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Vapour transport

The direction of vapour transport across a thermal gradient... [Pg.89]

Since in most practical circumstances at temperatures where vapour transport is used and at around one atmosphere pressure, die atomic species play a minor role in the distribution of atoms, it is simpler to cast the distribution equations in terms of the elemental molecular species, H2, O2 and S2, tire base molecules, and the derived molecules H2O, H2S, SO2 and SO3, and eliminate any consideration of the atomic species. In this case, let X, be tire initial mole fraction of each atomic species in the original total of atoms, aird the variables Xi represent the equilibrium number of each molecular species in the final number of molecules, N/. Introducing tire equilibrium constants for the formation of each molecule from tire elemental atomic species, with a total pressure of one aurros, we can write... [Pg.96]

The reaction mechanisms are quite complicated in these syntheses, the kinetics depending on inter-diffusion rates in neighbouring particles, the formation of transient liquid phases, and in some cases, the vapour transport of a reactant. The presence of the latter can be detected by dre retarding effect of increased pressure in an inert surrounding atmosphere. [Pg.217]

Another application is in tire oxidation of vapour mixtures in a chemical vapour transport reaction, the attempt being to coat materials with a tlrin layer of solid electrolyte. For example, a gas phase mixture consisting of the iodides of zirconium and yttrium is oxidized to form a thin layer of ytnia-stabilized zirconia on the surface of an electrode such as one of the lanthanum-snontium doped transition metal perovskites Lai j.Srj.M03 7, which can transmit oxygen as ions and electrons from an isolated volume of oxygen gas. [Pg.242]

Returning to the discussion of the movement of small molecules in plastic materials, the kinetics and mechanisms of gas and vapour transport have been described in several review 31 33) and need not to be repeated here. [Pg.201]

Van der Waals solid 123 Vapour transport 201 Vickers hardness 122 Viscoelastic 203... [Pg.222]

Both reactions involve the formation of a vapour-transporting species from four gaseous reactant molecules, but whereas the tetra-iodide of zirconium is a stable molecule, the nickel tetracarbonyl has a relatively small stability. The equilibrium constants for these reactions are derived from the following considerations ... [Pg.88]

Low levels of structural Ge" have also been observed in natural hematite from the Apex mine, Utah (Bernstein Waychunas, 1987) and to achieve charge balance, incorporation of two Fe for one Ge", i.e. similar to the two Fe" for one in ilme-nite, has been suggested. Synthetic, single crystals of Ge substituted hematite have also been grown by a chemical vapour transport method (Sieber et al. 1985). A range of elements including Zr, Ge, Hf, V, Nb, Ta, W and Pb has been used as low level dopants (2 10 - 0.2 g kg ) to improve the semiconductor behaviour of hematite anodes (Anderman Kermedy, 1988). The increase in unit cell c from 1.3760 to 1.3791 nm and in a from 0.50378 to 0.50433 nm indicated that Nd (as an inactive model for trivalent actinides of similar ionic size (Am r = 0.0983 nm Nd " r = 0.098 nm)) was incorporated in the structure (Nagano et al. 1999). [Pg.55]

Single crystals from 50-800 pm across can be synthesised by chemical vapour transport. Hematite powder is held for on week in a silica tube with a temperature gradient of 1000-850 °C in an atmosphere of HCl(5.3kPa)/02 (133 Pa) (Moukassi et al., 1984). [Pg.535]

The case of thin CuPc films is also intriguing. When grown by physical vapour transport under unit gravity conditions the films contain mixtures of both a- and -polymorphs (see Fig. 1.26), while under microgravity, again in the Space Shuttle, the films contain predominantly a new polymorphic form designated as M-CuPc... [Pg.137]

Fig. 5. UO2 single crystals prepared by chemical vapour transport with TeCl4... Fig. 5. UO2 single crystals prepared by chemical vapour transport with TeCl4...
Figure 2.8 Schematic diagram of the concentration of fruit juice by vapour transport across a porous Teflon membrane. Figure 2.8 Schematic diagram of the concentration of fruit juice by vapour transport across a porous Teflon membrane.
In CVD, solids are formed from gaseous compounds. In chemical vapour transport, a solid or solids interact with a volatile compound and a solid product is deposited in a different part of the apparatus. It is used both for preparing compounds and for growing crystals from powders or less pure crystalline material. [Pg.172]

Chemical vapour transport has been used to grow magnetite crystals using the reaction of magnetite with hydrogen chloride gas ... [Pg.172]

FIGURE 3.13 Growth of magnetite crystals using chemical vapour transport... [Pg.172]

Crystals of silica can be grown using the chemical vapour transport method with hydrogen fluoride as a carrier gas. The reaction involved is ... [Pg.178]

Table 3.8. Some crystals grown by chemical vapour transport method ... Table 3.8. Some crystals grown by chemical vapour transport method ...
Many methods have been used for synthesis of nano-sized particles vapour transport [2], precipitation of homogeneous solution [3], synthesis by sol-gel process [4], freeze-drying... [Pg.115]


See other pages where Vapour transport is mentioned: [Pg.2414]    [Pg.86]    [Pg.91]    [Pg.102]    [Pg.86]    [Pg.91]    [Pg.102]    [Pg.87]    [Pg.137]    [Pg.160]    [Pg.172]    [Pg.159]    [Pg.159]    [Pg.161]    [Pg.196]    [Pg.197]   
See also in sourсe #XX -- [ Pg.161 ]

See also in sourсe #XX -- [ Pg.161 ]




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