Vapor phase method

The most important nanomaterial synthesis methods include nanolithography techniques, template-directed syntheses, vapor-phase methods, vapor-liquid-solid (VLS) methods, solution-liquid-solid (SLS) approaches, sol-gel processes, micelle, vapor deposition, solvothermal methods, and pyrolysis methods [1, 2]. For many of these procedures, the control of size and shape, the flexibility in the materials that can be synthesized, and the potential for scaling up, are the main limitations. In general, the understanding of the growth mechanism of any as-... 

The operating parameters for the vapor phase method of growing crystals are shown in the following ... 

Figure 4. Kinetics of surface grafting of polyethylene (PE) and polypropylene (PP) films with acrylamide (AM) by the vapor phase method measured as light absorption at 600 nm after dipping in an aqueous solution of crystal violet (CV).

Figure 5. ESCA spectra of polyethylene film (PE) and polyethylene fiber (split film PE-F) after grafting for 2 min. with the vapor phase method.

Figure 9. Wide scan ESCA spectra of polyester film surface (PET) before grafting (A) and after grafting for 2 and 20 min. (B and C) with acrylamide (AM) using the vapor phase method.

Vapor-phase Methods 9.15.4.4.1 Chemical vapor deposition... 

Kiguchi, M. (1993). Chemical modification of wood surfaces by etherification. IV. Benzylation with solvent-dilution and vapor-phase methods. Mokuzai Gakkaishi, 39(1), 80-85. 

The alternate process, the vapor phase method, is carried out at higher pressures (450 psi) and temperatures (750—800°F), and hence, the vapor phase. Producers have been using a boron trifluoride catalyst but any trace water corrodes it unmercifully. Most have now switched to a crystalline aluminosilicate zeolyte catalyst, a more expensive but hardier catalyst. The newer catalyst is also noncorrosive and nonhazardous, cheaper to handle, and produces no waste streams to dispose of... 

Note that ethylbenzene is a derivative of two basic organic chemicals, ethylene and benzene. A vapor-phase method with boron trifluoride, phosphoric acid, or alumina-silica as catalysts has given away to a liquid-phase reaction with aluminum chloride at 90°C and atmospheric pressure. A new Mobil-Badger zeolite catalyst at 420°C and 175-300 psi in the gas phase may be the method of choice for future plants to avoid corrosion problems. The mechanism of the reaction involves complexation of the... 

Acetylation of cellulose to the triacetate has been carried out without breaking down of the structure with acetic anhydride containing pyridine to help open up the cell wall structure and to act as a catalyst (71). This led Stamm and Tarkow (72) to test the liquid phase reaction on wood. High dimensional stabilization without break down of the structure was obtained, but excessive amounts of chemical were used. They hence devised a vapor phase method at atmospheric pressure that proved suitable for treating veneer up to thicknesses of 1/8 inch. Acetic anhydride pyridine vapors generated by heating an 80-20% mixture of the liquids were circulated around sheets of veneer suspended in a box lined with sheet stainless steel. Hardwood veneer,... 

The problem of mass vapor-phase methods for the deacidification of books or textiles has received a great deal of attention in the last few years. Such treatments are best applied to current books in which the paper is still strong. Rebuilding strength into textiles or books by a vapor-phase treatment is eminently desirable. Both problems are discussed in this volume. When solved, the processes will probably be carried out in special plants by chemists rather than by conservators. 

More recently, Kiguchi reported benzylation of wood particles with the solvent dilution and vapor phase methods for reducing the amount of benzyl chloride in the etherification agent [12]. In the vapor phase benzylation below the boiling point of benzyl chloride, greatly thermoplasticized particles could be produced after 2-4 h at 140°C. However, in the solvent dilution method, higher reaction temperatures and longer reaction times than those in the ordinary liquid phase method were found to be necessary to obtain the thermoplasticized particles. 

Carlson, E.E., The growth of HgS and Hg3S2Cl2 single crystals by a vapor phase method, J. Cryst. Growth, 1, 271-277 (1967). 

Table II. Shale Oil Composition by Vapor-Phase Methods...

The crucial step of the new phenol synthesis is oxidizing the obtained benzoic acid to phenol. Early literature data indicated that heating copper benzoate or benzoic acid in the presence of copper salts gave various phenol precursors—e.g., phenyl benzoate and salicylic acid, as well as phenol itself (3, 10, 13, 24, 26, 36). In one of the initial approaches, by Dow Chemical Co., mixtures of benzoic acid vapors, air, and steam were passed over a CuO catalyst promoted with metal salts, giving phenol and phenyl benzoate (5). However, much tar was produced, probably because of the high reaction temperature, which led to excessive decomposition. Because of this, the vapor-phase method was abandoned in favor of the liquid-phase process. Next, benzoic acid was oxidized in aqueous solution with inorganic copper salts, as shown below (18) ... 

Another vapor phase method involves reacting a solid particulate phase with a gas to form particles. One method is the self-propogating high temperature synthesis (SHS) method. Also used for making sintered bodies, SHS can be used in reacting particles with the gas phase. An example of combustion synthesis involves forming ceramic carbide powders. ... 

Dealumination and Si-addition through vapor phase methods... 

The range of processing techniques that can be employed to produce FGMs is also broad [1]. Vapor-phase methods e.g., CVD, CVI, and PVD methods), liquid-phase methods e.g., electrodeposition, sol-gel, plasma spraying and molten metal infiltration methods), and a variety of solid-phase methods based on powder metallurgy are available. The solid-state methods include powder stacking techniques, powder infiltration techniques, slurry techniques e.g., sedimentation... 

W2. Wallace, J. E., and Dahl, E. V., Rapid vapor phase method for determining ethanol in blood and urine by gas chromatography. Am. J. Clin. Pathol. 46, 152-154 (1966). 

Ring systems containing two heteroatoms tend to feature less in the vapor-phase literature. This is partly because of the greater reactivity (i. e. reduced aromaticity) of these heterocyclic compounds. In addition, there has been less commercial incentive to develop catalyzed processes for these smaller-volume niche products. As an example, both pyrimidine (26) [51] and pyrazine (27) [52] can be made by catalyzed vapor-phase methods they can also be recovered from the pyri-dine- ff-picoline reaction. In principle, pyrimidine and pyrazine could then serve as platforms-much like pyridine does-for preparing a wide range of derivatives. The market for these derivatives is, however, best met by traditional convergent syntheses in the liquid phase. 

The fact that zeolite seed crystals can improve the mechanical strength of the synthesized discs, was reported in synthesis of zeolite ZSM-5 with vapor phase method. Zeolite ZSM-5 disc was prepared with ethylenediamine (EDA) and ammonia solution (or distilled water) as liquid phase while the mixture of amorphous aluminosilicate gel, zeolite ZSM-5 seed crystals was the solid phase. The obtained ZSM-5 discs not only have high mechanical strength (up to 3.5 X lO Pa/m ) but also high relative crystallinity. It was also found that the mechanical strength would further increase by replacing the water with ammonia solution in liquid phase. The increase of mechanical strength of zeolite seed crystal may result from the fact that seeds serve as binders to cause close assembly of small zeolite ZSM-5 particles. 

Exploration of Basic Catalyst Components The study of direct oxidative acetoxyla-tion of 1,3-butadiene began with the use of Wacker-type homogeneous catalyst Pd(OAc)2-CuCl2 [10]. This catalyst system gave low l,4-diacetoxy-2-butene selectivity, and there was a problem in separating the catalyst. After that, liquid-and vapor-phase methods using a Pd-based catalyst were studied in parallel. Catalyst activity was greatly improved by the addition of Bi or Sb to the Pd catalyst in the gas-phase reaction [11]. However, catalyst activity was reduced by the adhesion of resin by-product derived from unsaturated aldehydes on the catalyst surface. Various improvements have been tried in the gas phase, but catalyst robustness has never met industrial requirements. 

In order to obtain one-dimensional structures, there has to be a preferential growth direction (i.e. a faster growth rate in a particular direction). Even though the exact mechanism responsible for one-dimensional growth in the vapor phase is still not clearly understood, vapor phase methods have been explored and are extensively used by many research groups to synthesize one-dimensional materials. The main advantage is its simplicity in terms of the procedure and the experimental set-up used. 

CPs can be synthesized by chemically initiated polymerization, vapor-phase methods, photochemical polymerization or by electrochemical polymerization where the choice of polymerization method depends to a large extent on the final application in mind [2, 3]. Chemical polymerization usually produces powdery materials and is the preferred technique for large-scale production of CPs. The major disadvantages of chemical polymerization are the limited choice of suitable oxidants, introduction of impurities with the oxidant and difficulties to control the oxidation strength... 

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