine gas at 1000 °C, and transported along the temperature gradient via gaseous complex with aluminum chloride. The rare-earth chlorides were mainly crmdensed over the temperature range of 457-947 C. The purity of the rare-earth chlorides in this temperature range was about 95%. 

These reactions are thermodynamically unfavorable at temperatures below ca 1500°C. However, at temperatures in the range from 1000 to 1200°C a small but finite equiUbrium pressure of barium vapor is formed at the reaction site. By means of a vacuum pump, the barium vapor can be transported to a cooled region of the reactor where condensation takes place. This destroys the equiUbrium at the reaction site and allows more barium vapor to be formed. The process is completely analogous to that used in the thermal reduction of CaO with aluminum to produce metallic calcium (see Calcium AND CALCIUM alloys). 

Figure 5.5 Winds in the solar nebula might be one of the possible processes responsible for the mixing of hot and cold components found in both meteorites and comets. Meteorites contain calcium-aluminum-rich inclusions (CAIs, formed at about 2000 K) and chondrules (formed at about 1650K), which may have been created near the proto-Sun and then blown (gray arrows) several astronomical units away, into the region of the asteroids between Mars and Jupiter, where they were embedded in a matrix of temperature-sensitive, carbon-based cold components. The hot component in comets, tiny grains of annealed silicate dust (olivine) is vaporized at about 1600 K, suggesting that it never reached the innermost region of the disk before it was transported (white arrows) out beyond the orbit of Pluto, where it was mixed with ices and some unheated silicate dust ( cold components). Vigorous convection in the accretion disk may have contributed to the transport of many materials and has been dramatically confirmed by the Stardust mission (Nuth 2001).

Container Cleanliness of Marketing Product The previous cleanliness of containers filled with the product will depend on their transportation exposure, composition, and storage conditions. Glass containers usually carry at least mold spores of different microorganisms, especially if they are transported in cardboard boxes. Other containers and closures made with aluminum, Teflon, metal, or plastic usually have smooth surfaces and are free from microbial contamination but may contain fibers or insects [45], Some manufacturers receive containers individually wrapped to reduce contamination risks and others use compressed air to clean them. However, the cleanliness of wrapped containers will depend on the provider s guarantee of the manufacturing process and compressed-air equipment may release vapors or oils that have to be tested and validated [6],... 

Figure 3.9 shows a schemalic representation of the chemical filing process. The first step of the process involves the chlorination of the surface of the pyrochlore-based ceria-zirconia sample. The extent of the chlorination can be controlled by the concentration of the chlorine gas and/or chlorination time and the cerium and zirconium chlorides partially formed on the surface are vaporized and transported by the formation of gaseous complexes with aluminum chloride. This chemical filing process is carried out at 1273 K to stabilize the surface modification effects at high temperatures. A similar effect can also be achieved by chlorination with ammonium chloride followed by dominant vaporization of formed zirconium chloride. ... 

H-mordenites with various Si/Al ratios (5.9 - 16.9) have proved to be active for the SCR of NO with CH4 in the 400-600 C temperature range. However, they suffered an irreversible deactivation after an incursion at 650°C for 1 h under reaction stream, due to a dealumination process. While acid dealumination only affects the free exchange of gaseous molecules between the main channels and the side-pockets (as seen by t29Xe NMR), the aluminum extracted from the lattice of the mordenite during the SCR of NOx at 650°C (without water vapor in the feed) also hinders the diffusive transport along the main channels. 

For highly reactive gases/active surfaces (e.g., water vapor/aluminum), the rate of reaction of the environment with the newly created crack surfaces at the crack tip is limited by the rate of transport of gases by molecular (Knudsen) flow to the crack tip. The extent of reaction with the newly created crack surface, or surface coverage 9 is proportional to the rate of arrival of the gas and the time for reaction as described in Chapter 8 namely,... 

Pa are comparable with those obtained in air (at 40 to 60 percent relative humidity), distilled water, and 3.5 percent NaCl solution [1]. The data in dehumidified argon correspond to those in vacuum at less than 0.50 /uPa. These data are also shown in Fig. 9.2 as a function of water vapor pressure at three AK levels. The error bands represent ninety-five percent confidence intervals computed from the residual standard deviations in each set of data. The results in Fig. 9.2 show that at a frequency of 5 Hz, the rate of crack growth is essentially unaffected by water vapor until a threshold pressure is reached. (This threshold pressure is attributable to the significant transport limitation at these very low water vapor pressures.) The rate then increased and reached a maximum within one order of magnitude increase in vapor pressure from this threshold. The maximum rate is equal to that obtained in air, distilled water, and 3.5 percent NaCl solution (at 20 Hz). The transition range, in terms of pressure/frequency, is comparable to that reported by Bradshaw and Wheeler [9] on another aluminum alloy. 

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