Vapor-phase transfer

A CVD reaction can occur in one of two basic systems the closed reactor or the open reactor (also known as close or open tube). The closed-reactor system, also known as chemical transport, was the first typetobeusedforthe purification of metals. It is a hybrid process which combines vapor-phase transfer with solid-state diffusion. As the name implies, the chemicals are loaded in a container which is then tightly closed. A temperature differential is then applied which provides the driving force for the reaction. 

UV-induced surface grafting of a polymer sheet using vapor phase transfer of sensitizer and monomer from a volatile solution (9). 

Two methods for modification of polymer surfaces by photoinitiated graft copolymerization have been developed a discontinuous method (1) with vapor phase transfer of initiator and monomer and a continuous method (2) with presoaking of a film strip or a fiber bundle in a solution of initiator and monomer. Both methods have been applied to polyelefins and linear polyester. 

Capping. Capped silica-alumina was prepared by vapor phase transfer of hexamethyldisilazane (> 99.5%, Aldrich) onto calcined silica-alumina until there was no further uptake, as indicated by stabilization of the pressure. The reactor was evacuated and the material heated to 350°C under dynamic vacuum for 4 h to remove ammonia produced during the capping reaction. 

Deposition by sputtering and laser ablation (vapor-phase transfer from a target bombarded by inert gas ions or laser beam) or ion beam mixing of nanoscale multilayers, all of which similarly can produce nonequilibrium species Mechanical alloying, a process in which elemental powders are blended and alloyed by ball milling, can produce ultrafine grain sizes and nonequilibrium phases that store the mechanical energy imported in the process. ... 

The number of vapor phase transfer units is obtained from Equation (12.74), where the residence time Iq is based on the volume of gas flowing through the two-phase mixfiire on the tray. 

Figure 140. Change in nitroglycerin content uniformity in sublingual tablet due to vapor-phase transfer, before (a) and after storage at 25°C for 5 months (b). (Reproduced from Ref. 596 with permission.)...

The tight sides of Eqs. (5.6-5) and (S.6-6) define the number of vapor-phase transfer units and the number of overall vapor-phase transfer units (vapor concentration basis), respectively. Thus, the required height... 

The mess transfer cnefflcienis in Eq. (5.9-4) mey be evaluated by various means. According to the film medet, and for the example of vapor-phase transfer. 

Considering vapor-phase transfer as an example, and recogainng that Z = NyHv> the number of transfer anils may be enpressed as... 

Noie here that Eq. (5.7-6) has been used, Thus, the height of a vapor-phase transfer unit Is Hv = UJkyaf. In a similar fashion, and with the aid of Eq. (5.7-7). the number of liquid-phase transfer units mey he obtained ... 

Cyclohexene was dried and vacuum-distilled before use. It was degassed by three freeze-punp-thaw cycles and stored over activated molecular sieves in a glass bulb. It was introduced into the reactor via vapor phase transfer through a high vacuum manifold (base pressure <10 Torr). After 30 mins, the epoxide yield was quantified on an HP 6890 GC/MS equipped with a J W Scientific DBl capilary column. At the end of each experiment, Ti analysis was performed (15) and epoxide/Ti ratios were calculated. For kinetics experiments, silica powder containing the /ert-butylperoxotitanium complex was prepared in an in situ reactor and the reaction initiated by addition of olefin. The IR spectrum of the gas phase above the silica was recorded at timed intervals. Pseudo-first-order rate constants... 

The distribution of chemicals onto the foliar surface can occur by vapor-phase transfer, particle deposition (wet or dry), or from aqueous solution, which would be negligible for most organic compounds. It has been established that dry gaseous uptake is the predominant pathway for the foliar uptake of relatively nonvolatile compounds such as the chlorinated dibenzo-dioxins and -furans." The distribution of compounds between air and the cuticular polymer matrix follows Henry s law (Fig. 3.22)." This conclusion was drawn from observation of how a series of 50 low molecular weight (<175) compounds distributed between the vapor phase... 

There are a number of different pathways by which organic chemicals may enter vegetation [95]. The major paAways include (1) uptake by roots and subsequent translocation from roots to shoots (i.e., liquid phase transfer) in the transpiration stream, (2) foUo uptake of volatilized organic chemicals from the surrounding air (i.e., vapor phase transfer), (3) uptake by external contamination of shoots by soil and dust, followed by retention in the cuticle or penetration through it, and (4) uptake and transport in oil cells which are found in oil containing plants Hke carrots and cress. 

In distillation the vapor-phase resistance to mass transfer often contnds and thus the estimation of vapor-phase transfer units fends to be a critical issue. Equation (5.9-17) is used to evaluate the number of transfer units, and residence time is obtained from Eq. (5.7-6) or (5.7-8). The volumetric mass transfer coefficient is obtained from the expression of Chan and Fair ... 

Fig. 6 The loss of contrast in adhesive force mapping by the vapor phase transfer.

ZOOM (unprinted area) Vapor-phase transfer... 

Ohtsuka Y., Sugano T. / Studies on the light-focusing plastic rod 14 GRIN-rod of CR-39 (DEGBAK) trifluoroethyl metacrylate co-polymer by a vapor-phase transfer process.//Opt., 1983, vol. 22, No 3, pp. 413-417. 

The vapor-phase transfer (VPT) synthesis method consists of two steps covering the support with a synthesis gel and crystallization of the dried gel in saturated steam at a similar temperature or a mixture of steam and a structure-directing agent (SDA) under autogenous pressure [22-24]. Since one of the nutrient sources is limited to the support surface, zeolite membrane formation will be limited to the support surface. With this method, the membrane thickness can be well controlled since the amount of nutrient for growing zeolite is controlled directly by the amount of gel applied. However, the crystals produced are most likely randomly oriented. Furthermore, since the density of gel is much lower than that of zeolite crystals, the crystallization process... 

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